NUREG-1861

Peer Review of

GSI-191 Chemical Effects

Research Program

U.S. Nuclear Regulatory Commission

Office of Nuclear Regulatory Research

Washington, DC 20555-0001
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NUIREG-1861

Peer Review of

GSI-191 Chemical Effe cts

Research Program

Manuscript Completed: July 2006

Date Published: December 2006

Prepared by

P.A. Torres

P.A. Torres, NRC Project Manager

Prepared for

Division of Fuel, Engineering and Radiological Research

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

ABSTRACT

The U.S. Nuclear Regulatory Commission (NRC), Office of Nuclear Regulatory Research (RES),

has a policy of initiating formal peer reviews for research programs that are on the cutting-edge

of technology and will influence important regulatory decisions. Such is the case for the series

of research projects that RES has sponsored to (1) resolve Generic Safety Issue 191,

"Assessment of Debris Accumulation on PWR Sump Performance," and (2) inform the NRC's

regulatory decisions regarding the potential for chemical byproducts to clog sump screens

in the post-loss-of-coolant accident environment in pressurized-water reactors (PWRs).

This NUREG-series report describes the chemical effects peer review assessment process

and summarizes its significant findings. It is important to mention that this peer review is not

a consensus review. Each reviewer was asked to provide an individual evaluation based on

his or her particular area of expertise. The research projects addressed by the peer review

included integrated chemical effects testing (ICET) and ICET followup testing and analysis

conducted at Los Alamos National Laboratory, chemical speciation prediction conducted

through the Center for Nucle 'ar Waste Regulatory Analyses at Southwest Research Institute,

and accelerated chemical effects head loss testing conducted at Argonne National Laboratory.

The chemical effects peer review evaluated the technical adequacy and uncertainty associated

with the RES-sponsored research results, and identified outstanding chemical effects issues.

The results of this peer review will support NRC staff audits and evaluations of industry responses

to Generic Letter 2004-02, "Potential Impact of Blockage on Emergency Recirculation

During Design-Basis Accidents at Pressurized-Water Reactors." The final assessment reports

from the peer reviewers are included as appendices to this NUREG-series report.

iii

FOREWORD

The U.S. Nuclear Regulatory Commission (NRC), Office of Nuclear Regulatory Research (RES),

has a policy of initiating formal peer reviews for research programs that are on the cutting-edge

of technology and will influence important regulatory decisions. Such is the case for the series

of research projects that RES has sponsored to (1) resolve Generic Safety Issue 191 (GSI-1 91),

"Assessment of Debris Accumulation on PWR Sump Performance," and (2) inform the NRC's

regulatory decisions regarding the potential for chemical byproducts to clog sump screens

in the post-loss-of-coolant accident (LOCA) environment in pressurized-water reactors (PWRs).

Chemical effects in the sump pool of a PWR represent a relatively new research area that has

proven to be quite complex. Recognizing this complexity, RES decided that an independent

peer review was necessary to assess the technical adequacy of the chemical effects

research program and to help the staff identify outstanding chemical effects issues.

The chemical effects peer review group consisted of five members selected from industry and

academia for their diversity in their affiliations and technical expertise. The technical areas

reviewed were (1) the integrated chemical effects testing (ICET) and ICET followup analysis and

testing conducted at Los Alamos National Laboratory, (2) chemical speciation prediction

conducted at the Center for Nuclear Waste.Regulatory Analyses, and (3) accelerated chemical

effects head loss testing conducted at Argonne National Laboratory. The review group

participated in kickoff and final meetings, which promoted discussion and enabled the members

to exchange information and address questions. The members then developed individual

preliminary 'reports addressing various questions that arose during the kickoff meeting, as well

as individual final reports (provided as appendices to this NUREG-series report) that provided

formal assessments of both prior and ongoing research activities.

Significant general findings from the peer review included (1) the ICET was representative

and identified some important contributing materials and interactions; (2) the chemical speciation

prediction study identified required capabilities and limitations of commercially available codes,

and revealed that more rigorous code development is needed to develop an adequate

assessment tool; and (3) the chemical effects head loss testing project revealed that

smaller-scale testing should be conducted to allow more rapid evaluation, in parallel, so that

more parameters can be identified and evaluated in several smaller loops, rather than one loop.

The peer review panel did an excellent job of engaging the NRC staff and contractors

in discussing the research projects and sharing their insights. Their feedback has been

especially valuable in improving our understanding of the mechanisms underlying development

of chemical byproducts. This NUREG-series report captures those insights, and is expected

to be helpful to the nuclear power industry as it considers changes to plant designs and operation

toward the resolution of GSI-1 91. The information developed by the peer review group

will also assist the staff of the NRC's Office of Nuclear Reactor Regulation (NRR) in evaluating

licensees' responses to Generic Letter (GL) 2004-02.

Brian W. Sheron, Director

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

v

CONTENTS

Pagqe

ABSTRACT.................................................................... i

FOREWORD.................................................................... v

ACKNOWLEDGMENTS .................................. ......................... ix

ABBREVIATIONS................................................................ xi

SYMBOLS..................................................................... xiii

1. INTRODUCTION.......................................................... 1-1

1.1 Objectives.............................................. '*'******* 1-1

1.2 Description of Generic Safety Issue 191 and Chemical Effects Background ......... 1-1

1.3 Peer Review Mo tivation............................................... 1-3

1.4 Structure of this Report............................................... 1-4

2. PEER REVIEW STRUCTURE AND APPROACH.................................. 2-1

2.1 Peer Review General Approach and Information............................. 2-1

2.2 Peer Reviewer Selection and Qualifications................................ 2-3

3. PRINCIPAL REVIEW AREAS................................................ 3-1

3.1 Integrated Chemical Effects Testing ...... I................................ 3-1

3.1.1 Program Description........................................... 3-1

3.1.2 Summary of Peer Review Key Findings............................. 3-3

3.2 Chemical Speciation Prediction Program .................................. 3-4

3.2.1. Program Description............................................ 3-4.

3.2.2 Summary of Peer Review Key Findings ............................. 3-6

3.3 Chemical Effects Head Loss Testing Program .............................. 3-7

3.3.1 Program Description........................................... 3-7

3.3.2 Summary of Peer Review Key Findings............................ 3-10

4. CONCLUDING STATEMENT ........................................... 4-1

5. REFERENCES ........................................................... 5-1

vii
Appendices

Page

A. Final Assessment Report by John A. Apps, "Contribution to the Report

of the Chemical Effects Peer Review Group". .................................... A-i

B. Final Assessment Report by Wu Chen, "Chemical Effects in PWR Sump Pool Environments

Peer Review"............................................................ B-i

C. Final Assessment Report by Calvin Delegard, "Chemical Effect Peer Review:

Assessment of Test Facilities and Programs to Investigate Concerns Related to

Chemical Effects in Pressurized Water Reactor Emergency Core Cooling Systems"....C-i

0. Final Assessment Report by Robert Litman,

"Evaluation of Integrated Chemical Effects Testing"................................. D-i

E. Final Assessment Report by Digby Macdonald, "Characterization of Chemical

and Corrosion Effects Potentially Occurring Inside a PWR Confinement

Following a LOCA" ........................................................ E-i

Tables

- Paoe

2-i. External Peer Reviewers .................................................... 2-4

3-i. ICET Test Description....................................................... 3-1

viii
ACKNOWLEDGMENTS

The author wishes to thank Argonne National Laboratory for providing the contractual support,

hosting the chemical effects peer review kickoff meeting, and presenting and making available

the technical information that the peer reviewers needed to complete their mission. The author

also wishes to thank the Southwest Research Institute (SWRI) and the Center for Nuclear Waste

Regulatory Analyses (CNWRA) for hosting the second chemical effects peer review meeting.

In addition, the author wishes to thank SWRI, CNWRA, and Los Alamos National Laboratory

for presenting and, making available the technical information that the peer reviewers needed

to complete their mission.

The author would also like to acknowledge Robert Tregoning for his technical guidance

and leadership in discussions during the peer review meetings. Finally, the author would like

to thank Ann Ramey-Smith, Robert Tregoning, and Bhagwat Jain for their advice and review of

this report.

ix

ABBREVIATIONS

ACRS Advisory Committee on Reactor Safeguards

ANL Argonne National Laboratory

Cal-Sil Calcium Silicate

CNWRA Center for Nuclear Waste Regulatory Analyses

ECCS Emergency Core Cooling System

ECP Electrochemical Corrosion Potential

[also known as Reduction-Oxidation (Redox) Potential]

EDO Executive Director for Operations (NRC)

EDS Energy Dispersive Spectroscopy

EPRI Electric Power Research Institute

ESEM Environmental Scanning Electron Microscopy

ETI R Fourier Transform Infrared Spectroscopy

GL Generic Letter

GSI Generic Safety Issue

HPSI High-Pressure Safety Injection

ICET Integrated Chemical Effects Testing

ICP Inductively Coupled Plasma

LANL Los Alamos National Laboratory

LOCA Loss-of-Coolant Accident

NPSH Net Positive Suction Head

NRC U.S. Nuclear Regulatory Commission

PZC Point of Zero Charge

PSD Particle Size Distribution

PWR Pressurized Water Reactor

QLR Quick Look Report

RCS Reactor Coolant System

RES Office of Nuclear Regulatory Research (NRC)

RHR Residual Heat Removal

Ai
SEM Scanning Electron Microscopy

STB Sodium Tetraborate

SWRI Southwest Research Institute

TEM Transmission Electron Microscopy

TSP Trisodium Phosphate

TSS Total Suspended Solids

UNM University of New Mexico

XRD X-Ray Diffraction

xii
SYMBOLS

Al

AI(OH) 3

AI(N0 3)3

AI(NO3)3X9H 2O

A1203

Ca

CaCI 2

Ca3(P04)2

Cu

Fe3O4

H202

HCI

HN0 3

LiGH

NaOH

NaAI(OH)4

Na2B4O7

Na3PO4

Zn

Aluminum

Aluminum Hydroxide

Aluminum Nitrate

Aluminum Nitrate Nonahydrate

Aluminum Oxide

Calcium

Calcium Chloride

Calcium Phosphate

Copper

Magnetite (Black Iron Oxide)

Hydrogen Peroxide

Hydrochloric Acid

Nitric Acid

Lithium Hydroxide

Sodium Hydroxide

Sodium Aluminate

Sodium Tetraborate

Trisodium Phosphate

Zinc

xiii

1. INTRODUCTION

1.1 O1bjectives

The principal objective of the chemical effects peer review group was to assess the technical

adequacy of research activities, sponsored by the U.S. Nuclear Regulatory Commission (NRC),

Office of Nuclear Regulatory Research (RES), related to chemical effects in pressurized-water

reactor (PWR) sump pool environments. Toward that end, the peer review members focused

only on those programs in which RES is specifically evaluating chemical effects. A second

principal objective was to have the peer reviewers recommend improvements to RES programs

in the area of chemical effects, and to identify additional important technical issues that RES

is not currently addressing. A third objective was to attempt to gain a theoretical understanding

of the relevancy of these chemical effects in the post-loss-of-coolant accident (LOCA) environment.

The final objective was to address specific questions from NRC staff, as described in Section 3

of this report. In so doing, RES hoped that the peer reviewers' comments and suggestions,

together with their expertise in the various technical areas, would help the NRC staff

to better understand these questions. In addition, it is important to mention that this peer review

was not a consensus review. Rather, each reviewer was asked to provide an individual evaluation

based on his or her particular area of expertise.

1.2 Description of Generic Safety Issue 191 and Chemical Effects Background

Generic Safety Issue (GSI) 191, "Assessment of Debris Accumulation on PWR Sump Performance,"

was established to assess the potential for transportation and accumulation of debris that is

generated during a LOCA to impede or degrade emergency core cooling system (ECCS)

performance in operating commercial PWRs. The ECOS is required to meet the criteria

of Title 10, Section 50.46, of the Code of Federal Regulations (10 CFR 50.46), "Acceptance

Criteria for Emergency Core Cooling Systems for Light-Water Nuclear Power Reactors."

In particular, 10 CFR 50.46(b)(5) requires licensees to design their ECCS systems with capability

for long-term cooling. That is, after successful initiation, the ECCS must be able to provide

cooling to maintain the core at an acceptably low temperature for a sufficient duration.

In this report, "chemical effects" include corrosion products, gelatinous material, or other

chemical reaction products that form as a result of the interaction between the PWR containment

environment and containment materials following a LOCA. Reaction products or precipitates

may be generated as a result of chemical reactions between ECCS recirculation sump fluid

or containment spray fluid and exposed materials in containment, such as zinc in coating materials

or galvanized steel, aluminum in scaffolding, thermal insulation and electrical or electronic

materials, exposed carbon steel, concrete, fiberglass debris, and so forth.

In a meeting in February 2003, the NRC's Advisory Committee on Reactor Safeguards (ACRS)

raised a concern based on its review of staff activities related to the resolution of GSI-191

(Reference 1). Specifically, the ACRS was concerned that chemical effects could significantly

increase the pressure drop (or "head loss") across ECCS recirculation sump screen debris beds

at a PWR. The ACRS stated that previous work related to GSI-1 91 did not consider the potential

for chemical interactions between the cooling water and exposed materials within containment

to generate new forms of debris with unique screen blockage characteristics, or to affect

the head loss behavior of previously investigated debris types. To support this concern,

1-1
the ACRS cited evidence including the gelatinous material discovered in the post-LOCA

sump pooi of the containment following the 1979 accident at Three Mile Island, Unit 2

(References 2 and 3).

In response to the ACRS concern that gelatinous substances or agglomerates could form

and have the potential to affect head loss, especially in concert with other debris transported

to the sump screen, a small-scale study of head-loss flow and quiescent immersion corrosion

was performed at the University of New Mexico (UNM), under the direction of Los Alamos

National Laboratory (LANL). The purpose of this study was to determine whether debris

generation and sump screen head loss can be affected by chemical interactions between

the ECCS recirculation water and exposed metal surfaces, inorganic zinc-based paint chips,

and fiberglass insulation debris. This study is described in NUREG/CR-6868, "Small-Scale

Experiment: Effects of Chemical Reactions on Debris-Bed Head Loss" (Reference 3),

which assesses the potential for chemically induced corrosion products and chemical degradation

effects to impede the performance of ECCS recirculation following a LOCA. In addition,

NUREG/CR-6868 presents observations gleaned from scoping tests that were conducted

to experimentally assess the degree of influence and the mechanisms by which water chemistry

and temperature may influence the head loss characteristics of an ECCS sump screen following

a LOCA in a PWR nuclear power plant. An independent expert review panel reviewed

the NUREG/CR-6868 study, and recommended conducting a follow-on study involving

integrated chemical effects testing of representative amounts of multiple containment materials

in a simulated post-LOCA environment.

As part of the resolution of GSI-1 91, the NRC and the nuclear industry jointly developed

an integrated chemical effects testing (ICET) program to determine whether chemical reaction

products can form in representative PWR post-LOCA containment sump environments.

The ICET series, conducted at UNM under the direction of LANL, involved five tests, each of which

represented a different subset of expected post-LOCA environments within existing PWR plants

(References 4-9). Results showed that chemical byproducts were present in the test solutions,

fibrous insulation samples, and sediment of all five ICET environments, and some of these products

were amorphous in nature. Inductively coupled plasma (ICP) results, for example, indicated that

for Test #1, aluminum and sodium were present in the greatest concentrations in the test solution,

while for Test #5, the highest concentrations were sodium, aluminum, calcium, and silica.

A follow-on study was conducted at LANL to provide a better understanding of the aluminum

chemistry in post-LOCA PWR containment environments (Reference 10). More specifically,

that study addressed the conditions for generating aluminum-based precipitates, characterizing

properties and particle size distributions of those precipitates, developing surrogate precipitates

and solutions, and determinating the adequacy of the surrogates by comparison to ICETgenerated precipitates and solutions.

1-2
A second area of investigation involved chemical effects head loss testing conducted by

Argonne National Laboratory (ANL). The objective of this research was to measure the head loss

associated with simulated ICET environments, to improve our understanding of the effects

of key environmental variables on chemical product formation and head loss (Reference 11).

A third area of investigation involved a -chemical speciation analysis performed by the Center

for Nuclear Waste Regulatory Analyses (CNWRA) at the Southwest Research Institute (SWRI).

This research involved analytical, thermodynamic simulation of the ICET series to predict

the chemical species formed in those environments (Reference 12).

Given the significance of this issue, the NRC has requested all PWR licensees perform an

evaluation of the potential for excessive head loss attributable to the accumulation of debris on

the containment sump screen. Toward that end, Generic Letter (GL) 2004-02, "Potential Impact

of Blockage on Emergency Recirculation During Design-Basis Accidents at Pressurized-Water

Reactors," requests that licensees evaluate the maximum head loss postulated from debris

accumulation (including chemical effects) on the submerged sump screen (Reference 13).

Chemical effects in the sump pool of a PWR plant represent a relatively new research area

that has proven to be quite complex. Recognizing this complexity, RES decided that

an independent peer review was necessary to review the technical adequacy of RES-sponsored

research activities related to chemical effects in PWR sump pool environments. In addition to

reviewing and commenting on the research that was underway, this external peer review group

helped the staff identify and prioritize issues in the chemical. effects arena.

The NRC has an aggressive resolution schedule associated with GSI-191. Toward that end,

the staff will use information developed through the, peer review effort in evaluating licensees'

responses to GL 2004-02 and conducting audits to ensure appropriate resolution.

1.3 Peer Review Motivation

Following RES Office Instruction PRM- 010 (Reference 14), "Peer Review of RES Projects,"

all RES programs and products are candidates for peer review. This includes programs

conducted under contract, as well as research performed within NRC by RES staff members.

A peer review is defined as a form of deliberation involving an exchange of judgments

about the appropriateness of methods and the strength of the author's conclusion. Peer review

occurs when a draft product is reviewed for quality by specialists who were not involved

in producing the draft. Acceptable peer review can involve either NRC staff or specialists

who are external to, and do not work for, the NRC. Peer review involves either one independent

reviewer or a team of reviewers in which each member provides a final independent assessment,

and the results of peer reviews are made publicly available.

The RES policy with regard to peer review groups is to encourage a formal and independent

peer review of research products consistent with the nature, importance, and timeliness

of the information to be disseminated. Peer review fosters confidence in the research products

and helps maintain high standards of competence in research programs. It is expected that

peer reviews will provide critical assessments regarding those research products, will help in

judging the technical adequacy of the results for the proposed solutions, and can aid in bringing

the widest and best available knowledge to bear on the quality of the research products.

However, RES does not rely on peers to achieve resolution of technical issues. To the contrary,

the NRC staffs technical expertise, leadership, and effective communications are vital aspects

of the process of achieving resolution of technical issues.

1-3
External peer review is a recommended strategy for promoting broader understanding

and context for issues that are technically complex, have potentially significant implications,

span many technical disciplines, and are emerging within the agency. On the basis of those

criteria, the RES staff identified the research on sump pool chemical effects as a logical

peer review topic. There is little information on chemical product formation in representative

plant sump environments. This is a new technical area of investigation, and it is sufficiently

complex to warrant independent assessment and consultation. Moreover, the research

conducted in the chemical effects arena could significantly affect the resolution of GSI-1 91.

In addition, there is no clear idea of the appropriate approach and how applicable the results are

in comparison with the three areas of investigation. Thus, RES believed that the peer review

group members would help to improve our understanding of this issue by providing review

comments, suggestions, and possible contributions for issue resolution. RES decided that an

independent peer review was necessary to assess the technical adequacy of the chemical

effects research program and to help the staff identify outstanding chemical effects issues.

1.4 Structure of this Report

The body of this NUREG-series report is divided into five sections:

* Section 1 defines the objectives of the chemical effects peer review group assessment,

and provides related background information concerning GSI-191 and chemical effects,

as well as the peer review and motivation.

* Section 2 describes the structure and approach of the peer review group

(e.g., how the members of the group were selected).

* Section 3 describes each of three research areas, and summarizes the key findings

of the peer review in each area.

* Section 4 presents a concluding statement, which su mmarizes the insights that emerged

from the peer review, and discusses how those insights will be used.

* Section 5 lists the references cited in this report.

Finally, the five appendices that accompany this report present the final independent

assessment reports from each of the five chemical effects peer review group members,

as well as a more in-depth description of the motivation for this peer review.

1-4
2. PEER REVIEW STRUCTURE AND APPROACH

2.1 Peer Review General Approach and Information

The NRC established the chemical effects peer review group to evaluate the technical adequacy

of RES-sponsored activities related to chemical effects in PWR sump pool environments.

Toward that end, the review encompassed the integrated chemical effects testing conducted

at LANL, chemical speciation prediction activities conducted at CNWRA, and chemical effectsaccelerated head loss testing conducted at ANL. Because of the complexity of these programs,

RES aimed to ensure diversity in both the members' affiliations and their technical expertise.

Approximately 3-4 months were spent gathering recommendations for peer review candidates

and assembling a group that spanned a broad range of affiliations and also had diverse

technical expertise and experience.

To decide upon the final peer review group, RES considered recommendations from multiple

sources, such as the NRC staff, the ACRS, the nuclear power industry, and NRC contractors

who were conducting research in the chemical effects area. The selected chemical effects

peer review group consisted of five members drawn from national laboratories, academia,

and industry. These peer review group members possessed diverse backgrounds and expertise

in areas such as gel formation, filtration, analytical and experimental chemistry, corrosion

and metallic corrosion, experimental testing, nuclear waste, and electrochemistry. The intent

was that the individual members would interact as a group and look at the chemical effects issues

using a holistic approach. Each peer reviewer was asked to address a set of defined questions

in the three program areas. The questions and responses are defined and anwered in Section 3

of this report. The NRC also provided the peer review group members with initial documentation

relevant to the ongoing technical program areas. The formality of that documentation varied

as a function of the program. This initial documentation included the following references:

* ICET Data Reports 1, 2, and 3 and the accompanying appendices (References 15-17)

* ICET Test Plan (Reference 18)

* ANL Quick Look Report: Tests 1 and 2 (Reference 19)

* CNWRA 2004-07 Report (Reference 20)

* NUREG/CR-6873 (Reference 21)

After providing the peer review members with the initial documentation, the NRC conducted

a chemical effects peer review group kickoff meeting at ANL in October 2005. The purpose

of that meeting was to summarize the initial technical documentation and identify the important

technical issues and questions that the NRC wanted the peer review group to assess in its review.

In addition, representatives of the various program areas from the national laboratories

and nuclear power industry gave a number of oral presentations, which provided the latest

technical information and research findings since the initial documentation was prepared.

The meeting participants also discussed the plans and philosophy behind the ongoing

NRC-sponsored research, identified additional information that the peer reviewers needed

to complete their preliminary assessment, and planned the peer review group activities

for the next several months.

2-1
The peer reviewers submitted their preliminary individual assessment reports in December 2005.

The purpose of those reports was to provide an informal assessment of both prior and future

research activities. The NRC intended that these preliminary assessment reports would identify

any major deficiencies or course changes that the research programs should make at that time.

The peer reviewers' preliminary assessment reports also included lists of follow-on questions

to be discussed in the second chemical effects peer review group meeting. The NRC staff

especially wanted the peer reviewers to raise technical questions regarding the need for

additional information, so that the NRC staff could provide the needed information during

the second peer review group meeting so the peer reviewers would have the information

available to them as they prepared their final assessment reports.

The NRC staff subsequently summarized the results and recommendations of the reviewers'

preliminary assessment reports, and organized the key points of each program area. The staff

disseminated this summary of results and recommendations to LANL, CNWRA, and ANIL

for consideration, review, and action. Each research organization took the lead in addressing

the issues and questions identified by the preliminary assessment reports corresponding to

their technical area. This helped the NRC staff and the national laboratories to properly address

the issues and questions from the peer reviewers.

After a thorough review of the preliminary assessments reports, the staff then distributed

the preliminary assessment reports to the peer review group members. In so doing, the staff

expected the peer reviewers to continue their detailed review of NRC activities to raise issues

or concerns that arose subsequent to the preliminary assessments. Toward that end, the staff

also provided the peer reviewers with new information regarding ongoing research activities.

That information included the following followup technical documents:

* ICET Data Reports 4-5 and the accompanying appendices (References 11 and 12)

* ANL Quick Look Report: ICET-3 Tests 4-11 (Reference 22)

* CNWRA speciation draft NUREG/CR, "GSI-191 PWR Sump Screen Blockage

Chemical Effects Tests: Thermodynamic Simulations" (Reference 1)

In March 2006, the NRC staff held a second chemical effects peer review group meeting at SWRI.

The purpose of this second meeting was to provide the group members with new information

regarding research activities conducted between October 2005 and March 2006. Toward that end,

representatives from LANL, ANL, and CNWRA presented information relevant to their respective

research areas and, along with NRC staff, addressed the peer reviewers' questions and clarified

remaining issues that they raised in their preliminary assessment reports. Most importantly,

this second meeting fostered interaction among the reviewers to support their final assessments.

In addition, the NRC asked the reviewers to submit any additional requests for information

before providing their final individual assessment reports.,

In May 2006, the peer reviewers submitted their final individual reports, which provided formal

assessments of both prior and ongoing research activities. All five of these final assessments

are included as appendices to this NUREG-series report.

2-2
2.2 Peer Reviewer Selection and Qualifications

The NRC staff selected the peer review group members on the basis of their technical expertise,

experience, skills, and affiliations. Characteristics such as discipline, point of view, diversity

of experience, and type of institution played an important role in the selection process.

As a result, the selected group of peer reviewers is sufficiently diverse to fairly represent

the relevant scientific and technical perspectives and fields of knowledge needed to address

the program areas of interest. Specifically, the staff initially identified the following technical

specialties for the selection of the peer review group:

* gel/amorphous product formation and characterization

* analytical chemistry

* metallic corrosion processes

* experimental testing and analysis

* theoretical chemistry/speciation prediction

* industrial filtration processes

* fluid (e.g., water and wastewater) treatment processes

* manufacturing gels, chemicals, and insulation materials

In addition, to be selected, each reviewer had to be recognized as an expert in one or more

of these technical specialties. Each reviewer also had to demonstrate active participation

in numerous reviews in his or her respective area(s) of expertise, and had to have made numerous

presentations at technical conferences, and written numerous papers for publication in conference

proceedings and journals. Finally, the staff selected the peer review group members to cover

a broad range of technical expertise. Table 2-1 identifies the five selected peer reviewers,

along with their respective affiliations and areas of technical expertise.

2-3
____________Table 2-1. External Peer Reviewers

Name Position/Affiliation Areas of Technical Expertise

John Apps Senior scientist Geochemical modeling and gel formation

Earth Sciences Division (gel/amorphous product formation

Lawrence Berkeley National and characterization)

Laboratory

Earth Sciences Division Chemical speciation modeling

Berkeley, CA 94720 (theoretical chemistry/speciation prediction)

Nuclear waste isolation

Wu Chen Senior specialist Fluid/particle separation

The Dow Chemical Co.

B-1402, 2301 N. Brazosport Blvd. Industrial filtration processes

Freeport, TX 77541

Calvin Delegard Staff scientist Experimental testing and analysis

Pacific Northwest National

Laboratory Analytical chemistry PO Box 999, MS P7-25 (applied/process chemistry)

Richland, WA 99352

Nuclear materials safeguards

Robert Litman Independent consultant Analytical chemistry

Radiochemistry Laboratory

Basics Metallic/corrosion processes

28 Hutchinson Drive

Hampton, NH 03842 Nuclear plant systems and chemistry

Digby Macdonald Professor of Materials Science Electrochemistry and thermodynamics and Engineering, and Director science

of the Center for Electrochemical

Science and Technology Metallic/corrosion processes

Pennsylvania State University

0201 Steidle Bldg. Experimental testing and analysis

University Park, PA 16802

2-4
3. PRINCIPAL REVIEW AREAS

3.1 Integrated Chemical Effects Testing

3.1.1 Program Description

The primary objectives of the ICET research program were to (1) determine, characterize,

and quantify chemical reaction products that may develop in a PWR containment pool

in a representative post-LOCA environment, and (2) determine and quantify any gelatinous

material(s) that could be produced during the post-LOCA recirculation phase. Toward that end,

the ICET series simulated the chemical environment present in a containment water pool

following a LOCA, and monitored the chemical system for an extended period of time to identify

the presence, composition, and physical characteristics of chemical products that formed

during the test. By contrast, the ICET series was not designed to evaluate debris or sediment

transport, bound the chemical environment present in a containment water pool, or measure

head loss associated with any chemical byproducts. Within those constraints, the ICET series

was conducted at UNM under the direction of LANL, in accordance with the test plan shown

in Table 3-1.

_________ ~~~Table 3-1. ICET Test Plan__________

Test Buffering Agent Initial Boron (ppm) Insulation Mixture ____ ____ ____ ____ Target pH _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

1Sodium Hydroxide 10 2800 100% fiberglass (NaOH)__ _ _ _ _ _ _ _ _ _ _ _ _ _ _

2 Trisodium Phosphate 7 2800 100% fiberglass (TSP) (NaPO,)_____________ ______

80% cal-sil

3 TSP (NaPO,) 71 2800 __________________20% fiberglass

4 Sodium Hydroxide 10 280080 asi

(NaOH) ______20% fiberglass 5 Sodium Tetraborate 8- 8.5 2400 100% fiberg~las~s ____ ____ (STB3) (Na,BAO,)__ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _

The ICET research program consisted of five distinct 30-day tests, each of which was intended

to simulate a subset of current operating PWR plants. The ICET apparatus consisted of a large

stainless steel tank with heating elements, spray nozzles, and associated recirculation pump

and piping to simulate the post-LOCA chemical environment. Submerged samples of structural

metals, concrete, and insulation debris were scaled in proportion to their relative surface areas

found in containment, and in proportion to a maximum test dilution volume of 250 gallons

(946 liters) of circulating fluid.

3-1
The primary differences among the ICET tests were the buffering agent and insulation material.

The three types of buffering agents were sodium hydroxide (NaOH), trisodiumn phosphate (TSP),

and sodium tetraborate (STB, used in ice condenser plants). The materials tested in this.

environment included representative amounts of submerged and unsubmerged aluminum (Al),

copper (Cu), zinc (Zn), concrete, carbon steel, and insulation samples. Representative amounts

of concrete dust and latent debris were also added to the test solution.

All of the ICET tests were conducted in an environment that simulated expected containment

pool conditions during recirculation. The initial chemical environment contained 2,800 mg/L

of boron (2,400 ppm for STB plants), 100 mg/L of hydrochloric acid (HCI), and 0.7 mg/L

of lithium hydroxide (LiOH). Each test was conducted for 30 days at a constant temperature

of 60 'Cc (140 OF) and consisted of an initial 4-hour spray phase to simulate containment spray

interaction with the unsubmerged samples. Water was circulated through the bottom portion

of the test chamber throughout each test to achieve representative flow rates over the submerged

specimens. The system was then monitored while corrosion and mixing occured for 30 days

(a time frame comparable to the ECCS recirculation mission time).

The test solution pH also differed in each test, varying from approximately 7.3 in ICET Test #2

to approximately 9.8 in Test #4. Precipitates at test temperature were visible for only Test #3.

However, test sample solutions for Tests #1 and #5 produced precipitates upon cooling to room

temperature, although Tests #2, #3, and #4 did not. In each test, turbidity measurements were

taken at 60 0C (140 0F),and 23 OC (73 OF), and measurements at both temperatures yielded

similar results in Tests #2, #3, and #4. However, in Tests #1 and #5, the turbidity at 23 0C

(73 OF) deviated from those at 60 0

C (140 OF). Total suspended solids (TSS) were also

measured in each test and, with the exception of Test #5, all tests reached a maximum TSS

value by the first day and decreased to a value relatively close to the baseline measurement

for the duration of the test.

Throughout the ICET series, daily water samples were taken to determine the composition

of the solution by inductively coupled plasma (lOP) analysis with a standard list of elements.

Boron was present in high concentrations in all tests. In Test #1, aluminum and sodium

were present in the greatest concentrations of all tested elements. In Test #2, silica and sodium

were the dominant elements in solution. Silica, sodium, and calcium elements were present

in the greatest concentrations in Test #3. In Test #4, silica, sodium, calcium, and potassium

were present in the greatest concentrations. Sodium, aluminum, calcium, and silica were

the dominant elements in the Test #5 solution.

The amounts and types of deposits seen on the fiberglass insulation varied from test to test

because of differences in solution chemistry. Comparison revealed that the greatest degree of

deposition occurred in Test #3, followed in order by Tests #1, #4, and #2, while Test #5 samples

had the fewest deposits. Analyses of the cal-sil samples revealed large amounts of phosphorous

on the exterior of samples obtained from Test #3, but not those obtained from Test #4.

Moreover, the interior of the cal-sil samples from Tests #3 and #4 showed that the phosphorus

did not penetrate the solid.

3-2
The system effect on the coupons also differed for each test, as did the sediment produced.

Tests #1 and #5 showed the largest amount of coupon corrosion (e.g. 25% and 5% loss of pretest mass in submerged aluminum coupons respectively), while the conditions in Tests #2

through #4 did not appear to cause significant coupon corrosion. By contrast, Tests #3 and #4

produced the most sediment, which consisted of a large amount of chemical precipitate

and sediment attributable to the large amount of cal-sil added to the tank. Tests #1, #2, and #5

produced the smallest amount of sediment, which was largely composed of materials from

the insulation (fiberglass) and debris added to the tank. Overall, the ICET results demonstrated

that changes to one important environmental variable (e.g., pH adjusting agent, insulation

material) can significantly affect the chemical products that form.

3.1.2 Summary of Peer Review Key Findings

The review focused on a predetermined set of ICET-related technical questions. Those questions

and the related responses from the peer reviewers are summarized as follows:

Question 1:

Response:

Question 2:

Response:

Question 3:

Response:

Have the principal sump pool variables, which affect chemical byproduct

formation environment, been adequately simulated?

The majority of the reviewers agree that the types of materials that are present

in PWR containments have been appropriately selected. They also stated

that the concentrations of chemicals used during the operation of a PWR

are approximately in the range of anticipated chemical concentrations.

The reviewers also noted that other chemical constituents have not been simulated,

the analysis lacks consideration of redox effects and radiolysis, and the tests

did not adequately model the steep cyclic temperature transients of recirculating

coolant or the hot fuel cladding and pressure vessel surfaces.

Many ICET variables were held constant during the experiments. How would

changes in the most important constant variables affect chemical product

formation?

In general, the reviewers suggest comprehensive evaluation of the physical,

chemical, and mineralogical properties of the observed precipitates during

the experiments, along with detailed evaluation of all of the data to better

understand the effects of chemical product formation. Some of the reviewers

suggest that temperature has a significant effect on solubility and the types

of compounds that will form. They recognize temperature as a difficult aspect

to model and recommend further work.

What variables or materials not simulated by the ICET testing may have

the most impact on chemical product formation (e.g., coatings, free insulation,

flow through sediment and other materials on sump screen, galvanic effects),

and how should their effect be characterized by testing or analysis?

In general, the reviewers think that field visits to operating PWR facilities

could unearth limitations or omissions not otherwise anticipated. Considerations

from the reviewers are diverse and are summarized as follows:

3-3
(a) failure to control or monitor CO2 uptake, which could deviate significantly

from the actual post-LOCA environment of a PWR

(b) presence of suspended solids from the reactor coolant system (RCS)

and how they could change their chemical form

(c) effects of organic coatings to estimate the quantities of coatings involved,

their properties, and the secondary effects of radiation and hydrothermal

reactions (reactions with hot water) on the organic materials

(d) effects of high- and low-temperature heat transfer surfaces on collection

and dissolution of solid phases to determine the importance of surface

deposition

(e) effect of liquid coming into contact with fuel in the reactor vessel

to understand heat and radiolytic effects

(f) effects of silica in the water storage systems and RCS on the total mass

of material precipitating

(g) simulation of the production of hydrogen peroxide (1-20 2, to determine

redox potential) and nitric acid (HNO 3, lowers the pH of the solution)

Question 4: Were the methods used within the ICET program to characterize and analyze

chemical byproducts sufficient?

Response: The reviewers agree that the methods used within the ICET program were not

sufficient to characterize and analyze chemical byproducts. Much more serious

work needs to be done to characterize the physical, chemical, and mineralogical

properties of the precipitates and coatings as a basis for subsequent conceptual

and computer modeling. Some X-ray diffraction (XRD) and transmission electron

microscopy (TEM) work was performed during the course of ICET or during

follow-up work, but in general, the tests should have incorporated

the following analytical techniques as part of their standard analysis:

(a) Particle size distribution (PSD)

(b) Fourier transform infrared spectroscopy (FTIR)

(c) X-ray diffraction (XRD)

(d) Transmission electron microscopy (TEM)

3.2 Chemical Speciation Prediction Program

3.2.1 Program Description

The objective of the chemical speciation prediction program (performed at CNWRA)

was to evaluate the accuracy of thermodynamic predictions on the quantities and species

of chemical products formed. Toward that end, four chemical modeling software programs

EQ3/6, PHREEQC, Geochemist's Workbench REACT, and OLI Systems StreamAnalyzer -

were evaluated to assess their ability to perform aqueous speciation and mass transfer calculations

relevant to post-LOCA conditions. The code comparison exercise considered several example

simulations, each of which was representative of post-LOCA conditions in alkaline, borated

containment water at temperatures between 60 'C (140 'F) and 110 'C (230 'F).

3-4
The reactor system components included galvanized steel (a source of dissolved zinc),

carbon steel (a source of dissolved iron), aluminum scaffolding, copper fans and instrument lines,

glass fiber insulation material, and concrete. The modeling software was used to identify

the over-saturated secondary solids that would precipitate, and calculate the final solution

composition. The most important differences in results were traceable to different sets

of solid phases in the thermodynamic database files accompanying each modeling code,

rather than to different capabilities of the codes themselves.

The benchmarked simulations considered a set of blind predictions using the EQ3/6 code,

and the predicted results were compared to data from the corresponding ICET experiment.

In some cases, observed final concentrations in the sampled water were higher than the initial

source-term estimates, indicating that the input value source-term contribution for that element

had been underestimated. In other cases, the identity and quantity of precipitate did not conform

to observations from the ICET experiment, indicating kinetic restrictions on precipitation

under the modeled conditions.

Another set of simulations, called "informed predictions," used the OLI StreamAnalyzer code

and its accompanying thermodynamic database. The general modeling approach was similar

to the approach used for the blind predictions with EQ316. In this case, each ICET experiment

was represented by a set of source-term water compositions at different times of exposure,

estimated from the initial composition of the containment water and experimentally determined

corrosion rates of sample materials. The results of the informed predictions corresponded to

the ICET experiment results more closely than the blind predictions, largely because of

the revised element release rates for aluminum and insulation materials, for exposure times

of up to148hours. Beyond that timeframe, final- concentrations of calcium, silica, and aluminum

were typically over-predicted, indicating a possible inert stage of the metal surface or formation

of an inhibitive surface coating on the insulation material *during the experiment. These changes

in release rate were not included in the source-term water concentrations for informed predictions.

The differences in results for the blind and informed predictions were attributed to differences

in the lists of potential precipitates provided in the thermodynamic database files that accompany

the modeling software. For the informed simulations in which precipitation affected the so ilution

chemistry, good agreement was obtained between predicted and observed results for calcium

concentration under the conditions in ICET Test #1 (alkaline water buffered to pH values

near 10 by NaOH) because of the precipitation of monohydrocalcite, for silica concentration

under the conditions in ICET Tests #2 and #3 (solution buffered to near-neutral pH by TSP)

because of the precipitation of amorphous silicon dioxide, and for phosphorous concentration

under the conditions in ICET Test #3 because of the precipitation of calcium phosphate.

This study concluded that chemical modeling software is a broadly useful tool for assessing

the potential effects of post-LOCA interaction on sump screen blockage. However, its predictive

capability was hindered by insufficient thermodynamic data for relevant phases and aqueous

species in the code database, and by limitations in the kinetic data for the dissolution

of reactive materials in the presence of co-dissolving materials.

3-5
3.2.2 Summary of Peer Review Key Findings

The review focused on a predetermined set of technical questions related to prediction

of chemical speciation. Those questions and the related responses from the peer reviewers

are summarized as follows:

Question 1:

Response:

Question 2:

Response:

Question 3:

Response:

Is the speciation analysis expected to provide reasonable predictions

of chemical product formation over a range of possible sump environments?

The reviewers agree that even though this chemical speciation analysis

represents a significant improvement over earlier work, it does not exploit

existing capabilities of the selected codes to their fullest advantage.

Specifically, two physical effects not modeled were the radiation field from the fuel,

and the layer of corrosion products on the interior surface of the RCS.

The reviewers note that concessions had to be made for the seeming lack of

CO2 to form low-solubility carbonates. Reaction rates (kinetics) also are not

handled well by the modeling software; therefore, the models may not reflect the

evolving concentration profiles. As the models are refined, they should provide

closer matching of the observed ICET concentrations, the concentrations

observed in the supplemental CNWRA testing, and the concentrations in

systems not replicated in the ICET experiments. In addition, non-equilibrium

concentration of radiolysis products (and even species in the absence of radiolysis)

cannot be addressed by the selected codes.

Is the plan for benchmarking these codes using small-scale testing

and the ICET results appropriate?

The reviewers agree that the plan for benchmarking codes is satisfactory,

provided that the actual processes are accurately simulated. Some reviewers

think that the capabilities of the codes currently being used are not being used

to full advantage and, as a result, the value of the associated experimental studies

is diminished. In addition, the reviewers note that small-scale testing is a valid

approach to gain more information, especially on the kinetic and equilibrium

behaviors of the key solutes and solid phases.

What is the most appropriate way to measure the uncertainty associated with

these codes?

The reviewers suggest various ways to measure the uncertainty associated

with the codes, noting that it is difficult to measure the overall uncertainty

of the output of any multi-component chemical simulation, because a large number

of parameters are involved with widely varying levels of accura cy. First,

a sensitivity analysis of empirical or deterministic models is suggested. Second,

comparison of the code predictions against the results of targeted small-scale tests

is a feasible way to strengthen the codes and identify and measure their

uncertainties. Third, the most realistic values should be utilized, and runs

should be replicated using Monte Carlo methods to determine variations

in parameters deemed to have the greatest uncertainties and considered to be

most critical to model output. The cumulative variation in outputs can then be

adopted as a measure of uncertainty.

3-6
3.3 Chemical Effects Head Loss Testing Program

3.3.1 Program Description

The objective of the chemical effects head loss testing program (performed at ANL) was to

evaluate the head loss associated with chemical byproducts observed during the integrated

chemical effects testing by LANLJUNM, and to understand how relevant changes within

the environment affect chemical byproduct formation, physical characteristics, and any

associated head loss. The head loss testing was done in a piping loop containing a simulated

sump pool environment intended to be representative of post-LOCA buffering environments.

The test screen had an effective diameter of = 16.5 cm (=6.5 inches), and the fluid volume

in the loop was 0. 12 m' (4.2 ift). At 3.05 cm/s (0. 1 ftls), the transit time around the loop

was =4 minutes.

Two types of perforated plates were used in the testing. One had a 51 -percent flow area

and staggered holes with a diameter of 0.48 cm ('/i1inch), while the other had a 40-percent

flow area and staggered holes with a diameter of 0.32 cm (1/8 inch). In scaling results

from the ANL test facility, the mass of chemical product per unit area of screen must be considered.

Thus, the amount of chemicalFproduct produced scales with fluid volume, while the screen area

per fluid volume determines the product mass per unit screen area. The ANL initial tests results

are described in detail in ANL's 1st and 2 nd Chemical Effects/Head Loss Testing QLRs

(References 19 and 22), dated September 16, 2005, and January 20, 2006, respectively.

The initial head loss testing focused on the environment corresponding to ICET Test #3,

which contained cal-sil insulation and used TSP buffering. In that test, calcium phosphate

[nominally Ca3(P0 4)2] became apparent within 30 minutes after initiating TSP injection

into the recirculation loop. The first ANL head loss test (ICET #3-1) was intended to simulate

the Ca3(P04)2 precipitate concentration created by the initial burst of dissolved calcium (Ca)

that formed within the first 30 minutes of ICET Test #3, prior to metering TSP into the chamber.

Dissolution testing of the ICET Test #3 cal-sil loading [19 g/L (0.190 lb/gal) submerged cal-sill

showed that during the 30 minutes between the introduction of the cal-sil and the initiation

of TSP injection, head loss would increase significantly as a result of Ca3(P0 4)2 precipitate

corresponding to 200 ppmn of dissolved Ca.

The second ANL head loss test (ICET #3-2) was parametric and tested several dissolved Ca

concentrations to determine the effect of a range of cal-sil loadings on head loss. In both tests,

a physical debris bed was formed, approximately 1.59 cm (% inch) thick, consisting of equal

amounts [15 g (0.53 oz.)] of NUKON'~ fiber and cal-sil insulation. Dissolved Ca was then

added to the test loop, which contained TSP-buffered borated water, to form Ca3(P0 4)2

precipitates. In this configuration, ICET #3-2 resulted in head loss increases for precipitate

loadings that were one-twentieth of those used in ICET #3-1 (10 ppmn of dissolved Ca),

and loadings corresponding to 25 ppm of dissolved Ca increased the head loss to more than

4.2 m (13.8 ft).

3-7
ANL also performed additional head loss tests, tests of settling rates of Ca3(P0 4)2 precipitates,

and cal-sil dissolution tests in TSP solutions. The objective of the head loss tests was to assess

the pressure drop across debris beds created by various mixtures of cal-sil, fibrous insulation,

and Ca 3(P0 4)2 precipitates. In addition, ANL evaluated the effects of the degree of cal-sil

dissolution that will occur before the debris bed forms, as well as the relative arrival time

of the precipitates and insulation debris at the screen. Toward that end, ANL selected

debris loadings and test temperatures that were reasonably representative of those expected

in limiting design-basis analyses for plants with updated sump screen configurations. The test

conditions used in this series of tests are summarized in Reference 22.

The results of the ANL head loss tests in environments similar to those in ICET Test #3

demonstrate that chemical products [Ca3(P0 4)2 precipitates] associated with TSP-buffered

containment environments can significantly contribute to head loss. Moreover, the head losses

associated with fiberglass insulation and cal-sil debris beds can be much smaller than those

that occur across debris beds in which some of the cal-sil has been dissolved and the resulting Ca

reacts with phosphate to form Ca3(P0 4)2 precipitates. Notably, the rate of cal-sil dissolution

depends somewhat on the initial pH in the sump pool, as well as the rate of TSP dissolution.

However, even with instantaneous TSP dissolution and cal-sil concentrations as low as 0.5 gIL

(5.01 E-3 lb/gal), the equivalent dissolved Ca could be high enough within a few hours

to produce significant increases in head loss compared to that attributable to the equivalent

particulate loading. The Ca3(P0 4)2 precipitate settling rate is also important in determining

the transportability of the precipitate. The rate varies with concentration. For example,

at a concentration of 75 ppm Ca with no bulk directional flow, the estimated settling rate

is 8 mm/mmn (0.31 inch/min).

In an environment similar to that used for ICET Test #3, the chemical products in the ANL

head loss tests formed either by actual dissolution of cal-sil (an integral test) or by the addition

of dissolved Ca as calcium chloride (CaCI 2). Moreover, the chemical products formed

by either manner are calcium phosphates, and the surrogate product is very similar to that

formed in the integral test. By contrast, in the environment used for ICET Test #1, the main

chemical product is aluminum hydroxide [AI(OH) 3]. However, aluminum hydroxide may exist

in either amorphous or crystalline forms, and these forms can have very different properties.

For example, the solubility of amorphous AI(OH) 3 can be 500 times as great as the solubility

of some crystalline forms of aluminum hydroxide. Thus, itis important to note that in ICET

Test #1, dissolved Al formed slowly by corrosion of the Al plates.

The precipitation process is complex, and the Al can be present as dissolved Al, colloidal product,

and solid precipitates. The existing amounts of the various forms, even for the same total Al

content can be highly time-dependent, and may depend on the timing of the addition of material.

to the coolant, the change in temperature or pH over time, and the degree and order of mixing.

The solid products in ICET Test #1 have been shown to be primarily amorphous AI(OH) 3.

There is a very high degree of hydration, and product exists as agglomerations of nano-sized

particles, but the degree and strength of agglomeration and the actual effective hydrodynamic

size of the product is difficult to characterize.

3-8
The ANL head loss tests for the ICET Test #1 environment were based on the use of surrogate

chemical products. The test fluid had boric acid and lithium hydroxide levels consistent with

the ICET test, but aluminum nitrate nonahydrate [AI(N0 3)3X9H 2OI was added to generate

AI(OH) 3 products (rather than actual dissolution of Al metal). Nonetheless, bench scale tests

showed that the products were amorphous, and their physical appearance and behavior

were qualitatively similar to the products observed in the ICET #1 integral test. Particle size

measurements showed that products were agglomerated, and the measured particle size

could vary depending on whether the solution was quiescent or deflocculated by ultrasound.

The initial ANL head loss tests in the ICET Test #1 environment attempted to simulate the ICET

test where the dissolved Al level was =375 ppm. For these tests, ANL prepared a solution

containing boric acid, LiOH, and NaOH. A NUKON' debris bed was formed, and the system

was heated to 60 'C (140 OF). AI(N0 3)3x9H2O was then added to obtain a dissolved Al level

of 375 ppm, and the pH was adjusted to match the conditions in ICET Test #1.

In the first ANL test in this environment, the flow velocity in the loop was kept at 30 mm/s

(0.1 ftls), and a heavy "snowfall" was observed as the Al solution was added. [The addition

of AI(N0 3)3 appeared to result in a local decrease in pH and concomitant increase in Al

concentration that exceeded the solubility limit; however, the "snow" dissolved in a few minutes.]

High head losses were observed almost immediately upon introduction of the Al solution,

even though the temperature remained at 60 0C (140 OF) and there was no visible buildup

of precipitate on the debris bed or anywhere else in the loop. As the temperature decreased,

the pressure drop across the bed continued to increase, although no precipitate was observed

on the bed. At 32 00 (90 OF) the pressure drop was so high [4.2 mn and 6 psi] that flow velocity could not be maintained. In a repeat test with 375 ppmn dissolved Al, a new distribution header

was used for the Al solution, and much less snow formed when the solution was added

to the loop. In addition, in the repeat test at 375 ppm, no increase in pressure drop was observed

at temperature or as the loop cooled to 38 0C (100 OF) until about 120 minutes after addition

of Al. Once the pressure drop began to increase, it rapidly climbed from 0.015 m and 0.3 psi

to 2.6 m and 5 psi in approximately 30 minutes. Again, the pressure drop occurred

with no visible precipitate.

ANL also performed additional tests with lower levels of dissolved Al. In initial tests with 100 ppm

and 200 ppm of Al, no pressure drop increases were observed over a 6-hour test period

as the temperatures decreased from 60 00 (140 OF) to 27 00 (80 OF). A second test was run

with 100 ppm dissolved Al at 27 0C (80 OF) for 8 days, also with no significant increase

in pressure drop. Nitric acid was then added to decrease the pH by 0.2 units, and the pressure drop

immediately began to increase, although there was again no visible precipitate. The process

was at least somewhat reversible in terms of temperature. That is, when the temperature

increased, the pressure drop decreased, and when the temperature decreased, the pressure drop

increased. However, the temperature holds were not long enough to fully assess the degree

of reversibility.

In a third test with 100 ppm dissolved Al, 15 nmn aluminum oxide (A1203) particles were added

after = 1 day in an attempt to accelerate the precipitation process. The pressure drop began

to increase =4 days after the particle addition, so any connection seems remote. In this case,

the pressure drop increased to =2.6 m (5 psi), and loop velocity could no longer be maintained.

Again, no product was visible during the test, but a colloidal suspension did become visible

in samples of fluid removed from the loop at the end of the test and aged for 3-4 days.

3-9
ICET Test #5 involved an STB buffer, and the dissolved Al level (= 50 ppm) was lower than

in ICET Test #1, but the pH was also lower (=8.5). Only a limited amount of precipitates were

observed during the test, but somewhat more became visible during longer-term storage of fluid

from the test. The corresponding ANL head loss tests again used AI(N0 3)3x9H2O

as a surrogate for Al from actual dissolution. For these tests, ANL prepared a solution

containing boric acid, LiCH, and STB. A NUKON' debris bed was formed, and the system

was heated to 60 'C (140 'F). AI(N0 3)3X9H 2O was then added to obtain a dissolved Al level

of 50 ppm. Because the aluminum nitrate addition lowered the pH, ANL also added NaOH

to match the pH in ICET Test #5. The test was run for 6 days with no indication of increased

pressure drop. The pH was then decreased 0.2 units, nanoparticles were added, and the test

was continued for another =5 days with no indication of increased pressure drop. The dissolved

Al level was then increased to 100 ppm, which corresponds to a very conservative estimate

of submerged area of Al for most plants. With this amount of dissolved Al, the pressure drop

rapidly increased until the pump could no longer maintain the fluid velocity.

ANL also performed a second test with the STB3 buffer, in which the physical debris bed contained

15 g (0.53 ounce) each of NUKON® and cal-sil. The initial head loss when this debris

was added to the loop was somewhat greater than that observed in tests with similar

NUKON/cal-sil loadings, but this may be attributable to test-to-test variability. The pressure drop

decreased over time during the test to levels typical of pure NUKONO loading, suggesting that

the cal-sil was dissolving, the particulate loading on the bed was decreasing, and no chemical

products were forming that could lead to high pressure drops.

3.3.2 Summary of Peer Review Key Findings

The review focused on a predetermined set of technical questions related to chemical effects

head loss testing. Those questions and the related responses from the peer reviewers

are summarized as follows:

Question 1:

Response:

Is the accelerated head loss testing approach viable for evaluating the effects

of multiple chemical environments quickly?

The majority of the reviewers agree that the current head loss testing facility

is insufficiently flexible for evaluation of multiple chemical environments

or replication of tests to establish reproducibility, and the test loop does not

provide the same type of stagnant environment that would be encountered

in the submerged portion of the containment building. Some recommendations

are as follows:

(a) Use multiple small bench-scale facilities that could be run simultaneously, with

stepped variations in critical parameters, so that the sensitivity

and magnitude of potentially adverse conditions could be rapidly mapped

as a function of these parameters.

(b) A smaller test loop might be designed to model the operation of a vertical

screen, rather than the tested perpendicular dead-end screen.

(c) A smaller test loop would also allow easier testing at temperatures

that vary with time, and might allow exposed high and low temperature

surfaces.

3-10
Question 2: What is the best method for incorporating time-dependent effects

(e.g., material aging, evolving chemical environments) in simulation testing?

Response: The reviewers suggest various methods to incorporate time-dependent effects

in simulation testing:

(a) With the variability in individual PWR designs and differing operating

histories, there is a need to concentrate on the most critical parameters

and efficiently study their effects through small-scale bench tests.

Once the degree of variability and its importance has been established,

small-scale loop and head-loss tests could be conducted on a suitable

range of variably aged samples.

(b) Study the effect of temperature through small bench-scale tests,

followed by limited small-scale loop and head-loss tests.

Confirmatory tests using the present facilities should be conducted

only after assessing the impact of all relevant parameters.

(c) Kinetic models, coupled with thermodynamic codes, should be considered,

making sure that the codes accurately simulate radiolysis and redox effects.

Question 3: What metrics; are most appropriate for evaluating the results of simulated

chemical products with those that formed during the ICET program?

Response: The reviewers identified various metrics for evaluating the results of simulated

chemical products:

(a) In the filtration/head-loss testing, the aluminum corrosion product

was introduced by neutralizing aluminum nitrate [AI(N0 3)3] with sodium hydroxide (NaOH). This method is not representative

of the way aluminum solids arise in the post-LOCA cooling water system.

It is proposed that the aluminum be introduced in another manner,

either by corroding a coupon of aluminum in NaOH or by adding

sodium aluminate solution [NaAI(OH) 4].

(b) The testing performed for the ICET program showed the importance

of pH, Cal-Sil dissolution, borate, aluminum corrosion, phosphate,

NUKONO fiberglass, and concrete on solids formation. The head loss

testing could focus on varying these components, plus study the effects

of temperature differentials and hot and cold surfaces, to create

the solids present in the post-LOCA environment.

3-11
Question 4:

Response:

Are correlations available, or can they be developed, which can predict

the associated head loss if important physical characteristics

of a chemical byproduct are known?

The reviewers think that methods to predict head loss or filtration behavior

based on physical properties may or may not exist, noting that a reason for this

is the secondary effect of coprecipitated or agglomerated materials. Another

reviewer opined that models that predict head loss cannot account for the effects

of gelatinous or amorphous materials. However, even if such parameters

could be identified and measured, the coolant solutes and suspended solids

continue to react as shown by ICET and other testing. Another reviewer

suggested treating this problem with a kinetic model for hydrolysis, polymerization,

coagulation, and precipitation in a highly non-equilibrium environment,

recognizing that none of the present codes has this capability.

3-12
4. CONCLUDING STATEMENT

The principal objectives of the chemical effects peer review were met. Overall, the peer reviewers

assessed and independently confirmed the technical adequacy of the three research programs

related to chemical effects in PWR sump pool environments, including the integrated chemical

effects testing at LANL, chemical speciation prediction activities at CNWRA, and chemical effects

accelerated head loss tests at ANL.

The peer review members provided their final assessments of these three RES-sponsored

research programs areas, and independently offered recommendations for improvement.

Even though the peer reviewers sometimes expressed different opinions in addressing

the specific questions provided by the NRC staff regarding the various research programs,

their input based on their technical expertise is very valuable and will help the NRC to identify

important technical issues for further consideration. As a result, this peer review yielded

the following benefits for the NRC:

* The reviewers' comments and suggestions provided significant feedback

on how one might possibly refine the testing programs to ensure that they

are more representative of the actual PWR environment.

* The reviewers' comments and suggestions will provide the NRC's Office of Nuclear

Reactor Regulation (NRR) with a measure for use in assessing the reliability

and strength of industry-sponsored testing in the chemical effects arena. NRR will

consider outstanding technical issues identified by the chemical effects peer review

panel.

4-1

5. REFERENCES

(1) Bonaca, M. (ACRS), Memo to W.D. Travers (EDO), "Proposed Resolution of GSI-191,

Assessment of Debris Accumulation on PWR Sump Pump Performance,"

U.S. Nuclear Regulatory Commission, Washington, DC, February 20, 2003,

ADAMS Accession #ML030520101.

(2) Shults, W.D., Oak Ridge National Laboratory, Analytical Chemistry Report to J.A. Daniel,

GPUI Service Corporation, September 14, 1979.

(3) Letellier, B.C., "Small-Scale Experiment: Effects of Chemical Reactions on Debris-Bed

Head Loss," NUREG/CR-6868, U.S. Nuclear Regulatory Commission, Washington, DC,

March 2005, ADAMS Accession #ML050900260.

(4) Dallman, J., B.C. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe,

L. Archuleta, and F. Sciacca, "Integrated Chemical Effects Test Project:

Consolidated Data Report," NUREG/CR-6914, Volume 1, U.S. Nuclear Regulatory

Commission, Washington, DC, September 2006, ADAMS Accession #ML062560105.

(5) Dallman, J., B.C. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe,

L. Archuleta, and F. Sciacca, "Integrated Chemical Effects Test Project:

Test #1 Data Report," NUREG/CR-6914, Volume 2, U.S. Nuclear Regulatory

Commission, Washington, DC, September 2006, ADAMS Accession #ML0625601 11.

(6) Dallman, J., B.C. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe,

L. Archuleta, and F. Sciacca, "Integrated Chemical Effects Test Project:

Test #2 Data Report," NUREG/CR-6914, Volume 3, U.S. Nuclear Regulatory

Commission, Washington, DC, September 2006, ADAMS Accession #ML0625601 19.

(7) Dallman, J., B.C. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe,

L. Archuleta, and F. Sciacca, "Integrated Chemical Effects Test Project:

Test #3 Data Report," NUREG/CR-6914, Volume 4, U.S. Nuclear Regulatory

Commission, Washington, DC, September 2006, ADAMS Accession #ML0625601 12.

(8) Dallman, J., B.C. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe,

L. Archuleta, and F. Sciacca, "Integrated Chemical Effects Test Project:

Test #4 Data Report," NUREG/CR-6914, Volume 5, U.S. Nuclear Regulatory

Commission, Washington, DC, September 2006, ADAMS Accession #ML062560129.

(9) Dallman, J., B.C. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe,

L. Archuleta, and F. Sciacca, "Integrated Chemical Effects Test Project:

Test #5 Data Report," NUREG/CR-6914, Volume 6, U.S. Nuclear Regulatory

Commission, Washington, DC, September 2006, ADAMS Accession #ML0625601 33.

(10) Klasky, M., J. Zhang, M. Ding, B.C. Letellier, D. Chen, and K. Howe, "Aluminum

*Chemistry in Prototypical Post-LOCA PWR Containment Environment," NUREG/CR-6915,

U.S. Nuclear Regulatory Commission, Washington, DC, October 2006,

ADAMS Accession #ML062400465.

5-1
(111) K. Kasza, J.H. Park, B. Fisher, J. Oras, K. Natesan, and W.J. Shack, "Chemical Effects

Head-Loss Research in Support of Generic Safety Issue 191," NUREG/CR-6913,

U.S. Nuclear Regulatory Commission, Washington, DC, September 2006,

ADAMS Accession #ML06228041 5.

(12) J. McMurry, V. Jain, X. He, D. Pickett, R. Pabalan, and Y.M. Pan, "GSI-191,

PWR Sump Screen Blockage Chemical Effects Tests-Thermodynamic Simulations,"

NUREG/CR-69 12, U.S. Nuclear Regulatory Commission, Washington, DC,

September 2006, ADAMS Accession #ML060230442.

(13) Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency

Recirculation During Design-Basis Accidents at Pressurized-Water Reactors,"

U.S. Nuclear Regulatory Commission, Washington, DC, September 13, 2004,

available through the NRC's public Web site at hftp://www.nrc.Clov/readin-g-rm/

doc-collections/aen-comm/aen-letters/2004/o1200402. odf.

(14) RES Office Instruction PRM-010, "Peer Review of RES Projects," Revision 0,

U.S. Nuclear Regulatory Commission, Washington, DC, November 14, 2005,

ADAMS Accession #ML052690063.

(15) Los Alamos National Laboratory, "Integrated Chemical Effects Test Project:

Test #1 Data Report," Los Alamos, NM, June 2005, ADAMS Accession #ML051800488.

(16) Los Alamos National Laboratory, "Integrated Chemical Effects Test Project:

Test #2 Data Report," Los Alamos, NM, September 2005, ADAMS Accession

#ML052770402.

(17) Los Alamos National Laboratory, "Integrated Chemical Effects Test Project:

Test #3 Data Report," Los Alamos, NM, October 2005, ADAMS Accession

#ML053040479.

(18) Andreychek, T.S., "Test Plan: Characterization of Chemical and Corrosion Effects

Potentially Occurring Inside a PWR Containment Following a LOCA," Westinghouse

Electric Company, Revision 13, Monroeville, PA, July 2005, ADAMS ML052100426.

(19) Oras, J., J.H. Park, K. Kasza, K. Natesan, and W.J. Shack, "ANL Quick Look Report:

Tests 1 and 2," Argonne National Laboratory, Argonne, IL, September 16, 2005,

ADAMS Accession #ML052590238.

(20) Jain, V., L. Yang, and K. Chiang, "Chemical Speciation, Using Thermodynamic Modeling,

During a Representative Loss-of-Coolant Accident Event," Center for Nuclear Waste

Regulatory Analyses (CWNRA) Report 2004-07 (Revision 1), Southwest Research

Institute, San Antonio, TX, 2004. Published as Appendix C to NUREG/CR-6873,

ADAMS Accession #ML051610123.

(21) Jain, V., X. He, and Y.M. Pan, "Corrosion Rate Measurements and Chemical Speciation

of Corrosion Products Using Thermodynamic Modeling of Debris Components

To Support GSI-1 91," NUREG/CR-6873, U.S. Nuclear Regulatory Commission,

Washington, DC, April 2005, ADAMS Accession #ML051610123.

(22) Oras, J., J.H. Park, K. Kasza, K. Natesan, and W.J. Shack, "ANL Quick Look Report:

ICET-3 Tests 4-11," Argonne National Laboratory, Argonne, IL, January 20, 2006,

ADAMS Accession #ML060190709.

5-2
The following additional references are not cited in this report, but are integrally related

to the chemical effects peer review group assessment:

(23) Dale, C.B., and B.C. Letellier, "Screen Penetration Test Report," NUREG/CR-6885,

U.S. Nuclear Regulatory Commission, Washington, DC, October 2005,

available through the NRC's Agencywide Documents Access and Management System

(ADAMS), under Accession #ML053000064.

(24) Los Alamos National Laboratory, "Integrated Chemical Effects Test Project:

Test #4 Data Report," Los Alamos, NM, November 2005, ADAMS Accession

#ML0533501 63.

(25) Los Alamos National Laboratory, "Integrated Chemical Effects Test Project:

Test #5 Data Report," Los Alamos, NM, January 2006, ADAMS Accession

#ML053550355.

(26) NRC Information Notice 2005-26, "Results of Chemical Effects Head Loss Tests

in a Simulated PWR Sump Pool Environment," U.S. Nuclear Regulatory Commission,

Washington, DC, September 16, 2005, ADAMS Accession #ML052570220.

(27) NRC Information Notice 2005-26, Supplement 1, "Additional Results of Chemical Effects

Tests in a Simulated PWR Sump Pool Environment," U.S. Nuclear Regulatory Commission,

Washington, DC, January 20, 2006, ADAMS Accession #ML060170102.

For more information on the I CET program, see hftp://www. nrc.gov/reactors/operating/opsexoerience/Dwr-suMD-pDerformance/tech-references.html.

5-3

Appendix A

CONTRIBUTION TO THE REPORT

OF THE

CHEMICAL EFFECTS PEER REVIEW GROUP

John A. Apps

Ernest Orlando Lawrence Berkeley National Laboratory

Earth Sciences Division

1 Cyclotron Road

Berkeley, California 94720, U.S.A.

May 2006

FINAL REPORT

This work was supported by the Division of Engineering Technology, Office of Nuclear

Regulatory Research, U.S. Nuclear Regulatory Commission, through MPO (5T-00308 from the

University of Chicago, as Operator of Argonne National Laboratory, with the U.S. Department of

Energy, under Contract (DE-ACO2-O5CHl 1231 with the University of California.

A-I.
ABSTRACT

A joint U.S. Nuclear Regulatory Commission (NRC) and industry sponsored program was

conducted to evaluate the chemical processes following a Loss of Coolant Accident (LOCA) in a

pressurized water reactor (PWR), to address problems associated with the clogging of pump

recirculation screens by secondary precipitates and gels. The program consists of three tasks:

(1) Chemical modeling at the Center for Nuclear Waste Regulatory Analysis (CNWRA) at the

Southwest Research Institute, (2) Performance of an Integrated Chemical Effects Test (ICET)

series at the University of New Mexico under the direction of Los Alamos National Laboratory

(LANL), and (3) Accelerated head loss testing at Argonne National Laboratory (ANL). The

Chemical Effects Peer Review Group was asked to review the technical adequacy of the tree

tasks. In response, the reviewer studied three reports by CNWRA, five ICET reports by LANL,

and three reports by ANL. A number of documents supporting oral presentations at two

meetings held at ANL on October 18-19, 2005, and at Southwest Research Institute on March

27-29, 2006, respectively, were also reviewed together with material supplied by NRC.

Additional documents, scientific papers and reports were also consulted to aid in the

subsequent evaluation and provide corroborating arguments in support of the reviewer's

findings. This report constitutes the response by one of the members of the Peer Review Group,

who was chosen for his expertise in chemical modeling.

The reviewer concludes that the ICET program has made substantial progress towards

understanding and quantifying the chemical processes that could lead to sump screen blockage

during the emergency cooling phase following a LOCA at an operating PWR. However, the

chemical modeling conducted as part of this program falls far short of what is needed, either to

interpret the completed or ongoing experimental studies supporting the program, or ultimately,

to construct a simulator for evaluating PWR plant response following a LOCA; this, despite the

significant improvement in technical understanding and competence reflected in the third report

of the series generated by CNWRA. The reviewer recommends substantive refinements and

improvements to any future modeling, by taking better advantage of the kinetic data acquired in

the course of the program, developing a dedicated thermodynamic database, which

incorporates those aqueous species and product phases of relevance to the test conditions, and

more fully utilizing the reaction progress features available in state-of-the-art codes. Only after

these recommendations are implemented will it be possible to fully interpret the experimental

results of the ICET and head loss test series, refine the thermodynamic and kinetic parameters

in the chemical simulators, and provide ongoing support and guidance to future experimental

research.

A-2
CONTENTS

EXECUTIVE SUMMARY........................................................................... A-5

1 INTRODUCTION.................................................................................. A-8

1.1 ANALYTICAL SIMULATION ............................................................. A-8

1.2 ICET SERIES.............................................................................. A-8

1.3 HEAD LOSS SIMULATION TESTING AND ANALYSIS.............................. A-8

1.4 RESPONSE ............................................................................... A-9

2 ANALYTICAL SIMULATIONS.................................................................. A-10

2.1 THE ADEQUACY OF ANALYTICAL SIMULATIONS CONDUCTED IN SUPPORT

OF ICETS AND HEAD LOSS SIMULATION TESTING AND ANALYSIS.......... A-14

2.2 LIMITATIONS OF CURRENT MODELING WORK .................................. A-15

2.2.1 General Comments ............................................. I............... A-15

2.2.2 Detailed Comments ............................................................ A-19

2.3 RECOMMENDATIONS FOR FUTURE MODELING................................. A-29

2.4 ANALYTICAL SIMULATIONS: QUESTIONS AND ANSWERS..................... A-3 1

3 INTEGRATED CHEMICAL EFFECTS TESTS ............................................... A-33

3.1 ICET #1................................................................................... A-33

3.1.1 Specific Comments................................................ ............ A-33

3.2 ICET #2.................................................................................... A-37

3.2.1 Specific Comments ............................................................ A-37

3.3 ICET #3................................................................................... A-38

3.3.1 Specific Comments ............................................................ A-38

3.4 ICET #4................................................................................... A-41

3.5. ICET #5.................................................................................... A-42

3.6 RECOMMENDED POSTMORTEM EVALUATION OF ICET RUNS............... A-43

3.7 ICET QUESTIONS AND ANSWERS................................................... A-43

4 HEAD LOSS SIMULATION TESTING AND ANALYSIS .................................... A-46

4.1 GENERAL COMMENTS ................................................................ A-47

4.2 SPECIFIC COMMENTS ................................................................ A-48

4.2.1 Head Loss Tests .............................................................. A-48

4.2.2 Supplementary Studies Characterizing Dissolution of Debris and

Precipitation: Oral Presentations, October 18, 2005 ....................... A-50

4.3 HEAD LOSS SIMULATION TESTING AND ANALYSIS: QUESTIONS AND

ANSWERS................................................................................ A-51

5 REFERENCES .................................................................................. A-53

A-3
TABLES

Table 1: Simulations conducted by Jain et al. (2004).............................................. A-l I

Table 2: Simulations conducted by Jain et al. (2005).............................................. A-12

Table 3. ICET Matrix ................................................................................. A-33

Table 4. Chemical Effects Head Loss Tests ........................................................... A-46

A-4
EXECUTIVE SUMMARY

A joint U.S. Nuclear Regulatory Commission (NRC) and industry sponsored program was

conducted to evaluate the chemical processes following a Loss of Coolant Accident (LOCA) in a

pressurized water reactor (PWR), to address problems associated with the clogging of pump

recirculation screens by secondary precipitates and gels. The program consists of three tasks:

(1) Chemical modeling at the Center for Nuclear Waste Regulatory Analysis (CNWRA) at the

Southwest Research Institute, (2) Performance of an Integrated Chemical Effects Test (ICET)

series at the University of New Mexico under the direction of Los Alamos National Laboratory

(LANL), and (3) Accelerated head loss testing at Argonne National Laboratory (ANL).

NRC convened the Chemical Effects Peer Review Group, which was asked to review the

technical adequacy of the tree tasks. to focus on responding to the following technical

questions:

Analytical Simulation

* Is the speciation analysis expected to provide reasonable predictions of chemical product

formation over a range of possible sump environments?

" Is the plan for benchmarking these codes using small-scale testing and the ICET results

appropriate?

* What is the most appropriate way to measure the uncertainty associated with these codes?

ICET Series

*Have the principal sump pool variables, which affect chemical by-product formation in the

post-LOCA environment, been adequately simulated?

*Many ICET variables were held constant during the experiments. How would changes in

the most important constant variables affect chemical product formation?

*What variables or materials not simulated by the ICET testing may have the most impact on

chemical product formation (e.g., coatings, free insulation, flow through sediment and other

materials on sump screen, galvanic effects) and how should their effect be characterized by

testing or analysis?

*Were the methods used within the ICET program to characterize and analyze chemical byproducts sufficient?

Head Loss Simulation Testing and Analysis

" Is the accelerated head loss testing approach viable for evaluating the effects of multiple

chemical environments quickly?

* What is the best method for incorporating time-dependent effects (e.g., material aging,

evolving chemical environments) in simulation testing?

* What metrics are most appropriate for evaluating the results of simulated chemical products

with those that formed during the ICET program?

* Are correlations available, or can they be developed, which can predict the associated head

loss if important physical characteristics of a chemical by-product are known?

A-5
In order to respond to the technical questions posed, the reviewer studied three reports by

CNWRA, five ICET reports by LANL, and three reports by ANL. A number of documents

supporting oral presentations at two meetings held at ANL on October 18-19, 2005, and at

Southwest Research Institute on March 27-29, 2006, respectively, were also reviewed together

with material supplied by NRC. Additional documents, scientific papers and reports were also

consulted to aid in the subsequent evaluation and provide corroborating arguments in support of

the. reviewer's findings.

The following report constitutes the response by one of the members of the Peer Review Group, .who was chosen for his expertise in chemical modeling. The report is sub-divided into five parts.

The first is an introduction defining the background, scope and objectives of the review, the

second addresses the analytical computer simulations to evaluate the requirements for the

ICETs, the third contains a review of the adequacy of the ICET series, and the fourth part is a

review of the head loss tests and supporting research. The report concludes with a list of cited

references. Findings, conclusions and recommendations are not allocated separate parts, as

these topic are adequately covered within parts 2, 3 and 4 of the report that address the

modeling and experimental parts of the program, and are briefly summarized below.

Part 2 contains an in-depth review of three reports produced by the CNWRA. The simulations in

all three reports are summarized in tabular form, and the reviewer gives the conclusions

reached by the authors together with his comments and observations. The adequacy of the

modeling work in relation to support for the experimental studies is then reviewed. The

limitations of the work described in the three reports are then discussed, with both general

comments, and detailed comments relating to specific sections of each text.

Recommendations for future modeling are then made, based on the limitations of the reported

work, and required improvements. The section concludes with responses to the questions

posed by NRC for the Analytical Simulations, as listed above.

Part 3 lists the specifications for the ICET series. Both general and detailed comments by the

reviewer follow for each of the five reports describing the procedures and results of each test.

After reviewing all five reports, the reviewer concluded that a post mortem evaluation of the

ICET runs should be conducted in order to resolve issues of data interpretation and increase

confidence in subsequent modeling analyses. A section is therefore included with specific

recommendations. The section concludes with responses to the questions posed by NRC for

the ICET Series, as listed above.

Part 4 addresses the head loss testing and supplementary bench-scale testing and analysis to

aid in the interpretation of both head loss and the ICET series. Three preliminary reports

specifically addressing the head loss tests done to date and supplementary oral presentations

given at the December 18-19, 2005 meeting at ANL were reviewed. Specific head loss tests

completed to date are listed. Both general and detailed comments by the reviewer follow for the

reports and oral presentations. The section concludes with responses to the questions posed by

NRC for the head loss simulation testing and analysis, as listed above.

The reviewer concludes that. the ICET program has made substantial progress towards

understanding and quantifying the chemical processes that could lead to sump screen blockage

during the emergency cooling phase following a LOCA at an operating PWR. However, the

chemical modeling conducted as part of this program falls far short of what is needed, either to

interpret the completed or ongoing experimental studies supporting the program, or ultimately,

to construct a simulator for evaluating PWR plant response following a LOCA; this, despite the

significant improvement in technical understanding and competence reflected in the third report

A-6
of the series generated by CNWRA. The reviewer recommends substantive refinements and

improvements to any future modeling, by taking better advantage of the kinetic data acquired in

the course of the program, developing a dedicated thermodynamic database, which

incorporates those aqueous species and product phases of relevance to the test conditions, and

more fully utilizing the reaction progress features available in state-of-the-art codes. Only after

these recommendations are implemented will it be possible to fully interpret the experimental

results of the ICET and head loss test series, refine the thermodynamic and kinetic parameters

in the chemical simulators, and provide ongoing support and guidance to future experimental

research.

A-7
I INTRODUCTION

A joint U.S. NRC/industry sponsored program was undertaken through a memorandum of

understanding between NRC and the Electric Power Research Institute (EPRI) in order to

evaluate chemical processes following a Loss of Coolant Accident (LOCA) in a pressurized

water reactor (PWR), particularly with respect to problems associated with the clogging of pump

recirculation screens by secondary precipitates and gels. The program consists of three tasks:

1 . Chemical speciation prediction being conducted at the center for Nuclear Waste

Regulatory Analysis (CNWRA) (Analytical Simulation)

2. Integrated Chemical Effects Test (ICET) series being conducted at the University of

New Mexico under the direction of Los Alamos National Laboratory (LANL) (ICET

Series)

3. Chemical effects accelerated head loss testing being conducted at Argonne National

Laboratory (ANL) (Head Loss Simulation Testing and Analysis)

The Chemical Effects Peer Review Group was asked to review the technical adequacy of the

tree tasks. In particular, the group was asked to focus on responding to the following technical

questions:

1.1 Analytical Simulation

* Is the speciation analysis expected to provide reasonable predictions of chemical product

formation over a range of possible sump environments?

" Is the plan for benchmarking these codes using small-scale testing and the ICET results

appropriate?

* What is the most appropriate way to measure the uncertainty associated with these codes?

1.2 ICET Series

* Have the principal sump pool variables, which affect chemical by-product formation in the

post-LOCA environment, been adequately simulated?

* Many ICET variables were held constant during the experiments. How would changes in

the most important constant variables affect chemical product formation?

* What variables or materials not simulated by the ICET testing may have the most impact on

chemical product formation (e.g., coatings, free insulation, flow through sediment and other

materials on sump screen, galvanic effects) and how should their effect be characterized by

testing or analysis?

" Were the methods used within the ICET program to characterize and analyze chemical byproducts sufficient?

1.3 Head Loss Simulation Testing and Analysis

" Is the accelerated head loss testing approach viable for evaluating the effects of multiple

chemical environments quickly?

" What is the best method for incorporating time-dependent effects (e.g., material aging,

evolving chemical environments) in simulation testing?

* What metrics are most appropriate for evaluating the results of simulated chemical products

A-8
with those that formed during the ICET program?

*Are correlations available, or can they be developed, which can predict the associated head

loss if important physical characteristics of a chemical by-product are known?

1.4 Response

The program is here reviewed in three parts. The first addresses the analytical computer

simulations to evaluate the requirements for the ICETs, the second contains a review of the

adequacy of the ICET series, and the third part is a review of the head loss tests and supporting research.

A-9
2 ANALYTICAL SIMULATIONS

The Center for Nuclear Waste Regulatory Analysis (CNWRA) was asked to perform computerbased modeling with the following objectives:

1. To determine the need for a pressurized test ioop for the ICETs

2. To assess whether gelatinous products could form following a LOCA

3. To gain insights into important parameters

4. To attempt to predict ICET results.

The reason for conducting such computer based modeling was that it would "...allow rapid and

relatively inexpensive identification of the critical chemistry, time, temperature, pressure and pH

variables that affect chemical product formation" (Jain et al., 2005).

To meet the above-cited objectives, a literature survey was conducted to determine the

corrosion rates of materials exposed to cooling water following a LOCA. These materials

included aluminum, copper, carbon steel, and galvanized steel-(zinc), fiberglass insulation and

concrete. Estimated conservative values for corrosion rates of these materials were made on

the basis that corrosion rates at 9000 would be representative, and that the concentrations of

the corrosion products would be dependent on time (up to 15 days), and the estimated total

surface areas of the exposed materials. Two alternative aqueous solutions were assumed, one

consisting of a solution of 0.259 mol/L B(OH)3 Plus 0.15 mol/L NaOH, buffered at a pH = 10, and

the other consisting of 0.259 mol/L B(OH)3 plus Na3PO 4, buffered at a pH = 7.

Preliminary modeling was conducted using OLI system Inc.'s Stream Analyzer Version 1.2 and

Environmental Simulation Program (ESP) Version 6.6 (OLI Systems inc., 2002a,b) by assuming

the equilibrium partitioning of the total concentration of corrosion products between the aqueous

phase, and solid phases at given times following a LOCA, and at temperatures ranging

downwards from 15000 to 6000. Sensitivity studies were also conducted by varying the

concentrations of the individual corrosion products -by +/- 1-2 orders of magnitude at an

unspecified time at 60 and 130 00.

The results and findings of the preliminary modeling are described in a report by Jain et al.

(2004), which was subsequently attached as Appendix C to a later report by Jain et al. (2005).

A listing of the simulations conducted by Jain et al. (2004) is given in Table 1

Jain et al. (2005) conducted electrochemical corrosion rate studies on aluminum, carbon steel,

copper and zinc in 0.259 mol/L B(OH)3 plus 0.15 mol/L NaOH, solutions buffered at a pH = 10.

Studies were also conducted to measure the chemical corrosion of glass used to fabricate

NUKON fiberglass insulation, and the chemical corrosion of concrete in the same solution.

These measurements allowed for refinement of the postulated corrosion rates and

thermodynamic simulations were repeated using revised conservative estimates of the

corrosion rates of the tested materials. The follow-on simulations used the same software as in

the preceding report. A listing of the simulations conducted by Jain et al. (2005) is summarized

in Table 2.

A-10
Table 1: Simulations conducted by Jain et al. (2004)

B(OH)3/NaOH Solution Buffered at pH = 10 _ _____________

No. T, 'C P, kPa Time, hr SpecifiedConditions Output Reported

1 60 101 - 0.26 mau/L B(OH)3 PH, Eh (VSi4E)

90 101 0.23 moliL NaOH

130 304PH=1

150 507

2 60 110.5 As above, plus predicted concentrations of Solid phases precipitated in mot/L or

90 01dissolved components at 0.5 hr from Zn. Al, percent as f(T). Elemental distribution in

130 304carbon steel, Cu. NukonT"S concrete solid phases as f(T, P).

150 507particles and concrete. Amounts estimated ______ _______ ~~~~~~~based on corrosion rate at 90_C for_0.5_hr. ___________________

3 60 101 360 As above, but for an additional 0.24 molIL Solid phases precipitated in mol/L

B(OH)3 to maintain pH at 10.

4 60 101 0.5? As for 3, above, but pH varied between 7 Solid phases precipitated in molIL, plotted

130 304 and 11 as a function of pH

5 60 101 0.5? Sensitivity Study: As for 3, above, but Zn Variation in quantity of precipitated Zn130 304 aqueous concentration varied containing phases as a function of __________ _____________________________ concentration at 60 and 130 *C.

6 60 101 0.5? Sensitivity Study: As for 3, above, but Al Variation in quantity of precipitated Al130 304 . aqueous concentration varied containing phases as a function of __________ _____________________________ concentration at 60 and 130 *C.

7 60 101 0.5? Sensitivity Study: As for 3, above, but Fe Variation in quantity of precipitated Fe130 304 concentration varied containing phases as a function of ______concentration at 60 and 130 *C.

8 60 101 0.5? Sensitivity Study: As for 3, above, but Variation in quantity of precipitated phases

aqueous concentration of concrete as a function of dissolved Ca2SiO4

10 304 components varied concentration at 60 and ___ ___ _____ ______ ___________1_____ 130 *C.

9 60 101 0.5? Sensitivity Study: As for 3, above, but Variation in quantity of precipitated phases

__________aqueous concentration of NukonTý as a function of dissolved NukonTM

130 304 components varied components at 60 and 130 *C.

___ _____B(OH)3/Na3PO4 Solution Buffered at pH =7

1 60 101 - 0.26 mol/L B(OH)3 pH, Eh (VSHE)

90 101 0.0084 mol/L Na3PO4 pH = 7

130 304

150 507

2 60 101 0.5 As above, plus predicted concentrations of Solid phases precipitated in mol/L or

90 101 dissolved components at 0.5 hr from Zn, Al, percent as f(T). ). Elemental distribution in

130 304 carbon steel, Cu, Nukon'", concrete solid phases as f(T, P).

10 507 particles and concrete. Amounts estimated

FIN ____ based on corrosion rate at 90 *C for 0.5 hr.

3 60 101 360 As above, but for an additional 1.5 molIL Solid phases precipitated in mol/L

B(OH) 3 to maintain pH at 7. compared with results above at 130 *C.

5 60 101 0.5? Sensitivity Study: As for 3, above, but Zn Variation in quantity of precipitated Znaqueous concentration varied containing phases as a function of

130 304 concentration at 60 and 130 'C.

6 60 101 0.5? Sensitivity Study: As for 3, above, but Al Variation in quantity of precipitated Al130 304 aqueous concentration varied containing phases as a function of

______ _________concentration at 60 and 130 *C.

7 60 101 0.5? Sensitivity Study: As for 3, above, but Fe Variation in quantity of precipitated Feconcentration varied containing phases as a function of

130 34concentration at 60 and 130 'C.

8 60 101 0.5? Sensitivity Study: As for 3, above, but Variation in quantity of precipitated phases

______ ________aqueous concentration of concrete as a function of dissolved Ca2Si0 4

____ 130 304 ______ components varied concentration at 60 and 130 *C.

9 60 101 0.5? Sensitivity Study: As for 3. above, but Variation in quantity of precipitated phases

130 304 aqueous concentration of NukonTM as a function of dissolved NukonTM

________________ _________ components varied components atf60 and 130 *C.

A-l I
Table 2: Simulations conducted by Jain et al. (2005)

No. T, P, kPa Time, hr SpecifiedConditions Output Reported _ _ oc__ _ _ _

1 60 101 - 0.26 mol/L B(OH)3 pH, Eh (VSHE)

90 101 0.23 mol/L NaOH

___110 =140 pH =10

2 60 101 0.5 As above, plus predicted Solid phases precipitated in mol/L or

90 101 concentrations of dissolved percent as f(T)

110 f -10410 components at 0.5 hr from Zn, Al,

carbon steel, Cu, NukonTm, concrete _________ __________ particles and concrete

3 60 101 0.5 As above, except that dissolved Cu PH, Eh (VSHE)

4 and carbon steel components were Solid phases precipitated in mol/L or

32 omitted for times > 32 hr. For times Ž percent as f(time). Elemental

148 180 hr dissolved components from distribution in solid phases as f(time).

240 NukonTM were fixed. Concentrations of dissolved

360 components in aqueous phase as I __ I _ _ ______ ______ ________________ f(time).

It should be noted that in neither report was any consideration given to the corrosion of Cal-Sil

insulation, which is commonly used instead of fiberglass in many PWRs. Furthermore, Jain et

al. (2005) did not consider Na3PO4 buffering at pH = 7. Therefore, the modeling did not fully

account for all operating conditions in the subsequent ICETs

The conclusions reached by both Jain et al. (2004) and the covering report by Jain et al. (2005)

can be summarized as follows:

1 . The chemical processes occurring during the period following a LOCA, when

temperatures are greater than 10000C, are similar in character and magnitude to those

occurring at temperatures below 10000, and therefore, the costs associated with the

design and operation of a pressurized high temperature (150 0C), elevated pressure (5

atm) ICET circuit would not be justified by the additional information obtained.

2. The contributions to the formation of screen clogging precipitates arising from the

corrosion of copper, steel and zinc, are insignificant compared with those arising from

the corrosion of fiberglass insulation and aluminum.

3. The impact of concrete corrosion on screen clogging is expected to be minor, and is

associated primarily with cement dust and scaling debris, rather than corrosion of

concrete surfaces of the containment vessel and interior structural members

4. There would be a potential for gel formation, based on their finding that one of the

principal precipitants from the alkaline solution, NaAISi 3O83 would likely form a gel.

Such gel formation could enhance screen clogging following a LOCA.

The reviewer concurs with the first three conclusions. Conclusion (4 might also be valid in that

some siliceous precipitate might accumulate as a gelatinous solid. However, the extent to

which such a solid would form depends on the rapidity with which silica accumulates in solution,

the extent of neutralization due to the corrosion of aluminum, and falling temperature. The latter

two processes would destabilize colloidal silica and lead to gel formation. However, neither Jain

et al. (2004), nor Jain et al. (2005) provide adequate justification or arguments to support this

position. When reference is made to the original objectives of their work, it is clear that only

A-12
Objective (1 was fully met. Objective (3 regarding acquisition of insights into important

parameters governing the operation of ICETs, were met in part as a result of the literature

survey regarding corrosion rates in Jamn et al. (2004) and additional experimental work reported

in Jain et al. (2005). In this regard, the computer modeling provided only a limited contribution

towards meeting this objective.

The authors placed significant faith in the output generated by the computer si mulations, much

of which is misleading or erroneous, Other important conclusions are embedded in the text, or

could have been reached without recourse to the extensive simulations conducted in both

reports, The limitations, deficiencies and further conclusions are discussed below in Section 2.2:

Limitations of Current Modeling Work.

A third report was subsequently released in draft form by the CNWRA (McMurry et al. (2006)

The main purpose of the underlying study was-to further evaluate the use of thermodynamic

simulation software as a tool to investigate chemical interactions that could affect sump pump

performance after a LOCA. The report covers four tasks:

1 . An evaluation of aqueous chemical modeling software

2. EQ3/6 thermodynamic simulations of the ICET series.

3. StreamAnalyzer simulations of the ICET series

4. An assessment of modeling chemical effects under plant-specific conditions.

The software comparison involved the testing of four generally available chemical modeling

codes: EQ3/6 (Wolery, 1992; Wolery and Daveler, 1992; LBNL, 2003), the REACT module of

Geochemist's Workbench (xxx), StreamAnalyzer (OLI Systems, Inc., 200a) and PHREEQC

(U.S. Geological Survey, 200x). Model input for all four codes was based on the hypothetical

post-LOCA containment water composition derived from Jain et al. (2005), and representing the

species dissolved in 0.26 mol/L B(OH)3 adjusted to pH = 10 with NaOH. Separate runs were

conducted at 0.5 hr at 90 and 110 C, and at 0.5, 4, 72, 148 and 360 hr at 60 C, assuming

cumulative concentrations of debris or structural material corrosion products in solution at the

specified time and temperature. The codes were used to determine the final equilibrium

solution composition and the identity and quantity of co-existing phases that would precipitate

from an initially supersaturated solution of specified composition. The authors found that the

EQ316 code was most convenient to use for the problem at hand, as it never failed to converge,

and automatically identified the thermodynamically most stable phase assemblage. However,

the EQ3/6 thermodynamic database for aqueous species contained only a limited number of

borate species, and therefore the code's ability to simulate the properties of borate solutions

was questioned. In contrast, StreamAnalyzer contained a much more substantial borate species

database. McMurry et al. therefore decided to conduct replicate simulations of the ICET series

using both EQ3/6 and StreamAnalyzer.

The initial conditions for the ICET simulations using both EQ316 and StreamAnalyzer were as

specified in Table 3. For EQ3/6, separate runs were conducted at 0.5, 32, 148 and 360 hr at 60

C, assuming cumulative concentrations of debris or structural material corrosion products in

solution at the specified time and temperature. The corrosion rates were based on those

determined in Jain et al. (2005). Dissolved 02 and C02 , equilibrated with respect to the

atmosphere were accounted for in the input. The runs were repeated in under two separate

conditions: (1) By including all relevant phases in the thermodynamic database, and (2) By

A-13
suppressing some 40 odd phases that were deemed unlikely to form in the system under study,

or which had precipitated under Case (1), but which were known not to form under actual ICET

conditions. The StreamAnalyzer runs were conducted at 0.5, 32, 148, 360 and 720 hr at 60*C.

The corrosion rates of Nukon and cal-sil were based on more recent experimental data.

Because Al in solution was found to inhibit Nukon dissolution, the dissolution rate in the ICET #1

and ICET #5 was fixed at that after 90 hours for all runs representing times greater than 90 hr.

The corrosion products of Cu and Fe were omitted in order to avoid convergence problems.

Dissolved 02 and 002 were. not included in the input. The selective suppression of those

phases not observed to form in favor of those observed during the ICET series was also

practiced. For example, all silicates were suppressed. Therefore the outputs from the EQ3/6

and StreamAnalyzer runs could not be compared rigorously.

The comparison between the ICET series and model results provided a basis for a critical

assessment of limitations of the simulations due to (1) lack of thermodynamic data for relevant

phases and aqueous species in the code databases, (2) limitations in the kinetic data relating to

the dissolution of reactive materials in contact with buffered borate cooling waters, especially in

relation to a failure to take into account coupled effects on dissolution kinetics due to the codissolution of other materials (3) an inadequate characterization of, Al corrosion under ICET

conditions including the effects of passivation by Ca silicates, (4) inhibition of Nukon dissolution

by dissolved aluminum, (5) saturation of cal-sil containing phases in solution, (6) an incomplete

characterization of secondary precipitates and (7) limitations in accounting for the role Of CO 2

and the precipitation of carbonates. Overall, the modeling in McMurry et al. (2006) reflected a

better understanding of the issues involved.

McMurry et al. (2006) reached essentially the following conclusions:

1 . Despite the noted limitations, the StreamAnalyzer generally provide good agreement

with experimental results, particularly at modeled times of •5140 hr.

2. I mproved results with StreamAnalyzer compared with those using EQ316 depended less

on the software than on revised and more accurate estimates of the aqueous phase

starting compositions, and on the preferential selection of secondary precipitates.

3. More generally, widely supported programs such as EQ316 or PHREEQC provide

modeling advantages in terms their flexibility in suppressing the precipitation of specified

phases, and the ease with which thermodynamic databases can be modified to better

represent the system being modeled.

2.1 The Adequacy of Analytical Simulations conducted in Support of ICETs and

Head Loss simulation Testing and Analysis

The objectives of the NRC sponsored work at the CNWRA and whether these objectives were

met is spelled out below.

To determine the need for a pressurized test loop for the ICET'. s

The evaluation showed that there was no compelling need for a pressurized test loop for ICETs.

However, actual chemical processes likely to take place at any temperature and pressure

following a LOCA, were not quantitatively demonstrated.

To assess whether gelatinous products could form following a L OCA.

A-14
No information was provided that would demonstrate that gelatinous products would form

following a LOCA.

To gain insights into important parameters.

The experimental studies to quantify metal and other debris corrosion rates by Jain et a[. (2005)

ands subsequent refinement of Nukon and cal-sil leaching kinetics by McMurry et al. (2006) are

a valuable contribution towards model development, and helped show which debris components

were important, and which were less so. However, the data developed were not used to their

fullest advantage in subsequent modeling.

To attempt to predict ICET results.

ICET results were predicted only in a rudimentary sense.

In the following discussion, the reviewer is responsive to pertinent technical questions posed by

NRC for the Chemical Effects Peer Review Group. However, because the current modeling

work falls short of what is needed, the reviewer also provides and expanded critique of the

limitations of the work done so far, and recommends an amended approach that would be both

scientifically defensible, and provide a more meaningful basis for model calibration and

verification using the results of the ICETs; and the Head Loss Simulation Testing. Such an

approach might permit the resulting model to be customized for predictive simulations of the

consequences of hypothetical LOCAs with respect to specific PWR designs. The work done so

far has only begun to address the requirements for model calibration or validation with the

ICETs and the Head Loss Simulation Testing.

2.2 Limitations of Current Modeling Work

2.2.1 General Comments

The modeling work described by Jain et al. (2004), Jain et al. (2005) and McMurry et al. (2006)

suffers from several limitations and deficiencies. The limitations and deficiencies apply primarily

to the first two reports, as some have been partially addressed, or at least identified, in the last

report. Full advantage has not been taken of available software capabilities to provide an

adequate framework for follow-on experiments and analysis. Specific issues are as follows:

1 . The thermodynamic database for OLI Systems Inc. codes lists phases solely by their

chemical composition, e.g., NaAlSi 3O8. Specific polymorphs are not identified by their

mineral names, properties, or Greek alphabet prefix, as is customary in the

geochemical or materials science literature, respectively. Thus there are 5

polymorphs of albite (NaA[Si 3O8) listed in the output provided in Appendix B to Jain et

al. (2004), i.e., Appendix C of Jain et al. (2005). The source of the data contained

within the database is not given, so there is no way of finding out whether the data is

correct or when it was last updated or revised. Inspection of the listing of participating

phases suggests that they might be rock-forming minerals that would form under

hydrothermal, metamorphic or magmatic conditions. Such a database is largely

unsuitable or useless for the simulations being conducted, and would yield

meaningless results.

2. The OLI Systems codes are designed to explore the operation of. systems in which

reaction rates are sufficiently fast that equilibrium is assumed, and that complex flow

A- 15
streams between multiple reactors can be modeled. A particular feature of the OLI

Systems codes is that they are capable of modeling very high ionic strength solutions

(up to 30 Md) using Pitzer (1991) or Bromley (1972) electrolyte models. The

capabilities of these codes are either insufficient, or not critical for the system being

modeled. The absence of provisions that would allow for the evolution of a system

under specified kinetic controls is particularly critical.

3. For reasons that are discussed further below, phases that would nucleate and

precipitate following a LOCA, would probably be amorphous or poorly crystalline, and

colloidal or microcrystalline in size. Such phases would be far more soluble than the

thermodynamically most stable phases for the specified conditions. A more suitable

thermodynamic database than that used with the OLI Systems codes for phases that

would form under such conditions is that used with the MINTEQ code (Felmy et al.,

1984), which is designed for relatively low temperature (0 - 100'C) aqueous chemical

processes. However, it is up to the modeler to ensure that the thermodynamic

database contains those phases most likely to nucleate and precipitate under the

conditions to be modeled. It is not sufficient to take an off-the-shelf code and

associated database without first establishing its suitability, or revising the database

through addition of more appropriate phases and their properties. Jain et al. (2005)

may have been aware of the limitations of the OLI Systems database, as they refer to

the phases as "potentially amorphous", but took no action to correct for the problem.

McMurry et al, in contrast, were fully aware of the limitations, and attempted to correct

the problem,, at least in part, by suppressing certain phases from participating in the

equilibrium calculation while using both EQ316 and the OLI Systems StreamAnalyzer.

3. All of the calculations performed using OLI Systems Inc. codes assume a given initial

concentration of components in solution, which are then distributed between the

aqueous phase, and thermodynamically most stable solid phases. However, in Jain

et al. (2004) and Jain et al. (2005), the initial conditions are incompletely specified,

i.e., whether a vapor phase is assumed to be present, and if so, how much? How

was the oxidation state specified? Was the pH fixed, as suggested in the text, or was

it a dependent variable? The "Typical OLI Simulation Output", given in Appendix B of

Jain et al. (2004) indicates that Zn, Al, Cu and Fe were specified as being in their

metallic state in the "Stream Inflows", and as cited in Table 3-3 of Jain et al. (2005).

Furthermore, the output indicates that hydrogen was generated, but remained entirely

in the aqueous phase, instead of partitioning into a vapor phase. No mention is made

of the input pH, so it must be presumed to be a dependent variable, i.e. pH = 6.977 1

as cited for the output. The code option "Redox selected" was also invoked, which

allowed calculation of the Eh = -0.339 V.

4. The purpose of the studies by Jain et al. (2004) and Jain et al. (2005) was to provide

guidance in the design and operation of the ICET and head loss experiments.

Because the ICETs and Head Loss Simulation tests are both conducted With limited

headspace, the absence of a coexisting vapor or vapor phase should be of limited

concern if the computer calculations are used for the purpose of predicting, or

simulating these tests. However, this presumes that the limited headspaces have not

been exposed to atmospheric exchange for a significant period of time. Such

exchange, particularly with respect to 002, could have a significant impact on the

chemical evolution of the system over time, and should require that such uptake be

taken into account, if necessary. Jain et al. (2004) and Jain et al. (2005) did not

consider the effect of scavenging 002 from the air as possibly impacting the evolving

A-16
chemistry and nature of the precipitates. Calculations by the reviewer suggest that

the potential quantity of calcium precipitated, as calcite through uptake of atmospheric

002 in a containment building would be less than 1 % of the total calcium brought into

solution by the dissolution of fiberglass. However, calcite might nucleate and

precipitate early in the post-LOCA cooling cycle, and facilitate subsequent

heterogeneous nucleation and precipitation of calcium phosphates and silicates.

Furthermore, the amount of C02 taken up during operation of any of the ICETs may

have proportionately exceeded that which could have been scavenged from the

atmosphere in the containment building. Thus, although the omission might be

justified, because atmospheric 002 would be a minor component, its effect on

precipitation kinetics could be significant. McMurry et al. have drawn attention to the

limitations in accounting for the role Of CO2 and the precipitation of carbonates. The

ultimate goal of all simulations undertaken in the program should be to predict

adverse conditions following a LOCA in an operating PWR. Due consideration should

therefore be given to eventually simulating actual post-LOCA cooling operations by

including a coexisting gas phase equivalent in volume to that of the containment

building.

5. The calculated Eh values presented in Tables 3-2 and 4-1 of Jain et al. (2004) and in

Tables xx of MoMurry et al (2006) are probably meaningless under the conditions of

the ICETs, as it is highly unlikely that the circulating aqueous phase would achieve

internal equilibrium with respect to participating redox pairs. Therefore, Eh should not

be emphasized. This same caveat applies with even greater force to actual

conditions following a LOCA. Hydrogen from the corrosion of aluminum would degas

into the air of the containment building, and oxygen would continue to saturate the

circulating coolant water. However, as other members of the Chemical Effects Peer

Review Group have pointed out, e.g. McDonald (2006), significant radiolysis of the

circulating coolant could occur with formation of H202, depletion of oxygen, and

production of additional hydrogen. Attainment of a meaningful calculated solution Eh

would be unlikely, as the circulating coolant would not be able to achieve

homogeneous equilibrium during the frame it would be recirculated. Furthermore,

radiolytic effects could be adequately simulated only through modification of the

existing a geochemnical modeling code to account for an imposed radiation flux.

6. As noted above, the thermodynamic calculations presented by Jai et al. (2004) and

Jain et. (2005) assume a certain quantity of Zn, Al, Cu or Fe is available for corrosion

after a given time, and is supplied as input to the model in the metallic state.

Thermodynamic equilibrium is then assumed through reaction of the constituent

metals with the aqueous phase, and precipitation of corrosion products. This causes

the calculated Eh to fall sharply to approximately -0.4 V at pH = 7, (e.g., see

Appendix B of Jain et al., 2004), and even lower at higher pH. Under such conditions,

Cu is stable in its native state, rather than as an oxide, as is confirmed by the

reported results of the simulations in both Jain et al. (2004) and Jain et al. (2005).

Dissolved copper in the recirculating coolant would plate out on exposed aluminum

and steel surfaces, and be quantitatively removed from solution, in conformity with the

modeling results. The presence of native copper in contact with exposed steel or

aluminum could enhance the corrosion rate of either through galvanic coupling. In

contrast, the dissolution of metallic Fe, i.e., steel, would lead to immediate oxidation

with precipitation of Fe oxides under oxidizing alkaline conditions, as oxidation of Fe 2 +

is catalyzed by 01-1 (Singer and Stumm, 1968, 1970). Passivation of the Fe could

result if Fe 3O4 precipitates on exposed steel surfaces, as is suggested by Jain et al.

A-17
(2005, p. 2-2). At lower pH, i.e., at a pH =7, Fe 2+ is likely to accumulate in the

aqueous phase, but the presence of oxygen will ensure that precipitation in the Ill

state will occur during circulation of the coolant. It is quite unlikely that iron would at

any time precipitate in the Fe(ll) state as reported in the simulations, i.e., see p. 3-4 of

Jain et al. (2004). It would have been more appropriate, therefore, to assume an

excess of oxygen to have been present during the computation of the species

distribution between the aqueous and solid phases, rather than ignoring it as was

done by the authors.

7. The chemical composition of the concrete and concrete dust is presumed to consist

of Ca2SiO4 (belite), a phase known to occur in five polymorphic forms (Taylor, 1997).

However, Ca2SiO4 is one of the principal ingredients of cement before it is mixed with

water to produce a cement paste, and *does not persist in concrete or concrete dust.

Ordinary Portland cement (OPC) reacts with water to form principally C-S-H (CaOSiO2-H 20) "gel' and portlandite (Ca(OH)2). It is these phases that should be

considered if fresh concrete were to be leached by the recirculating coolant.

However, neither the exposed concrete faces nor concrete dust in the containment

building are likely to be fresh. After 30 years exposure to the atmosphere, a

substantial fraction of both the exposed C-S-H gel and the portlandite would have

been carbonated (Parrot and Killoh, 1989), i.e. they would have converted to a

mixture of amorphous silica and either vaterite or calcite (Slegers and Rouxhet,

1976). Therefore, exposed cementitious materials would most likely be carbonated,

and the modeling should reflect this state of affairs.

8. There are inherent limitations to all modeling work done to date, because the

dissolution rates of debris and construction materials are represented by computing a

fictive accumulated concentration of dissolved species in solution after fixed time

periods, and then distributing the dissolved species among precipitated phases. While

it is understandable that the initial stage of modeling should involve such scoping

calculations, this approach seriously limits realistic simulations of the ICETs or head

loss tests. Several codes are available in either the academic or commercial sector

that allow simulations in which dissolution and precipitation rates are kinetically

controlled, e.g. EQ6 (Wolery and Daveler, 1992), TOUGHREACT (Xu et al., 2004),

the Geochemist's Workbench (Bethke, 2005) and PHREEQ-C (Parkhurst and Appelo,

2005). While some effort would be required to incorporate appropriate kinetics for

heterogeneous reactions in these codes, this is not insuperable, and would greatly

enhance the value of the modeling. The major difficulty with the study of the evolution

of a chemical system with time is largely overcome in this program, because Jain et

al. (2004) and Jain et al. (2005) have already undertaken an extensive literature

search and conducted experimental studies to measure the corrosion rates of

affected materials, and this work is supplemented by further studies of the dissolution

rates of Nukon and cal-sil reported by McMurry et al. (2006). Furthermore, the

TOUGHREACT code also permits non-isothermal simulations to be conducted.

Therefore, a simulation of both variable dissolution and precipitation rates during

cooling could be accomplished. Such modeling would also possess the added

advantage that the kinetic parameters could be refined using output data from the

ICET and head loss tests.

9. McMurry et al. (2006) correctly identify additional limitations hindering an improved

predictive capability for current modeling activities. They include (1) a lack of

thermodynamic data for relevant phases and aqueous species in the code databases,

A-18
(2) limitations in the kinetic data relating to the dissolution of reactive materials in

contact with buffered borate cooling waters, and (3) an incomplete characterization of

secondary precipitates. However, these problems are not insuperable, and much

progress can be made by a further review of the literature, particularly in relation to

work conducted with respect to metastable calcium phosphate precipitates (Van

Kemenade and de Bruyn, 1987) and metastable aluminum oxy-hydroxides (Van

Straten and De Bruyn, 1984). The extensive data on borate species in solution

undoubtedly has a source (ref), and suitable analysis could permit its consolidation in

the databases f the code of choice. The limitation in current kinetic data, e.g.,

inhibition of Nukon dissolution by dissolved aluminum, and the potential passivation of

aluminum by dissolved silica (+ calcium?), clearly mandate additional experimental

studies to characterize the interactive kinetic behavior of concurrently corroding

materials. Finally, the inadequate characterization of precipitates during the ICETs

may necessitate dedicated experiments to collect sufficient material for more detailed

characterization.

10. In Jain et al. (2005), sensitivity studies were conducted by arbitrarily varying the

corrosion rates of the various materials, one at time, over very large, and possibly

unrealistic ranges. Apart from the fact that the kinetic rate parameters are only a few

of the total number of parameters in the models that contribute to uncertainty, the

selection of the magnitudes of these parameters tended to be made on the basis of

conservatism rather than accuracy. Ideally, the uncertainties in all parameters should

be embedded in the chemical modeling simulator, and the uncertainties in all

calculated results carried through to the output. Attempts to do this have so far been

exceedingly limited, e.g. see Najm et al. (2003) and Reagan et al. (2004). Add-on

modules to address this problem have been developed for the PHREEQC code

(Ekberg and Emren, 1996; Ekberg et al., 2000). Given the current limitations of code

development, it would seem that the most pragmatic approach would be to conduct

multiple realizations, each time varying the critical input parameters using a Monte

Carlo approach, and evaluating the overall uncertainty in output parameters.

11. It has been noted that all simulations conducted to date ignore the presence of a

radiation flux, which would induce radiolysis in the water and some of the dissolved

species, e.g. bicarbonate. Preliminary simulations show that a variety of radiolysis

products are formed, including H202, H2, with corresponding reduction in dissolved

oxygen. Radiolysis could cause the oxidation state of the aqueous phase to rise, as

H2 would partition into the atmosphere of the containment building. It is not certain

what the overall effect would be on precipitate formation and sump-screen clogging.

However, the issue should be reviewed in the event that it may have a significant

impact on real world behavior.

2.2.2 Detailed Comments

2.2.2.1 Jain et al. (2005)

2-2. Reference is made to the variability in Fe corrosion with temperature due to lower

dissolved oxygen at elevated temperatures. However, rates of reaction are likely to

increase and 02 diffusion rates also. A more likely reason is the more rapid and

coherent build-up of a passivating oxide layer on the steel surface.

A-19
2-4. Reference is made to "stones" in concrete. The correct terminology is "coarse

aggregate".

Dicalcium silicate is referred to as the reactant in concrete. This is incorrect. It should

be C-S-H gel or Ca(OH) 2.

4-1 The simulation is limited to pH = 10 with a B(OH) 3INaOH mixture. However, that is not

what is meant. The pH would vary with time depending on the amount of debris

dissolved and the initial contribution Of 002 that would be stripped from the air in the

containment building. The latter process would not be relevant to ICET or head loss

tests, where the air headspace is small.

It is stated that corrosion rates at pH = 7 are expected to be similar to those at pH =10,

but the corrosion of Nukon is reported as being three times slower at the lower pH.

It is not clear whether the cited pH values are measured or calculated at the operating

temperature, or are referenced to 250C. As noted elsewhere, pH should be considered

a dependent parameter, as treated in the modeling.

4-2 The text is confusing. No reference is made to whether corrosion products of metal are

incorporated or the metals themselves. Only reference to the incorporation of a metals

is the reference that ".. .most of the copper added as copper metal in the simulation

remained as copper metal", and in Table 3-3.

Repeated reference is made to "...potentially amorphous solid phases..." Either they

are or they are not amorphous in the simulation. Did the authors check to find out

whether the product phases in the simulation were specified as amorphous or

crystalline?

Repeated reference is made to "...soluble phases of silica [such as] H3SiO4 _

1 and

NaHSiO3 .. ." or "...the calcium-bearing soluble phase was CaH 2SiO3". This is incorrect.

What the authors are referring to as aqueous species in a homogeneous aqueous

phase.

Reference is made to the "...speciation of solid phases.." Presumably, the authors

mean distribution of solid phases?

A statement is made that "Copper was thermodynamically stable and showed no

corrosion." Yet published Eh-pH diagrams show that under the Eh-pH conditions

reported in Table 3-2 of Appendix C, CuO, i.e. a Cu(ll) containing phase would be more

stable than copper. Only by reference to Appendix B of Jain et al. (2004) can it be

discerned that the redox potential is determined by the corrosion principally of aluminum,

and that the Eh and pH are in the region of -0.4 V and 7.0 respectively.

4-5 Reference is made to the formation of CaSiO 3 and Si0 2. These formulas correspond to

the minerals wollastonite and quartz, which are unlikely to coexist at the temperatures

and pressures of post LOCA coolant circulation. A more likely assemblage would be

tobermorite + gyrolite or the Z-phase, or gyrolite or the Z phase + amorphous silica.

CaSiO3 and Si0 2 is a fictive model assemblage generated by the simulator, and

highlights the problem associated with the use of off-the-shelf databases and uncritical

acceptance of the model results.

A-20
4-10 It is inappropriate to discuss the stability field of albite (NaAlSi 3O8) in relation to gibbsite

AI(OH) 3 using an Eh-pH diagram. No redox reactions are involved. If the stability

relations of these two phases require graphical examination, then an activity diagram

using chemical potentials Na2O, A1203 and SiO2 should be generated. The authors

would then discover that other phases should also be taken into consideration such as

beidellite, kaolinite, halloysite or allophane.

4-11 The solubility boundaries in this Eh-pH diagram should be defined by a Total Aluminum

concentration. Without such data, the figure is inadequately defined.

Appendix B

B-2 The authors note that the rates of Nukon dissolution clearly vary as a function of time,

as. Yet, for reasons of conservatism, they adopted a maximum initial rate of corrosion

as being representative. The cause of the non-linearity in rates over time was not

evaluated, although it was assumed that it was due to the formation of secondary layers

[leached layers?] on the surface (Appendix C, p. 2-10). However, it could also be due to

the dissolution of a more highly reactive disturbed layer, the precipitation of secondary

phases, or an approach to metastable equilibrium of the glass with the aqueous solution.

For meaningful modeling, the mechanisms should be identified, and a suitable algorithm

describing the temperature dependent process incorporated in a simulator. See notes

elsewhere concerning the use of "conservative" versus realistic values in modeling.

2.2.2.2 Jain et al. (2004) [Appendix C of Jain et al. (2005)]

xii Throughout Appendix C, reference is made to the precipitation of Ca5(OH)(P0 4)3, or

apatite as the phase that would precipitate through the reaction of dissolved Ca 2+ with

Na3PO 4. In actual fact, this phase is slow to crystallize, and it is far more likely that

metastable poorly crystallized phosphates will form, especially at high degrees of

supersaturation (Van Kemenade and De Bruyn,1987; Van Cappellen, 1991). Therefore,

permitting this phase to control the solubility of Ca 2 + and P0 4 3 in solution is unrealistic.

1-3 Table 1-2. The analysis of the "gel" in this table is essentially meaningless, as the

reported constituents add up to only 0.0131 % of the total mass. What accounted for the

remaining 99.99%?

2-8 Concrete is not a mixture of tricalcium silicate, dicalcium silicate, etc. The first two are

the principal phases present in cement before it is mixed with water and aggregate to

produce concrete. Corrosion rates cited in Jantzen (1984) are with respect to fresh

concrete. The assumption is that none of the cementitious materials exposed in the

interior of a containment building would have undergone carbonation, which is highly

unlikely given the duration of exposure of exposed concrete faces to the atmosphere.

Concrete dust would be especially subject to very rapid carbonation, converting the

cement reaction products into CaCO3 (calcite, vaterite) + Si0 2 (amorphous silica).

3-1 It is stated that "Simulations were conducted at pH 10..." and that a pH of 10 was

obtained by adding 0.23 [mol/LJ. ... NaOH." and that "Additional 0.24 [mol/L] 1- 3130 3 was

needed to maintain pH at 10." The statements are confusing. As far as the reviewer can

ascertain, the input to the OLI Systems codes did not permit the specification of pH, and

furthermore, pH could not be maintained in the simulation through the addition of

B(OH) 3. Throughout Section 3, figures contain captions referring to "simulated

A-21
containment water at pH 10" or similar phraseology. It is not stated whether "pH 10"'

refers to the initial pH before reaction or after, and whether the pH is referenced to 25 'C

or the temperature of the simulation. Inspection of Table 3-2 and reference to Appendix

B suggests that "pH 10" refers to the pH of the simulated containment water alone at

6000, and therefore does not reflect the final pH of the aqueous phase in equilibrium

with secondary precipitates.

The authors refer to the "hourly corrosion amount of each component", when in fact, they

are referring to the half-hourly corrosion amount.

3-2 It is not clear what reaction determines the redox state for borated water in Table 3-2.

Note that reference is made elsewhere that oxygen and 002 was not included in the

initial chemical composition of the aqueous phase.

3-5 Note the argument that "...similar solid phases are formed in the first half hour of the

LOCA event at 150'C as those from a 15-day or longer simulation test at 600C."

Presumably, this is one of the reasons justifying the exclusion of elevated pressure

ICETs. However, these results are primarily an artifact of the database, and might not be

valid if more realistic secondary precipitates were incorporated in the model.

3-7 It is noted that the formation of iron phases depends on pH. Thus, with increasing pH, iron is found in F'e3Si 2O5(OH) 4, then Fe304, then Ca3Fe2Si301 2 and finally CaFe2O4. This

sequence shows that the oxidation state for iron goes from 11 to Il/Ill to Ill to Ill, indicating

higher oxidation states with increasing pH. This finding is the result of allowing native

metals to dissolve in a system where the only oxidant is the water itself. This is

inconsistent with the role of oxygen in oxidizing Fe to the 11 state in neutral to alkaline

solutions. See the reviewer's comment regarding OH- catalysis under item 6 on p. 9.

Therefore, 02 should have been specified as an input species.

3-16 The final statement: "This fiber insulation..." is ambiguously worded. The reviewer

presumes that the authors are referring to the lack of variation in the makeup of the

precipitated phases with varying fiberglass concentrations, rather than the mass of

secondary precipitates, which does vary. Also, it should be noted that in the simulations

the concentration of fiberglass reaction products is roughly equivalent to that of concrete,

e.g., see Table 3-1. Therefore, it would not be expected that variation of fiberglass

reactant composition would have much impact on the results.

4-1 It is stated that "An additional amount of 1.5 [mol/L] 1- 3B303 was needed to maintain a pH

7." Yet subsequent tables refer only to simulated containment water containing 0.26

mol/L Boron. What does the quoted statement mean? Was this additional quantity of

B(OH) 3 added to the input composition in order to maintain an output pH of 7?

It is not clear what reaction determines the redox state for borated water in Table 4-1.

What causes the Eh to be lower than that of the alkaline borated water given in Table 3-

2?

4-12 It is stated that "The fiber insulation sensitivity analysis at pH 7 indicated no significant

impact on the formation of solid phases..." See comment for pp. 3-16. The real reason

for the lack of variation is primarily because its reaction products are roughly equivalent

to those that form from concrete.

A-22
5-2 Item (v). There is a real danger in placing too much faith in the finding that the

retrograde solubility of secondary calcium silicate phases could assist in the unclogging

of pump strainers. In reality, secondary colloidal/gelatinous hydrated calcium aluminum

silicates, once formed, would be unlikely to redissolve within the time frame of interest.

The ICET and Head Loss tests would help answer this question.

6-1 This section on gel formation is devoid of meaningful content. Better descriptions of

gelation phenomena, and their causes, especially with respect to the formation of silica

gel, can be found in the literature (Scherer, 1999; Lasaga, 1998; Lyklema, 1991; Weres

et al., 1980).

7-1 It is claimed that the report validates OLI Systems, Inc software for speciation in borated

waters.. However, the relevant validation study is reported only in Appendix A, Section 2.

If the findings of the validation study are of sufficient importance to be included in the

Conclusions, then this work should have been incorporated in the main body of the text.

7-2 7.1 Conclusions For convenience, the eight bulleted conclusions relating to the

circulated alkaline borate water are numbered in order to facilitate comment.

NaAISi3O8, Ca3Fe2Si3O12 and Fe3Si4O1O(OH) 2 were dominant solid phases that contributed

to over 90 percent of the solid phases formed between 1500C [3020F]. 507 kPa [5 atm] and

600C [1400FJ.

Phases cited are unlikely to form under LOCA conditions

The CaaFe2Si3Oi 2 solid phase was formed at 150*C [302 0

F]. 507 kPa [5 atm]l. while

Fe3Si2O5(QH)4 was formed at 60'C [140 0F]. This transformation was attributed to the

retrograde solubility of calcium in iron bearing minerals. Despite these phase changes, all

the iron was present in the solid phase.

Cited phases are unlikely to form under LOCA conditions. Stabilization of Ca3Fe(llI) 2 Si301 2

and Fe(Il) 3Si205(OH)4 with iron in different oxidation states is an artifact of the specified

initial conditions for the distribution of species. As noted above, the distribution of Fe is a

function of (OH)- dependent oxidation kinetics

Copper had no influence on the precipitation of solid phases, and no corrosion of copper is

expected.

This conclusion is correct.

The contribution from zinc was insignificant compared to other solid phases and was limited

to 5 percent to the total quantity of solid phases.

This conclusion is justified by the presented literature data on zinc corrosion, and the

magnitude of exposed galvanized steel.

Sensitivity analyses for aluminum indicated formation of A I(OH) 3 for aluminum

concentrations exceeding 2 x 10-4 mo/IL at 600C [1400F]. The formation of AI(OH)3 was not

observed at 130 0C [266 0F]. 304 kPa [3 atm].

A-23
The precipitation of AI(OH) 3, or AIO(OH) at temperatures higher than 600C, depends on their

being an insufficiency of silica to form phases such as beidellite, kaolinite, halloysite,

allophane, etc. Their failure to precipitate as stable phases in the simulations suggests

either an insufficiently comprehensive thermodynamic database, or erroneous data.

Sensitivity analyses for concrete indicated, irrespective of the temperature and pressure, for

Ca2SiO4 exceeding I x 10-3 mo/IL, the concentration of CaSiO3 increased with an increase

of concrete concentration.

Wollastonite (CaSiOA) is a high temperature phase, and is unlikely to precipitate under post

LOCA conditions. The fact that fresh concrete contains C-S-H gel and portlandite, rather

than Ca2SiO 4, and that aged concrete most likely to be exposed to the atmosphere would be

carbonated to a significant depth, essentially invalidates this conclusion.

In a 15-day simulation at 600C [1400F], all solid phases (except copper) present in the

simulated containment water were solid silicates.

This conclusion is generally valid except for the precipitation of minor calcite and magnetite

or hydroxy-magnetite on exposed steel surfaces. Both phases would probably be present if

more accurate simulations had been performed.

As silicon concentration was reduced, the concentration of silicate phases reduced also. In

an alkaline environment, the solubility of silica increased with an increase in pH and

temperature. Since silicates were major corrosion products, a strong influence of pH and

temperature was observed on the formation of the dominant solid phases in the simulated

containment water. However, at pH 10, irrespective of the temperature, pressure, and

concentration, silicates of aluminum and iron contribute 90 percent of the solid phases.

The conclusions of this item are generally correct.

7-3 For convenience, the eight bulleted conclusions relating to circulated Na3PO4 buffered

borate water are numbered in order to facilitate comment.

There were significant differences in the solid phase formation in Na3PO4 containing

simulated containment water at pH .7 from that in alkaline simulated containment water at pH

10.

This conclusion is valid

At pH 7, Ca5(OH)(P0 4)3 was the dominant solid phase containing almost 100 percent of

calcium, while at pH 10, calcium was approximately 1 percent insoluble at 600C

[140 0FJ.

Precipitation of apatite (Ca 5(P04)3(OH)) as a dominant phase is unlikely. Amorphous to

poorly crystalline precursors such as Ca4(P0 4)3H (Van Kemenade and De Bruyn, 1987;

Van Cappellen, 1991) are more likely .

A significantly larger quantity of solid phases was formed in a solution containing Na3PO4

compared to alkaline containment water. Ca5(OH)(P04)3 and NaAISi3O8 contributed to over

90 percent of the solid phases.

A-24
This conclusion is, likely valid.

Sensitivity analyses for concrete indicated increase in the Ca5(OH)(P0 4)3 concentration with

a increase in the concrete concentration. For concentrations of concrete exceeding 3 x 10-4

moliL, Ca5(OH)(P04)3 coexisted with solid SiO2 phase. The concentrations of these two

phases far exceeded contributions from other soid phases.

This conclusion is generally valid. However the precipitating phases are unlikely to be

apatite and quartz.

Copper had no influence on the precipitation of solid phases.

This conclusion is correct.

The sensitivity analyses for aluminum indicated an increase in the concentrations of

NaAISi3O8 with an increase in aluminum concentration. Formation of AI(OH) 3 and AIO(OH)

was observed for aluminum concentrations exceeding 3 x 10-4 moliL at 600C [140*F] and

130 0C [266 *F1, 304 kPa [3 atm], respectively. In a 15-day simulation, aluminum was present

exclusively as NaAISi3O8."

The precipitation of AI(OH)3, or AIO(OH) at temperatures higher than 600C, depends on their

being an insufficiency of silica to form phases such as beidellite, kaolinite, halloysite,

allophane, etc. Their failure to precipitate as stable phases in the simulations suggests

either an incomplete thermodynamic database, or erroneous data.

Both iron and zinc showed a decrease in solid phase concentration with decrease

intemperature and pressure. The contribution of zinc was below 2 percent and that of iron is

below 9 percent compared to the, total solid phases. Other than a reorganization of iron

phases, no significant changes were observed.

This conclusion is likely valid.

The dominant solid phases formed after 15 days were Ca5(OH)(P04)3 and NaAiSi3Oa with

minor quantities of Ca 2Mg5SiBO22(OH] 2, Fe3Si4O 10(OH)2, SiO2, and Zn2SiO4 in the simulated

containment water.

For reasons stated elsewhere, the phases identified are unlikely to form under post LOCA

cooling operation.

Appendix A.

A-16 The test results for the dissociation constant of boric acid in 3 mol/L NaCI are only fair.

Although the discrepancies between experimental and modeled values are significant, it

is difficult to ascertain whether such would adversely affect the findings of the report.

A-18 The differences *between the calculated concentrations of Zn 2 ' and Ca 2" and the

respective measured concentrations, illustrated in Tables A-8 - A-il1 are substantial, and

suggest defects in the either the thermodynamic data or the electrolyte model being

used in the code.

A-25
2.2.2.3 McMurry et al. (2006)

1-1 It would be helpful if specific references could be given regarding the previous at the

Barsback plant in Sweden, and strainer clogging events in U.S. boiling water reactors.

Otherwise the assertions appear to be merely anecdotal.

2-5 It is not clear why StreamAnalyzer generated an output Eh of -0.600 V at pH = 10, as

specification of dissolved iron as Fe 31 (Table 2-2) should have poised the Eh at a much

higher value. The actual conditions that result in such a low initial Eh should be

explained. In any event, it is not clear why Eh had to be specified as input in any of the

runs, unless the objective was to ensure final equilibrium with respect to some reduced

phase, such as copper or magnetite. The outputs of subsequent runs to model the ICET

series did not report Eh.

2-6 With reference to Table 2-4, note that B(OH)4-and B02- are essentially equivalent. Also,

the extensive list of borate species listed in the StreamAnalyzer database may be

because this code is capable of modeling high ionic strength solutions, i.e. up to 30

molal where such species may be present in significant concentrations. It is quite

possible that under the conditions of the present simulations, most, if not all of those

additional species would be present at concentrations too low to significantly affect the

results. Because the dissociation constants for these species are not listed in the report,

it is not possible to check this postulate. However, the authors should check how

significant these species are in affecting the results.

2-7 Charge balancing is a necessary requirement if total mass is to be redistributed among

several phases, and should not be considered an artificial constraint. Much depends

how it is accomplished. It appears that charge balancing was performed through

adjustment of pH, which is satisfactory in strongly buffered systems, but may not always

be an appropriate strategy.

2-8 Perhaps it should be emphasized that the inter-code comparison presented in section 2

is really an evaluation of the consequences of using different databases. The databases

of all four codes are unsuitable for the problem at hand. Therefore the main purpose of

the study is defeated, unless the databases are modified through incorporation of the

thermodynamic properties of phases known to be relevant to the ICETs.

Tbl 3.2 The corrosion rates of metals, Nukon, and concrete and cal-sil insulation are given in

different units (g/m2/hr, mg/h, moIIL). An explanation is called for in the accompanying

text.

3-2 It is stated that cal-sil insulation was assumed to dissolve such that Ca and Si0 2 ions

were contributed to the containment water in "equal molecular proportions". Yet the

analysis in Table 3-3 indicates that the molar ratio is 2.4:1. Some explanation for the,

ratio chosen is called for. In view of the fact that a significant quantity of Na + seems to

be released from cal-sil during leaching experiments, e.g. see ref, this should have been

included in those simulations where cal-sil was involved.

3-2 Mention is made that the water supplied tO the tank was in equilibrium with dissolved

carbon dioxide. Is this in reference to solution buffered with NaOH to pH = 10? If so, far

too much CO 2 would have been taken up to realistically represent the amount of C02

likely absorbed during the ICET series.

A-26
Tbl 3.3 The sources of the analyses for both Nukon and cal-sil are not given.

3-3 The most serious discrepancy between the EQ3/6 modeled results and the ICET #1lis

the almost quantitative removal of Al from solution in the modeled results. The

suppression of diaspore is appropriate, but the resulting induced precipitation of

dawsonite and near quantitative removal of Al raises questions regarding the validity of

the thermodynamic data for the participating phases and aqueous species. The cause

of the discrepancy should be identified.

3-4 Note that the chemical analysis of the precipitate from ICET #1, which contained

carbonate as well as aluminum, boron and sodium, could have taken up carbon dioxide

from the atmosphere after sampling.

3-5 Inspection of the EQ316 simulation 2 nd trial results for ICET #2 suggest that the

depressed silica concentration is due to the precipitation of kaolinite rather than a less

stable form such as allophane. The depressed Ca concentration is probably due to

precipitation of apatite rather than a metastable form of Ca3PO4 , e.g. see van Kemenade

and De Bruyn (1987).

3-6 Inspection of the EQ316 simulation 2 nd trial results for ICET #3 suggest that the

depressed pH is due at least in part to the precipitation of apatite rather than a

metastable form of Ca3PO 4. The elevated Ca concentration is a cons .equence of the

lowered pH. The elevated phosphorus concentration may also be due to the equilibrium

of the system with respect to apatite at lowered pH, as raising [OH]- by 102-4 would

depress phosphate accordingly. This assertion appears to be supported by the ICET #3

results of the StreamAnalyzer simulation, (see note to pp. 4-7).

3-7, Although EQ316 simulation 2 nd trial results for ICET #4 corresponds well with the

experimental results for Ca, Si and Al, these results may be fortuitous. It is unlikely that

kaolinite would be a precipitant at the prevailing pH of the system, and within the short

time frame of the test. In nature, smectitic phases would be replaced by zeolites at pH=

10. Bench-scale testing to determine the nature of any precipitates that would form

under the spec 'ified conditions might help identify the composition and nature of

precipitants that control the aqueous phase composition.

3-8 The EQ3/6 simulation 2 nd trial results for ICET #5 predict the precipitation of gibbsite,

which is less stable than boehmite at 600C. In actual fact, it is more likely that

pseudoboehmite would precipitate under the conditions of the test (Van Straten and De

Bruyn, 1984), as is suggested by a prediction of a lower Al concentration in solution than

actually observed.

3-10 Note that the rationale for using StreamAnalyzer in subsequent simulations was because

of the expanded database of borate species in the database for this code. However, the

significance of these species under the conditions of the ICET series was not evaluated

in the report. Appendix C to this report is a summary of a StreamAnalyzer run for ICET

#1 after 148 hr at 6000. The output of this run allows an example calculation of the

distribution of borate species for the specified conditions, where B = 0.259 mol/L and pH

= 10. It shows that B(OH) 4-= 69.2%, B(OH) 3 = 8.O%and B40 5(OH)4

2- = 6.7%. All other

species contribute less than 6% each to the total boron concentration.

Thermodynamically, the only other borate species of potential importance is CaH 2BO 3 +,

which, although of insignificant concentration (0.00017 mol/L), is actually responsible for

A-27
complexing 76% of the dissolved Ca 21, and could therefore have a profound impact in

lowering the chemical potential of CaO in solution.

4-2 If X-ray diffraction analysis indicated that aluminum oxyhydroxide formed during ICET

#1, it would be interesting to know whether the pattern reflected truly crystalline

boehmite, or pseudoboehmite, which is a poorly crystalline precursor, and commonly

confused with the former. See note to pp. 3-8, above. As noted elsewhere, merely

specifying the formula of the precipitate INS not sufficient, and a serious disadvantage to

using the OLI Inc. codes.

Tbl 4-3 Note that borate species but not their concentrations are listed in this table and others in

the StreamAnalyzer simulations. Therefore their significance in affecting the results

cannot be compared to model results using EQ3/6.

4-4ff The simulation results for ICET #2 using StreamAnalyzer indicate several problems. The

Ca concentration is still too low; suggesting that the Ca3(P04)2 phase in the

StreamAnalyzer databases is not appropriate for the case under study. Furthermore, it

is unlikely that berlinite would precipitate, as very acid conditions are required to prevent

Al hydrolysis. The literature should be searched for more suitable AI-hydroxy-phosphate

phases to substitute for berlinite.

4-5 The assumption. that cal-sil can be represented by CaSiO3 is inconsistent with the

chemical analysis for this material in Table 3-3.

4-6 The dissolution tests for cal-sil suggest that saturation with respect to some Ca bearing

phase was attained within 200 hr of the start of leaching. Failure to take this into

account may explain the excessive Ca concentrations in solution in the ICET #3

simulations. The authors allude to this possibility on pp. 4-7. If this phenomenon was

observed during the cal-sil dissolution experiments, why was this not taken into account

in the simulations?

4-7 The precipitation of Ca3(P0 4)2 in the StreamAnalyzer simulation of ICET #3 avoids the

pH shift due to apatite precipitation in the EQ316 ICET #2 simulation. This indirectly

confirms that apatite could not be the phosphate phase precipitating in this experiment.

4-8ff The very large difference in Al concentration between ICET #1 and ICET #4 may

suggest that reaction is taking place between the dissolved Al and the cal-sil to produce

some hydrated Ca-Al silicate. However, other explanations include the inhibition of Al

corrosion by hydrated Ca silicate coating, or secondary precipitation of a hydrated Ca-Al

silicate, as suggested by the authors. Resolution of this issue should be particularly

amenable to bench-scale testing.

5-3 The authors point out that precipitation and subsequent dissolution of Ca-phosphate

precipitate after 9 days in ICET #3 is not explained by the modeling. The Na and P04

analyses of the aqueous phase reveal sharp discontinuities at about 15 days, the former

falling in concentration by 500 mg/L and the latter rising by 0.2 mg/L. If these

discontinuities are real and not artifacts of sampling and/or analysis, then some clue

might be provided regarding the chemical reactions that could have taken place. Both

CNWRA and LANL should coordinate their efforts in attempting to resolve this question

regarding the purported disappearance of the initial calcium phosphate precipitate.

stable.

A-28
5-5 Note that the occurrence of borax and tincalconite may have been due to the effects of

sample drying in the presence of the coexisting aqueous phase from which the

precipitate was taken, resulting in concentration of borate and precipitation of the

observed phases. Note, however, that neither the EQ316 nor the StreamAnalyzer

databases appear to contain data pertaining to a range of naturally occurring Ca- and

Na- borosilicates, amorphous or poorly crystalline forms of which might precipitate in the

systems under investigation.

2.3 Recommendations for Future Modeling

Before serious modeling is undertaken, a conceptual understanding of the chemical processes

involved is essential. The nature of the problem then determines what algorith ms would most

satisfactorily represent the processes involved, and whether computer codes exist that would do

justice in realistically simulating those processes. Chemical reactions between water containing

B(OH) 3 and suitable pH adjusters, such as NaOH or Na3PO4, and insulating and structural

materials results in supersaturation with respect to various silicates, aluminosilicates,

phosphates and minor oxides and borates. Because of the presence of pre-existing particulate

material, much of it in active suspension, heterogeneous nucleation of solid phases would be

induced upon reaching a critical nucleation threshold (Lasaga, 1998; Stumm, 1992). Empirical

calculations indicate that this would probably be at a concentration about 10 times that required

to achieve saturation, but could be significantly less.

The nucleating phase is commonly that which possesses the minimum interfacial free energy of

all candidate phases. Usually such a phase is also the least stable phase when present as a

macroscopic particle. Once nucleation has occurred, the degree of supersaturation falls

rapidly, and the crystal growth rate slows, the interfacial free energy contribution also falls, and

the crystallites become increasingly stable. At some point, the nucleating phase becomes

supersaturated with respect to a more stable phase with higher interfacial energy, and that

phase can initiate growth on a suitable substrate, as illustrated by Parks et al. (1990) for the

system SiO 2.

Solutions containing silica commonly nucleate and grow as small colloidal particles of uniform

size that can be stabilized in solution by the enveloping electrical double layer (e.g., see Iler,

1979). Because saturation has been reached, the colloidal particles can persist indefinitely in a

metastable state. Destabilizing factors such as a change in ionic strength or pH can, however,

overcome the repulsive effects of the electrical double layer (EDL) and lead to the aggregation

of the colloidal particles to form a viscoelastic gel, a form of polymerization. Such gels can

contract and fracture through syneresis (Scherer, 1999), and will eventually redissolve and

recrystallize to thermodynamically more stable phases, but over time frames far longer than that

required for coolant circulation following a LOCA.

During a LOCA, su persatu ration, heterogeneous nucleation, colloid stabilization, and gel

formation are likely to be the important processes. Recrystallization to form more stable phases

would generally take place over timescales longer than the period of coolant recirculation.

Therefore, the most suitable model for simulating a post LOCA system is one that takes such

mechanisms into account. Unfortunately, although the theory for such chemical processes is

quite well understood (Lyklema, 1991), only rarely have attempts been made to model such

systems (Steefel and Van Cappellen, 1990; Ozkan and Ortoleva, 2000), and no off-the-shelf

simulator is presently available to simulate these processes. Given the nature of the problem

and time and financial constraints, it would probably be difficult to justify formulation of the

needed algorithms and generation of appropriate code for this project. Therefore, an alternative

A-29
simpler, but less rigorous approach should be taken, which ignores nucleation phenomena and

coagulation, and gelatinous products are allowed to precipitate directly from solution. Several

codes, noted above can be readily adapted for such a purpose, provided that the

thermodynamic properties of the least stable phases are incorporated in the thermodynamic

database and the more stable phases are suppressed. It should be borne in mind that very fast

kinetic reactions that would achieve essential equilibrium in a matter of minutes should be

ignored and equilibrium assumed, whereas reactions taking a year or more to achieve 90%

equilibration can also be ignored as being too slow to be relevant.

In summary, the following steps should be taken for meaningful simulation of ICET and loop

tests in addition to the debris and metal dissolution studies already accomplished:

1. Review the literature to identify candidate metastable colloidal and micro particulate

phases that form or nucleate from solutions with similar chemical compositions to those

postulated.

2. Analyze data to determine phase solubilities as a function of composition and pH, and

temperature, if possible.

3. Calculate the solubility products of the phases as a function of temperature, using

suitable approximation techniques, where appropriate thermodynamic data is

unavailable.

4. Derive kinetic data for dissolution and precipitation reactions, where available, and

calculate their temperature dependence, i.e., the apparent activation energies. If

temperature dependent data is unavailable, estimates should be taken from closely

analogous reactions. Although such estimates could be very inaccurate, this is not

critical, as the rates of reaction and specific characteristics of the precipitates can be

refined from the experimental results of the ICET and loop tests, and supplementary

laboratory experiments as needed.

5. Insert the resulting data in the thermodynamic and kinetic databases of an appropriate

code, e.g., EQ316 or TOUGHREACT, and run simple simulations to duplicate nucleation

and precipitation data from which the thermodynamic and kinetic data were derived.

6. Depending on the selection of code and its features, conduct non-isothermal simulations

of the kinetics of dissolution of debris and precipitation of reaction products, assuming

oxygen saturation and CO 2 uptake. Depending on the features available in the

simulator, hydrogen might be beneficially treated as an "inert' product species, i.e., one

that cannot react chemically with an oxidant to produce water, whereas oxygen can be

made reactive. Such conditions would lead to more realistic simulations of the system

being modeled.

7. As Jamn et al. (2005) have determined, the omission of zinc and copper components from

the simulations is unlikely to have a significant impact on results. If the simulations are

conducted with an initial elevated pH, i.e., pH = 10, then the impact of Fe corrosion

products might be omitted. However, if Na3PO4 buffers the pH at =7, then the effect of

iron corrosion might be included to accommodate the early nucleation of amorphous

ferric hydroxides in suspension. This matter'should be evaluated further before a final

determination is made.

8. If possible, simulations should be set up to duplicate precisely, the actual sequence of

steps undertaken during the course of ICET and lop tests.

9. Results of the ICET and loop tests can be used to refine the kinetics of reactions under

operating conditions, which, in turn could be used for simulations of postulated LOCA

events at actual PWR plants.

A-30
Even with perfect algorithms simulating the chemical processes that could take place, there will

undoubtedly be aspects of the chemistry that are not fully understood or may be omitted from

the model. Some possible limitations and how they might be addressed are given below.

1. The Nukon fiberglass insulation is coated with a phenyl formaldehyde resin based

insoluble polymer (Jain et al. (2004, p 2-8). Yet experiments to measure corrosion of the

fiberglass were conducted on uncoated glass coupons. The extent to which this coating

would impede corrosion of the underlying glass appears to be minor. However, if the

resin dissolves into an alkaline aqueous phase, the dissolved species could inhibit

nucleation and growth of solid phases. Small-scale testing should be conducted to

ascertain the importance or otherwise of dissolved organics on nucleation and

precipitation kinetics of solid phases.

2. As noted by Jain et al. (2005) and McMurry et al. (2006), all kinetic parameters were

determined either from experimental studies in the literature, or on additional

experimental studies, where the complex interaction between dissolution processes of

separate materials was not addressed. Examples already noted include inhibition of

Nukon fiber dissolution by dissolved Al, and possible inhibition of Al corrosion by

dissolved Ca and Si02. Another example is the suppression of copper dissolution in the

presence of less noble metals, thus: Cu>Fe (steel) ,>Zn> Al. Such second order

interactions are difficult to identify, but could adversely affect the value of any simulator

as a predictive tool for potential real events. Should circumstantial evidence from the

ICET or head loss tests suggest second order interactions, experimental factorial design

studies might be necessary to identify the second-order effects even though they may

not be adequately defined.

3. Corrosion data for various participating metals, was extracted from the published

literature and tabulated in Jain et al. (2004). The data showed wide variability depending

on the specific corrosion conditions, and the nature of the alloy being subject to

corrosion. Numerous different aluminum alloys are commercially available, but the

variability in alloy dependent corrosion rates was not addressed. Given the corrosive

environment of alkali borate solutions, the nature of the alloy in setting corrosion rates

may not be important, but this issue does not appear to have been addressed.

2.4 Analytical Simulations : Questions and Answers

NRC posed the following questions relating to analytical simulations for consideration by the

Peer Review Group. Answers are provided in response.

Q Is the speciation analysis expected to provide reasonable predictions of chemical

product formation over a range of possible sump environments?

R (The speciation analysis conducted by McMurry et al. (2006) represents a significant

improvement over earlier work, but does not exploit existing capabilities of the selected

codes to fullest advantage. Nor is the present analysis adequate, because of overreliance on existing and irrelevant thermochemnical data for solid phases that were

provided with the selected codes.

Q Is the plan for benchmarking these codes using small-scale testing and the ICET results

appropriate?

R Yes. The plan is generally satisfactory, but, as noted above, the capabilities of the

codes currently being used are not being used to full advantage, and therefore, the value

of the associated experimental studies are diminished. Furthermore, modeling studies

A-31
supporting ongoing small-scale testing are currently not being done. With full

exploitation of codes currently being used, and ongoing modeling support for small-scale

testing, the program could be much more effective.

Q What is the most appropriate way to measure the uncertainty associated with these

codes?

R Measurement of overall uncertainty of the output of any multi-component chemical

simulation is difficult, because a large number of parameters are involved with widely

varying levels of accuracy. In general, methods to address uncertainty in such

simulations are in their infancy and have not been developed to a satisfactory level. The

best approach in the present circumstances is to avoid the temptation to adopt

unrealistically conservative values for the base case, but to utilize those values deemed

to be most realistic. Then replicate runs can be made using Monte Carlo methods to

determine variations in those parameters deemed to have the greatest uncertainties and

most critical to model output. The cumulative variation in outputs can then be adopted

as a measure of uncertainty. Further discussion of this issue is given in section 2.2

Limitations of Current Modeling Work.

A-32
3 INTEGRATED CHEMICAL EFFECTS TESTS

The NRC Office of Nuclear Regulatory Research (RES) sponsored the- Integrated Chemical

Effects Test (ICET) program at the University of New Mexico under the direction of the Los

Alamos National laboratory (LANL). The primary objectives for the ICET series were to:

1. Determine, characterize, and quantify chemical reaction products that may develop in

the containment sump under a representative post-LOCA environment

2. Determine and quantify any gelatinous material that could be produced during the postLOCA recirculation phase.

There were five tests in the series. The test matrix is given in Table 3.

Table 3. ICET Matrix

Test PH Control System Insulation Material

No.

I Sodium Hydroxide: pH -10 100% Fibrous (NUKON)

2 Tni-sodiumn phosphate: pH =7 100% Fibrous (NUKON)

3 Tni-sodiumn phosphate: pH -7 80% Particulate (Cal-Sil)

20% Fibrous (NUKON)

4 Sodium Hydroxide: pH =10 80% Particulate (Cal-Sil)

20% Fibrous (NUKON)

5 Sodium Tetraborate: pH =8 100% Fibrous (NUKON)

Extended reports have been written for all five tests, (Dallman et al., 2005a,; Dallman et al.,

2005b; Dailman et al., 2005c,d Dallman et al., 2006) and brief summary reports have been

written for the first two and last two (Anonymous, 2005c, Anonymous, 2005a,b). In addition, an

oral presentation regarding all tests was given at Argonne National Laboratory on October 18-

19, 2005 (Letellier, 2005).

Reviews follow of the work summarized in the above-cited references.

3.1 ICET #1

The ICET #1 used a circulating fluid consisting of 2,800 mg/L boron, 100 mg/L HCI (about 12 N,

as cited in a subsequent ICET report) and 0.7 mg/L LiOH. According to Letellier (2005) the

solution was made up using 15.14 kg B(OH) 3, 5.87 kg NaOH, 0.66 g LiOH and 214 mL HCI in

250 gallons. Within 30 minutes of the start of the test, an additional 2.27 kg NaOH was

introduced during an initial 4-hr spray stage., the quantity of NaOH added being that necessary

to attain an initial pH = 10. The primary insulation debris consisted of NUKON fibers.

3.1.1 Specific Comments

p. 1 Section 2.0. In view of what follows from the tests, what are the concerns that the decay

heat removal (DHR) heat exchangers might be fouled with. precipitates of the type

observed to form during ICET test #1? Letellier (2005, Slide 21) believes there is

A-33
justification for concern that calcium silicate will coat heat exchanger pipe internals, but

other precipitates do not appear to be considered..

p. 2 It is noted that "...the test tank is capable of maintaining both a liquid and vapor

environment...". However, a realistic air/liquid volume ratio that would replicate that

typical of a post-LOCA environment was not attempted. The post-LOCA air volume in a

containment building would be effectively isolated from the atmosphere outside.

Therefore, the mass Of C02 available that would be stripped from the air inside the

containment building is limited, However, during initiation of the ICET #1, the system

was exposed to atmospheric 002 for some period of time, and an unknown quantity of

002 was absorbed, possibly proportionately in excess of that which would be absorbed

in a real LOCA. Chemical analyses for dissolved 002 during the test have not been

reported, so it is not possible to say whether the observed decline in pH could be

attributed to 002 uptake.

p. 19 The discussion of the XRD technique does not indicate what the composition was of the

target anode. Presumably, it is copper. This information, is needed to interpret the XRD

patterns of Figs 55 and 56.

With respect to wet chemical analyses, no mention is made of sample handling, other

than the sample size, and whether or not the sample was filtered. In the handling of all

alkaline solutions, it is essential to avoid atmospheric exposure to prevent 002 uptake.

There is no mention that stabilizing agents were added to the solutions to prevent

precipitation. Nor is any information given as to how the samples were conditioned prior

to lOP analysis. If precipitates formed, as is noted subsequently, are the lOP analyses

of the supernatant or the total supernatant plus precipitate? See also comments to p. 28

of the ICET #3 report.

p. 20 Apparently the pH meter was calibrated with certified buffers at pH = 4, 7 and 10. and

automatic temperature compensation was used. But at what temperature was the pH

measured? At 25 or 6000? Was provision taken to ensure that 002 uptake did not

occur during measurement? Elsewhere, it is noted that the pH electrode for continuous

monitoring of pH was calibrated initially, but not at the end of the experiment. After 30

days of continuous operation, the pH could have drifted substantially, and it would have

been essential to recalibrate to quantify the extent of drift during the course of the

experiment.

p. 24 Under hydrogen generation, it is stated that nearly constant levels of hydrogen were

observed for the first 17 or 18 days ... but that they subsequently declined and hydrogen

"...was undetectable for the last 5 days of the test...". This raises the question, why?

One would have expected that the aluminum coupons would have corroded relatively

uniformly throughout the test. pH did not fall sufficiently for passivation to have occurred.

What about the role of dissolved Cu(ll) as a catalyst? Was there a build-up of silica or

other passivating material on the aluminum coupons? A suitable explanation found or

this matter should be investigated further. It would be helpful in the post mortemn

analysis of ICET experiments to have some redundancy built into the analytical

procedures, so that appropriate mass balance calculations could have been conducted

with confidence. Thus, it would have been useful to have made quantitative

determinations of hydrogen concentration in the vapor and the aqueous phase, as well

as monitoring d~issolved oxygen concentration.

A-34
p. 28 Mg(ll) in the NUKON glass fiber could, if it were to go into solution, adversely affect the

kinetics of calcium carbonate precipitation, and possibly other calcium containing

phases. This consideration might have to be addressed, or at least recognized, in

subsequent computer modeling and calibration studies.

p. 28 Reference is made to the NUKON glass fiber containing 3% of a phenolic resin binder.

Elsewhere (p. 33) it is noted that the resin was responsible for causing a yellow

coloration of the water. Furthermore, it is noted that precipitation did not seem to affect

the intensity of this color. This raises the question as to what the solubilized constituents

are, and whether they affect the kinetics of nucleation and precipitation. Letellier (2005)

noted that the circulating ICET solutions were analyzed for Total Organic Carbon (TOC),

and that a search was made for organic compounds causing the yellow, amber or tea

colored solution. However, these analyses have not been incorporated in any reports so

far. Such analyses might help identify potential sorbents. A small bench-scale test

could be conducted to determine whether nucleation and precipitation kinetics are

affected.

pp. 28f Regarding the SEM images of the fiberglass 'after exposure to the circulating water for

30 days,, i.e., see Fig. 22 and 23, the reviewer is concerned about the mechanism of

formation of the membrane-like material stretching between the exposed glass fibers.

So far, the identity of this material remains unclear although Letellier (2005) and Klasky

(2005) believe it to consist primarily of Na, B and 0. Elsewhere, Letellier noted that the

membrane like material is "an artifact of draining", and Klasky (2005) noted that rinsing

of the film with Dl water resulted in its disappearance. This suggests that it is most likely

a solution residue.

p. 35 4.5.2 Turbidity. The turbidity analyses at 25 0C, reproduced graphically in Fig. 29 (p. 37)

raise some interesting questions. It appears that the turbidity at 23 00 remained low until

after Day 7, when a sharp rise is observed, gradually flattening off and stabilizing after

,Day 20. the break in continuity is also observed in other data sets for Total Suspended

Solids (Fig. 30), kinematic viscosity (Fig. 36, p. 42), Ca concentration (Fig. 44, p. 47),

Cu concentration (Fig. 45, p. 48), Zn concentration (fig. 47, p. 49, Na concentration (Fig.

48, p. 49). Although the discontinuities may in some cases be the product of a vivid

imagination, the data do suggest that critical (heterogeneous) nucleation threshold may

have been reached in the aqueous solution after 7 days at operating temperature

(60'C). Thereafter, the system might have achieved saturation with respect to one or

more phases at 6000, as is evidenced by the fact that samples held at 600C did not form

precipitates (p. 36). Furthermore, only a small depression in temperature of 5 *C is

sufficient to induce precipitation (Fig. 31). The linear relationship between TSS and

temperature in Fig.31 also intersects at T = 6000 at approximately 0 mg/L TSS, again

suggesting that the solution is just saturated with respect to some phase. It appears that

any precipitates, even if formed in suspension, became entrained or grew within the

debris accumulations in the test loop. Tiny particles also appear to have grown on the

NUKON fibers, perhaps having nucleated and grown in situ, rather than having been

entrained from suspension. Unfortunately, current information on the nature and identity

of the precipitates provides only a limited basis for developing a working hypothesis.

Further characterization work, already underway, i.e., Klasky (2005) and modeling is

needed to help resolve the unanswered questions.

p. 35 4.5.3 Total Susgended Solids. The study conducted to measure the quantity of

suspended solids as a function of temperature (Fig. 31), and the follow-on test in which

A-3 5
cooled samples were reheated to 600C provides tantalizing evidence that the saturating

phase at 600C in the circulating loop was metastable with respect to a less soluble

phase, at least above 40*C. Whether this was due to Ostwald ripening, or the

nucleation and growth of another phase, or to precipitation of a carbonate due to 002

absorption from the atmosphere, can only be guessed at without more detailed analysis.

p. 40 4.5.4 PH. The decline in DAS pH over the course of the experiment could be due to

instrument drift. Discrepancies between the DAS and grab sample pHs could be due to

the former being measured at a different temperature than 600C, and that temperature

compensation was insufficient. Fluctuations in the grab sample readings appear to be

random, when compared with the DAS measurements.

p. 42 4.5.6 Shear-dependent Viscosity This technique can provide valuable supplementary

information concerning colloid formation and subsequent gelation in the aqueous phase.

The results, indicating non-Newtonian behavior in quenched 25 00 samples during the

later stages of the test, are suggestive. But does the technique allow one to discriminate

between colloid formation, flocculation, or gelation? The filter clogging behavior of the

observed precipitates could differ substantially, depending on their aggregation

characteristics.

p. 47 4.5.7 Metal Ion Concentrations Note the reviewer's caveats concerning sample

handling under the comments to p. 19. The Al concentration stabilizes after 15 - 20

days, but Ca, Cu and Si stabilize after about 7 days,. and decline slowly thereafter. Zn

declines to 8 days, then shows a "hop". Na shows a discontinuity at about 7 days, and a

maximum after 15 days, followed by a decline to 20 days after which the concentration

stabilizes. This suggests that the precipitate in the circulating loop may have been a Ca

(+ Na) silicate, with minor Al substitution for tetrahedral Si. and possibly minor calcium

carbonate (either calcite, or a les stable polymorph such as aragonite or vaterite).

However, the system is somewhat undersaturated with respect to C-S-H "gel" (Chen et

al., 2004), and is the precipitate is therefore unlikely to be a disordered tobermorite

(Merlino et al., 2000). Because B and Na are major components in the aqueous phase, it

is not surprising that the mineralogical analysis of the precipitates that form in the

sample containers following cooling to room temperature, and after separation and

drying, may contain proto-tincalconite and borax. However, the precipitate observed

upon cooling might well also be present at saturation in the loop at 6000. A distribution

of species analysis and calculation of the saturation indices of potential precipitates may

shed further light on this matter.

p. 50 Precipitated Solids The 15-day filtered test sample at 50,000-x magnification suggests

that primary particulates, approximately 5 nm in diameter, formed initially. The 30-day

unfiltered sample (Fig. 52) indicates a somewhat coarser primary particle about 10 nmn in

size. Both Fig 49 and 52 show that the initial particles tend to coagulate into larger

particles containing between 5 and 20 of the initial particles, and that these, in turn,

tended to agglomerate in still larger particles. However, apart from the initial

aggregation into 6-20 membered nanoparticles, subsequent aggregations cannot be

described as gelation, but rather as flocculation. Neither the degree of adhesion, nor the

concentration of aggregated particles is sufficient to induce the formation of a true gel.

The authors of the report note this. The initial particles, by virtue of their small size,

would have a very large surface area, and, even if well crystallized, would contain only a

few unit cells. Therefore, the solubility of such material is probably one to two orders of

magnitude greater than the equivalent macroscopic solid. The observations substantiate

A-36
the contention that the precipitating phases are metastable with respect to more stable

phases in the same multi-component chemical system, and that computer modeling

studies must take this condition into account.

3.2 ICIET #2

The solution was made up using 15.14 kg B(OH)3 and 0.66 g LiOH in 250 gallons. A mix of

1.893 kg trisodium phosphate (TSP) and 0.300 kg B(OH)3 was metered into the system during

the first two hours of the test, an a similar mix of TSP plus B(OH) 3 plus 214 mL concentrated

HCI was added during the next two hours. The primary insulation debris consisted of NUKON

fibers.

3.2.1 Specific Comments

p. 27 The presence of secondary Cu2(C0 3)(OH) 2 on the copper coupons, and the signal for

C appearing in many of the EDS scans raises the question as to whether the collected

samples were exposed to atmospheric contamination following sampling, or whether

carbonates precipitated because the circulating fluid had been exposed to atmospheric

CO 2. The carbon observed in the EDS traces might also be due to the adsorption of

dissolved organic components of the phenolic resin. Also, it is noted in section 3.3 (p.

12) that confusion may have occurred identifying carbon for boron. The absence of

analytical data for dissolved carbonate species (or alkalinity) in the circulating water,

makes it difficult to establish whether carbonates are contributing to the precipitate load

in addition to phosphate, and indeed, whether mixed carbonate-phosphates might be

precipitating. Letellier (2005) noted that carbonate analyses were performed. However,

it is not clear whether these analyses were of the circulating solution.

p. 42 In this report, no results are presented of high magnification TEM of secondary

precipitates or coatings. Therefore, it is not possible in this case to determine whether

the precipitates represent an aggregation of nanoparticles, or are fine crystals with

distinct morphology. We do not know whether the particles have a narrow or broad size

distribution, or whether the distribution might be bi-m~odal. Also, TEM studies would help

determine whether more than one phase had precipitated during the run. It is not clear

whether XRD analyses revealed a crystalline or substantially amorphous solid. This kind

of information is critical in formulating conceptual models for computer simulations of

both laboratory tests and real scenarios.

p. 42 Some effort should have been made to characterize the chemistry and mineralogy of the

adhering coating on the metal coupons. In particular, the deposits on the submerged Al

coupons appeared to be discrete "rosettes" (Figs 4-3 and 4-5 on p. 22). It would be

interesting to know why this aggregation of material occurred, and whether it is really

aluminum hydroxide as claimed.

p. -46 The adhering material on the fiberglass, imaged by ESEM, and illustrated in Figs 4-50

and 4-52 display shrinkage cracks. If they were caused by dehydration during sample

preparation, then the material could be a flocculent. However, if they are due to

syneresis, then the adhering material could legitimately be considered a gel.

p. 50 Examination of the 30-day fiberglass sample from within the birdcage, revealed the

presence of lath-like crystals, which were analyzed by EDS. It would have been

desirable to have characterized this crystalline material further using TEM.

A-37
p. 58 The inadvertent generation of enhanced turbidity in the sample taken on Day 3, due to

excessive cooling before measurement, indicated that the solution may have been

saturated or near saturation with respect to some phase at operating temperature, and

that prolonged cooling might have induced precipitation. It is unfortunate that the studies

conducted in ICET #1, were not repeated to determine the degree of under-cooling

needed to generate a precipitate, and the stability of the precipitate upon reheating.

Note that such a study provides helpful information regarding the thermodynamic and

kinetic properties of precipitates, especially in relation to the fouling of heat exchangers

in the system.

p. 65 As with ICET #1, a yellow coloration of the circulated water occurred, which is probably

due to the leaching of the phenolic resin. As noted in the comments to ICET #1, the

presence of organics may affect the rate of precipitation of phases from a

supersaturated solution.

3.3 ICIET #3

The solution was made up using 15.14 kg B(OH) 3 and 0.66 g LiGH in 250 gallons. A mix of

1.893 kg TSP and 0.300 kg B(OH)3 was metered into the system during the first two hours of

the test, an a similar mix of TSP plus B(OH) 3 plus 214 mL concentrated HCI was added during

the next two hours. The primary insulation debris consisted of 80% particulate cal-sil and 20%

NUKON fibers.

3.3.1 Specific Comments

p. i The abstract notes that "...the bottom of the tank was filled with a sediment that had a

pinkish white deposit on top." Elsewhere, on p. 78 it was noted that the sediments were

both yellowish and pink, but the order was not stated.. On p. 68 it is also noted that the

cal-sil that was heated, had a pinkish hue, and that the untreated cal-sil was yellowish,

the color change being potentially due to the transformation of ferric hydroxide to

hematite. This suggests that the last layer to sediment out was the heat-treated

.material, suggesting a smaller particle size. The report does not discuss the likely

particle distribution of cal-sil debris. A size distribution analysis of heat-treated and

untreated samples would be useful in quantifying the behavior of this material following a

LOCA.

p. I It is not clear whether 3.786 kg of STP was added as the hydrate (Na3PO4 .12H 20) or in

the anhydrous form. This ambiguity extends to citations elsewhere in the text.

p. 20 It is noted that an apparent "...dissolution of white particulate was observed occurring

from Day 7 through Day 9." This phenomenon appears to be correlated with a

measurable perturbation in the Al concentration, which persisted from Day 8 through

Day 15, a slight fluctuation in Si0 2(aq) commencing on Day 7, and a progressive rise in

Na concentration, starting about Day 9 and returning to a normal trend after Day 15.

The authors are silent on these matters, so it is not clear whether the observed analytical

fluctuations in solution chemistry are artifacts or are real. See also comments to p. 58 of

ICET #2. Although this issue may not be important in the overall scheme of things,

computer modeling that does not account for such fluctuations would be considered

suspect in predictive modeling. Therefore it is important that these observations be

explained. Kieser and Park (2005?) noted that if the dissolved concentration of TSP

exceeds 1000 ppm, the initially precipitated Ca phosphate begins to dissolve, while the

A-38
solution pH rises to 8-8.75. These conditions were not evident in the current test, but a

possible relationship between these disparate observations should be investigated.

p. 20 The fact that the flow meter fouled with precipitate after Day 8 is an indication that such

precipitates are also likely to coat the interior of the heat exchangers that cool the

circulating coolant. Whether they would also coat the reactor core is uncertain, because

it depends on the degree of supersaturation of the precipitating solid, and whether the

temperature dependence on solubility is pro- or retrograde. (indications are that it is

prograde. See comments to p. 20). Kieser and Park also note that a rise in pH permits

the bonding of calcium phosphate particulates to steel piping. This issue would further

complicate cooling following a LOCA. Letellier (2005) has already noted that there is

concern regarding the precipitation of calcium silicate on the internal surfaces of pipes.

p. 20 The differential variation in pH between the bench-top measurements and the in line

measurements over the course of the test is -0. 18 units. This again raises the question

of post test calibration of the in-line pH probe, and whether bench-top measurements

were taken at room temperature or at 600C, The automatic temperature compensation

may not have been adequate.

p. 28 The Al concentration in Fig. 3-8 shows an inexplicable jump in concentration between

Day 8 and Day 16. No explanation is given. However, Letellier (2005) notes that it is

not significant. Strange and inexplicable variations in chemistry are noted elsewhere.

One cannot help speculate that these fluctuations may have been the result of sample

aging. It looks suspiciously like aqueous samples were collected and Submitted for

analysis in batches, and that the fluctuations observed are the consequence of faulty

sample preservation. See also comments to p. 19 of ICET #1.

p.. 30 In Fig. 3-13, the Si0 2(aq) concentration reaches a maximum on Day 2, suggesting that

nucleation occurred around that time.

p. 32 Fig. 3-16 shows an inexplicable jump in P0 4 concentration between Day 13 and Day 16.

No explanation is given. See p. 20 comments regarding dissolution/precipitation.

p. 33 It is stated that deposits formed in the interior of the fiberglass insulation are likely to

have been "chemically originated". However, elsewhere it is also noted that. "deposits

are pervasive throughout the fiber", and further, "... [tlhe drying process caused the

formation of flocculence through chemical precipitation" (whatever that means). The

reviewer is concerned that the sample preparation procedures for SEM examination may

be introducing artifacts that could be confounded with chemical processes that occurred

during the test run. Note that the EDS spectra of the flocculent precipitates displayed in

Figs 3-24,3-30, 3-33, 3-36, 3-41, 3-43 and 3-47 are all somewhat similar and consist

primarily of 0, Na, Si and Ca, those principal components in aqueous solution, which are

measurable by EDS. The presence of C may be due to carbonate species in solution,

analyses of which, unfortunately, have not been reported. Thus it is important that either

the sample preparation procedure needs to be changed, or some way of discriminating

between the artifact and the real thing needs to be devised.

p. 34 Note that the adhering flocculent material appears to be physically entrained, rather than

having nucleated on the fibers, and that the fibers do not appear to have been corroded.

This suggests that the fibers may have been protected from corrosion by saturation with

respect to Si0 2(aq) by the cal-sil and with respect to Al and B by the corroding Al

A-3 9
coupons and by the presence of B(OH) 3 component in solution. Thus, the measured

corrosion rates of NUKON, reported in Appendix B of Jain et al. (2005), might not be

applicable to systems in which. cal-sil debris are present.

p. 55 With refe rence to the particles shown in Fig. 3-55, and the EDS spectrum of the same in

Fig. 3-56, it should be noted that fine particles of cal-sil could be chemically altered in the

presence of TSP solution to form mixed Ca-phosphate/silicate phase. The authors

allude to this possibility on p. 68. They note further that phosphate diffusion into the

interiors of the particles is limited, but unfortunately provide no quantitative evidence to

support this contention. The phosphate uptake should be examined through separate

bench-scale tests and instrumental analysis. Note also, on pp. 58-60, white and dark

particles are separately analyzed, one showing elevated P (dark particles), in

comparison with the other light particles. This again suggests more than one generation

of particulate formation, which is not readily explained by the simple precipitation of a

calcium phosphate compound. (The reviewer recognizes that EDS analyses of small

particles may result in overlap with adjacent particles with differing chemical

composition.

p. 63 Care should be taken not to assume that an EDS spectrum of a particle is representative

of the bulk composition. The particle illustrated in Fig. 3-70 looks like some coarse

particulate material that has been coated with a secondary amorphous or

microcrystalline material. Thus the EDS spectrum is that of the coating, and it cannot be

assumed that the interior is of the same composition, i.e., some calcium phosphate.

p. 68 The source and provenance of the cal-sil is not disclosed. Therefore the reader cannot

ascertain whether the cal-sil is of recent manufacture, is old stock, or was removed from

an operating PWR after having been in service for a protracted period of time. The fact

that some of the material was heat treated., suggests that the cal-sil was not previously

exposed to operating conditions. Like concrete, the cal-sil could have undergone.

carbonation during storage, and the chemical composition of the sample included

secondary calcite and amorphous silica, decomposition products of C-S-H gel or

tobermorite. The fact that the XRD spectra on p. 82 includes that due to calcite, a large

diffuse peak at 120 20 in addition to tobermorite spectra (9A-tobermorite and 14A(?)-

tobermorite) is suggestive of an old-stock sample that has significantly carbonated, and

that subsequent thermal treatment led to the formation of 9A-tobermorite. The chemical

analysis of the 30-Day sediment on p. 82 (which is presumably dominantly cal-sil)

suggests there is a slight excess Of SiO2 over that required to form tobermorite alone.

However, a significant portion of the tobermorite may have been carbonated. It is

essential the analyses for contained CO2 be conducted.

Note that the cal-sil insulation in an operating PWR, and exposed to temperatures as

high as 2600C, might not have undergone carbonation to the same extent, as calcium

silicate tends to be more stable than calcite in the presence of reactive silica at

atmospheric pressure at 2600C. Furthermore, containment with SS or aluminum

cladding could limit access by atmospheric CO 2. Thus the cal-sil used in ICET #3 and in

ICET #4 may not be representative of a real world condition.

p. 69 Very little information is given anywhere in the report on the chemistry and structure of

the adhering coatings on the metal coupons. Clearly, the corrosion of Al is non-uniform

as evidenced by the illustrations on p. 69. It would be useful to know why. Also, the

coatings should be fully characterized with supporting TEM and XRD studies. Finally,

A-40
we do not know whether the Al coupons are pure aluminum sheet or some Al alloy,

which might corrode differently from the pure substance.

p. 84 XRD analyses confirm that the initial gel like Ca phosphate contains Ca4H(P0 4)3.H20 as

anticipated in the reviewer's comments regarding the CNWRA report on computer

modeling. However, it is interesting to note that a double salt incorporating

NaHCO3.H20 actually formed. The XRD pattern in Fig. 3-122 also contains a diffuse

ring at about 120 2 0, which is not explained. Does it relate to the sample or to sample

preparation? The gel-like calcium phosphate should be more fully characterized, with

additional high magnification TEM, surface area measurements, anid chemical analyses.

This again indicates the importance of monitoring the alkalinity or 002 content of the

circulating water in order to permit calculation of the solubility characteristics of this

material.

3.4 ICET #4

Before the start of the test, 15.14 kg of B(OH) 3, 8.47 kg of NaOH, 212 mL of 12.24 N HCI and

0.663 g LiOH were dissolved in the circulating fluid. Within 30 minutes of the start of the test,

additional NaOH solution of unspecified strength was introduced during an initial. 4-hr spray

phase, the quantity of NaOH added being that necessary to attain an initial pH = 10. The

solution formulation appears to be essentially similar, if not identical to that for ICET #1.

However, instead of exposure to insulation composed entirely (100%) of NUKON fiberglass, the

insulation consisted of 80% cal-sil and 20% NUKON. This is assumed, based on the test series

parameters given in Table 2 of the test report for ICET #1. However, the ICET #4 deviated from

the initial plan in using NaOH to buffer the pH at 10 rather than TSP to buffer the pH at 7.

Results can be compared with those of ICET #1, which utilized circulating water of the same

composition. The major difference between the two tests is the presence of cal-sil, which

significantly impacted the solution chemistry.

Noteworthy differences are:

" The turbidity measurements at 6000 and 250C were essentially identical. Therefore,

unlike ICET #1, there was no tendency for precipitation to occur during sample cooling.

" Instead of a progressive buildup of Al in solution to about 350 mg/L apparently reflecting

the solubility of AI(OH)3, Al quickly fell to undetectable concentrations in solution after

two days

* Ca 2 + concentration was about 3 times higher.

" SiO2(aq) rose progressively to about 180 mg/L compared with 13 - 18 mg/L in ICET #1.

Na showed an upward trend in concentration from 6,000 mg/L to about 11,000 mg/L

after 30 days. This is in contrast to the trend in ICET #1, which remained essentially

constant at about 5,000 mg/L between 3 and 30 days.

The upward trend in Na concentration over the course of the test needs to be explained. It

could be due to the leaching of Na from the cal-sil, as suggested by the bench-scale dissolution

tests of Park et al. (2005) (See comments under Park et al., 2005). However, the associated

Nukon fiberglass contains about 17% Na20, and the relatively slow release rate might be

attributed to Na leaching from the fibers.

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There appears to be no evidence for the formation of secondary precipitates, which suggest that

precipitation, if it occurred, was minor in quantity. Only minor corrosion products were observed

on the submerged metal coupons. Corrosion products on submerged Al coupons appear to be

limited to minor oxidation products, and perhaps minor adsorbed SiO2.

The most striking feature of this test is the lack of corrosion of the submerged Al coupons. A

SEM/EDS study of the uncontaminated surface indicates that only an al hydroxide layer is

present on the surface, with minor adsorbed(?) silica. It is tempting to speculate that the

adsorbed silica passivates the aluminum and inhibits corrosion at pH = 10. Letellier (2005),

however, attributes the lack of corrosion to the formation of a "calcium-carbonate passivation

layer'. Further electrochemical studies to investigate the potential role of silica in passivating Al

are merited.

One other interesting set of results pertains to the XRD and XRF analyses of the Day 30

sediment, which is believed to consist primarily of fine cal-sil debris. It appears that cal-sil is

composed primarily of three phases: tobermorite, 9-A tobermorite and calcite (Fig. 3-129).

From Table 3-6, the Si:Ca molar ratio is calculated to be 1:0.89, which is consistent with a

material originally containing tobermorite-like phases with excess portlandite, the latter

converting to calcite upon exposure to air. However, the Si:Ca molal ratio is inconsistent with

that reported by McMurry et al. (2006) in their Table 3-3, which shows a molar ratio of 1:2.4. An

explanation for this discrepancy is called for.

3.5 I1CET #5

Before the start of the test, 6.48 kg of B(OH) 3, 10.0 kg of borax, and 0.284 g LiOH were

dissolved in the circulating fluid. Apparently, HCI was also added, leading to a bench top pH of

8.34 at 6.00C. The primary insulation debris consisted of 10% NUKON fibers.

The ICET #5 results can be compared with those of ICET #11, which utilized circulating water of

somewhat similar composition, and insulation debris was similarly restricted to 100% Nukon. A

major difference between ICET #1 and #5 is the lower pH of the latter, which varied between 8.1

and 8.5, compared with about 9.4 for the former. This directly affected the Al concentration in

solution, i.e., a concentration between 30 and 50 mg/L in ICET #5 compared with about 350

mg/L in ICET #1. Ca concentrations are somewhat higher (about 20-30 mg/L versus 12 mgIL), whereas the Si0 2(aq) concentration is about 10 mg/L versus 13 - 18 mgIL. Another similarity

between ICET #5 and ICET #1 is the tendency for precipitates to form from solution samples

after cooling to room temperature as determined by turbidity analysis., see Fig. 4. Precipitates

were also observed to have formed in the test loop, although the quantities were minor, and

were not explicitly characterized.

It is difficult to speculate what went on during this test without more information. Some of the

fluctuations in turbidity, and in Al, Ca, Si and Na concentrations, suggest erratic behavior under

conditions that should have been relatively stable once saturation and precipitation had

occurred. It is not clear whether these effects are real or are artifacts. If they are real, then an

interpretation is called for. Such an interpretation could. be aided by supplementary

thermodynamic and kinetic modeling of the test.

Most, if not all of the corrosion product SEM/EDS analyses show significant concentrations of

carbon. When compared with the associated oxygen concentrations, there is too much carbon

present to represent the carbon as being exclusively due to the presence of carbonate. It

seems more likely that the carbon may be due to adsorption or co-precipitation of the phenolic

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resins originally coating the Nukon insulation. It is, of course, recognized that the sensitivity of

EDS to carbon is poor, and therefore, the computed atomic percentages of carbon are subject

to large uncertainties.

The presence of quartz in the particulate deposits at the bottom of the tank, as reported in

section 3.5, is unlikely to have originated with a crystalline form of fiberglass debris, but rather

was associated with the concrete particulate material deliberately added at the beginning of the

test.

3.6 Recommended Post Mortem Evaluation of ICET Runs

If aqueous solution samples are still available, analyze for alkalinity or 002 content. Remeasure pH at ambient, i.e., room temperature.

Perform a distribution of species analysis using a standard distribution of species code, e.g.

EQ316 or PHREEQ-C using the initially measured pH at 60'C to determine the degree of

imbalance between cations and anions. Explore the option that calcite, vaterite or aragonite

might be saturated, through charge balancing on HCO&-. If carbonate saturation cannot be

demonstrated, proceed with an evaluation of saturation solubilities of the precipitates.

Conduct in-depth evaluations of the morphology, crystallinity, specific surface area, and

chemistry of precipitates and coatings using available instrumentation.

Review the literature on microcrystal line and amorphous phases that form in the multicomponent system under study.

Derive solubility data of the participating solid phase precipitates, taking into account possible.

contributions by the interfacial free energy.

Attempt to establish rates of precipitation at 600C., based on an interpretation of available data,

supplemented with any available literature data.

Formulate and conduct additional lab tests to quantify poorly known parameters of critical

importance.

The thermodynamic and kinetic parameters can be used as input to a non-isothermal chemical

reaction simulator, e.g. TOUGHREACT.

Implementation of the above guidance is seriously complicated by the omission of alkalinity or

carbonate analyses. It is not certain a priori how much useful information can be obtained from

such an analysis, but the resulting information is absolutely necessary if a satisfactory computer

simulator is to be developed.

3.7 ICET Questions and Answers

Answers are provided below to the questions posed to the Peer Review Group by NRC.

Q. Have the principal sump pool variables, which affect chemical by-product formation in

the post-LOCA environment, been adequately simulated?

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A. Given the complexity of the problem, and the need to get started on some kind of

simulation, the reviewer believes that the approach to simulating a post-LOCA

environment (Andreychek, 2005) was satisfactory, and the ICET series yielded useful

information.

Q. Many ICET variables were held constant during the experiments. How would changes

in the most important constant variables affect chemical product formation?

A. This question can only be answered through a comprehensive evaluation of the

physical, chemical and mineralogical properties of the observed precipitates, a detailed

evaluation of all of the data, especially that which relates the aqueous phase

composition, with the thermodynamic properties (i.e. solubilities) and kinetic properties

(i.e. nucleation and growth) of the precipitates. Quantitative information concerning the

kinetics of corrosion of the debris and metal coupons under the full range of operating

conditions is also required. Additional bench-scale testing to evaluate the temperature

dependence of key kinetic processes, such as that currently under way at ANL (See

comments regarding Park et aL., 2005). Electrochemical corrosion studies also should

be made of aluminum alloys in solutions with varying chemical compositions, including

those resulting from cal-sil dissolution. Further work needs to be accomplished before

a satisfactory computer simulator could be calibrated using the experimental data

obtained from the ICET series, this simulator being necessary for more realistic nonisothermal runs replicating realistic post-LOCA conditions.

0. What variables or materials not simulated by the ICET testing may have the most

impact on chemical product formation (e.g., coatings, free insulation, flow through

sediment and other materials on sump screen, galvanic effects) and how should their

effect be characterized by testing or analysis?

A. The most glaring omission is the testing was failure either to control or to monitor C0 2

uptake. This has resulted in conditions that could deviate significantly from the actual

post-LOCA environment in the containment building of a PWR. The second is an

adequate a priori characterization of the cal-sil used in some of the tests. The history of

the material may differ from that in an operating PWR, especially with respect to the

degree of carbonation. This same problem also applies to the cementitious materials

used in the test. Under real conditions, these materials could be substantially

carbonated at the time of a hypothetical LOCA. As noted in the preceding question, the

temperature dependent variation of a number of key parameters have not been studied

in the presence of cal-sil disintegration and dissolution products. This applies

especially with respect to aluminum corrosion. Regarding other materials omitted from

consideration, such as coatings, free insulation, etc., the reviewer can only express his

opinion that no significant adverse consequences would be expected from these

materials, as already noted by Andreychek (2005). Some protective paint coatings

could peel off en masse, and accumulate as flakes on the screens.

Some variables and materials were included in the ICET runs, but could well have been

omitted, based on the earlier computer simulations conducted at CNWRA (Jain et al.,

2005) and in hindsight. For example, copper, galvanized steel, lOZ coated steel, and

uncoated steel coupons were incorporated, but appeared to have had little impact on

precipitate formation or ultimately on screen clogging. These materials could be

omitted from further consideration, unless the impact of post-LOCA cooling on corrosion

and the integrity of structural materials is of interest, i.e. see Andreychek, 2005, p. 13).

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The reviewer is similarly of the opinion that the release of small quantities of HCI from

PVC insulation may have only a minor effect on precipitate production.

The reviewer believes that field visits to operating PWR facilities could unearth other

limitations or omissions not otherwise anticipated. Out-of-scope issues relating to the

fouling of heat exchangers and possibly the reactor core with precipitating phosphates

or other compounds have not been addressed, and could also adversely affect reactor

cooling.

Q. Were the methods used within. the ICET program to characterize and analyze chemical

by-products sufficient?

A. In terms of the diversi ty of instrumental methods used, the ICET program was

satisfactory. For the purposes of detailed modeling, it would have been useful to have

measured the specific surface areas of the precipitates, using either the BET method or

possibly a dye adsorption technique. However, the real criticism that might be leveled

at the test reports is not so much the diversity of facilities used, but rather the lopsided

emphasis on the ESEM, SEM and EDS characterization of precipitates and coatings.

Much more serious work needs to be done characterizing the physical, chemical and

mineralogical properties of the precipitates and~ coatings as a basis for subsequent

conceptual and computer modeling. As noted in answers to preceding questions, this

characterization work needs to be done in conjunction with additional laboratory testing

and computer modeling. Fortunately, this deficiency is being rectified through

supplementary bench-scale studies at ANL and LANL.

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4 HEAD LOSS SIMULATION TESTING AND ANALYSIS

Supplementary Chemical Effects Head Loss Tests are being conducted at the Argonne National

Laboratory. The objective of the tests is to assess the pressure drop across a surrogate sump

screen due to debris with or without secondary calcium sulfate precipitates. The tests are

therefore conducted to augment the findings of ICET #3 by establishing a basis for predicting

sump screen performance degradation following a LOCA in PWR s using STP as a pH buffer in

the circulated coolant. The findings of completed tests are presented in two informal reports

(Oras et al., 2005, 2006). Head-loss testing is also described in a preliminary 8-page report

(Anonymous, 2005c), which briefly describes Tests ICET-3-1 and ICET-3-2. Shack et al. (2005)

also made an oral presentation on October 19, 2005, in which the preliminary results of Test #3

were described. A listing of the completed tests is summarized in Table 4.

Table 4. Chemical Effects Head Loss Tests

Test No. Insulation Material Conditions

NUKON Cal-Sil Presoak TSP and or Ca additions

g g _ _ _ _ _ _ _ _ _ _

ICET-3-1 15 15 No TSP: initially in loop. 200 ppm Ca as

CaCI 2 added to simulate Ca dissolving

from Cal-Sil.

JICET-3-2 15 15 No TSP: initially in loop. 10, 25, 50 ppm Ca

as CaCI 2 added stepwise, in loop.

ICET-3-4 7 25 Yes TSP: 118 initially in loop, 7/8 metered

ICET-3-5 7 25 Yes TSP: none

ICET-3-6 15 15 Yes TS.P: 1/8 initially in loop, 7/8 metered

ICET-3-7 15 15 Yes TSP: none

ICET-3-8 15 0 No TSP: initially in loop. 43.5 ppmn Ca as

CaC12 added (= dissolution of cal-sil.)

ICET-3-9 15 0 No TSP: initially in loop.

ICET-3-10 15 15 Yes TSP: 1/2 metered during pre-soak; 1/2

metered. 9, 18, 27 ppmn Ca as CaCI 2

added stepwise, in loop.

ICET3-3-11 15 15 Yes TSP: none

-0 0 No Al(N03)3-9H2O addition to simulate

corrosion of Al structures.

Associated research is also being conducted at Argonne National Laboratory. The work is

ongoing and only oral presentations and a summary in Oras et al. (2006) are available for

review. The primary purpose of the associated work is to identify important environmental

variable governing the screen clogging associated with the formation of chemical precipitates.

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In particular, the investigators are concerned with the dissolution of cal-sil and formation of

calcium phosphates over a range of simulated sump pool conditions.:

* To examine a broader range of conditions than examined in ICET

" To simulate chemical precipitate formation rather than conduct integrated tests

" Answer critical questions relating to the appropriateness of the produced precipitates

and the right amounts. Especially critical is the mass of chemical precipitate that can

accumulate per unit area of sump screen.

4.1 General Comments

The overall scope of the research under way at ANL is appropriate and reasonable. Of

particular interest were slides # 6 and 8 supporting the oral presentation (Shack et al., 2005), in

which were tabulated the parameters of relevance to post-LOCA cooling (See also, Andreychek,

2005, Table 7). It is clear that the large variability in parameters between different plants

presents a challenge in designing a test program that adequately addresses this variability.

Noteworthy is the observation that the ICET #1 achieved a circulating aluminum concentration

of 375 mg/L, which is for the most part well over an order of magnitude greater than expected in

all plants but one containing a large quantity of structural aluminum. Addressing such variability

could tax the resources of the research team at ANL unless a suitable strategy is adopted for an

efficient set of experiments. This strategy might be best implemented through a series of

bench-scale tests to evaluate critical processes and their controlling parameters, with suitable

data developed for incorporation in a computer simulator. Factorial design studies might also

be conducted using appropriate test designs, particularly where parameter interactions are not

understood.

Of the test work done so far, most has concentrated on the use of a TSP to buffer pH following

a LOCA in a PWR containing cal-sil insulation. The head loss test series ICET-3-1 - ICET-3-1 1

have effectively demonstrated the potentially serious consequences associated with the use of

STP as a pH buffer. The various conditions studied in this series represents the very worst-case

scenario with the predictable formation of abundant flocculent calcium phosphate precipitates.

The series appears to be conducted with a definite plan in mind. However, the large potential

range and variability in parameters under study, and the limited number of tests possible

prevents formal study of the sensitivity of the various parameters to screen blockage under

actual field conditions. This is especially relevant to the reported non-linear behavior of head

loss in response to stepwise additions of CaC12, and to the fact that head losses became

excessive before the full range of TSP additions could be metered in to the test loop.

Furthermore, the discrepant results between tests that were essential duplicates, e.g., ICET-3-7

and ICET-3-1 1, raises the question of reproducibility. Clearly, it would be both time consuming

and costly to run the tests a sufficient number of times to obtain a quantitative measure of

reproducibility. It is not clear how the investigators plan to overcome these limitations. Although

work is progressing well, the reported results give the impression of an 'ad hoc rather than

s ystematic approach at tacking the problems involved.

An independent test used added AI(NO 3)3 .9H20 to simulate the corrosion of Al structures at

post-LOCA elevated pH conditions (pH =10) where precipitates are relatively minor and are

most likely to form during progressive cooling. The test was conducted at a series of declining

temperature steps, and therefore approximated the non-isothermal conditions prevailing during

post-LOCA cooling. Unfortunately, the test was compromised by the "instantaneous" addition of

Al, which would not reflect the progressive corrosion of aluminum components following an

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actual LOCA. It is not certain that precipitates, as observed in the course of ICET #1 and #5,

would in combination with NUKON cause screen blockage. However, the test is suggestive that

an adverse condition could arise. Emphasis should therefore be placed on the defining the

range of conditions where screen blockage is probable under ICET #1 and ICET #5 conditions.

Many of the tests could be simulated using chemical modeling software. Coordination of work

by CNWRA and ANL would greatly assist in the interpretation of results, and facilitate model

refinement.

4.2 Specific Comments

4.2.1 Head Loss Tests

4.2.1.1 Anonymous, 2005c

p. 1 Reference is made to the precipitate being Ca 3(P04)2, which "...was confirmed by later

analysis." Since there are a variety of known Ca-phosphates, the identity should have

been better characterized.

4.2.1.2 Oras et al. (2005)

p. 2 Reference is made to the hydrolysis of potassium and sodium released from the cal-sil.

Potassium is a minor component of cal-sil, and sodium constitutes a smaller molar

concentration than Ca. It is not clear what the state of the sodium is in the cal-sil, i.e.,

whether present as NaOH or NaHCQ3, or combined with Ca as a silicate. However,

leaching tests by Park et al. (oral presentation, October 18-19, 2005) suggest that a

significant quantity of Na is released upon leaching of cal-sil. This appears to be

corroborated by the ICET #4 test results, which show a progressive increase in Na

concentration with time during exposure to cal-sil. In any case, the Ca probably

contributes as much to raising the pH as the Na.

It is also stated that cal-sil is "...mostly CaSiO 3..." In fact, it appears to consist primarily

of tobermorite and minor calcite. See comments .to p. 82 of the ICET #3 report.

4.2.1.3 Oras et al. (2006).

.Figures Some of the figures are difficult to follow. Labels describing the test conditions can be

confused with the legend, e.g., see Figure 4, or appear to be labels describing some

aspect of a graph, e.g., Figure 2. In one case, a label has no explanation in the

associated text, e.g., the label "Add 1/2 NUKON/CalSil slurry" in Figure 2. The onset

of physical screen clogging by debris is claimed on p. 8 to occur "within the first 6

minutes (or after approximately one test loop recirculation)", but elsewhere, it is

claimed that one pass round the loop is =4 minutes (p. 13). However, clogging is

shown to occur within 2 minutes in Figure 18. It would help if test conditions were

boxed on the graphs to avoid confusion with labels. Also, it would help if additional

information were added to the graphs, where appropriate, such as the timing of STP

additions.

p. 3 Reference is made to cal-sil dissolution being limited by the solubility of calcium

silicate (CaSiO3). See comment regarding p. 2 of Oras et al. (2005). Any sodium

silicate that might have been used in the manufacture of cal-sil has probably been

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converted to calcium carbonate and amorphous silica by the time it was used for the

head loss loop tests.

p. 5 in Table 1 it is stated that any remaining fraction of TSP was metered in during a 30-60

minute period after the debris was added to the -loop, but it is not clear when that

period started. Thus, for ICET-3-6, it looks as if the balance of the TSP was metered

in between 30 and 60 minutes after the start of the test. But for the ICET-3-10

procedure, it merely states that the remaining TSP was metered in "...after introduction

of the debris".

p. 18 1st par. It seems that a direct graphical comparison between ICET-3-6 and ICET-3-10

would be better than those with ICET-3-11 in Figures 17a and 17b.

p.18 2 nd par. The strongly non-linear relationship observed due to stepwise additions of

CaC12 in ICET-3-9 suggests a relatively high degree of sensitivity to screen clogging

due to small increases in Ca once a critical calcium phosphate concentration is

reached. Several factors may be involved; the degree of supersaturation with respect

to calcium phosphate before nucleation is induced, the relative growth rate of calcium

phosphate particles, the Ca2+ and P043-saturation concentration with respect to

calcium phosphate, the extent of Ca borate complexing, and the conditions needed to

induce coagulation. These factors suggest that the test may not be reproducible,

unless great care is taken to control all parameters. Because ICET-3-9 has unearthed

this issue, which could be very important in predicting the behavior of screen clogging

in a PWR, further testing and characterization work may be needed.

p. 19 It is pointed out that the effect of cal-sil loading, even without the effect of calcium

phosphate precipitates is to cause head loss to increase "...very rapidly to a high

level". Yet this head loss is only 40% of that due to calcium phosphate precipitation.

p. 23 Hydroxyapatite is highly unlikely to form, as noted elsewhere, when discussing the

work of McMurry et al. (2006). Indeed, these authors indirectly demonstrate that

hydroxy apatite could not form without seriously depressing the pH of the solution, a

phenomenon that is not observed in ICET #3.

Table 2 The experiments conducted respectively at 1.5 gIL and 0.5 gIL cal-sil are not identified.

p. 24 The rate of cal-sil dissolution is discussed, and the conclusion is made that the

experimental work being reported supports an earlier assumption that the cal-sil

dissolution rate is not too strongly dependent on the [Ca] concentration [in solution].

How do these findings compare with the cal-sil dissolution studies reported by

Mcmurry et al. (2006) in their Appendix A?

p. 25 The observation that some of the tests could not be completed as planned, because of

excessive head losses, raises the questions as to what should be done next. It is

tempting to fiddle with the test parameters so that quantifiable results can be obtained

within the range where head losses are less than 100 %, i.e. when substantially

complete blockage of the screen has occurred under conditions comparable to that

would exist in a PWR. However, how would such results be used to modify existing

plant design, or how does the resulting information bear on modified sump screen

changes that have already been implemented at operating PWRs?. Will any additional

A-49
changes be required? How will this be demonstrated using the results of current and

ongoing testing?

4.2.2 Supplementary Studies Characterizing Dissolution of Debris and Precipitation:

Oral Presentations, October 18, 2005

4.2.2.1 Park et al. (2005)

This presentation includes some experimental results regarding the dissolution of cal-sil in

borated water at pH = 4, in borated water adjusted with NaOH to pH = 7.14, and in water

containing dissolved STP. Information was also provided on a simulated short-term test of the

ICET #1 aluminum chemistry, designed to mimic the conditions involving precipitation on

cooling. This work is interesting and should be pursued with the. goal of generating

temperature dependent kinetic data on cal-sil dissolution, and aluminum hydroxide nucleation

and precipitation from pH = 10 borate solutions.

4.2.2.2 Klasky (2005)

In this presentation, the major observations of ICET #1 were summarized, and a number of

issues identified for more detailed exploration. In general, the reviewer concurs with the

objectives, the issues raised, the approach and the methodology. A commentary follows

regarding specific issues.

Particulate Nature of Precipitates. Slides 6 and 7, representing TEM images of 15-day a nd 30-

day high volume filtrates indicate that the material is made up of clusters of sub-equant particles

(See comments to p. 50 of ICET #1). It seems likely that the particles, once nucleated from a

supersaturated solution, were inhibited from further growth by the adsorption of boron (as

B(OH)3 or B(OH)4-) on the surface. Sorption of B on amorphous aluminum oxides approaches

a maximum at pH = 8.5 - 9.0, but falls off steeply above pH = 9, so that the amount adsorbed

at pH = 10, is less than 50% of that at maximum adsorption at pH -8.5. (Goldberg et al., 2001).

In another paper, Goldberg et al. (2004) have successfully modeled B adsorption on soils using

a constant capacitance model:

SOH + B(OH) 3(aq) = SH3B30 4 + H

Thus, B(OH)3 adsorption would be favored with increasing p H until B(OH) 3(aq) itself dissociates

in solution at pH =8.6. At still higher pH values, the B(OH)4 would tend to be repelled from the

hydroxylated surface, thus causing borate adsorption to decline. The solid state 1183 NMR

spectrum of the ICET #1 precipitate (Slide 20) indicates that B is present in both tetragonal and

trigonal coordination, raising the question whether B is adsorbed in more than one way on the

precipitate.

B(OH) 3(aq) adsorption could not only stabilize the AI(OH) 3 particles, but also inhibit Ostwald

ripening. In other words, a suspension of borate-coated particles is thermodynamically

metastable. However, it is possible that certain cluster configurations, consisting of 6 - 20

particles, may be slightly more stable than the individual particles, and that particle adhesion

can overcome the repulsive effects of the adsorbed B(OH)3. Thus, the multi-modal particle size

distribution shown in slides 25 and 26, may reflect the stable formation of such multi-particle

assemblages or clusters. An extensive literature exists on the thermodynamic stability of

clusters, e.g., Sciortino et al (2004), which might be relevant to the problem at hand It is

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suspected, however, that adhesion between the particles is generally weak in the system under

consideration, and that turbulence would limit aggregation to form a gel.

The small size of the discrete particles (- 2-5 nm) approaches in size some of the larger

polynuclear Al complexes, which have been identified in solution, and have been reviewed by

Casey et al. (2001),. The fact that most of the Al present in the precipitates is octahedrally

coordinated, with only a small proportion in tetrahedral coordination (see 27Al NMR, Slide 19) is

consistent with the coordination state of Al in the Keggin molecule, which has 12 Al in

octahedral coordination and one in tetrahedral coordination (Casey et al., loc. cit.)

The reviewer endorses additional bench-top solubility studies on the observed precipitates

(Slides 35 and 36), and concurs in the use of the MINTEQ codes for evaluation of, and

comparison with the solubility products of known precipitates. However, the thermodynamic

data used in MINTEQ may be neither up to date, nor sufficiently comprehensive for the problem

under study. Therefore a literature study should complement the ongoing experimental studies,

and the results of both be used to augment the thermodynamic database.

4.3 Head Loss Simulation Testing and Analysis: Questions and Answers

Answers are provided below to the questions posed to the Peer Review Group by NRC.

0. Is the accelerated head loss testing approach viable for evaluating the effects of multiple

chemical environments quickly?

A. The general impression gained is that the current head loss testing facility is

insufficiently flexible for evaluation of multiple chemical' environments or replication of

tests to establish reproducibility. A better approach would be to use replicate small

bench-scale facilities that could be run simultaneously, with stepped variations in critical

parameters, so that the sensitivity and magnitude of potentially adverse conditions could

be rapidly mapped out as a function of these parameters. The rapid acquisition of'

results would also facilitate focusing the experimental program on important issues as

they are recognized. Factorial design experiments might be considered if parameter

interactions are poorly understood and unpredictable. The current test loop should be

reserved for confirmatory 'demonstration" tests, based on the results of small-scale

scoping studies.

Q. What is the best method for incorporating time-dependent effects (e.g., material aging,

evolving chemical environments) in simulation testing?

A. This is a very broad and non-specific question, without a simple answer. Clearly, with

the variability in individual PWR designs and differing operating histories, there is a need

to concentrate on the most critical parameters and efficiently study their effects through

small-scale bench tests. Thus, for example, the impact of cal-sil carbonation during

aging could be investigated through field sampling from operating PWRs followed by

mineralogical and bench-scale leaching studies. Once the degree of variability and its

importance has been established, then small-scale loop and head-loss tests could be

conducted on a suitable range of variably aged samples. Similarly, the effect of

temperature could also be studied through small bench-scale tests followed by limited

small-scale loop and head-loss tests. Only after the impact of all relevant parameters

has been assessed, should confirmatory tests be conducted using the present facilities.

Even confirmatory tests are limited in what they can accomplish. For example, it would

A-51
be difficult to conduct, or analyze the results of a non-isothermal test simulating postLOCA cooling history.

A second approach is to develop a sufficiently powerful chemical modeling simulator that

the consequences of material aging and evolving chemical environments can be studied

in simulation mode. Simulations would allow multiple complex non-isothermal cases to

be run that would be difficult, expensive, or impractical using current facilities For this

approach to be successful requires active ongoing coordination between the modeling

group at SW Research Institute and the experimental investigators at ANL and LANL on

an experiment by experiment basis This is not happening at present.

Q. What metrics are most appropriate for evaluating the results of simulated chemical

products with those that formed during the ICET program?

A. By "metrics" the reviewer presumes that this is to mean measurement methods. By "simulated chemical products", it is assumed that the investigator is attempting to

simulate conditions in the laboratory that would permit the formation of similar or

identical products that formed during the ICETs, and that are also likely to form under

actual conditions in a PWR. The purpose of such studies is to identify the processes

taking place, quantify certain parameters under controlled conditions, and characterize

the chemical and physical properties of any precipitates that form. Such investigations

should take advantage of all instrumental techniques that are currently available. It

appears that the scientific staff is already well versed as to what should be done. The

reviewer's primary concern is that there appears to be little if any attempt to coordinate

experimental studies with model developers. At present this is a serious limitation, as it

leaves the investigator conducting bench-scale. tests without the needed focus, or

incentive to tailor his work to the requirements of a model that encompasses the diverse

range, of conditions expected in current operating plants.

Q. Are correlations available, or can they be developed, which can predict the associated

head loss if important physical characteristics of a chemical by-product are known?

A. The reviewer has limited experience in this particular area, but is confident, that even if

correlations are currently unavailable, they could be developed, and could predict the

associated head loss if the physical properties of a given precipitate are known. There

must be a huge literature concerning filtration technology that could be readily adapted

to the problem at hand. This should be initiated promptly. One could conceive of the

development of a post-LOCA coolant circulator simulator, which would utilize as input,

the precipitation conditions generated by a chemical simulator module alluded to in the

reviewer's response to the preceding question. With such. an integrated simulator,

critical screen blockage scenarios could be defined, and system modifications tested for

effectiveness.

A-52
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A-5 7

Appendix B

Final Assessment Report

Chemical Effects in PWR Sump Pool Environments

Peer Review

Wu Chen

Abstract

This report evaluated the results of the project work for investigating the chemical effect

on the sump screen head loss at the post LOCA sump environment. The evaluation was

done from the view point of filtration. Once particles are formed in the post LOCA sump

environment, the key information to look at are if these particles can reach the sump

screen and how many (represented by the total suspended solid value) and what kind of

particle (characterized by particle size and morphology). Based on the ICET runs by

LANL and loop tests by ANL, there is a high possibility that the sump screen will

encounter head loss problems during the post LOCA recirculation.

Executive Summary

This report is the results of the Chemical Effect Peer Review. The project was to

investigate the possible scenarios of chemical effect in the sump during a post LOCA

situation. It was a concern that the particles generated in the post LOCA sump

environment might cause the increase of head loss at the sump screen and reduce or stop

the flow of the recirculating cooling water.

The investigation was conducted by Los Alamos National Laboratory (LANL) and

Argonne National Laboratory (ANL) and the results were discussed in two peer review

meetings and team communications.

In this report, the assessment of the results from the project work was evaluated from the

filtration perspective as the head loss in the sump screen is a filtration process.

Once particles are formed in the post LOCA sump environment, the key information to

look at is

(1) Will these particles reach the pump. screen?

(2) How many (represented by the total suspended solid value)?

(3) What kind of particle (characterized by particle size and morphology)?

Based on the ICET runs by LANL and loop tests by ANL, it is a highly possible that the

sump screen will encounter head loss during the post LOCA recirculation.

Final Report-WCB- B-1
Contents

1. Introduction ................................................................. B-3

2. Integrated Chemical Effects Testing (ICET) ................................... B-3

2.1 Total suspended solids (TSS) ............................................. B-3

2.2 Particle size.............................................................. B-6

2.3 Gel particles .............................................................. B-6

3. Head Loss Simulation Testing ................................................. B-7

3.1 Test suspensions .......................................................... B-7

3.2 Laboratory filtration tests ................................................. B-7

4. Conclusion .................................................................. B-8

Appendix A Procedure for Total Suspended Solids (TSS) Measurement............ B-9

Al.1I Measure solid concentration by drying ................................... B-9

A 1.2 Measure solid concentration by Filtration (with wash) ................... B-10

Al. 3 Measure solid concentration by Filtration (without wash) ................. B-1Il

A 1.4 Measurement of dissolved solid......................................... B-12

Final Report-WC B-2-
1. Introduction

This report is the results of the Chemical Effect Peer Review. The project was to

investigate the possible scenarios of chemical effect in the sump pool during a post

LOCA situation. There was a concern that the particles generated in the post LOCA sump

environment might cause the increase of head loss at the sump screen and reduce or stop

the flow of the circulating cooling water.

The investigation was conducted by LANL (Los Alamos National Laboratory) and ANL

(Argonne National Laboratory) and the results were discussed in two peer review

meetings and team communications.

In this report, the assessment of the results from the project work was focused o n the

filtration aspect as the head loss in the sump screen is a filtration process.

2. Integrated Chemical Effects Testing (ICET)

This work was conducted by LANL. Excellent work has been done to investigate the

potential chemical effects in the sump pool under the post-LOCA environment. The

experimental parameters were derived from surveys of operation nuclear power plants

and should be representative. The type and quantity of coupon material, degree of

submergence were thoroughly considered. Advanced tools and analytical methods were

used to analyze the chemical species generated under each condition.

The Phenomenon Identification and Ranking Table (PIRT) process conducted at the end

of the 2nd review meeting and the teleconference afterward were very useful in

identifying additional potential post-LOCA scenarios which can be investigated in future

work. Perhaps PIRT process can be conducted at the beginning or the early phase of the

project to guide the research plan.

The head loss process in the sump screen during post-LOCA is the same as the pressure

drop development across the filter medium in any filtration process. The pressure drop in

a filtration process can be caused by either a cake build up or the clogging of the filter

medium. In either case, the rate of pressure drop increase can be affected by particle

concentration, particle size, particle shape, particle charge, particle-particle interactions

(such as coagulation- and flocculation), liquid viscosity, and chemical reaction around the

filter medium. Among these factors, particle concentration and particle size have the

most profound impact on the head loss of the post-LOCA sump screen.

2.1 Total suspended solids (TSS)

Total suspended solid (TSS) is the key parameter to quantify the amount of particles

generated in different sump environments. It is also important to monitor TSS as a

function of time to determine if the rates of chemical effects change.

Final Report-WCB3 B-3
Based on the Integrated Chemical Effect Testing (ICET) reports, TSS data were collected

during ICET runs. As these results are the most important information toward the

assessment of sump screen plugging and head loss tendencies, TSS data were reported

and discussed during both review meetings. It is recommended that the TSS data and

procedure used for measuring them be reported in the final project report. These data are

the key information for finding solutions for the sump screen head loss challenges. The

head loss tests at Argonne National Laboratory (ANL) simulated the ICET conditions.

Although it probably made no difference on the final conclusion in this case but the

common practice is to match the TSS values to ensure the testing conditions are the same.

The primary sources of particles are the insulation material (fiberglass and/or calcium

silicate) and particulates generated by chemical effects in the sump pool. It is expected

that the insulation material will get into the recirculation water during LOCA and most of

the particles from chemical effect won't be present until a few hours or a few days later.

The filtration process at the post-LOCA sump screen can be divided into two stages, the

first stage is the filtering of insulation material with cake build up (it is a cake filtration

process). Later, the particles from chemical, effect will be filtered by the insulation cake

and most particles are caught inside the cake (depth filtration process). These two

mechanisms will be the reasonable approach for post-LOCA filtration simulation if so

desired. Although it is unlikely, in this author's opinion, the chemical effects can also

occur inside the debris cake and grow solids to generate more resistance to water flow.

In the building of insulation material cake, it is important to know the amount of

insulation material suspended in the sump water. There was a good estimate of insulation

material per unit sump water (0.137 ftl/ft3

). It will be helpful to estimate how much of

this insulation material remains in the suspension during recirculation. The 268 mg/l

initial value in ICET #3 may refer to this information but it was not clear. It is expected

that all the suspended insulation materials will end up in the cake on the sump screen.

Even those particles which escape the initial filtration will be caught once the cake builds

up. Therefore, it is recommended that the suspended portion of the insulation material

for each ICET test run be clearly quantified. With these numbers, the cake thickness and

its depth filter capacities can be estimated.

The amount of insulation material remains in the suspension vs. those settle depends on

the recirculation rate. For the ICET's, 25 gpm recirculation rate and 0.3 cm/s cross flow

velocity were mentioned. It is important to ensure this rate simulate the actual sump

water recirculation rate.

Presume all the data presented in the ICET runs are due to chemical effects, a summary

of these TSS data is shown in the following table. Based on these results, sump

environment under the conditions of Test #1 and #4 will have the tendency of generating

more particulate materials and causing severe head loss (by plugging the insulation

material cake). Conditions simulated by Test #3 will have the lowest risk of plugging the

insulation cake.

Final Report-WCB- B-4
TSS (mg/i)

ICET #1 30-15--30

ICET #2 35 - 10 leveled to 10

ICET #3 14 stable

ICET #4 30~-40 stable

ICET #5 25-15 leveled to 15

Table 1 Total Suspended Solid (TSS) in ICET runs

It is understood that during the TSS measurement, the sample was filtered but not was hed.

As there are dissolved solids in the water and will show up as solid after being dried, the

TSS numbers may be a few mg/i higher than the actual solid concentration.

The higher the particle concentration, the more head loss is expected. In industrial

applications, the impact of TSS can be semi-quantitatively classified as the following.

The sump screen with insulation debris cake can be considered as a deep bed filter.

<1I mg/liter a deep bed filter can last for over a month

1-10 mg/liter a deep bed filter can last for a week

10~- 30 mg/liter a deep bed filter needs to be regenerated within 1-3 days

30-70 mg/liter a deep bed filter can only run for hours

70-100 mg/liter deep bed filters are struggling and cake starts to form on top of

filter media

100-500 mg/liter expect very fast deep bed plugging and cake forming on top of

filter media

>500 mg/liter cake filtration

Bed height, inter-particle porosity of the bed, and size of the particles in the suspension

can affect above assessment to a small degree. Nevertheless, it provides a good rule of

thumb of what to expect of the head loss in the sump screen with insulation material cake.

Based on the ICET data, the sump screen can be plugged in a few days no matter which

sump condition we are considering.

As mentioned, particle size distribution and gelatinous properties can also impact the

filtration. These will be discussed in the following sections.

The project team did a good job in TSS measurement by considering the temperature

effect and avoided the additional precipitation of solids during cooling down process.

As a filter sample is dried to measured the amount of solid collected on the filter, the

dissolved solids in the liquid will also precipitate (this is a similar but different

phenomena from the precipitation due to cooling) and add to the solid mass. The

common practice for the correct TSS measurement is to wash the filter cake with pure

liquid (purified DI water in this case) to wash off any dissolved solids before drying. The

alternative method is to analyze the amount of total dissolved solids and then

mathematically subtract (not direct subtraction) it from the measured TSS value. A

procedure of the TSS measurement is shown in Appendix A.

Final Report-WCB- B-5
Turbidity values are also used in the filtration industry to quantify the content of solids

particles and filtration effectiveness. As turbidity is affected by liquid colors and does

not always reflect solid concentration well, turbidity data are not as useful as TSS values

for evaluating a filtration system.

2.2 Particle size

The particles need to be retained by the sump screen (and anything that got caught on the

screen) before they can contribute to the head loss. Small particles (<I micron) have

good chances of passing through all barriers without being caught. On-the other hand,

higher particle concentration enhances the bridging effect and makes the particles easier

to be filtered. Therefore, the effectiveness of filtration is determined by the combined

effect of particle size and.total suspended solids.

For solid/liquid separation applications, the particle size measurement needs to be

conducted in the mother liquor. Any modification (dilution, drying, and additives) to the

particle suspension should be avoided as it can change the particle size distribution. For

the purpose of post-LOCA environment, the best particle size measurement methods are

optical microscope and laser diffraction particle size analyzer (such as Horiba LA-91 10 or

Coulter LS-13-320). Particle counters (like Particle Size System Accusizer or Hiac

particle counters) can be used if the TSS is below 20 mg/l as it is very dilute and may be

difficult for the laser diffraction particle size analyzer to work. Taking particle photos

with an optical microscope allows a visual comparison of particle size, shape, and

agglomerateionlflocculation characteristics under different simulated environment. A

laser diffraction particle size analyzer (or a particle counter) will generate the particle size

distribution.

Sometimes, dilution is necessary for particle size analyzer to work. It needs to be noted

that pure water should be avoided as the dilution agent smice it may dissolve some fine

particles and the change of ionic strength in the solution will change the agglomeration

state. The standard procedure is to filter the particles out of some suspension to obtain

the particle free mother liquor for dilution.

Limited particle size data were presented in the report and during review meeting. It is

recommended that the project team re-evaluate the particle size information and present

data for all ICET runs in the final report.

2.3 Gel particles

These types of particles were reported in the first review meeting but later investigation

by the LANL team discovered that was due to measurement issues.

In case gel particles become an issue, some understandings of the impact of these types of

particles are useful. There are two distinct gel particles behaviors which can affect

filtration. Some gel particles can be easily torn apart by hydrodynamics forces (during

recirculation) and very difficult to be caught by any filters. This property is to the favor

Final Report-WCB- B-6
of the sump screen and will not cause head loss problems. Another type of gel particles

can be sticky and easily plug up filter media even at very low TSS. If this type of gel is

present in the post-LOCA sump pool, fast head loss can be encountered in the sump

screen.

The only method to understand the impact of these gelatinous coating materials to the

sump screen filter is by experiments. A cake of insulation material can be formed based

on the estimated amount (as discussed earlier) and a sample suspension containing the gel

material be poured through this cake. By measuring the presence of gel in the filtrate and

the head loss of the filter, a qualitative to semi-quantitative measurement of the effect of

this kind of gel to the sump screen can be evaluated.

3. Head Loss Simulation Testing

This work was conducted by ANL. A very good test ioop was constructed at ANL and

suitable for the intended head loss test. The challenges seemed to be on the confirmation

of the representative type and amount of material used for testing. The test suspension

should match the environment in the ICET runs and the actual post-LOCA sump pool.

3.1 Test suspensions

It is important to match the particle size and concentration from the ICET findings. It is

difficult to generate exactly the same materials given the time and scale of tests. As long

as the particle size and concentration are matched, the head loss experiment will generate

useful information about the screen plugging tendencies.

Head loss test #1 mimics the condition of ICET #3. ICET#3 reported a stable TSS of 14

mg/l. The "cloud" and the fast pressure drop increase encountered in head loss test #1

right after CaCl2 was added indicted the TSS must be higher than 14 mg/l and could be in

200 mg/i range. It would be useful if the TSS data were collected during the head loss

test to document the test conditions.

There are more opportunities for solids to settle in the ICET tank as the cross flow rate is

not uniform throughout the whole system and some stagnant portion cannot be avoided.

The flow ioop in ANL is easier for maintaining a uniform cross flow velocity so fewer

particles can settle and most of them will be caught by the filter.

3.2 Laboratory filtration tests

It is time and efforts consuming to run the big test flow loop. Valuable information can

be obtained by running simple laboratory filtration test or a smaller flow loop. One

example is shown in Figure 1.

As the first step in a post LOCA sump recirculation is the build up of a cake by the

insulation material, it is important to understand the filtration behavior of the insulation

material. Tests can be conducted with different amount of insulation material to build a

Final Report-WC 1- B-7
correlation of the pressure drop as a function of cake height. It may not be linear. This

correlation allows the assessment of the risk of sump screen plugging right after LOCA

(without any chemical effect) for different insulation materials.

Conducting tests with same amount of insulation material but under diffierent pressures

can detect the compressibility of the insulation material cake. Compressible cakes can be

compacted by the flow during the post LOCA recirculation and generate more head loss.

The material generated from chemical effects can then be added to the system to

understand their impacts on the insulation cake.

A small filter device allows the project team to evaluate filtration behaviors under

different conditions with less effort. With information from small scale tests, the design

of experiments for the large flow loop can be conducted more effectively and relevant

data can be obtained.

P

screen

Peristaltic pump

to provide

constant flow rate

Figure I A constant rate filter device

4. Conclusion

Once particles are formed in the post LOCA sump environment, the key information to

look at is

(1) Will these particles reach the pump screen?

(2) How many (represented by the total suspended solid value)?

(3) What kind of particle (characterized by particle size and morphology)?

Based on the ICET runs by LANL and loop tests by ANL, it is highly possible that the

sump screen will encounter head loss during the post LOCA recirculation.

Final Report-WCB8 B-8
Appendix 1 Total Suspended Solid (TSS) Measurement Proceudre

Al 1. Measure solid concentration by drying

For cakes, very thick suspensions or difficult to filter suspensions, it is impractical to run

a filtration to measure solid concentration. Oven drying should be used.

Equipment: Weighing dishes

Balance

Oven

Procedure:

1. Put a proper amount of sample in a weighing dish and weigh it.

2. Put the sample and dish into the oven to dry.

3. Measure the weight of the dried solids.

4. Calculate according to the following formula.

.Sometimes there are solids (like salt) dissolved in the liquid and need to be accounted for.

Weight of liquid =

weight of initial sample-weight of dried solids

1 - % total dissolved solid

Weight of true solid = weight of initial sample - weight of liquid

Weight% weight of true solid

weight of initial sample

Volume %

weight of true solid

solid density

weight of true solid weight of liquid

solid density- liquid density

Final Report-WCB- B-9
A 1.2 Measure solid concentration by Filtration (with wash)

This method is good for dilute suspension or fairly easy to filter materials.

Equipment: Weighing dishes, Buchner vacuum filter,

Filter media (the selected filter medium need to be chemically compatible

and capable of catching all the particles)

Volumetric pipets (50 ml, 20 ml, and 5 ml with large tip to prevent plugging)

Balance, Oven

Procedure:

1. Set up the vacuum filter and select a proper filter medium. Weigh the filter medium.

2. Keep the slurry well mixed.

3. Use volumetric pipet to move slurry to the filter.

4. Filter as much slurry as possible until the filter start to show the sign of plugging.

Record the total volume of slurry filtered.

[Steps 3 & 4 can be replaced by filtering a known amount (volume or weight) of slurry.]

5. If there is too much solid in the filtrate, the test needs to be re-run with another medium.

6. Use clean liquid to wash the cake. This step is to remove any dissolved solids (like

salt) in the mother liquor. The amount of wash liquid varies but use sufficient

amount to ensure the cake is well washed.

7. Remove the filter cake with filter medium and dry them in the oven.

8. Measure the density of the filtrate.

9. Measure the weight of the dried cake.

10. Measure the density of the solids (use the dried cake for measurement).

10. Calculate according to the following formula.

weight of liquid =(total volume filtered - segtoli dren soityd liquid density

Weightweight of dried solids

Weight/oweight of solid + weight of liquid

weight of dried solids

Volume %solid density

Volum ~ =total volume filtered

Tota Supened olispm -mg -weight of dried solids

Tota Supened olis pm =liter -total volume filtered

Final Report-WCB- B-10
Al .3 Measure solid concentration by Filtration (without wash)

This method is used cake washing is difficult due to cake cracking or low filtration rate.

Equipment: Weighing dishes , Buchner vacuum filter,

Filter media (the selected filter medium need to be chemically compatible

and capable of catching all the particles)

Volumetric pipets (50 ml, 20 ml, and 5 ml with large tip to prevent plugging)

Balance, Oven

Procedure:

1. Set up the vacuum filter and select a proper filter medium. Weigh the filter medium.

2. Keep the slurry well mixed.

3. Use volumnetric pipet to move slurry to the filter.

4. Filter as much slurry as possible until the filter start to show the sign of plugging.

Record the total volume of slurry filtered.

[Steps 3 & 4 can be replaced by filtering a known amount (volume or weight) of slurry.]

5. If there is too much solid in the filtrate, the test needs to be re-run with another medium.

6. Remove the filter cake with filter medium and measure the wet weight of the cake

7. Dry the cake in the oven.

8. Measure the density and the total dissolved solids in the filtrate.

9. Measure the weight of the dried cake.

10. Measure the density of the solids (by measuring the dried cake). If there is dissolved

solids in the liquid, this measurement should be done with a washed cake.

11. Calculate according to the following formula.

Weiht f lqui inthecak =weight of wet cake-weight of dried cake

Weigt ofliqud inthe ake(l-% total dissolved solid)

Weight of solid in the cake =weight of wet cake - weight of liquid in the cake

Weigt% =weight of solid

Weight %weight of solid + weight of liquid

weight of dried solids

Volume %solid density Volum %=total volume filtered

Totl Sspnde Soid pp =mg weight of solids

Tota Supened olis pm =liter -total volume filtered

Final Report-WC Bl-I I
A 1.4 Measurement of dissolved solid

Equipment: Weighing dish, Balance, and Oven

Procedure:

1 . Remove all the suspended solid from the liquid by a Buchner vacuum filter or a

laboratory centrifuge.

2. Measure the weight of an empty dish (Wdihb).

3. Put some liquid in the dish and measure the weight (Wdish+Iiquid).

4. Dry the sample in the oven.

5. After drying, measure the weight of dish plus the remaining non-volatile.

(Wdish~nonvolatiles).

6. Calculate according to the following formula.

Wdish+ non volatile -Wdish

Total dissolved solids= Wdish+liquid -Wdish

Final Report-WC B1 B-12
Appendix C

CHEMICAL EFFECT PEER REVIEW:

ASSESSMENT OF TEST FACILITIES AND PROGRAMS

TO INVESTIGATE CONCERNS RELATED TO CHEMICAL EFFECTS

IN PRESSURIZED WATER REACTOR

EMERGENCY CORE COOLING SYSTEMS

Calvin H. Delegard

Pacific Northwest National Laboratory

C-1
SUMMARY

The Generic Safety Issue 191 was formulated by the Nuclear Regulatory Commission (NRC) to

evaluate the potential for and phenomena associated with debris accumulation on sump

screens located upstream of pressurized water reactor pumps used in the emergency core

cooling system following a loss-of-coolant accident (LOCA). To help understand the

phenomena and the magnitudes of debris generation and accumulation, the NRC

commissioned the performance of three technical studies - "Integrated Chemical Effects

Testing," "Chemical Speciation Prediction," and the "Accelerated Chemical Effects Head Loss

Testing."

The "Integrated Chemical Effects Testing" experiments endeavored to re-create the post-LOCA

environment in five engineering scale tests. The test conditions, following both chemical and

temporal evolution of the post-LOCA, included reactor building containment spray-down,

corrosion of both spray-wetted and immersed reactor containment test coupons, insulation

materials, and recirculating solution. The "Integrated Chemical Effects Testing" apparatus and

experimental design thus were devised to provide an approximate scale model of the postLOCA reactor and containment environment and endeavored to encompass the primary

material and environmental conditions present in the post-LOCA PWRs.

In doing these extensive and complicated tests, the ICET matrix provided much valuable

information on material phase behavior and interaction. On one hand it was learned that many

of the materials in the test matrix, including many of the metals, had little, if any, effect on solids

formation either by direct contribution or by secondary interactions. On the other hand, the

following materials had larger effects on solids formation:

o Hydrogen and hydroxide ion concentration (pH)

o Dissolved boron from borate buffers and burnable poisons

o Dissolved phosphate from trisodium phosphate pH buffer

o Aluminum metal (largely present as temporary structural material)

o Fiberglass thermal insulation material

o Cal-Sil, a calcium silicate thermal insulation material

" Concrete.

The "Chemical Speciation Prediction" work was. accomplished by assessing the ability of

geochemnical and process chemical thermodynamic modeling software to replicate the solute

concentrations and reaction sequence in the post-LOCA coolant system. The task ensured that

each candidate model contained a sufficient thermochemnical database. For this, the presence

of boron aqueous solutes and compounds was a key discriminator. The models also needed to

be valid for temperatures up to about 11 00C and ionic strength up to 0.5 molal. Four chemical /

geochemnical models met these and other criteria:

o OLI "StreamAnalyzer", version 2.0

o Lawrence Livermore National Laboratory "EQ3/6", version 7.2b

o RockWare, Geochemist's Workbench7, REACT, version 5.0

o US Geological Survey "PHREEQC", version 2.8.

Each model then was tested for seven different starting solution conditions representative of the

post-LOCA environment. It was found that EQ3/6 was the most robust, avoiding the

convergence problems that the other codes suffered. The EQ3/6 code was selected, with the

C-2
OLI StreamAnalyzer, to predict the outcomes of the five ICET experiments and the results

compared with the results actually found by ICET. Small scale experiments to determine the

dissolution rates of insulation materials and the corrosion rates of aluminum in post-LOCA

solution environments also were performed under the "Chemical Speciation Prediction" task and

the results provided support to improving the accuracy of the chemical models. The small scale

tests gave valuable insights into chemical behaviors of the complex post-LOCA solid/solution

mixtures. The modeling refinements might be nearing the point that compositions in non-tested

solid/solution conditions can be predicted.

The "Accelerated Chemical Effects Head Loss Testing" simulated the loading of the sump

screen with debris materials and solids produced by chemical precipitation under recirculating

coolant conditions. The test apparatus created seemingly the most severe pump screen

geometry, perpendicular to stream flow, to provide the most definitive (conservative) test

conditions. The testing focused on the chemical conditions studied in the one (of the five)

"Integrated Chemical Effects Testing" experiments that produced finely divided calcium

phosphate precipitates. The testing showed the severity of sump screen blockage that could

occur even with relatively low debris loads and small amounts of calcium phosphate precipitate.

Some small scale tests also were performed under the "Accelerated Chemical Effects Head

Loss Testing" to determine the dissolution of Cal-Sil and the subsequent precipitation of calcium

phosphate under simulated sump pool conditions. It was found that the Cal-Sil dissolution is

sufficiently rapid, even in the presence of trisodium phosphate (which inhibits Cal-Sil

dissolution), to precipitate significant amounts of calcium phosphate within a few hours and

engender prohibitive pressure drops in the debris bed.

The results of these three studies were presented to a group of five peer reviewers in technical

reports, and in workshop meetings in October 2005 and March 2006, by the NRC and the

studies' researchers. The reviewers, with reactor, nuclear, industrial, and academic credentials,

were charged by the NRC to review test approaches and results, recommend improvements to

the testing and analysis, and to identify any important but overlooked technical issues for

additional consideration or, perhaps, experiments. The evaluations of the author, one of the five

peer reviewers, are presented in this report.

As seen, the three technical studies provided substantial information to understanding to the

effects of various~factors in the post-LOCA environment germane to Generic Safety Issue 191.

The scope of the post-LOCA conditions in the many PWR configurations, however, forced

certain simplifications in the experimental design. The results of the studies also suggested

potential avenues of further investigation. The following additional investigations are suggested

based on the evaluations made during review of the three technical studies:

o Further parametric studies could be performed both to understand the

observations from the completed rounds of experiments and to investigate the

roles of temperature variation, temperature gradient (heated and cooled

surfaces), boron concentration variation, radiolysis, and organic materials.

Because of the large size of the "Integrated Chemical Effects Testing" apparatus

and resulting large quantity of required materials, the execution of more large

scale tests under more widely varying conditions may be inefficient. Instead, the

testing should be done on a smaller scale to gain, at lower cost, most of the

pertinent information.

C-3
" The influence of organic materials to act as glues to accrete solid particles could

be great. Therefore, determination of the behavior of electrical insulations,

plastic coatings, and paints when treated to steam and hot liquid water should be

done to investigate their coalescence and ability to collect inorganic solids as

they cool.

" Kilorad (10~3 Rad) per hour fields may exist away from the reactor core in the

post-LOCA coolant system while megarad (106 ) Rad per hour fields may exist

around the core. Tests of the effects of radiolysis, particularly for organic

materials, should be performed. The organic materials, besides providing

radiolysis products that contribute additional chemical effects to the solution, can

act as radiolytic radical scavengers and impose reducing conditions to the

system.

o The effects of high temperature and low temperature heat transfer surfaces and

heat cycling should be studied. The test approach perhaps could use a

recirculation loop in which simulated post-LOCA coolant slurries, containing the

dissolved and undissolved solids, would be exposed to surfaces at temperatures

representative of the hotter fuel and cooler heat exchangers.

o Aluminum metal surface analysis by x-ray diffractometry may be useful to

determine the competing or complementary effects of calIcium ion, silicate, or

both on inhibiting aluminum corrosion. The effects of phosphate and borate

species on aluminum corrosion also might be monitored in this fashion. In a like

manner, surface analyses could be done to assess the effects of the various

solutes, particularly aluminum, on fiberglass or other silicates corrosion.

" The accelerated head loss test apparatus appears to be too large to encourage

multiple tests. A smaller test loop perhaps would allow more of the needed tests

to be performed with the same resources. The test conditions could include

temperatures that ramped down with time, exposed high temperature surfaces

(as provided in the post-LOCA system by the exposed fuel rods), and exposed

lower temperature surfaces.

o The redox conditions and concentrations of water radiolysis products, such as

hydrogen peroxide, in the post-LOCA waters should be estimated taking into

account the particularly high radiation fields imposed by the core.

" The potential presence of hypochlorite from radiolysis of chloride ion in the

aqueous post-LOCA coolant should be investigated. If hypochlorite is present,

its effect on metal corrosion under post-LOCA conditions should be investigated.

o The potential for hot sodium tetraborate or boric oxide to act as a flux to attack

and perhaps dissolve the magnetite oxide layer from the reactor vessel wall or

the cladding from fuel should be examined.

o The relative impact of the quantity of the solids formed by reaction of the mineral

tobermorite (from Cal-Sil) with carbonic acid from absorption of atmospheric

carbon dioxide to form calcite and amorphous silica, though likely to be small,

should be assessed.

C-4
oThe potential for algae and other biological growth in the post-LOCA water

recirculation system should be investigated either through examination of the

technical literature or through testing. The boron concentration in the post-LOCA

water (-0.2 molar) may prove to be sufficiently high to preclude biological activity.

C-5
CONTENTS

Summary ............................................................................................... C-2

Abbreviations........................................... ............................................... C-7

1 Introduction.................................................................................... C-8

2 Principal Technical Questions .............................................................. C-1

2.1 Integrated Chemical Effects Testing................................................. C-1 1

2.1.1 Principal Sump Pool Variables and Constant Variables................. C-1 2

2.1.2 Variables or Materials for Most Importance But Not Considered ICET C-13

2.1.3 Sufficiency of ICET Analysis Methods .................................... C-14

2.2 Chemical Speciation Prediction ...................................................... C-i5

2.2.1 Credibility of Product Predictions.......................................... C-16

2.2.2 Code Benchmarking by Tests ............................................. C-1 7

2.2.3 Measuring the Code Uncertainties ........................................ C-17

2.3 Accelerated Chemical Effects Head Loss Testing.................................. C-1 7

2.3.1 Adequacy of the Head Loss Testing Approach .......................... C-18

2.3.2 Methods for Observing Time-Dependent Effects ........................ C-19

2.3.3 Evaluation of Simulated Chemical Products.............................. C-1 9

2.3.4 Identifying Key Physical Parameters to Predict Head Loss

Performance................................................................. C-20

3 Unexamined and Little Examined Conditions............................................. C-21

3.1 Radiolysis and Its Effect on Metal Corrosion........................................ C-21

3.2 Solution Composition Effects on Metal Corrosion .................................. C-22

3.3 Spallation of Deposits from the Hot Fuel Cladding and Reactor Vessel.......... C-23

3.4 Atmospheric Contributions ............................................................ C-25

3.5 Biological Activity...................................................................... C-26

4 References................................................................................... C-27

Appendices

1 Curriculum Vitae - CH Delegard........................................................... C-29

2 Preliminary Assessment Report............................................................ C-31

3 Informal Comments to ICET Reports - May 7, 2006 and Responses -

May 10, 2006 ................................................................................ C-36

Tables

1 ICET Matrix................................................................................... C-il1

2 Dissolution and Corrosion Rate Measurement Results.................................. C-1 6

C-6
ABBREVIATIONS

ANL Argonne National Laboratory

CNWRA Center for Nuclear Waste Regulatory Analyses

ECCS emergency core cooling system

GSI-191 Generic Safety Issue 191

ICET Integrated Chemical Effects Testing

LANL Los Alamos National Laboratory

LOCA loss-of-coolant accident

NRC Nuclear Regulatory Commission

PSID particle size distribution

PWR pressurized water reactor

SwRl Southwest Research Institute

TSP Trisodium phosphate

UNM University of New Mexico

XRD x-ray diffractometry

C-7
I INTRODUCTION

During a loss-of-coolant accident (LOCA) in a pressurized water reactor (PWR) operating at full

load power, the primary coolant will be lost rapidly from the reactor pressure vessel and heat

exchangers. The superheated water, at nominally 250-3300C temperature, will escape from the

pressurized coolant system, flash off as steam as it attains normal atmospheric pressure, and

scour the region surrounding the break, removing thermal insulation, paint, and even concrete.

Immediately after the LOCA event, alkaline water jets near the top of the reactor containment

dome will spray down within the containment building with the purpose of scrubbing

radionuclides from the air space. Within about 30 minutes after the LOCA, emergency cooling

water will be injected into the cooling system.

The condensed primary cooling water, the spray water, and the emergency cooling water will

flow downward in the containment building, through sump screens, and into a pump located at

the physical low point in the containment building. There, the water will be collected and, once

the emergency cooling water is exhausted, pumped to the reactor pressure vessel, over the

core, and through the cooling circuit breach where it will again flow down to the sump. This

recirculating water system, which serves to cool the reactor core and reactor vessel in the postLOCA period, is called the emergency core cooling system (ECCS).

The Generic Safety Issue 191 (GSI-1 91) was formulated to evaluate the phenomena associated

with debris creation and bed accumulation on the sump screens located upstream of the PWR

sump pump for the ECCS following a LOCA. The GSI-11 91 was engendered by the observation

of gelatinous material in the containment building of the reactor, Three Mile lsland-2, some time

after its accident. The Nuclear Regulatory Commission (NRC) has defined the impacts of the

pump blockage in Bulletin 2003-0 1 and in Generic Letter 2004-02 (NRC 2003 and NRC 2004).

As part of the resolution of GSI-1 91, three areas of technical investigation were undertaken at

the behest of the NRC to define the nature and magnitude of the debris formation which would

serve to block the sump screens.

The first area of investigation, the "Integrated Chemical Effects Testing" (ICET), was conducted

by researchers at the Los Alamos National Laboratory (LANL) and the University of New Mexico

(UNM). The ICET experiments endeavored to re-create the post-LOCA environment, including

spray-down conditions, corrosion of reactor containment test coupons under both spray-wetted

and immersed conditions, degradation of thermal insulation materials, and recirculating of

coolant solution at a selected nominal temperature (60*C) in 30-day tests. The test scale was

250 gallons (-946 liters). Five different combinations of insulation materials and reactor solution

compositions, thought to be broadly representative of the conditions in United States PWRs,

were investigated. The results of the five tests were reported both formally (Dallman et al.

2005a-2005e) and during review meetings held October 18-19, 2005, at the Argonne National

Laboratory (ANL) and March 27-29, 2006 at the Southwest Research Institute (SwRl). Followup testing and analysis by this same group is underway.

The second area of investigation was "Chemical Speciation Prediction". This work was

performed by the Center for Nuclear Waste Regulatory Analyses (CNWRA) of the SwRI.

Geochemnical and process chemical thermodynamic modeling software was. used to attempt to

replicate the solute concentrations and reaction sequence in the post-LOCA coolant system.

Initial evaluations used starting conditions postulated for post-LOCA environments. The studies

were informed by the results from metal corrosion rate laboratory studies and insulation material

C-8
dissolution rate experiments performed by SwRl staff and by the results of the LANL/UNM ICET

experimental series as they became available. The results of the experiments and the model

testing and development are provided by formal reports (Jain et a[. 2004, Jain et al. 2005, and

McMurry et al. - draft) and by presentations during the October 2005 and March 2006 review

meetings.

The third area of investigation, "Accelerated Chemical Effects Head Loss Testing," is being

performed by ANL researchers. The objective of the head loss testing is to create a simulation

of the loading of the sump screen. The tests are conducted with debris solids (primarily arising

from insulation materials) and precipitating solids in a recirculating loop containing flowing

simulated coolant. The differential pressure across the 6-inch (-15-cm) diameter model sump

screen, consisting of a plate perforated with holes of 3/1 6-inch (-0.4-cm) diameter, was

measured as the flow continued to circulate. The test conditions to date have been based on

variations of the third ICET experiment. Results of the experiments have been presented in two

informal "quick look" reports (Oras et al. 2005 and Oras et al. 2006) and by presentations during

the October 2005 and March 2006 review meetings.

A technical peer group, comprised of five members with reactor, nuclear, industrial, and

academic credentials, was convened by the NRC to review the three sponsored activities

related to understanding the post-LOCA PWR sump pool environments and the GSI-191. The

peer review group also was charged to recommend improvements to the testing and analysis

approaches in the three activities and identify any important but overlooked technical issues for

additional consideration or, perhaps, experiments.

The NRC requested judgments from the peer reviewers on the technical soundness and

potential shortcomings of the "ICET," the "Chemical Speciation Prediction," and the "Accelerated

Chemical Effects Head Loss Testing." The evaluations of the present report author (Cal

Delegard), one of the five peer reviewers, are presented in this report. The specific questions

posed by the NRC guidance to the peer reviewers and the author's responses are given in

Section 2 of this report. Some areas for new or expanded work to help understand effects not

yet investigated by the existing program are proposed and discussed in Section 3. Technical

references are given in Section 4.

The author's credentials (curriculum vitae) are summarized in Appendix A. Brief comments and

questions on the research results provided to the NRC by the author in a preliminary

assessment report dated November 30, 2005 are found in Appendix B. Some further questions

.on ICET experiments, and the answers obtained from the researchers, are given in Appendix C.

These questions were raised in an e-mail message on May 7, 2006.

C-9
2 PRINCIPAL TECHNICAL QUESTIONS

Three areas of investigation were pursued in the studies conducted to help resolve the impact of

GSI-1 91, concerned with the potential for debris to accumulate on the sump screens located

upstream of the PWR sump pump for the ECCS following a LOCA. The three investigation

areas are called "Integrated Chemical Effects Testing" (dubbed ICET), "Chemical Speciation

Prediction", and "Accelerated Chemical Effects Head Loss Testing". A technical peer group was

convened by the NRC to review the three sponsored activities. As part of the review, a set of

Principal Technical Questions was posed to the review panel by the NRC.

The questions posed to the review panel are:

Integrated Chemical Effects Testing

" Have the principal sump pool variables which affect chemical by-product

formation in the post-LOCA environment been adequately simulated?

o Many ICET variables were held constant during the experiments. How would

changes in the most important constant variables affect chemical product

formation?

o What variables or materials not simulated by the ICET testing may have the most

impact on chemical product formation (e.g., coatings, free insulation, flow through

sediment and other materials on sump screen, galvanic effects) and how should

their effect be characterized by testing or analysis?

0 Were the methods used within the ICET program to characterize and analyze

chemical by-products sufficient?

Chemical Speciation Prediction

" Is the speciation analysis expected to provide reasonable predictions of chemical

product formation over a range of possible sump environments?

" Is the plan for benchmarking these codes using small-scale testing and the ICET

results appropriate?

o What is the most appropriate way to measure the uncertainty associated with

these codes?

Accelerated Chemical Effects Head Loss Testing

o Is the accelerated head loss testing approach viable for evaluating the effects of

multiple chemical environments quickly?

o What is the best method for incorporating for time-dependent effects (e.g.,

material aging, evolving chemical environments) in simulation testing?

o What metrics are most appropriate for evaluating the results of simulated

chemical products with those that formed during the ICET program?

o Are correlations available, or can they be developed, which can predict the

associated head loss if important physical characteristics of a chemical byproduct are known?

The responses to the principal technical questions are addressed, in the order given above, in

this section of the report.

C-10
2.1 integrated Chemical Effects Testing

The ICET experiments consisted of an ambitious set of five relatively large scale tests. The test

matrix, given in Table 1, attempted to encompass the various water chemistry and materials

environments present in the PWRs of the US and to emulate, on an engineering laboratory

scale, the evolution of the post-LOCA situation with spray-down sequences, periods of little flow,

and then active pumping. Each test had present a number of metallic coupons (galvanized

steel, zinc primer coating, aluminum, copper, and carbon steel), crumbled and massive

concrete, and thermal insulation materials. Two primary insulation types were considered. The

first, Nukon®, is a fiberglass material with some included organic binder. Because of its

widespread use, this insulation type was part of the constituents in all five tests. The second

insulation type is a foamed calcium-silicate material called Cal-Sil. The Cal-Sil was included in

two of the five tests. With the goal of emulating the distribution of exposed surfaces in the

reactor containment, some of the coupons were submerged while others were in the vapor

space and exposed to liquid only during the brief spray-down phase and to what was very little

condensation.

Table 1. ICET Matrix

TetTemp, Buffering Initial BoronComn Tes_ c Agent pH (PPM) omen

1 60 NaO 10 800100% fiberglass insulation, high pH, NaOH

1 60 NaO 10 800concentration determined by pH

2 0 Trisodium 7 80100% fiberglass insulation, lower pH, TSP

_______________fn concentration determined by pH

Trisodium 80% Cal-Sil/20% fiberglass insulation, lower

3 60 phophat 7 800pH, TSP concentration determined by pH

4 60 NaO 10 80080% Cal-Sil/20% fiberglass insulation, high

4 ~~ 60-O1 80PH, NaOH concentration determined by pH

5 0 Sodium 8.-. 40100% fiberglass insulation, pH determined

5~ 60 8 - 8.r240 by achieving target boron concentration.

The tests used 250 gallons of water (949 liters) and were conducted isothermally at 600C for 30

days during which the solutions were monitored for pH and the solutions sampled for analysis.

After the 30 days of testing, the test apparatus was opened, the coupons measured and

photographed, and the solution and solids analyzed.

The ICET campaign was ambitious, attempting to re-create the post-LOCA environment for five

conditions broadly representative of the various PWR insulation and ECCS water compositions.

To ensure that the conditions in all PWRs were represented, an extensive survey of the PWRs

was conducted such that the five tested conditions covered the various PWR environments.

The scale of the test apparatus was sufficiently large ensure that surface area - to - volume

ratios followed those of the genuine reactor containments. The tests also followed the temporal

sequence of events and conditions in the post-LOCA situation. Test control was excellent, with

little deviation from the planned temperature or other test conditions.

To ascertain the key factors controlling the potential sump screen blocking phenomena, a broad

suite of analyses was performed over the course of the testing and especially after the testing.

Examinations of the metallic, concrete, and insulation (Nukon® and Cal-Sil) test coupons, by

weighing and scanning electron microscopy, and analyses of the test solutions provided key

C-11
information on the evolution of solid phase formation. The wide-ranging testing helped identify

potential reactions or conditions that might lead to sump screen blockage in the post-LOCA

system and provided key information for the activities in the Chemical Speciation Prediction and

the Accelerated Chemical Effects Head Loss Testing activities.

2.1.1 Principal Sump Pool Variables and Constant Variables

The first two questions for the Integrated Chemical Effects Testing are closely related and, for

simplicity, are addressed together. .

Have the principal sump pool variables which affect chemical by-product formation in the

post-LOCA environment been adequately simulated? and Many ICET variables were

held constant during the experiments. How would changes in the most important

constant variables affect chemical product formation? The ICET experiments

considered only five post-LOCA situations while within these five situations, certain

parameters were held constant for simplicity. These simplifications may have caused

significant parameters to be overlooked.a

The test program was designed to provide an approximate "scale model" of the post-LOCA

reactor and containment environment and endeavored to encompass the primary material and

environmental conditions present in the post-LOCA PWRs. In doing these extensive and

complicated tests, the ICET matrix provided much valuable information on material phase

behavior and interaction. On one hand it was learned that many of the materials in the test

matrix had little, if any, effect on solids formation either by direct contribution or by secondary

interactions. On the other hand, the following materials had profound effects on solids

formation:

*Hydrogen and hydroxide ion concentration (pH)

*Dissolved boron

*Dissolved phosphate

*Aluminum metal

*Fiberglass

*Cal-Sil

*Concrete.

In preparing the testing matrix, some system simplifications were required that may have

masked effects perhaps present under actual post-LOCA conditions. Such simplifications are:

1. Test temperature. The static 600C temperature was selected to minimize the difficulties

in operating the tests at temperatures ranging from -1 000C (boiling) to -40'C. Hence,

the influence of temperature variation is not known. For example, higher temperature

would accelerate corrosion rates and the rates of other reactions, and could increase or

decrease the solubilities of various salts.

2. Boron concentrations. High and static total boron concentrations (2400-2800 ppm) were

used during the testing. The concentration was near the maximum used in the primary

coolant circuit of a freshly refueled reactor. However, the boron concentration

decreases to as low as -50 ppm by neutron capture over the fueling cycle. The ECCS

water, constituting about 3 to 4-times the volume of the primary coolant, was introduced

a The original questions posed by the NRC are given in italics. The bases of the question as perceived by

the author are stated and expanded, in ordinary font, after the original NRC questions.

C-I12
about 20-30 minutes after the LOCA. Because the boron solution concentration in the

ECCS also is -2400-2800 ppm, the boron concentration in the first part of the LOCA

could vary widely from -50 ppmn to -2000 ppm, for a reactor near the end of its cycle, to

little variance, for a reactor near the beginning of its cycle. This wide boron

concentration variation effect was not examined in the ICET experiments.

3. Heat transfer. The tests did not model well the cyclic steep temperature transients the

recirculating coolant will experience in passing by the reactor core, where the fluid slurry

will heat, and the heat exchanger, where the fluid slurry will cool. In a related way, the

tests also did not model the extremely hot fuel cladding and pressure vessel surfaces,

where dissolved and suspended solids plating and scale formation might occur, or the

colder surfaces at the heat exchangers, where solids deposition and scale formation

also can occur.

4. Radiation fields. Though testing on the magnitude of ICET experiments could only be

performed non-radioactively, no supporting small-scale tests were performed to

investigate the effects of radiation.

5. Organic materials. Aside from the organic materials present with the Nukon®) fiberglass

insulation, no organic materials (for example, from electrical insulation or paint except for

that in zinc primer coating) were present in the testing.

Further parametric studies could be performed both to understand the test observations

obtained from the ICET #1-45 experiments and to investigate the roles of temperature variation,

temperature gradient (heated surface and cold surface), boron concentration variation,

radiolysis, and the presence of organic materials. Because of the large size of the test

apparatus and resulting large quantity of required materials, the execution of more large scale

tests under more widely varying conditions may be prohibitively expensive. However, the

testing could be done on a smaller scale to gain, at lower cost, most of the pertinent information.

2.1.2 Variables or Materials of Most Importance But Not Considered by ICET

What variables or materials not simulated by the ICET testing may have the most impact

on chemical product formation (e.g., coatings, free insulation, flow through sediment and

other materials on sump screen, galvanic effects) and how should their effect be

characterized by testing or analysis? The ICET testing may have overlooked chemical,

physical, or mechanical effects that might prove to be key contributors to sump screen

blockage.

It is surmised that the variables and materials of most importance to the post-LOCA coolant

blockage but not simulated by the ICET are the presence of organic materials, the effects of

radiolysis, and the effects of hot and cold heat transfer surfaces.

The effects of organic coatings such as paints and electrical insulation (coatings) were

intentionally overlooked in the ICET experiments. The severity of this simplification is not

immediately evident without a reasonable estimate of the quantities of coatings involved, their

properties, and the secondary effects of radiation and hydrothermal reactions (reactions with hot

water) on the organic materials. The organic coatings mobilized by the LOCA and post-LOCA

conditions and added to the coolant system likely would do so by being melted and blasted from

their substrates (note - the area near a LOCA would be treated to a virtual steam cleaning, an

effective means to remove paint). This area of influence, however, would not encompass the

total of the coatings present in the containment and, in any case, the quantities should be

relatively small compared with the quantities of the fiberglass and Cal-Sil thermal insulation

materials.

C-13
However, the influence of such organic materials to act as glues to accrete and grow. solid

particles could be great. Therefore, it would be worthwhile, in a set of small scale tests, to

determine the behavior of various broadly representative electrical insulations, plastic coatings,

and paints when treated to steam and hot liquid water. A steam cleaner, as alluded above, may

provide a suitable test apparatus. The tests also could investigate the ability of the watertreated organic materials to coalesce and collect inorganic solids (primarily the thermal

insulation materials) as they cool, thus simulating their transport away from the LOCA blowdown region.

The organic materials also are more susceptible to radiolysis than the remaining inorganic

matrix, aside from water. Therefore, the organic paints and coatings might be expected to

break down in the kilorad (103~ Rad) per hour fields of the post-LOCA coolant system and in the

megarad (10~6 Rad) per hour fields near the reactor core. -Because the oxygen and hydrogen

gaseous radiolysis products will be quickly removed from solution by heat and agitation;

radiolysis of unconfined water is expected to lead to increasing concentrations of hydroxyl

radicals, -OH, and hydrogen peroxide, H202 - Small scale testing of the effects of radiation on

the various organic materials in representative post-LOCA environments should be performed.

The effects of high temperature and low temperature heat transfer surfaces on the collection

and dissolution of solid phases were not studied in the ICET experiments. Such tests could be

performed in a recirculation loop in which the post-LOCA coolant slurries, containing the

dissolved and undissolved solids, would be exposed to surfaces at temperatures representative

of the fuel and heat exchangers. Examination of the hot and cold surfaces during and after the

testing then would be performed to determine the importance of surface deposition.

2.1.3 Sufficiency of ICET Analysis Methods

Were the methods used within the ICET program to characterize and analyze chemical

by-products sufficient? Analytical methods used to characterize the ICET experiments

may not be adequate or appropriate; other analysis methods may yield more or better

insight.

The ICET experiments generally used accepted methods to identify and quantitate the starting

and product solutions and solids. The magnitude of the tests left no shortage of sample for

analysis. It has been proposed (see Appendix B) that the aluminum metal coupon surface

analyses be augmented by x-ray diffractometry (XRD). The XRD technique seems to be well

suited to understanding surface compound formation on the corroding metal and has been used

in other areas to identify corrosion films on mild steel, copper, zirconium, uranium, and

aluminum.

The surface appearances and XRD of the aluminum coupons might show the presence of

boehmite (AIOOH) for the tests without added Cal-Sil. It was noted that though ICET #1 and

ICET #4 were run at pH 10, aluminum corrosion for ICET #4, which contained Cal-Sil, had much

lower aluminum corrosion than ICET #1, which had no Cal-Sil. As noted in the March 2006

presentation on ICET results at the peer review meeting held at the SwRl, research is underway

to investigate the possibility that the lower rate in the presence of Cal-Sil is caused by surface

deposition of silicate onto the aluminum and the resulting formation of a protective film.

It is noted that surface precipitation of calcium aluminate phases (as tricalciumn aluminum

hydroxide [Ca3A12(OH) 12] and hydrocalumite [Ca2AI(OH) 7-2H2OJ) onto aluminum metal has been

C-14
found from tests of grouting of aluminum with portland cement and from reaction with calcium

hydroxide [Ca(OH) 2] slurries.b Such coatings also can suppress aluminum corrosion and should

be investigated. Surface examination of the aluminum metal coupons after ICET #1 and #4 by

XRD and other methods would help determine the relative roles of calcium and silicate to

suppress aluminum corrosion. Surface analyses also might be done for fiberglass and for other

silicates including concrete and Cal-Sil.

Analyses of p article size distribution (PSD) during the evolution of the ICET experiments would

have been useful. However, measurement of the PSID without performing new experiments

would not be valid because of alterations, with time, of the particles. If other smaller scale

experiments were to be performed, an on-line assay of PSID would be a useful complement to

the other analytical approaches as used in the original ICET experiments.

2.2 Chemical Speciation Prediction

The Chemical Speciation Prediction task was performed at the Center for Nuclear Waste

Regulatory Analyses (CNWRA) of the Southwest Research Institute. Chemical speciation,

algorithms were run to attempt to model the post-LOCA coolant conditions, as observed in the

ICET experiments, and to use the developed model or models to predict the post-LOCA

conditions (particularly, types and quantities of precipitates) based on input values germane to

reactors operating under conditions not exactly represented by the five ICET conditions. To do

this, geochemnical and process chemical modeling software was tested for robustness and

accuracy in predicting ICET observations. Some laboratory testing also was performed to

measure dissolution and corrosion rates to provide input data to test the models.

The Chemical Speciation Prediction task screened the available modeling software, first taking

care that each model had present a sufficient thermochemnical database. For this, the presence

of boron aqueous solutes and compounds was a key discriminator. The models also needed to

be valid for temperatures up to about.1 I100C and ionic strength up to 0.5 molal. The CNWRA

selected four che micalI/geoch emical models that met these and other criteria:

o OLI "StreamAnalyzer"', version 2.0

o Lawrence Livermore National Laboratory "EQ3/6", version 7.2b

o RockWare, Geochemist's Workbench7, REACT, version 5.0

o US Geological Survey "PHREEQC", version 2.8.

and then compared their performances in modeling post-LOCA solutions and solids.

Each code was tested for seven different starting solution conditions representative of the postLOCA environment. It was found that the code EQ3/6 was the most robust, avoiding the

convergence problems that the other codes suffered. The EQ3/6 code was selected, with the

OLI StreamAnalyzer, to predict the outcomes of the five ICET experiments. The predicted

experimental results of both EQ316 and StreamAnalyzer for ICET then were compared with the

results actually found by ICET. Modeling simulations were also run for post-LOCA conditions

involving metal corrosion and for interactions of the post-LOCA fluids with the fiberglass

insulation, Cal-Sil, and concrete.

b See Short and Parker (2005) for a description of the results of reacting aluminum metal with Ca(OH)2

aqueous slurry and with portland cement grout.

C-I15
Finally, the CNWRA performed laboratory tests to investigate the static leaching (dissolution)

rates of the fiberglass insulation and Cal-Sil insulation and the corrosion rate of aluminum in

small scale tests under a variety of conditions (containing borated solution) relevant to the postLOCA environment. The experimental conditions and some rate observations are summarized

in Table 2 (from Table A-5 of McMurry et al., to be issued).

Table 2. Dissolution and Corrosion Rate Measurement Results

Corn pnent RateObsrvaion

Nukon®) Cal-Sill Aluminum pH Buffer aeOsrain

Yes No No 7, TSP* Rates, = 0.79 mg Si/L-hr; simulated ICET #2

Yes o Ys 7,TSP Ratesi = 0.76 mg Si/L-hr; Al does not affect

Yes o Ys 7,TSP Nukon® leach rate; Al corr. rate not measured

Yes No No 10, NaOH Ratesi = 35 mg SilL + 0.73 mg SilL-hr

Rates, = 14 mg SilL + 0.14 mg Si/L-hr; Al inhibits

Yes No Yes 10, NaOH Nukon® leaching; RateA, = 1. 16 glm2 -hr; ________simulated ICET #1

Ratesi = 5.61 x P mg SiUL + 1.27 mg SiIL-hr;

No Powder No 7, TSP calcium silicate reaction with TSP observed;

simulated ICET #3

NoSolid No 7, TSP Ratesi = 5.61 x P mg Si/L + 3.02 mg Si/L-hr;

calcium silicate reaction with TSP observed

Ratesi 51.6 mg Si/L + 0.87 mg Si/L-hr;

No Powder & Solid No 10, NaOH Rateca =32.2 mg Ca/ll + 0.13 mg Ca/L-hr;

Isimulated ICET #4

RateAl = 0.986 g/m~-hr (electrochemical) No No Yes 10, NaOH RateAl = 1.31 g/M2 -hr (weight loss)

No No Yes 7, TSP RateAl = 0.0039 g/M2 -hr

No Yes Yes 7, TSP RateAl = 0.028 g/m2-hr

No Yes Yes 10, NaOH RateAl = 0.80 glm2-hr *TSP is trisodiumn phosphate.

These experiments provided fundamental concentration and kinetic data useful for the model

testing effort, corroborative data to the ICET results, and helped in understanding the key

reactions of the most active solid phase reactants (Nukon®, Cal-Sil, and aluminum) and their

interactions with each other and with the. key solution parameters (pH and presence of TSP).

2.2.1 Credibility of Product Predictions

Is th e speciation analysis expected to provide reasonable predictions of chemical

product formation over a range of possible sump environments? Chemical speciation

prediction by the presently available codes may not be adequate to predict sump

environment products.

For many but not all solutes, the modeling software made reasonable predictions of solute

concentration and pH based on comparison with experimentally derived values. At the level of

model development available in March 2006, the results of the analytical simulation still seemed

to follow, rather than lead, the observations made in the experimental testing and thus required

further refinement. For example, some of the observed precipitating phases [e.g., Ca3(P0 4)2

and silica, Si0 2, for calcium/phosphate and silicon, respectively] were not the equilibrium

phases predicted by the software [e.g., apatite, Ca5OH(P04)3, and albite, NaAlSi 3O8, respectively]. In addition, amorphous (poorly crystalline) phases generally are not part of the

C-i16
model databases but may be the compounds controlling the concentrations of many of the

solutes in the relatively short 30-day time frames of the post-LOCA systems.

It was observed that concessions to the seeming lack of the role Of 002 to form low solubility

carbonates had to be made. Reaction rates (kinetics) also are not handled well by the modeling

software; the models thus may not reflect the evolving concentration profiles. As the models are

refined, they should provide closer matching of the observed ICET concentrations, the

concentrations observed in the supplemental CNWRA testing described in Table 2, and

ultimately the concentrations in systems not exactly mimicked in the ICET experiments.

Of the software modeling codes tested, the StreamAnalyzer® by OLI seemed best, likely

because of its industrial pedigree and ability to handle the higher solute concentrations. It would

be useful for the purposes of GSI-l 91 if the modeling could predict, with more certainty, the

chemical precipitation behaviors at the higher and lower post-LOCA temperatures in addition to

the conditions not yet investigated by ICET or other testing. It is not evident from the results todate that the predictions would be successful.

2.2.2 Code Benchmarking by Tests

Is the plan for benchmarking these codes using small-scale testing and the ICET results

appropriate? Other methods may exist that are better in calibrating and determining the

adequacy of the thermodynamic modeling codes.

The small-scale testing is a valid approach to gain more information on the kinetic and

equilibrium behaviors of the key solutes and solid phases. From the present results, it seems

that benchmarking these codes is constructive because it reveals where gaps exist in the data.

Further small-scale testing, as is being done under this activity to validate the code predictions,

likely will be useful.

2.2.3 Measuring the Code Uncertainties

What is the most appropriate way to measure the uncertainty associated with these

codes? The ability of the codes to predict behaviors accurately for chemical regimes

having no experimental results may not be adequate.

Comparison of the code predictions against the results of targeted small-scale tests is a feasible

way to strengthen the codes and to identify and measure their uncertainties. Again, however,

the codes seem to be following, rather than leading, the chemical testing. Predicting the

behaviors and evolutions of the complicated and rapidly changing post-LOCA coolant systems

may be beyond the sophistication of present geochemnical and industrial chemical modeling codes. However, the models are approaching the ability to predict compositions at non-tested

conditions.

2.3 Accelerated Chemical Effects Head Loss Testing

The objective of Accelerated Chemical Effects Head Loss Testing is to simulate the loading of

the sump screen by recirculating dissolved and suspended solids generated in the post-LOCA

system. This is done by directing the simulated coolant flow containing suspended debris

solids, primarily arising from insulation materials and precipitating solids, through a screen in a

recirculating loop. The quantity of cake that ultimately forms on the screen is measured; the

rate of cake formation and the cake's flow properties also are measured.

C-i17
The Head Loss Testing focused on the environments for which trisodium phosphate (TSP)

buffering is used to control pH and Cal-Sil insulation is present. These conditions, found in

ICET #3, lead to the precipitation of finely particulate calcium phosphate with the calcium arising

from dissolution of the Cal-Sil. The effects of the degree of Cal-Sil dissolution, amount of

fiberglass and Cal-Sil debris (which is adjusted to match the areal mass loading on the screen),

and the relative arrival times of the debris and the calcium phosphate precipitates were studied.

The effects of the Nukon® fiberglass and Cal-Sil insulation debris beds alone and the debris

beds with the calcium phosphate precipitate were compared.

Some small scale tests also were performed to determine the dissolution of Cal-Sil and the

subsequent precipitation of calcium phosphate under simulated sump pool conditions. It was

found that the Cal-Sil dissolution is sufficiently rapid, even in the presence of TSP (which inhibits

Cal-Sil dissolution), to precipitate significant amounts of calcium phosphate within a few hours

and engender flow-prohibitive pressure drops in the debris bed.

2.3.1 Adequacy of the Head Loss Testing Approach

Is the accelerated head loss testing approach viable for evaluating the effects of multiple

chemical environments quickly? Perhaps other, more efficient, or more definitive

methods are available to test head loss effects.

The accelerated head loss test apparatus and associated reagent requirements as practiced in

the testing to-date (Oras et al. 2005 and 2006) has produced a large foundation of data

germane to the those reactors having both TSP buffering and Cal-Sil insulation and thus having

the prospect of calcium phosphate solids generation in the post-LOCA coolant. Such conditions

are exemplified by ICET #3. The calcium phosphate, in concert with the debris from remaining

undissolved Cal-Sil and fiberglass insulation, produce significant pressure drops across the.

prototypical screen bed. Note that it would be valuable to determine if the calcium leached or'

rinsed from concrete alone and without the Cal-Sil (i.e., ICET #2 conditions) would be sufficient

to produce enough calcium phosphate to create a significant pressure drop in the prototypical

screen bed.

The testing approach demonstrably provides valuable information on the behavior of the mixed

debris and precipitate bed formed in a dead-end screen loop. Nonetheless, the test apparatus

seems overly large. The apparatus also forces 'all solution to go, in a parallel flow, through the

screen. This design would seem to be the most prone to blockage and may have been chosen

in the test design for this reason. In some of the sump screen designs being created for reactor

application, the screens are vertical and the solution would pass through the debris bed only

near the screen bottom. The debris bed depth would decrease with screen height with the more

easily suspended precipitates flowing over the top without encountering significant fiberglass or

remaining solid Cal-Sil debris.

Because of the large scale of the tests, fewer tests can be performed than would be performed

if tests were at smaller scale. This limitation decreases the information that could otherwise be

obtained to characterize the multiple chemical environments of the post-LOCA coolant. A

smaller apparatus might accomplish the needed testing and generate much less waste per test

thus encouraging more and more varied testing. A smaller apparatus might also be designed to

model the operation of a vertical screen rather than the tested perpendicular dead-end screen.

A smaller test loop also would make possible, or make easier, testing at temperatures that vary

(ramp down) with time and might allow exposed high temperature surfaces (as provided in the

c-I18
post-LOCA system by the cooling fuel rods) and exposed lower temperature surfaces (at the

heat exchangers) to be examined more economically.

2.3.2 Methods for Observing Time-Dependent Effects

What is the best method for incorporating for time-dependent effects (e.g., material

aging, evolving chemical environments) in simulation testing? The simulation of head

loss effects in laboratory testing can involve shortcuts in creation of the cake on the

screen to overcome slowly evolving reactions and environments. The adequacy of this

approach is questioned.

The evolution over time of TSP and Cal-Sil dissolution and the accumulation of a solids deb ris

bed in an actual post-LOCA event are unknown. Therefore, various modes of creating the

debris and calcium phosphate precipitate bed were emulated in the testing program. The test

results indicated the approximate quantities of solids necessary to provoke bed blockage.

Because the only way to incorporate time-dependent effects is to run the experiments over time,

the testing program endeavored to recreate the evolution of the debris bed. As shown in the

following section, the solids created in some post-LOCA environments, were unlikely to have

been adequately recreated by certain chemical shortcuts.

2.3.3 Evaluation of Simulated Chemical Products

What metrics are most appropriate for evaluating the results of simulated chemical

products with those that formed during the ICET program? Chemical products created

to simulate those created during the ICET experiments are used in some of the head

loss testing. The adequacy of the simulated products to perform like the genuine

products must be measured to determine their legitimacy.

The ICET experiments generated aluminum corrosion products from the actual corrosion of

aluminum. However, in the filtration / head-loss testing, the aluminum corrosion product was

introduced by neutralization of AI(N03)3 with NaOH. This method is not representative of the

way aluminum solids arise in the post-LOCA cooling water system. This introduction method

also may have caused the non-prototypical so-called "snowfall" behavior. At a minimum, the

aluminum nitrate method introduces nitrate, an anion not otherwise present in the real postLOCA system. It is proposed that the aluminum be introduced in another manner, either by

corroding a coupon of aluminum in NaOH (simulating the actual conditions, but potentially

difficult to achieve under experimental conditions) or by adding sodium aluminate solution,

NaAI(OH) 4. Sodium aluminate is what is initially dissolved from the corroding aluminum metal

by the NaOH and is available as a solid material through chemical supply houses or can be

made by dissolving AI(OH)3 in hot excess NaOH.

Similarly, several of the head loss tests used calcium chloride (CaCI 2) solution addition to

simulate the dissolution of Cal-Sil. Use of CaCI 2 provides chloride at concentrations

overwhelming the small chloride concentrations normally present in the post-LOCA

environment. Besides giving an unrealistically high chloride concentration, the addition of CaCI2

in place of Cal-Sil fails to provide other solutes (e.g., sodium, silicate, some carbonate) and solid

phases (e.g., amorphous silica) gained by dissolving the Cal-Sil. It is proposed that dissolved

Cal-Sil (as used in many of the tests), rather than CaC12, provide the desired dissolved Cal-Sil

addition.

C-19
To be consistent with the ICET experiments, the head loss testing emulated the ICET solids

generation sequence. However, it is more important that the simulated chemical products

created in the head loss testing emulate the products arising in the containment building during

the 30-day post-LOCA interval. The testing performed for the ICET program has shown the

importance of pH, Cal-Sil dissolution, borate, aluminum corrosion, phosphate, the Nukon

fiberglass, and perhaps concrete on solids formation. The head loss testing could focus on

varying these components, plus study the effects of temperature differentials and hot and cold

surfaces, to create the solids present in the post-LOCA environment.

2.3.4 Identifying Key Physical Parameters to Predict Head Loss Performance

Are correlations available, or can they be developed, which can predict the associated

head loss if important physical characteristics of a chemical by-product are known?

Certain key physical parameters, such as particle size and shape, might be useful to

predict the filtration/screening behavior of fluids bearing such suspended solids.

Methods to predict head loss or filtration behavior based on physical properties may or may not

exist. Therefore, in such, an effort, it likely would be useful to consult experts, including experts

in the review panel, with backgrounds in water treatment, wastewater treatment, mineral mining

and milling, or similar process industries for correlation methods.

However, even if such parameters could be identified and measured, the coolant solutes and

the suspended solids continue to react as shown by ICET and other testing. Thus, chemical

interactions of the various particles and the coolant solutes themselves (e.g., borate, phosphate)

can influence head loss due to material corrosion, surface precipitation, self-cementation, or

other chemical and even radiolytic effects.

C-20
3 UNEXAMINED AND LITTLE EXAMINED CONDITIONS

In Section 3, certain post-LOCA conditions are identified that require more examination.

Discussions of these important post-LOCA conditions and some possible avenues of research

are presented in this section. The phenomena being examined are radiolysis, solution

composition effects on metal (particularly aluminum) corrosion, material deposition and

spallation, atmospheric contributions, and biological activity. Recommendations for additional

testing and analysis are presented for each topic.

3.1 Radiolysis and Its Effect on Metal Corrosion

The effects of radiolysis on water and its subsequent effects on the corrosion of vulnerable

metals such as aluminum (Al; present in scaffolding and ladders) and zinc (Zn; present on

galvanized metal), were not examined in any of the testing. The current studies show that

aluminum can be one of the primary contributors to solids loading in the post-LOCA recirculating

coolant waters. The behavior of aluminum and other metals as influenced by water radiolysis

remains to be studied.

The review panel, in the meetings held March 27-29, 2006, at the SwRI, discussed the radiolytic

conditions of the cooling water as the LOCA event evolves. Under operating reactor conditions,

water radiolysis produces primarily hydrogen (H-2), diatomic oxygen (02), and hydrogen peroxide

(1-20 2). These components recombine, however, under the pressurized conditions in the PWR.

The concentrations of these three species at full reactor power, where the dose rate is taken to

be 10 gray/second (-3.6x 109 rad/hour) at 280*C, are _1i0 5 moles per liter in H2 and H20 2 and

_10-6 moles per liter in 02 (Ishigure et al. 2006). At the same time, corrosion of the reactor steel

pressure vessel exposed to the water imposes reducing conditions by being oxidized to

magnetite (Fe304) and related spinel phases. These reactions chemically reduce water to

produce H2. A H2 overpressure is also actively maintained by injection of H2 gas within the

primary coolant system to preserve reducing conditions and impede metal corrosion. This

overpressure gives much higher H2 concentrations than those produced by radiolysis.

During a LOCA, however, the confining overpressure is released and the gaseous H2 and 02

constituents are flashed from the liquid water and lost to the air. And though nuclear fission

ceases during the LOCA, water radiolysis continues by fission and activation product decay to

produce the estimated mega rad-per-hou r fields in the core. Though the gaseous H2 and 02

constituents continue to be created but escape readily from the hot irradiated solution, the

hydroxyl radical, 0OH, continues to be formed but is retained by the solution. Two 0OH radicals

combine to form H20 2 which likewise stays dissolved in solution.

The H202 can build in the solution to give conditions more oxidizing than deaerated or even

oxygenated water. This effect may be augmented by the radiolysis of chloride ion, Cr-,

dissolved in water to produce hypochlorite (OC[-) or hypochlorous acid (1-1Cd), both strong

oxidants. The ICET experiments #14#5 contained 100 ppmn HCI (~-2.7x 10-3 moles Cl- per liter).

On the other hand, organic compounds present in the recirculating water from post-LOCA

cooling water, from paint, plastic, the organic coating on the fiberglass insulation, or other

sources, can act as scavengers of the radiolytically generated oxidants. This scavenging can,

in itself, engender reducing conditions. As a result of these conflicting effects, the

reduction/oxidation, or redox, conditions extant in the post-LOCA recirculating water are not

immediately evident.

C-2 1
Recommendation: It is suggested that the redox conditions and concentrations of radiolysis

products, such as hydrogen peroxide, in the post-LOCA waters be defined taking into account

the radiation fields imposed by the core.

It was recognized early in the design of nuclear reactors that the effects of radiolyticallygenerated H202 on engineering materials must be considered. The role of aluminum in metallic

uranium fuel cladding and in reactor fuel tubes led to much early work on the durability of

aluminum in radiolytic conditions. For expediency, instead of studying aluminum performance

under radiolysis, initial studies simply tested aluminum in the presence of H20 2. In these tests,

the H202 was added to water in concentrations expected during reactor operations. These early

tests showed that H20 2 had very little effect on aluminum corrosion. Subsequent tests of

aluminum performance in water by direct irradiation under reactor conditions showed enhanced

aluminum corrosion rates. Because of the higher corrosion observed under direct exposure, it

was thought that the primary but transitory oxidizing radiolytic products - free hydroxyl or atomic

oxygen - rather than the subsequent H202 or dissolved diatomic oxygen, 02, were responsible

(Goldsmith 1953). These findings were confirmed in subsequent studies (Richman 1958).

Such direct irradiation of aluminum should not occur under the postulated post-LOCA situation

in which the fuel is defined to remain intact and radiolysis only to occur on the recirculating

coolant. Hence, the effects of radiolysis should be confined to the secondary reactions of the

irradiated water, and its contained solutes and entrained solids, on the corroding metals.

3.2 Solution Composition Effects on Metal Corrosion

Continued parametric testing of the susceptibility of aluminum to corrosion caused by typical

water constituents was conducted (Troutner 1957). The results of these studies are very

germane to the present considerations of aluminum durability in the post-LOCA environment.

The constituents whose effects were studied included chloride, nitrate (NO3-), sulfate (SQ4 2-)

bicarbonate (HC0 3), hydrogen peroxide, acetate (CH 3CO2j), oxalate (C2042-), citrate

[C3H4OH(COO)3 

3

-], arsenate (AsO42}) phosphate (P04 -), silicate (HSi423) , dichromate

(C- 2O7 

2-), molybdate (Mo70 246) , and mixtures of these ions. Individual tests, run at 920C

(-1 980F) with 100 ppm of the respective constituents, showed that only citrate increased

corrosion, and phosphate decreased corrosion.

Significantly, again hydrogen peroxide had no effect on aluminum corrosion rate. Though the

effects of hypochlorite were not studied, chloride even up to 10,000 ppmn concentration (-0.28

moles of chloride per liter) also had no effect on uniform corrosion rate. In addition, tests

containing both chloride and hydrogen peroxide, even up to 100 ppm CI- and 100 ppmn H202

(-3x 0-3 moles per liter) showed no enhanced corrosion.

Recommendation: It is suggested that the potential presence of hypochiorite in the post-LOCA

coolant be investigated. If present, its effect on metal corrosion under post-LOCA conditions

should be investigated.

As noted in the ICET testing, pH had a significant effect on aluminum corrosion rates with much

higher rates observed at pH -10 than at pH -7. In the tests by Troutner (1957), minimum

corrosion rates were exhibited at pH -6 with rates increasing steeply above and below this pH.

Further study of the corrosion of aluminum (Troutner 1957) showed that measurable inhibition

occurred with as little as 5 ppm (-0.0005 M) phosphate. It was postulated that the inhibition

occurred because of the surface deposition of a protective layer of aluminum phosphate.

C-22
Subsequent X-ray diffraction studies of the surface of aluminum exposed to 5 ppm phosphate at

195*C (383'F) for 24 days showed the formation of the aluminum phosphate compound

augelite, A12P04(OH) 3, on the metal surface and is even formed on aluminum at 0.5 ppmn

phosphate (Groot 1957). Such deposits might be postulated to form on the aluminum coupons

in the ICET experiments 2 and 3 having the phosphate buffer at pH 7.

Recommendation: It is suggested that further post-test XRD examination of the corroded metal

coupon surfaces be conducted, especially for aluminum, and to examine the role of phosphate

in coupons prepared during the ICET and other testing.

Some salts including chromates, dichromates, silicates, and borates are reported to inhibit

aluminum corrosion (Shreir et al. 1994). Borates are common additives to automotive

antifreeze formulations and can encounter aluminum parts. The formation of perborates, B0 3 ,

from the reaction of sodium metaborate, sodium hydroxide, and hydrogen peroxide, also should

be considered to be possible under radiolytic conditions (p. 980, Wiberg 2001). Perborates are

used as bleaches and thus indicate that they are oxidizing.

Recommendation: Compare the effects of sodium tetraborate and perborate on aluminum

corrosion.

3.3 Spallation of Deposits from the Hot Fuel Cladding and Reactor Vessel

The LOCA event produces a rapid alteration in the pressure, temperature, and local chemical

conditions on the fuel cladding and reactor vessel walls. In the initial moments of the LOCA, the

pressure within the vessel drops to atmospheric, the vessel itself undergoes mechanical

shuddering attendant to the loss of coolant, and the temperature of the fuel fluctuates as the

coolant supply and condition varies. Under such thermal and mechanical transients, the.

magnetite corrosion layer in the reactor vessel, though nominally adherent, may vibrate loose

and report to the recirculating coolant. The fuel itself, generally clad in zirconium alloy, may

spall its metal oxide outer layer (in this case, zirconium oxide, ZrO2) though this is much less

likely than magnetite spallation from the reactor vessel. Note, however, that thick -50-pm films

of ZrO2 have been observed under certain conditions (Johnson 1989).

Deposits of "crud" from stainless steel and nickel hardware in the primary coolant circuit also

occur on fuel cladding. In one study, the crud deposits from operating PWRs were less than

one mil (-0.025 mm) thick, were composed of a nickel-substituted magnetite (formula NiFe3-,O4

with 0.45<x<0.75) spinel, and were more highly concentrated on fuel having lower power

(Solomon and Roesmer 1976; Sandler 1979). Chromium also was found in some cruds,

substituting for iron in the spinel structure to give the composition CryNi,,Fe3-),-O 4. Other

contaminants found in the crud included aluminum and silicon, which were not incorporated in

the spinel but apparently formed amorphous aluminosilicates, and carbonaceous material,

postulated to arise from ion exchange resin (Sandler 1979). In both reactor vessel and fuel

cladding cases, the spalled solids would report to the recirculating coolant and then travel to the

sump and sump screens where they would contribute to the solids loading and may impede

coolant flow.

Recommendation: Tests should be conducted to examine the possibility and extent of corrosion

product spallation from reactor vessel walls and from fuel cladding surfaces under conditions

that would occur under LOCA thermal and mechanical shock conditions.

C-23
It is more likely that solids spallation from reactor vessel and fuel cladding surfaces will occur

from cyclic deposition onto and spallation from hot surfaces during the subsequent recirculating

coolant flow. The deposition would occur by the transport of the dissolved and suspended boric

acid (H3BO03), sodium tetraborate (Na 2B4 O4), trisodiumn phosphate (TSP; Na3PO4), Cal-Sil

insulation, aluminum corrosion products [e.g., Al(OH) 3, AIOOH, aluminum phosphate phases],

calcium phosphate, fiberglass fibers, concrete particles, and other suspended debris to the hot

fuel cladding and reactor vessel surfaces. The characterization of crud found on PWR fuel

cladding from operating reactors (Sandler 1979) informs this hypothesized post-LOCA scenario

in that organic and aluminosilicate deposits were found in addition to nickel ferrites.

Note that most of the suspended solids, by virtue of being transported into the reactor vessel

and past the sump screen, would be in the form of fine particulates. The coolant water, bearing

the dissolved and suspended solids, would flash away as it encountered the hot fuel cladding

and reactor vessel surfaces and leave its solids load behind. There, the deposited solids could

undergo higher temperature hydrothermal reactions and likely undergo self-cementation. With

time, as the deposits thickened, thermal shock and mechanical vibration caused by the

recirculating water would loosen the deposits and transport the caked, dried, and matted solids

to the sumps and sump screens. Overall, the fine particulates and dissolved salts could

agglomerate and become cemented to create much larger particles that would present greater

barriers to fluid flow.

The solid deposits likely would be shaped by the depositional surfaces and take the form of

curved flakes. As such, they could be both easily transported by the flowing coolant and be

readily caught upon, and thus clog, the sump screens. Much of the deposit would arise from

.drying of dissolved salts. The dried salts (e.g., sodium tetraborate, sodium phosphate) may

easily re-dissolve in hot water and with agitation once they were re-introduced to the water flow

after spallation. However, the phosphate and borate salts themselves also undergo

polymerization upon heating to produce polyphosphates and polyborates that resist redissolution.

In addition, sodium tetraborate dehydrates on heating to 350-4000C (662-7520F) to form

Na2B34O7 and, if heated to the 878*C melting point of Na2B34O7, can act as a fluxing agent to

dissolve zirconium oxide, ZrO2, from the cladding and transition metal oxides (such as the

magnetite coating on the reactor pressure vessel; Bock 1979). Boric acid (1-3B303) and its

dehydrate, B20 3, also can act as fluxes. The sodium tetraborate and boric acid thus might act

as an additional vector to displace iron and nickel from the reactor vessel and zirconium from

the fuel cladding and direct the 'm to the cooling water where they would precipitate as fine

hydroxides. More importantly, attack by the hot boron compounds might compromise the

zirconium and, more so, any stainless steel fuel cladding to expose the irradiated fuel to the

flowing coolant.

The solids might also cling tenaciously to the fuel cladding and compromise the heat transfer

meant to occur during the post-LOCA period. If such deposition occurs, it might sufficiently

impede the desired heat transfer as to lead to fuel cladding failure due to thermal stresses.

Recommendation: The behavior of recirculating coolant, bearing dissolved and suspended

solids, upon encountering reactor fuel and vessel surfaces heated to the immediate post-LOCA

temperatures should be investigated. Of particular interest are examination of solids deposition,

spallation, shape, re-dissolution or re-suspension, and the resistance of the solids to transport.

The formation of tenaciously held deposits on the fuel surfaces is of high impact because of its

effect on heat transfer. The potential effect of hot sodium tetraborate or boric oxide to act as

C-24
fluxes to dissolve the magnetite oxide layer from the reactor vessel wall or the clad fuel should

be examined in separate tests.

3.4 Atmospheric Contributions

The alkaline post-LOCA spray-down of the reactor containment building will scrub carbon

dioxide (C0 2) from the air to contribute from -25 to 170 kg of CO 2 to the coolant solution.c

Accounting of the solids budget due to CO 2 absorption shows that the effect may be minor. For

CO2 to have an effect, it must first be absorbed by water to form carbonic acid, H2C0 3. The

formation of H2C0 3 would move the pH towards -5.5, either up or down depending on the

starting pH imposed by the other solution components. The carbonic acid would react with

calcium with the calcium source most likely being from the dissolution of Cal-Sil insulation.

Water attack of concrete, another potential source of calcium, would provide little soluble

calcium; the calcium would already be in stable solid phases including CaCO 3.

The Cal-Sil insulation contains both CaCO3 and tobermorite, Ca 2.25(Si3O7.5(OH)1.5)-H20 (Dallman

et aL. 2005c). The reaction of solid tobermorite with CO2 dissolved in water produces solid

CaCO3, solid amorphous silica, SiO 2, and releases some water:

4 Ca2.25(Si 3O7.5(OH)l.5)-H20 (S) + 9 C02~ (9-+ 9 CaCO 3 (S) + 12 SiO2 (am) + 4 H20 (1)

The parent tobermorite, without reacting with carbonic acid, forms amorphous silica and

hydrated lime, Ca(OH) 2, by reaction with water:

4 Ca2.

25(Si3O7.5(OH)1. 5)-H20 (,) + 2 H20 (1) -~9 Ca(OH) 2 (.) + 12 SiO2 (am)

It is seen that the difference between the two reactions of tobermorite is the replacement of the

Ca(OH) 2 product from reaction with water with the CaCO3 from the reaction with CO2. The net

effect is that the hydrated lime from tobermorite reacts with CO 2 to produce calcite and water:

Ca(OH) 2 (s) + CO 2 (g) --. CaCO 3 (s) .+ H20 (1

The 107 ft3 (-280,000 in) volume of the largest containme nt building holds about 171 kg Of CO 2.

Therefore, the net increase in solids weight, caused by the reaction of Ca(OH) 2 with C0 2, would

be -100 kg. The weight increase for other containment buildings would be lower by about a

factor of 4. These quantities likely are negligible contributors to the total suspended solids

budget in the coolant system. For both reactions, finely divided solids, consisting of amorphous

silica and either hydrated lime or calcite, would form. The solids in either case are physically

similar'and are unlikely to be significantly different in affecting sump screen flow.

cAccording to the presentation, "Principal Attributes of the LOCA Accident Sequence", made on March

27, 2006, during the second peer review meeting, the air volumes in one of the PWR containment

buildings is about 10 million cubic feet. The remaining 29 PWR containment buildings have volumes

around 1.5-3 million ft3 . Because the concentration Of CO 2 in air is about 330 parts per million on a mole

basis, the quantity Of C0 2 present in 107 ft3 of air is

10f3arx28.3 liters X0.00033 liters CO 2 X mole X-0.044 kg =11k 0 ft liter air 24 liters gas mole C0 2

C-25
Recommendation: The relative impact of the quantity of the solids formed by reacting

tobermorite from Cal-Sil with carbonic acid from CO 2 absorbed from the air to form calcite and

amorphous silica, though likely to be small, should be assessed.

3.5 Biological Activity

Temperatures during the immediate post-LOCA period will not be sufficiently high to sterilize the

interior of the reactor containment building. As a result, as the reactor and surroundings cool,

warm moist conditions, augmented in many cases by phosphate buffer, will be conducive to

growth of algae and perhaps other life forms. With time, the algae and other growths may

develop mats and help block flow through the sump screens.

However, it is noted that boron is an effective algaecide and may be a sufficient biocide to

thwart growth of biota in the coolant water system. Therefore, the presence of boric acid

(H3B0 3) in all tests and sodium tetraborate in Test #5 may be adequate to block growth in any

situation.

The total boron concentrations in Tests #14#4 was 2800 ppm, or about 0.26 moles of boron per

liter, and 2400 ppm in Test #5, about 0.22 moles boron per liter. These high boron

concentrations may be toxic and preclude biologic growth. Though boron is consumed by

neutron capture during irradiation and its concentration decreases to -50 ppm towards the end

of the fueling cycle, its concentration is quickly restored to near starting levels within about 30

minutes after LOCA by the injection of 3- to 4-fold volumes of emergency cooling water

containing -2800 ppm boron.

Recommendation: The potential for algae and other biological growth in the post-LOCA water

recirculation system should be investigated either through testing or through examination of the

technical literature. The -2000 ppm boron concentration in the post-LOCA. coolant may be

sufficiently high to preclude biological activity.

C-26
4 REFERENCES

Bock, R. 1979. A Handbook of Decomposition Methods in Analytical Chemistry, International

Textbook Company, Edinburgh, UK.

Dailman, J., J. Garcia, M. Kiasky, B. Letellier, and K. Howe. 2005a. Integrated Chemical Effects

Test Project: Test #1 Data Report, LA-UR-05-1024, Los Alamos National Laboratory, Los

Alamos, NMV.

Dailman, J., B. Letellier, J. Garcia, M. Kiasky, W. Roesch, J. Madrid, K. Howe, and D. Chen.

2005b. Integrated Chemical Effects Test Project:, Test #2 Data Report, LA-UR-05-6146, Los

Alamos National Laboratory, Los Alamos, NM.

Dailman, J., B. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe, L. Archuleta and F.

Sciacca. 2005c. Integrated Chemical Effects Test Project: Test #3 Data Report, LA-U R-05-

6996, Los Alamos National Laboratory, Los Alamos, NM.

Daliman, J., B. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe, L. Archuleta and F.

Sciacca. 2005d. Integrated Chemical Effects Test Project: Test #4 Data Report, LA-U R-05-

8735, Los Alamos National Laboratory, Los Alamos, NM.

Daliman, J., B. Letellier, J. Garcia, J. Madrid, W. Roesch, D. Chen, K. Howe, L. Archuleta and F.

Sciacca. 2005e. Integrated Chemical Effects Test Project: Test #5 Data Report, LA-UR-05-

9177, Los Alamos National Laboratory, Los Alamos, NM.

Goldsmith, S. 1953. Interim Report - Production Test Number 105-510-E Determination of Pile

Irradiation Effects on Corrosion of 2-S Aluminum, HW-27531, Hanford Atomic Products

Operation, Richland, WA (http://www2.hanford.gov/ddrs/search/RecordDetails.cfm?AKey=Dl198147099).

Groot, C. 1957. Phosphoric Acid Corrosion Inhibition in Present Reactors, HW-5021 9, Hanford

Atomic Products Operation, Richland, WA

(hftp://www2.hanford.gov/ddrs/common/findpage.cfm?AKey=D8370590)-

Ishigure, K., T. Nukii, and S. Ono. 2006. "Analysis of Water Radiolysis in Relation to Stress

Corrosion Cracking of Stainless Steel at High Temperatures - Effect of Water Radiolysis on

Limiting Current Densities of Anodic and Cathodic Reactions Under Irradiation," Journal of

Nuclear Materials 350:56-65.

Jain, V., L. Yang, and K. Chiang. 2004. Chemical Speciation, Using Thermodynamic Modeling,

During a Representative Loss-of-Coolant Accident Event, CNWRA 2004-07, Rev. 1, Center for

Nuclear Waste Regulatory Analysis, San Antonio, TX (Appendix C in NUREG/CR-6873, Jain et

al. 2005).

Jain, V., X. He, and Y.-M. Pan. 2005. Corrosion Rate Measurements and Chemical Speciation

of Corrosion Products Using Thermodynamic Modeling of Debris Components to Support GSI191, NUREG/CR-6873, US Nuclear Regulatory Commission, Washington, DC

(http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6873/cr6873.pdf).

Johnson, A. B. Jr. 1989. Thick-Film Effects in the Oxidation and Hydriding of Zirconium Alloys,

PNL-SA-17065, Pacific Northwest Laboratory, Richland, WA.

C-27
McMurry, J., V. Jain, X. He, 0. Pickett, and R. Pabalan. To be issued. GSI-191 PWR Sump

Screen Blockage Chemical Effects Tests - Thermodynamic Simulations, NUREG/CR-xxxx

(draft), US Nuclear Regulatory Commission, Washington, DC.

NRC. 2003. Potential Impact of Debris Blockage on Emergency Sump Recirculation at

Pressurized- Water Reactors, NRC Bulletin 2003-01, US Nuclear Regulatory Commission,

Washington, DC (http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/2003/bIO3001 .pdf).

NRC. 2004. Potential Impact of Debris Blockage on Emergency Recirculation During Design

Basis Accidents at Pressurized- Water Reactors, NRC Generic Letter 2004-02, US Nuclear

Regulatory Commission, Washington, DC

(http://www. nrc.gov/reading-rm/doc-collections/gen-comm/-aen-lefters/2004ý/a1200402.pdf)

Oras, J., J. H. Park, K. Kasza, K. Natesan, and W. J. Shack. 2005. Chemical Effects/ HeadLoss Testing Quick Look Report, Tests I & 2, Argonne National Laboratory, Argonne, IL.

Oras, J., J.. H. Park, K. Kasza, K. Natesan, and W. J. Shack. 2006. Chemical Effects /HeadLoss Testing Quick Look Report, Tests ICET-3-4 to 11, Argonne National Laboratory, Argonne,

IL.

Richman, R. B. 1958. Radiation Effects on Aluminum Corrosion in Process Water -Analysis of

Data from Supplement A, PT-105-550-E, HW-57854, Hanford Atomic Products Operation',

Richland, WA (http://www2.hanford.gov/ddrs/search/Recordoetails.cfm?AKey=D8431 132).

Sandier, Y. L. 1979. "Structure of PWR Primary Corrosion Products," Corrosion 35(5):205-208.

Short, S. M. and B. M. Parker. 2005. Potential for Generation of Flammable Mixtures of

Hydrogen from Aluminum-Grout Interaction in the K Basins During Basin Grouting.,

PNNL-15156, Pacific Northwest National Laboratory, Richland, WA

(http://www.pnl.gov/main/publications/externaI/technical-reports/PNNL-1 51 56.pdf).

Shreir, L. L., R. A. Jarman, and G. T. Burstein. 1994. Corrosion, Volume 1, "Metal/Environment

Reactions," Butterworth-Heinemann, Oxford, UK.

Solomon, Y. and J. Roesmer. 1976. "Measurement of Fuel Element Crud Deposits in

Pressurized Water Reactors," Nuclear Technology 29:166-173.

Troutner, V. H. 1957. Uniform Aqueous Corrosion of Aluminum - Effects of Various Ions, HW50133, Hanford Atomic Products Operation, Richland, WA

(http://www2.hanford.gov/ddrs/search/RecordDetails.cfm?AKey=D850681 1).

Wiberg, N. 2001. Inorganic Chemistry, Academic Press, San Diego, CA.

C-28
APPENDIX 1

Curriculum Vitae - Calvin H. Delegard

Professional Activities

Twenty-six years (1970; 1972-1976; 1979-1987; 1992-present) in applied/process chemistry

and nuclear materials safeguards at the Hanford Site.

" Plutonium process and waste chemistry (speciation, separation, purification, processing)

" PUREX and Plutonium Finishing Plant process chemistry

" Environmental chemistry of radionuclides (Co, Sr, Tc, Cs, U, Np, Pu, Amn)

" Technical liaison with the Institute of Physical Chemistry, Russian Academy of Sciences, on

chemistry of the actinides and technetium in alkaline media, on K Basin sludge

treatment/disposal, chromium phase dissolution, and uranium metal corrosion

" Hanford tank waste chemistry (bulk and radionuclide components)

" Tank farm evaporator chemistry (concentration and crystallization)

" Organic decomposition reactions in tank waste (e.g., gas generation in 101l-SY)

* Tank waste treatment chemistry (ozonation, electrolysis, calcination/dissolution,

leaching/sludge washing)

" Material corrosion; Zr and other metals in nitric acid; copper and mild steel in basalt

groundwater

" Chemical characterization, processing, and U metal corrosion of K Fuel Storage Basins

sludge

* Domestic (234-5) and design of int'l. (Hanford, RFES, SRS) nuclear materials safeguards

" Development and qualification of plant calorimeters for international safeguards

" Development of prompt gamma analysis for Pu materials characterization

*Plutonium materials stabilization for storage.

Eight years (1976-79; 1987-92), nuclear materials safeguards at the International Atomic

Energy Agency, Vienna, Austria.

* International nuclear material safeguards inspection execution

" Subsidiary arrangements, design information, and facility attachments preparation

" Destructive and non-destructive nuclear materials verification methods development.

Technical Publications

Contractor and National Laboratory Documents

* Atlantic Richfield Hanford Company e Los Alamos National Laboratory

" Rockwell Hanford Operations e Brookhaven National Laboratory

" Westinghouse Hanford Company 9 Pacific Northwest National Laboratory

* B&W Hanford, Duke ESH, B&W Protec, Numatec Hanford

Symposium Proceedings

*Institute of Nuclear Science, *Institute of Nuclear Materials

Boris Kidri6, Vin~a, Yugoslavia Management

e American Nuclear Society @ American Chemical Society

* American Society Metallurgical e European Safeguards Research and

Engineers Development Association

C-29
" Minerals, Metals & Materials Society * Waste Management

" Russian Conference on Radiochemistry e Materials Research Society

" NATO Advanced Research Workshop e International Atomic Energy Agency

Scientific Journals

" Radiochimica Acta * Journal of Alloys and Compounds

" Radiochemistry * Journal of Nuclear Material Management

" Nuclear and Chemical Waste Management

Selected Recent Publications

- Peretroukhine, V. F., and C. H. Delegard, 1998, "Some Comparisons of Plutonium-Bearing Radwaste

Management in the USA and Russia," The Environmental Challenges of Nuclear Disarmament,

NATO Advanced Research Workshop, Cracow, Poland.

- Barney, G. S. and C. H. Delegard, 1999, "Chemical Species of Plutonium in Hanford Site Radioactive

Tank Wastes," in Actinide Speciation in High Ionic Strenogth Media, D. T. Reed, S. B. Clark, and L.

Rao (editors), Kluwer Academic/Plenum Publishers, New York.

- Bredt, P. R., C. D. Carlson, C. H. Delegard, K. H. Pool, A. J. Schmidt, D. B. Bechtold, J. Bourges, 0.

A. Dodd, T. A. Flament, N. N. Krot, and A. B. Yusov, 2000, "Studies of Chemical Processing of K

Basin Sludge," Waste Management 2000, Tucson, AZ.

- Delegard, C., 2001, "K Fuel Basin Sludge - Characterization, Reactions, Retrieval, and Storage,"

presentation to Washington Group Intemnational, Warrington, UK, October 9, 2001, PNWD-SA-5513,

Pacific Northwest Division, Battelle, Richland, WA.

- Fedoseev, A. M., V. P. Shilov, N. A. Budantseva, A. B. Yusov, 1. A. Charushnikova, and C. H.

Delegard, 2002, "Selective Recovery of Chromium from Precipitates Containing d Elements and

Actinides: I-Ill. Effect of 02, H202 , S2O8 2, " Radiochemistry 44(4):347-365 (three articles). - Clark, S. B. and C. Delegard, 2002, "Plutonium in Concentrated Solutions," Chapter 7 in Advances in

Plutonium Chemistry 1967-2000, D. C. Hoffmann, Editor, American Nuclear Society, La Grange

Park, IL (hftp://www.ans.org/store/Vi-300029).

- Boak, J., E. A. Conrad, C. H. Delegard, A. M. Murray, G. D. Roberson, and T. J. Venetz, 2003,

"Recommendations on Stabilization of Plutonium Material Shipped to Hanford from Rocky Flats," LAUR-03-3789, Los Alamos National Laboratory, Los Alamos, NM (http://lib-www.lanl.gov/cgibin/getfile?00937076.pdf).

- Schmidt, A. J., C. H. Delegard, S. A. Bryan, M. R. Elmore, R. L. Sell, K. L. Silvers, S. R. Gano, and B.

M. Thornton, 2003, "Gas Generation from K East Basin Sludges and Irradiated Metallic Uranium

Fuel Particles - Series III Testing," PNNL-14346, Pacific Northwest National Laboratory, Richland,

WA (http://www.pnl.gov/main/publications/external/technical-reports/PNNL-1 4346.pdf).

- Delegard C. H., A. J. Schmidt, R. L. Sell, S. 1. Sinkov, S. A. Bryan, S. R. Gano, and B. M. Thornton,

2004, "Final Report - Gas Generation Testing of Uranium Metal in Simulated K Basin Sludge and in

Grouted Sludge Waste Forms," PNNL-1481 1, Pacific Northwest National Laboratory, Richland, WA

(http://www.pnl.gov/main/publications/external/technical-reports/PNN L- 1481 1.pdf)

- Yusov, A. B., A. M. Fedosseev, and C. H. Delegard, 2004, "Hydrolysis of Np(IV) and Pu(IV) and Their

Complexation by Aqueous Si(OH)4," Radiochimica Acta 92(12):869-881.

- Shilov, V. P., A. M. Fedoseev, A. B. Yusov, and C. H. Delegard, 2004, "Behavior of Np(VII, VI, V) in

Silicate Solutions," Radiochemistry 46(6):574-577.

Education

BS, Chemistry, with distinction, Phi Beta Kappa, Washington State University, 1970;

Graduate course work at the University of Colorado (1970-72) and Washington State

University (1973-2001).

calvin.delegard@pnl.gov, (509) 376-0548

Pacific Northwest National Laboratory

PO Box 999, MS P7-25

Richland, WA 99352 USA

C-30
APPENDIX 2

Preliminary Assessment Report

To: Robert Tregoning, US Nuclear Regulatory Commission

From: Cal Delegard, Chemist

Pacific Northwest National Laboratory

PO Box 999, MS P7-25

Richland, WA 99352

(509) 376-0548

calvin.delegard~pnl.gov

Date: November 30, 2005

Subject: Peer Review Preliminary Assessment Report

Thank you for the opportunity-to participate in the Chemical Effect Peer Review of the PWR

sump pool chemistry. The following comments are based on the peer review meeting at

Argonne National Laboratory, October 18-19, 2005, the associated view graph materials, and

listed reports.

The comments are provided in fulfillment of the obligation to provide a 'Preliminary Assessment

Report" of the Chemical Effects studies by November 30, 2005. The comments are grouped in

five sections according to general remarks and the major areas of investigation:

1. General Questions and Comments

2. Integrated Chemical Effects Testing (ICET)

3. Modeling

4. Chemical Effects Head Loss Testing

5. Chemical Effect on the Sump Water.

I look forward to the follow-on review meeting in January 2006.

1. General Questions and Comments

" The overall testing approach is comprehensive, ambitious, and sound. Many of the

questions, comments, and suggestions given below arise from the fact that much of the

work still is in progress. However, some areas of investigation may still need to be done.

The suggested additional work is noted within the following questions and comments.

" Was chemical and physical characterization done of the sump materials from the TMI-2 and

Barseback-2 LOCAs? d If so, what were the findings? How do they compare. with the ICET

and other experimental results?

* Flashing of the cooling water bearing dissolved and entrained mineral solids and the

retrograde solubility of calcite (CaCOA) calcium phosphate [Ca3(P0 4)2], and perhaps other

minerals may leave solids deposited on the hot fuel and vessel surfaces. What is the

influence of this caking on the fuel rods and the heat transfer that the post-LOCA

dI was not able to find the reference by Hermannson and Erixon (SKI Report 98:12) cited in NUREG/OR6873 and in LA-UR-03-641 5 Small-Scale Experiments: Effects of Chemical Reactions on Debris-Bed

Head Loss, by R.C. Johns et al., nor a description of the TMVI-2 solids (reference 7 in LA-UR-03-6415).

C-31I
recirculation is designed to achieve? For the purposes of the present task, spallation of the

deposits from the fuel cladding surfaces also would be expected. These spalled crusts

would contribute to the solids loading in the cooling cycle and likely would adopt curled

shapes imparted by the fuel pin surface. Therefore, tests might be proposed to test for this

potential effect and, if operant, project the type and characteristics of the spalled materials.

* Some interesting discussion arose during the first day's meeting regarding the spallation of

the protective magnetite (Fe3O4) corrosion layer from within the stainless steel pressure

vessel due to the abrupt thermal and pressure shocks in a LOCA. I do not know the

thickness of the protective film nor to what degree this spallation might occur but per ,haps

some industry experts could be consulted.e The magnetite spallation, if it should happen,

would contribute to the solids load that must be considered in the post-LOCA cooling cycle.

* The same discussion also provoked speculation on the rapid corrosion of the internal

surface of the pressure vessel under high temperature oxic water to produce dissolved Fe 2 +

that would air oxidize to give fine Fe(OH) 3 particles. Again, some industry experts might

have insight on the amount of corrosion that would occur.

2. Integrated Chemical Effects Testing (ICET)

The Integrated Chemical Effects Testing (ICET) results were presented in five separate reports,

one for each of the five tests in the series. The first three tests were described in full reports

(the third one in draft version), and the fourth and fifth in -10-page "quick look" reports. ICET

results also were summarized in presentations by Bruce Letellier ("Integrated Chemical Effects

Tests - Design and Operations" and - "Survey of Results") and Marc Klasky ("Chemical Product

Analysis and Simulation") of LANIL at the "Chemical Effects Peer Review Kick-off Meeting,"

October 18-19, 2005. Observations, suggestions, and critiques on the ICET laboratory

investigations are provided.

* The ICET experiments must cover the range of anticipated chemical and physical (primarily

temperature) conditions, and combinations of conditions, which might occur for the US

PWRs. It would be useful in the presentation of the ICET results to assign the various

PWRs to the conditions encompassed by the 2x2 test matrix (i.e., high/low pH,

presence/absence of Cal-Sil) plus the fifth test for the sodium tetraborate ice melt (i.e., Tests

#1 through #5). Such assignment would ensure that all of the US PWRs were represented

by at least one of the five test conditions.

* The close proximities of the metallic test coupons may have influenced their respective

behaviors as noted in the surmised plating of copper on the aluminum (ICET #2, LA-UR-OS6146, page 21; ICET #3, Bruce Letellier presentation, page 56). Could the close metal

coupon proximities also have affected their corrosion rates? It is evident from the

experimental results (and also what would be expected) that the biggest metallic corrosion

contributor is aluminum followed distantly by zinc. Therefore, the influence of copper on

potentially decreasing or increasing the corrosion rate of aluminum is of concern and may

be profound.

*Related to the above question, what was the arrangement of coupons in the test racks (e.g.,

AI-Cu-GS-US etc.)? According to the photos of the test racks (e.g., Figures 11 and 18 of

LA-UR-05-0124), it seems that the metals were placed in groups. Were the aluminum and

e I did not find mention of this phenomenon in the report Development of a Phenomena Identification and

Ranking Table (PIRT) for Thermal-Hydraulic Phenomena During a PWR Large-Break LOCA, R. A. Shaw,

S. Z. Rouhani, T. K. Larson, and R. A. Dimenna, NUREG/CR-5047, Idaho National Engineering

Laboratory, Idaho Falls, ID (1988). However, I am not conversant in the literature. Is magnetite spallation from the inside of the reactor vessel a credible outcome from a large break LOCA?

C-32
copper coupons always or mostly adjacent to each other? Were any systematic differences

noted in the weight loss observations for the immersed aluminum coupons? For example,

were the greatest or least losses of aluminum weight consistently observed for coupons

closest to copper?

*What was the aluminum alloy that was tested? Is it representative of aluminum used in

scaffolding or in other equipment exposed to the spray and sump water?

*More detail on the compositions of the other metals also should be provided in the ICET

reports for completeness.

*Results of the surface examinations of the metallic test coupons (particularly aluminum and

particularly in Test #11) would be useful to sort out the corrosion rates and the effects of

borate and other agents on passivation/activation. Surface examinations could include xray diffractometry. The diffraction pattern of the corrosion product (likely boehmite, vAIOOH; see Oxides and Hydroxides of Aluminum by K. Wefers and C. Misra, 1987, Alcoa

Laboratories) should be evident even though the diffraction pattern may also disclose the

underlying aluminum metal pattern. Some scoping tests might be useful here.

*Both Test #1 and Test #4 were run at pH 10. However, Test #4 seemed to have much

lower aluminum corrosion than Test #11. Why? Note that Test #4 had the Cal-Sil and Test

#1 did not. Do the surface appearances (or XRD) of the aluminum coupons give any hints

(e.g., calcium aluminate as tricalcium aluminum hydroxide [Ca3AI 2(OH) 121 and hydrocalumite

ECa 2AI(OH) 7*2H20D) deposit on the surface)? See Potential for Generation of Flammable

Mixtures of Hydrogen from Aluminum-Grout Interaction in the K Basins During Basin

Grouting, S. M. Short and B. M. Parker, 2005, PNNL-1 5156

(http://www.pnl.gov/main/publications/external/technical_reports/PNN L-1 51 56.pdf) for a description

of the results of reacting aluminum metal with Ca(OH) 2 and with portland cement grout.

Bruce Letellier (LANL) speculated that CaCO 3 passivation layer formed (page 49 of October

18 viewgraphs) but these calcium aluminates also should be considered.

" The concentration of calcium observed in Test #3 (Figure 3-9) is about 110 mg/liter or

-0.0028 M. This is near the solubility of calcite, CaCO 3, in pH 8 water. The large amount~of

Cal-Sil in the system may indicate that CaCO 3 (if present in Cal-Sil) is the solubilitycontrolling phase for this test. On the other hand, the calcium concentration in Test #4 is

about 45 mg/liter or -0.0011 M, at pH -9.9. This concentration is too high to be controlled

by CaCO 3 and may indicate that Ca(OH) 2 (or something else) is controlling the calcium

concentration (also see note below in discussion of head loss testing).

* The incipient boehmite phase also would be forced to crystallization by heating. Some

useful discussion on the formation of gelatinous boehmite, the influence of anions to retard

further crystallization, and the influence of temperature on boehmite solubility are in the

excerpt (provided separately) from the monograph, Oxides and Hydroxides of Aluminum by

K. Wefers and C. Misra of Alcoa (1987). The excerpt also gives some information on the

boehmite corrosion layer formed in water on aluminum (see page 4 and pages 66-68 from

the excerpt). This monograph is available in printed form from Alcoa (Nickolas C. Kotow,

Senior Information Scientist, Alcoa, 724 337-5704).

* There should be more description of the "dirt" added to the ICET experiments to establish

that these "dirt" components'are representative of what might be found in the reactor

containment. What is the source of the dirt; what is its composition? I recall montmorillonite

(or bentonite) being mentioned as a component.

" For completeness, there should be some description of the aggregate incorporated into the

concrete used in the testing. The contribution of the aggregate to the dissolved and

suspended solids is probably minor but this should be stated. Also, the aggregate used to

construct the various PWRs may vary (for example, most of the crushed rock in this area is

basalt; other areas may use river rock from granite).

C-33
" One of the other reviewers, Wu Chen, suggested that the particle size distribution and

particle concentration be measured for the ICET runs. The -physical characteristics of the

solids are important in selecting the solid/liquid separation equipment and media to be used

upstream of the containment sump. The technique of small angle x-ray scattering (SA)(S;

hftp://www.mri.psu.edu/mcl/techniaues/saxs.asr)) could be used to discern the particle sizes of the

microcrystallites in the 1-100 nmn particle size range. However, one should be wary of the

particle size data if measured on the ICET #14#5 slurries that have now aged for several

months. Some new, small scale, tests are needed to create materials for characterization.

" What is the reason for the abrupt spike (though only to 0.06 to 0.11 and one at 0.19 mg/liter)

in aluminum concentration shown in Figure 3-8 in Test #3? Is this a case of having

detectible concentrations for these samples and the non-detectible concentrations being

plotted as zero?

3. Modelinq

The modeling work, conducted by Vijay Jain and colleagues at the Center for Nuclear Waste

Regulatory Analyses (CNWRA), is presented in "Chemical Speciation, Using Thermodynamic

Modeling, During a Representative Loss-of-Coolant Accident," CNWRAf 2004-07, and in

"Corrosion Rate Measurements and Chemical Speciation of Corrosion Products Using

Thermodynamic Modeling of Debris Components to Support GSI-1 91," NUREG/CR-6873. The

findings were reviewed in the October 19, 2005, presentation "GSI-191 Chemical Effects:

Modeling and Experiments," by Vijay Jamn.

* The postulated NaAlSi3O8 phase (albite) seems to be plausible for the alkaline (pH 10)

systems with aluminum and silica (Tests #1 and #4). Similar phases are found in Hanford

Site waste tanks.

* The apatite phase, Ca5OH(P0 4)3, postulated by CNWRA for the Test #3 system having high

calcium and phosphate, seems more reasonable than the Ca3(P0 4)2 phase postulated by

Shack and colleagues at ANL in their head loss tests. Apatite has very low solubility.

" Carbonation of concrete and Cal-Sil (i.e., formation of CaCO 3) is to be expected and seems

to have occurred in the Cal-Sil that was characterized by CNWRA. Some limited amount of

carbonation also will occur during spraydown of the containment building atmosphere but

that contribution should be relatively minor. CaCO 3 has retrograde solubility (becomes less

soluble as temperature increases) and thus is prone to plate out on hot surfaces such as the

irradiated core fuel and the pressure vessel. Other minerals also have retrograde solubility

and could plate out. As noted by Bruce Letellier (LANL) on page 21 of his October 18

presentation, an internal pipe coating by calcium silicate was thought to be a concern for

heat conduction from fuel.

*The characterization of the Cal-Sil (8 th slide of October 19 presentation) showed a loss on

ignition (LOI) of 35.2 wt%. According to follow-up questions, this LOI was done to '-10000C.

This temperature is too high to distinguish the loss of water, typically occurring below 200'C,

from the decomposition of CaCO3 or other carbonates, which occurs 600-850*C for CaCO3. It would be useful to perform a thermal analysis [e.g., "Determination of Free Lime and

Carbonate in Calcium Silicate Hydrates by Thermobalance," F. M. Biffen, Analytical

Chemistry, 28(7):1133-1136, 1956; more recent references certainly exist] or use some

alternative method to find out how much CO2 as carbonate is present in the Cal-Sil. The

actual condition of the Cal-Sil in the operating plants then must be considered as one would

expect the Cal-Sil composition to change with aging.

fNote that the document number is given as CWNRA 2004-07 on the cover page.

C-34
4. Chemical Effects Head Loss Testina

The chemical effects head loss testing was conducted by Bill Shack, J. Oras, and colleagues at

ANL. Their results were given in "Chemical Effects / Head-Loss Testing Quick Look Report,

Tests 1 & 2" and in the October 19 viewgraphs, "Chemical Effects Head Loss Tests".

* The introduction of the aluminum phase to the filtration / head-loss testing, accomplished by neutralization of AI(N0 3)3 with NaOH, is not representative of the way aluminum is

introduced to the post-LOCA system (and may have caused the so-called non-prototypical

snowfall behavior). For one thing, it introduces nitrate, an anion otherwise not present. It is

proposed that the aluminum be introduced in another manner, either by corroding a coupon

of aluminum in NaOH (simulating the actual conditions, but potentially difficult under

experimental conditions) or by adding sodium aluminate solution, NaAI(OH) 4. Sodium

aluminate is what is initially dissolved off the corroding aluminum metal by the NaOH.

Sodium aluminate is available as a solid material through chemical supply houses

(https://wwwl .fishersci.com/Coupon?catnum=NC9365903) or can be made by dissolving AI(OH) 3 in

hot excess NaOH.

" The calcium concentration dependence on pH given by Cal-Sil dissolution tests (Figure 1 of

"Quick Look" report) is interesting in that it is practically flat - i.e., the calcium concentration

decreases only about a factor of 10 for a pH increase of 6. Most minerals would become

less soluble by about a factor of 100 per increase of one pH unit. Has the solid phase(s)

been identified?

5. Chemical Effect on the Sump Water

The "Chemical Effect on the Sump Water" presentation describes work by J. H. Park and

colleagues of ANL. Perhaps some of their findings also were given in the "Small Scale

Dissolution Test" section in the "quick look" report by J. Oras and colleagues of ANL.

*The Cal-Sil dissolution information (below) shows increasing dissolution with time. Does

this increase continue with time? What do the solids look like?

(a) __ _ _ _ _ _ _ _ (b)

T = 600

C TWCN

250% pH = 7.14 (NaOH) Na sc 50 pH- = 7.14 (N~aOH)

252-0 CaISiIIL P Ca V E 25-.g CaISiIIL

C,,a

-I ~kC&predict

0 0 53 50 0 80 Iu0 0.1 I 10 100 t (h) S! (ppm)

Elements in the solution as a function of time (a) and Ca and Na vs. Si (b)

*The experiments using AI(N0 3)3 to introduce the aluminum (slides 8-10 of the presentation)

again are not representative of the system being studied (which contains no nitrate).

Suggest repeating the tests using sodium aluminate.

C-35
APPENDIX 3

Informal Comments on ICET Reports to B. Letellier - May 7, 2006

And Responses - May 10, 2006 (in italics)

* Will an ICET comparison report be prepared? It would be usefut to see, in one report, a side-by-side

comparison of the various tests and their outcomes. A comparison report is being prepared.

* It would be useful to provide a more detailed description of the inorganic zinc / coated steel coupons.

For example, they are called (I think) cold galvanizing spray paints and they contain high, -93%, zinc

concentrations. Is this what is meant? Yes, paint containing high metallic zinc content is what is

meant.

* Please describe if more or different deposits were observed on the heat exchanger surfaces. This

might give some information on what may be expected for the potential for deposits on hot fuel in the

post-LOCA reactor. The deposits on the heat exchanger surfaces did not appear to be materially

different from the recirculating solids and were not present in noticeably higher concentrations.

* Was any biological activity noticed in any ICET bath? This might be the presence of green slines or

some checking with a microscope. The presence or lack of biological activity should be noted,

whatever the case. No particular microscopic study looking for algae or other biota was done;

however, no apparent "green slines" were observed.

* When RO water was added on Day 8 of Test #3 (p. 21), and cloudiness observed, was it because of

temperature drop? If so, how much did the temperature drop? The cloudiness is thought to be due to

turbulence that moved previously deposited solids when the water was added.

* In Figure 3-5 of the Test #3 report, (p. 26), what is the label on the y-axis? What was the average

NTU, excluding the potential~ly spurious day #1 and day #15 results? The label will be remedied in

future reports.

" Also check y-axis label on Figure 3-7 of Test #3 report. The label will be remedied in future reports.

" How was chloride analyzed? Was it by ICP or instead by ion chromatography? Ion chromatography

was used to analyze chloride concentration.

" In the proposed overview report, it would be useful to compare Ca concentrations with respect to

phosphate concentrations (for example, in the Test #3 report, compare Figures 3-16 (phosphate) with

Figure 3-9 (Ca). The direct comparison could be done, as suggested, or another means used to

correlate the data.

" In Figure 3-8 of Test #3, the Al concentrations look anomalous around days 8-15 inclusive. Is this a

minimum detection limit phenomenon in which "real" values were found on days 8-15 and the other

days had "less-than' values? As suspected, this is an artifact of the minimum detection limit.

* In Figure 3-39 of the Test #3 report, was EDS (energy dispersive spectroscopy) done on the large flat

fibers to identify the elements present? What is their origin? Were the large flat fibers observed in

the original fiberglass insulation? The large flat fibers were postulated to come from the cal-sil

materials, as noted on page 47 of the report.

* On p. 56 of the ICET #3 report, is there further substantiation of the identification of the Ca3(P04)2

phase? This identification is based on EDS data, not on XRD. Therefore, the speculation that the

phase is Ca3(P04)2 is not supported.

* Suggest X-ray diffraction be done to identify phases on metal coupons though your XPS and surface

infrared analyses might give other complementary information. This suggestion is acknowledged.

* In the Summary of the test #3 report, at the bottom of p. 97, identify the "crystalline substances". The

crystalline substances were identified earlier in the report (e.g., p. 81 and Figure 3-117) as

tobermorite, Ca2.25('Si 3O7.5(OH) 1.5) (H20).

" In test #4, p. 20, did the RO water addition and cooling cause precipitation? As in the Test #3 result,

this is probably from loosening of solids deposits caused by turbulence.

*On p. 99 of the test #4 report, and as you indicated in one of the presentations at the SwR1,

aluminosilicate surface precipitation may be occurring. This is also suggested by comparison of the

Test #1 and Test #4 conditions, which differ in that Test #4 has Cal-sil and Test #1 does not; both at

pH 10. However, on slide #22 of Jude McMurry's presentation of March 27 (excerpted below), little

change in corrosion rate found between the pH 10 tests with and without Cal-sil. The tests done at

C-36
SwRI measured initial corrosion rates, so may not have benefited from the formation of a passive

layer.

Test Conditions Method

Aluminum in borated alkaline contairnment water

(pH 10)

Aluminum in borated alkaline contairment water

(pH 10) with Nukan glass fiber insulation

Aluminum in borated alkaline containment water

(pH 10) with Nukon glass fiber insulation

Aluminum in borated trisodium phosphate containment water (pH 7)

Alurninum in borated trisodium phosphate

containment water (pH 7) with calcium ciliczte

insulation

Aluminum in Borated.Alkaline Containment Water

(pH 10) with Calcium silicate Insulation

Electrochemical

Weight loss

Chemical analysis

Electrochemical

Electrochemical

Electrochemical

Corrosion Rate

glrr?-h [nil/yr]

0.986

(126]

1.31

(168]

1.16

[148]

0.0039

[0.51

0.028

[3.61]

0.80 [103]

*In Test #5, why the daily pH spikes -- see Figure 3-1 on page 21 ? This phenomenon was noted

during the data collection for this meter installed with the tank system. Efforts to locate the cause of

the spikes were not successful. However, the pH data for record are those from samples taken daily

and measured using a pH meter that was calibrated for each use. The tank system pH meter was

used for indication only.

*Thank you for showing how H2 tracks with Al concentration in y our summary presentation at the

SwRI. This explanation also should be given on p. 22 of the Test #5 report. Acknowledged.

C-37

Appendix D

EVALUATION OF

INTEGRATED CHEMICAL EFFECTS TESTING

Robert Litman, PhD

RADIOCHEMISTRY

LABORATORY BASICS

28 Hutchinson Drive

Hampton, NH 03842

drbob2064,comcast.net

(603)926-4863

Prepared for

Argonne National Laboratory Sub-Contract No. 5F-00556

and

United States Nuclear Regulatory Commission

May 2006

D-1
Abstract

The potential formation of gels, as a result of containment materials interacting with

reactor coolant fluid following a large break loss of coolant accident (LOCA), was

studied under various conditions. The principal concern is that formation of gels, or other

insoluble materials, could block the screens on the containment recirculation sumps of

pressurized water reactors (PWR). A series of experimental chemical simulations were

performed by Argonne National Laboratory (ANL), Los Alamos National Laboratory

(LANL) and Southwest Research Institute (SwRI) to determine if the chemicals resulting

from reactor coolant system post-LOCA containment spray reacting with Reactor

Coolant System (RCS) insulation and other materials in containment (metals and

concrete) could be identified, and if the containment recirculation sump screens would, in

fact, become blocked due to formation of these chemicals.

This report reviews the fidelity of these simulations, and addresses how the simulations

can be further refined to address more closely all significant, potential factors in the

complex mixture of materials that are exposed to RCS liquid during a large break LOCA.

D-2
CONTENTS

Abstract D-2

Abbreviations D-4

Executive Summary D-5

Summary of Key Points D-6

Introduction D-7

Discussion D-7

Part I D-8

Part 11 D-1 5

Conclusions D-20

Recommendations D-21

Attachment I D-23

D-3
.ABBREVIATIONS

CBS Containment Building Spray

CRUD A term used to identify insoluble corrosion products present in the

Reactor coolant system and located on the piping

ICET Integrated Chemical Effects Test

ICP Inductively Coupled Plasma Spectrometry

LOCA Loss of Coolant Accident

pH The negative logarithm (base 10) of the H' concentration

PWR Pressurized Water Reactor

RHR Residual Heat Removal

RCS Reactor Coolant System

SAT Spray Additive Tank

SEM Scanning Electron Microscopy

SG Steam Generator

TSP Trisodium Phosphate

TSS Total Suspended Solids

XRD X-ray Diffraction

D-4
Executive Summary

The Integrated Chemical Effects Test (ICET) Program was implemented to assess the

effects that certain chemical constituents of post-LOCA materials, particularly insulation,

latent debris and the chemicals found in a PWR containment spray environment, would

have on recirculation sump flow in a PWR should a LOCA occur. The tests examined

the principal parameters, which could affect transport of water flow into the containment

sump. The principal parameters examined were:

" pH

* RCS chemicals

o Boric acid

o Lithium hydroxide

* pH control agent

" Sodium Hydroxide

" Trisodium Phosphate

o Sodium Tetraborate

" Insulation Materials

o Fiberglass

" Calcium Silicate

o Reflective Metal

" Latent Debris generated in situ as a result of the LOCA

o Concrete fines

o Miscellaneous Organics from insulation and paint

o Paint chip particulates

o Halide ions resulting from the destruction of electrical cable insulation

* Materials of construction of different components found in containment

o Aluminum

o Zinc

o Copper

" Temperature

This document reviews the work to date and identifies parameters which have yet to be

accounted for, and conditions of significant conservatism in the modeling.

Overall the tests show that the formation of insoluble chemicals will occur in all cases of

containment spray interacting with insulating materials and metals used in PWR

containment buildings. Each combination of spray additives and insulation forms

different types of precipitates. These precipitates may cause an impediment to water

flow to different degrees based on the types of precipitates and the types of materials

that may be transported to the debris screens at the containment sump area.

D-5
Summary of Key Points

The ICET tests provide information regarding the chemical environment of the liquid in

the containment sump following a large break LOCA. The time period involved is from

the onset of sump recirculation to containment spray headers, through the termination of

spray (approximately 4 hours) and to the 30-day mark. The elements of these tests that

are of significance with regards to containment sump screen blockage are:

* The pH values used are representative of the long term recirculation pH values in

the three different types of PWR containment spray systems

* The chemical concentrations used approximate the PWR post LOCA RCS

chemicals.

* The materials used as latent debris and as accident generated debris, although

limited in scope, are representative of some of the PWR materials

" The predominant metals that can undergo significant corrosion are included as

coupon materials during the tests

" Significant masses of compounds are precipitated as a result of the interaction

with the RCS post LOCA chemicals and plant materials such as insulation,

uncoated metals and general debris

* The compounds that are precipitated in the presence of TSP are generally

amorphous. These compounds will adhere to fragmented pieces of insulating

materials and can impede complete flow of water when this debris is embedded

against engineered screens.

* The precipitate that forms from the interaction of TSP and Cal-Sil forms the

greatest impediment to flow of the materials tested.

Certain physical and chemical parameters were not addressed in these tests. Those of

greatest significance are:

* A radiation field for the debris bed was not simulated (this can have a significant

effect on the species of precipitate material as well as its ability to agglomerate

* The effects of two temperature gradients in the post-LOCA environment: RHR

heat exchanger and the passage of the RCS over the reactor core

* The effects of the core radiation field on the formation of radicals and reactive

compounds, and in particular hydrogen peroxide.

* The rate of the settling of the insulating material and precipitates during their

transport to the containment sump screens is not effectively modeled by the

settling tests performed.

D-6
Introduction

The objective of the Integrated Chemical Effects Test is determine if during a Loss of

Coolant Accident (LOCA) in a PWR chemical reactions may occur with materials already

in containment, which may form insoluble compounds that can block containment

recirculation sump screens. This review will examine the key parameters used to

establish the test conditions, the implementation of those conditions and the analytical

techniques used to measure the chemical effects.

Discussion

The discussion section of this final assessment is divided into three parts. Part I

addresses the tests conducted using tni-sodium phosphate, sodium hydroxide and

sodium tetraborate on containment materials and if all major parameters that could affect

the results have been considered. The specific materials examined were fiberglass

insulation, Cal-Sil insulation, concrete debris, non-metallic jacketed insulation and

combinations of these materials. Specific questions were posed to the peer review

group that serves as the structure for Part 1.

Part 11 discusses individual test results and their potential impact on the blockage of

containment sump screens

Part Ill identifies plant specific configurations that will have an impact (either mitigation or

exacerbation) on the applicability of these test results, and need to be considered on a

plant-by-plant basis.

D-7
Part I.

1 . Did the ICET tests have the principal sump pool variables that could affect

chemical by-product formation in the post-LOCA environment properly

simulated?

The concentrations of chemicals used during the operation of a PWR are

approximately in the range of anticipated chemical concentrations.

The concentration of boron is slightly higher than would be expected. Based on

a beginning of life (BOL) boron concentration of 1200-1400 ppm the final B

concentration would only reach about 2200-2600 ppm. It is not expected that

this will result in any significant difference in the results.

The lithium concentration used in some of the tests was as high as 3.5 ppm. The

maximum post-LOCA lithium concentration would be 0.3 ppm. This overestimate

of lithium concentration will have a small effect on changing the final pH of the

test solutions.

The concentrations of NaOH or TSP in the final sump volume are appropriate for

the post-LOCA environment model.

The types of materials that are present in containments of PWRs have been

appropriately selected. The ratios of these materials exposed to the liquid in the

test loop likewise are in the correct proportions as would be expected within a

containment building. These components susceptible to leaching and dissolution

contain the elements Zn, Al, Mg Ca, Si in addition to those materials of

construction elements of Fe and Cu. In at least one test (#3) it appears that the

mass of Cal-Sil insulation, which would come into contact with the RCS, is

greater than would be expected following a LOCA.

Chemical constituents that have not been simulated are:

* initial RCS silica concentrations up to 1 ppmn (and in the refueling storage

tanks of several PWRs this concentration may be as high as 5-10 ppm),

* CRUD concentrations (which will contain mixtures of nickel ferrite,

magnetite, nickel oxide and hematite) of up to 100 ppm from the

thermal/hydraulic transient caused by the LOCA,

" the presence of hydrogen peroxide resulting from the gamma radiation

field of the core,

* Miscellaneous containment materials like other forms of insulation, the

presence of organic matter, and bacteria.

The first three together have the potential for altering the outcome of the test

program. The fourth is estimated to have a relatively minor effect over 30 days.

2. Many ICET variables were held constant during the experiments. How would

changes in the most important constant variables affect chemical product

formation?

Chemical Constituents:

Of the chemical constituents used, variation in their equilibrium concentration

would not produce significantly different effects. However incorporation of the

D-8
chemical constituents not included which will most certainly be part of a real postLOCA environment, will have significant impacts on the test results.

It is likely that as time after the LOCA progresses the mass of Fe(OH) 3 present

will increase. This material has a significant effect on coagulating and

precipitating other materials. Its effect has not been modeled.

The instantaneous, high concentration of TSP used at the start of the ICET tests,

in combination with the precipitating agent calcium (from Cal-Sil) is unrealistic for

the manner in which the materials would initially mix in the sump.

Physical Parameters:

Temperature has a significant effect on solubility and the types of compounds

that will form with the mixture of ionic constituents present. The two temperature

gradients that are critical to the formation of scales and other insoluble

compounds (such as flocculants like AIOOH) are not incorporated into the design

of the test loop.

The first of these temperature gradients is the fuel surface. The temperature at

the clad surface will cause materials with retrograde solubility (calcium

carbonate, sodium-aluminosilicates, etc.) will precipitate out and bind to these

surfaces. This may have secondary precipitation effects (i.e. other materials

being flocculated or trapped by this primary precipitate), as well as fuel decay

heat removal effects (heat transfer is reduced potentially leading to other fuel

clad concerns). Once water that has passed through the core exits at a higher

temperature, it can dissolve additional ions from containment materials. This will

lead to more precipitate being formed from the mixture of materials (i.e., the

equilibrium initially established will be pushed to yield more precipitate).

The second temperature gradient is at the RHR system heat exchangers. These

heat exchangers use service water or a closed loop cooling system to maintain

less than the maximum design temperature of the water leaving the heat

exchanger. No effort is made to control this output temperature as long as it

remains less than the design temperature. Since the ultimate heat sink for this

system is water from a river, lake or ocean, this temperature will vary over the

course of days. Chemicals with normal solubility profiles will precipitate in this

heat exchanger due to the temperature drop.

How these two heat exchange surfaces affect these test results is not easily

predicted. The main reason is that in both cases there are co-precipitation effects

that cannot be modeled (co-precipitation is a non-thermodynamic parameter). A

modified design, which incorporates these heat sources and sinks, would be

important to the overall understanding of the formation of insoluble materials that

may have a deleterious effect on the recirculation flow path.

Another physical parameter not modeled in this design is radiation fields. This is

a difficult aspect to model. However the effect of high-level radiation fields (in the

core in the mega-rad range, if material is caught on the sump screens this would

most likely be in the kilo-rad range) on chemical characteristics cannot be

ignored. A specific example is the chemical state of silica. This element in water

may form the following: SiO3 

2-, HSiO3'-, H2SiO3, SiO 2, and poly-silicate

compounds. The spent fuel pools at PWR sites have been plagued with

D-9
decomposition of their Boraflexaby the radiation fields from the spent fuel. T his

decomposition has led to concentrations of reactive silica (usually as HSiO3, or

reactive silica) as high as 100 ppm. Contrary to this phenomenon, reactive silica

in solutions from pH 3-9 has been known to form poly-silicates (in the absence of

radiation) that are highly insoluble. One possible resolution to this issue may be

to take the solids formed from the lOFT Test Runs and expose them to high

radiation doses for several days, then re-examine their morphology. This would

help to assess if there is any effect by the high intensity radiation fields within the

coolant system.

3. What variables or materials not simulated by the ICET testing may have the most

impact on chemical product formation (e.g.., coatings, free insulation, flow through

sediment and other materials on sump screen, galvanic effects) and how should

their effect be characterized by testing or analysis?

The effect of the liquid coming into contact with fuel in the reactor vessel will

have considerable impact. There are two missing variables here: heat and

radiolytic effects. Heat at the fuel surface will be several hundred degrees

Fahrenheit. This will have an affect as the materials with retrograde solubility,

the scale formers, will concentrate on this surface and not be available to form

other precipitates. [See additional notes on this effect above].

The presence of suspended solids from the reactor coolant system, which will

have a very high iron and nickel content were not considered as one of the

solution constituents. Specifically, magnetite, nickel ferrite, bonaccordite, nickel

oxide and nickel metal are materials that would be produced in large amounts

(10-500 ppm) following a LOCA. Over the course of a thirty-day test these

materials will change their chemical form, including the formation of ferric

hydroxide (a strong flocculating material).

Another variable not simulated is the presence of silica in the water storage

systems and the RCS. The concentration of silica in the storage tanks may be

as high as 1 ppm and in the RCS the silica concentration will be in the range of

0.3 ppm to 3.0 ppm. Since silica in combination with magnesium, calcium and

aluminum can form materials with retrograde solubility; silica can have an effect

on the total mass of material precipitating.

4. Were the methods used within the ICET program to characterize and analyze

chemical by-products sufficient?

The analytical techniques. used for characterizing the chemical by-products were:

A. Inductively -Coupled Plasma-Atomic Emission Spectrometry (ICP -AES):

Method for determining the elemental content qualitatively and

quantitatively present in the solutions produced by the tests. Although it

does not identify oxidation state or molecular environment it will identify

all elemental components in the percent to the ppb range. The

concentration ranges used for analysis were appropriate for the

concentrations expected in the simulated post-LOCA environment.

B. Scanning Electron Microscopy (SEM):

D-10
A microscopic technique used to identify the topography of a solid

material. This aids in identifying, qualitatively, whether a material is

crystalline or amorphous. It is limited to materials that have, been predried and can only view the surface molecules/atoms. This morphological

characteristic of a solid is important to its ability to act as a gel. This

technique is very useful in characterization of the solid materials

produced during the ICET program.

C. Energy Dispersive Spectroscopy (EDS):

Another elemental analysis tool that can aid in assessing the composition

of the material at the surface of the substrate. However it does not

identify molecular structure or oxidation state. This technique is

supplemental to SEM and can non-destructively determine element

concentration in solids

D. Transmission Electron Microscopy (TEM):

A microscopic technique designed to view solids at the atomic level.

General structure and arrangements of atoms can be determined, but this

may only be semi-quantitative due to the unusual nature of the solids we

are examining. However it cannot discriminate between the surface

material and sub-strata. This technique also suffers from the sample

preparation that requires loss of water in order to provide an appropriate

sample medium. It does provide important structural information

regarding the materials that form during the tests.

E. X-Ray Fluorescence (XRF).

An elemental technique based on the generation of x-rays by the

elements in the sample matrix using particles from the instrument source.

In matrices of the type we are examining this technique will be semiquantitative since the duplication of a standard geometry is very difficult.

F. X-ray Diffraction (XRD):

A technique used to determine the crystalline structure of materials. Its

shortcoming is that amorphous materials cannot be analyzed and if

present will interfere with the diffraction pattern of minor crystalline

components. Based on the type of crystalline material one can infer an

oxidation state of the elements. This is a very important technique in

helping to identify specific molecular species that may play an important

part in potential clogging issues.

G. Wet Chemical Techniques, Kinematic Viscosity, Turbidity, pH, Total

Suspended Solids and Temperature:

These techniques are all applicable. to the parameters that we are trying

to assess. They will be helpful in determining the general physical

characteristic of the post-accident fluid. None of the methods is material

or compound specific. However in these circumstances, the instrumental

methods noted above will be able to identify the major and minor

contributors to the overall make-up of the fluid.

D-11I
The analytical techniques used to characterize the chemical compounds that

were formed are complementary. Taken as a whole they are the most extensive

analytical tools that could be used for this assessment and are adequate to

address changes that would be observed during the ICET program.

The only additional test that might be of value would be FTIR of the colored

materials/solution to identify the chemical identity of those colored materials. It

should be noted that in a strong radiolytic field that most color-bearing organic

materials would be transformed to carbon dioxide and water.

The one analytical test that yields very little useful information is the mass

determination of the coupons before and after the tests. These co upons should

be used for qualitative observation of the mechanism of corrosion and deposition

of other insoluble compounds.. XRD may be useful in assessing the types of

compounds not related to the coupon material that may be formed on its surface,

and TEM may provide qualitative insight as to the materials present. Unless a

total mass balance is attempted using the interior system surfaces as well as the

coupons, the actual mass of the coupons will not provide any significant

information.

5. Analytical Simulation. Is the speciation analysis expected to provide reasonable

predictions of chemical product formation over a range of possible sump

environments?

The average temperature and concentration ranges used for the ICET program

do simulate the bulk water, average temperature and concentrations of

constituents (with the exceptions noted in Al (above).

However, two important temperature profiles and two physical effects are not part

of the ICET simulation. The increase in temperature as the water passes over

the hot fuel surface will cause scale to form at that surface, potentially

scavenging the gel formers from the solution. The decrease in temperature as

the water passes from the containment sump to the residual heat removal

system can also cause precipitation of materials on the inlet tubesheet and tube

surfaces of the heat exchanger (this particular effect was seen in Test#1 with

turbidity see Figure 29 of test report).

The two physical effects not modeled are the radiation field from the fuel, and the

layer of corrosion products on the interior surface of the reactor coolant system.

The radiation field will promote the formation of radicals that can expand the

potential number of mineral products that can be formed. The presence of

corrosion products on the interior surface of the system can provide a

mechanism for removal of some contaminants. The corrosion products released

during he LOCA can contribute to the settling rate of other insoluble compounds

of lower density prior to reaching the containment sump. The exact location of

this settled material would need to be modeled in a future experiment.

6. Is the plan for benchmarking these codes using small-scale testing and the ICET

results appropriate?

It would be appropriate to use the codes to help bound the characteristics that we

expect to observe. However, it is important to note that not all of the important

D-12
physical and chemical parameters present in the post-LOCA environment have

been appropriately modeled in the ICET tests. Thus using the models with the

existing data can give us limited information.

7. What is the most appropriate way to measure the uncertainty associated with

these codes?

Not within the reviewer's area of expertise.

8. Was the Head Loss Simulation Testing & Analysis for the accelerated head loss

testing approach viable for evaluating the effects of multiple chemical

environments quickly?

One of the difficulties in this testing mechanism is that the- concentrations of

several of the potential fouling species will increase over time. The effects of

aging of the insoluble materials are that they generally will increase in size and

crystalline character, increasing density. The test loop does not provide the same

type of stagnant environment that would be encountered in the submerged

portion of the containment building. The relatively lower flow rate would promote

better agglomeration of particulate material due to the effect of relatively high

concentration of the precipitants at the surface of the insulation. This will promote

settling that will not be modeled in these tests.

The test loop as designed does not allow for insoluble materials to drop out, as

would occur during transit along the containment floor following a LOCA. The

relatively long flow paths and impediments to flow caused by structural

components are not simulated. These provide 'drop out' areas for

insoluble/suspended materials before they can approach the screens. Thus

there is a bias towards a rapidly increasing pressure across the filtering media,

which does not depict the actual mechanism of transport in the containment.

Furthermore the test loop design has forced impingement, vertically down on the

filter screen. In containment sump the flow of water is horizontal, and the water is

not confined to a pipe. If the surface area of the screen at, and below the water

level is clogged, the water will rise to a higher level where the screen is not

clogged. This type of 'overflow effect' cannot be realized in the current design. A

proposed modification where the effect of long term clogging could be more

realistically evaluated is shown in Attachment I.

9. What is the best method for incorporating for time-dependent effects (e.g.,

material aging, evolving chemical environments) in simulation testing?

The techniques that have been used by the test groups thus far seem to be the

most appropriate.

The only exception is the preparation of the stainless steel surface of the test

loop. In a PWR the interior surfaces of all the metals will be covered with

relatively thick oxide coatings (100-250 microns, compared to the test loop which

is most likely only about 10 microns). The stainless steel will visibly be black,

D-13
and several hundred microns thick. Although this is an initial material condition, it

goes to the heart of developing the right conditions of materials to supply

accurate data for simulations.

10. What metrics are most appropriate for evaluating the results of simulated

chemical products with those that formed during the ICET program?

Not within the reviewer's area of expertise.

11. Are correlations available, or can they be developed, which can predict the

associated head loss if important physical characteristics of a chemical byproduct are known?

Models that predict head-loss cannot account for the effects of gelatinous or

amorphous materials. At least one reason is the secondary effect of

coprecipitated or agglomerated materials. Flow rate-AP curves for specific

filtration media have been developed by filter manufacturers. These relationships

are almost all made for closed systems, where flow is impacted on a constant

filtration area, and a specific well-characterized material is used for the tests. In

the early stages of the event this type of curve would not be representative of

what would occur in containment. Additionally should the entire screen become

covered with debris and the level of water should rise above the screen level,

buoyant effects for the solid debris may come into play and change the effected

area of blockage.

Although the preliminary data provides some information regarding head loss

due to a certain type of compound, there is insufficient information to make valid

predictions of head-loss based on physical or chemical characteristics of the

containment mixture of materials.

D-14
Part 11.

In this portion of the report, the individual tests and their results are evaluated.

Three parameters not included in the test conditions that will have a significant effect on

the conclusions reached are:

*Radiation Field (a flux of approximately 1012 e/cm2 -sec in the fuel vicinity) in

addition to the gamma flux from the fuel (mega rad level)

*Presence of magnetite as an insoluble material which would be present in

concentrations of upwards of 50 ppmn in the post LOCA environment

*Presence of several ppm of hydrogen peroxide due to air-saturated-water

radiolysis in the fuel area

These conditions would favor the formation of an agglomerated precipitate that would

have a large density compared to the precipitates measured in these tests, and would

settle or be filtered more easily. The only way to determine whether the test represents

the post-LOCA condition is to add these additional items as test parameters.

The above comments apply to all five ICET programs.

Test# 1.

The introduction of chemicals into the loop simulates the containment spray initiation

process when NaOH would be used. The pH attained in the bulk fluid is representative

of what would be expected in this situation. In this test, 100% of the insulation was

fiberglass.

In section 4.3 SEM examined the effects of the test solution -on the fiberglass insulation.

However it does not appear that a control was run for this experiment, i.e., demnineralized

water soaking of the fiberglass that would assess whether the same type deposits would

form. This is relatively important since in containment the, humidity is about 100%

saturation during operation. This means that fiberglass will be moisture saturated while

in service. It would be important to distinguish what is caused post-LOCA and normal

operations.

Section 4.4 describes the grinding of concrete into dust prior to introducing it into the test

loop. This technique appears to be overly conservative. Although it is possible for

concrete to be ground up by a water jet during the LOCA, it would be rather limited due

to the short duration of the blowdown period and the relatively small surface area that

would be scoured. Once the material settled (and it most certainly would during the first

four hours) the concrete would begin to "heal" over, forming a protective coating of

CaCO3 over the open scar and over any deposited material. This would take place in

aerated waters in particular due to the enhanced solubility Of CO 2 in the post-LOCA

basic pH.

In Figure 43 the solubility of aluminum is plotted as a function of time. It is noted that

filtration through a 0.7 micron filter did not affect the filtered vs. non-filtered results so

that all samples after day 25 were not filtered. The solubility of AI(OH) 3 at pH 7.0 is 0.14

ppb, but increases substantially above pH 9.0 due to the formation of the complex

AI(OH) 4-

1. These compounds when heated will have waters of hydration removed and

condense to AIO(OH) [boehmite] or A1203 [alumina] depending upon the temperature.

D-15
The conditions to promote the formation of these materials will exist at the fuel surface,

which is at a much higher temperature than the titanium immersion heaters. ICET#1 has

the highest concentration of aluminum in solution as a direct result of the high pH

yielding a soluble aluminate complex.

One conclusion of the test was, "Most of the aluminum remained in solution and passed

through the 0.45 pm filter at 60 00, e.g., the aluminum did not settle." This conclusion is

consistent with the results of Test #1 conditions. It is important to note that once the

solution cooled, that a significant solubility effect was observed. The reheating of the

precipitated material during this test did not completely rea-dissolve the precipitate. This

is an important effect for this combination of materials, since the post-LOCA sump water

is passed through a heat exchanger that will significantly lower the temperature of the

solution. This will cause precipitation to occur in both the heat exchanger and other

portions of the RCS, that precipitate will then not completely redissolve. This

precipitated material may then act to trap or coprecipitate other species.

Qualitatively, the SEM photographs show that the precipitated material forms bridges

between the fiberglass fibers. These precipitates are somewhat structured, but this is a

very qualitative observation. The amount of material seen in these photographs may

have an effect on flow, but this would need to be specifically measured versus a clean

filter bed to determine any quantitative effects.

Test#2.

The test condition s were targeted for a pH of 7.3 using Na3PO4 (TSP).

The TSP is immediately injected into the test line, which flows over the test coupons in

the tank. This condition does not simulate the containment environment during the initial

4 hours. Immediately following the break, water to the spray header and the RCS will be

supplied by the RWST. This is borated water at a pH of approximately 4.2. TSP is

contained in baskets in the sump or surrounding the sump and slowly dissolves as the

volume of water from the break depletes the RCS and RWST inventory. Once the

inventory is depleted, containment recirculation phase begins. At this point (-30 minutes

later, depending upon the size of the LOCA) the pH 7.3 solution will come into contact

with the bulk of the materials in containment.

During the initial phase of containment spray for TSP based plants the pH of the spray

will be closer to 4.5 (due to the presence of some Li+ in the RCS). This will mean that

more dissolution of metals contacted will occur during that 30-minute period when the

TSP is not buffering the containment spray.

The non-detectable concentration of aluminum in the solution for Test #2 is consistent

with the presence of a mixture of very insoluble aluminum hydroxide and calcium

phosphate precipitates. As noted in the Test#1 discussion, the solubility at pH 7.0 is

approximately 0.14 ppb for aluminum hydroxide. This is much less than the detection

level for the ICP-AES analysis of 50 ppb. The limiting reagent in this test was the

phosphate as calcium and magnesium were found in solution as a soluble species.

The deposits on the aluminum metal coupons were found to be predominantly AI(OH)3,

with insoluble calcium, magnesium, sodium and silica materials. These additional

compounds were most likely coprecipitated with the aluminum hydroxide. Although the

appearance of the coupons indicates significant weight gain due to precipitate

D-16
deposition, generally speaking, the weight loss/gain by the coupons is going to be of little

analytical value. The real value is in identifying the qualitative nature of the deposits

(see pages 45-50 in the ICET #2 Report). The amorphous, precipitated material

attached well to the fiberglass fibers and appears that it would provide significant

impedance to water flow through a debris bed comprised of these fibers.

A significant quantity of white precipitate consisting of calcium phosphate and aluminum

hydroxide were found in the bottom of the test tank. Although this material precipitated

within the first day, its amorphous nature, density and attachment to fiberglass materials

make it a concern for flow through sump screens.

Test#3.

Test#3 had an initial pH of -4.2 and used a mixture of 80% Cal.-Sil and 20% fibrous

insulation, as well as "latent debris". Based on the amount of concrete dust added (21.3

g) and the surface are of exposed concrete (solid) it is surprising that the pH did not

initially rise to close to 9.0. The concrete dust and soil that were added as "latent debris"

are may no be representative of what is present in the reactor containment building.

Those materials from concrete would provide a significant alkaline environment for water

in contact with them even over short period of time.

This starting condition is out of synchronization with the LOCA starting sequence. At the

onset the high velocity jet that would impinge the insulation would be closer to a pH of 5-

6.0 rather than 4.2. This is because the boric acid concentration during the blowdown

phase will be dominated by the ambient RCS boron concentration (1-1600 ppm) and not

the much higher (2300+ ppm) in the storage tanks.

As the leak progresses and the water collects in the sump the water washing over the

insulation is maintained at that pH. Until the containment recirculation spray initiates. At

that time a swing in pH from about 5.0 to about 8.0 then back to about 7.1 will occur over

the next 30.minutes to 4 hours as the water in the containment begins to mix to

equilibrium concentrations. During the time period prior to recirculation the insulation

would be lying in a stagnant pool of water on the containment floor or caught on another

component.

Table 2-1 shows the ratio of mass or ft3 of contaminant per ft3 of sump water. The ratio

of Cal-Sil to water mass (0. 137 ft3/ ft3

), in particular, seems very high. If this is scaled up

to the PWR case, the mass of insulation that would be getting soaked is about 7,400 ft3.

This particular parameter should be revisited to determine if the long-term recirculation

solution would contact this significant a mass of Cal-Sil.

The introduction of the TSP as a concentrate directly into the wetted insulation matrix

does not simulate what would happen in the containment situation. The concentration of

TSP would be far more dilute before it initially contacted the insulation due to dilution

with the remaining volume in the RCS and containment floor. Additional tests within the

ICETTest#3 matrix was performed which varied the concentrations of insulation used

with the matrix. The purpose was to ascertain if there would be significant differences in

the measured head loss when the solution is pumped through the in situ debris bed.

The results show that even though with lower concentrations of Cal-Sil insulation that

D-17
less head loss was initially experienced, the head loss continued to increases for the

duration of the test (approximately one hour). One variation of this test used the test

solution without the introduction of TSP. The purpose was to ascertain what the direct

effect of the TSP-Calcium precipitate had on head loss. Although an initial pressure

increase of -2.8 pounds was measured, it stabilized at that value and did not change for

the remainder of that test.

The concentration of boron in the test ioop increased by -18% during the 30 day trial.

The reason for this is most likely leaching from the fiberglass insulation. It is possible

that this would occur in the post-LOCA environment since the much of the containment

insulation would eventually become wetted. It would be important to determine if this is

the case (note this also happened in Test #4; a boron concentration increase of about

21%).

The results from Test #3 show that significant mass of precipitate can form in the

presence of TSP and the Cal-Sil insulation. The data presented indicate that this is a

mixture of Ca3(P0 4)2 and some other amorphous materials that either co-precipitate with

the calcium phosphate or are innately insoluble. The SEM/EDS results provide evidence

that at least part of the precipitated material is a carbonate. This is also significant in

that it adds to the mass of precipitate that will be formed from the carbon dioxide that is

'scrubbed' from the containment air. The TEM results were not able to provide

conclusive evidence for a specific type of crystalline material being formed.

Test#4.

The solution for Test #4 was made up to pH 10 using NaOH with a mixture of Cal-Sil

(80%) and Fiberglass (20%) insulation.

The high pH and presence of Cal-Sil yielded solution samples that had high TSS values

and turbidity, but low aluminum. A significant mass of precipitate was collected from the

screen at the tank bottom at the test conclusion. Although analysis of this precipitate did

not detect aluminum, a small quantity must be present form the initial solution

measurements. The precipitates of (calcite) CaCO 3, Lime (Ca(OH) 2)and tobermorite

(CaSiOA) most likely coprecipitated any aluminum from the fiberglass insulation. It is

also likely that the aluminum coupon was coated with a thin film of the tobermorite that

inhibited the further dissolution of the aluminum metal. The significant decrease in

turbidity over the first day identifies the flocculent nature of this mixed precipitate.

Additionally, the precipitate would 'stick' to surfaces like fibers of insulating material, but

it could not be found on materials like the nylon bag used to hold the unfractured

insulation pieces. This is most likely due to the 'common ion' effect (decreasing

localized solubility) that exists at the surface of the insulating materials (containing one

of the precipitate ions) while in other materials this cannot occur. This is also seen in the

metal test coupon photographs taken at the end of the 30-day period. The amount of

deposited material is minimal because of this lack of 'common ion' effect.

As compared toTest#3 the precipitated material in Test#4 was more crystalline.

Crystalline precipitates are less likely to cause attract significant amounts of other

materials and block flow, than are amorphous, hydrated gels.

D-18
Test#5.

This test used sodium tetraborate as the chemical additive for the spray system. Only

fiberglass insulation was used for the test. In general, very little mass of precipitated

material was observed over the 30-day test. These materials were composed of sodium

aluminum and silicates.

Borax was added before the spray phase began. Borax is a constituent in "icecondensers", and would only be added into the mix after the spray phase had initiated.

Thus the initial interaction of the 'blowdown" liquid with containment materials would be

with acidic borated solution. The addition of boric acid with the components in the

initiation of the test is out of sequence with actual LOCA conditions. It would take at

least 2 hours for the pH to approach 8.0 in the containment sump. Thus the interaction

of the RCS with the containment metallic components would yield additional metal ions

in solution (lower pH generally will favor more significant dissolution of the metallic

components).

The step decreases in aluminum on days 14 and 21, and the step increase in calcium on

day. 25, appear to be unrelated. This type of behavior is not expected in a system, which

has solid material in excess with a soluble counterpart (i.e., a saturated solution). These

changes do not appear to correspond to system changes during those time periods that

have been noted in the report thus far.

The significant change in appearance of the coupon materials and the general weight

loss is evidence for corrosion occurring in this chemical environment. The qualitative

analysis of the aluminum coupons shows deposition of some iron and zinc corrosion

products. The exception to this was for the concrete 'coupon' which showed a large

weight gain. This is presumably from the deposition of sodium-alumino-silicates.

The rise in aluminum concentration over the first 14 days is consistent with the small

amount of hydrogen gas generation during that same period. The continued presence of

aluminum in solution, and the lack of additional hydrogen generation after day 18,

suggests that the corrosion film that was observed on its surface has mitigated the

aluminum corrosion.

Copper and iron corrosion played a part in the inhibition of the aluminum corrosion. The

copper concentration in solution was constant after about 8 days at 0.7 ppm. The iron

concentration either in the filtered or unfiltered solution was undetectable.

The qualitative effect of the precipitated material was that it formed a more structured

solid on the fiberglass surfaces than was observed in previous tests (especially ICET#3).

The mass of material observed was significantly smaller. Both of these observations

generally support the notion that flow through the debris bed on a screen would be less

impeded with this chemical combination in the post-LOCA environment.

D-19
Conclusions

The ICET test clearly shows that there are a variety of different chemical environments

formed when containment spray is initiated and interacts with materials within the

containment building. The effects observed which are of note are:

" In all cases insoluble precipitates are formed as a result of the containment spray

chemicals reacting with insulation and metallic components in the containment

building

" The precipitated materials are different depending upon the type of spray

chemical and the type of insulation.

* Aluminum metal corrosion contributes most significantly to the dissolved metal

concentration of the post-LOCA environment

" Significant concentrations of magnesium, silica and calcium may be leached from

the two insulating materials used in these tests

" The corrosion of metal coupons (with the exception of aluminum) used in these

tests show that in the 30-day trial that their contribution to the metal loading in

solution is small, but that they can provide a surface for the adherence of

precipitated materials

Plant specific characteristics will impact how the results of these tests can be used to

assess the acceptability of current sump and screen designs.

It is important to note that although the different classes of post-LOCA spray have been

identified, not all containment materials have been tested in these programs. Each PWR

will need to carefully examine all materials that could potentially come into contact with

post-LOCA spray, and assess the effects of leaching, precipitation of leached ions and

coprecipitation of ionic substances on these plant specific materials.

The most significant impacts on post-LOCA sump chemistry occur with systems that

have both TSP and Cal-Sil type insulation. The formation of amorphous calcium

phosphate and the apparent coprecipitation of other materials create a significant

impediment to forced water flow in the system used in the ICET programs.

The information in the ICET programs provides plant personnel with a direction for

focusing any testing that they may need to perform if modifications to their sump screens

are going to be made. Each plant should use their plant specific information as part of

test program for assessing feasibility of design. The methods of analysis used in the

ICET programs that should be considered as part of the design testing are:

*SEM

*XRD

*TSS

*Turbidity

*Metal concentration (by an lOP or related spectroscopic technique)

*EDS

These analyses will help to characterize the precipitated materials and establish specific

bases for flow testing.

D-20
Recommendations

1. Chemical constituents that have not been simulated are:

a. Initial RCS silica concentrations up to 1 ppm (and in the refueling storage

tanks of several PWRs this concentration may be as high as 5-10 ppm),

b. CRUID concentrations (which will contain mixtures of nickel ferrite,

magnetite, nickel oxide and hematite) of up to 100 ppm from the

thermal/hydraulic transient caused by the LOCA, and

c. The presence of hydrogen peroxide resulting from the gamma radiation

field of the core.

Consideration should be given to include these parameters in the experimental

simulations.

2. The relatively high concentration of TSP used at the start of the ICET tests, is

very conservative compared to the manner in which the materials would finally

mix in the sump. Consideration should be given to inject the TSP into the loop at

a lower concentration over a longer period of time to simulate more closely actual

post-LOCA condition.

3. Temperature profiles of the reactor coolant system have not been modeled. The

temperature profiles will have a significant effect on the rate and type of

precipitate that is formed, and also where the precipitates will be formed. This

may have a significant effect on the head loss modeling. These temperature

profiles should be included in the test loop.

4. Radiation fields from the nuclear fuel also have not been modeled. Free radical

formation will have a significant effect on the type of compounds that can be

formed and where they will precipitate. One possible resolution to this issue may

be to take the solids formed from the ICET Test Runs and expose them to high

radiation doses for several hours, then re-examine their morphology. This would

help to assess if there is any effect by the high intensity radiation fields within the

coolant system.

5. The analytical techniques used to characterize the chemical compounds that

were formed are complementary. Taken as a whole they are the most extensive

analytical tools that could be used for this assessment and are adequate to

address changes that would be observed during the ICET program.

The only additional test I could recommend would be ETIR of the colored

materials/solution to identify the chemical identity of those colored materials. It

should be noted that in a strong radiolytic field, most color-bearing organic

materials would be transformed to carbon dioxide and water.

6. The mass determination of the coupons yields little quantitative information (if

any). I would recommend deleting this part of the coupon analysis unless a total

mass balance approach is performed. Coupons should be used strictly for

qualitative assessment of what transformations of the coupon materials occur

and what insoluble products are formed or precipitate on these surfaces.

7. The test loop as designed does not allow for insoluble materials to drop out, as

would occur during transit along the containment floor following a LOCA. The

D-21
relatively long flow paths and impediments to flow caused by structural

components are not simulated. Recommend using the modification as shown in

Attachment 1.

8. The interior surface of the test ioop does not simulate the conditions of the

interior surfaces of a PWR. Recommend that the test loop internal surfaces that

are designed to mimic the internal PWR surfaces be treated with the initial test

solution at 550OF and 2200 psig before additional testing is performed.

9. The concentration of boron in the test loop, in Tests 3 and 4 increased by -18%

and 21 % respectively, during the 30 day trial. The reason for this may be

leaching from the fiberglass insulation. It is important to determine if this is the

source of the increase, or if not where the increase is coming from.

10. In Test 5, Borax was added before the spray phase began. Borax is a

constituent in "ice-condensers", and would only be added into the mix after the

spray phase had initiated. This is out of sequence with actual LOCA conditions.

This should be corrected in a subsequent run of this test.

11. The ICET tests did not include all combinations of materials (i.e., insulation) in

the reactor containment buildings. If additional tests are performed, other

materials should be put into the mix to help assess the extent of materials that

may be precipitated.

12. The submerged mass/volume of Cal-Sil insulation involved in the long-term

testing is greater than expected during a post-LOCA recovery. Although this is a

conservatism in the ICET programs, it would be beneficial to identify more

realistic submerged materials and th~eir effect compared the existing information.

D-22
Attachment I

Height of

Water - 1/4

height of the

screen

D-23

Appendix E

Final Report

Characterization of Chemical and Corrosion Effects Potentially

Occurring Inside a PWR Confinement Following a LOCA

By

Digby D. Macdonald

3222 Shellers Bend Rd.

State College, PA 16801

Submitted to

Paulette Torres

Robert L. Tregoning

Division of Engineering Technology

Office of Nuclear Regulatory Research

US Nuclear Regulatory Commission

Washington, DC 20555-0001

June 28, 2006

E- 1
Abstract

A review is presented of the fundamental physico-electrochemistry of those processes

that are reckoned to contribute to the evolution of the chemical properties of the containment

pool after a LOCA (Loss of Coolant Accident) in a Pressurized Water Reactor (PWR). The

processes and issues considered include the establishment of the redox and corrosion properties

of the environment, due to the radiolysis of water and the presence of hydrogen from the PWR

primary coolant and the oxygen contained within containment; the impact of the redox potential

on the chemistry of the pool 'in a post-LOCA environment; co-precipitation of other species with

FeOOH, AlOGH, etc; Ostwald ripening; the Schikorr reaction and the generation of hydrogen in

situ; the pH of zero charge (PZC) and coagulation; y-AIOOH formation; precipitation on fibers;

thermal hydrolysis of organic material; the maximum particle size that can be tolerated; the

reason(s) why a bimodal distribution exist might exist in particle size; and the corrosion of

aluminum. These are all issues that figure prominently in the generation of solid products that

have the potential for clogging the sump pump screens that are designed to enable recirculation

of the coolant ejected from the primary circuit upon a LOCA, the injection of emergency core

coolant into the core, and the functioning of the building spray system that is designed to remove

the fission product, iodine. The purpose of this report is not to provide a time-line for the events

that occur during a LOCA, but rather to identify and articulate some of the fundamental

processes involved. This process does, however involve an assessment of how well the

Integrated Chemical Effects Tests (ICETs) and the analytical simulations were able to reasonably

reproduce the effects that might occur in an actual LOCA. It is concluded that the ICETs and

analytical simulations have serious shortcomings, because redox potential effects and the impact

of radiolysis were not taken into account. For example, the redox potential, which arises from

non-equilibrium processes, cannot be simulated analytically using current chemical modeling

codes, because they lack an effective mixed potential model. The redox potential determines the

driving force for the transition between different oxidation states. Possibly, of much greater

importance, is the radiolytic conversion of nitrogen from the ambient containment air into nitric

acid, because preliminary modeling work indicates that, if the dose rate is sufficiently high in the

pool, the production of nitric acid may overwhelm the buffering capacity of the boric

acid/lithium hydroxide in the pool. If this were the case, the pH would drop precipitously and

the conditions would lie well outside those simulated in the ICETs and in the analytical modeling

performed to date. Indeed, if the pH drops by the amount predicted for a high (but realistic)

gamma-photon dose rate (16 Oradlh), massive corrosion of structural materials might be expected,

which, in turn, might have unforeseen consequences for the operation of vital systems that

maintain effective cooling of the core. Therefore, it is recommended that radiolytic acidification

of the pool and changes in the redox properties be explored to determine the exact impact that

they might have on pool chemistry.

E-2
Executive Summary

A review is presented of the fundamental physico-electrochemistry of those processes

that are reckoned to contribute to the evolution of the chemical properties of the containment

pool after a LOCA (Loss of Coolant Accident) in a Pressurized Water Reactor (PWR). Eleven

critical issues were identified: (1) The evolution of the electrochemical properties of the

containment pool, and scoping calculations were performed using the radiolysis/corrosion

potential code, FOCUS, and variants thereof, that was developed to model electrochemical

phenomena in the primary coolant circuits of Boiling Water Reactors (BWRs) and PWRs; (2)

Co-Precipitation of Other Species with FeOOH, AlOOH, etc.; (3) Ostwald Ripening, which

transforms newly precipitated* phases into thermodynamically more stable phases; (4) the

Schikorr reaction and the in situ generation of hydrogen; (5) the pH of zero charge (PZC) and its

role in coagulation; (6) y-AIOOH formation; (7) precipitation of solid particles and corrosion

products on fibers; (8) degradation of organic materials; (9) whether there is a particle size that

can be tolerated; (10) possible reasons why a bimodal distribution exists in the particle size; and

(11) the corrosion of aluminum. Additionally, an assessment was made of the effectiveness of

the experimental programs that were supported at various national laboratories (ANL, LANL)

and at the Center for Nuclear Waste Regulatory Analysis (CNWRA) at the Southwest Research

Institute in San Antonio, Texas, in addressing vexing issues and in simulating the chemical

processes that might 'occur in a containment pool after a PWR LOCA.

The processes. and issues considered include the establishment of the redox and corrosion

properties of the environment, due to the radiolysis of water and the presence of hydrogen from

the PWR primary coolant and the oxygen contained within containment, and the impact of the

redox potential on the chemistry of the pool in a post-LOCA environment. This issue is judged

to be particularly important, because the redox potential controls the oxidation states of all

components in the pool and the valency of dissolved species. The production of hydrogen

peroxide via the radiolysis of water is expected to raise the redox potential substantially, thereby

promoting precipitation of oxides, oxyhydroxides, and hydroxides through the formation of more

highly charged cations (Fe 3+ versus Fe2+) . The second overriding issue arises from the

tendencies of surfaces to acquire electrical charge through the protonation (at low pH) or

ionization (at high pH) of surface hydroxyl groups to yields positive and negative charges

respectively. The pH at which the net charge is zero is known as the "pH of zero charge" (PZC).

If a multi-component system contains particles of opposite charge, the particles will coagulate to

form macroscopic precipitates. Even if the particles are not oppositely charges, increasing the

ionic strength of the medium will cause the electrical double layers to shrink to the extent that

the attractive van der Waal forces will overcome electrostatic repulsion and coagulation will

occur, as in the Alum water clarification technology. The third, principal issue that is addressed

is corrosion, particularly the corrosion of aluminum. This phenomenon is expected to be a

significant source term for solid materials in the containment pooi after a LOCA. It is noted that

the theory of corrosion is highly developed and that meaningfuil predictions of corrosion rate can

be made if the corrosion evolutionary path can be defined (i.e., the path in terms of various

parameters that the system travels after the LOCA). The important point is that these are all

issues that figure prominently in the generation of solid products that have the potential for

clogging the sump pump screens and pumps that are designed to recirculate the coolant ejected

from the primary circuit upon a LOCA, the emergency core coolant, and the building spray that

is designed to remove the fission product, iodine, through the core to remove decay heat. The

E-3
purpose of this report is not to provide a time-line for the events that occur during a LOCA, but

rather to identify and articulate some of the fundamental processes that require attention and

analysis, if a reasonably accurate picture of the post-LOCA environment in a PWR is to be

developed.

A number of recommendations were formulated that might advance the technology of

predicting the evolution of the containment pool environment after a. LOCA. The principal

recommendations are as follows:

Equilibrium models must be used with great caution, because the environment produced

by a LOCA is unlikely to be at equilibrium, at least during the initial stages. Furthermore, the

processes that occur during corrosion, precipitation, and ripening are generally slow, as has been

shown in some of the work carried out by ANL. The kinetics of many of these processes are

such that the system may still be far from equilibrium as it enters the recirculation system.

Accordingly, equilibrium calculations need to be bench-marked to the greatest extent possible

against experiment to assess the reliability of the thermodynamic equilibrium codes.

Given the likelihood that equilibrium models may not be appropriate, emphasis should be

placed on developing kinetic models for the precipitation and ripening (coagulation) processes.

These models must recognize the most important driving force for coagulation; the charge (sign

and magnitude) that develops on the surfaces of particles, as characterized by the zeta potential

and the PZC (pH of zero charge). None of the commercial codes employed by SwRI appear to

have the necessary sophistication to effectively model non-equilibrium precipitation phenomena.

The possible generation of hydrogen from the Schikorr reaction

3Fe(OH)2 -4 Fe3O4 + H2 +.2H 2 0

and related chemical transformations should be explored, as they might contribute significantly

to the inventory of hydrogen in containment immediately after a LOCA and to the inventory of

magnetite (Fe3O4) in the system.

.Realistic and viable models for the corrosion of aluminum, iron, and zinc, and of the

dissolution of concrete and polymeric materials in contact with hot coolant under high mass

transfer rate conditions (e~g., due to impinging jets) need to be developed that are capable of

predicting corrosion rates under LOCA environmental conditions.

The hydrothermal hydrolysis of various organic/inorganic coating and insulation

materials needs to be explored under conditions that realistically simulate a LOCA. It is

expected that hydrothermal hydrolysis will partially de-polymerize polymeric materials,

producing materials ranging from particles. to gels. These materials need to be screened for their

physical and chemical properties and, in particular, for their tendencies to "set" into more

resilient forms.

The models that are produced to predict corrosion rates and phase properties must be, to

the greatest extent possible, deterministic in nature. Thus, a deterministic model is one whose

output (prediction) is constrained by the natural laws to that which is physically. viable. These

constraints are generally the conservation laws, such as the conservation of mass, charge, energy,

and momentum.

Development of a radiolysis code specifically for a containment pool is absolutely

essential, since the redox potential controls the speciation within the pool. This model should

incorporate boric acid/LiGH + TSP (tni-sodium phosphate) models for estimating the pH. The

model should be calibrated and evaluated against laboratory experiments to establish efficacy.

A thorough analysis should be carried out to estimate the likely y-dose rates in the containment

pool as a function of time after a LOCA in a PWR. The contribution of a-dose rate from fission

E-4
products also needs to be evaluated. The latter is completely ignored in the present analysis and

the former (y-dose rate) is little more than a guess. No information of guidance on this subject

could be found in the open literature.

A better database for the kinetics of the hydrogen electrode reaction, the oxygen electrode

reaction, and the hydrogen peroxide electrode reaction needs to be established. Some of the

"raw" data are already in the literature, but the information is incomplete and the data are

generally not in a form that is readily interfaced with radiolysis/redox potential models. In some

cases, however, the required data must be experimentally measured.

It is concluded that the ICETs and analytical simulations have serious shortcomings,

because redox potential effects and the impact of radiolysis were not taken into account. For

example, the redox potential, which arises from non-equilibrium processes, cannot be simulated

analytically using current chemical modeling codes, because they lack an effective mixed

potential model. The redox potential determines the driving force for the transition between

different oxidation states. Possibly of much greater importance is the radiolytic conversion of

nitrogen from the ambient containment air into nitric acid, because preliminary fniodeling work

by the author indicates that, if the dose rate is sufficiently high in the pool, the production of

nitric acid may overwhelm the buffering capacity of the chemicals in the pool. If this were the

case, the pH would drop precipitously and the conditions would lie well outside those simulated

in the ICETs and in the analytical modeling performed to date. Furthermore, if the pH drops to

the extent predicted by preliminary scoping calculations, massive corrosion of structural

materials might be expected with unforeseen consequences for the operation of vital systems that

maintain effective cooling of the core.

E-5
Contents

Abstract................................................................................................ E-2

Executive Summary.................................................................................. E-3

List of Figures ........................................................................................ E-7

List of Tables......................................................................................... E-8

1 . Introduction .................................................................................. E-9

2. Charge to Reviewers ........................................................................ E-9

2.1. Peer Review Objectives ............................................................ E-9

2.2. Principal Technical Questions .................................................... E-10

2.3. Motivation........................................................................... E-10

3. Reviewer's Expertise ....................................................................... E-1 1

4. Review of Simulations...................................................................... E-I1I

4.1 Integrated Chemical Effects Testing (LANL) ................................... E- 12

4.2 ICET Follow-up Testing and Analysis (LANL)................................. E-14

4.3 Chemical Speciation Prediction (CNWRA) ..................................... E- 14

4.4 Accelerated Chemical Effects Head Loss Testing (ANL) ...................... E- 15

4.5 Limitations of the Current Tests .................................................. E-15

5. Issues

5.1.

5.2.

5.3.

5.4.

5.5.

5.6.

5.7.

5.8.

5.9.

5.10.

5.11.

.............................................................................. E-17

Electrochemical Properties of the Containment Pool ........................... E- 17

Radiolytic Yield................................................................ E-19

Chemical Reactions............................................................ E-2 1

Convection................................... .... E-24

General Solution of the Equations............................................ E-24

Mixed Potential Model and the Redox and

Electrochemical Corrosion Potential ..................................... E-26

Impact of Radiolysis in the Containment Pool .............................. E-3 1

Co-Precipitation of Other Species with FeOOH, AlOOH, etc ................. E-39

Ostwald Ripening................................. I.................................. E-39

Schikorr Reaction Generates Hydrogen In Situ.................................. E-40

PZC and Coagulation .............................................................. E-40

y-AlOOH Formation ................................................................ E-43

Precipitation on Fibers ............................................................. E-44

Thermal Hydrolysis of Organic Materials ....................................... E-44

Is There a Particle Size that Can be Tolerated9 ............. . . . . . . . . . . . . . . . . . . . . . E-45

Why Does a Bimodal Distribution Exist in Particle Size?9 ....... . . . . . . . . . . . . . . E-45

Corrosion of Aluminum............................................................ E-45

6. Recommendations........................................................................... E-49

Appendix 1 ........................................................................................... E-52

E-6
Figures

Figure 1. Summary of the defect generation and annihilation reactions envisioned at the

interfaces of the barrier oxide layer on a metal, according to the Point Defect

Model (PDM). V,ý- cation vacancy in the film; v. = vacancy in the metal

substrate; M(X+ cation interstitial;, VO'* = oxygen (anion) vacancy; MI-+ (aq)

cation in solution; MM cation in cation site on the metal sublattice; 00 oxide

ion in anion site on the oxygen sublattice; and MO., 2 stoichiometric barrier

layer oxide. Note that Reactions 1, 2, 4, 5 and 6 are lattice conservative processes

(they do not result in the movement of the interface) whereas Reaction 3 and 7

are non-conservative [D. D. Macdonald, Pure Appl. Chem., 71, 951 (1999)] .... E-27

Figure 2. Comparison of calculated and measured ECP for the Leibstadt BWR.

The "measured" data were acquired in a test cell attached to the

recirculation piping ..................................................................... E-29

Figure 3. Calculated ECP vs. [02] or [H 202] for a simulated PWR coolant system.

T = 320 0C, [H12] = 25cc(STP)/kg(H20), [B] = 1000 mg/kg, [Li] = 2 mg/kg,

pH =7.36, flow velocity = 100 cmls, channel hydrodynamic

diameter = 100 cm...................................................................... E-30

Figure 4: Schematic plot of surface charge density versus pH for two surfaces in

contact with the same aqueous solution .............................................. E-37

Figure 5: Schematic representation of the electrical double layer in the solution

side of an oxide/solution interface..................................................... E-3 8

Figure 6: Point defect model for the anodic oxidation of aluminum in aqueous solution.

The species Al, A13~, vA, AlA!, Vý*, Al13+, and 00 represent aluminum metal,

an aluminum cation interstitial, a vacancy in the metal substrate, an aluminum

cation on the cation sublattice of the barrier layer., an oxygen vacancy on the

anion sub lattice of the barrier layer, an aluminum cation in solution, and an

oxygen anion on a normal anion site on the anion sublattice, respectively. The

subscripts "oP' and "b" designate outer layer and bulk solution locations......... E-38

Figure 7: Schematic plot of surface charge density versus pH for two surfaces in

contact with the same aqueous solution .............................................. E-41

Figure 8: Schematic representation of the electrical double layer in the solution side

of an oxide/solution interface.......................................................... E-42

Figure 9: Point defect model for the anodic oxidation of aluminum in aqueous solution.

The species Al, A VA3, v AlA, Vý*, A131 , and 00 represent aluminum metal,

an aluminum cation interstitial, a vacancy in the metal substrate, an aluminum

cation on the cation sublattice of the barrier layer, an oxygen vacancy on the

anion sublattice of the barrier layer, an aluminum cation in solution, and an

oxygen anion on a normal anion site on the anion sublattice, respectively. The

subscripts "or' and "b" designate outer layer and bulk solution locations......... E-47

E-7
Tables

Table 1. Radiolytic Yields (G Values) for Primary Radiolytic Species....................... E-20

Table 2. Reaction set used in the PWR radiolysis model ...................................... E-21

Table 3. Preliminary calculation of the generation of hydrogen peroxide, oxygen,

and hydrogen in water at 30'C as a fuinction of ambient oxygen concentration

(concentration in the absence of radiolysis), pH, and y-dose rate ................... E-3 1

E-8
1. Introduction

By any metric, a loss of coolant accident (LOCA) in a Pressurized Water Reactor would

be a catastrophic event, potentially resulting in the over-heating of the core to the extent that a

"'melt-down" might occur. Such a possibility has been anticipated, of course, and the coolant

system has been designed to provide for emergency core cooling via a gravity-fed supply of

water that can be used to flood the core and remove the heat from the continuing fission and

decay processes. However, the supply of emergency coolant is limited and it is insufficient to

remove the decay heat from the core that continues to be generated well after the fission process

has been shut down. Accordingly, the system relies upon the recirculation of the coolant that has

been injected from the LOCA onto the containment floor, together with the emergency core

coolant from the same location, to remove the decay heat. The free flow of the coolant from the

containment floor through the pumps, screens, and filters is vital for the success of this strategy.

The occurrence of a LOCA, with water from the pipe break being directed onto a variety

of surfaces, including concrete, steel, plastic (polymer, including coatings and paints), and

aluminum, will result in a complex mixture of compounds that could further react to produce a

veritable "soup"~. The high temperature of the water is assumed to result in significant

dissolution and corrosion, resulting in the formation of precipitates and gelatinous material that,

potentially, might block filters and screens and hence impede flow in the recirculating system.

Thus, the goal of this program is to provide critical analysis and review of experiments that are

being carried out at various national laboratories or affiliated units to identify the reaction

products that may form by hydrothermal hydrolysis and other processes, resulting from the

impingement of high temperature coolant [boric acid + lithium hydroxide solution] on the

structural materials. The exact conditions (temperature and chemical composition) of the

impinging coolant are somewhat uncertain, because of adiabatic expansion and flashing of the

coolant from the break lowers the temperature and because much of the resulting chemistry

remains unknown or not understood.

2. Charge to the Reviewers

The charge to the reviewers was presented by the Nuclear Regulatory Commission (NRC)

(Paulette Torres and Robert L. Tregoning) in the kick-off meeting that was convened at the

Argonne National Laboratory on August 18-19, 2005. The charge comprises specific tasks and

issues that are best summarized by adopting, verbatim, the material presented by the NRC, as

follows:

2.1. Peer Review Objectives

Review technical adequacy of RES-sponsored activities related to chemical effects in PWR

sump pool environments. The Technical Review Areas (TRAs) are listed as follows:

* Integrated Chemical Effects Testing (ICET): LANL

* ICET Follow-up Testing and Analysis: LANL.

* Chemical Speciation Prediction: CNWRA.

* Accelerated Chemical Effects Head Loss Testing: ANL.

E-9
2.2. Principal Technical Questions

" ICET

* Have the principal sump pool variables which affect chemical by-product

formation in the post-LOCA environment been adequately simulated?

* Many ICET variables were held constant during the experiments. How would

changes in the most important constant variables affect chemical product

formation?

" What variables or materials not simulated by the ICET testing may have the most

impact on chemical product formation (e.g., coatings, free insulation, flow

through sediment and other materials on sump screen, galvanic effects) and how

should their effect be characterized by testing or analysis?

" Were the methods used within the ICET program to characterize and analyze

chemical by-products sufficient?

" Analytical Simulation

" Is the speciation analysis expected to provide reasonable predictions of chemical

product formation over a range of possible sump environments?

* Is the plan for benchmarking these codes using small-scale testing and the ICET

results appropriate?

" What is the most appropriate way to measure the uncertainty associated with these

codes?

* Head Loss Simulation Testing & Analysis

" Is the accelerated head loss testing approach viable for evaluating the effects of

Imultiple chemical environments quickly?

" What is the best method' for incorporating for time-dependent effects (e.g., .material aging, evolving chemical environments) in simulation testing?

* What metrics are most appropriate for evaluating the results of simulated

chemical products with those that formed during the ICET program?

" Are correlations available, or can they be developed, which can predict the

associated head loss if important physical characteristics of a chemical by-product

are known?

2.3. Motivation

" NRC Policy

" Encourage formal and independent peer review of research products consistent

with the nature, importance, and timeliness of the information to be disseminated.

" The results of peer reviews should be made visible.

" Sump Pool Chemical Effects: Logical Peer Review Topic.

" Relatively new research area (2003) with an aggressive resolution schedule

(2007).

" Technical area is sufficiently complex to warrant independent assessment and

consultation.

" Research could significantly affect resolution path.

E- 10
3. Reviewer's Expertise

The author of this report is an electrochemist/corrosion scientist who has 30± years of

technical experience in the nuclear industry. In particular, the author has been extensively

involved in the modeling of the chemistry and electrochemistry of heat transfer circuits in BWR,

PWR, and CANDU reactors. This modeling work has resulted in the prediction of the

accumulated damage due to pitting corrosion, stress corrosion cracking, and corrosion fatigue

using deterministic models whose outputs (p~redictions) are constrained by the natural laws

(conservation of mass, charge, etc). The author has also developed the Point Defect Model and

Damage Function Analysis, which provide the most current view of the phenomena of passivity

and passivity breakdown and the accumulation of localized corrosion damage, which are critical

issues in the present study. Finally, the author has spent three decades studying the properties of

high temperature aqueous solutions and has been instrumental in developing methods for

measuring pH (at a maximum temperature of 5280C), [H 2], [02], and redox and corrosion

potential at temperatures exceeding the critical value (374.1 50C). A resume for the author is

appended to this report.

4. Review of Simulations

An important function of the review was to assess the effectiveness of work carried out at

the Argonne National Laboratory (ANL), Los Alamos National Laboratory (LANL), the Center

for Nuclear Waste Regulatory Analysis (CNWRA) at the Southwest Research Institute (SwRI),

San Antonio, Texas, and at the University of New Mexico to address some of the issues related

to chemical effects in the containment pool post LOCA. This work was performed to support

resolution of Generic Safety Issue (GSI)- 191, which addresses the potential for post LOCA

debris accumulation on PWR pump screens to interfere with the emergency-core-cooling-system

(ECCS). The specific task was to address the role that might be played by chemical processes

("chemical effects") in the interference.

Both experimental work and thermodynamic simulations have been performed to provide

a broad basis for predicting chemical processes in the pool as a function of time after a LOCA.

While these data provide a basis for predicting what might develop in the pool they are, by

themselves, insufficient to develop a thorough understanding of the chemical processes that

might occur, because: (1) The processes that are expected to occur in the pooi are much more

complex than can be reasonably simulated in "ideal" laboratory experiments; (2) Assumptions

made in the simulations (e.g., equilibrium in the case of thermodynamic calculations) may not

hold in practice, or: (3) Certain phenomena [e.g., radiolysis due to fission products ('y- and axemitters)] may be difficult or even impossible to accurately reproduce in the laboratory and may

not be incorporated in current, commercially-available codes. Nevertheless, selected

experiments provide the means of checking expected behavior and hence of building confidence

in the predictions of pool behavior as the containment environment evolves after a LOCA.

ICETs (Integrated Chemical, Effects Tests) were designed to address certain aspects of

the evolution of the chemistry of the containment pool after a LOCA. These tests sought to

reasonably simulate the chemical properties of the pool, so that the responses of certain materials

(e.g., fiberglass insulation, concrete, electrical insulation, and various metals and alloys) could be

assessed. These tests were carried out with an initial chemical environment containing 2800

mg/L of boron as boric acid, 100 mg/L of HCl, and 0. 7 mg/L of lithium as LiOH. The tests were

generally carried out over 30 days at a temperature of 600C, and pH control was affected by the

E-1 1
addition of NaGH, TSP (tri sodium phosphate), or TSB (tetra sodium borate). The principal

analyses that were performed were chemical (total concentrations of elements), physical (e.g.,

pressure drop, viscosity, total suspended solids, and turbidity measurements), and

microscopic/visual examination. Thermodynamic simulations, including speciation calculations,

were also performed.

4.1. Integrated Chemical Effects Testing (LANL)

In this first ICET (ICET # 1), pH control was affected by the addition of NaOH with a

target pH of 10. The pH was found to decrease during that test, such that after 30 days the pH

was about 9.4. The drop in pH corresponds to the consumption of protons by metal corrosion

and oxide dissolution (concrete, fiberglass), even though the solution is strongly buffered. The

materials exposed to the environment were scaled amounts of thermal insulation (NUKON T M

fiberglass), 373 metal coupons, and one concrete sample. The metals included representative

amounts of aluminum, copper, carbon steel, and zinc. Representative amounts of concrete dust

and other latent debris were added to the system to simulate in-service conditions. Parameters

that were measured included pH, turbidity, total suspended solids, kinematic viscosity, and shear

dependent viscosity. The test incorporated an initial, 4-hour spray phase to simulate the LOCA.

Apparently, no attempt was made to reproduce the redox conditions, through the addition of

hydrogen, and through the addition of hydrogen peroxide to simulate the impact of radiolysis.

The solution apparently remained clear during the test, but a precipitate formed upon

cool-down. The concentration of aluminum in the solution was found to build-up to

approximately 350 mg/L over the 30-day exposure period. The most important finding of this

test was the formation of a web-like precipitate that spanned individual fibers. This precipitate

grew more expansive with time and could represent a significant impediment to flow through the

screen. Finally, an increase in the viscosity of cooled samples was detected after four days. The

increase in viscosity is almost certainly due to polymerization of hydrolyzed cations in a

precursor step to coagulation and precipitation.

In the opinion of this reviewer, ICET # 1 was carefully planned and provided a

reasonable simulation of the pool without the involvement of TSP or TSB, yet contained

representative amounts of many of the solid phases of interest. The results demonstrate the

importance of precipitation processes and indicate that polymerization, coagulation, and

precipitation are far from instantaneous process and, indeed, are irreversible processes that are

far from equilibrium. This finding has important implications for the modeling of the pool using

thermodynamic equilibrium models (see below). However, as in all of the ICETs, the failure to

realistically simulate the redox conditions is considered to be a significant shortcoming.

ICET #• 2 was generally similar to ICET #t 1, except that pH control was affected by TSP

(tri sodium phosphate) with a target pH of 7. This test appeared to differ from ICET #t 1 in that

no aluminum was detected in the solution, but significant amounts of Si, Ca, Mg, and Zn were

found. Furthermore, large amounts of white deposits (nominally 0.125 to 0.250 inches thick)

were found to form on the submerged galvanized steel, aluminum, and zinc specimens. These

results indicate that the TSP inhibits the corrosion of aluminum (not a surprising result), but also

that it inhibits the dissolution of aluminates (e.g. calcium aluminate?) from concrete and other

phases, most probably by forming a metal phosphate of lower solubility on the surface. Again,

the greatest objection to ICET #t 2 is the apparent lack of appreciation of the role played by the

redox potential in determining the solution chemistry in the pool and the lack of appreciation of

the role of radiolysis with respect to establishing the redox potential and pH.

E- 12
The third ICET (ICET # 3) was similar to ICET #f 2, except that the target pH (established

with TSP) was 7.0. Process control comprised monitoring on-line recirculation flow rate,

solution temperature, and pH. The flow rate and temperature were controlled at 25gpm and

140'F (600C), respectively. The pH of the solution initially rose to 7.32 four hours after the

addition of the TSP and the experiment ran uninterrupted for 30 days. No corrosion products

were visible in the solution at either the test temperature or at room temperature. However,

chemical analysis of the solution revealed the presence of Al, but of only trace amounts of Ca, Si,

and Na. Examination of the fiberglass specimens revealed chemical, products and the web-like

material spanning the fibers. Shear-rate dependent viscosity measurements showed that the

solution behaved as a Newtonian fluid, indicating the lack of significant amounts of hydrolytic

polymers that are precursors to precipitation. Again, no attempt was made to control the redox

potential or to simulate the impact of radiolysis.

ICET #f 4 was generally similar to ICET if 1, in that NaOH was used to control the pH.

The sodium hydroxide (6.65N) was added during the spray cycle, causing the pH to rise to 9.92

(in-line pH probe) at the end of the 4-hour cycle. Thereafter, the pH declined to 9.79 after 30

days of operation. The turbidity declined over the 4-hour spray period from about 1 3ONTU to a

little less than 4ONTU, indicating the agglomeration of colloidal particles into larger species and

eventually into precipitates. Thereafter, the turbidity remained constant at a very low value, for

the remainder of the test. This finding is consistent with a similar variation observed in the total

suspended solids (TSS), indicating that the formation and settling of solids occurs primarily

during the spray period. No significant changes were detected in the viscosity of the solution in

this test at either the test temperature (60 0C) or at 25 0

C. Finally, the concentration of dissolved

aluminum remained low (< lmg/L), but those of Ca (40 - 55mgIL), silica (0 - 200mg/L), and

sodium (6,000 - 12,0O0mgIL) were high (note that the initial concentration of Na+ was due to the

added NaOH, but, nevertheless, the sodium concentration doubled over the term . of the

experiment). The concentrations of zinc and copper were found to remain low (< 1 mg/L)

throughout the entire ICET if 4. These results all indicate that, because of the high pH, the

principal source of dissolved species is the concrete (sample and dust) with a possible

contribution from the fiberglass. However, and again, no attempt was made to simulate the

redox, properties or the impact that radiolysis might have on this important parameter or on the

pH.

in ICET # 5, the pH of the initial solution (6.48kg of boric acid + 10kg of borax + 0.284g

of LiOH) was modified by the addition of HCl to achieve a value of 8.2 - 8.4. The in-line pH

probe gave a value of 8.5±0.1 while the bench-top probe gave values that are slightly lower at

8.25±1-0.15 over the same period, possibly because of solution of carbon dioxide from ambient air

during the sampling procedure. In this case, the turbidity during the initial spray period

decreased slightly from 14NTU to about 12.5NTU; a much smaller decrease than in ICET if 4 at

a higher pH. This is a consistent finding and indicates that cation hydrolysis, polymerization,

agglomeration, and precipitation become more prevalent as the pH increases. At longer times,

the turbidity measured at 25'C was found to be consistently higher than that measured at the test

temperature of 60'C with the difference increasing with time. These data are indicative of

continued formation of colloids over the entire period of the test, particularly upon cool-down.

This finding is also consistent with the measured TSS (total suspended solids), which remained

constant at 15 - 30mg/L over the entire test. The viscosity at 25'C and at 60'C remained

constant during this test. The concentration of aluminum was found to build-up to about S0mg/L

over the term of the experiment, while the concentrations of Ca and SiO2 ranged over a few tens

E- 13
of mg/L. The concentrations of Cu, Zn, and Mg remained low (< lmg/L), while that of sodium

remained constant at 1150 - l400mg/L. These data are consistent with enhanced corrosion of

the aluminum metal coupons, probably because of the lower pH than employed in some other

experiments. Finally, the initiation of this test resulted in significant turbidity and precipitation,

resulting in the fouling of an in-line flow meter. Precipitates continued to form throughout the

entire test, particularly from solution samples removed from the system. Also, the submerged

metal samples appeared to be coated with a white precipitate. In this test, the rate of hydrogen

generation was monitored, but no attempt was made to relate th e hydrogen concentration to the

redox conditions.

4.2. ICET Follow-up Testing and Analysis (LANL)

The issues raised in this follow-up analysis have been largely dealt with in the material

presented above.

4.3. Chemical Speciation Prediction (CNWRA)

.Extensive thermodynamic simulations of chemical effects associated with PWR sump

screen blockage have been carried out by the Center for Nuclear Waste Regulatory Analyses at

the Southwest Research Institute in San Antonio, TX. [J. McMurray, et.al., "GSI-191 PWR

Sump Screen Blockage Chemical Effects Tests '- Thermodynamic Simulations", Report

NUREG/CR-XXXX (Working Draft)], These studies were performed using four widelyavailable chemical modeling programs, including the OLI System's StreamAnalyzer, EQ3/6

(LLNL), Geochemist's Workbench REACT (distributed by Rockware, Inc.), and PHREEQC

(USGeological Survey). All four programs are largely equilibrium in nature and hence are

significantly restricted in their ability to simulate the dynamic conditions that exist in the pool as

the conditions evolve with time after a LOCA. However, the latter two (Geochemist's

Workbench REACT and PHREEQC) also have the capability of simulating kinetically

controlled (including irreversible) and mass transfer processes. None have the ability to simulate

radiolysis phenomena, nor do the have the capability of calculating the redox potential via a

mixed potential model, and these limitations are judged by the author to be severe. In this regard,

it is also important to note that, in the geochemical literature, the Eh that is commonly referred to.

as the "redox potential" is, in fact, an equilibrium potential that is calculated for a specific charge

transfer reaction. The term, redox potential, as used in electrochemistry (from which it

originates), is. a mixed potential that reflects the occurrence of two or more charge transfer

reactions occurring simultaneously at a metal surface. The mixed potential not only reflects the

equilibrium properties of the individual reactions (through their equilibrium potentials), but is

also determined by their kinetics (through the exchange current densities or rate constant and

through the transfer constants) and by mass transfer processes. Because the exchange current

densities, rate constants, and the transfer coefficients for the individual redox reactions depend

upon the substrate, the redox potential is substrate specific. Thus, the value obtained for

platinum will differ from that calculated for carbon, for example. If one or more of the redox

reactions that occur at the surface involves oxidation of the substrate itself (e.g., dissolution

and/or oxide formation), the potential is termed the "electrochemical corrosion potential" (ECP),

which is a quantity of great importance in corrosion science. Thus, it is evident that the true

redox potential that characterizes the oxidizing/reducing power of an environment is not the

same as that commonly defined in geochemistry as Eh and that it cannot be calculated by

equilibrium thermodynamics. This issue is discussed at greater length later in this report.

E-14
The predictions of the four codes were compared by simulating identical containment

water after 30 minutes of exposure at temperatures of 1 I100C, 90'C, and 60TC. The four codes

generally produced identical results for the major component elements that exhibit a single

oxidation state and hence that are not susceptible to changes in the redox conditions. For those

elements that have multiple, accessible oxidation states the comparison is quite poor. The

authors of the report attribute the discrepancies to the listing of different sets of solid phases in

the data bases and, presumably, inconsistent thermodynamic data among these phases. However,

the general lack of recognition of the importance of redox effects may also be an important,

contributing factor. Furthermore, the lack of the ability of these codes to simulate radiolytic

effects must, however, be judged a serious shortcoming in simulating actual pooi conditions, in

light of simulations discussed elsewhere in this report that predict significant acidification of the

pooi water due-to the radiolytic generation of nitric acid from nitrogen in the ambient air..

Nevertheless, comparison with ICET data from the University of New Mexico (obtained

in the absence of radiolysis) show generally fair (qualitative to semi-quantitative) agreement

between theory (thermodynamic calculation) and experiment, as might be expected when

modeling complex, kinetically-controlled chemical systems using equilibrium models.

Combining this limitation with the lack of radiolysis modeling and the lack of viable modeling of

redox effects raises serious doubts in the reviewer's mind of the viability of employing "off the

shelf' codes to model a unique system such as the containment pool after a LOCA.

4.4. Accelerated Chemical Effects Head Loss Testing (ANL)

Head loss testing, which provides a measure of the likelihood of clogging of the screens

during a LOCA, was performed during the ICETs by monitoring the pressure drop across, and

the volume flow rate through, the screen. Precipitation was found to clog the screen, particularly

in the presence of a debris bed of fiber glass and other material. In particular, the injection of

Ca2+ in the presence of TSP (e.g., in ICET #3) led to the precipitation of Ca3(P0 4)2, which

effectively blocked the screen. Accordingly, the ICETs have effectively confirmed that the

clogging of pump screens is a practical reality and they have defined the general conditions

under which it may occur.

4.5. Limitations of the Current Tests

In Section 2.2, "Principal Technical Questions", the reviewers were asked to comment on

the appropriateness and the effectiveness of the ICETs, analytical simulation, and head-loss

testing work in accurately resolving various "chemical" issues related to clogging of the sump

screens after a LOCA. These issues are addressed below in the order that they are presented in

Section 2.2.

0 ICET

* Ha~ve the principal sump pooi variables *which affect chemical by-product

formation in the post-LOCA environment been adequately simulated? No. The

lack of consideration of redox effects and radiolysis, particularly upon the pH, due

to the production of nitric acid, and upon the redox potential are serious

shortcomings that need to be addressed. During the course of this study, the

author and his colleagues modified radiolysis/corrosion models to predict the

production of highly oxidizing H20 2 and highly acidic HNO3. These simulations

are important, because both the redox. potential and pH are of great importance

E- 15
with regard to corrosion processes and chemical speciation in the pool. It is

predicted that, if the LOCA results in the release of copious amounts of fission

products from damaged fuel, with dose rates exceeding 1 05 _ 106 radlhr, the

problem may be severe, because radiolysis may overwhelm the buffering capacity

of the pool. In that case, the pH could easily drop to values (I - 3) at which the

corrosion of metals and the leaching of inorganic ions from concrete (for example)-

would bec~me severe.

.M Many ICET variables were held constant during the experiments. How would

changes in the most important constant variables affect chemical product

formation? As an initial approach, I would use the radiolysis/ECP (redox

potential) models to bound the values of the redox potential and pH that might be

experienced in the pool, post LOCA, and then simulate these effects by injecting

hydrogen peroxide and HN0 3 into the solution at formation rates that are

predicted by the radiolysis codes.

* What variables or materials not simulated by the ICET testing may have the most

impact on chemical product formation (e.g., coatings, free insulation, flow

through sediment and other materials on sump screen, galvanic effects) and how

should their effect be characterized by testing or analysis? The most important

omission from the current tests is simulation of the production of H20 2 (which,

along with hydrogen, essentially determines the redox potential) and production

of HNO 3, which lowers the pH, by radiolysis.

" Were the methods used within the ICET program to characterize and analyze

chemical by-products sufficient? No. Probes (Pt electrodes) should have been

incorporated in the tests to measure the ECP (redox potential) and (in retrospect,

because the effects apparently had not been predicted when the experiments were

planned) injections of hydrogen peroxide and nitric acid should have been made

to simulate radiolysis effects. The measurements that have been made effectively

characterize the physico-chemical, not the electrochemical, properties of the

system.

U Analytical Simulation

" Is the speciation analysis expected to provide reasonable predictions of chemical

product formation over a range of possible sump environments? No. Again,

none of these codes (to my knowledge) accurately predict redox effects, because

the redox potential is a non-equilibriium phenomenon that can only be predicted

using a mixed potential model. Thus, in a post LOCA environment, nonequilibrium concentrations of radiolysis products (and even species in the absence

of radiolysis) render the system far from equilibrium, which cannot be addressed

by the four codes chosen [OLI System's StreamiAnalyzer, 'EQ3/6 (LLNL),

Geochemist's Workbench REACT (distributed by Rockware, Inc.), and

PHREEQC (US Geological Survey)].

* Is the plan for benchmarking these codes using small-scale testing and the ICET

results appropriate? Yes, provided that the actual processes are accurately

simulated (see above).

" What is the most appropriate way to measure the uncertainty associated with

these codes? Sensitivity analysis on empirical or deterministic models.

E- 16
0 Head Loss Simulation Testing & Analysis

" is the accelerated head loss testing approach viable for evaluating the effects of

multiple chemical environments quickly? Yes, again, only provided that the

relevant processes are simulated (see above).

" What is the best method for incorporating for time-dependent effects. (e.g.,

material aging, evolving chemical environments) in simulation testing? Kinetic

models, coupled with thermodynamic codes. However, the codes MUST

accurately simulate radiolysis and redox effects.

" What metrics are most appropriate for evaluating the results of simulated

chemical products with those that formed during the ICET program? Speciation

and concentration. However, if equilibrium models are to be used, they must

involve a global Gibbs energy minimization algorithm to predict the existence of

-stable and meta-stable phases (and their relative stabilities). Because I do not

have access to the source codes for OLI System's StreamAnalyzer, EQ3/6

(LLNL), Geochemist's Workbench REACT (distributed by Rockware, Inc.), and

PHREEQC (US Geological Survey, it is not possible'for me to ascertain their

capabilities with regard to this issue. Furthermore, the codes would only be

effective if they incorporate effective means of handling redox effects in highly

non-equilibrium systems.

*Are correlations available, or can they be developed, which can predict the

associated head loss if important physical characteristics of a chemical byproduct are known? This is a difficult problem that could only be treated by a

kinetic model for hydrolysis, polymerization, coagulation, and precipitation in a

highly non-equilibrium environment, coupled with codes for. To my knowledge,

none of the present codes [OLI System's StreamAnalyzer, EQ3/6 (LLNL),

Geochemist's Workbench REACT (distributed by Rockware, Inc.), and

PHREEQC (US Geological Survey)] have this capability.

5. Issues

Review of the documents supplied to the review team and review of the presentations that

were made by NRC, ANL, LANL, SwRL, and EPRI personnel raised a number of issues that

should be addressed in developing an understanding of the chemical processes that might occur

in containment during a LOCA and for developing predictive models.. In the opinion of this

reviewer, certain aspects of the chemistry and the electrochemistry of the system are not

adequately covered or understood. Accordingly, it is recommended that the NRC request the

contractors involved in the program to address the issues raised in this report through analytical

assessment or by experiment. The issues are summarized below:

5.1. Electrochemical Properties of the Containment Pool

Upon the occurrence of a LOCA, it is likely that a significant amount of radioactive

material will be released into containmnent. This material will arise from two principal sources;

(1) Fission products from failed fuel, and (2) Neutron activated corrosion products and deposits.

that form on the fuel and coolant circuit surfaces. More than a, hundred fission product isotopes

exist, with some of the more prominent that are expected to be released from the fuel being I31,

E- 17
1

34Cs, 137CS , and 90

Sr, among others. The isotopes of iodine ("31, 134, etc) are particularly

dangerous, because they are gaseous and are readily absorbed by the human thyroid gland,

resulting in carcinomas. Iodine is removed by the building spray system within containment.

Neutron activated corrosion products contain 60 ,Co"5, Zn 65 , Fe5

", Fe"5 , and Ni6

1

3, together with

many other radio nuclides, all of which are y-photon emitters, and hence all of which, depending

upon their activity and photon energies, will contribute to greater or lesser extents to the

radiolysis of water in the containment pool. Many of the fission products are a-particle emitters,

which also cause the radiolysis of water and should be taken into any account in any analysis of

the radiolysis issue.

The radiolysis of water in Water Cooled Nuclear Reactor (WCNR) heat transport circuits

has long been recognized as a potential source of corrosive, oxidizing species, such as 02, H202,

OH, etc., and for this reason hydrogen is added to PWR primary coolant circuits, and, in more

recent years, to BWR coolant circuits, to suppress their radiolytic generation of oxidizing species

and/or to displace the corrosion potentials of structural components in the coolant circuits in the

negative direction. This has been accomplished in the case of PWR primary coolant by adding

large amounts of hydrogen to the coolant [20 - 7Occ(STP)/kg, 8.93xl0A4 - 3.13x 0-3M,

respectively], seemingly with the philosophy that "if a little is good, a lot more must be better.

In the case of BWRs, the Intergrannular Stress Corrosion Cracking (IGSCC) of sensitized Type

304SS primary coolant components (particularly the recirculation piping system, but more

recently in-vessel components) has been linked to excessively high corrosion potentials, resulting

from the generation of oxidizing species (02, H20 2 due to the radiolysis of water), and to a

sensitized microstructure, due to either thermal sensitization or neutron irradiation above a

certain fluence (accumulated dose > 1 021n/cm2,ý energy > I MeV). That the Electrochemical

Corrosion Potential (ECP) is the prime parameter in determining the accumulation of corrosion

damage has been slowly accepted in the power reactor community, possibly because

electrochemistry is seldom, if ever, included in Mechanical and Nuclear Engineering curricula at

universities. The impact that ECP has on crack growth rate is roughly exponential [D. D.

Macdonald and M. Urquidi-Macdonald, Corr. Sci., 32, 51 (1991). D. D. Macdonald and M.

Urquidi-Macdonald, "An Advanced Coupled Environment Fracture Model for Predicting Crack

Growth Rates", Proc. TMS Parkins Symp. Fund. Aspects Stress Corros. Crack., pp. 443-455,

Oct. 20-24, 1991, Cincinnati, OH, (TMS, Warrendale, PA, 1992). D. D. Macdonald, P.C. Lu,

M. Urquidi-Macdonald, and T. K. Yeh, Corrosion, 52, 768 (1996). D. D. Macdonald, Corr. Sci.,

38, 1033 (1996). X. Zhou, 1. Balachov, and D. D. Macdonald, "The Effect of Dielectric

Coatings on Sensitized Type 30455S in High Temperature Dilute Sodium Sulfate Solution",

Corr. Sci., 40, 1349 (1998). D. D. Macdonald and L. Kriksunov, "Flow Rate Dependence of

Localized Corrosion Processes in Thermal Power Plants" Adv. Electrochem. Sci. Eng.,5, 125,

(1997) [John Wiley & Sons, New York, N.Y.]. M. P. Manahan, Sr., D. D. Macdonald, and A. J.

Peterson, Jr., Corr. Sci., 37, 189 (1995)], if the ECP is above a critical potential for IGSCC

(EIGSCc), although the rate also depends upon the stress intensity, the extent of cold-working of

the substrate, the conductivity of the environment, and the flow velocity of the coolant across the

surface [D. D. Macdonald, and G. Cragnolino. "The Critical Potential for the IGSCC of

Sensitized Type 304 SS in High Temperature Aqueous Systems". Proc. 2nd Int'l. Symp. Env.

Deg. Mat. Nuci. Power Syst. - Water Reactors. (September 9-12, 1985). Monterey, CA., ANS].

Note that in much of the discussion that follows, the focus is on the primary'coolant circuits of

operating reactors, but the author emphasizes that the same principles apply to the containment

pool post-LOCA.

E- 18
As noted above, the redox potential (Eredox) and the ECP (the redox potential is simply

the ECP of an inert substrate) are the key parameters in describing the susceptibility of reactor

coolant circuit components to corrosion damage. The direct measurement of ECP in reactor

coolant circuits has proven to be very difficult, notwithstanding the monumental efforts of

researchers and plant operators worldwide [M. E. Indig and J. L. Nelson, Corrosion, 47, 202

(1991)]. The major challenge in in-reactor ECP measurements has been to devise a reference

electrode that can withstand the harsh environmental conditions that exist within a reactor

pressure vessel (RPV).

Electrochemists will recognize that the Eredox. and ECP are both mixed potential, the

values of which are determined by the balance of the oxidizing and reducing species in the

environment and the kinetics of dissolution (corrosion) of the substrate. In order to calculate

Eredox and ECP, then, it is important, in principle, that the concentrations of all of the radiolytic

species be determined, since all of these species are electroactive. However, theory shows that

the contribution that any given species makes to the these potentials is determined by its

concentration, so that only the most prevalent electroactive species in the system determine the

ECP. This is a fortunate finding, because the various radiolysis models that are available for

calculating species concentrations do not determine the concentrations of the minor species

accurately, nor are there available electrochemical kinetic data for most of these highly energetic

species.

In order to calculate the species concentrations, the combined effects of the radiolytic

yield of each species due to the absorption of ionizing radiation by water, and the changes in

concentration due to chemical reactions and fluid convection, must be taken into account. This

problem reduces to one of solving as many stiff, coupled, simultaneous first order differential

equations as there are species in. the system. One of the major problems in describing the

radiolysis of water is to devise efficient algorithms for performing that task. Details of the

calculations may be found in the literature [T. K.. Yeh, D. D. Macdonald, and A. T. Moffa, Nucl.

Sci. and Eng., 121, 4.68 (1995). T. K. Yeh, D. D. Macdonald, and A. T. Motta, NucI. Sci. and

Eng., 123, 295 (1996). T. K. Yeh, D. D. Macdonald, and A. T. Motta, NucI. Sci. and Eng.., 123,

305 (1996). D. D. Macdonald, et al., "Estimation of Corrosion Potentials in the Heat Transport

Circuits of LWRs," Proceedings of the International Conference on Chemistry in Water

Reactors: Operating Experience & New Developments, Nice, France, Apr. 24-27, 1994. D. D.

Macdonald and M. Urquidi-Macdonald. Corrosion, 46, 380 (1990). C. P. Ruiz, et al., "Modeling

Hydrogen Water Chemistry for BWR Applications", EPRI-NP-6386, Electric Power Research

Institute, June 1989. K. Ishigure, Rad. Phys. Chem., 29, 195 (1987). E. Ibe, J. Nucl. Sci. Tech.,

24, 220 (1987)].

Below is presented a brief (but incomplete) review of the current state-of-the-art in

modeling the radiolysis and electrochemistry of PWR and BWR primary coolant circuits. The

material is presented, so that the reader may appreciate the level of sophistication that has been

achieved and to indicate the techniques that might be used to model radiolysis and

electrochemical effects in the containment pool subsequent to a LOCA.

Radioytic Yield

The rate at which any primary radiolytic species is produced is given by

GiyrT- Gi-F- Gap-a

Rl ( + + ' )Fp() lOONv lOONv JOONv

E- 19
where the rate of production of species "i", R-', has units of mollcm3 .s, G , G9, and G'are the

radiolytic yields for neutrons, gamma photons, and alpha particles, respectively, in number of

particles per 100eV of energy absorbed, Nv is Avogadro's number, F equals 6.25x101 3 (the

conversion factor from Radls to eV/gram.s), and p is the water density in g/cm3 . r', T", and I'

are the gamma photon, neutron, and a-particle energy dose rates, respectively, in units of radls.

Table 1. Radiolytic Yields (G Values) for Primary Radiolytic Species

Species Species Gy GUn 0 O

No. (No./IOOeV) (No./ IOOeV) (No./lOOe'I)

1 e 2.66 0.61 0.06

2 H 0.55 0.34 0.21

3 OH 2.67 2.02 0.24

4 H2 02 0.72 0.65 0.985

5 HO2 0.00 0.05 0.22

6 HO2 - 0.00 0.00 0.00

7 02 0.00 0.00 0.00

8 O2f 0.00 0.00 0.00

9 H2 0.45 1.26. 1.3

10 0- 0.00 0.00 0.00

I11 0 0.00 0.00 0.00

12 02 0.00 0.00 0.00

13 OH- 0.01 0.00 0.00

14 H+ 2.76 10.00 10.06 1

Values for the radiolytic yields for various species considered in the author's radiolysis

model for PWR coolants are listed in Table 1. A review of the literature reveals a wide variance

in the U-values, even from the same author. The current G-values should be regarded as being

little more than rough estimates.

.The third term in Equation (1) accounts for the radiolysis of water by a-particles (4 He 2

nucleus), which are produced by the 1

0B5('no,4 He2)7Li3 reaction in PWR primary coolant

environments, but this nuclear reaction does not occur on BWR environments, because of the

absence of boron (specifically 1

0 B5). The importance of a-particle radiolysis in PWR cores has

been recently assessed and it was concluded that the contributions from a-radiolysis to the

concentrations of the radiolytic species are small, when compared with those from neutrons and

y-photons at the prevailing dose rates. Nevertheless, in a PWR primary coolant circuit, there are

regions where a-particle radiolysis contributes significantly to the formation of the radiolytic

species (> 10 %), and hence the third term in Equation (2) is necessary. In the case of BWR

cores, the radiolysis models have tended to be based on that originally proposed by Burns and

Moore, with modification being made in light of the later studies by Elliot. The models used by

the author and his colleagues for modeling BWR primary coolant circuits contains 34 reactions,

as discussed further below.

E-20
A word of caution is needed at this point; the radiolytic yields employed in radiolysis

modeling should be the primary yields corresponding to events that occur within the time of

scission of a bond within a water molecule. These values are impossible to measure, because no

techniques are available for sampling the concentrations of primary radiolysis products in the

sub-femnto second time frame. Thus the radiolytic yields that are used to devise water radiolysis

models are strictly not the values that are appropriate or needed. However, as with many

physico-chemical models, values for various parameters are often selected, such that the original

observations are reproduced. A major problem in radiolysis modeling is that there are many

more unknown parameters than there are experimental observations, so that the values assigned

to the models are not unique and they should not be transferred from model-to-model.

Nevertheless, the models have proven to be quite robust, in the sense that reasonable values for

the calculated concentrations of the various majo .r radiolysis products are obtained. (However, it

should be noted that the concentrations of minor radiolysis products are seldom measured and

compared with those that are predicted).

Chemical Reactions

The chemical reactions occurring in the system essentially determine the species

concentrations. The reaction set used previously by Urquidi-Macdonald and Macdonald for

modeling PWR primary coolant circuits has 48 reactions describing the interactions between the

14 species listed in Table 2, along with the rate constants and the activation energies.

Table 2. Reacti'on set used in the PWR radiolysis model

Rate Activation

*Reaction Constant, k Energy

No. (1mls jkca/My l) Reaction

1 1.6D+l 3.ODO e-+ H 2 0=H±+0H2 2.4D+10 3.013D e &+H + = H

3 2.4D+ 10 3.013D e &+OH = OH4 1.3D+10 3.ODO e-+ H 2 0 2 0= H±+OH

5 1.OD+1O 3.0130 H+H=H2

6 2.OD+1O 3.ODO e-+ H0 2 =H02

7 1.9D±10 3.013D e &+02 =02-

8 5.OD+9 3.0130 2e- + 2H20 = 20H- + H2

9 4.5D+9 3.0130 OH + OH = H 20 2

10 1.2D'+10 3.ODO OH±+H0 2 =H 20 +0 2

11 I .2D+10 3.0130 OH +02f= OH-+ 0 2

12 2.OD+7 3.ODO OHW+H=e-±H 20

13 4.5D+8 3.013D e &+H +H 2 0 =OH + H 2

E-2 1
14 6.3D+7 3.ODO e- + H02- + H20 = OH + 20H15 1.44D+1 I 3.ODO H+±+OH-= H2 0

16 2.6D-5 3.ODO H20 = H+ +OH

17 2.OD+10 3.ODO H +OH = H 20

18 3.4D+7 4.6D0 OH+H 2 =H+H 2 0

19 2.70D+7 3.4D0 OH + H1202 = H20 + HO2

20 4.4D+7 4.5D0 H + H20 2 = OH +1H20

21 1.9D±10 3.ODO H +0 2 =H02

22 8.OD±5 3.ODO HO2 = 02- +H

23 5.OD±10 3.ODO 0 2-+ H = H0 2

24 2.7D+6 4.5D0 21102 = H20 2 + 02

25 1 .7D+7 4.5D0 202- ± 2H20 = H 2 0 2 +0 2 +20H26 2.OD+1O 3.ODO H +H0 2 =H2 0 2

27 2.OD+10 3.ODO H__+ __02___=__H02__

28 1 .3D+8 4.5D0 e- + O2f +1120 = H02- + OH29 1.8D+8 4.5D0 OWf +1H202 = H02- + H20

30 1 .9973D-6 14. 8D0 211202 = 2H 20 + 02

31 1.04D-4 3.ODO H +H 20 =H 2 +OH

32 1 .02D+4 3.ODO 1120 -I H02 = H20 2 + OW33 1 .5D+7 4.5D0 HO2 + 02- =02 + H02-

34 7.7D-4 7.3D0 11202 = 20H1

35 7.88D+9 3.ODO 0H1+1H02- = O2f +1120

36 1.28D+10 3.ODO OH+OHW=&+H 2 0

37 6.14D+6 3.ODO 0O+ H 2 0 =OH + OH

38 3.97D+9 3.ODO e-+ H02= 0-+Off

39 6.42D+14 3.ODO O2f + O2f + H+ = 1102 + 02

40 2.72D-3 15.ODO H20 2 H 120 + 0

41 2.84D+ 10 3.ODO 0+ 0=02

42 1.I1D+6 I 3.ODO 0 2 2-+H20 =1H02- +01H

E-22
43 1.3D+10 3.0130 e-___+_02___=__02__2-

44 0.5D0 3.ODO H20 2 + HO2 = H20 + 02 + OH

45 0.13D0 3.ODO 02- + H20 2 = OH + OH- + 02

46 2.56D-8 3.ODO H20 2 = H+ + H02-

47 1.39D+10 3.2D0 e- + HO2 + H20 = H20 2 + OH48 1.39D+10 3.2D0 e- + O2f ± H20= H0 2 - + OHThis reaction set includes hydrogen peroxide decomposition. The impact of

including H20 2 decomposition in a radiolysis, which has been used extensively in our

BWR modeling work and which has been extensively evaluated against BWR plant data,

is unknown, because no independent check on specie concentrations is currently available

for a P WR primary circuit or for a containment pool. This is due to the fact that the

concentration of oxygen, which is monitored on a routine basis in a BW~R, is so low in a

PWR primary circuit that it is not measured. Furthermore, the hydrogen that is present in

a PWR primary circuit is primarily the result of hydrogen additions and not radiolysis, so

that [H21 measured in the circuit is not a good indication of the state of radiolysis. Finally,

the ECP, which is now measured on a routine basis in BWRs, is not monitored in any

PWR primary circuit, to the authors' knowledge, even on an experimental basis, although

some measurements have been made in VVER 440 reactors.

Other radiolysis mechanisms were examined during the development of models to

describe radiolysis in reactor coolant circuits, and the codes that have been developed by

the author have been written to facilitate, to the greatest extent possible, the inclusion of

new mechanisms. As expected, insertion of different reaction sets requires considerable

reprogramming of the code.

The rate of change of each species at a given location is given by reaction rate

theory as

N N N

Xc=zY ksmCsCm C- X i~ (2)

where ksm is the rate constant for the reaction between Species s and m, ks is the rate

constant for the reaction between Species s and i, and Ci, Cm, and Cs are the

concentrations of Species i, m, and s, respectively. N is the number of reactions in the

model (i.e., N = 48). Explicit expressions for the gain and the loss of each species are

included in the algorithm.

The rate constant, Ic1 is a function of coolant temperature. Since the~temperature

throughout the heat transport circuit is not constant, the actual rate constant for each

chemical reaction must be calculated for each specific position using Arrhenius' law

kc = k,, exp[ E.( --- ) (3) R T, T

E-23
where Ic0 is the rate constant at temperature To, Ea is the activation energy, R is the

universal gas constant, and T is the temperature in Kelvin. The rate constant for

hydrogen peroxide decomposition (Reaction ft 30) was calculated separately using an

experimentally derived relationship:

kc30 =1.9973e - 6.e' 4800 /RT) (4)

Table 1 lists the species considered and the number assigned to them. Note that [H+] and

[OH] are calculated from the pH and the speciation that is afforded by the chemistry of

the coolant.

Convection

As in all of the radiolysis models of reactor coolants, convection is considered to

be the only mode of transport (i.e. diffusion and electro-migration are neglected). In both

PWR and BWR primary coolant circuits, single-phase (water) flow is assumed to exist in

all regions of the circuit, except in the core channels of a BWR, where boiling produces

the steam that carries the energy directly to the turbines. Boiling results in the transfer of

volatile species (02 and, in particular, H2 ) to the steam, which in turn reduces their

presence in the liquid phase. This transfer significantly modifies the radiolysis processes

in the liquid, with the result that the coolant becomes more oxidizing in nature, because

of the higher rate of loss of H2 compared with 02 or H20 2. In the case of PWRs, nucleate

boiling within the power-producing channels, where the local saturation vapor pressure

exceeds the prevailing hydrostatic pressure, has a much less effect on the coolant

chemistry than does the sustained boiling in the fuiel channels of a BWR, because the

volatile species are returned to the liquid phase when the bubbles collapse. In nucleate

boiling, the steam bubbles that form on the fuel collapse when they detach from the

surface. Accordingly, any volatile radiolysis species that transfers to the steam phase is

immediately returned to the primary coolant (liquid phase), so that the net effect of

nucleate boiling on the bulk concentrations is expected to be small, if it exists at all. This

situation contrasts with that in a BWR, where a continuous steam phase is formed that

leaves the primary coolant. In this case, the irreversible transfer of volatile species (H2 ,

02) to the steam has an enormous impact on the electrochemistry of the primary circuit.

General Solution of the Equations

The approach used in our work to solve the set of coupled ordinary differential

equations (ODEs) for modeling PWR primary coolant circuits makes use of a publicly

available subroutine (DVODE), which was developed by Hindmarsh at the Lawrence

Livermore National Laboratory in California [www.netlib.gov]. This algorithm is

designed to solve first degree, stiff ODE equation sets. Our system of equations is

coupled throughout via the concentrations of the 14 species considered. To solve the i -

coupled differential equation (i =number or species), the DVODE subroutine needs to

have the set of equations and the corresponding Jacobians described. The calculation

begins by assuming that the coolant is an incompressible fluid (V -: = 0) and that the

flow is turbulent (efficient mixing). Accordingly, the flux of each dissolved species is

given by

E-24
N. = -Z1UFciV 0- DVC1±+Cv (5)

flux = migration + diffusion + convection

Because of efficient mixing and in the absence of an electric field, we may ignore

diffusion and migration, respectively, and hence the material balance can be written as

ac, !V +--

at -VN+,(6)

(accumulation = net input + production), where R1 is the rate of production of the

*species in the fluid due to homogeneous reactions.

The primary coolant circuit of a water-cooled reactor (including BWRs and

PWRs) has several loops, including the main coolant loop, a core heat removal system,

and a reactor water clean-up system. However, it is convenient, for computational

purposes, to differentiate between the main loop, which has a high flow fraction and the

secondary loops, for which the flow fractions are small. The species concentrations and

electrochemical potential (ECP) are solved for in the main loop and the values at the

entrance to the secondary loop are used as the initial conditions for solving the system of

equations for the secondary loops of interest. Mass balance is applied' at each point

where more than one section comes together.

By adopting the rates of change of species mass from the various sources discussed

above, we write the total rate as

GGF n 1-n' Gi'Fa N N N

Ri+ + )Fp +[z Y ~ksm CS CM -Ci Yksi Cs ] (7) lOONy JOONV JOONV s=J m=J s=I

The equations must be solved iteratively until satisfactory convergence is obtained. Note

that, because the mass flow rate (dm/dt) in a single (un-branched) channel is constant at

all points, the linear flow rate is given by v = (din / dt) / pA , where A is the crosssectional area of the channel.

By solving Equation (6) numerically, we are able to calculate the concentrations of

each species at any point in a reactor heat transport circuit. In the actual numerical

simulation, all of the parameters, except the flow velocity, circuit geometry, and

temperature can be found in the published literature.

Transients during operation, for example those that result from a sudden increase

in power or from a step change in feedwater oxygen level, may be modeled as a series of

steady-states, with the initial conditions reflecting the progressive changes in the reactor

operating parameters.

The above approach describes the method used by Macdonald and UrquidiMacdonald in modeling PWR primary coolant circuits, but that employed by Yeh, Motta,

and Macdonald and others for modeling BWR primary coolant circuits is somewhat

different, but yields similar results. The reader is referred to the original literature for

details.

E-25
Mixed Potential Model and the Redox and Electrochemical Corrosion

Potentials

After the concentration of each radiolysis species is calculated, the corrosion

potential of the component can be estimated using a mixed potential model (MPM) [D.

D. Macdonald, Corrosion, 48, 194 (1992)].. The MPM is based on the physicoelectrochemical condition that charge conservation must be obeyed at the corroding

interface. Because electrochemical reactions transfer charge across a metal/solution

interface at rates measured by the partial currents, the following equation expresses the

charge conservation constraint

ZiR,oj(E)+ i.., E) = 0 (8)

j=1

where ipIjQ is the partial current density due to the j-th redox couple in the system and

icorr is the metal oxidation (corrosion) current density. These partial currents depend on

the potential drop across the metal/solution interface.

In the current version of the MPM, which was developed for modeling the ECP of

Type 304 SS in BWR primary circuits, the steel oxidation current density, icrr was

modeled as an empirical function of voltage,

e(E-Eo)lbf e-(E-E0 ) /b,

384.62e 44 6 /T + X(9

where

e(E -E0 ) / b

2.6 lxl 03 e -44 16 /T+O.523(E-E 0 )U5 (0

and

E0 =0. 122 -1.5286A10-'T (t1)

In these expressions, bj and br are the forward and reverse Tafel constants, respectively,

for the metal dissolution reaction, with values of 0.06 V being assumed for both. In

actual fact, they are empirical constants that were assumed a priori in fitting Equation (9)

to the current/voltage data. It is important to note that Equation (9) applies strictly to

Type 304 SS in near neutral solutions and hence that this expression may not be a good

empirical model for stainless steels in PWR primary circuits or for metals and alloys in a

containment pool. More recently, the Point Defect Model [D. D. Macdonald, Pure Appl.

Chem., 71, 951 (1999)] has been used as the basis for calculating the corrosion current

density of the metal substrate.

E-26
Metal IBarrier Layer Solution/Outer Layer

()M +V k M m~m±%e ()M ', a)+V" F-X

k2 k >MX + V +X - ()M k

(2 M M + e (5 Mix k6 I '+(q F Xe

(3) m k3 +MM+iVo'+Xe (6 +~H O k6 0 0 +2H+

(7) MOZ1 2 +zH+ M-+k(q) 2H2+(F-Xe

Figure 1. Summary of the defect generation and annihilation reactions

envisioned at the interfaces of the barrier oxide layer on a metal, according

to the Point Defect Model (PDM). VM'= cation vacancy in the film;

Vm vacancy in the metal substrate; MX+ cation interstitial;V'

oxygen (anion) vacancy; MF (aq) =cation in solution; MM cation in

cation site on the metal sublattice; 00 oxide ion in anion site on the

oxygen sublattice; and MO./2 stoichiometric barrier layer oxide. Note

that Reactions 1, 2, 4, 5 and 6 arc lattice conservative processes (they do

not result in the movement of the interface) whereas Reaction 3 and 7 are

non-conservative [D. D. Macdonald, Pure AppI. Chem., 71, 951 (1999)].

The PDM yields the, passive current density in the form

'ss = F[k 0e aayveae~s +k~ea yeafw ±ko .C+ (12)

where the film thickness is given by

1S -a 1+ I 2.303n pH 'l(3 (13)

C a3% a ~ k7 )

[D. D. Mac donald, Pure Appl. Chem., 71, 951 (1999)]. The parameters in these

equations are as follows: X~, a, 86, and n are the oxidation state of the cation in the

barrier layer;, the polarizability of the film/solution interface (i.e., the dependence of the

potential drop across the film/solution interface on the applied voltage); the dependence

of the potential drop across the film/solution interface on the pH; and the kinetic order of

the film dissolution reaction with respect to hydrogen ion concentration; respectively.

Note that, in deriving Equations (12) and (13), the oxidation state of the cation in the

barrier layer (xý) is set equal to the oxidation state of the same cation in the solution/outer

E-27
layer. The standard rate constants, ko, and a1 correspond to the reaction shown in

Figure 4, e is the electric field strength, y =F / RT , and K = ey. The three terms on

the right side of Equation (12) arise from the transmission of cation interstitials, the

transmission of cation vacancies, and the transmission of oxygen vacancies (or

dissolution of the film), respectively. Values for these parameters are readily obtained by

optimizing the PDM on electrochemical impedance spectroscopic (EIS) data.

Because electrochemical kinetic data are available only for the hydrogen electrode

reaction (HER, H2/H~), the oxygen electrode reaction (GER, 02/1120), and the hydrogen

peroxide electrode reaction (HPER, 11202/1120), only H2, 02, and 11202 are considered as

the redox species in the MPM. The redox reactions of interest are therefore written as:

H+ +e->112H2 or H 2 0+e- -J/12H2 +0OH- (14)

02+ 4H+ +4e--> 2H2 O or 0 2 ±+2H2 0 +4e- -*40H- (15)

H 2 0 2 + 2H+ + 2e_ --* 2H2 0 or H 2 0 2 + 2e- --> 2H0- (16)

depending upon the pH. For pH values of less than about 4, the acid forms of the

reactions prevail (left side), while at higher p11 values the base forms predominate. The

exact form of the reaction has an important impact on the MPM, because it determines

the reaction order with respect to the concentration of hydrogen ion in the expression for

the exchange current density.

The current density (ipJo) for a redox couple (e.g. 02/H120, H+/H2, 11202/1120)

R <* O+ne (17)

(where R is the reduced species and 0 is the oxidized species) can be expressed in terms

of a generalized Butler-Volmer equation as

e-EE'1)b e-(E-E~O)Ib, 1

RI0 = (18)

1 0,R/O 1

iif ii

where iop~lo is the exchange current density, izf and j' r are the mass-transfer limited

currents for the forward and reverse directions of the redox reaction, respectively, and ba

and b~ are the anodic and cathodic Tafel constants. E' 1 steeulbru oeta o

this reaction, as computed from the Nernst equation:

EI= E0 -2.303RT~o~R

O/ OIR nF log-) (19)

E-28
where aR and a0 are the thermodynamic activities of R and 0, respectively, and EO,,R is

the standard potential. Limiting currents are calculated using the equation:

'l,O/R =±O.0165nFDC-bRRe 0 -

6SCO.33 Id (20)

where the sign depends on whether the reaction is in the forward (+) or reverse(-

direction, F is Faraday's number, D is the diffusivity of the redox species, COIR is the

bulk concentration of 0 or R, as appropriate, Re is the Reynolds number (Re= Vd/q7), Sc is

the Schmidt number (Se 7 / D), d is the channel diameter, V is the flow velocity, and q7 is

the kinematic viscosity.

An important point that needs to be emphasized again is that the maximum

contribution that any given radiolytic species can make to the ECP is roughly

proportional to its concentration. Thus, in BWR simulations the concentrations of H2 , 02,

and 11202 are calculated to be orders of magnitude greater than any other radiolytic

species and hence only these three need be considered. In the case of PWR primary

HTCs, our previous modeling work suggests that aquated electrons, H atoms, and OH

radicals may be significant species in regions of very high-energy dose rate (e.g. near the

fuel). However, no electrochemical kinetic data exist for these reactions and hence they

cannot be incorporated at this time.

0.3

0.2-*CIVCI Figure 2. Comparison of cacltdand

0.1 measured ECP for the Leibstadt BWR.

*0.0 T The "measured" data were acquired in a

-0.1 test cell attached to the recirculation

-0 .2 piping.

-0.5

0 .0 0.5 1.0 1.0 2.0 2.5

Feedwater [H2] (mg/kg)

The accuracy of the Mixed Potential Model has been evaluated by comparing

calculated ECP values for Type 304 SS against measured BWR plant data [D. D.

Macdonald, Corrosion, 48, 194 (1992)]. While modeling of the ECP in BWR primary

coolant circuits will be discussed at length later in this section, a brief discussion of some

of the data is appropriate at this point. Thus, the most comprehensive comparison is

probably that which employed data obtained during a Hydrogen Water Chemistry (HWC)

mini-test at the Leibstadt BWR in Switzerland (Figure 2). The reactor water chemistry

modeling and the prediction of the ECP was carried out in a "double blind" manner (i.e.,

we did not have access to the plant [02], [H12, or ECP data prior to submission of our

calculations and the contractor did not have access to our calculations while performing

the mini-test). We were, of course, provided with the flow velocity, hydrodynamic

diameter, and temperature data for the test system. The calculated and measured (plant)

E-29
ECP data for this case are summarized in Figure 2. Excellent agreement is obtained in

systems to which hydrogen -had been added, with the measured and calculated ECP

values agreeing within the combined uncertainty levels. .In the normal water chemistry

case ([H2] = 0), the measured ECP is significantly higher than the calculated value. This

is almost certainly due to the presence of hydrogen peroxide in the coolant, which was

not measured by the personnel conducting the HWC mini-test. Accordingly, we were

unable to input a value for [H 20 2] into the MPM. However, if we use the calculated

values for [H 2], [02], and [H20 2] obtained from RADIOCHEM, excellent agreement is

obtained.

At this point, it is of interest to explore the impact that oxygen and hydrogen

peroxide are predicted to have on the ECP under typical PWR primary circuit conditions.

This is done in Figure 9 for the system parameter values as summarized in the caption. In

the case *of both oxygen and hydrogen peroxide, the ECP is predicted to be displaced in

the positive direction for [02] or [H 20 2] greater than 0.001 mg/kg (1 pp~b). Below this

concentration, the ECP is dominated by the hydrogen electrode reaction. At high oxidant

concentrations (> 0. 1 mg/kg), the stronger oxidizing power of H20 2 becomes evident, in

that the ECP is progressively displaced to more positive values compared with that for

oxygen as the oxidant concentration is increased. The critical. oxidant concentration of

lI pg/kg (lppb) at which the ECP is displaced from the hydrogen electrode behavior is in

good semi-quantitative agreement with experimental data obtained from laboratory

studies by Bertuch, et.al. [A. Bertuch, J. Pang, and D. D. Macdonald, "The Argument For

Low Hydrogen and Lithium Operation in PWR Primary Circuits ", Proc. 7rh Int'l. Symp*

Env. Deg. Mat. Nuc. Pwr. Sys. - Water Reactors, 2, 687-697 (August 1995)].

0.0

6a0 Figure 3. Calculated ECP vs. [02] or -0 ,O, [H 20 2] for a simulated PWR coolant

system. T = 320 TC, [H2]1

;!7 -. 4 -25cc(STP)/kg(H 20), [B] = 1000 mg/kg,

[Li] = 2mg/kg, pH = 7.36, flow velocity -06

-100 cmls, channel hydrodynamic

-08 . diameter= 100 cm.

le-6 le.5 1le-4 1e-3 le-2 1-i le-. le-l

1021 or [1H2021 (mglkg)

Finally, we note that, at least for BWR, coolant conditions, and possibly for PWR

primary conditions, also, when the ECP is not "clamped" by the hydrogen electrode

reaction, the corrosion potential is a sensitive function of the hydrodynamic conditions in

the channel. This sensitivity to flow arises because the hydrodynamic conditions control

the rate of mass transport of the redox species to the metal surface. This is an extremely

important issue when comparing the calculated ECP with laboratory and plant data,

because the measurements are seldom carried out in a channel that is well characterized

hydrodynamically. Indeed, a well-characterized channel should be a prerequisite for

performing measurements of this type.

E-30
Impact of Radiolysis in the Containment Pool

The computer code FOCUS, which was developed to describe the radiolysis of.

water and the accumulation of damrage due to stress corrosion cracking in Boiling Water

Reactors (BWRs) and which is outlined above, was modified to calculate the

concentrations of oxygen, hydrogen peroxide, and hydrogen in the containment pool as a

function of y-dose rate, pH, and temperature. While this is a "stop gap" measure, given,

the lack of resources available to develop a code designed to specifically model the pool,

it does yield useful information that provides a qualitative indication of the likely impact

of radiolysis on the chemistry of the containment po 'ol after a LOCA. Scoping

calculations are summarized in Table 3, in which the concentrations of hydrogen

peroxide, oxygen, and hydrogen are calculated for a temperature of 30'C as a function of

the ambient oxygen concentration (that concentration that would exist due to equilibrium

with the ambient atmosphere in the absence of radiolysis), pH, and 'y-dose rate.

Calculations were also carried out at temperatures of 60'C and 900C with broadly sim ilar

results. In the interest of brevity, they will not be presented at this time.

Table 3. Preliminary calculation of the generation of hydrogen peroxide,

oxygen, and hydrogen in water at 30'C as a function of ambient oxygen

concentration (concentration in the absence of radiolysis), pH, and y-dose

rate.

02 Conc y-Dose tH20 21 [021 11121 pH Rate

(ppm) (radls) (ppb) (ppb) (ppb)

0.1 10 44.00518, 73.38579 1.91507

100 58.57714 85.27291 4.34055

8 1000 83.31808 116.1293 9.83723

10000 129.3054 168.6386 21.76393

100000 756.4755 862.5814 151.4454

10 43.90286 73.38271 1.91325

100 58.43296 85.26128 4.33657

9 1000 83.13144 116.0977 9.83043

10000 137.4481 181.3297 22.55719

100000 756.297 863.5652 151.582

10 43.89336 73.38182 1.91308

100 58.41952 85.25942 4.3362

10 1000 83.11398 116.0935 9.82978

10000 129.0472 168.6263 21.75823

100000 756.278 863.6576 151.595

11 10 43.89242 73.38173 1.91306

100 j 58.41819 85.25923 4.33616

E-3 1
1000 83.11225 116.0931 9.82972 1

10000l 137.4217 181.3244 22.55634

100000 756.276 863.6668 15 1.5963

10 214.5571 720.4191 3.60908

8

1001 401.6951 677.9821 9.53419

10001 483.10181 722.1711 20.17785

10000 j 576.0389 j834.3471 43.23481

100000 1171. 148 1504.855 205.1361

1

10 214.5038 720.2722 3.60841

100 401.4674 677.7833 9.5308

9 1000 482.7655 721.9559 20.16937

10000 575.5655 834.1186 43.2132

100000 1170.635 1505.187 205.1646

10 214.4986 720.256 3.60835

100 401.4446 677.7611 -9.53047

10 1000 482.7322 721.9315 20.16856

10000 575.515 834.0901 43.21096

100000 1170.584 1505.218 205.1673

10 214.498 720.2544 3.60834

I1I

100 401.4424 677.7588 9.53044

1000 482.7288 721.9291 J 20.16848

10000 575.5104 834.0874 43.21076

100000 1170.579 1505.22 1 205.1676 + i i

8 10 390.266 6020.668 4.60369

8

100 1884.806 5619.741 20.20714

1000 3166.904 5229.377 47.54566

10000 3579.936 5380.753 91.93316

100000 4627.551 6649.682 398.6037

10 390.2369 6020.403 4.60325

100 1884.622 5619.026 20.20429

9 1000 3166.315 5228.681 47.53422

10000 3579.17 5380.175 91.89964

100000 4626.253 6648.662 398.4206

10 390.2337 6020.374 4.60321

10

100 1884.603 5618.949 20.20402

1000 3166.254 j5228.605 47.53312

10000 3579.093 5380.112 91.89642

100000 4626. 123 6648.559 398.4024

E-32
10 390.2334 6020.371 4.6032

I1I

100 1884.601 5618.941 20.20399

10001 3166.2481 5228.598 47.53301

100001 3579.0851 5380.106 91.8961

I ______1 ____ 11000001 4626.111 6648.549 j 398.4006

Of particular interest is the hydrogen peroxide concentration, because this species

is a strong oxidizing agent. The calculations indicate that the H202 concentration is a

very strong function of the y-dose rate and ambient oxygen concentration, as expected,

but is predicted to be insensitive to pH. At high ambient oxygen concentration (8ppm)

and high y-dose rate (100,OO0rad/s), the hydrogen peroxide concentration is predicted to

exceed 4ppm. Likewise, the concentrations of oxygen and hydrogen are also predicted to

be sensitive functions of the y-dose rate (in particular) and oxygen concentration, but not

of pH. One interesting prediction is that as the ambient oxygen concentration is

increased, the concentration of hydrogen is also found to increase, which is counterintuitive. We currently do not know whether this latter prediction is "real", in that it

arises from the radiolysis mechanism, or whether it is an artifact that is produced by

attempting to apply a model to describe a scenario for which it was never intended.

Assuming that. the predictions are qualitatively correct, it is evident that radiolysis

can have a major impact on the chemistry of the containment pool, if y-dose rate can rise

to the 104 to 105 rad/s level through entrapment of neutron-activated corrosion products

and fission products from failed fuel in the debris bed of the pool. The concentration of

H20 2 is sufficiently high that the redox potential is expected to be correspondingly high.

Unfortunately, the code FOCUS does not yield the redox potential of the solution, only

the corrosion potential of stainless steel in contact with the environment is calculated.

While both the redox. potential and the corrosion potential (ECP) are mixed potentials,

their values in the same environment can be greatly different, depending upon the

kinetics of the charge transfer reactions that occur at the surfaces of platinum (the

substrate that is normally used for defining the redox potential) and the steel, respectively.

Thus, an unequivocal resolution of this issue will require the following:

* Development of a radiolysis code specifically for a containment pool. This model

should incorporate boric acidlLiOH + TSP (tni-sodium phosphate) +TSB (tetrasodium borate) modules for estimating the pH. The model should be

calibrated/evaluated against laboratory experiments to establish efficacy.

" A thorough analysis should be carried out to estimate the likely y-dose rates in the

containment pool as a fuinction of time after a LOCA in a PWR. The contribution

of at-dose rate from fission products also needs to be evaluated. The latter is

completely ignored in the present analysis and the former (y-dose rate) is little

more than a guess. No information of guidance on this subject could be found in

the open literature.

" A better database for the kinetics of the hydrogen electrode reaction, the oxygen

electrode reaction, and the hydrogen peroxide electrode reaction needs to be

established. Some of the "raw"~ data are already in the literature, but the

information is incomplete and the data are generally not in a form that is readily

E-33
interfaced with radiolysis/redox potential models. In some cases, however, the

required data must be experimentally measured.

Given the above, it is useful at this point to speculate on the likely chemical

effects that radiolysis might have on the containment pool chemistry. Thus, the solubility

of species that are electroactive themselves (e.g., FeOOH) or yield species that are

electroactive (Fe 2 +, Fe 3+) generally depend upon the redox conditions of the environment.

Thus, we may write as the solubility reactions for FeOOH as

FeOOH + 3Hf'- = Fe'+ + 2H20 (21)

which clearly is not an electrochemical reaction and hence does not depend upon the

redox conditions, but if the environment is sufficiently reducing, such that Fe 2 + is Stable,

the reaction becomes

FeOOH + 112H2 +2HJ' = Fe2+ + 2H20 (22)

The equilibrium concentration of Fe 2+ may be written as

[Fe2+] P1/2[H]2 e AG0/ RT (3

wher PHis the partial pressure of hydrogen and AGO is the change in standard Gibbs

energy for Reaction (22). Clearly, as written, the solubility of FeOOH depends upon the

hydrogen partial pressure and pH and, since the coolant in a LOCA contains hydrogen

[approx. 25 cc/kg (H 2 0) in the virgin coolant], the partial pressure of hydrogen after the

LOCA becomes important (as does the pH), if the solubility is to be accurately calculated.

However, when the hydrogen is released in a LOCA, the gas space presumably contains a

mixture of H2 and 02, with [H2] being below the explosive limit, such that the solubility

cannot be defined by Equation (3), because the system is not at equilibrium. Instead, the

system is non-equilibrium in nature and a different approach must be used to estimate the

solubility.

The dissolution Reaction (22) may be written in slightly different form as:

Fe00H + 3HP+ e-=Fe2 + 2H2 0 (24)

for which the concentration of Fe 2 + can be written as:

[Fe 2+ = [H+ 12 2eF(E2,E,)/RT (25)

In this expression, E24 = -AGO /IF is the standard potential for Reaction (24), AGO4 is

as previously defined, F is Faraday's constant, R is the universal gas constant, and T is

the Kelvin temperature. The parameter Eh is the redox potential. This potential cannot

be calculated from equilibrium thermodynamics, because the system is not at equilibrium,

as noted above, due to the simultaneous generation of H2 , 02, and H2 0 2 , among other

E-34
products, by the radiolysis of water. If the system was at equilibrium, the partial

pressures of oxygen and hydrogen would satisfy

PHP 12 = AGH01 10 RT (26)

where AGHO2Q is the standard Gibbs energy of formation of water. At 25'C (298.15 K),

AGOJ = -237,178J/mol. Thus, substituting this value for AO into Equation (26) and

noting that, po, 0.2 1latin and R = 8.3 14J/K..mol, I obtain the hydrogen partial pressure

as PH2 = 6.12x 0-4 atm, which is the partial pressure of hydrogen in equilibrium with

atmospheric oxygen and liquid water under the stated conditions. This partial pressure of

hydrogen is orders of magnitude lower than that in the confinement volume, post-LOCA,

from which we must conclude that hydrogen and oxygen are present simultaneously in

the system at highly non-equilibrium concentrations, even though they may be present at

well below the explosive limit. The message is that it is not possible to use equilibrium

thermodynamic codes to estimate the solubility of electroactive components in nonequilibrium systems, such as that which must exist immediately after a LOCA in a PWR

confinement. It is equally clear that calculation of the solubility requires knowledge of

the redox potential, Eh. The redox potential may be estimated using the Mixed Potential

Model (MPM) that was originally developed for calculating corrosion potentials of

components in reactor coolant circuits [D. D. Macdonald, A. C. Scott, and P. Wentrcek.

"Redox Potential Measurements in High Temperature Aqueous Systems". J.

Electrochem., Soc., 128, 250-257 (1981), D. D. Macdonald, "Viability of Hydrogen

Water Chemistry for Protecting In-Vessel Components of Boiling Water Reactors".

Corrosion, 48(3), 194-205 (1992)], as described above. For calculating Eh it is important

to note that the potential corresponds to that which would exist when the net current due

to all of the redox reactions occurrng at a surface is zero. -For the] t redox reaction, Rj =

9, + nje-, in the system, the partial current density can be represented by the generalized

Butler-Volmer equation as (repeated here for convenience):

ebij- e ebj7

e b,,l - e -b,,jl' (27)

io~j 1f I] r,l1j

where 77 E - E'is the overpotential, and E'> bý 1,j b, 1, 0 , and 'r~lj are the

equilibrium potential, the anodic Tafel constant, the cathodic Tafel constant, the

exchange current density, the forward mass transfer-limited current density, and the

reverse mass transfer-limited current density, respectively. The equilibrium potential is

calculated from the composition of the system with respect to each redox reaction using

the Nernst equation, the Tafel constants and the exchange current density must be

measured for the reaction of interest, and the mass transfer-limited current densities can

E-35
be calculated from the mass transfer correlations for the system. Thus, for the net current

at the surface of an inert electrode-being zero, the following equation results

e b.,j(Eh-Ej) _-e -b,,(Eh-E.ý) 0(8

L0j if~lij i"

Equation (28) must be solved for the redox potential, Eh. This normally is done by direct

substitution or by using the Newton-Raphson iterative technique. It is important to note

that, in applying Equation (28), the summation must be made over all redox reactions in

the system. Thus, in the present case,, the summation should be carried out over

Fe +/Fe2+in addition to 0 2 1H2 0, and H2/H20, and possible even over reactions involving

various radiolytic species, such as H2 0 2 /H2 0, if their concentrations are significant. An

important conclusion from many years of modeling the redox potential and corrosion

potential properties of a wide range of physico-electrochemical systems is that the

contribution that any given species makes to the redox or corrosion potential is roughly

proportional to its concentration. That is why, in modeling nuclear reactor coolant

circuits, all radiolysis species except 02, H2, and H 2 0 2 can be ignored. The same

principle holds for a LOCA environment. 2

It may be argued that, if there is sufficient hydrogen in the water that Fe2 is the

predominant dissolved species and that the stable phase is not FeOOH, but is Fe3 0 4 or

even Fe (OH) 2 (see Issue 4 below), then the reaction of interest should be

Fe (OH) 2 + 2H+ Fe~+2 2 0 (29)

This argument would be valid, if the system was at equilibrium but, as shown above, we

are dealing with a system that is far from equilibrium. Thus, in my opinion, the only

rational way of modeling the chemistry of the system is in tenns of the non-equilibrium

redox potential and not in terms of equilibrium concepts.

There are a number of points that need to be made at this point:

" Precipitation, particularly if it occurs by rapid cooling and/or flashing, rarely

results in an equilibrium product. Instead, the precipitate that forms is that which

is least hindered kinetically in its formation and not that which is

thermodynamically the most stable.

* For any given set of conditions, the most unstable solid exhibits the highest

solubility. Thus, from the Second Law of Thermodynamics, the least stable form

will dissolve to form a super saturated solution with respect to the more stable

form, resulting in the precipitation of the latter. On the other hand, the least stable

form may convert to the more stable form via a solid state reaction, although these

are generally very slow at the temperatures of interest in this analysis.

* To ensure that a system is at equilibrium, the solubility should be approached.

from both sides of an independent variable (e.g., redox potential, pH, temperature).

Furthermore, before any equilibrium model calculations can be believed or

E-36
accepted, the models must be bench marked against appropriate experiments to

determine efficacy.

While this report was being prepared, the author and his colleagues prepared a

radiolysis/ECP code that incorporates a boric acid/lithium hydroxide solution chemistry

module and a radiolysis model that incorporates reactions for the oxidation of ambient air

nitrogen to nitric acid and other nitrogen species in solution, in addition to the water

radiolysis model outlined above. The code also incorporates the mixed potential model

described above for calculating the corrosion potential (ECP) of stainless steel, using

kinetic parameters that had been previously developed for modeling the electrochemistry

of Boiling Water Reactor primary coolant systems.

0.8-

0.7- r = 106 rad/h Figure 4. Predicted corrosion

potential (ECP) for stainless steel

w0.6- T 2 0 as a function of time and

:rT2

U) .5- temperature for a gamma photon

>V.1 dose rate of 1 O6

radlhr. Solution

0.4 60 0 Ccomposition: [B] =2800ppm, [Li] oL .- ... ... ............ 2ppm, P02 = O.2atm, pN2

0.2 0.8atm, [H 2]1i~it Oppm, and ------ ' T =95 0C [H202]i~it = Oppm. 0.1t I I I I I

le-4 1le-2 1le+0 1le+2 le+4 Ile+6 le+8 le+10

Time, s;

Scoping calculations using this code are summarized in Figures 4 to 6 for a

solution of 2800mg/L boron (as boric acid) + 2mg/L lithium (as LiOH) in equilibrium

with ambient air (O.2atm 02 + O.8atm N2) as a fuinction of irradiation time, temperature,

and gamma-photon dose rate. The initial concentrations of hydrogen and hydrogen

peroxide were assumed to be zero. As shown in Figure 4, for a dose rate of 106 radlhand

for all temperatures the ECP begins to increase after about 1 OO0s (17 minutes) due to the

initial production of H20 2 and subsequent acidification of the solution. Note that, at

shorter times, the ECP is predicted to become more negative with increasing temperature.

This is a well-established trend in corrosion science. Note also that, at long times, the

ECP is insensitive to temperature. In this case, the ECP is dominated by the hydrogen

peroxide formed by radiolysis and the nitric acid, that results from the radiolytic oxidation

of nitrogen from the ambient air.

E-37
0.8

0.7 -1 - Iu IdUIlI

Figure 5. Predicted corrosion

W0.6 -potential (ECP) for stainless steel as __F 1 rad/h a function of time and gamma

>0.5 photon dose rate for [B] = 2800ppm,

O0.4 -FIF 10 rad/h .. [Li] = 2ppm, P02 = O.2atm, PN2

W .* .8atm, [H2

]init = Oppm, and

0.3---- [H2O2]i~it =Oppm. T =25 0C.

0.2- 1 1 1 I

1le-4 1le-2 I e+0 1le+2 1le+4 Ie+6 le+8 le+10

Time, s

As expected, the time at which the ECP is predicted to increase is a sensitive

function of the dose rate, as shown in Figure 5. Thus, for a dose rate of 106 rad/h, the

ECP at 25'C is predicted to increase after about 100~s, but for a dose rate of 1 Oradlh no

change is predicted until after about one year. Interestingly, for long times, the rate at

which the ECP increases is predicted to be insensitive to the dose rate, a finding whose

origin is not immediately apparent.

6-

5- ~Figure 6. Predicted pHas a function

4 of time and gamma photon dose rate

Gama atefor Poto D~se [B] = 2800ppm, [Li] = 2ppm, P02=

:r 0.2atm, PN2 0 .8atm, [H-2]1init Oppm,

2 - rand [H 2O2]1init Oppm. T 250C.

-1 I -5 -4 -3 2 -1 0 1 2 3 4 5 6 7 8 9 10 11

Logj,(Time /s)

As noted above, the model predicts that the containment pool solution will

become acidified due to the radiolytic oxidation of dissolved nitrogen from the

atmosphere to nitric acid, a process that can be written in overall form as

N2 +H 2 0+S5[0]--> 2HN03

where the species in square brackets represents an oxidizing species derived from the

radiolysis of water. The model predicts that, even in the presence of strongly buffering

2800mg/L of boron as boric acid + 2mg/L of lithium as lithium hydroxide, radiolytic

production of nitric acid overwhelms the buffer in a time that is as short as a few tens of

minutes, provided that the dose rate is sufficiently high. At lower dose rates, longer times

arc required to overwhelm the buffer, but it is predicted to be overwhelmed within times

that are relevant to PWR LOCA analyses, even for dose rates as low as I OO0rad/h.

E-38
Although the model does not incorporate other buffer systems that exist in

containment (TSP, TSB) or captures the complexity of the containment pool chemistry, it

does demonstrate that radiolytic effects can not and should not be ignored. Furthermore,

the changes predicted in the ECP for stainless steel reflect large changes in the redox

properties of the pooi that will surly have an important impact on pool chemistry.

5.2. Co-Precipitation of Other Species with FeOOH, A100H, etc.

Co-precipitation is a phenomenon that can have a profound impact on the

composition of a precipitated phase. Indeed, great use is made of this phenomenon in

separation science, particularly in radiochemistry. Thus, it is possible that the

precipitation of A100H will co-precipitate FeOOH, and vice versa, even though

conditions are not right for the precipitation of the co-precipitated phase alone. To my

knowledge, no thermodynamic equilibrium code is capable of predicting co-precipitation

phenomena and, hence, this phenomenon needs to be explored experimentally. This

topic is discussed further below.

5.3. Ostwald Ripening

Once a precipitate forms, usually as a floc, Ostwald Ripening may occur, in which

the precipitate densifies by losing water and larger crystals grow from smaller crystals,

because the latter have higher solubility. Fundamentally, this latter effect is due to the

Gibbs-Thompson effect, which stipulates the dependence of the surface free energy (Pr~

on the radius of curvature (r) as:

Pr = .+ (30)

r

where A is a constant and po is the Gibbs surface free energy of a flat surface (infinite

radius of curvature). Thus, as r decreases, the Gibbs energy of the surface becomes

larger and the equilibrium concentration of dissolved products increases. Thus, the

solution becomes super-saturated with respect to a surface of larger radius, r, and hence

precipitation occurs on that surface via the dissolution of the smaller particles. That is,

larger particles tend to grow at the expense of smaller particles. Additionally,

precipitates frequently become more mechanically resilient after Ostwald Ripening, with

the result that they are easier to filter. However, the same property causes the precipitate

to be more effective at blocking filters, which is the concern in a LOCA scenario.

Ostwald Ripening of the precipitated phases in a LOCA needs to be clearly understood

when designing and evaluating filters.

One other process plays an important role in "Ostwald ripening" and that is

chemical reaction to form a new phase. For example, Ostwald ripening of a mixed

precipitate, such as Fe(OH) 2 and Ni(OH)2 Will generally result in the formation of the

mixed oxide, NiFe2O4 , which has the structure of magnetite (i.e., a spinel) with Fe(II)

being replaced by Ni(II). A huge number of reaction examples of this type exist, and

indeed they are used to synthesize a wide range of materials, usually under hydrothermal

conditions to obtain rapid reaction rates.

E-39
5.4. Schikorr Reaction Generates Hydrogen In Situ.

The Schikorr reaction describes the conversion of ferrous hydroxide, which is the

immediate precipitated product of Fe 2+ hydrolysis, results in the conversion of Fe (OH) 2

into magnetite (Fe3 04):

3Fe (OH)2 --4 Fe3O4 + H2 + 2H20 (31)

This reaction not only forms a hard, crystalline deposit of black magnetite, but it

produces one mole of hydrogen for every mole of magnetite formed. The hydrogen can

have a profound impact on the redox potential of the system, and hence upon the

solubility of those phases that are electroactive (i.e., dissolve with a change in oxidation

state) - see Issue 1, above. This reaction has been recognized for many decades as being

of great importance in boiler water chemistry and corrosion phenomena and, indeed,

evidence suggests that the hydrogen that is produced is responsible for the hydrogen

embrittlement of steels. Calculations need to be made as to how much hydrogen may be

generated and what the consequences of that hydrogen may be for the redox potential

assuming realistic values for Fe 2+ [and hydrolyzed Fe(II) ions] in the coolant at the point

of a LOCA, The author wishes to stress that there are many reactions that exist in the

Fe/H20 system (and .indeed in the Ni/H20 and Cr/H20 systems) that are "Schikorr-like"

and that may result in the conversion of hydroxides into oxides with the concomitant

generation of hydrogen. These reactions need to be defined within the LOCA context

and included in any discussion of chemical effects.

5.5. PZC and Coagulation

Certain aspects of the precipitation and coagulation of particles in aqueous

environments are well understood, including the role played by the zeta potential and the

PZC (pH of zero charge). Thus, all oxide/oxyhydroxide/hydroxide surfaces are

amphorteric; that is, they undergo acid/base reactions to produce a surface charge. Thus,

at sufficiently low pH (sufficiently high H+ activity), surface hydroxide groups are

protonated, S-OH- + H+ 4 S-OH2+, whereas at a sufficiently high pH, deprotonation

occurs,' S-OH- + O1- -* S-0- + H2 0, where S designates the surface. Thus, at some

pH value, there will be equal populations of protonated and deprotonated hydroxyl

groups on the surface or all groups will be the charge neutral, S-OH-. In either case, the

surface will have a net zero charge. This pH is known as the PZC (pH of zero charge).

Thus, for pH < PZC, the surface will be positively charged, but for pH > PZC, the surface

is negatively charged. The variation of the surface charge with pH for two different

surfaces (A and B) is shown schematically in Figure 1. The true variation is sigmoid in

shape (without the sudden changes in slope as shown) and the PZC is indicated by the pH

at which the curve crosses the horizontal axis ((Y = 0). The charge saturates at high and

low pH, because there is a fixed density of adsorption sites on the surface, corresponding

to the density of S-OH groups. A rough estimate of the density of sites is lnmollcm 2,

giving a charge density at saturation of 97[tC/cm 2.

E-40
+

Figure 7: Schematic plot of surface charge density versus pH for two

surfaces in contact with the same aqueous solution.

The importance of the surface charge that forms spontaneously on an oxide

surface is that: (1) An electrical double layer forms in the solution side of the interface,

such that the excess charge in the double layer is equal, but opposite in sign, to that on the

surface. (2) The PZC of any given surface depends upon the identity of the substrate,

such that different surfaces in an aqueous solution of a given pH may be oppositely

charged (Figure 7, where the surface charge of A at pH,,,,, is negative while that on B at

the same pH is positive. Thus, the excess charge in the double layer on A is positive,

while that on B is negative. Clearly, in this case, a coulombic attraction exists between

the surfaces and, if the surfaces are those of particulates, the particles will coagulate. If,

on the other hand, the system comprises like particles, such that all have the same charge

(including sign),or if the pH of the solution containing unlike particles lies outside of the

region defined by PZC-A *-*PZC-B, Figure 1, the electrical double layers repel one

another and the dispersion is stable and precipitation will not occur. However, if the

distance from the surface over which the double layer exists can be shrunk, the particles

may approach one another to sufficiently small distances that van der Waal forces

overcome the electrostatic repulsion and coagulation occurs.

E-41
CD 0

Surface o (

(D 0

L I.. TH.Lmnce krmi Eileclrode

Poteuntia

Surface 011P' Diffuse oyeI*

Figure 8: Schematic representation of the electrical double layer in the

solution side of an oxide/solution interface.

The double layer comprises two layers (actually, three, but two is sufficient to

facilitate the present discussion). In this simplified picture, closest to the surface, there

exists an adsorbed layer of hydrated ions have a charge that is opposite to that due to

the ionized or protonated hydroxyl groups, which is determined by the pH. In the case

shown, this layer. of adsorbed ions, the centers of Which define the Outer Helmholtz

Plane (OHP), only partially neutralizes the negative charge on the hydroxyl groups, so

that the potential at the OHP is less than that in the bulk solution, 9,* Outside of this

plane, the relative concentrations of positive and negative ions is determined by

electrostatic interaction and thermal randomization. Solution of Poisson's equation

yields a roughly exponential (actually a hyperbolic sine) dependence of electrostatic

potential on distance in the "diffuse layer", as indicated in Figure 8. The characteristic

length is the distance from the surface to the point where the potential drop across the

diffuse layer has decayed to I/e of the value at the OHP.

The characteristic length of the diffuse layer depends inversely upon the square

root of the ionic strength of the medium, which is defined as

I1= 0.5yz'Ci (32)

where zi is the charge number of the ion i, and ci is its concentration, with the summation

being carried out over all ions in the system. If the solution is 0. 1 M NaCI, for example,

Equation (1) yields an ionic strength of 0. 1 M. On the other hand, if the electrolyte is 0. 1

M A12 (S0 4 )3 (Alum), the ionic strength becomes 1.5, fifteen times that of a NaCI solution

of equivalent concentration. The characteristic length of the diffuse layer is then reduced

E-42
by a factor of nearly 4 and this reduction is sufficient to cause coagulation and

precipitation of colloidal particles (e.g., clay, organic matter, and polymeric hydrolyzed

ions), due to van der Waal attraction, followed by Ostwald ripening. Additionally, the

hydrolysis and polymerization of Al(III) produces a gelatinous precipitate that coprecipitates other matter (ions,. colloids, or even particles), as discussed in Issues 2 and 3

above and further discussed below. The above is nothing more or less than the Alum

process for clarifying domestic and industrial water su'plies and has been practiced for

more than 140 years.

An important consequence of coagulation via surface charge effects is the

phenomenon of co-precipitation and/or co-coagulation, in which the hydroxides and or

oxyhydroxides and oxides of different metals may coagulate together to form, after

ripening, mixed oxides, hydroxides and oxyhydroxides. Indeed, this is a well-established

route for the synthesis of such materials. If the starting system is a colloidal mixture,

then the charges (sign and magnitude) on the different material particles play key roles in

determining the form and extent of the co-precipitates. Because the charge (again, the

sign and magnitude) are determined by the activity of hydrogen ion in the solution, the

pH is a key variable in determining the nature of the product. After a LOCA, it is

envisioned that various oxides, oxyhydroxides, and hydroxides of elements, such as Al,

Zn, Fe, Si, and Ca, will be present in the system. These oxides, oxyhydroxides, and

hydroxides have widely differing PZC values, so that the relative charges on the different

particles may change drastically as the pH of the medium is changes. Clearly an

understanding of the dynamics of co-precipitation and co-coagulation requires a thorough

characterization of the surface charge characteristics of all components in the system.

These concepts must be used to develop an understanding and, eventually, a

predictive model for precipitation and coagulation post LOCA. This model should then

be combined with a model for Ostwald ripening to provide a quantitative tool for

predicting the identities and yield of solid precipitates in a LOCA. The combined model

should be capable of predicting the temperature and pH at which precipitation occurs (see

Issue 6, below) and the rate of particle growth. The process should begin by first

collecting the extensive data that exist in the literature for the PZCs of the materials that

are expected to come into contact with water and with one another; if the data are not

available, they should be measured using standard techniques. The critical ionic

strengths for coagulation should then be measured for the various colloidal systems, from

which the van der Waal parameters may be estimated. From there, the rate of

precipitation can be modeled as a Brownian motion problem (see collisional theory for

gases) by assuming a sticking probability of one. Little attention seems to have been paid

to these important factors in the analysis to date, but they provide guidance as to the rate

of precipitate formation and may allow formulation of strategies to control the

precipitation, so as to avoid clogging of the filters.

5.6. y-A100H formation

The hydrothermnal formation of boehmite, y-AlOOH, from A13+ solutions has been

studied [see D. D. Macdonald, P. Butler, and D. Owen. "Hydrothermal Hydrolysis of

A13+ and Precipitation of Boehmite from Aqueous Solution". J. Phys. Chem., 77(20),

2474-2479 (1973)], and this work provides useful data on the buffering capacity of that

reaction as the precipitate forms. The reader will note that, as the temperature increases,

E-43
the pH of the solution becomes independent of the initial concentration of A13+ in the

system. This may have important implications in modeling the precipitation process.

The paper also provides a model for the speciation of the principal polymeric ionic

species in the system as hydrothermal precipitation of boehmite (y-AlOOH) occurs. For

example, starting with a solution of 0.038m A13+ in 1.0 mn KCl at an initial pH of 2.59, the

principal hydrolysis product is predicted to be the dimer, A12 (OH)2 , over the entire

temperature range (25TC - 1 500C). However, at temperatures above about 1 25'C, the

highly polymerized species, Al14(OH)34

8+, is predicted to become significant, coincident

with the precipitation of boehmite. Thus, this study shows that the hydrothermal

precipitation of boehmite, for example, proceeds by the progressive formation of more

highly hydrolyzed cationic species with the ratio of 0 to Al converging onto the ratio that

exists in the precipitate (ratio = 2), with some species being preferred for structural

reasons. Finally, this paper contains a model, which after updating with later data for the

hydrolysis of A13 +' should allow accurate simulation of the formation of the

oxyhydroxides of aluminum in a LOCA environment.

Similar models have been developed for the precipitation of the oxyhydroxides of

iron, but the author is not aware of similar treatments for the thermal hydrolysis of Zn 2 +

and Ca2 ~ for example.

5.7. Precipitation on Fibers

I believe that an explanation for the initial precipitation of y-AIOOH onto glass

fibers might be found in an analysis of the PZCs of the fiber and the precipitating

material, with respect to the pH of the solution, and in the impact of ionic strength on the

critical lengths of the diffuse layers and their impact, in turn, on the rate of particle

agglomeration, as discussed in Issue 5. The viability of this mechanism might be tested

by studying the rate of growth on different surfaces (and hence of different surface charge)

and from solutions of different ionic strength using a quartz crystal microbalance. This

technique is capably of detecting mass changes of nano-grams per square centimeter, is

readily applied in situ, and can be used over a range of temperatures. The principal

challenge will be in obtaining low mass fiber glass samples mounted on the silicon

oscillator. Nevertheless, QCM would allow a high throughput in the experiments and

would permit the determination of quantitative data for deposit growth rate.

5.8. Thermal Hydrolysis of Organic Material

Considerable organic material exists in confinement in a PWR, ranging from paint

to plastic insulation. Some of this material would be partially pulverized and rendered

into a colloidal form by hydrothermal hydrolysis. The reader should note that the PZC

concept also applies to organic particles, so that PZC values for the organic colloids that

are produced by the thermo-hydrolysis of the organic materials need to be determined.

Thus, organic colloids need to be included in the list of particles that should be explored

under Issue 6. It is most important to note that the hydrothermal hydrolysis of organic

materials results not only in depolymerization, and hence in the production of particles of

micro- to nano-meter dimension, but also in surfaces that are partially oxidized to

produce alcoholic (-OH), ketonic (C=0), and acidic (-COGH) moeties, which contribute

to defining the acid/base properties of the surfaces and hence the PZC.

E-44
Organic species also have an important effect of modifying surfaces by adsorption.

In doing so, they may change the surface charge characteristics completely, causing

precipitation or inhibiting coagulation. Many of these effects are currently very poorly

defined and understood and, hence, are very difficult, if not impossible, to predict from

first principle calculation. Those systems that have been studied at any depth tend to be

"4simple systems", that are of only marginal value to the problem of interest in this work.

5.9. Is There a Particle Size That Can Be Tolerated?

Accepting that clogging of the filters most likely would result from the initial

formation of colloidal particles followed by coagulation and Ostwald ripening, the

question arises: Is there a particle size that can be tolerated? A closely related question

concerns the impact of flow velocity and fluid shear rate on the particle size distribution.

This issue needs to be explored under realistically simulated LOCA conditions, because

presumably there exists a particle size below which the particles will pass through the

filter and hence will not impede flow. The formation of larger particles would be

discouraged by the high shear rate that tends to inhibit coagulation. However, the current

information on this process is very qualitative in nature, whereas quantitative information

is required in order to synthesize predictive models. The models would then be used to

assess the risk of clogging of the filters (and the pump) for different pump speeds.

However, it is doubtful that such a model would yield a definitive answer without

calibration using a full mock-up of the pump and filter system.

5.10. Why Does a Bimodal Distribution Exist in Particle Size?

A bimodal distribution in particle size commonly indicates parallel growth processes

from a common population of nuclei, with the two growth processes occurring at

different rates. The different growth rates may reflect different Ostwald ripening rates or

a bimodal distribution in the nuclei with regard to surface charge (and hence with respect

to agglomeration rate). The latter should be detectable by measuring the particle mobility

electrophoretically, in which case a bimodal distribution in mobility should be found.

Another method that might be tried is to fractionate the sample using centrifugation at

different rotation speeds and then use each fraction as seeds for further growth. If there

are two preferred sizes for growth, they might be detected in the final particle size

distribution.

5.11. Corrosion of Aluminum

The corrosion and passivity of aluminum has been studied extensively and space does

not exist here for me to summarize all that is known. Aluminum is a very active metal,

particularly at elevated temperature, as indicated by the potential-pH diagram [D. D.

Macdonald and P. Butler. "The Thermnodynamics of the Aluminum-Water System at

Elevated Temperatures". Corros. Sci., 13, 259-274 (1973)]. The potential-pH diagram

displays a large predominance region for the oxyanion aluminate, Al(OH)4i that becomes

larger with respect to that for AP3+ as the temperature increases (reflecting a lower surface

charge density for the former than for the latter). At intermediate pH values, there exists

a stability region for the oxide, A1 2 03 , which passivates the surface.

E-45
The formation of passivating oxide films on metal surfaces is well understood in

terms of the Point Defect Model (PDM) [D. D. Macdonald, Pure Appi. Chem., 71, 951

(1999)]. Briefly, the film forms as a bi-layer structure, comprising a defective oxide

barrier layer adjacent to the metal and an outer, precipitated layer of Al(OH) 3 adjacent to

the solution. A point defect model for the passive layer in acidic solutions, where Al3+ is

the predominant species, is presented below, assuming that the mobile cation in the

barrier layer is the metal interstitial. A similar model is easily formulated for the passive

film on any metal under the conditions of interest.

The validity of the PDM for describing passivity and the corrosion of passive

metals has now been demonstrated by the author and other researchers. The model is

capable of accounting for not only the properties of the passive state, but also the

transition to the transpassive state, passivity breakdown, and depassivation phenomena.

When combined with the generalized Butler-Volmer equation for the cathodic reduction

of oxygen and hydrogen evolution, and after imposing the conservation of charge, the

resulting mixed potential model (MPM) is capable of calculating the corrosion potential

and corrosion rate quantitatively, as has been demonstrated by the author's extensive

modeling of corrosion processes in the heat transport circuits of water-cooled nuclear

power reactors.

By using a two-component brick wall analogy (red bricks for cations and cation

vacancies and blue bricks for oxygen ions and oxygen vacancies), and noting that the

minimum unit of the barrier layer is one red brick and one blue brick in adjacent

pos itions, it is apparent that Reactions (1), (3), and (4), Figure 3, are lattice conservative

processes (i.e., the barrier layer boundaries do not move with their occurrence), whereas

Reactions (2) and (5) are lattice non-conservative processes. Note that the entity

A/Al + 3 - Il (I~) seuiaett A12 03 , because vacancies can be regarded 2 V ~ 12 V)iseuvlnto2

as being real species. Experimentally, we know that the barrier layer on a metal achieves

a steady-state thickness and, hence, there must exist two non-conservative reactions at the

barrier layer interfaces; specifically, the other must be at the barrier layer/outer layer

interface. That reaction is Reaction (5), which describes the dissolution of the barrier

layer. Thus, in the steady-state, the rates of Reactions (2) and (5) must be equal. The

formation of the outer layer is due to precipitation of Al(OH) 3 from a super-saturated

solution of Al+ that forms via dissolution from thermodynamically less stable sources;

namely, aluminum metal via interstitials in the barrier layer and the defective barrier

layer, itself, Al1+,O1-y. In any event, the outer later forms by precipitation and may

contain substantial quantities of other species, such as borate, that are present in the

solution.

E-46
Al All±,Ol-y A1(OH) 3 Solution

I k, 13I3 3 3

(1) Al-- -A? + VAl +3e- (3) A ~ 3 A 01 - - - - - - - ->A

(2) Al k2 >AlAl +-3V'* + 3e (4) Vc7 +H2 0 k4 -->0+2H+~

2 0

(5) A1203 +6H+--k 5 -2Al3+ +3H 2 0 --- >Al3+

(6) A 131 + 3 H 2 0 k6 4Al(OH)3 ,

1 + 3H+01

(7) Al(OH)3 ,o1 + 3H+ k7 Alb~ + 3H0

Figure 9: Point defect model for the anodic oxidation of aluminum in

aqueous solution. The species Al, A i3 VAI I A/Al I Vý, A13+' andO00

represent aluminum metal, an aluminum cation interstitial, a vacancy in

the metal substrate, an aluminum cation on the cation sublattice of the

barrier layer, an oxygen vacancy on the anion sublattice of the barrier

layer, an aluminum cation in solution, and an oxygen anion on a normal

anion site on the anion sublattice, respectively. The subscripts "of' and

"b" designate outer layer and bulk solution locations.

When the outer layer comprises a hydroxide, such as Al(OH) 3 , which is a good

proton conductor, the phenomenon of passivity can be attributed to the barrier layer

alone. However, under some conditions, the outer layer forms as a porous oxide, A1 2 03 ,

with the pores being oriented normal to the surface in a more-or-less regular array. In

this case, the outer layer may contribute substantially to the interfacial impedance. The

pores may be sealed, most commonly by boiling the specimen in water, in which case the

outer layer acts as an impervious coating and may completely dominate the corrosion

resistance of the substrate. The formation of such a film most commonly occurs under

anodizing conditions and sealing is performed to enhance the corrosion resistance of the

surface.

E-47
The corrosion rate of aluminum is due to Reactions (1) and (2), Figure 3, and may

be written as

CR =f2,41(k, +k 2 ) (cm/s) (33)

where k, and k2 are the rate constants (mollcm2.s), as indicated in Figure 3, and nA1 is

the molar volume of aluminum metal. The corrosion rate may also be expressed in terms

of mass per unit area per unit time as:

CR =MAI (k, + k2 ) (g/cm .s) (34).

where MAI is the atomic weight of aluminum. Regardless of which expression is used, it

is necessary to determine the rate constants k, and k2. Partial charge transfer theory and

activated complex theory show that the rate constants may be written in more

fundamental form as

ki ki0e ajV e-~Le cjpH (35)

and

2 2kooea2V e b2L eC2PH (36)

where the coefficients a, b, and c are functions of still more fundamental parameters,

including the electric field strength, the polarizability of the barrier layer/outer layer

interface, and the transfer coefficients for the interfacial reactions, among others, V is the

voltage (the corrosion potential, in this case), and L is the thickness of the barrier layer.

Values for these parameters are readily determined by using electrochemical impedance

spectroscopy (EIS) [D. D. Macdonald, A. Sun, Priyantha, N., P. Jayaweera, "An

Electrochemical Impedance Study of Alloy 22 in NaCl Brine at Elevated TemperaturefII.

Reaction Mechanism Analysis", J. Electroanal. Chem., 572, 421-431 (2004)], and hence

the corrosion rate may be calculated.

In highly alkaline solutions, corrosion is believed to occur in the transpassive

state, in which the metal has been depassivated by the loss of the barrier layer. In this

case, the corrosion rate is controlled by the dissolution of the metal in the presence of the

precipitated outer layer, which offers only moderate resistance to corrosio n. This case

has been studied extensively under the DOE program in the 1980s that aimed at

developing fuiels for aluminum-air batteries for automotive appli cation [D. D.

Macdonald, K. H. Lee, A Moccari, and D. Harrington, "Evaluation of Alloy Anodes for

Aluminum/Air Batteries I. Corrosion Studies". Corrosion, 44, 652-657 (1988); S. Real,

M. Urquidi-Macdonald, and D. D. Macdonald, "Evaluation of Alloy Anodes for

E-48
Aluminum/Air Batteries II. Delineation of Anodic and Cathodic Partial Reactions". J.

Electrochem. Soc., 135(7), 1633-1636 (1988); D. D. Macdonald, S. Real, and M.

Urquidi-Macdonald. "Evaluation of Alloy Anodes for Aluminum-Air Batteries 111.

Mechanisms of Activation, Passivation, and Hydrogen Evolution", J. Electrochem. Soc.,

135(10), 2397-2409 (1988); D. D. Macdonald, S. Real, S. 1. Smedley, and M. UrquidiMacdonald, "Evaluation of Alloy Anodes for Aluminum-Air Batteries IV.

Electrochemical Impedance Analysis of Pure Aluminum in 4M KOH at 25'C", J.

Electrochem. Soc., 135(10), 2410-2414 (1988)]. That work produces a model for

aluminum dissolution in highly alkaline solutions that involves the stepwise

electrochemical discharge of OH onto the metal surface followed by the chemical

dissolution of Al(OH)4 from the surface. The key question concerns which model to

adopt (with or without a barrier layer) for the conditions that prevail in a LOCA.

In my opinion, a quantitative model for calculating, the corrosion rate of

aluminum, or of any other metal or alloy, could be developed and used to estimate the

inventory of aluminum corrosion products in confinement as a function of time during a

LOCA. This would require an EIS study of aluminum in various enviromnments as a

function of voltage, pH, and temperature, followed by optimization of the Point Defect

Model (Figure 3) on the experimental data, in order to extract values for various model

parameters. Work on developing a PDM for the corrosion of aluminum has been

initiated in the author's laboratory with a visiting student from Spain. The results of this

work will be made available to NRC/ANL as they become available.

Similar models may (and in some cases, have been) formulated for the other

metals of interest, including iron and zinc. The models are readily available in the

literature published over the past twenty years.

6. Recommendations

In the light of the issues identified above, a number of recommendations have

been formulated that, in the author's opinion, will significantly aid in developing a

quantitative understanding of, and a predictive capability for, the chemical processes that

might occur during and after a LOCA in confinement of a PWR. The recommendations

are supported by a number of publications that are cited in this report, but it is to be

understood that the literature review was not exhaustive.

Equilibrium models must be used with great caution, because the environment

produced by a LOCA is unlikely to be at equilibrium, at least during the initial

stages. Furthermore, the processes that occur during corrosion, precipitation, and

ripening are generally slow, as has been shown in some of the work reviewed

during the Kickoff Meeting at ANL. The kinetics of many of these processes are

such that the system may still be far from equilibrium as it enters the recirculation

system. Accordingly, equilibrium calculations need to be bench-marked to the

greatest extent possible against experiment to assess the reliability of the

thermodynamic equilibrium codes. This has been done to a significant extent in

the present program, but the results are hampered by the lack of consideration of

radiolysis and redox effects.

E-49
*Given the likelihood that equilibrium models may not be appropriate, emphasis

should be placed on developing kinetic models for the precipitation and ripening

(coagulation) processes. These models must recognize the most important driving

force for coagulation; the charge (sign and magnitude) that develops on the

surfaces of particles, as characterized by the zeta potential and the pzc (PH of zero

charge). PZC and zeta potential data should be experimentally measured,

although many of the required data may be obtained from the enormous literature

that exists on the subject. Certainly, extensive data are available for the oxides

and oxyhydroxides of iron and aluminum, but data may not be available for

various organic entities.

*The possible generation of hydrogen from the Schikorr reaction

3Fe(OH)2 -4 Fe3O4 + H2 + 2H120

and related chemical transformations should be explored, as they might contribute

significantly to the inventory of hydrogen in containment immediately after a

LOCA and to the inventory of magnetite (Fe304) in the system. On the positive

side, the Schikorr reaction will decrease the inventory of gelatinous Fe (OH) 2,

which may react with other components [e.g., Si(OH)4] to produce mixed

oxides/oxyhydroxides, and even mixed hydroxides that may be even more

troublesome. This issue can probably be resolved by calculation, using data given

in the literature.

*Realistic and viable models for the corrosion of aluminum, iron, and zinc, and of

the dissolution of concrete and polymeric materials in contact with hot coolant

under a wide range of mass transfer conditions (ranging from impinging jets to

quiescent pools) need to be developed that are capable of predicting corrosion

rates under realistic LOCA environmental conditions. The models for the metals

must incorporate passive dissolution, transpassive dissolution, and active

dissolution, as well as delineation of the conditions under which each occurs, as

all three processes may occur in a LOCA environment. The models for metallic

corrosion must also incorporate the appropriate cathodic partial processes

(reduction of oxygen and the evolution of hydrogen). Note that any hydrogen

evolved during corrosion must be added to the inventory generated by the

Schikorr reaction and to that which was present in the virgin coolant. While

estimates have been made of the corrosion rates of various materials, it is unclear

that the empirical models used are comprehensive in their coverage of the relevant

conditions.

*The hydrothermal hydrolysis of various organic/inorganic coating and insulation

materials needs to be explored under conditions that realistically simulate a

LOCA. It is expected that hydrothermal hydrolysis will partially de-polymerize

polymeric materials, producing materials ranging from particles to gels. These

materials need to be screened for their physical and chemical properties and, in

particular, for their tendencies to "set" into more resilient forms. The physical

properties that need to be explored include the iso-electric points (PZC), zeta

potentials, and rheological properties. The propensity for interactions between the

E-50
various components produced by hydrothermal hydrolysis among themselves and

with. other materials in the system must be clearly defined.

*The models that are produced to predict corrosion rates and phase properties must

be, to the greatest extent possible, deterministic in nature. Thus, a deterministic

model is one whose output (prediction) is constrained by the natural laws to that

which is physically viable. These constraints are generally the conservation laws,

such as the conservation of mass, charge, energy, and momentum. The

equivalence laws, such as Faraday's law of the equivalence of mass and charge,

or Joule's law of the equivalence of heat and work, are generally part of the

constitutive equations of a model. Importantly, in the art of prediction, it is not

sufficient for a model to be "mechanism based"; it must be implicitly constrained

by the conservation laws, which are a summation of scientific experience. Thus,

the researchers working on this program, and who are involved in the process of

model building, are urged to ensure that their models are deterministic within the

context stated above.

" Development of a radiolysis code specifically for a containment pooi is absolutely

essential, since the redox potential controls the speciation within the pool. This

model should incorporate boric acidlLiOH + TSP (tni-sodium phosphate) + TSB

(tetra-sodium borate) modules for estimating the pH. The model should be

calibrated/evaluated against laboratory experiments to establish efficacy.

* A thorough analysis should be carried out to estimate the likely y-dose rates in the

containment pool as a function of time after a LOCA in a PAIR. The contribution

of a-dose rate from fission products also needs to be evaluated. The latter is

completely ignored in the present analysis and the former ('y-dose rate) is little

more than a guess. No information of guidance on this subject could be found in

the open literature.

* A better database for the kinetics of the hydrogen electrode reaction, the oxygen

electrode reaction, and the hydrogen peroxide electrode reaction needs to be

established. Some of the "raw"~ data are already in the literature, but the

information is incomplete and the data are generally not in a form that is readily

interfaced with radiolysis/redox potential models. In some cases, howeve~r, the

required data must be experimentally measured.

* Possible acidification of the pool by radiolysis is a matter of essential importance

and must be explored to ascertain whether unacceptable conditions may develop

due to the radiolytic generation of nitric acid from nitrogen in the ambient air. Of

all of the recommendations given above, this recommendation and that on

including redox effects is by far the most important.

E-5 1
Appendix 1.

Resume of Digby D. Macdonald

Distinguished Professor of Materials Science and Engineering

Director, Center for Electrochemical Science and Technology

The Pennsylvania State University

201 Steidle Bldg.

University Park, PA 16802

(814) 863-7772, (814.) 863-4718 (fax), ddm2@psu.edu

EDUCATIONAL IBACKGROUND

B.Sc. (1965) and M.Sc. (1966) in Chemistry, University of Auckland (New Zealand);

Ph.D. in Chemistry (1969), University of Calgary (Canada).

PROFESSIONAL EXPERIENCE (past 35 years)

Distinguished Professor of Materials Science and Engineering, 6/2003 - present.

Chair, Metals Program, Penn. State Univ., 6/200 1 - 6/2003

Director, Center for Electrochemical Sci. & Tech., Penn. State Univ., 7/99 - present.

Vice President, Physical Sciences Division, SRI International, Menlo Park, CA, 1/98 -

7/99

Director, Center for Advanced Materials, Penn. State Univ., 7/91-3/2000

Professor, Materials Science and Engineering, Penn. State Univ., 7/91 - 6/03.

Deputy Director, Physical Sciences Division, SRI International, Menlo Park, CA, 4/87 -

7/91

Laboratory Director, Mat. Research Lab., SRI International, Menlo Park, CA, 4/87 - 7/91

Laboratory Director, Chemistry Laboratory, SRI International, Menlo Park, CA, 3/84 -

4/87

Director and Professor, Fontana Corrosion Center, Ohio State University, 3/79 - 3/84

Sr. Metallurgist, SRI International, Menlo Park, CA, 3/77 - 3/79.

Sr. Research Associate, University of Calgary, Canada, 3/75 - 3/77.

Lecturer in Chemistry, Victoria University of Wellington, New Zealand, 4/72 - 3/75.

Assist. Research Officer, Whiteshell. Nuclear Research Establishment, Atomic Energy of

Canada Ltd., Pinawa, Manitoba, Canada, 9/69 - 4/72.

CONSULTING ACTIVITIES (Partial list for the last five years))

Integrated Design Technologies

OLI Systems

Electric Power Research Institute

SRI International

Stone & Webster Engineering Co.

Science Applications International Corp.

Framatome

Metallic Power Inc.

E-52
Los Alamos National Laboratory

PA TENTS

1 . D. D. Macdonald and A. C. Scott, "Pressure Balanced External Reference Electrode

Assembly and Method", US Patent 4,273,63 7 (198 1).

2. D. D. Macdonald, "Apparatus for Measuring the pH of a Liquid", US Patent

4,406,766 (1983).

3. S. C. Narang and D..D. Macdonald, Novel. Solid Polymer Electrolytes", US Patent

5,061,581 (1991).

4. S. Hettiarachchi, S. C. Narang, and D. D. Macdonald, "Synergistic Corrosion

Inhibitors Based on Substituted Pyridmnium Compounds", US Patent 5,132,093

(1992).

5. S. Hettiarachchi, S. C. Narang, and D. D. Macdonald, "Reference Electrode

Assembly and Process for Constructing", US Patent, 5,238,553 (1993).

6. D. D. Macdonald, et al, "Conducting Polymer for Lithium/Aqueous Syst.", US Prov.

Pat. 60/119,360 (1998).

7. D. D. Macdonald, et al, "Polyphosphazenes as Proton Conducting Membranes", US

Pat. Appl. 09/590,985 (1999).

8. D. D. Macdonald, et al, "Impedance/Artificial Neural Network Method...", US Prov.

Pat. 60/241,871 (1999)

9. D. D. Macdonald, "Electrochemical Conditioning of Wine", US Prov. Pat.

60/295,080 (2001).

PUBLICATIONS (from 180 published over the past five years and from a total of

650+).

I1. Engelhardt, G.R., M. Urquidi-Macdonald, and D. D. Macdonald. "A Simplified

Method for Estimating Corrosion Cavity Growth Rates". Corros. Sci., 39(3), 419-441

(1997).

2. Gao, L. and D. D. Macdonald. "Characterization of Irreversible Processes at the

Li/Poly[bis(2,3-di-(2-methoxyethoxy)propoxy)phosphazene] Interface on Charge

Cycling". J. Electrochem. Soc., 144(4), 1174-1179 (1997).

3. Sikora, E. and D. D. Macdonald. "Defining the Passive State". Solid State Ionics, 94,

141-150 (1997).

4. Engelhardt, G. R. and D. D. Macdonald, "Deterministic Prediction of Pit Depth

Distribution", Corrosion, 54, 469-479 (1998).

5. Macdonald, D. D., E. Sikora, and J. Sikora, "The Kinetics of Growth of the Passive

Film on Tungsten in Acidic Phosphate Solutions", Electrochim. Acta, 43, 2851-61

(1998).

6. Pensado-Rodriguez, 0., J. Flores, M. Urquidi-Macdonald, and D. D. Macdonald,

"The Electrochemistry of Lithium in Alkaline Aqueous Electrolytes. Part 11: Point

Defect Model". J. Electrochem. Soc., 146, 1326-1335 (1999).

7. Macdonald, D. D, I. Balachov, and G. Engelhardt, "Deterministic Prediction of

Localized Corrosion Damage in Power Plant Coolant Circuits", Power Plant

Chemistry, 1, 9 (1999).

8. Engelhardt, G. R., D. D. Macdonald, and P. Millett, "Transport Processes in Steam

Generator Crevices. 1. General Corrosion Model", Corros. Sci., 41, 2165-2 1 90 (1999).

E-53
9. Macdonald, D. D., "Passivity: The Key to Our Metals-Based Civilization", Pure Appi.

Chem., 71, 95 1-986 (1999).

10. Quiroga. Becerra, H., D. D. Macdonald, and C. Retamosa, "The Corrosion of Carbon

Steel in Oil-in-Water Emulsions Under Controlled Hydrodynamic Conditions",

Corros. Sci., 42, 561-575 (2000).

11. Sikora, E. and D. D. Macdonald, "The Passivity of Iron in the Presence of EDTA.

Part 1. General Electrochemical Behavior". J. Electrochem. Soc., 147(11), 4087-4092

(2000).

12. Macdonald, D. D., M. AI-Rafaie and G. R. Engelhardt, "New Rate Laws for the

Growth and Reduction of Passive Films", J. Electrochem. Soc., 148(9), B343 - B347

(2001).

13. Macdonald, D. D., "Probing the Chemical And Electrochemical Properties of SCWO

Systems", Electrochim. Acta, 47, 775-790 (2001).

14. Zhou, X.Y., S. N. Lvov, X. J. Wei, L. G. Benning, and D. D. Macdonald,

"Quantitative Evaluation of General Corrosion of Type 304 Stainless Steel in

Subcritical and Supercritical Aqueous Solutions via Electrochemical Noise Analysis".

Corros. Sci., 44(2), 84 1-860 (2002).

PROFESSIONAL ASSOCIATIONS AND HONORS

" Selector of the Kuwait Prize for Applied Sciences, 1985.

* Research Award, College of Engineering, Ohio State University, 1983.

* The 1991 Carl Wagner Memorial Award from The Electrochemical Society.

* The 1992 Willis Rodney Whitney Award from NACE International.

" Chair, Gordon Research Conference on Corrosion, New Hampshire, 1992.

* Member, Board of Visitors, Office of Naval Research.

" W.B. Lewis Memorial Lecture by Atomic Energy of Canada, Ltd., 1993, "in

recognition of [his] contributions to the development of nuclear power in the

service of mankind".

* Elected Fellow, NACE-International, 1994.

* Member, USAF Scientific Advisory Board, Protocol Rank: DE-4 (Lieutenant

General equivalent), 1993-1997

" Elected Fellow, The Electrochemical Society, 1995.

" Elected Fellow, Royal Society of Canada, 1996. ("National Academy" of

Canada).

" Wilson Research Award, College of Earth and Minerals Sciences,

Pennsylvania State University, 1996.

" Elected Fellow, Royal Society of New Zealand, 1997. ("National Academy" of

New Zealand).

* H. H. Uhlig Award, The Electrochemical Society, 2001.

" U. R. Evans Award, The British Corrosion Institute, 2003.

*Appointed Adjunct Professor, Massey University, New Zealand, 2003.

*Appointed Adjunct Professor, University of Nevada at Reno, 2003.

*Elected Fellow, World Innovation Foundation, 2004.

.Elected Fellow, ASM International, 2005.

E-54
NRC FORM 335 U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER

(9.2004) (Assigned by NRC, Add Vol.. Supp.. Rev..

NRCMD 3.7 and Addendum Numbers, if any.)

BIBLIOGRAPHIC DATA SHEET

(See instructions on the reverse) NUREG-1861

2. TITLE AND SUBTITLE 3. DATE REPORT PUBLISHED

Peer Review of GSI-191 Chemical Effects Research Program MONTH YEAR

December 2006

4. FIN OR GRANT NUMBER

__________________________________________________________N6100

5. AUTHOR(S) 6. TYPE OF REPORT

Paulette A. TorresToia

7. PERIOD COVERED (inclusive Dates)

8. PERFORMING ORGANIZATION -NAME AND ADDRESS (if NRC, provide Division. Office or Region, U.S. Nuclear Regulatory Commission, and mailing address; if contractor.

provide name and mailing address.)

Division of Fuel, Engineering and Radiological Research

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

9. SPONSORING ORGANIZATION - NAME AND ADDRESS (If NRC, type "Same as above'; if contractor, provide NRC Divsion, Office or Region. U.S. Nuclear Regulatory Commission,

and mailing address.)

Same as above

10. SUPPLEMENTARY NOTES

11. ABSTRACT (200 words or less)

The NRC and RES has a policy of initiating formal peer reviews for research programs that are on the cutting-edge of technology

and will influence important regulatory decisions. Such is the case for the series of research projects that RES has sponsored to

resolve GSI-1 91, "Assessment of Debris Accumulation on PWR Sump Performance,' and to inform the NRC's regulatory

decisions regarding the potential for chemical by-products to clog sump screens in the post LOCA environment in PWRs.

This report describes the peer review assessment process and summarizes its significant findings. It is important to mention

that this peer review is not a consensus review. Each reviewer was asked to provide an individual evaluation based on their

particular area of expertise. The research projects addressed by the peer review included integrated chemical effects testing

(ICET) conducted at Los Alamos National Laboratory, chemical speciation prediction conducted through the Center for Nuclear

-Waste Regulatory Analyses at Southwest Research Institute, and accelerated chernical effects head loss testing conducted at

Argonne National Laboratory. The peer review evaluated the technical adequacy and uncertainty associated with the

RES-sponsored research results, and identified outstanding chemical effects issues. The final assessment reports from the peer

reviewers are included as appendices to this report.

12. KEY WORDS/DESCRIPTORS (List words or phrases that will assist researchers in locating the report.) 13. AVAILABILITY STATEMENT

Peer Review unlimited

Generic Safety Issue 191 14. SECURITY CLASSIFICATION

Chemical Effects (This Page)

Head Loss unclassified

Chemical Speciation (This Report)

unclassified

15. NUMBER OF PAGES

16. PRICE

NRC FORM 335 (9-2004) PRINTED ON RECYCLED PAPER
Federal Recycling Program
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NUCLEAR REGULATORY COMMISSION

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