U.S. Nuclear Regulatory Commission Plan 

for Monitoring Disposal Actions Taken by 

the U.S. Department of Energy at the 

Savannah River Site F-Area and H-Area Tank 

Farm Facilities in Accordance With the National 

Defense Authorization Act for Fiscal Year 2005

October 2015

U.S. Nuclear Regulatory Commission

Office of Nuclear Material Safety

 and Safeguards

Washington, DC 20555-0001
U.S. Nuclear Regulatory Commission Plan 

for Monitoring Disposal Actions Taken by 

the U.S. Department of Energy at the 

Savannah River Site F-Area and H-Area Tank 

Farm Facilities in Accordance With the National 

Defense Authorization Act for Fiscal Year 2005

October 2015

U.S. Nuclear Regulatory Commission

Office of Nuclear Materials Safety

 and Safeguards

Washington, DC 20555-0001
ii

CONTENTS

Section Page

FIGURES...................................................................................................................................iv

TABLES.....................................................................................................................................iv

ACRONYMS AND ABBREVIATIONS .........................................................................................v

DEFINITIONS........................................................................................................................... vii

EXECUTIVE SUMMARY ............................................................................................................x

1 MONITORING PROCESS............................................................................................1-1

Background.......................................................................................................1-1

Objective...........................................................................................................1-2

Roles and Responsibilities ................................................................................1-3

Coordination with the State of South Carolina...................................................1-5

Monitoring Approach.........................................................................................1-6

1.5.1 Technical Reviews ................................................................................1-6

1.5.2 Data Reviews ........................................................................................1-6

1.5.3 Onsite Observation Visits ......................................................................1-6

1.5.4 Periodic Data Reports and Closure Documentation...............................1-7

Periodic Compliance Monitoring Report ............................................................1-7

Notification Letters ............................................................................................1-7

Monitoring Plan...............................................................................................1-11

1.8.1 Linkage Between Recommendations in the Technical Evaluation 

Report and Monitoring Factors ............................................................1-11

1.8.2 Closing Monitoring Factors..................................................................1-11

2 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.40................................2-1

3 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.41................................3-1

MA 1 “Inventory” ...............................................................................................3-7

3.1.1 Monitoring Factor 1.1: Final Inventory and Risk Estimates ...................3-9

3.1.2 Monitoring Factor 1.2: Residual Waste Sampling ...............................3-10

3.1.3 Monitoring Factor 1.3: Residual Waste Volume..................................3-12

3.1.4 Monitoring Factor 1.4: Ancillary Equipment Inventory.........................3-13

3.1.5 Monitoring Factor 1.5: Waste Removal (As It Pertains to 

ALARA) ...............................................................................................3-13

MA 2, “Waste Release”...................................................................................3-14

3.2.1 Monitoring Factor 2.1: Solubility-Limiting Phases/Limits 

and Validation .....................................................................................3-18

3.2.2 Monitoring Factor 2.2: Chemical Transition Times..............................3-20

MA 3, “Cementitious Material Performance”....................................................3-21

3.3.1 Monitoring Factor 3.1: Hydraulic Performance of Concrete Vault 

and Annulus (As It Relates to Steel Liner Corrosion and Waste 

Release)..............................................................................................3-25

3.3.2 Monitoring Factor 3.2: Groundwater Conditioning via 

Reducing Grout ...................................................................................3-27

3.3.3 Monitoring Factor 3.3: Shrinkage and Cracking of Reducing 

Grout...................................................................................................3-29
iii

3.3.4 Monitoring Factor 3.4: Grout Performance..........................................3-30

3.3.5 Monitoring Factor 3.5: Vault and Annulus Sorption.............................3-30

3.3.6 Monitoring Factor 3.6: Waste Stabilization (As It Impacts 

ALARA) ...............................................................................................3-31

MA 4, “Natural System Performance”..............................................................3-32

3.4.1 Monitoring Factor 4.1: Natural Attenuation of Key Radionuclides .......3-33

3.4.2 Monitoring Factor 4.2: Calcareous Zone Characterization ..................3-35

3.4.3 Monitoring Factor 4.3: Environmental Monitoring................................3-35

MA 5, “Closure Cap Performance”................................................................3-388

3.5.1 Monitoring Factor 5.1: Long-Term Hydraulic Performance of the 

Closure Cap ........................................................................................3-38

3.5.2 Monitoring Factor 5.2: Long-Term Erosion Protection Design...........3-399

3.5.3 Monitoring Factor 5.3: Closure Cap Functions That Maintain 

Doses ALARA ...................................................................................3-399

MA 6, “Performance Assessment Maintenance” .............................................3-40

3.6.1 Monitoring Factor 6.1: Scenario Analysis............................................3-41

3.6.2 Monitoring Factor 6.2: Model and Parameter Support ........................3-42

3.6.3 Monitoring Factor 6.3: Tank Farm PA Revisions.................................3-42

4 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.42................................4-1

MA 1, “Inventory” ..............................................................................................4-2

MA 2, “Waste Release”.....................................................................................4-5

MA 3, “Cementitious Material Performance”......................................................4-5

MA 4, “Natural System Performance”................................................................4-6

MA 5, “Closure Cap Performance”....................................................................4-6

MA 6, “Performance Assessment Maintenance” ...............................................4-7

5 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.43................................5-1

Monitoring Factor 7.1: Protection of Workers During Operations......................5-2

Monitoring Factor 7.2: Air Monitoring ...............................................................5-2

Monitoring Factor 7.3: As Low As Is Reasonably Achievable...........................5-3

6 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.44................................6-1

Monitoring Factor 8.1: Settlement ....................................................................6-1

Closure of MA, 8 “Site Stability” ........................................................................6-2

7 REFERENCES.............................................................................................................7-1

8 LIST OF CONTRIBUTORS ..........................................................................................8-1

APPENDIX A—CROSS-WALK OF CONSULTATIVE RECOMMENDATIONS TO MONITORING 

FACTORS LISTED IN THIS PLAN

APPENDIX B—CROSS-WALK BETWEEN TECHNICAL REVIEW REPORTS AND 

MONITORING FACTORS

APPENDIX C—MONITORING AREA 2 “WASTE RELEASE”

APPENDIX D—MONITORING AREA 3 “CEMENTITIOUS MATERIAL PERFORMANCE”

APPENDIX E—MONITORING AREA 4 “NATURAL SYSTEM PERFORMANCE”
iv

FIGURES

Figure Page

1-1 Types of Noncompliance With the POs in 10 CFR Part 61, Subpart C .........................1-8

3-1 Potential Pathways of Exposure to a Member of the Public and Points of

Compliance for 10 CFR 61.41 {100 m [328 ft] and 61.42 1 m [3 ft]} Analyses...............3-2

3-2 Approximate 1 m [ 3 ft] and 100 m [328 ft] Boundaries Where the DOE

Evaluates Compliance in Its FTF PORFLOW Model Domain .......................................3-3

3-3 Intruder Well Locations at the 1-m [3 ft] Boundary (Inner Boundary Grouped

in Sectors A–F) and within the 1-m [3 vt] Boundary (Yellow Squares) at HFT...............3-4

3-4 Example Barriers in the DOE’s FTF Performance Assessment Reference Case..........3-6

3-5 Barriers to Timing in the DOE’s FTF Reference (or Best Estimate) Performance

Assessment Case ......................................................................................................3-16

3-6 Tank Grout Features Important to Performance: Panel A Is View of Grout Seams

and Gaps....................................................................................................................3-24

3-7 Proposed FTF and HTF Groundwater Monitoring Locations.......................................3-37

TABLES

Table Page

ES–1 List of Monitoring Areas and Associated Performance Objectives ................................ xiv

ES–2 NRC Prioritization of Monitoring Factors That Support 10 CFR 61.41 and 61.42........... xv

1-1 Documents Prepared by DOE That Would Be Useful to NRC ......................................1-8

1-2 types of Notification Letters ..........................................................................................1-9

3-1 Relative Risk and Contributions of FTF Barriers to Reducing Risk for

Three Key Radionuclides (Tc-99, Pu-239, and Np-237) in DOE’s FTF PA ...................3-8

3-2 Summary of Chemical Transition Times in the HTF and FTF PAs ..............................3-17

3-3 Summary of Steel Liner Failure Times in the HTF and FTF PAs.................................3-21
v

ACRONYMS AND ABBREVIATIONS

ALARA As Low As Is Reasonably Achievable

Am Americium

ASR Alkali Silica Reaction

CERCLA Comprehensive Environmental Response Compensation and Liability Act

CFR Code of Federal Regulations

CNWRA® Center for Nuclear Waste Regulatory Analyses

Cs Cesium

CY Calendar Year

DOE United States Department of Energy

DOD U.S. Department of Defense

DO Dissolved Oxygen

EDS Energy Dispersive Spectroscopy

EPA United States Environmental Protection Agency

EXAFS Extended X-Ray Absorption Fine Structure

FEPs Features, Events, and Processes

FFA Federal Facility Agreement

FTF F-Tank Farm or F-Area Tank Farm

FY Fiscal Year

GA Gordon Aquifer

GCL Geosynthetic Clay Liner

GCP General Closure Plan

GSA General Separations Area

HDPE High Density Polyethylene

HLW High-Level Waste

HRR Highly Radioactive Radionuclide

HTF H-Tank Farm or H-Area Tank Farm

Kds Distribution Coefficients

LAZ Lower Aquifer Zone

LLW Low-Level (Radioactive) Waste

MA Monitoring Areas

Nb Niobium

MEP Maximum Extent Practical

MFs Monitoring Factors

NDAA Ronald W. Reagan National Defense Authorization Act for Fiscal Year 2005

NEA Nuclear Energy Agency

Np Neptunium

NRC United States Nuclear Regulatory Commission

OOV Onsite Observation Visit

OU Operable Unit

PA Performance Assessment

PO

POC

Performance Objective

Point of Compliance

Pu Plutonium
vi

ACRONYMS AND ABBREVIATIONS (continued)

Ra Radium

RAI Request for Additional Information

RPP Radiation Protection Program

SCDHEC South Carolina Department of Health and Environmental Control

SEM Scanning Electron Microscopy

Sr Strontium

SRS Savannah River Site

Tc Technetium

TER Technical Evaluation Report

Th Thorium

TRR Technical Review Report

U Uranium

UCL Upper Confidence Level

UAZ Upper Aquifer Zone

UTRA Upper Three Rivers Aquifer 

WD Waste Determination

WIR Waste Incidental to Reprocessing

XANES X-Ray Absorption Near Edge Structure

XRD X-Ray Diffraction

Zr Zirconium
vii

DEFINITIONS

As Low As (Is) Reasonably Achievable (ALARA): From 10 Code of Federal Regulations 

(CFR) 20.1003—Making every reasonable effort to maintain exposures to radiation as far below 

the dose limits as is practical, consistent with the purpose for which the licensed activity is 

undertaken, taking into account the state of technology, the economics of improvements in 

relation to the state of technology, the economics of improvements in relation to benefits to 

public health and safety, and other societal and socioeconomic considerations, and in relation to 

utilization of nuclear energy and licensed materials in the public interest.

Closed Monitoring Factor: State of a monitoring factor after U.S. Nuclear Regulatory

Commission (NRC) staff determines and documents that the monitoring factor is no longer 

applicable or the technical issue or uncertainty has been resolved.

Disposal: The isolation of radioactive wastes from the biosphere.

Follow-Up Action: Items identified during monitoring that require additional effort by the 

U.S. Department of Energy (DOE) to resolve. Examples include DOE providing answers to 

questions generated during technical reviews or DOE providing results of a particular 

experiment once it becomes available. Follow-up actions are generally less risk significant than 

Open Issues. Follow-up actions can become Open Issues if the follow-up action is related to a 

technical issue that is later found to be risk significant, or if insufficient progress is being made 

on addressing what is thought to be a risk-significant technical issue.

High-Level Radioactive Waste (HLW): (i) irradiated reactor fuel; (ii) liquid wastes resulting 

from the operation of the first cycle solvent extraction system, or equivalent, and the 

concentrated wastes from subsequent extraction cycles, or equivalent, in a facility for 

reprocessing reactor fuel; and (iii) solids into which such liquids have been converted.

Highly Radioactive Radionuclides (also called Key Radionuclides): Those radionuclides 

that contribute most significantly to risk to the public, workers, and the environment. In the 

context of the Ronald Reagan National Defense Authorization Act for Fiscal Year 2005 (NDAA),

NRC staff considers the term “highly radioactive radionuclides” to be equivalent to the term “Key 

Radionuclides” used in the manual for DOE Order 435.1 (DOE M 435.1-1), the West Valley 

Policy Statement, and in some NRC reviews of DOE waste determinations. In the context of an 

NRC review of a DOE waste determination conducted under the NDAA, “Highly Radioactive 

Radionuclides” are not (in general) limited to radionuclides with high specific activity.

Indeterminate: With respect to NRC staff’s monitoring responsibilities under the NDAA, an 

NRC staff finding that it has insufficient information to adequately assess compliance of DOE 

disposal actions with the Performance Objectives (POs) in 10 CFR Part 61, Subpart C. 

Additional information is forthcoming from DOE within a reasonable timeframe to allow NRC 

staff to assess compliance with the POs.

Monitoring Area (MA): General features (or aspects) of the disposal facility or action that NRC 

has determined to be important to assessing compliance with the POs in 10 CFR Part 61, 

Subpart C. MAs are further divided into more specific monitoring factors (MFs).

Monitoring Factor: Specific features (or aspects) of the disposal facility or action that NRC has

determined to be important to assessing compliance with the POs in 10 CFR Part 61, Subpart 

C. NRC typically identifies MFs through the review of a DOE waste determination, Performance 
viii

Assessment (PA), information DOE generates during monitoring (e.g., technical reports on 

laboratory or field experiments), or other information collected during monitoring (e.g., during 

NRC onsite observation visits). MFs are a subset of MAs and tracked as open or closed.

Onsite: Areas of the DOE site where monitoring activities will be carried out. This may include 

areas that have some relationship to, but are outside the physical boundaries of, a particular 

Waste Incidental to Reprocessing (WIR)-related facility.

Onsite Observation: A formal, preannounced site visit to a DOE WIR-related facility by NRC 

staff for purposes of observing DOE facilities, activities, processes, or experiments related to 

compliance with 10 CFR Part 61, Subpart C POs.

Open Issue: A concern that NRC staff identifies during monitoring activities, which requires 

additional information from DOE to address. Examples include a MF that DOE has not taken 

sufficient action to address or instances where data collected by DOE are not consistent with 

assumptions (e.g., conceptual model assumptions, mathematical assumptions, or parameter 

values) that DOE made in the PA. Open Issues are generally more risk significant than 

Follow-up Actions. An Open Issue could lead to a finding that DOE disposal actions are not in 

compliance with the POs in 10 CFR Part 61, Subpart C.

Operations: The actions taken by DOE while carrying out waste disposal actions through the 

end of the institutional control period, including PA development (analytical modeling), waste 

removal, grouting, stabilization, observation, maintenance, or other similar activities.

Performance Assessment: A type of systematic (risk) analysis that addresses (i) what can 

happen, (ii) how likely it is to happen, (iii) the resulting impacts of that happening, and (iv) how 

those impacts compare to specifically defined standards.

Performance Objectives: One of five 10 CFR Part 61, Subpart C, requirements for Low-Level 

Waste (LLW) disposal facilities: (i) general requirement (10 CFR 61.40), (ii) protection of the 

general population from releases of radioactivity (10 CFR 61.41), (iii) protection of individuals 

from inadvertent intrusion (10 CFR 61.42), (iv) protection of individuals during operations 

(10 CFR 61.43), and (v) stability of the disposal site after closure (10 CFR 61.44).

Recommendations: NRC suggestions made during the Savannah River Site tank farm 

consultation phase that DOE might consider to further enhance its approach for management of 

incidental waste. Recommendations are typically made during the consultation phase. A 

crosswalk-walk between the F-Area Tank Farm facility and H-Area Tank Farm facility

recommendations made during the consultation phase to MFs described in this plan is provided 

in Table A–1.

Technical Review: NRC technical staff review of reports, studies, analyses, experiments, and 

other information prepared by DOE, South Carolina Department of Health and Environmental 

Control, or other stakeholders that is important to NRC staff’s assessment of compliance of 

DOE disposal actions with the POs in 10 CFR Part 61, Subpart C.

Waste Determination (or Non-High-Level Waste Determination): DOE documentation 

required by Section 3116 of the NDAA that demonstrates that a specific waste stream is not

HLW.
ix

Worker: DOE or contractor staffs who carry out operational activities at the land disposal

facility.
x

EXECUTIVE SUMMARY

The Ronald Reagan National Defense Authorization Act for Fiscal Year 2005 (NDAA) 

authorizes the U.S. Department of Energy (DOE) in consultation with the U.S. Nuclear 

Regulatory Commission (NRC) to determine whether certain radioactive waste related to 

reprocessing of spent nuclear fuel is not high-level waste (HLW), provided certain criteria are 

met. The NDAA applies specifically to DOE facilities in South Carolina and Idaho and not to 

similar DOE facilities located in other states. The NDAA also requires NRC to coordinate with 

the covered state (i.e., South Carolina or Idaho) to monitor DOE disposal actions to assess 

compliance with the Performance Objectives (POs) for Low-Level Waste (LLW) in Title 10 Code 

of Federal Regulations (10 CFR) Part 61, Subpart C. These POs include (i) general 

requirement (10 CFR 61.40), (ii) protection of the general population from releases of 

radioactivity (10 CFR 61.41), (iii) protection of individuals from inadvertent intrusion (10 CFR 

61.42), (iv) protection of individuals during operations (10 CFR 61.43), and (v) stability of the 

disposal site after closure (10 CFR 61.44). This monitoring plan details the NRC’s path forward 

to assessing DOE disposal action compliance with each of these POs for residual waste 

remaining in the HLW tanks at the Savannah River Site (SRS) near Aiken, South Carolina, at 

the time of facility closure.

In fiscal years 2010 and 2013, DOE issued draft Waste Determinations that concluded that 

stabilized waste residuals in F-Area Tank Farm facility (FTF) and H-Area Tank Farm facility 

(HTF) tanks and auxiliary components, as well as the tanks and auxiliary components 

themselves, could meet NDAA criteria for Waste Incidental to Reprocessing at the time of 

closure and as such could be managed as LLW. As required by the NDAA, DOE consulted with 

NRC regarding DOE’s conclusions in its draft waste determinations for the tank farms. Results 

of a multiyear consultative review culminated in NRC staff’s issuance of a Technical Evaluation 

Report (TER) in October 2011 (ML112371751) for FTF, and later in June 2014 for HTF

(ML14094A496). As DOE is in the early stages of tank farm closure, information regarding final 

waste distributions and factors influencing facility performance is incomplete. This type of 

information is necessary to enable NRC staff to adequately assess compliance of the DOE 

disposal actions with the POs in 10 CFR Part 61, Subpart C. Therefore, rather than reaching 

conclusions regarding DOE’s ability to meet the POs in 10 CFR Part 61, Subpart C, NRC staff 

instead provided a series of comments and recommendations in its TERs with respect to the 

type of additional information NRC staff needed to have reasonable assurance that the POs 

could be met (ML112371751, ML14094A496). If NRC staff’s comments and recommendations 

are addressed by DOE, NRC staff expects that NRC will be in a better position to assess 

compliance with the POs. NRC staff rationalized that sufficient time was available for DOE to 

implement many of the recommendations as tank farm closure progresses.

DOE issued a final waste determination in March 2012 (DOE/SRS–WD–2012–001) for FTF; 

DOE commenced grouting of Tanks 18F and 19F in April 2012 and Tanks 5F and 6F in August

2013. NRC has issued nine Technical Review Reports (TRRs) and conducted five On-site 

Observations (OOVs) since it began monitoring FTF in April 2012. Monitoring activities focused 

on (i) closure of FTF Tanks 5F, 6F, 18F, and 19F, including review of grouting documentation 

and observation of grouting operations, and (ii) review of inventory and revised risk estimates 

for Tanks 5F, 6F, 18F, and 19F and the entire FTF through special analyses. NRC staff also 

reviewed updated waste release experiment and modeling reports; documentation of features, 

events, and processes applicable to the site; and environmental monitoring data. Most of the 

findings in the FTF TRRs were applicable to and discussed in the HTF TER. The technical 

issues identified in the TRRs performed for FTF to date, as well as technical issues unique to 

HTF that are documented in staff’s HTF TER (ML14094A496), have been considered in revising
xi

the FTF monitoring plan to encompass both FTF and HTF (see Tables A–1 and B–1). Thus, the

U.S. Nuclear Regulatory Commission Plan for Monitoring Disposal Actions Taken by the U.S. 

Department of Energy at the Savannah River Site F-Area Tank Farm Facility in Accordance 

With the National Defense Authorization Act for Fiscal Year 2005, January 2013 (FTF 

monitoring plan) (ML12212A192) is being replaced by this combined SRS Tank Farm 

Monitoring Plan.

DOE issued a final waste determination in December 2014 (DOE/SRS–WD–2014–001) for HTF 

but had not yet completed closure of any single HTF tank at that time. Tanks 12H and 16H

have been cleaned and are the first HTF tanks scheduled for grouting. The Tank 16H closure 

module was approved by the South Carolina Department of Health and Environmental Control 

(SC DHEC) in the spring 2015, and DOE commenced grouting of the tank shortly thereafter. 

DOE also prepared a Special Analysis and Final Removal Report for Tank 16H in the spring 

2015. DOE issued the Tank 12H closure module for public comment in spring 2015 and plans 

to supplement the closure module after final characterization is complete.

In accordance with the NDAA, NRC will assess FTF and HTF compliance with the POs in 

10 CFR Part 61, Subpart C. A Performance Assessment (PA) is typically used to demonstrate

compliance with two of the four POs: 10 CFR 61.41, “Protection of the General Population from 

Releases of Radioactivity,” and 61.42, “Protection of Individuals From Inadvertent Intrusion,” 

which are assessed using dose-based criteria. A PA is a type of systematic risk analysis that 

addresses (i) what can happen, (ii) how likely it is to happen, (iii) what the resulting impacts are, 

and (iv) how the impacts compare to specifically defined standards. Considering the long time 

period over which long-lived radionuclides pose a hazard to human health, a robust PA is 

needed to establish that the POs will be met for releases from the Tank Farms that may occur 

many hundreds or thousands of years in the future. NRC considers sufficient PA model 

support, coupled with observation of disposal actions that are carried out in conformance with 

detailed closure plans, necessary for NRC to have reasonable assurance that the POs can be 

met. Many key features of DOE’s disposal facility design are important to the compliance 

demonstration for the Tank Farms, as documented in the PAs for the Tank Farms. These key 

features are the focus of NRC staff’s monitoring efforts.

NRC’s monitoring plan focuses on the most risk-significant aspects of DOE disposal actions. 

These risk-significant aspects were binned under eight monitoring areas (MA). The first six MAs

relate to protection of the general public and intruder protection. NRC staff developed MA 1, 

“Residual Waste Inventory,” to ensure that the final postcleaning inventory developed for the 

tank farms is consistent with assumptions made in DOE’s final waste determination and PA, or 

that the final waste inventory at the time of closure does not lead to a finding of noncompliance 

with the POs. NRC will also perform monitoring activities related to engineered and natural 

features of the disposal facility that are also found to be important to meeting the POs. NRC 

staff developed MA 2, “Waste Release,” to ensure that releases of key radionuclides remain 

below levels that would lead to an exceedance of the POs during the compliance period. NRC 

staff developed MA 3, “Cementitious Material Performance,” to ensure that cementitious 

materials act as effective barriers to fluid flow for some period of time, mitigate or attenuate 

releases of radioactivity from the tanks, and otherwise perform consistently with DOE PA 

assumptions, and that the impact of any deviations in assumed performance is evaluated. NRC 

staff developed MA 4, “Natural System Performance,” to ensure the hydrogeological system 

acts as an effective natural barrier to attenuate key radionuclide releases as assumed in DOE’s 

PA models. Additionally, under MA 4, NRC staff will review environmental data collected by 

DOE as an additional assurance that the Tank Farms are operating as predicted by DOE 

models. NRC staff developed MA 5, “Closure Cap Performance,” to evaluate key features of 
xii

the closure cap identified in NRC staff’s review. All of these MAs are directly related to the 

facilities’ long-term ability to limit or mitigate releases of constituents from the Tank Farms and 

are considered important to assessing compliance with the POs. Items of lower risk 

significance or longer term activities are addressed in MA 6, “PA Maintenance.” PA 

maintenance is also necessary to ensure that a mechanism is in place to consider new and 

significant information that may be collected in the future that might significantly alter results 

presented in DOE’s PA.

While DOE relies on a PA to demonstrate compliance with POs related to general public and 

intruder protection, evaluation of compliance with 10 CFR 61.43, “Protection of Individuals 

During Operations,” can be more directly assessed through observation of DOE closure 

activities. NRC plans to perform a graded review of DOE’s radiological protection program 

while observing DOE’s most risk-significant closure activities (e.g., tank cleaning, sampling, and 

grout placement activities) to assess compliance with 10 CFR 61.43. For example, NRC staff 

will review radiation records and environmental data or reports and possibly conduct interviews 

during closure activities to assess compliance with 10 CFR 61.43. NRC staff’s assessment of 

compliance with 10 CFR 61.43 is addressed under MA 7, “Protection of Individuals During

Operations.”

Finally, monitoring activities to assess compliance with 10 CFR 61.44, “Stability of the Disposal

Site After Closure,” partially overlap those activities developed to support assessment of 

compliance with 10 CFR 61.41 and 61.42. NRC considers unique factors affecting stability of 

the disposal site not already discussed under 10 CFR 61.41 and 61.42 under MA 8, “Site 

Stability.”

To prepare this monitoring plan, NRC staff, in consultation with SCDHEC, began by 

comprehensively considering all of its previous comments and recommendations on each Tank 

Farm PA and waste determination review and crosswalked each of the items to one of the eight 

MAs described previously that NRC considers important to DOE’s compliance demonstration.

1

 

This crosswalk is provided in Appendix A. As such, this monitoring plan will serve as the 

starting point from which NRC staff will assess compliance with the POs in 10 CFR Part 61, 

Subpart C, in fulfillment of its monitoring responsibilities under the NDAA. As discussed in the 

preceding paragraphs, the eight MAs are as follows:

• MA 1, “Inventory”

• MA 2, “Waste Release”

• MA 3, “Cementitious Material Performance”

• MA 4, “Natural System Performance”

• MA 5, “Closure Cap Performance”

• MA 6, “PA Maintenance”

• MA 7, “Protection of Individuals During Operations”

• MA 8, “Site Stability”

MAs are supported by a number of Monitoring Factors (MFs). While MAs are mainly used to bin 

technical topics, MFs are smaller, specific items that NRC staff will monitor in fulfillment of its 

 

1NRC recognizes that some of its previous review comments and recommendations are less risk significant or may

require longer time periods to address than others. Lower risk or long-term activities are binned into MA 6,

“PA Maintenance.”
xiii

NDAA responsibilities. MFs will help facilitate monitoring by providing specific activities for NRC 

staff to focus on. These MFs will be tracked as open or closed. If issues arise related to MFs, 

NRC staff may develop an “open issue” to document concerns related to the MF. In this way, 

NRC staff will have a mechanism to communicate to DOE, early in the process, the need for 

additional information, prior to NRC’s issuance of a notification letter of concern or letter of 

noncompliance. NRC staff will note the status of each MF in the periodic monitoring compliance 

reports prepared for the Idaho National Laboratory and SRS (see NUREG–1911 NRC Periodic 

Compliance Monitoring Report for U.S. Department of Energy Non-High-Level Waste Disposal 

Actions, Rev. 3 [ML111890412]).

Because Congress directed NRC to monitor DOE disposal actions to assess compliance with 

the POs in 10 CFR Part 61, Subpart C, this monitoring plan is first organized by PO, with one

chapter devoted entirely to each of the four POs. As indicated previously, NRC staff evaluates 

what MAs are important to DOE’s demonstration of compliance with each PO—MAs are, 

therefore, listed directly beneath each PO and support NRC staff’s assessment of Tank Farm

facility compliance with the POs, as required by the NDAA. As stated previously, each MA 

supports one or more POs. If the MA supports multiple POs, the monitoring plan will indicate 

whether the MA and underlying factors are an exact duplicate of a previously listed MA and 

underlying set of factors (in which case the MA and factors will not be repeated) or whether

there are unique aspects of the MA or underlying factors that pertain to just that PO (in which 

case only the unique aspects of the area and relevant factors will be discussed under the PO). 

Table ES–1 lists each MA and indicates the POs each MA supports. 

Table ES–2 provides NRC staff’s prioritization of each MF under MAs 1–5 developed to support 

assessment of compliance with the 10 CFR 61.41 PO. Many of these factors also support 

assessment of compliance with the 10 CFR 61.42 PO because an inadvertent intruder is also

assumed to be exposed to Tank Farm waste through the groundwater pathway, similar to the 

pathways considered for evaluation of the 10 CFR 61.41 PO, although the compliance point is 

assumed to be onsite rather than offsite for the inadvertent intruder. Additionally, unique 

considerations may apply to assessing compliance with 10 CFR 61.42 because additional 

scenarios related to direct intrusion into the disposal facility are also considered in assessing 

compliance with the 10 CFR 61.42 PO. MA 6, “Performance Assessment Maintenance,” MFs 

are not listed in Table ES–2, because PA Maintenance items are considered items of lower risk 

significance or longer term monitoring activities by default. Each of the MFs for MAs 1 through 

8 is discussed in more detail in the chapters that follow.

This monitoring plan also provides information regarding the types of monitoring reports NRC 

plans to prepare to document its monitoring activities. For example, NRC plans to issue a 

report following each onsite observation and will summarize monitoring activities and changes 

to the status of its monitoring activities in periodic reports. If NRC concludes that actions taken 

by DOE are not in compliance with POs, NRC will notify DOE, the covered State, and Congress,

as required by the NDAA. The types of notification letters related to a finding of noncompliance 

are listed in Section 1.9 of this document.
xiv

Table ES–1. List of Monitoring Areas and Associated Performance Objectives

MA Monitoring Areas

10 CFR Subpart C 

Performance Objective

61.41 61.42 61.43 61.44

1 Inventory X X

2 Waste Release X X

3 Cementitious Material Performance X X

4 Natural System Performance X X

5 Closure Cap Performance X X

6 Performance Assessment Maintenance X X

7 Protection of Individuals During Operations X

8 Site Stability X* X* X

*Note: 10 CFR 61.44 PO related to site stability impacts DOE’s ability to meet the 10 CFR 61.41 and 10 CFR 

61.42 POs (i.e., site stability is important to meeting the POs for protection of general population from releases of 

radioactivity from the disposal facility and protection of individuals from inadvertent intrusion). Therefore, MA 8,

“Site Stability,” is important to demonstrating 10 CFR 61.41 and 10 CFR 61.42 POs are met, as well as 

demonstrating that the 10 CFR 61.44 PO is met.

CFR = Code of Federal Regulations, PO = Performance Objective, DOE = U.S. Department of Energy,

MA = Monitoring Areas
xv

Table ES–2. NRC Prioritization of Monitoring Factors That Support 10 CFR 61.41 and 61.42

MA 1

Inventory

MA 2

Waste Release

MA 3

Cementitious 

Material 

Performance

MA 4

Natural System 

Performance

MA 5

Closure Cap

1.1—

Final Inventory 

and Risk 

Estimates*

2.1—

Solubility-Limiting 

Phases/Limits and 

Validation†

3.1—

Hydraulic 

Performance of 

Concrete Vault 

and Annulus (As it 

Relates to Steel 

Liner Corrosion 

and Waste 

Release)‡

4.1—

Natural 

Attenuation of Key 

Radionuclides†

5.1—

Long-Term 

Hydraulic 

Performance§

1.2—

Residual Waste 

Sampling*

2.2—

Chemical 

Transition Times‡║

3.2—

Groundwater 

Conditioning via 

Reducing Grout‡║

4.2—

Calcareous Zone 

Characterization*

5.2—

Long-Term 

Erosion Protection 

Design§

1.3—

Residual Waste 

Volume*

3.3—

Shrinkage and 

Cracking of 

Reducing Grout*

4-3—

Environmental 

Monitoring*

5.3—

Closure Cap 

Functions That 

Maintain Doses 

ALARA§

1.4—

Ancillary 

Equipment 

Inventory§

3.4—

Grout 

Performance*

1.5—

Waste Removal 

(As It Impacts

ALARA)§

3.5—

Vault and Annulus 

Sorption‡

3.6—

Waste

Stabilization (As It 

Impacts ALARA)§

║In the FTF PA, certain HRRs such as technetium and plutonium, which are initially assumed to be in a low solubility 

state, are eventually assumed to be released at risk-significant solubilities that could exceed the performance 

objectives over long periods of time. Therefore, chemical transition times to a higher solubility, which are related to 

the extent of groundwater conditioning afforded by the reducing grout, are important to the compliance demonstration 

in the FTF PA. In contrast, chemical transitions to a higher, risk-significant solubility only occur in alternative cases in 

the HTF PA. Therefore, chemical transition times are less important to DOE’s compliance demonstration in the HTF 

PA.

NRC = U.S. Nuclear Regulatory Commission, MA = Monitoring Areas, ALARA = As Low As Is Reasonably 

Achievable, DOE = U.S. Department of Energy, FTF = F-Area Tank Farm, PA = Performance Assessment, 

HRRs = Highly Radioactive Radionuclides, HTF = H-Area Tank Farm

§Lower Priority

*

Medium Priority

†High Priority Recommended

‡High Priority Dependent or More Difficult (The monitoring factors in orange‡ are risk significant to the DOE 

performance assessment, but the need for their implementation may be dependent on results of other monitoring 

factors. Because the monitoring factors in orange‡ are also expected to be more difficult to study or support, work on 

monitoring factors in red† are recommended first.)
xvi

References

DOE/SRS–WD–2012–001, Rev. 0. “Basis for Section 3116 Determination for Closure of FTank Farm at Savannah River Site.” Washington, DC: U.S. Department of Energy. 2012.

ML112371751. “Technical Evaluation Report for F-Area Tank Farm Facility, Savannah River 

Site, South Carolina—Final Report.” Washington, DC: U.S. Nuclear Regulatory Commission. 

2011.

ML14094A496. “Technical Evaluation Report for H-Area Tank Farm Facility, Savannah River 

Site, South Carolina—Final Report.” Washington, DC: U.S. Nuclear Regulatory Commission. 

2014.

ML12212A192. “U.S. Nuclear Regulatory Commission Plan for Monitoring Disposal Actions 

Taken by the U.S. Department of Energy at the Savannah River Site F-Area Tank Farm Facility 

in Accordance With the National Defense Authorization Act for Fiscal Year 2005.” Washington 

DC: U.S. Nuclear Regulatory Commission. 2013.

SRS–WD–2014–001, Rev. 0. “Basis for Section 3116 Determination for Closure of H-Tank 

Farm at Savannah River Site.” Washington, DC: U.S. Department of Energy. 2014.
1-1

1 MONITORING PROCESS

Background

The Savannah River Site (SRS) is an 803 square kilometer [310 square mile] facility developed 

in the 1950s as part of the country’s growing weapons program. Many activities took place at

the site, including the reprocessing of spent nuclear fuel in reinforced concrete buildings called

canyons. Liquid waste from the reprocessing process was managed in 51 underground storage 

tanks contained in the F-Area Tank Farm (FTF) and H-Area Tank Farm (HTF) facilities. These 

tank farms are the subject of this monitoring plan. 

The U.S. Department of Energy (DOE) is engaged in an expansive campaign to clean, stabilize,

and close 49 of the 51 underground waste storage tanks at the FTF and HTF. DOE closed two

FTF tanks (Tanks 17 and 20) in the 1990s prior to U.S. Nuclear Regulatory Commission (NRC)

involvement pursuant to the Ronald W. Reagan National Defense Authorization Act for Fiscal 

Year 2005 (NDAA). DOE cleanup activities also include supporting ancillary structures (i.e., 

evaporators, pump pits, pump tanks, diversion boxes, transfer valve boxes, and piping) used to 

process and transfer generated waste. The waste tanks and ancillary structures are several 

decades old. The original service life for these tanks was projected as 40 years; however, 

several of the aging waste tanks are approaching 60 years of service life. Given the inherent 

risks of exhuming the aging waste tanks and disposing them as high-level waste (HLW), DOE 

plans to clean, grout, and close the waste tanks and ancillary structures in place to reduce the 

risks to the workers, the public, and the environment.

In accordance with Section 3116 of the NDAA, on March 27, 2012 the Secretary of Energy, in 

consultation with NRC, made a determination that waste remaining within the tanks and 

ancillary facilities in FTF does not have to be considered or managed as HLW, requiring

disposal in a geologic repository. Rather, the tank farm waste can be disposed of, in place, as 

Low-Level Waste (LLW).

NRC’s consultation included the review of DOE’s Draft Basis for Section 3116 Determination for 

Closure of F-Tank Farm at the Savannah River Site, which DOE submitted in September 2010. 

A detailed Site Performance Assessment (PA) accompanied the basis document (SRS–REG–

2007–00002). During the review process, NRC staff held a number of technical exchange 

meetings with DOE and submitted a written Request for Additional Information (RAI) regarding 

certain aspects of the DOE basis document (ML103190402)

2

. DOE completed its response to 

NRC in the summer of 2011. NRC staff completed a Technical Evaluation Report (TER) in 

October 2011 (ML112371751). In its TER, NRC staff provided a number of recommendations 

to DOE that, if implemented, would allow NRC to assess compliance with the performance 

objectives (POs) in Title 10 of the Code of Federal Regulations (10 CFR) Part 61, Subpart C, 

and increase the likelihood that the NRC would find that it had reasonable assurance that 

disposal actions at the FTF would be in compliance with the 10 CFR Part 61, Subpart C POs. 

DOE submitted additional information regarding several NRC TER recommendations prior to 

completing the final waste determination (DOE/SRS–WD–2012–001) and has plans to address

other NRC recommendations, as indicated in its “Savannah River Site Liquid Waste Facilities 

 

2 Accession numbers are provided for NRC documents and begin with the letters “ML.” These accession numbers 

can be used to search for NRC documents in NRC’s Agencywide Document Access and Management System 

(ADAMS) found at http://www.nrc.gov/reading-rm/adams.html. 
1-2

Performance Assessment Maintenance Program, fiscal year 2012 Implementation Plan” (SRR–

CWDA–2012–00020), as updated for fiscal year 2015 (SRR–CWDA–2014–00108).

NRC’s consultation on the HTF began in February 2013 when DOE issued the Draft Basis for 

Section 3116 Determination for Closure of H-Tank Farm at the Savannah River Site for NRC

review, as part of DOE’s consultation with NRC under NDAA Section 3116 [DOE/SRS–WD–

2013–001]. A detailed PA (SRR–CWDA–2010–00128) accompanied the draft basis document,

providing much of the supporting information. Prior to submittal of requests for additional 

information, NRC exchanged information with DOE during a number of consultative telephone 

calls and public meetings held in early 2013. NRC submitted written RAIs in July 2013 

(ML13196A135). DOE formally responded to the RAIs in November 2013 (SRR–CWDA–2013–

00106). NRC had several follow-up clarifying questions regarding DOE’s RAI responses. DOE 

responded to the clarifying questions in January 2014 (SRR–CWDA–2013–00144). On June 

17, 2014, the NRC issued its Technical Evaluation Report For H-Area Tank Farm Facility,

Savannah River Site, South Carolina [ML14094A496]. The TER presents NRC’s consultative 

observations and recommendations. In the TER, NRC provided a number of recommendations 

to DOE, the implementation of which NRC believed was necessary for NRC to find reasonable 

assurance disposal actions at the HTF would meet the POs in 10 CFR Part 61, Subpart C. 

DOE completed its final waste determination or basis document for HTF in December 2014 

(DOE/SRS–WD–2014–001). The DOE considered the NRC comments and recommendations 

in preparing the HTF 3116 Basis Document [SRR–CWDA–2014–00080].

NRC assumed its monitoring role, per the NDAA, once DOE issued its waste determination in 

March 2012 for the remaining tanks and ancillary structures at the FTF facility. NRC expanded 

its monitoring role to include HTF when DOE completed its final waste determination for HTF in 

December 2014. The NDAA provides a very specific responsibility for NRC to monitor disposal 

operations to ensure DOE disposal actions comply with the POs in 10 CFR Part 61, Subpart C. 

While NRC staff reviewed and provided comments on DOE’s PA and waste determination for 

the entire FTF, NRC’s TER (ML112371751) included a more detailed evaluation of the 

effectiveness of completed waste removal activities for Tanks 18F and 19F and provided 

recommendations related specifically to the closure of those two tanks that were further along in 

the closure process and for which DOE provided more detailed closure information. Between 

issuance of the final FTF waste determination and the final HTF waste determination, NRC also 

reviewed final inventories and risk estimates for FTF based on additional information collected 

on Tanks 5F and 6F that were grouted in 2013. Similarly, NRC’s TER for HTF (ML14094A496) 

included a more detailed recommendation for Tanks 12H and 16H, which are further along in 

the closure process. This is important to note because the monitoring plan will include 49 tanks 

in the two tank farms, including 43 tanks for which little or no waste removal has occurred.

Objective

In accordance with Section 3116 of NDAA, after the Secretary of Energy has made a 

determination that some residual waste does not have to be managed as HLW, NRC is required 

to monitor subsequent disposal activities to assess compliance with the POs in 10 CFR Part 61, 

Subpart C. NRC must coordinate these monitoring activities with the South Carolina 

Department of Health and Environmental Control (SC DHEC), the primary site regulator.

This monitoring plan describes monitoring activities to be conducted in the context of their 

relationship with the ability for DOE to comply with the 10 CFR Part 61, Subpart C, POs. In 

most cases, compliance or potential noncompliance with the POs must be demonstrated 

through indicators of future performance. The monitoring plan identifies eight Monitoring Areas 
1-3

(MAs) that NRC and SC DHEC find to be important to demonstrating compliance with the POs. 

DOE activities associated with disposal of tanks and associated waste will take decades to 

complete. NRC anticipates that implementation of this monitoring plan will take place 

concurrently with DOE closure activities. NRC staff activities related to the MAs will include the

following:

• Technical reviews of DOE work products, experiments, and analyses tied to one or more 

MAs, including collection of environmental and radiological data.

• Periodic onsite (quarterly or less frequent) observations of aspects of DOE disposal 

activities and, as appropriate, related experiments.

NRC monitoring activities will be accomplished by NRC headquarters and regional personnel. 

In general, NRC staff will work in concert with SCDHEC personnel regarding accomplishment of 

monitoring tasks supportive of each organization’s program.

Roles and Responsibilities

U.S. Department of Energy

The SRS Federal Facility Agreement (FFA) (WSRC–OS–94–42), a formal agreement between

DOE, Region IV of the U.S. Environmental Protection Agency (EPA), and SCDHEC, specifies 

the order and time in which SRS waste tanks are closed. The organizations who are parties in 

the FFA have regulatory authority over certain activities at SRS. NRC is not a party to the FFA 

and does not have regulatory authority over waste disposal activities.

The FFA establishes that, among other things, the SRS waste tanks that do not meet secondary 

containment standards (older style tanks, specifically Types I, II and IV) must be removed from 

service according to the FFA schedule. The current FFA calls for operational closure of 

Tanks 18F and 19F (Type IV) by December 2012 and staggered operational closure of the other 

eight FTF (Type I) and twelve HTF (Type I, II, and IV) waste tanks (tank numbers not specified 

in the FFA) by September 2022 (WSRC–OS–94–42). Grouting of Tanks 18F and 19F was 

completed August 24, 2012 (SC DHEC and EPA concurred that tank closure was complete on 

September 19, 2012); and grouting of Tanks 5F and 6F was completed on December, 18, 2013

(SC DHEC concurred that tank closure was complete on January 22, 2014 [EPA concurred on 

January 23, 2014]). DOE addresses the closure of the remaining FTF and HTF tanks and 

ancillary structures in the SRS Liquid Waste System Plan (SRR–LWP–2009–00001).

DOE will pursue closure of the FTF and HTF and monitor its activities to ensure compliance with 

all requirements. DOE’s relevant authority stems from the Atomic Energy Act of 1954, as 

amended, and applicable DOE Orders, manuals, and policies. DOE uses a documented 

process to review and resolve any disposal questions and develop any mitigation measures, as 

appropriate. Tank waste storage and removal operations are governed by an SCDHEC 

industrial wastewater construction permit (DHEC–01–25–1993). DOE will carry out removal 

from service and stabilization of the waste tanks and ancillary structures pursuant to a 

state-approved closure plan and the FTF and HTF General Closure Plans, which contain the 

overall plans for removing from service and stabilizing the waste tanks and ancillary structures 

(LWO–RIP–2009–00009 and SRR–CWDA–2011–00050). A specific Closure Module for each 

waste tank, ancillary structure, or groupings of waste tanks and ancillary structures will be 

developed and submitted to the State of South Carolina for approval. Final waste tank 

stabilization activities shall not proceed until the State of South Carolina grants approval. 
1-4

Stabilization of individual waste tanks and ancillary structures is anticipated to take place after 

individual component cleaning is complete.

South Carolina Department of Health and Environmental Control

SCDHEC is the primary regulator of DOE closure activities at SRS. The FTF and HTF waste 

storage and removal operations are governed by an SCDHEC industrial wastewater 

construction permit, issued January 25, 1993 (DHEC–01–25–1993). The State issued the

permit under the authority of the South Carolina Pollution Control Act (State of South Carolina, 

1985, Section 48-1-10) and all applicable regulations implementing the Act. The State of South

Carolina has authority for approval of wastewater treatment facility operational closure under 

Chapter 61, Articles 67 and 82 of the SCDHEC Regulations (SCDHEC R.61-67, SCDHEC R.61-

82).

The tank farm General Closure Plan (GCPs) address the State’s regulatory authority relevant to 

removing the SRS waste tanks and ancillary structures from service. The GCP sets forth the 

general protocol by which DOE intends to remove from service the SRS waste tanks and 

ancillary structures to protect human health and the environment. The SCDHEC approved the

FTF GCP on January 24, 2011, and conditionally3 approved the HTF GCP on August 2, 2012. 

Prior to approval by SCDHEC, the GCPs were made available to the public for review and 

comment (LWO–RIP–2009–00009, SRR–CWDA–2011–00022).

U.S. Environmental Protection Agency

As previously stated, the FFA is an agreement between the EPA, DOE, and the State of South

Carolina. EPA is a party to the FFA pursuant to its authority in accordance with the 

Comprehensive Environmental Response Compensation and Liability Act (CERCLA), also 

known as Superfund, under which EPA is tasked with protecting citizens from the dangers 

posed by abandoned or uncontrolled hazardous wastes. EPA’s involvement with the State is 

focused on ensuring that proper disposal actions are taken, assisting the state with the design 

and installation of those actions, and monitoring and evaluating their effectiveness. 

Executive Order 12580 delegates the responsibility of implementing the provisions in CERCLA 

to DOE and the U.S. Department of Defense (DOD). CERCLA also names DOE and DOD as 

the lead agencies for their respective areas. DOE has several facilities in EPA’s Region IV. 

EPA added SRS to the Superfund National Priorities List in December 1989, which also is the 

year that SRS was required to have an FFA with the State and EPA.

U.S. Nuclear Regulatory Commission

Section 3116 of the NDAA authorized the Secretary of Energy to manage and dispose of certain

waste associated with facility cleanup in Idaho and South Carolina as LLW, in accordance with 

POs in NRC regulations. Prior to such a determination, DOE is required to consult with NRC 

regarding its waste determination. Following the Secretary’s waste determination, NRC is 

required to monitor disposal activities in coordination with the covered State.

 

3 SC DHEC reserved the right to amend the General Closure Plan following review of NRC staff’s TER for HTF.
1-5

NRC’s role in monitoring DOE’s closure activities derives from Section 3116 of the NDAA. 

While NRC is not given a formal regulatory role, the NDAA requires that NRC monitor, in 

coordination with SCDHEC, DOE disposal activities to assess compliance with the POs in 

10 CFR Part 61, Subpart C. Thus, DOE complies with a subset of NRC regulations in 10 CFR 

Part 61, “Licensing Requirements Land Disposal of Radioactive Waste,” in carrying out such 

disposal activities. The regulations in 10 CFR Part 61 establish, for land disposal of radioactive 

waste, procedures, criteria, and terms and conditions upon which NRC issues licenses for the 

disposal of radioactive wastes containing byproduct, source, and special nuclear material 

received from other persons.

NRC recognizes that many of the activities that DOE must carry out prior to tank closure are

beyond the scope of NRC monitoring authority. For instance, NRC is concerned with and will 

monitor aspects of residual waste inventory in each tank because of its direct relationship to 

compliance with the POs. However, NRC staff will focus only on more risk-significant activities

related to the residual waste inventory. For example, while NRC staff will monitor heel removal 

activities insofar as these activities pertain to as low as is reasonably achievable provisions in 

10 CFR 61.41, NRC staff does not plan to monitor more routine inventory-reducing activities,

such as bulk waste removal. 

This monitoring plan articulates NRC’s role to ensure DOE disposal activities associated with

residual waste covered by the Secretary of Energy’s waste determinations for FTF and HTF are 

in compliance with the POs of 10 CFR Part 61, Subpart C.

Coordination with the State of South Carolina

Per Section 3116 of the NDAA, NRC’s monitoring role includes coordination with State of South

Carolina. During the waste determination reviews, NRC staff began coordinating with SCDHEC

by conducting discussions to determine the types of activities that the State monitors under its 

regulatory authority. These discussions also enabled the State to get a better understanding of 

NRC’s activities. NRC continues to coordinate with the SCDHEC throughout the monitoring 

process by consulting with SCDHEC in the development of this monitoring plan and reviewing 

the State’s Environmental Surveillance and Oversight Program for use as a source of 

information to supplement NRC’s monitoring plan. SCDHEC uses a holistic monitoring 

approach with regard to overall performance and safety of SRS. The NRC objective with this

NDAA monitoring program is limited to assessment of DOE’s compliance with the 10 CFR 

Part 61 POs. Ultimately, NRC and SCDHEC are concerned with the potential for environmental 

contamination in ground and surface water, air, milk, and meat. While it is unlikely that any 

contribution to such contamination from the tank farms could manifest itself offsite in the 

foreseeable future, review of environmental monitoring data is nonetheless useful to NRC staff 

in betterer understanding the natural system, as well as providing reassurance that the tank 

farm facilities are operating as assumed in DOE’s models.

During the monitoring phase, NRC activities will be closely coordinated with SCDHEC. To the 

extent practical, NRC will request SCDHEC’s assistance in following up on certain monitoring 

activities that require a local or onsite presence (e.g., activities related to daily tank grouting 

activities). SCDHEC also will be invited to contribute to the development of monitoring reports,

as well as the overall monitoring plan.

NRC will keep the State abreast of the status of monitoring activities at the site, including any 

potential findings of noncompliance that require a notification letter as described in Section 1.7 

of this Monitoring Plan. At least two business days prior to the release and dissemination of any
1-6

notification letters, SCDHEC officials will be briefed, in detail, on the reasons for such

notification. 

Monitoring Approach

Monitoring is an ongoing process consisting of technical reviews, data reviews, and periodic 

(i.e., quarterly or less frequently) onsite observation visits of DOE disposal activities related to 

compliance with the 10 CFR Part 61 POs.

1.5.1 Technical Reviews 

Technical reviews by NRC include review and evaluation of analyses conducted by DOE or 

others related to one or more aspects of site or facility performance. In general, technical 

reviews are used to evaluate new information that either supports or refutes assumptions made 

by DOE in the PA that are considered important to DOE disposal action compliance. NRC will 

document each technical review in a report, which will be publicly available. 

1.5.2 Data Reviews

Data reviews focus on real-time monitoring data that may indicate future system performance or

a review of records or reports that can be used to directly assess compliance with POs (e.g.,

review of radiation records). NRC will document each data review, which will be publicly

available. Data reviews are a subset of technical reviews and are oftentimes folded into a 

technical review report. In some cases data may be reviewed during an onsite observation, in 

which case the data review will be documented in the onsite observation report.

1.5.3 Onsite Observation Visits

As described in NUREG–1854, NRC Staff Guidance for Activities Related to U.S. Department of 

Energy Waste Determinations, Draft Final Report for Interim Use (ML072360184), onsite 

observation visits are opportunities for NRC to observe and review certain operations as they 

are being performed, or to discuss results of experiments or technical reviews. Onsite 

observation visits are performed by NRC staff or its representatives and may include a variety of

specific activities that could be used to assess an aspect of current or future site performance. 

A visit is generally performed to either (i) ensure data collected for a technical review are of 

sufficient quality or (ii) observe key disposal actions that are important to DOE’s compliance 

demonstration.

Prior to each onsite observation visit, NRC will prepare an Observation Guidance Memorandum 

that discusses the scope and specific activities that will be monitored during the visit in more 

detail than is described in this monitoring plan. The activities NRC selects will be based on 

many aspects, such as completion of DOE technical reports, emergent issues, timely DOE 

actions related to a Monitoring Factor (MF), availability of staff (i.e., NRC, SCDHEC, DOE), 

availability of locations at the site, length of time since reviewing an item in an MF, scheduled 

follow-up actions to previous visits, and available NRC resources. NRC will coordinate with 

SCDHEC in development of the memorandum to take into account areas that SCDHEC is 

interested in and availability of SCDHEC experts in those areas of interest. NRC plans to 

provide the final memorandum to DOE within 30 calendar days prior to the visit. The final 

memorandum will be publicly available. During a visit, the agenda may change based on what 

happens during the visit (e.g., new areas of interest are identified) or unforeseen circumstances.
1-7

Each visit will be documented in an observation report. The report will include, for the actual 

areas covered during the visit, specific activities, results of discussions, status of any open 

issues/follow-up actions, and any NRC conclusions. The areas covered may differ somewhat

from the areas of interest identified in the Observation Guidance Memorandum. NRC plans to

finalize each report within 60 calendar days after the visit. The final report will be publicly

available.

1.5.4 Periodic Data Reports and Closure Documentation

Several DOE documents, including performance assessment documentation, tank closure 

documents, and environmental monitoring reports, are prepared by DOE to satisfy DOE Orders 

and regulations or are prepared for DOE’s regulators (i.e., DOE, EPA, SCDHEC). NRC staff 

plan to leverage many of these documents to help fulfill its monitoring responsibilities under the 

NDAA (i.e., to assess compliance with the POs). In the future, it would be beneficial if DOE 

could provide to NRC the documents listed in Table 1-1. Some of these reports are issued on a 

periodic basis, and other documents are triggered by a specific event (e.g., closure of a tank).

Periodic Compliance Monitoring Report

NRC will publish a Periodic Compliance Monitoring Report [i.e., currently, ML111890412)] to

document the major findings associated with the monitoring activities during each calendar year

(CY). The report will be for the entire NRC NDAA program for that CY (or CYs) and will be 

publicly available.

Notification Letters 

In accordance with NRC guidance in NUREG–1854 , there are five types of notification letters. 

Three of the letters are noncompliance letters (i.e., Types I to III) that NRC developed to 

implement the authority it has inferred from the statutory language in Section 3116 of the NDAA,

and the two other types of letters are for NRC to issue as an interim step when identifying or 

resolving major issues. NRC may issue a Type IV letter to express a concern and a Type V 

letter to confirm resolution of a concern. Table 1-2 describes each of the five letters, including 

NRC’s reason for issuing the letter, which NRC staff member signs the letter, and who receives 

the letter. The information in Table 1-2 is similar to the information in NUREG–1854, Table 10-

2, but is supplemented by information that reflects current experiences and lessons learned 

from previous monitoring activities.

The NRC expects that if it were to issue a Letter of Concern (i.e., Type IV), the timing of this 

letter would allow DOE sufficient time to respond to NRC concerns prior to issuance of one of 

the three noncompliant notification letters (i.e., Type I, Type II, Type III). However, that may not 

be possible or appropriate in all situations. For example, if a worker were to be overexposed in 

an accident (i.e., received greater than 5 rem exposure) and the NRC was going to issue a Type

I Letter of Noncompliance, then the NRC may decide to send that notification letter to Congress, 

DOE, and the covered State rather than first sending a Type IV Letter of Concern to DOE and 

the covered State. The NRC would utilize other means of notification (e.g., telephone 

conference calls or meetings) with both DOE and the covered State before sending the Letter of 

Noncompliance. Figure 1-1 shows the types of noncompliance with the POs in 10 CFR Part 61, 

Subpart C, which are based on the collection of indirect and direct evidence.
1-8

Table 1-1. Documents Prepared by DOE That Would Be Useful to NRC

Topical Area Document

Approximate 

Availability/Frequency

Groundwater Eastern OU Groundwater 

Monitoring Report

August

Western OU Groundwater 

Monitoring Report

August

FTF Groundwater Monitoring 

Report

March

HTF Groundwater Monitoring 

Report

March

Air Monitoring SRS Annual Environmental 

Report

September

Performance Assessment 

Documentation

SRS Liquid Waste Facilities 

Performance Assessment 

Maintenance Annual 

Implementation Plan

March

Performance Assessment 

Revisions

As issued

Special Analyses As issued

Tank Operational Reports Annual Radioactive Waste 

Tank Inspection Program 

Report

June

Tank or Tank Farm Closure 

Documentation

Presentation Requesting 

Preliminary Approval to 

Cease Waste Removal and 

Enter Sampling and Analysis

As issued to support tank 

closure

Closure Modules As issued to support tank 

closure

Final Configuration Reports As issued to support tank 

closure

DOE = U.S. Department of Energy, NRC = U.S. Nuclear Regulatory Commission, OU = Operable Unit

SRS = Savannah River Site, FTF = F-Area Tank Farm, HTF = H-Area Tank Farm
1-9

Table 1-2. Types of Notification Letters

Type Description/Notification Signature Distribution

Non-Compliant Performance Objective Notifications

I Evidence Performance Objective Is Not Met

NRC staff concludes that direct evidence 

(e.g., environmental sampling data) exists that

indicates DOE disposal actions do not meet one 

or more POs in 10 CFR Part 61, Subpart C.

Notification: NRC will issue a Type I letter of

noncompliance if DOE cannot demonstrate that 

disposal actions currently meet the requirements 

specified in the POs.

Chairman DOE, Covered State, 

and Congress

II Lack of Compliance Demonstration

NRC staff concludes that indirect evidence 

(e.g., experimental data on a key modeling 

assumption) exists that indicates DOE disposal

actions do not meet one or more of the POs in 

10 CFR Part 61, Subpart C.

Notification: NRC will issue a Type II letter of 

noncompliance if DOE cannot adequately 

address NRC technical concerns.

Chairman DOE, Covered State, 

and Congress

III Insufficient Information

NRC staff concludes that insufficient information 

is available to assess whether DOE disposal

actions meet the POs in 10 CFR Part 61, 

Subpart C. It is not clear to NRC staff that DOE 

(i) has plans to or (ii) is able to provide the 

information in a reasonable timeframe to allow 

NRC staff to assess compliance. 

Notification: NRC will issue a Type III letter of 

noncompliance if DOE cannot adequately 

address NRC technical concerns.

Chairman DOE, Covered State, 

and Congress

Other Notification Letters

IV Concern

NRC staff has concerns that DOE disposal 

actions do not comply with the POs in 10 CFR 

Part 61, Subpart C.

Notification: NRC will issue a Type IV letter of 

concern if DOE cannot adequately address the 

NRC concerns.

NRC Staff 

Management

DOE and 

Covered State

V Resolution

NRC staff concludes that DOE has provided 

sufficient information to resolve the concerns 

identified in a Type IV letter of concern.

Notification: NRC will issue a Type V letter of 

resolution if DOE adequately addresses the NRC 

concerns identified in a Type IV letter of concern.

NRC Staff 

Management

DOE and 

Covered State

Note: The NRC expects that if it were to issue a Letter of Concern (i.e., Type IV), the timing of this letter would 

allow DOE sufficient time to respond to NRC staff concerns prior to issuance of one of the three notification 

letters of noncompliance (i.e., Type I, Type II, or Type III) listed in this table.

NRC = U.S. Nuclear Regulatory Commission, DOE = U.S. Department of Energy, PO = Performance Objective, 

CFR = Code of Federal Regulations
1-10

Figure 1-1. Types of Noncompliance With the POs in 10 CFR Part 61, Subpart C
1-11

Monitoring Plan

This monitoring plan presents the basic framework for NRC to perform monitoring activities in 

accordance with the NDAA for the Tank Farms. The monitoring plan starts with the high level 

consideration of the four POs. Under each PO, the relevant MAs are identified. Each MA 

contains a set of MFs important to NRC’s assessment of how DOE disposal actions comply with 

the POs listed in 10 CFR Part 61, Subpart C. New MAs are not expected in the future, but they 

may be identified and added to the monitoring plan. The MFs were created from the concerns 

identified in NRC’s TERs (ML112371751, ML14094A496). These concerns will now be 

addressed under the MFs in this monitoring plan. A crosswalk between NRC staff’s consultative 

comments and MFs listed in this monitoring plan is provided in Appendix A.

The identification, description, and status (i.e., open or closed) of each MF will change as

monitoring activities continue in the future. New MFs are expected to be added to the

monitoring plan in the future as more information is known about the future DOE disposal

actions and experiments. Other MFs may be closed in the future as technical issues are 

resolved or information is provided that decreases the risk significance of the MF(s). NRC 

expects to revise the monitoring plan in the future to address such items as an updated DOE PA 

or a new NRC TER.

1.8.1 Linkage Between Recommendations in the Technical Evaluation 

Report and Monitoring Factors

Appendix A provides a crosswalk between each consultative review comment or 

recommendation to the MAs and factors developed in this monitoring plan. Appendix A, 

Table A–2, also provides a crosswalk between DOE’s PA Maintenance Plan 

(SRR–CWDA–2014–00108) and MFs listed in this plan.

1.8.2 Closing Monitoring Factors 

NRC will document closure of MFs (e.g., TER, technical review report, or periodic monitoring 

compliance report). To the extent practical, the information needed by NRC staff to close an MF 

is provided in Chapters 3 through 6, following each MF identified herein. NRC anticipates that 

as DOE tank farm closure activities continue, it will identify additional MFs and close others. In 

general, DOE must provide transparent and technically robust reports, studies, analyses, or 

experiments that specifically address the technical issues associated with each MF before NRC 

will close an MF.
2-1

2 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.40

Land disposal facilities must be sited, designed, operated, closed, and controlled after closure 

so that reasonable assurance exists that exposures to humans are within the limits established 

in the POs in 10 CFR 61.41 through 61.44.

The requirements in 10 CFR Part 40 are general requirements for near-surface disposal of 

LLW. The DOE disposal actions at the FTF and HTF are unique in that the sites and the waste 

are pre-existing. Consequently, certain activities specified in the POs are limited in applicability. 

Siting requirements do not apply, and design is only applicable with respect to the prospective 

design features of waste disposal, as described in the waste determination. These might 

include such things as design of the grout mix introduced to the tanks and the site cover. Other 

activities (i.e., operations, use, closure, and postclosure) are applicable as they relate to 

disposal of waste covered by the waste determination.

This section requires reasonable assurances that exposures to humans are within the limits 

established in the other four POs (i.e., 10 CFR 61.41 through 61.44). If DOE provides 

reasonable assurance that it will meet the other four POs, then DOE will likely have met 

10 CFR 61.40. If DOE does not provide reasonable assurance that it will meet the other four 

POs (i.e., 10 CFR 61.41 through 61.44), then DOE will likely not have met 10 CFR 61.40. 

Therefore, there are no specific MAs or MFs for 10 CFR 61.40 in this monitoring plan.

With the exception of 10 CFR 61.43, the ability to observe and measure any direct violation of 

the POs will be very limited in the foreseeable future. The public will have limited and controlled

access to environmental media (air or water) that could be contaminated by residual tank farm

waste until the federal government cedes the site. Similarly, a receptor who may occupy the 

site in the future is expected to have low probability of directly intruding upon residual waste. 

Finally, while current activities could result in long-term stability concerns, major activities that 

will impact long-term stability (i.e., emplacement of the site cover) will not occur for many years.

Therefore, the NRC will rely on indirect indicators, referred to as key MAs, to assess DOE

compliance with the POs as it proceeds with closure operations over the next several decades. 

The key MAs, rationale for their relevance, and specific monitoring activities related to them are 

summarized herein. 
3-1

3 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.41

Concentrations of radioactive material which may be released to the general environment in

groundwater, surface water, air, soil, plants, or animals must not result in an annual dose 

exceeding an equivalent of 25 millirems to the whole body, 75 millirems to the thyroid, and 

25 millirems to any other organ of any member of the public. Reasonable effort should be 

made to maintain releases of radioactivity in effluents to the general environment as low as is 

reasonably achievable (ALARA). 

Protection of the general population from releases of radioactivity is a dose-based standard that

considers potential releases of radioactivity from a LLW disposal facility, such as the tank farm 

facilities, into the general environment. These releases may cause a receptor to be exposed 

through direct or indirect contact with various environmental media such as soil, water, air, and 

plant or animal products (Figure 3-1). Direct pathways include direct radiation exposure or 

inhalation of buried waste residuals that may migrate to the surface. Indirect (groundwater) 

pathways include ingestion of crops irrigated with contaminated water, ingestion of animals or 

animal products exposed to contaminated water and fodder (grown in soil irrigated with 

contaminated groundwater), ingestion of contaminated groundwater, and incidental ingestion of 

soil (irrigated with contaminated water). Because tank waste is located several meters below 

grade underneath closure caps, the primary pathway of exposure of potential receptors to 

residual waste associated with closed tanks is through leaching of radionuclides into 

groundwater. Shielding of buried radiation by engineered barriers lowers the potential dose 

from direct radiation exposure. Transport of buried radioactivity from tank farm components to 

the surface in the vapor phase also is considered a less risk-significant process. Therefore,

direct radiation exposure from buried contamination and releases of radioactivity to air and 

subsequent transport to the surface are not a focus of the NRC staff’s monitoring under 10 CFR 

61.41. Review of air monitoring data is, however, an aspect of NRC’s evaluation of 10 CFR 

61.43 as it pertains to protection of members of the public, particularly during active disposal 

facility operations such as cleaning, sampling, and grouting of the HLW tanks when the risk of 

airborne releases is the greatest.

Because the 10 CFR 61.41 evaluations are prospective, a PA analyst must select an evaluation 

period. However, the time period over which the evaluation should be conducted is not 

specified in the 10 CFR Part 61 regulation. LLW and waste incidental to reprocessing (WIR)

guidance, found in NUREG–1573, A Performance Assessment Methodology for Low-Level 

Waste Disposal Facilites (ML053250352) and NUREG 1854, suggests that generally a 10,000-

year period of performance is sufficient to demonstrate compliance with the PO. However, 

longer evaluation periods may be necessary to capture the peak dose and provide insights on 

facility (natural and engineered) performance for certain long-lived wastes. The 10 CFR 61.41 

standard also has an ALARA component to ensure that operations and closure are optimized to 

achieve the lowest overall risk to members of the public, workers, and the environment.

NRC staff evaluates compliance with 10 CFR 61.41 using more recent internal dosimetry 

methods than available when the 10 CFR Part 61 rule was developed. In lieu of using whole 

body and individual organ dose limits specified in the 10 CFR Part 61 rule, NRC uses a single 

dose criterion of 0.25 mSv/yr [25 mrem/yr] total effective dose equivalent to evaluate 

compliance with 10 CFR 61.41. This departure from the 10 CFR 61.41 rule is explained further

in NUREG–1854 (ML072360184) and is consistent with the “Disposal of High-Level Radioactive 

Wastes in a Proposed Geologic Repository at Yucca Mountain, Nevada” rulemaking (66 FR 

55752). 
3-2

Figure 3-1. Potential Pathways of Exposure to a Member of the Public and Points of 

Compliance for the 10 CFR 61.41 {100 m [330 ft] and 61.42 1 m [3 ft]} Analyses

To determine the dose to a potential receptor, NRC also must select a point of compliance

(POC). NRC guidance in NUREG–1854 (ML072360184) indicates that after the end of the 

institutional control period,

1 the receptor evaluated to demonstrate compliance with the 

10 CFR 61.41 PO is assumed to be located at the point of highest projected dose beyond a 

100-m [330 ft] buffer zone surrounding the disposal facility. Figure 3-2 denotes the 100-m 

[330 ft] and 1-m [3 ft] boundaries, the points at which the dose-based standards in 

10 CFR 61.41 and 10 CFR 61.42, respectively, are assessed in the DOE’s FTF PA

(SRS–REG–2007–00002).

2

 Figure 3-3 denotes the 100-m and 1-m boundaries, as well as 

additional intruder well locations (yellow squares) within the 1-m [3 ft] boundary that were 

evaluated in DOE’s HTF PA (SRR–CWDA–2010–00128).

 

1Before the end of the institutional control period, the point of compliance is located on the larger site boundary over 

which DOE maintains access control. 

2A similar approach is taken for HTF in the HTF PA, although DOE evaluates several points within HTF, in addition to 

evaluation points along the 1-m boundary outside the footprint of the HTF. 

Direct Pathways—Direct Radiation 

and Inhalation; Indirect Pathways—

Ingestion of Plant, Animal/Products,

Water, and Soil

Additional 

Surface 

Water 

Pathways: 

Fish 

Ingestion
3-3

Figure 3-2. Approximate 1-m [3 ft] and 100-m [330 ft] Boundaries Where DOE Evaluates 

Compliance in Its FTF PORFLOW Model Domain 

(Adapted from SRS–REG–2007–00002, Figure 5.2-5)

Considering the specific objectives and established paradigms for assessing compliance with 

10 CFR 61.41, NRC staff identified key aspects of disposal facility performance that have the 

largest impact on the 10 CFR 61.41 compliance demonstration based on information provided in 

DOE’s PAs. NRC staff found that several MAs are important to meeting the 10 CFR 61.41 PO. 

For example, the residual inventory remaining in the cleaned tanks and annuli of certain Type I 

and II HTF tanks are good indicators of the potential risk associated with each tank (see Section 

3.1 on MA 1 “Inventory”). 

100-m boundary

1-m 

boundary
3-4

Figure 3-3. Intruder Well Locations at the 1-m [3 ft] Boundary (Inner Boundary Grouped 

in Sectors A–F) and Within the 1-m [3 ft] Boundary (Yellow Squares) at HTF.

Also Illustrated Are Particle Tracks (Blue Lines).

(Adapted from Figure 6.5-5 in SRR–CWDA–2010–00128)

However, the extent to which the inventory of key radionuclides affects facility risk also is 

strongly influenced by the assumed rate of release of the inventory from the tanks. Because the 

key radionuclides are highly concentrated in a very small volume of waste, solubility limits apply 

for many key radionuclides. In some cases, solubility control of the radionuclides is the single 

most important factor controlling release and dose. Therefore, NRC staff established waste 

release as a key MA (Section 3.2 on MA 2 “Waste Release”). 

In the case of primary tank and annular inventories, the reducing grout used to fill the tanks and 

annuli can serve as a significant barrier to waste release. Additionally, for both solubility and 

nonsolubility controlled radionuclides, releases generally cannot occur from the tanks until the 

primary and secondary steel liners fail.

3

 Furthermore, even after release of radionuclides from 

the primary tank (and annuli of HTF tanks), key radionuclides must traverse the concrete vault

walls surrounding the tanks or concrete basemats underneath the tanks. Thus, because DOE 

assumes (i) the concrete vaults that house the HLW tanks provide a passive environment that 

drastically slows corrosion of the tanks, (ii) the reducing grout used to stabilize the inventories in 

the tanks (and annuli of certain HTF tanks) can be a significant barrier to waste release, and 

(iii) the walls and floor of the concrete vaults can also substantially attenuate or provide a barrier 

 

3This is true with the exception that Type IV tanks do not have a liner top, and annular waste can be released through 

a path around the secondary liner.
3-5

to the release of radionuclides out of the tanks, NRC staff established cementitious material 

performance as a key MA (Section 3.3 on MA 3 “Cementitious Material Performance”). 

Following release from the tanks, the final barrier to waste release is the natural environment 

surrounding the disposal facility. The natural environment acts as a barrier because it interacts 

with radioactivity leaving the tanks and causes key radionuclides to move at a slower rate than 

water and in some cases decreases concentrations in a downgradient well where a potential 

receptor may be exposed. Dilution of key radionuclides leaching from the tanks into the aquifer 

below also is an important natural attenuation mechanism that NRC staff will monitor. 

Therefore, NRC staff created MA 4 “Natural System Performance” as a key MA (Section 3.4). 

Figure 3-4 provides details regarding the assumed capabilities of each FTF barrier described 

previously in limiting or mitigating long-term releases from the closed FTF HLW tanks. Similar 

barriers are relied upon in DOE’s HTF Performance Assessment.

NRC staff also established MAs to address more routine or longer term monitoring activities 

including the following:

• MA 5, “Closure Cap Performance”

• MA 6, “Performance Assessment Maintenance”

Although NRC staff concluded that the closure cap is oftentimes a redundant barrier4 in DOE’s 

PAs, NRC staff nonetheless established MA 5, “Closure Cap Performance,” as an MA because 

staff concluded that in certain cases, the closure cap could be important to mitigating risk from 

the disposal facility and in maintaining doses ALARA. Therefore, NRC staff created MA 5 as an 

MA, given the potential for the closure cap to serve as an important barrier that may help ensure 

compliance with each of the 10 CFR Part 61, Subpart C, POs. Section 3.5 contains additional 

details on the MFs related to the closure cap.

NRC staff binned all comments and recommendations from its TERs (ML112371751,

ML14094A496) that were of relatively lower risk significance or required long-term action to 

address in a single category: MA 6, “Performance Assessment Maintenance.” The MA 6 term 

“Performance Assessment Maintenance” should not be confused with a similar but broader term 

used by DOE to describe all of the short-term and longer term activities it plans to undertake to 

maintain its PA, including planned research and tank characterization activities, the results of 

which may be reflected in future PA revisions. In other words, DOE’s PA maintenance plan 

encompasses all activities NRC staff might discuss under each key MA, as well as lower priority 

activities NRC staff discusses under MA 6, “Performance Assessment Maintenance.” 

 

4NRC staff concluded that DOE’s reference or best-estimate PA case shows the closure cap is a redundant hydraulic 

barrier because other, more robust hydraulic barriers, such as the steel liners and tank grout used to fill the cleaned 

tanks, are present and expected to outperform the closure cap for longer periods of time under most scenarios,

including the reference case used by DOE in its PAs. However, it is important to note that the closure cap is the only 

barrier assumed to provide long-term, infiltrating-reducing capabilities, albeit at modest levels. Figure 3-4 shows 

barriers to timing of tank farm releases in DOE’s reference case for FTF. The dark blue barrier represents the 

closure cap that is assumed in DOE’s PA to be fully or nearly fully effective for less than 1,000 years before its 

performance drops off rapidly compared to the light blue (tank grout) or green (steel liner) barriers that last in most 

cases for tens of thousands of years following disposal facility closure. However, it is important to note that after a 

few thousand years, infiltration through the closure cap is assumed in DOE’s PA to stabilize to a constant rate of 

approximately 30 cm/yr [12 in/yr] for all time, less than the background infiltration rate of 37 cm/yr [15 in/yr], while no 

other barrier serves to permanently reduce infiltration.
3-6

Figure 3-4. Example Barriers in the DOE’s FTF Performance Assessment Reference Case. Similar Barriers Are Assumed

in DOE’s HTF Performance Assessment.
3-7

MA 1 “Inventory”

Inventory for key radionuclides is important to the compliance demonstration because inventory 

is linearly related to dose for those radionuclides that are not solubility limited. Even for key 

radionuclides that are solubility controlled, in some cases (e.g., when solubility control is not the 

primary barrier to release from the engineered disposal system) doses also can be very 

sensitive to inventory. This is true because with higher inventory more activity can accumulate 

in a downgradient barrier (e.g., concrete basemats underneath the tanks that may control

release for certain key radionuclides). For those radionuclides that are solubility limited, 

inventory also can be important from a mass depletion perspective. For example, the inventory 

of a key radionuclide could be released at very low concentrations over a long period of time,

such that little to no activity remains when the solubility of the key radionuclide increases to 

risk-significant values. In these cases, a higher inventory could lead to a significantly higher 

peak release and dose from the engineered system compared to a lower inventory, because it 

would take a longer period of time to deplete a radionuclide with a higher residual inventory. 

Thus, inventory can be very risk significant for both solubility-controlled and non-solubilitycontrolled constituents and, therefore, is listed as an MA for the Tank Farms.

Because facility risk is sensitive to key radionuclide inventory, in most cases a threshold 

inventory exists below which a key radionuclide ceases to be important to the compliance 

demonstration. For some key radionuclides (e.g., relatively long-lived and mobile

radionuclides), it may be more cost effective to remove additional activity from the tanks than it 

would be to provide additional information to support a key modeling assumption relied on for 

compliance. For example, DOE provided additional information from Tanks 5H and 6H to 

support a significantly lower inventory estimate for technetium (Tc)-99 in Type I tanks. Until

then, Tc-99 had been regarded as the single most risk-significant radionuclide for FTF over

longer periods of performance in DOE’s base case analysis, owing to its relatively high mobility 

in the environment. NRC staff will continue to monitor progress on FTF Type I and other tank 

closures to ensure the inventory of Tc-99 is reduced to non-risk-significant levels. If Tc-99 

inventory cannot be reduced to these non-risk-significant levels, then other barriers to waste 

release for Tc-99 (such as coprecipitation with iron mineral phases) will become increasingly 

important. In contrast to assumptions made in the FTF PA, in the HTF PA, DOE assumes that 

the entire Tc-99 inventory is coprecipitated with iron mineral phases into perpetuity (in the FTF 

PA Tc-99 was eventually assumed to be released with no solubility control). Because NRC staff 

does not think that DOE has provided sufficient support to conclude that 100 percent of the 

Tc-99 inventory remaining in the HTF tanks is coprecipitated with iron and will remain so for all 

time, additional supporting information will be needed for the longevity and assumed level of 

solubility control of Tc-99, if the residual inventory of Tc-99 in HTF tanks is found to be risk 

significant considering no solubility control. If the residual inventory of Tc-99 in HTF tanks is not 

found to be risk significant, no additional support for the assumed level of solubility control is

needed.

Row 1 of Table 3-1 provides information on the relative hazard of three key radionuclides at FTF

based heavily on the residual inventory of the radionuclides assumed in the PA 

(SRS–REG–2007–00002). The relative hazard associated with these radionuclides is 

expressed in terms of the orders of magnitude reduction needed to reduce the concentrations to 

a level that would meet the 10 CFR 61.41 PO, if the concentrations were located at the point of 

compliance (i.e., assuming the entire inventory is placed in the contaminated zone pore water). 

While assuming the entire waste inventory is in the contaminated zone pore water is unrealistic, 
3-8

Table 3-1. Relative Risk and Contributions of FTF Barriers to Reducing Risk 

for Three Key Radionuclides (Tc-99, Pu-239, and Np-237)

* in DOE’s FTF PA

Tc Pu Np Notes

1

Total Barrier 

Performance 

Needed (Function 

of Inventory)†

6‡§

(Type I) 

9║

(Type IV, 

Tank 18F)

6‡

(Type I)

Factor reduction in concentration 

needed to meet the 10 CFR 61.41 

dose standard. The tank/type 

producing the highest dose for 

each key radionuclide is provided 

in parentheses.

Engineered System

2a Solubility Control 0‡ 2‡║ 1 to 2‡ Final solubility

2b (9 to 11)¶ (9 to 11)¶ (5 to 6) Initial solubility

3

Basemat 

Attenuation 

(Sorption)

<1 2¶ 2¶ Very important for Pu and Np.

Can compensate for solubility.

4

Near-Field

Diffusion or 

Dispersion+

2║ 1¶ 1¶

Additional reduction in 

concentration due to upward 

diffusion into tank grout, large cell 

size, or dispersion.

Natural System

5 Aquifer Dilution 1 1 1 Based on simple aquifer mixing 

model; comparison of 

concentrations between vadose 

zone and saturated zones; and 

between source and POC.

Pu sorption can compensate for 

other barrier underperformance.

6 Sorption <<1 1‡ <<1

7 Additional 

Dispersion+ to POC 1–2¶ 1¶ 1¶

8 Total Barrier 

Performance 5 8 6 to 7 Sum of rows 2a, 3-7.

9 Calculated 

Safety Margin −1§ −1║ 0 to 1 Difference between Row 8 and Row 1. *All values in the table are approximate (order of magnitude). Values only are intended to provide relative information on the 

contributions of various barriers in DOE’s FTF PA and are not expected to be exact. Many of the values for the various barriers 

were estimated based on tracking the concentrations of the three key radionuclides from the contaminated zone to the point of

compliance in DOE’s PORFLOW models for the tank/type listed in Row 1.

†The “total barrier performance needed” is calculated by assuming the single tank inventory assumed in the FTF PA is located in 

the pore water of the contaminated zone. While virtually impossible, assuming the total inventory is available to a potential 

receptor is necessary to provide a starting point from which to evaluate the contributions of various barriers to reducing risk and to 

provide a measure of the relative hazard associated with each key radionuclide listed based on inventory and groundwater 

pathway dose conversion factor of each radionuclide. The contaminated zone is assumed to be 1 in thick with a porosity of 0.27. 

For example, a value of “6” for Tc-99 in the first row corresponds to a factor of 106, or 1,000,000, the factor by which the 

concentration in the waste zone needs to be reduced to produce a groundwater concentration at the point of compliance 

equivalent to 0.25 mSv/yr [0.25 mSv/yr] total effective dose equivalent based on DOE biosphere modeling in the FTF PA.

‡Most tractable

§In the Tanks 5F and 6F Special Analysis SRR–CWDA–2012–00106, DOE showed that the Tc-99 inventory was overestimated by 

one to two orders of magnitude (i.e., Row 1 could be as low as four orders of magnitude and Row 9 could be one order of 

magnitude safety margin).

║In the Tanks 18F and 19F Special Analysis SRR–CWDA–2010–00124, DOE’s updated best estimate final solubility (Row 2) was 

significantly higher than that assumed in the FTF PA, leading to a peak dose from Pu-239 less than the 10 CFR 61.41 PO (i.e., 

positive safety margin in Row 9). Using what was described as a more conservative Pu solubility, the results could also be similar 

to those reported in the FTF PA and this table.

¶Potentially optimistic

+Dispersion is used in a broad sense to describe diffusion, numerical, and physical dispersion in DOE’s PA models. Because Tc 

is ultimately assumed to be highly soluble and mobile in DOE’s PA model, almost all the attenuation of Tc-99 is due to dilution and 

dispersion. No solubility control is assumed for Tc upon transition to the final chemical state.

FTF = F-Area Tank Farm, Tc = technetium, Pu = Plutonium, Np = Neptunium, U.S. Department of Energy,

PA = Performance Assessment, POC = Point of Compliance
3-9

the calculation was performed to indicate the relative hazard of these three key radionuclides 

based primarily on inventory and groundwater pathway dose conversion factors alone. The 

calculation was also performed to illustrate how DOE assumes each of the barriers acts to 

reduce the risk associated with release of the radionuclides into the accessible environment. In 

subsequent sections of this plan, NRC staff will describe in more detail which barriers are 

important to DOE’s compliance demonstration and which barriers require additional support. 

Table 3-1 is introduced in this section, because it provides information on NRC staff’s current 

thinking that inventory reduction may be one of the most effective means of demonstrating that 

the 10 CFR 61.41 PO can be met for Tc-99 and Neptunium (Np)-237. NRC staff thinks that 

additional support for the assumed level of performance of natural or engineered barriers for 

these two radionuclides is needed, but supporting information may be difficult to obtain. It is 

important to note that the inventory of Americium (Am)-241, parent to Np-237, should also be 

considered in assessing the residual risk associated with Np-237 in the tank farms. While 

Table 3-1 presents information for FTF based on the original FTF PA, parallels can be drawn to 

HTF. A notable exception is that while Radium (Ra)-226 was identified as an important

radionuclide contributing to dose in the FTF PA, the long-term risk associated with Ra-226 due 

to in-growth from its parents (i.e., Plutonium (Pu)-238, Uranium (U)-234, Thorium (Th)-230) is 

expected to be relatively greater for HTF compared to FTF due to the relatively high inventory of 

Pu-238 expected to remain in HTF tanks compared to FTF tanks (e.g., factor of 20 times higher 

Pu-238 inventory expected in HTF).

Additionally, DOE included Ra-228 and Th-232 in the list of 54 radionuclides for consideration in 

the assessment of compliance with the POs in DOE’s HTF PA because thorium fuel was 

exclusively processed at the H-Canyon. Because the two tank farms were fed from different 

processing facilities, differences between the FTF and HTF inventories are expected (SRNL–

STI–2012–00479). 

NRC Monitoring Under MA 1 “Inventory”

As listed in Appendix A and documented in more detail in NRC’s TERs (ML112371751,

ML14094A496), NRC staff will consider the following MFs related to inventory that are 

considered important to meeting the 10 CFR 61.41 PO: MF 1.1 “Final Inventory and Risk 

Estimates.”

The following factors support development of the final inventory (e.g., sampling and volume data

are used to estimate a final inventory) and also are listed as MFs under MA 1, “Inventory.”

• MF 1.2 “Residual waste sampling”

• MF 1.3 “Residual waste volume”

• MF 1.4 “Ancillary equipment inventory”

The following factor, related to the final tank inventory, is important to meeting ALARA criteria in 

10 CFR 61.41 and will therefore be listed as an MF under MA 1, “Inventory”: MF 1.5 “Waste 

Removal As It Pertains to ALARA.”

3.1.1 Monitoring Factor 1.1: Final Inventory and Risk Estimates

DOE has committed to sample each tank following waste retrieval activities. During the 

monitoring period, NRC staff will review special analyses typically performed at the time of 

closure of each tank that provide updated inventories and risk estimates for the entire tank farm 
3-10

that is the subject of the special analysis.

8

 NRC staff will assess the degree to which DOE 

demonstrates that the tank farm meets the POs with the new projected radionuclide inventories

and will assess other PA updates. As part of the evaluation, NRC staff will assess the degree to 

which DOE’s special analyses evaluate uncertainty in the revised inventory. NRC staff should 

independently verify whether the change in inventory, or changes to other modeling parameters,

are expected to lead to an exceedance of the dose-based POs (i.e., a 0.25 mSv/yr [25 mrem/yr]

limit to a member of the public under 10 CFR 61.41 or an applied 5 mSv/yr [500 mrem/yr] limit 

to an intruder under 10 CFR 61.42). This factor can be closed following NRC review of the last 

tank or equipment-specific special analysis prepared by DOE for FTF and HTF.

Several FTF and HTF tanks have known leak sites. The waste tank annulus provides a 

collection point for any potential leakage from the primary tank. Type I Tanks 9H and 10H and 

Type II Tanks 14H and 16H in HTF are known to have leak sites that led to a potentially 

risk-significant inventory in their annuli as noted in the final waste determination for HTF 

(DOE/SRS–WD–2014–001). Following issuance of the final waste determination for HTF, DOE 

developed a special analysis for Tank 16H (SRR–CWDA–2014–00106). NRC staff is in the 

process of evaluating updated risk estimates for Tank 16H to assess the risk of the final residual 

waste inventory estimated to remain in the Tank 16H annulus at the time of closure. The results 

of NRC staff’s evaluation of the Tank 16H Special Analysis may influence conclusions regarding 

the acceptability of annulus waste inventories with regard to their ability to meet the 

10 CFR Part 61, Subpart C, POs.

3.1.2 Monitoring Factor 1.2: Residual Waste Sampling

To accurately estimate the postcleaning inventory that will be stabilized in FTF and HTF tanks, 

DOE must sample and analyze the residual waste concentration in each tank after it is cleaned, 

as well as characterize the solids density and estimate residual waste volumes. NRC staff will 

review sampling and analysis plans developed for each tank. 

NRC’s technical review of sampling and analysis plans should include, but may not be limited 

to, the following considerations:

• Consideration of intratank waste variability that is important to the sampling design,

including the basis for assumptions regarding homogeneity and the number of samples 

to be collected

• Use of floor concentration samples for assigning residual waste inventory for tank walls

 

8It is important to note that DOE must demonstrate compliance with an entire tank farm; therefore, a single tank can 

put DOE out of compliance with the POs. Additionally, the distribution of residual waste may also be important to the 

compliance demonstration (e.g., waste located in tanks located nearer the 100-m [330 ft] boundary may pose a 

greater risk than tanks located further upgradient of the boundary due to greater modeled natural attenuation). 

Additionally, following closure of each tank, DOE prepares a special analysis that evaluates the impact of updates to 

the inventory and other modeling changes to the results of the performance assessment considering not only the 

single tank, but all of the tanks in the tank farm. Therefore, it is important for NRC to review each special analysis 

that is completed following closure of each tank or groups of tanks addressed in the special analysis.
3-11

• DOE’s support for assumptions regarding normality of radionuclide concentration when 

developing deterministic and probabilistic inventory parameters

• Sampling of HRRs or basis for removal of HRRs from the list of radionuclides to be

sampled

As documented in NRC’s review of Tanks 5F and 6F Final Inventories (ML13085A291), the

NRC expects DOE to address the following technical concerns in future tank sampling efforts:

• DOE should consider, in its tank sampling design, historical information on tank waste 

receipts, and information related to the alteration and redistribution of waste due to 

cleaning operations that may impact horizontal and vertical waste heterogeneity.

• DOE should evaluate the option to composite samples within segments (or strata) to 

preserve information about segment (or strata) variance.

• DOE should evaluate and present information on the relative contributions of various 

forms of uncertainty in its estimation of mean tank concentrations.

• DOE should clarify the statistical approach used to estimate the 95th percent upper 

confidence level (UCL95) (e.g., treatment of all nine measurements as independent 

when computing the UCL95).

• DOE should also consider how it can better assure sample representativeness by 

improving tank sampling designs, collection tools, and instructions.

The technical issues documented in the Tanks 5F and 6F technical review report 

(ML13085A291) with respect to residual waste sampling were repeated in the HTF TER 

(ML14094A496). In addition to review of sampling and analysis plans, NRC staff also will 

conduct its own independent assessment to verify the list of HRRs in DOE’s assessment is 

complete. If additional HRRs are identified, NRC staff will meet with DOE to resolve the 

discrepancies in the list and suggest actions, as appropriate, that DOE could take to ensure that 

risks are appropriately assessed and managed. The NRC staff recommends that DOE continue 

to evaluate its HRR list and provide sufficient justification for any changes as additional 

information becomes available. The HRR list should be evaluated especially where it is used to 

inform decisions, such as the selection of radionuclides characterized in residual waste and the 

screening of radionuclides for the purpose of detailed PA calculations. Technical review efforts 

under this MA should be coordinated with onsite observations of waste sampling to evaluate 

whether samples are being collected in accordance with sampling analysis plans and the quality 

of data is sufficient to meet data quality objectives. 

This MF can be closed following review of the last sampling and analysis plan for a tank and 

following the last planned onsite observation of sampling of a tank (may occur prior to the last 

tank or ancillary equipment being sampled). NRC will use a graded approach in reviewing 

sampling and analysis plans. After technical issues are resolved, NRC staff’s reviews will be 

focused on changes to the programmatic approach and/or a cursory review to make sure DOE 

is implementing the plan as documented.
3-12

3.1.3 Monitoring Factor 1.3: Residual Waste Volume

Residual waste volume is multiplied by density and radionuclide concentrations to estimate the 

residual inventory and is, therefore, important to development of the final inventory. As 

documented in its FTF TER (ML112371751), NRC staff noted there is significant uncertainty in 

DOE’s current material mapping approach used for volume estimation. NRC staff 

recommended DOE explore methods to improve the process by which it estimates residual 

waste volumes and associated uncertainty, including evaluation of the costs and benefits of 

alternative technologies available for mapping. 

As documented in NRC’s more recent review of Tanks 5F and 6F Final Inventories 

(ML13085A291), NRC expects DOE to address the following technical concerns when 

estimating residual tank waste volumes in the future:

• DOE should better understand the accuracy of mapping team height estimates through 

additional field validation activities for a range of solid material heights.

• DOE should clearly communicate how it determines the size of areas to be mapped and 

how it manages uncertainty related to height estimates for discretized areas in its 

deterministic analysis. Likewise, DOE should clarify how it represents uncertainty in the 

assignment of high and low end heights to these areas (e.g., whether it uses a height 

that is clearly below/above the nonuniform surface of the delineated areas).

• DOE should consider uncertainty in the volume estimates resulting from the transfer of 

data from photographic and video evidence to hand-contoured maps (and then to Excel®

spreadsheets with a finer discretization).

• DOE should be more transparent with respect to its approach to (i) mapping annular

volumes, including use of a crawler to inspect internal surfaces, and (ii) estimating

residual waste volumes in ventilation ducts. DOE should consider uncertainty in annulus 

volume estimates.

In lieu of improving the method by which DOE estimates residual waste volume, DOE could 

manage inventory uncertainty with conservative estimates (i.e., volume estimates that clearly err

on the side of higher values). The technical issues documented in the Tanks 5F and 6F

technical review report (ML13085A291) with respect to development of final volume estimates 

were repeated in the HTF TER (ML14094A496).

DOE indicates its intent to improve the method of estimating residual volumes in its PA 

Maintenance Programs (e.g., SRR–CWDA–2012–00022 and SRR–CWDA–2014–00108). NRC 

staff will monitor DOE’s progress in this area. NRC staff also will attempt to observe DOE’s use 

of video and photographic records to develop residual waste volumes during an onsite 

observation. This factor will be closed once NRC staff concludes DOE has taken steps to 

improve the process by which it estimates residual volumes or shows that DOE has 

appropriately managed volume uncertainty. This factor may be reopened if NRC staff identifies 

issues with DOE’s approach to developing or considering uncertainty in volumes estimates.
3-13

3.1.4 Monitoring Factor 1.4: Ancillary Equipment Inventory

The low risk significance of ancillary equipment to meeting the 10 CFR 61.41 PO is predicated 

on the assumed inventory for key radionuclides in DOE’s PAs. Therefore, the inventory for 

ancillary equipment should be confirmed to support NRC staff’s understanding of the low risk

significance of these tank components. DOE indicated, in response to NRC comment 

(SRR–CWDA–2009–00054), its intent to verify PA assumptions regarding transfer line 

inventories consistent with Section 8.2, “Further Work,” in DOE’s PA (SRS–REG–2007–00002). 

NRC staff will meet with DOE to discuss DOE’s schedule for characterization of transfer lines to 

ensure conclusions regarding the relatively low risk estimates for transfer lines are confirmed. 

Additionally, transfer line inventories are important for the intruder analysis because DOE 

assumes an intruder can more easily access the residual inventory in a transfer line than in a 

tank. Transfer line inventories are discussed in more detail in Chapter 4, which includes 

information on MFs related to assessing compliance with the 10 CFR 61.42 PO.

This MF can be closed once NRC staff concludes that DOE characterization has confirmed the 

low risk of ancillary components.

3.1.5 Monitoring Factor 1.5: Waste Removal (As It Pertains to ALARA)

In the final FTF and HTF waste determinations, DOE cites its ability to meet the NDAA criteria 

“removal of HRRs to the maximum extent practical” (MEP demonstration) as the primary means 

by which it meets the ALARA criteria in 10 CFR 61.41. NRC will evaluate removal to the 

maximum extent practical for each cleaned tank to ensure DOE disposal actions are consistent 

with ALARA criteria. Because none of the HTF tanks had undergone an MEP demonstration at 

the time of issuance of the final waste determination, the NRC evaluated the process for MEP 

demonstration as opposed to reaching a conclusion for any of the HTF tanks. NRC staff will 

assess DOE compliance with ALARA objectives through review of DOE documentation 

completed in conjunction with the federal facility agreement closure process. As provided in 

NRC guidance in NUREG–1854 (ML072360184), NRC staff also should pay special attention to 

the distribution of residual inventory in the cleaned tanks to ensure compliance with ALARA

(e.g., removal of waste from areas susceptible to preferential pathways, such as tank walls). 

This MF can be closed once all the tanks are cleaned and NRC staff has reviewed DOE 

documentation of removal to the maximum extent practical.

Closure of Monitoring Factors Related to MA 1, “Inventory”

NRC staff expects that MFs related to inventory will be closed after tank cleaning activities and 

subsequent postcleaning sampling activities are completed for the tank farms. 
3-14

MA 2, “Waste Release”

Importance of MA 2, “Waste Release”

In the FTF and HTF PA reference (or best estimate) cases, DOE assumes for many key 

radionuclides that concentrations released from the primary liners of the tanks are limited to low 

values for long periods of time.

9

 Key radionuclide concentrations in the aqueous phase of the 

waste zone are controlled by solubility (or concentration) limits. If waste zone aqueous-phase 

concentrations are limited to low values, then exposure to a member of the public that may 

result from use of contaminated groundwater at the points of compliance (maximum 

concentrations on the 1- or 100-m boundaries) will also be limited. Solubility (or waste release) 

assumptions are, therefore, important to DOE’s demonstration of compliance with the 10 CFR 

61.41 PO, as well as the 10 CFR 61.42 PO discussed in Section 4, and are therefore a focus of 

NRC staff’s monitoring of the SRS tank farms.

The solid phases that are assumed to be present in the waste (or contaminated) zone within the 

primary liner dictate the solubility (or aqueous-phase concentration) limits of key radionuclides. 

The key radionuclides that are (i) important to dose and (ii) sensitive to solubility limits are Tc, 

Np, and Pu. Solubility limits for these elements are modeled, in DOE’s PAs, for (i) pure phases 

consisting only of the key radionuclide itself as a precipitated solid and (ii) as coprecipitated10

with iron-bearing mineral solids in the waste residue. NRC staff will, therefore, focus on these 

three elements, their assumed solubility-limiting phases, and associated solubility limits during 

tank farm monitoring as part of this MA, under MF 2.1.

In addition to the solubility-limiting phases and associated solubility limits for key radionuclides,

assumptions regarding the length of time that key radionuclides remain in a low solubility phase

may also be important to the compliance demonstration from a timing perspective (e.g., if the 

higher solubilities lead to peak doses above the PO but following the period of compliance). 

DOE assumes groundwater vertically infiltrating the tank system will typically be conditioned by 

the tank grout11 through which it must first flow to get to the contaminated zone located in the 

primary liner. Conditioning of the groundwater through its interaction with the tank grout is 

assumed to occur for thousands to tens of thousands of years (e.g., see purple barriers in 

Figure 3-5 for FTF tanks and times listed in Table 3-2 for FTF and HTF tanks that signal the 

assumed transitions of key radionuclides to higher solubility).12 Conditioning of the groundwater 

 

9MA 2 focuses on waste located in the primary liner. DOE also considers a waste inventory in the annuli of Types I 

and II tanks in the HTF PA; however, the waste in the annuli of these tanks is not assumed to be solubility controlled 

and is not considered under MA 2. MF 3.5, “Vault and Annulus Sorption,” under MA 3, “Cementitious Material 

Performance,” discusses monitoring of waste release assumptions for the annuli of these HTF tanks. 

10DOE uses the term “coprecipitated” in a broad sense to refer to the incorporation of key radionuclides into a solid 

iron mineral (rather than being a pure solid composed of just that key radionuclide). The solubility of the key 

radionuclide is assumed to be controlled by the solubility of the iron mineral.

11Grout is added to the tank and annulus to stabilize the waste residuals and to provide stability to the engineered 

system at the time of closure. Reductants are added to the grout to help retain certain key radionuclides in a low 

solubility form. 

12The primary difference between chemical transition times for FTF and HTF tanks are related to the timing of steel 

liner failure. For example, certain Type I and II tanks in HTF are assumed to have initially failed liners, and therefore, 

water is able to begin infiltrating the tank and depleting the tank grout of reducing and buffering components earlier in 

time leading to more rapid chemical transitions. Additionally, four Type I tanks at HTF are fully submerged in the 

water table aquifer and are treated differently than other tanks at HTF or FTF. To determine the chemistry of the 

water in contact with the contaminated zone in the primary liner for Type I tanks at HTF, DOE considers various 
3-15

through its interactions with tank grout is important because in most cases DOE assumes the 

chemical properties of the conditioned groundwater helps to maintain the low solubility of key 

radionuclides in the contaminated zone. In some cases, aging of the grout through its

interactions with infiltrating groundwater can lead to chemical transitions to relatively high Eh13

(or what is referred to as “oxidized” conditions) or relatively low pH14 (or what is referred to as 

“Region III” conditions) and associated higher solubility releases of key radionuclides. In these 

cases, the timing of the risk-significant release may be important to the compliance 

demonstration if the releases result in peak doses above the compliance limits. The longevity of 

the chemical conditioning of infiltrating groundwater via the tank grout that maintains key 

radionuclides in a low solubility form is primarily a function of (i) the flow path of water 

movement through the grout mass (i.e., bypass flow through preferential pathways leading to

minimal contact of water with grout or matrix flow through the grout monolith with maximum

contact of water with the grout) and (ii) the geochemical interactions between the water and the 

contacted grout mass. The assumptions regarding the movement of infiltrating water through 

the grout mass are discussed further in MA 3, “Cementitious Material Performance,” 

Section 3.2. Assumptions regarding the longevity of reducing conditions and high pH that are 

based on DOE’s geochemical modeling (and associated assumptions regarding the tank grout 

components that provide reductive and buffering capacity and their ability to interact with 

infiltrating groundwater) are the subject of this MA and are discussed in more detail under

MF 2.2.

 

cases where unconditioned saturated groundwater flowing primarily horizontally through the engineered system 

mixes with a smaller quantity of conditioned groundwater that is assumed to flow vertically through the tank grout into 

the contaminated zone to determine the chemistry of the water in contact with the contaminated zone in the primary 

liner. However, after considering the combined effect of assumptions regarding the chemistry of the saturated 

groundwater (low dissolved oxygen that tends to prolong chemical transition times) and additional horizontal flow 

through the tank grout (that tends to shorten chemical transition times), the chemical transition times for Type I tanks 

are generally faster than other comparable tanks (see, for example, Table 3-2 Type I tanks versus Type II tank 

transition times). Additional discussion regarding DOE assumptions with respect to the chemistry of the saturated 

groundwater at HTF and the cross-flow factors used by DOE at HTF are provided in Appendix C. 13Eh is a measure of oxidation-reduction potential or electron activity (or concentration). Eh is measured in millivolts 

and varies from approximately −500 to +800 in natural environments. Many key radionuclides are less mobile or less 

soluble at lower values of Eh or what is referred to as “reducing conditions.” Solubility of many key radionuclides 

increases when Eh value rises (e.g., Pu solubility increases significantly when Eh rises above a value of around +0.5 

volts in DOE’s solubility modeling (SRNL–STI–2012–00087 and SRNL–STI–2012–00404) or when the system 

becomes “oxidized”). Oxidation signals the transition from a chemical state that DOE refers to as Reduced Region II 

to a chemical state referred to as Oxidized Region II. For example, the transition from reduced to oxidized conditions 

is marked in Figure 3-5 by the vertically oriented, green dashed line. 14Measure of hydrogen ion activity (or concentration) or measure of acidity. The pH is a unitless number calculated 

as the negative of the log of the hydrogen ion concentration that is measured in mol/L. The pH of the Upper Three 

Runs aquifer at SRS ranges from 5.2 to 7.7 (ML073510127). Undegraded cementitious materials tend to increase 

pH to values as high as 12.5. In DOE’s reference (or best estimate) case, a decrease in pH to approximately nine 

generally leads to a chemical transition from what DOE refers to as Oxidized Region II to Oxidized Region III. The 

effect of this pH transition on radionuclide solubility limits (i.e., increasing versus decreasing solubility limits) depends

on the radionuclide. The Eh-based chemical transition discussed in the preceding footnote occurs prior to the 

pH-based chemical transition, with the two transitions delineating the three chemical states and a solubility specified 

for each key radionuclide and chemical state, which DOE assumes in its PAs.
Figure 3-5. Barriers to Timing in the DOE’s FTF Reference (or Best Estimate) Performance Assessment Case15

 

15This figure is consistent with the results of the FTF PA (SRR–CWDA–2010–00128). DOE provided updated PA results in its special analyses for Tanks 18F and 

19F (SRR–CWDA–2010–00124) and Tanks 5F and 6F (SRR–CWDA–2012-00106), which this figure may not reflect (e.g., updated geochemical modeling result 

which show that Pu could be released at high solubility significantly earlier in time upon transition to Oxidized Region II (see green vertical dashed lines), or it could 

remain in a relatively low solubility state into perpetuity, dependent on the assumed Eh in the contaminated zone; chemical transition times were also updated in 

the Tanks 18F and 19F Special Analysis and are estimated by DOE to be slightly prolonged (see Table 3-2)).

3-16
3-17

Table 3-2. Summary of Chemical Transition Times in the HTF and FTF PAs

Submergence 

of Tank Transition Number of Pore Volumes Required[CZ Transition Time (Year)]

HTF PA FTF PA

Partially and 

Nonsubmerged

Reduced Region II

to

Oxidized Region II

523

(7,900 Type IV;

9,200 Type II NL;

15,000 Type II;

16,000 Type III)

371†

(10,500 Type IV;

15,500 Type I;

15,500 Type III/IIIA)

Oxidized Region II

to

Oxidized Region III

2,119

(19,000 Type II NL;

22,000 Type IV;

25,000 Type II;

28,000 Type III)

2,063‡

(20,000 Type IV;

20,000 Type I;

20,000 Type III/IIIA)§

Submerged

Reduced Region II

to

Oxidized Region II 

(Condition C to D)

1,787

(7,700 Type I NL;

12,000 Type I)

NA

Oxidized Region II

to

Oxidized Region III 

(Condition D

to

Oxidized Region III)

2,442

(8,100 Type I NL;

12,000 Type I)

NA

Notes: 

†Transition to Oxidized Region II occurs at 371 DPV in original FTF PA (SRR–CWDA–2010–00128) but changed 

to 523 DPV in the Tanks 18 and 19 Special Analysis (SRR–CWDA–2010–00124), consistent with what was later 

used in the HTF PA.

‡Transition to Oxidized Region III occurs at 2,063 DPV in original FTF PA (SRR–CWDA–2010–00128) but 

changed to 2,119 DPV in Tanks 18 and 19 Special Analysis (SRR–CWDA–2010–00124), consistent with what 

was later used in the HTF PA.

§Although the calculated chemical transition time based on the displaced pore volume count would occur after 

20,000 years, the final chemical transition was assumed to occur at 20,000 years, because most of the 

simulations ended prior to the transition from Oxidized Region II to Oxidized Region III. DOE did provide results 

to 100,000 years in one simulation.

NL=no liner, HTF = H-Area Tank Farm, FTF = F-Area Tank Farm, CZ = Contaminated Zone, PA = Performance 

Assessment 
3-18

NRC Monitoring Under MA 2, “Waste Release”

As listed in Appendix A and documented in more detail in NRC’s TERs (ML112371751,

ML14094A496), NRC will consider the following MF related to waste release that is considered 

important to meeting the 10 CFR 61.41 PO: 

MF 2.1 “Solubility-Limiting Phases/Limits and Validation”

Due to DOE’s reliance on timing of peak dose to demonstrate compliance, NRC staff also will 

monitor the following factor, which may be important to DOE’s demonstration of compliance with 

the 10 CFR 61.41 PO: 

MF 2.2 “Chemical Transition Times”

Additional discussion regarding NRC’s MFs related to waste release is available in Appendix C.

3.2.1 Monitoring Factor 2.1: Solubility-Limiting Phases/Limits 

and Validation 

Given its importance to the timing and magnitude of peak dose, in its TERs, NRC staff 

recommended DOE conduct waste release experiments to increase support for key modeling 

assumptions related to (i) chemical forms of key radionuclides in residual wastes and 

(ii) expected solubility of key radionuclides under a range of environmental or service conditions 

that the contaminated zone is expected to be exposed to over time. DOE has provided 

additional support for several waste release assumptions because the NRC staff first 

recommended a need for increased support for key modeling assumptions. This included

(i) convening a Pu solubility peer review that provided expert technical advice related to residual 

Pu in Tank 18F (LA–UR–12–00079), (ii) conducting spectroscopic analyses of residual waste 

samples from Tank 18F (SRNL–L3100–2012–00017), (iii) conducting updated geochemical 

modeling of Pu in Tank 18F using the Nuclear Energy Agency thermodynamic database 

(SRNL–STI–2012–00087), and (iv) expanding the updated geochemical modeling to include 

additional radionuclides and effects of oxalic acid in the HTF PA (SRR–CWDA–2010–00128). 

However the additional model support has not obviated the need for experimental support for 

modeled waste release.

NRC continues to recommend that DOE design and perform waste release experiments using 

actual tank residual samples as soon as practical. DOE staff should continue to discuss its 

plans with NRC to ensure experiments are designed to optimize their potential usefulness in 

supporting the 10 CFR 61.41 compliance demonstrations. This monitoring activity is considered 

to be the highest priority by NRC staff at this time from both a timing and importance 

perspective. Furthermore, as indicated in Table 3-1, NRC staff thinks that in addition to being 

one of the most important barriers in the PAs, determining the solubility of Tc, Pu, Np, and other 

key radionuclides is expected to be one of the more tractable key technical issues.

16 

To address NRC staff’s MF related to the need for waste release experiments, DOE developed 

 

16Following issuance of NRC staff’s FTF TER, DOE convened a Pu peer review group to evaluate the need for 

solubility experiments. LA–UR–2012–00079 concurred with NRC staff’s recommendations in this area and 

concluded the following: “To provide a stronger scientific foundation to justify the use of geochemical modeling in the 

tank closure performance assessment, validation and verification of the model and assumptions is required. This 

involves both solid phase characterization of the residual wastes (as described previously) and leachability testing.”
3-19

a technical task and quality assurance plan to perform waste release experiments using

Tank 18F residuals (SRNL–RP–2013–00203). Preliminary testing results were presented at the 

March 2014 onsite observation (ML14106A573). NRC staff encourages DOE to continue the 

work that was initiated in FY2014 with respect to obtaining support for the assumed solubility 

limits of key radionuclides in tank farm waste. Pending results of the waste release 

experiments, NRC will evaluate the need for additional experiments for other tank waste.

Given its importance to risk and overall tank closure, NRC supports DOE’s efforts to obtain 

support for the assumed Np-237 solubility (SRNL–RP–2013–00203). Although NRC staff 

generally found DOE’s assumed Np-237 solubilities reasonable in the FTF PA, updated 

geochemical modeling performed to support the HTF PA indicates that Np solubility is fairly 

uncertain as it appears to be very sensitive to Eh over a range of Eh that may be encountered in 

the field.

17 Further, DOE has not provided sufficient support for the assumed level of 

performance of the basemats in its PAs. Experimental support for the assumed solubility limits 

could alleviate the burden of providing additional support for other Np-237 barriers, such as the 

vault basemats. Table 3-1 shows the importance of the basemat in meeting the 10 CFR 61.41

PO for FTF.

18 If the basemat does not perform as well as assumed in DOE’s reference of “best 

estimate” case, data on solubility control may assist in demonstrating that POs can be met.

For tanks that have not been cleaned, DOE should consider the effects of reagents (e.g., oxalic 

acid) used to remove radionuclides from the tank residue, including formation of new 

compounds that may alter leachability of key radionuclides. Execution of this monitoring activity

may be contingent on results of other analyses. For example, final estimated Tc-99 inventories 

in Type I tanks, as described in Section 3.1, may determine the need for Tc-99 waste release

experiments. Final Tc-99 inventories estimated for Tanks 5F and 6F were significantly lower 

than assumed in the FTF PA, alleviating the need for waste release experiments to support the 

assumed low solubility of Tc-99 for those tanks. 

This MF can be closed once DOE provides experimental support for the assumed solubilities of 

key radionuclides relied on for performance. The results of near-term waste release 

experiments may inform the extent to which additional recommendations made in NRC’s TERs

(ML112371751, ML14094A496) would need to be implemented by DOE. Should the results of 

the experiments indicate less than favorable performance, NRC staff expects DOE to assess 

the impact of the results on the PAs. NRC staff also will assess the need for additional 

experiments, data collection, and modeling to provide support for key barriers in DOE’s PAs that 

might serve to mitigate underperformance of chemical barriers. If the results of the experiments 

show that key radionuclides are strongly retained in the residual waste, NRC staff expects that 

in addition to this MF, other MAs or MA components will become less important and can be 

closed.

 

17In the HTF TER (ML14094A496), NRC staff note that the solubility limit for Np is sensitive to Eh in Oxidized 

Region III; however, the Eh transition occurs from Reduced Region II to Oxidized Region II and is assumed to remain 

stable from Oxidized Region II to Oxidized Region III. Figure 24 in SRNL–STI–2012–00404 shows Np solubility is 

highly sensitive to Eh over a relevant range of Eh/pH that may be encountered in the field, which includes both 

Oxidized Region II and Oxidized Region III conditions calculated and for which solubility limits are derived in the PA 

modeling.

18In the FTF PA, the basemats were shown to be an important barrier in attenuating the releases of key radionuclides 

(e.g., Pu, Np). Although solubility control may be more important for Pu and Np in the HTF PA compared to the FTF 

PA, the NRC staff also expects the basemats to be important in the HTF PA.
3-20

3.2.2 Monitoring Factor 2.2: Chemical Transition Times

In some cases, DOE relies on barriers that delay the timing of peak dose to demonstrate 

compliance with the POs in 10 CFR 61.41; therefore, PA assumptions regarding the timing of 

transition of key radionuclides to higher solubility phases can be important to the compliance 

demonstrations. DOE relies on geochemical modeling to estimate the time at which two key 

chemical transitions take place: (i) the transition from reduced to oxidized conditions reflected in 

an increase in Eh (e.g., see bright green, vertically oriented dashed lines in Figure 3-5 and time

of transition from Reduced Region II to Oxidized Region II in Table 3-2) and (ii) the transition 

from a relatively high to a relatively low pH (see red, vertically oriented dashed lines in Figure 3-

5 and time of transition from Oxidized Region II to Oxidized Region III in Table 3-2) as the 

cementitious materials continue to degrade over time. In its TERs (ML112371751,

ML14094A496), NRC staff discussed concerns with the geochemical modeling results, which 

may be attributable to assumptions such as (i) the characteristics of the infiltrating groundwater, 

including the chemistry of the saturated groundwater assumed to impact the chemistry in the 

contaminated zone for submerged, Type I tanks at HTF; (ii) the solid phases that comprise the

tank grout; (iii) uncertainties in the thermodynamic data used in the modeling; or 

(iv) assumptions regarding the ability of grout components to react with and condition infiltrating 

groundwater and the residual waste. 

As part of this MF, NRC staff also will evaluate the efficacy of DOE’s use of two chemical 

transitions, three chemical states, and no more than three solubilities for each key radionuclide

with solubility changes assumed in DOE’s PAs to occur at the same time for each key 

radionuclide for a given tank type. It may be more reasonable to assume that solubility of each 

key radionuclide has a unique sensitivity to Eh and pH, making it difficult to make 

generalizations about the manner in which solubility changes over time. This assumption is 

important because the timing of transition to higher solubility and releases, if they occur, may be

critical to DOE’s compliance demonstration, as indicated previously. The adequacy of DOE’s 

approach to modeling solubility changes will be evaluated through NRC review of the literature, 

DOE-generated geochemical modeling, or independent geochemical modeling.

NRC staff also may observe DOE experiments related to this MF in conjunction with an onsite

observation at the FTF or HTF. This MF can be closed when (i) DOE shows that chemical 

transition times are no longer important to its compliance demonstration (i.e., predicted dose is 

less than the dose standards for all time) or (ii) DOE provides adequate experimental support 

for its assumptions regarding chemical transition times.

Closure of the Group of Monitoring Factors Related to MA 2, “Waste Release”

The MF regarding chemical transition times can be closed when DOE completes experiments to 

study the evolution of pH and Eh in the tank grout over time to provide additional support for its

estimates of chemical transition times to higher solubility chemical conditions. Alternatively, this

MF can be closed if DOE can provide (i) support that the highest solubility for each key 

radionuclide developed under MF 2.1, under any relevant geochemical condition, will not lead to

an exceedance of the 10 CFR 61.41 and 10 CFR 61.42 PO (i.e., DOE does not rely on timing of 

the peak dose to demonstrate compliance) or (ii) adequate support for other barriers relied on to 

delay the timing or reduce the magnitude of peak dose for key radionuclides is generated to 

demonstrate compliance.

Depending on the results of initial waste release experiments and other factors (e.g., continued 

confirmation of the relatively low risk significance of final estimated inventories for Tc-99), the 
3-21

factors in this MA can be closed in the short term following waste release experiments. 

Likewise, if closed, NRC could reopen the MFs in this MA as additional information is obtained 

on expected final tank inventories or the performance of other important barriers.

MA 3, “Cementitious Material Performance”

Importance of MA 3, “Cementitious Material Performance”

As illustrated in Figure 3-5 (see dark green barrier) and steel liner failure times listed in 

Table 3-3 for FTF and HTF tanks, the steel liners (or tanks) often serve as an important barrier 

significantly delaying the timing of releases from tank farm tanks for thousands to tens of

thousands of years. In the case of Types I, II and III/IIIA tanks with initially intact liners,19 DOE 

assumes the tanks do not fail until after the 10,000-year compliance period in the reference 

case. The longevity of the steel liners is directly related to PA assumptions regarding the 

capability of the concrete vaults, which house the steel liners, to provide an effective barrier to 

fluid flow, thereby minimizing the transport of corrosive agents such as chloride, oxygen, and 

carbon dioxide through the concrete or to the surface of the steel liners. Additionally, NRC staff 

considers assumptions regarding the hydraulic performance of the concrete vaults with respect 

to their ability to mitigate groundwater inleakage an important component of DOE’s compliance 

demonstration. Type IV tanks at FTF are particularly susceptible to early corrosion due to the 

fact that the tanks (i) have a thin layer of concrete applied using a technique known as 

Shotcrete, (ii) do not have an annulus between the Shotcrete and liner, (iii) do not have a tank 

top, (iv) have bottoms located in close proximity to the water table, (v) have experienced 

groundwater in-leakage in the past, and (vi) have the thinnest steel liners. Although Type IV 

tanks at HTF are not located in the zone of water table fluctuation, these tanks are also 

expected to be susceptible to corrosion for the reasons stated previously.

Table 3-3. Summary of Steel Liner Failure Times in the HTF and FTF PAs

HTF

(Years)

FTF

(Years)

Type I 11,397* 12,747

Type II 12,687† N/A

Type III/IIIA 12,751 12,751

Type IV 3,638 3,638

*Tank 12H is initially failed in HTF PA

†Tanks 14H, 15H, and 16H are initially failed in HTF PA

HTF = H-Area Tank Farm, FTF = F-Area Tank Farm, PAs = Performance Assessments 

While all Types I and II tanks at HTF are assumed to contain an inventory in the annulus of the 

tank vaults due to leakage from the primary liner, Tanks 9H, 10H, 14H, and 16H are assumed to 

have a more risk-significant inventory in the annulus (12.5 m3 of residual waste compared to 

0.4 m3 of waste in other Types I and II tanks). The waste in Type I and II tanks at HTF is 

assumed to be located in the annulus grout in Type I tanks that do not have sand pads, and in 

 

19DOE assumes Type I Tank 12H and Type II Tanks 14H, 15H, and 16H are initially failed at HTF.
3-22

the sand pads of Type II tanks. As discussed in the HTF TER, DOE may not have adequately 

assessed the risk of release of the annular inventory in Types I and II tanks at HTF through 

preferential pathways. DOE attempted to address NRC staff’s HTF TER comments related to 

annular waste release in the Tank 16H Special Analysis. NRC staff will evaluate DOE’s efforts 

to consider the risk of annular waste releases, including the presence of preferential pathways 

through the tank vaults, annulus, and sand pads. 

As discussed in MA 2, “Waste Release,” in some cases, DOE relies on the timing of peak dose 

occurring after the 10,000-year compliance period to meet the 10 CFR 61.41 PO.

20 Therefore, 

barriers that delay the timing of peak dose may be important to DOE’s compliance 

demonstration for the FTF. In the HTF PA, DOE assumes Tc and Pu are never released at 

risk-significant solubilities in their reference case. However, in alternative cases, risk-significant 

releases of Tc and Pu at higher assumed solubilities have been shown to lead to exceedances

of the POs. The reducing tank grout and contaminated zone chemical barriers (represented by 

a single purple barrier in Figure 3-5 and the transition time listed in Table 3-2) are two of the 

most effective barriers in DOE’s FTF PA in delaying the timing of the peak dose. Chemical 

transition times are directly dependent on the nature of water flow through the grouted tanks 

and on the likelihood and frequency of tank flooding due to water table rise. For example, NRC 

staff has technical concerns related to the potential for (i) groundwater to bypass or have 

minimal contact with the reducing tank grout as a result of flow via preferential pathways such 

as cracks or shrinkage gaps and (ii) water table rise above the tank bottoms.

21 NRC staff is 

concerned because these scenarios could lead to a situation where relatively oxidized and 

acidic groundwater has minimal contact with the tank grout that DOE’s PA assumes will 

condition the groundwater to higher pH and lower Eh, thereby maintaining the low solubility of

key radionuclides in the contaminated zone. If the infiltrating groundwater is not well

conditioned, key radionuclides may have higher solubility and be released at significantly higher 

concentrations much earlier in time. In fact, the peer review group tasked by DOE to review 

DOE’s Pu solubility modeling indicated that flow through cracks in the grout should be expected 

(LA–UR–2012–00079). Therefore, NRC staff will monitor DOE’s PA assumptions related to the 

nature of water flow into the contaminated zone, including assumptions regarding the extent to 

which in-tank water is conditioned by the tank grout, the timing of chemical transitions, and the 

magnitude of key radionuclide releases and dose. 

Additionally, because preferential flow through the tank grout is a strong function of the extent to

which tank grout shrinks and cracks, NRC staff also will monitor DOE’s PA assumptions 

regarding shrinkage and cracking. Specifically, NRC staff will monitor DOE’s efforts to minimize 

tank grout shrinkage through additional shrinkage compensating admixtures. Shrinkage of 

grout away from tank walls and intratank components may lead to formation of preferential flow 

pathways. The Center for Nuclear Waste Regulatory Analyses (CNWRA®) staff, who have 

developed and tested physical analog models of NDAA-type grout monoliths, have observed 

 

20Type I tanks and Tank 18F are the sources of exceedance of the 10 CFR 61.41 standard in DOE’s FTF PA over 

longer periods of compliance (beyond 10,000 years). DOE thinks the Type I tank inventories of Tc-99 that led to the 

exceedance were overestimated in the FTF PA; based on the final inventories developed for Tanks 5F and 6F, this 

appears to be supported. Updated special analyses show the peak dose from Tank 18F may be above or below the 

0.25 mSv/yr [25 mrem/yr] dose standard, depending most significantly on assumed solubility of Pu-239. Additional 

information is needed to support the updated best-estimate solubility listed in DOE’s Tank 18F and 19F Special 

Analysis, as indicated in NRC staff’s waste release technical review report (ML12272A082). 21Water table rise is especially important for Type IV FTF tanks, which have bottoms located at or near the water 

table, and for FTF Type I tanks (SRNL–STI–2012–00079). At HTF, Type II tanks are partially submerged in the 

saturated zone and tank waste can be in the zone of water table fluctuation.
3-23

shrinkage between grout lifts and flow lobes22 with both horizontally and vertically oriented, 

imperfectly bonded seams that form at their interfaces when placing relatively viscous 

formulations that tend to form lobes (Figure 3-6), enhancing preferential flow through the grout

monolith. Although the CNWRA experiments may not be completely analogous to SRS tank 

conditions23 (e.g., differences in final formulations and difficulty in exactly replicating curing 

conditions), significant effort was made to mimic actual conditions. Important insights can be 

gained from these experiments that may be applicable to NDAA tank closure.

Because temperature rise and gradients that form due to grout curing can lead to thermal 

cracking, NRC staff will monitor DOE’s assessment and, as applicable, plans to reduce the 

potential for thermal cracking. NRC staff will also monitor other tank farm design features to 

minimize adverse conditions, such as Alkali-Silica Reaction (ASR) that results in dissolution of 

silica phases and cracking due to alkali-silicate gel formation and expansion. The risk of 

ASR-based dissolution and cracking increases in the presence of cement or externally

introduced alkalis, amorphous silica phases of certain concrete aggregates, and moisture. 

Although the final formulation has a relatively low cement content compared to other concretes 

used in construction applications, DOE’s final formulation uses an aggregate potentially 

susceptible to ASR. Current standards calling for short-term testing (16 day tests) may not be 

sufficiently robust to evaluate the potential for long-term degradation associated with ASR. 

Finally, NRC staff will monitor tank farm design features to minimize cracking of the tank grout 

due to differential settlement. Differential settlement may occur due to loading stresses 

imposed by the weight of the closure cap and may be enhanced by dissolution of calcareous 

zone materials at depth and subsequent collapse of overlying materials (see Chapter 6).

Because the DOE PAs made a number of assumptions regarding the chemical and hydraulic 

properties of the as-emplaced grout used to fill the tanks and vault annuli, NRC will monitor 

DOE’s efforts to develop and test grout formulations that will meet PA requirements. 

Additionally, NRC staff will monitor DOE’s efforts to deliver a high-quality grout from design to 

placement in the field that performs as well as DOE assumed in its PAs.

After releases occur through the steel liners, the tank basemats are estimated by DOE’s PAs to 

serve as an important barrier for many key radionuclides. In fact, in some cases, the tank

basemats can work alone to mitigate releases and compensate for other failures such as 

solubility control (i.e., barriers can act in isolation to mitigate releases from the tanks when all 

other engineered barriers have failed). For instance, the basemats may serve as the most 

effective barrier in the FTF PA after long periods of time when the closure cap, steel liner, and 

tank grout have all failed as hydraulic barriers and key radionuclide solubility limits are at their 

highest levels (Oxidized Region III). Likewise, HTF PA sensitivity cases suggest that the 

basemats provide significant retention of key radionuclides (e.g., Np) in cases with higher 

solubilities than assumed in the base case. However, anecdotal and other evidence discussed 

 

22A grout flow lobe is a fan-shaped mass of grout that forms on a slope by the changing direction of flow. 23DOE has raised concerns with differences in climate between San Antonio, Texas, and SRS. It is important to note 

that Dinwiddie, et al. (2012b) concluded that “the climate of San Antonio, Texas, is similar to that of the SRS, 

South Carolina, in terms of temperature and humidity, but has lower mean annual precipitation. Like the SRS, 

San Antonio is subject to extreme precipitation events associated with tropical storms and the remnants of 

hurricanes.” Dinwiddie, et al. (2012b) concluded that San Antonio, Texas, would serve as a good analog to SRS for 

engineered cover testing with respect to average climate conditions.
3-24

Panel A

Panel B

Figure 3-6. Tank Grout Features Important to Performance: 

Panel A Is a Close-In View of Grout Seams and Gaps (Dinwiddie, et. al., 2012a, Figure 3-

8) and Panel B Is an Example of Grout Lobes From FTF Tank 18F Grouting 

(Photo Taken During June 12, 2012, Onsite Observation)
3-25

previously suggests that preferential flow pathways may be present in the tank vaults and that 

these pathways may have a significant impact on contaminant flow and transport. 

For example, in 1960, waste that leaked from HTF Tank 16H is thought to have breached the 

concrete vault and entered the surrounding soil (DPSPU–77–11–17). Tank documentation 

suggests that groundwater has historically intruded into tank vaults (DPSPU–82–10–11,

SRR–ESH–2013–00078). Therefore, NRC staff is concerned that assumptions regarding the 

ability of the concrete vaults to reduce radionuclide releases from the tanks are overly optimistic. 

For these reasons, NRC staff will monitor assumed basemat performance for key radionuclides 

such as Pu and Np.

Finally, the vault, sand pads, and annular grout can be a significant barrier to waste release in 

tanks with waste located outside of primary containment. Although release of waste from the 

annuli of these tanks is not assumed to be solubility controlled, NRC staff noted potential issues 

with the modeling treatment of the waste located in the annulus of Types I and II tanks. NRC 

staff will monitor cementitious material sorption to verify that the assumed level of performance 

in the PAs will be achieved in the field following closure. 

NRC Monitoring Under MA 3, “Cementitious Material Performance”

As listed in Appendix A and documented in more detail in NRC’s TERs (ML112371751,

ML14094A496),

24 NRC staff will consider the following MFs related to cementitious material 

performance that are considered important to meeting the 10 CFR 61.41 PO:

• MF 3.1 “Hydraulic Performance of Concrete Vault and Annulus (As It Relates to Steel 

Liner Corrosion and Waste Release)”

• MF 3.2 “Groundwater Conditioning via Reducing Grout”

• MF 3.3 “Shrinkage and Cracking of Reducing Grout”

• MF 3.4 “Grout Performance”

• MF 3.5 “Vault and Annulus Sorption”

• MF 3.6 “Waste Stabilization (As It Impacts ALARA)”

More detailed discussion regarding NRC’s concerns related to some of the aforementioned MFs 

is available in Appendix D.

3.3.1 Monitoring Factor 3.1: Hydraulic Performance of Concrete Vault and 

Annulus (As It Relates to Steel Liner Corrosion and Waste Release)

DOE assumes the grouted25 concrete vaults that house the HLW tanks act as hydraulic barriers

to fluid flow and provide a relatively passive environment for the steel liners or tanks,

significantly limiting tank corrosion following closure. In some cases (for some Types I and II 

and for all Type III tanks26), DOE assumes steel liners are a barrier to fluid flow and prevent 

significant releases from the tanks for over 10,000 years. DOE also assumes the concrete 

 

24Monitoring factors related to cementitious material performance are described in NRC staff’s TERs (ML112371751,

ML14094A496) except for MF 3.3 related to tank grout design measures to minimize shrinkage and cracking. 

Mitigation of cracking is important to minimizing the occurrence of preferential flow pathways through the tank 

system, which is discussed in detail in NRC staff’s TERs. 25Type IV tanks have no annulus and, therefore, do not require grout outside of the primary liner. 26DOE assumes Type I Tank 12H, and Type II Tanks 14H, 15H, and 16H, are initially failed at HTF.
3-26

vaults will limit releases of radioactivity from the annuli of Types I and II HTF tanks with annular 

contamination. However, observations of cracking and groundwater in-leakage and previous 

release from Tank 16H27 into the environment suggest a limited ability of the vault concrete to 

either act as a fully effective and uniform barrier to the transport of species controlling steel 

corrosion over the vault’s lifetime or to mitigate the releases of radioactivity from the annulus. 

In its HTF TER (ML14094A496), NRC staff also questioned DOE’s assumption of low corrosion 

rates because the oxidation and reduction reactions that control corrosion could be 

macroscopically separated. Metal locations where oxygen reduction occurs can be physically 

separated from locations where iron is oxidized and dissolved if the two locations are electrically 

connected. In other words, limited supply and transport of oxygen to the liner surface may not 

necessarily limit corrosion rates.

Therefore, NRC staff will review reports, analog studies, and other information used to support 

DOE’s assumption regarding initial conditions and performance of the concrete vaults to protect 

the steel liner and limit releases of radioactivity from the annulus. For example, NRC staff will 

review annual tank inspection reports that provide information regarding trenching, scarifying, 

and cracking of the concrete vaults, as well as information about groundwater intrusion into the 

tank vaults. NRC staff will review reports related to previous events that led to potential 

releases or groundwater in-leakage through joints or cracks in the concrete vaults. Analog 

studies could include review and evaluation of information obtained from West Valley or other 

analog sites to better understand the potential for and rates of corrosion of HLW 

tanks/components, as well as mitigative design measures. As part of this MF, NRC staff also 

will consider the potential for earlier steel liner failure than assumed in DOE’s PA due to 

corrosion of steel components (e.g., rebar) in the concrete vaults that are close to the vault 

surface or that may be physically separated but electrically connected.

If DOE performs additional modeling or experiments to study the potential for transport of 

deleterious species into the tank vaults or the separation of iron dissolution and oxygen 

reduction and subsequent corrosion of steel liners or tanks, NRC staff will review the 

documentation or provide input on the design and results of the experiments. Experiments to 

study steel liner corrosion are expected to be relatively difficult to implement with unknown 

benefit compared to other experimental investigations recommended in NRC’s TERs and 

discussed in this monitoring plan. Therefore, NRC staff does not consider these experiments to 

be a high priority at this time. Until such time that DOE provides additional support for the 

estimated lifetimes of the steel liners, NRC staff (i) will assume steel liners will not be effective at 

mitigating releases for the long time periods DOE relies on the steel liners for performance in 

the tank farm PAs and (ii) will investigate the support for the performance of other barriers to 

ensure POs can be met until such support for steel liner performance is provided. Should 

results of other investigations indicate other barriers that DOE relies on in its reference (or best

estimate) PA cases are not expected to perform as well as assumed, additional thought can be 

given to methods that may be used to provide additional support for steel liner performance 

assumptions.

 

27See WSRC–TR–93–761, WSRC–STI–2009–00352, SRR–STI–2010–00283, DOE/SRS–WD–2013–001,

SRNS–STI–2008–00096, and SRR–CWDA–2010–00128 for groundwater in-leakage observations. See DP-1358 for 

waste release from Tank 16H annulus into the environment.
3-27

3.3.2 Monitoring Factor 3.2: Groundwater Conditioning via 

Reducing Grout

As stated previously, DOE assumes that groundwater infiltrating from above is able to flow 

through every pore space of the grout monolith, rather than coming into contact with a relatively 

small volume of potentially armored28 tank grout along crack or fracture faces. Reactions 

between the infiltrating groundwater and tank grout cause the pH to increase from 

approximately 5 to 12 and the Eh to decrease from as high as +500 mV to as low as −600 mV. 

Conditioning the groundwater contacting the waste to high pH and low Eh is important to 

maintaining low solubility, concentrations, and dose, because the chemistry of the groundwater 

dictates the solubility limits assigned to key radionuclides in the contaminated zone in DOE’s 

reference PA cases. If the infiltrating groundwater that has a drastically different chemistry than

DOE assumed in the PAs is able to contact the radioactivity in the contaminated zone, then 

concentrations leached from the tanks could be significantly higher than predicted much earlier 

in time.

For Type I tanks at HTF, which are fully submerged, DOE assumes that a fraction of the 

groundwater contacting the waste will be conditioned by the reducing grout, which can still 

provide a significant chemical barrier to release. Some FTF and HTF tank bottoms29 are 

located in the zone of water table fluctuation, and water table rise could result in unconditioned 

groundwater contacting the waste zone at the bottom of the tanks. The potential for 

groundwater to contact the residual waste in these tanks without contacting reducing grout calls 

into question whether groundwater contacting the waste will be conditioned by the reducing 

grout to a significant degree. 

Because groundwater table rise and preferential flow through the tank grout may lead to higher 

solubilities and releases from the tanks, NRC staff will monitor DOE experiments to study the 

potential for groundwater flow through cracks that may form in the tank grout (the potential for 

cracking is addressed in MF 3.3). If DOE cannot rule out bypass flow through the tank grout 

under MF 3.3 or water table rise above the bottom of FTF tanks under this MF, then it will be 

important for DOE to demonstrate the extent to which groundwater is conditioned when flow is 

primarily through preferential pathways through the tank grout. Although DOE assumes little to 

no conditioning in Configuration30 G, a tank grout bypass scenario evaluated for the FTF in 

response to NRC RAIs,

31 the dose prediction in Configuration G exceeded the 10 CFR 61.41 

PO within the 10,000-year compliance period. Although DOE assumes the likelihood of 

Configuration G is low, NRC staff thinks the likelihood of this scenario may be underestimated. 

Likewise, DOE’s sensitivity analyses of the impact of varying the grout transition time and the

number of pore volumes required for chemical transition indicate that the PO could be exceeded 

within 10,000 years if the water contacting the waste is not conditioned by the overlying grout 

 

28Armoring may occur through precipitation of calcium carbonate on fracture and crack faces through a concrete 

degradation process referred to as carbonation. Armoring may preclude interaction of infiltrating groundwater with 

tank grout components interior to fracture faces that serve to condition the groundwater and maintain low solubilities 

or concentrations of key radionuclides.

29Water table rise is especially important for Type IV FTF tanks, which have bottoms located at or near the water 

table and for FTF Type I tanks (SRNL–STI–2012–00079). Type II tank bottoms at HTF are also located within the 

zone of water table fluctuation (SRNL-STI-2010-00148). 30The term “configuration” is used in DOE’s PA to describe various scenarios that are generally run to evaluate 

differences in waste release model and parameter assumptions. 31Configuration G is evaluated in DOE RAI responses (SRR–CWDA–2009–00054) and discussed in more detail in 

NRC staff’s FTF TER (ML112371751).
3-28

(as in Case E of the HTF PA). Therefore, more credit for groundwater conditioning may be 

needed in alternative flow scenarios to demonstrate compliance with the PO.

NRC staff will monitor DOE experiments or perform its own independent experiments to better 

understand the nature of flow through the tank grout as it impacts the extent to which infiltrating 

groundwater interacts with and is conditioned by the tank grout (this factor is closely related to 

MF 2.2).32 If NRC staff concludes that bypass flow through preferential pathways in the tank 

grout is significant, DOE should implement an alternative conceptual model consistent with 

preferential flow through the tank grout to compute chemical transition times.

NRC staff also will review information regarding water table rise to evaluate the likelihood of this

alternative conceptual model for waste release. Based on the results of the water table rise

investigation, an alternative conceptual model may be proposed for a subset of tanks to assess 

the impact on the compliance demonstration. Specifically, NRC staff will review historical water 

table elevation data for wells to assess the likelihood of water table rise above the bottom of the 

tanks. NRC staff also will review design and construction of any DOE mitigation measures used 

to ensure that the water table remains below the bottom of the tanks. The water table is most 

likely to rise above FTF Type IV tank bottoms, followed by FTF Type I tank bottoms because of 

the lower elevations at which these tanks were constructed (SRNL–STI–2012–00079). Type II 

tank bottoms at HTF are also located within the zone of water table fluctuation (SRNL-STI-2010-

00148).

In the case where flow is primarily through preferential pathways, such as shrinkage gaps and 

cracks, DOE should design experiments to provide information on the expected level of 

groundwater conditioning for this type of flow. DOE has designed and constructed a lysimeter 

field experiment at the SRS to study the mobility of various radionuclides in a saltstone waste 

form. This experiment could be leveraged to study the potential for groundwater conditioning for 

what is expected to be a relatively impermeable cementitious waste form. If infiltrating 

groundwater is not conditioned, DOE could design and construct column experiments with 

cracked tank grout to study the extent to which groundwater may be conditioned by the tank 

grout under what is currently considered a more realistic scenario by NRC staff. 

Under contract with the NRC, CNWRA is conducting experiments to study the extent of 

groundwater conditioning when flow is primarily through preferential pathways or through a 

cracked grout specimen. The objectives of these experiments are to understand the extent to 

which infiltrating water chemistry (primarily pH and Eh) is modified by contact with the tank grout

and how the tank grout buffering capacities for pH and Eh may change with contact to infiltrating 

water. Documentation of results of these experiments are expected in CY2015.

NRC will also review documentation provided by DOE to support assumptions regarding the 

extent of groundwater conditioning for as-emplaced tank grout. NRC staff may conduct the

technical review activities in conjunction with an onsite observation to observe any laboratory or 

field experiments in this area. If results of waste release experiments conducted under MF 2.1 

show key radionuclides in waste residuals have sufficiently low solubility when in contact with 

unconditioned SRS groundwaters, MF 3.2 related to the extent of conditioning (and 2.2 related 

 

32The difference between MF 2.2 and MF 3.2 is that MF 2.2 focuses on the actual geochemical reactions that are 

occurring between groundwater and tank grout components that determine how the chemistry of the groundwater 

changes over time, whereas MF 3.2 assesses the nature of flow through the tank grout. In other words, MF 2.2 is 

focused on the chemical aspects of how groundwater and tank grout components interact, while MF 3.2 is focused on 

the extent to which groundwater physically interacts with (i.e., flows through) the tank grout.
3-29

to the longevity of conditioning) will no longer be needed by DOE to support the compliance 

demonstration and can be closed. If MF 2.1 results indicate unconditioned flow may lead to 

unacceptably high doses, then this MF will need to be evaluated by NRC and can be closed 

after DOE (i) shows matrix flow through the grout will dominate waste release or (ii) provides

information to support assumptions regarding the level of groundwater conditioning for 

degraded (cracked) grout.

3.3.3 Monitoring Factor 3.3: Shrinkage and Cracking of Reducing Grout

As discussed, there are many mechanisms that could lead to cracking or creation of void space 

in the tank and vault grout, which increases the likelihood of early, risk-significant releases and 

doses from the tanks or annuli,

33 including the following:

• Steel component corrosion

• Shrinkage gap development and poor grout-bond quality

• Thermal cracking

• ASR

• Differential settlement and related cracking

DOE should consider design measures to minimize the occurrence of negative features, events, 

or processes that may promote shrinkage or cracking. For example, DOE should consider 

removal of in-tank equipment that could lead to development of shrinkage-induced annuli 

around equipment or corrosion of steel components and associated cracking due to corrosion 

product expansion. DOE also should promote the ability of the grout to fill all void spaces 

(e.g., grout should be self-leveling) to minimize imperfectly bonded grout seams and voids that 

may form in between grout pours. DOE should research and evaluate shrinkage compensating 

agents for use in its grout formulations to minimize shrinkage, shrinkage gap formation, and 

creation of annuli and void space within the grout. DOE should ensure temperature gradients 

are sufficiently low to prevent excessive thermal cracking. Calculations could be conducted to 

evaluate potential thermal gradients and/or instrumentation could be used to evaluate 

as-emplaced thermal evolution of the grout. Finally, DOE should ensure the grout is designed 

to consider the potential for cracking due to differential settlement (see Chapter 6 on site

stability for more detailed discussion). It may also be useful for DOE to research and deploy 

methods of detecting early crack development in reducing grout used to fill tanks and vaults 

(e.g., through use of devices such as acoustic sensors). For instance, under contract with the 

NRC, CNWRA is conducting an acoustic emission feasibility study on small scale tank grout 

samples to develop an approach to passively monitor larger scale monoliths for cracking events 

during the curing process. The primary objective of this study is to develop an acoustic 

emissions monitoring technique to locate and timestamp cracking events within a curing grout 

monolith using commercially available acoustic emissions equipment. Results of this feasibility 

study are expected to be documented in CY2015.

NRC staff will review grout formulations, calculations, research, test methods, and results to 

ensure the disposal facility is designed to minimize fast flow path development. NRC staff may 

conduct technical reviews in conjunction with onsite observations that could include such 

 

33Types I and II tanks at HTF contain residual waste in the annulus between the primary and secondary tank liners. 
3-30

activities as video inspections of grout pours, observations of grout tests, and inspection of test

specimens.

It is important to note the intended low matrix hydraulic conductivity of the grout monolith may 

accentuate fast crack or bypass flow through the system because the grout matrix is expected 

to be quite impermeable to water flow,

34 particularly for Type IV tanks that do not have cooling 

coils and are assumed, therefore, to degrade more slowly than grout in tanks containing internal 

fixtures. If it becomes clear that (i) it will be difficult to prevent preferential pathways from 

forming in the system, (ii) these preferential pathways may conduct a significant amount of 

unconditioned water; and (iii) unconditioned releases may exceed the dose standard, then it 

might be useful for DOE to explore methods under MF 3.2 to enhance contact of infiltrating 

water with the tank grout if such contact is shown to condition infiltrating groundwater and limit 

releases from the tanks and vaults to non-risk-significant levels. 

MF 3.3 can be closed when DOE demonstrates (i) preferential fast flow into the waste zone of 

the tanks or through the waste in the annuli for Types I and II tanks at HTF will not occur or

(ii) preferential fast flow into the waste zone of the tanks or through the annuli for Types I and II 

tanks at HTF will not adversely impact performance (e.g., the PO can be met under all chemical 

conditions as discussed in more detail under MA 2, “Waste Release”).

3.3.4 Monitoring Factor 3.4: Grout Performance

NRC will perform technical review activities related to DOE’s testing and development of grout 

formulations to meet design specifications. Additionally, NRC will monitor DOE’s efforts to 

deliver a grout mix of sufficient quality to meet performance assumptions in DOE’s PAs from 

design to as-emplaced conditions in the field. NRC staff will review relevant procedures and 

documentation related to such items as grout material procurement, production, testing, 

acceptance, and placement in tank farm components. NRC staff will perform technical review 

activities in conjunction with onsite observations. Onsite observations will include such activities 

as observations of grout material storage, tests, and acceptance of grout materials; live video 

streams of grouting operations; review of archived video footage; review of batch tickets for 

accepted and rejected loads; tour of the command center; and observation of mock-up tests or 

visual examination of test specimens. NRC staff can close this MF after it completes (i) review 

of DOE-generated grouting documentation and (ii) monitoring of grouting operations. If NRC 

identifies any issues, DOE must also adequately address the issues or provide plans to address 

the issues under another MF.

3.3.5 Monitoring Factor 3.5: Vault and Annulus Sorption

The concrete vaults and annulus grout are the last engineered defense against releases from 

SRS tanks and the annuli of tanks with a significant annular inventory (e.g., Types I and II tanks 

at HTF). In particular, the concrete basemats can be the most effective barrier, limiting peak 

releases and doses in DOE’s reference PA cases for some key radionuclides such as Np and 

Pu. Attenuation in the vault and annular grout may also be significant for some short-lived 

radionuclides such as Strontium (Sr) and Cesium (Cs) that are present in risk-significant 

 

34The lower the hydraulic conductivity of the matrix, the more likely water will flow through cracks. A low permeability 

matrix may not be sufficiently conductive to transmit all of the incoming moisture. If the matrix cannot accommodate 

all of the moisture, then locally saturated conditions will exist and fracture flow is more likely to occur.
3-31

quantities in the annuli of the Types I and II tanks at HTF. Because the basemats are, in most 

cases, more than 50 years old and have supported the weight of the waste-filled HLW tanks for 

many years, the basemats may be chemically degraded and cracked. Additionally, tank vaults 

may contain features conducive to bypass flow (e.g., leak detection channels or construction 

joints). Because attenuation of Np and Pu in the basemat can be very important to the 

compliance demonstration and may be less than assumed in DOE’s PAs in the case of flow 

through cracks or other preferential pathways or if sorption potential for these two constituents is 

overestimated, NRC staff will monitor DOE efforts to study basemat sorption for these two 

constituents. DOE should evaluate whether experiments used to develop basemat distribution 

coefficients (Kds) for Pu and Np represented solubility rather than sorption and otherwise 

provide defensible basemat Kds for key radionuclides that rely heavily on basemat sorption 

performance. DOE should also address the potential for degradation of the attenuating 

properties of the basemats over time (i.e., old, cracked concrete materials may be less sorptive 

than newer, uncracked concrete materials). NRC staff will review documentation and any 

analog studies that may provide additional information regarding the ability of the concrete 

basemats to attenuate release from the tanks or annuli of Types I and II tanks at HTF, including 

information regarding groundwater in-leakage and release from construction joints or other 

discrete features such as those implicated in the release from HTF Tank 16H. 

This MF can be closed when (i) sufficient information is available to support assumptions 

regarding attenuation of key radionuclides (e.g., Pu, Np, Cs, Sr) in the basemats, vaults, or 

annular grout or (ii) DOE provides sufficient information to show that doses from key 

radionuclides will be below the dose limits prescribed in the POs with little to no performance 

from the concrete basemats and vaults and annular grout (e.g., solubility limits for unconditioned 

groundwater are sufficiently low or natural attenuation of key radionuclides is sufficiently high to 

compensate for underperformance of the concrete basemat and vaults and annular grout).

3.3.6 Monitoring Factor 3.6: Waste Stabilization (As It Impacts ALARA)

DOE considers tank and vault grouting consistent with ALARA criteria. In its final Waste 

Determinations (WD) (DOE/SRS–WD–2012–001 and DOE/SRS–WD–2014–001), DOE 

explains that residual material remaining in the waste tanks after key radionuclides have been 

removed to the maximum extent practical will be stabilized with reducing grout, a chemically 

reducing environment known to minimize the mobility of the contaminants after closure. DOE 

indicates that waste tank grout fill is designed to have a low matrix permeability to enhance its 

ability to limit the migration of contaminants after closure. DOE also indicates that waste tank 

concrete vaults serve to significantly retard water flow through the waste tanks. In addition, 

DOE will fill the waste tank liners and annular space between liner and vault, if applicable, with 

cementitious material to further limit the amount of water infiltration into the waste tanks. 

Consistent with WIR guidance in NUREG–1854 (ML072360184), NRC staff will review use of 

stabilizing materials to determine whether DOE has made a reasonable effort to optimize mixing 

or encapsulating the waste with the stabilizing material. DOE should evaluate options to move

or stabilize the waste present along the edge of the tanks that may present a relatively higher 

risk, including options to minimize shrinkage along the tank wall, if deemed ALARA. NRC staff 

will evaluate DOE’s use of stabilizing materials to grout features of the tank and vault system 

that might otherwise lead to preferential flow through the engineered system and into the 

environment (e.g., grouting of leak detection channels and sumps contained within the concrete

basemats). 
3-32

NRC staff will conduct technical reviews and onsite observations under MFs 3.1 to 3.5, bearing 

in mind the additional function of the stabilizing grout to maintain doses ALARA. NRC staff can

close MF 3.6 when MFs 3.1 through 3.5 are closed, and if NRC staff finds DOE’s use of 

stabilizing cementitious materials consistent with ALARA criteria.

Closure of the Group of Monitoring Factors Related to MA 3, “Cementitious 

Material Performance”

MF 3.1 is contingent on the results of other studies. MFs 3.2 and 3.3 can be closed after DOE 

demonstrates that preferential pathways will not occur or will not significantly alter the 

compliance demonstration. MF 3.4 can be closed following grouting of the tanks. MF 3.5 can 

be closed when DOE demonstrates that vault materials can effectively immobilize key 

radionuclides such as Np and Pu that are released from the tanks or annuli, that solubility 

control is effective at reducing key radionuclide releases to non-risk-significant levels, or that 

natural system attenuation is sufficient to compensate for underperformance of the vault 

materials. MF 3.6 will be closed when MFs 3.1 through 3.5 are closed, if NRC staff finds 

stabilization operations consistent with ALARA criteria.

MA 4, “Natural System Performance”

Importance of MA 4, “Natural System Performance”

The hydrogeological system at the tank farms performs as a significant natural barrier, helping 

to attenuate key radionuclide releases from tanks to groundwater through such processes as 

dilution, dispersion, sorption,

35 and decay.36 Natural attenuation can serve to (i) delay the timing

of the peak dose and (ii) reduce concentrations and dose at the POC. Therefore, NRC staff will 

monitor natural system performance to assess compliance with the 10 CFR 61.41 PO.

NRC staff made two primary recommendations related to natural system performance in its FTF 

TER (ML112371751): (i) DOE should obtain support for averaging Kds of multiple oxidation

states to simulate the transport of Pu in the natural environment and (ii) DOE should provide 

additional data from tracer tests and calcareous zone outcrop locations to allow NRC and DOE 

to evaluate the significance of calcareous zone dissolution on flow and transport from the FTF. 

As shown in Figures 3-4 and 3-5 and Table 3-1, DOE assumes a significant amount of 

performance is achieved for sorption of Pu in the natural system: (i) an approximately 

10,000-year delay in the timing of the peak dose due to travel times in the vadose and saturated 

zones (Figure 3-5) and (ii) a reduction in the peak dose from Pu due to sorption in the natural 

system by approximately a factor of 10 (Table 3-1). The risk significance of the Pu Kds is 

evident. Regarding characterization of the calcareous “soft zones” that are located in the lower 

portion of the Upper Three Runs Aquifer (UTRA), NRC staff is concerned these zones could act 

as conduits for fast groundwater flow, decreasing travel times and potentially minimizing dilution 

and natural attenuation in the aquifer. Site-specific sorption coefficients for the calcareous 

zones have not been developed, and it is not clear the extent to which key radionuclide mobility 

will be affected by the presence of these zones. Faster travel times could lead to less decay,

 

35Sorption is used in a broad sense to describe the association of a groundwater contaminant with subsurface 

materials that can lead to (i) longer travel times or (ii) decreased concentration at the point of compliance. 36Decay can be significant when travel times to a well are expected to be similar to the half-life of key radionuclides 

[e.g., for key radionuclides such as Pu-239, Sr-90, and Cs-137 in DOE’s reference (or best estimate) PA case].
3-33

higher concentrations, and earlier peak doses; less dilution and natural attenuation also could 

lead to higher predicted concentrations and doses at the POC.

In the HTF TER (ML14094A496), NRC staff continued to express the same concerns expressed 

in the FTF TER with respect to the Pu Kd averaging approach as well as concerns with 

assumptions regarding the impact of calcareous zones on flow and transport from HTF tanks. 

NRC staff also listed several concerns with calibration of DOE’s HTF local groundwater model in

the HTF TER. However, the technical issues associated with DOE’s far-field model calibration 

are not expected to be addressed in the near-term but will be monitored by NRC staff under 

longer term performance assessment maintenance activities (MA 6, “Performance Assessment

Maintenance”).

During its review of the Tanks 5F and 6F Special Analysis (SRR–CWDA–2012–00106), NRC 

staff noted that additional information related to the Niobium (Nb) distribution coefficient, or Kd, 

is needed to have reasonable assurance that DOE disposal actions at the FTF will meet the 

POs in 10 CFR Part 61, Subpart C. Therefore, MF 4.1 is being broadened to address key 

radionuclide natural attenuation (only Pu natural attenuation is addressed in the FTF Monitoring

Plan).

NRC Monitoring Under MA 4, “Natural System Performance”

As listed in Appendix A and documented in more detail in its TERs (ML112371751,

ML14094A496),

37 NRC staff will consider the following MFs related to natural system 

performance that it considers important to meeting the 10 CFR 61.41 PO: 

• MF 4.1 “Natural Attenuation of Key Radionuclides”

• MF 4.2 “Characterization of Calcareous Zones”

• MF 4.3 “Environmental Monitoring”

3.4.1 Monitoring Factor 4.1: Natural Attenuation of Key Radionuclides

This monitoring factor is focused on the models and parameters used to simulate natural 

attenuation in the subsurface. In the FTF Rev. 0 Monitoring Plan (ML12212A192), this 

monitoring factor was titled, “Natural Attenuation of Plutonium.” The monitoring factor was 

originally focused on the Kd averaging approach employed by DOE to simulate Pu transport in 

the subsurface given the risk significance of Pu-239 in Tank 18F at the time of preparation of 

the monitoring plan. The Kd averaging approach used by DOE in the FTF Performance 

Assessment (SRS–REG–2007–00002) was retained in the HTF performance assessment 

(SRR–CWDA–2010–00128) and is still a technical issue; however, Monitoring Factor 4.1 is 

broadened to include other model and parameter issues related to natural attenuation of key 

radionuclides at the tank farms.

Depending on the Kd of Pu assumed in the natural environment, travel times from Tank 18F to

the 1-m or 100-m points of compliance used in the intruder and member of the public dose 

assessments, respectively, could range from hundreds to tens of thousands of years. This 

issue is also a concern for other tanks with a significant inventory of Pu. NRC staff concludes

 

37MF 4.3 related to environmental monitoring is not discussed in NRC staff’s TERs. Nonetheless, NRC staff will 

review environmental monitoring data to ensure the disposal facility is performing as assumed in DOE’s PAs.
3-34

that DOE has not addressed issues associated with its Kd averaging approach.

38 Site-specific 

studies indicate a range of Kd anywhere from a few (three) L/kg to thousands (1,000s) L/kg for 

different oxidation states of Pu, with higher oxidation states of Pu tending to be more mobile. If 

arguments based on travel times are relied on to demonstrate compliance with the POs, then 

DOE should demonstrate that more mobile forms of Pu that can be transported to the 1- or 100-

m [3-ft or 330-ft]-points of compliance in hundreds of years cannot exist in risk-significant 

quantities in the subsurface at SRS. If arguments based on magnitude of peak dose are relied 

on to demonstrate compliance with the POs, then DOE should show that consideration of a

combination of barriers leads to a dose below the POs and that adequate support exists for the 

assumed level of barrier performance.

Appendix E discusses technical issues with DOE’s assumed plutonium Kd for sandy sediment. 

The sandy sediment Kd for plutonium of 650 mL/g is derived from SRNL–STI–2011–00672. 

This study bases the recommended value on (i) information from a modeling analysis 

(Demirkanli, et al., 2007) of long-term lysimeter studies (Kaplan, et al., 2006) indicating that the 

Kd should be 1,800 mL/g and (ii) the site-wide statistical analysis showing that the 290 mL/g 

value used for the FTF PA is in the lower quantiles. The sediment in the lysimeter appears to 

have had more clay in it than typically found at the FTF location; therefore, the 1,800 mL/g value 

was lowered to 650 mL/g. The NRC staff does not find the argument for the 650 mL/g to be well 

supported. Furthermore, as expressed in the HTF TER (ML14094A496), NRC staff has 

technical issues associated with the cement leachate factors applied in the HTF PA

(SRR–CWDA–2010–00128, Table 4.2-25) based on information provided in 

SRNL–STI–2009–00473. NRC will monitor DOE’s efforts to develop site-specific sorption 

coefficients that consider the impact of cement-impacted leachate released from the tanks.

In a technical review report related to FTF monitoring (ML13273A299), NRC staff included a 

follow-up action for DOE to provide additional support for the revised Nb distribution coefficient it 

selected in the Tanks 5F and 6F special analysis. A low value distribution coefficient of 0 L/kg 

was selected in the FTF Rev. 1 PA (SRS–REG–2007–00002) because no additional credit was 

needed for Nb sorption at the time. However, after DOE updated its inventories and risk 

projections in the Tanks 5F and 6F Special Analysis (SRR–CWDA–2012–00106), DOE revised 

the distribution coefficient (Kd) for Niobium (Nb) from 0 L/kg to 160 L/kg. This adjustment was 

needed because the final Zirconium (Zr)-93 inventory estimated from characterization and 

sampling of Tanks 5F and 6F at the time of closure was a factor of 10,000 times higher than 

estimated in the FTF Rev. 1 Performance Assessment, increasing the risk significance of 

Zr-93’s daughter product, Nb-93m. NRC staff will review any DOE-generated reports or other 

documentation that provides additional information related to site-specific Nb distribution 

coefficient values.

Technical review activities may be conducted in conjunction with onsite observations of any

experiments developed to study the attenuation of Pu, Nb, and other key radionuclides in SRS 

soils. This MF can be closed when DOE provides support for its treatment of Pu, Nb, and other 

key radionuclide sorption in the subsurface at FTF or DOE shows that Pu, Nb, and other key 

radionuclide sorption in the subsurface is not needed to support its compliance demonstration 

 

38In lieu of modeling different oxidation states of Pu that may be present in the natural system, DOE averages the Kds 

of multiple oxidation states together in assigning a Kd for Pu.
3-35

(e.g., solubility control effectively limits Pu releases into the natural environment to non-risksignificant levels).

3.4.2 Monitoring Factor 4.2: Calcareous Zone Characterization

Another source of uncertainty in DOE’s far-field model is the treatment of the calcareous “soft 

zones,” located in the lower portion of the UTRA. Calcareous zone studies have focused on

facility or site stability. NRC staff observed that DOE studies appear to give less attention to the 

hydrogeologic properties of these zones that may impact contaminant flow and transport from 

the tank farms. DOE argues that monitoring data have not revealed any noticeable impacts on 

hydraulic heads or contaminant transport to date, but no tracer testing has been performed to 

improve understanding of transport within the pseudo-karst-like soft zones, nor has downhole 

imaging of water velocities been performed at known soft zone locations. Additional information 

was provided in the HTF PA regarding the occurrence and impact of soft zones on site stability 

and contaminant flow and transport (SRR–CWDA–2010–00128), including a new reference: “A 

Review of Subsurface Soft Zones at Savannah River Site with Emphasis on H Area Tank Farm 

(U)” (SRNL–TR–2012–00160). NRC staff reviewed the new reference but still concludes that 

additional information is needed to assess the impact of calcareous zones on contaminant fate 

and transport.

DOE could monitor flow velocities at screen levels both consistent and inconsistent with known 

existing soft zones to assess local fast flow path gradients of soft zones to provide additional 

confidence that current PA groundwater modeling treatment is acceptable. To date, mapping of 

surface water seeps from the UTRA-Lower Zone rocks along Upper Three Runs Creek and 

Four Mile Branch has not focused on surface seeps or other features associated with these 

zones, but DOE has suggested it is willing to perform both tracer testing and outcrop mapping of

seeps.

NRC staff should observe field tests and review and evaluate results of tracer tests and field 

mapping DOE may conduct to ascertain the significance of existing calcareous soft zones on 

flow and transport from the tank farms. NRC staff will review relevant geotechnical logs 

acquired in the vicinity of tank farms to stay informed of the potential for and characteristics of 

soft zones that may be identified in the future. Finally, if DOE opts to employ downhole 

visualization or other methods to monitor local groundwater velocities associated with soft 

zones, NRC staff will review and evaluate DOE’s analysis of these data. NRC may conduct 

technical review activities in conjunction with onsite observations of field activities, such as 

calcareous zone outcrop mapping on Upper Three Runs Creek. This MF can be closed when 

DOE has provided NRC sufficient information to show its treatment of calcareous zones in the 

tank farm PAs is reasonable or adequate to assess risk. If NRC concludes that DOE’s 

treatment of calcareous zones in the tank farm PAs is not reasonable or appropriate, DOE 

should evaluate the risk significance of a more adequate representation.

3.4.3 Monitoring Factor 4.3: Environmental Monitoring

NRC staff will review any data collected by DOE for the tank farms for the purpose of evaluating 

disposal facility performance. While early releases from the disposal facility are not expected, 

groundwater monitoring can serve as a valuable tool for early detection of potential issues with 

the disposal facility design to allow sufficient time to institute mitigative measures. Additionally, 

groundwater monitoring data can provide useful validation data from which to assess the 

adequacy of DOE PA models in evaluating risk from the tank farm disposal facilities. For these 
3-36

reasons, NRC staff will review and evaluate groundwater monitoring data as a technical review 

activity under this MF. 

The FTF Farm Groundwater Sampling and Analysis Plan (SRNS–RP–2012–00287) and the 

HTF Groundwater Monitoring Plan and Sampling and Analysis Plan (SRNS–RP–2012–00146) 

provide specific details of the groundwater monitoring programs. Monitoring well locations are 

provided in Figure 3-7(a) for FTF and Figure 3-7(b) for HTF. The groundwater monitoring plan 

for the FTF includes sampling twice per year at a network of 13 monitoring wells consisting of 6 

existing wells and 7 newer wells installed in 2012. The well network is located around the 

downgradient perimeter of the tank farm and includes wells screened in the Upper Aquifer Zone 

or UAZ) (7) and Lower Aquifer zone or LAZ (4) and two background wells (UAZ and LAZ). As 

required by the FTF Sampling Analysis Plan, FTF samples were analyzed for gross alpha, 

nonvolatile beta, tritium, nitrate-nitrite, cadmium, chromium, manganese, and sodium. In 

addition, Tc-99 was analyzed to provide information on existing Tc-99 activities. As provided in 

the FTF Sampling Analysis Plan, SRS will perform contingent analyses for specific 

radionuclides if screening results for gross alpha and nonvolatile beta exceed trigger levels of 

15 pCi/L and 50 pCi/L, respectively.

The groundwater monitoring plan for the HTF indicates that sampling will be conducted twice 

per year at a network of 46 monitoring wells consisting of 36 existing wells and 10 newer wells 

(HAA 17 through HAA 21) installed in 2012. The well network is located around the 

downgradient perimeter of the tank farm facility and consists of wells screened in the UAZ (17), 

LAZ (28), and Gordon Aquifer or GA (1), including three background wells. The wells are set in 

three aquifer zones. The “A” wells are set in the GA. The “B” and “C” wells are set in the LAZ, 

and the “D” wells are in the UAZ of the UTRA. The same constituents are analyzed at HTF as 

are analyzed at FTF, as well as tritium and Tc-99.

NRC staff reviewed DOE’s F-Tank Farm monitoring well network as part of a technical review 

activity (ML12272A124). In the technical review report, NRC staff indicated that it will continue 

to review the adequacy of the tank farm monitoring well network with respect to its ability to 

detect releases from the tank farms (see Appendices B and E for additional details).

Closure of the Group of Monitoring Factors Under MA 4, “Natural System

Performance”

NRC may conduct technical review activities for this monitoring activity in conjunction with 

onsite observations related to groundwater sampling, well construction, and other field activities. 

SCDHEC oversight may be leveraged in this area to ensure the quality of data collected. MA 4 

will be renamed “Environmental Monitoring” once MF 4.1 and 4.2 have been closed. MA 4 will 

remain open indefinitely.
3-37

(a)

(b)

Figure 3-7. Proposed FTF and HTF Groundwater Monitoring Locations 

(SRNS–RP–2014–00226)
3-38

MA 5, “Closure Cap Performance”

Importance of MA 5, “Closure Cap Performance”

Although DOE’s sensitivity and uncertainty analyses indicate the closure cap has minimal 

impact on peak dose and in most cases serves as a redundant barrier,

39 NRC staff concluded 

that in certain cases, the closure cap could be important to mitigating risk from the disposal 

facility and in maintaining doses ALARA. In fact, DOE’s barrier analysis shows that if other 

barriers do not perform as well as expected, the closure cap could become a more important 

barrier limiting release from the disposal facility. Over long periods of time, DOE also assumes 

that the closure cap limits infiltration rates to 30.5 cm/yr [12 in/yr], below the background 

infiltration rate of 38 cm/yr [15 in/yr]. Longer term lowering of the infiltration rate helps to

(i) decrease releases of key radionuclides from the disposal facility and (ii) prolong transition 

times to higher solubility of many key radionuclides. Based on the potential importance of the 

closure cap in meeting the POs in 10 CFR Part 61 and the fact that DOE is in the early stages 

of closure cap design, NRC staff will monitor progress on the design and construction of the 

closure cap, as well as development of support for the assumed level of performance of this 

engineered barrier. 

NRC Monitoring Under MA 5, “Closure Cap Performance”

As listed in Appendix A and documented in more detail in its TERs (ML112371751,

ML14094A496), NRC staff will consider the following MFs related to the closure cap that are 

considered important to meeting the 10 CFR 61.41 PO:

• MF 5.1 “Long-Term Hydraulic Performance of the Closure Cap”

• MF 5.2 “Long-Term Erosion Protection Design”

• MF 5.3 “Closure Cap Functions as They Pertain to ALARA”

3.5.1 Monitoring Factor 5.1: Long-Term Hydraulic Performance of the 

Closure Cap

In its TERs (ML112371751, ML14094A496), NRC staff discussed (i) the uncertainty in the 

processes being modeled for the closure caps and (ii) the limited support for several of the 

closure cap assumptions. DOE should provide additional support for the long-term hydraulic 

conductivity of the foundation layer, which acts to reduce the long-term infiltration to the disposal

facilities. DOE assumed the foundation layer would limit the infiltration rate to 30.5 cm/yr, 

slightly less than the estimated background infiltration rate of 38 cm/yr. NRC will monitor 

additional information to support the assumed long-term hydraulic conductivity of the foundation 

layer.

 

39NRC staff concluded that DOE’s reference (or best estimate) PA case shows the closure cap is a redundant 

hydraulic barrier because other, more robust hydraulic barriers, such as the steel liners and tank grout used to fill the 

cleaned tanks, are present and expected to outperform the closure cap for longer periods of time under most 

scenarios, including the reference case DOE used in its Tank Farm PAs. However, several points are important to 

Note: (i) several of the steel liners at the HTF are assumed to be initially failed, (ii) several of the tanks have 

contamination outside of the primary steel liners, and (iii) the closure cap is the only barrier assumed to provide 

long-term, infiltration-reducing capabilities, albeit at modest levels. Figure 3-5 shows barriers to timing of FTF

releases in DOE’s reference case.
3-39

In addition, NRC staff will monitor construction quality and settlement at the Tank Farms to help 

ensure assumed performance of the High Density Polyethylene/Geosynthetic Clay 

Liner (HDPE/GCL) composite layer is not adversely impacted. Although the HDPE/GCL 

composite layer does not significantly contribute to the long-term hydraulic performance of the 

closure cap, DOE assumes it is a significant barrier to infiltration for several hundred years after 

site closure. Because the performance of the HDPE/GCL layer is sensitive to construction 

quality and differential settlement, NRC will monitor the quality assurance/quality control for 

closure cap construction and settlement data collected during Tank Farm operations as well as 

at nearby facilities. NRC also will review relevant studies and tests related to HDPE/GCL 

performance. This MF can be closed after DOE’s construction of the closure caps and 

demonstration of its hydraulic performance.

3.5.2 Monitoring Factor 5.2: Long-Term Erosion Protection Design

As documented in its TERs (ML6112371751, ML14094A496), NRC staff recommended that 

DOE provide additional support for the long-term erosion of the topsoil layer and conduct a 

preliminary evaluation of erosion protection designs. Long-term maintenance of the topsoil and 

vegetative closure cap is important to closure cap performance because evapotranspiration 

dominates the modeled water balance distribution for SRS precipitation. DOE should evaluate 

potential loss of soil and development of gullies due to cumulative effects of soil loss from 

frequent rainfall events. Effects of high frequency and low intensity events can dominate 

long-term erosion processes. In addition, DOE did not evaluate the resistance of a degraded 

vegetation cover to gully erosion. A Bahia grass, bamboo, or pine forest vegetative cover could 

be degraded by fire or extended drought, thereby affecting the capability of the engineered 

cover to resist erosion. NRC staff will review and evaluate information pertaining to erosion

processes of the vegetative and topsoil layers, including cover maintenance activities.

DOE should conduct a preliminary evaluation of erosion protection designs (e.g., evaluation of 

an acceptable rock source, the ability of an integrated drainage system to accommodate design 

features) to verify assumptions related to closure cap performance can be met. The design of 

perimeter drainage structures that convey runoff and infiltration from the cover and divert runoff 

from surrounding areas will affect resistance of these structures to erosion that could also affect 

the stability of the cover side slopes and the cover itself. If the vertical hydraulic conductivity of 

the native soil, on which the perimeter drainage channel is constructed, is not sufficiently high to 

allow ponded water to infiltrate vertically, it could flow toward the tanks. The final design for the 

cover and associated drainage structures should consider their performance and degradation 

during the long, post-institutional control period. If DOE performs simulations of the influence of 

clogging and ponding in the perimeter drainage structures on flow in the vadose zone, NRC will 

review results of these simulations to evaluate risk significance of the uncertainties in the 

long-term performance of the perimeter drainage structure. This MF can be closed after DOE’s 

construction of the closure cap and demonstration of its physical stability.

3.5.3 Monitoring Factor 5.3: Closure Cap Functions That Maintain 

Doses ALARA

DOE lists the infiltration-reducing function of the closure cap as part of its ALARA demonstration 

under 10 CFR 61.41. In addition to reducing short-term, as well as long-term, infiltration rates, 

the closure cap serves many functions that are not specifically discussed in DOE’s Tank Farm

PAs. For example, the closure cap provides defense in depth to ensure relatively high specific 

activity radionuclides present in significant quantities, such as Sr-90 and Cs-137, are not 

released from FTF tanks and ancillary equipment before they decay to negligible levels. During 
3-40

the period of a few hundred years after closure, the closure caps may reasonably be assumed 

to be effective in minimizing infiltration through the disposal facilities. 

Although not specifically discussed in DOE’s PA, another important function of the closure cap 

is that it may limit infiltration and transport of deleterious species, such as carbon dioxide, 

oxygen, chloride, sulfate, and slightly acidic groundwater, into the engineered disposal system 

that could accelerate material degradation of cement vaults, as well as corrosion of the HLW 

tanks. Therefore, construction of a well-designed closure cap also may benefit the longevity of 

other engineered barriers at the Tank Farms.

Finally, the closure caps may have a minor but detectable impact on water table elevations local 

to Tank Farms. Barriers constructed to reduce the likelihood of periodic water table rise above 

the bottom of the tanks may be needed to support the compliance demonstration and may be 

considered ALARA. The alternative waste release configuration where the water table rises and 

falls above and below the tank bottoms is especially important for Type IV tanks at FTF and 

Type II tanks at HTF that are located at or in close proximity to the water table, based on 

historical water table data because the configuration could lead to accelerated corrosion and 

higher release rates of key radionuclides to the UTRA.

For these reasons and other closure cap functions listed in Chapter 4, related to the 

10 CFR 61.42 PO, NRC staff will monitor DOE’s disposal actions as they pertain to Tank Farm

closure cap design, construction, and maintenance consistent with ALARA criteria. 

Closure of the Group of Monitoring Factors Under MA 5, “Closure 

Cap Performance”

This MA will remain open throughout DOE’s development, construction, and completion of final 

closure caps, unless final design information indicates the MFs are not risk significant. When 

DOE develops final closure cap designs, NRC will revise the monitoring plan, as appropriate, to 

describe the monitoring activities relevant to the final designs. NRC staff will monitor DOE’s

development of specific designs for the closure caps and determine whether these designs are 

likely to significantly alter DOE and NRC conclusions regarding the conceptual design analyzed 

in the PA. Prior to any construction activities, NRC staff will review specifications for closure 

cap construction materials and quality assurance/quality control procedures for assuring these 

materials meet specifications. During construction, NRC staff should observe the placement of 

these materials and the quality control testing to assure the as-built closure cap will meet design 

specifications. NRC staff also will evaluate available data from similar covers built on the larger 

SRS site and other humid sites.

MA 6, “Performance Assessment Maintenance”

Importance of MA 6, “Performance Assessment Maintenance”

DOE Manual 435.1-1, Change 1, requires DOE PAs to be maintained to evaluate changes that 

could affect the performance, design, and operation bases for the facility. DOE Manual 435.11-

1 requires the maintenance to include research, field studies, and monitoring necessary to 

address uncertainties or gaps in existing data. DOE prepares an annual PA maintenance 

program implementation plan that summarizes activities related to the following areas for the 

tank farms: (i) annual maintenance program activities, (ii) PA development or revisions, and 

(iii) research and testing activities. The implementation plan for fiscal year 2015 is documented

in SRR–CWDA–2014–00108.
3-41

NRC used risk insights to prioritize the recommendations identified in its TERs (ML112371751, 

ML14094A496) and anticipates that DOE, as part of its PA maintenance program, might use a 

graded approach to focus on development of support for key modeling assumptions, such as 

those identified under other MAs (e.g., MA 2) to enhance confidence in the PAs. NRC will 

monitor DOE’s PA maintenance activities related to key modeling assumptions under other MAs 

identified in this monitoring plan. The insights generated from focusing on key modeling 

assumptions would then inform the need for further data collection, experimental studies, and 

modeling to address MFs identified under this MA.

NRC Monitoring Under MA 6, “Performance Assessment Maintenance”

Under this MA, NRC will monitor DOE activities associated with the PA maintenance program 

that are related to NRC recommendations to improve model support and parameter justification,

including representation of uncertainty in models and parameters. Appendix A provides a 

crosswalk of specific NRC recommendations identified in its TERs (ML112371751, 

ML14094A496) that fall under this MA. Specifically, NRC will consider the following MFs related 

to DOE’s PA maintenance activities for recommendations that NRC, based on the current 

understanding, identified as being of lower significance to demonstrating compliance with the 

POs or may require a longer time horizon to complete based on current information:

• MF 6.1 “Scenario Analysis”

• MF 6.2 “Model and Parameter Support”

• MF 6.3 “Tank Farm PA Revisions”

3.6.1 Monitoring Factor 6.1: Scenario Analysis

During the monitoring period, NRC staff will review PA revisions to evaluate adequacy of

scenarios considered. Specifically, NRC staff will review the DOE methodology for 

identification, screening, and dispositioning of features, events, and processes (FEPs) and the 

formation of scenarios considered in the PAs. NRC staff should verify FEPs identified by DOE,

including all FEPs having a potential to influence compliance with POs. NRC staff should 

examine the technical basis for screening FEPs from further consideration in the PA. NRC staff

also should examine DOE bases for the formation of scenarios considered in the PAs to

determine whether they include all FEPs that have not been screened from further

consideration.

Since NRC issued its FTF TER (ML112371751), DOE documented an evaluation of FEPs for

the SRS and crosswalked the FEPs to the FTF PA. NRC staff reviewed the FEPs analysis 

(SRR–CWDA–2012–00011) and documented the results of its review in a technical review 

report (ML13277A063). The NRC staff’s review of DOE’s identification of FEPs found that 

DOE’s identification is adequate. The NRC staff’s review of the DOE screening methodology 

finds that DOE properly focused on likelihood and impact as criteria for screening, but identifies 

several concerns with DOE’s screening of FEPs, including the membership of the FEPs 

screening team and the documentation of each subject matter expert’s basis for judgment. 

Finally, the NRC staff indicated that is it not confident that all relevant FEPs were adequately 

considered in the FTF PA due to lack of transparency and traceability in documentation, which

crosswalks FEPs with the FTF PA (SRR–CWDA–2012–00022). NRC indicated that the 

questions and issues raised in the technical review report could be addressed as part of DOE’s 

PA maintenance program or as part of special analyses for specific tank closures. In the HTF 

TER (ML14094A496), similar to the findings in the technical review report for FTF, NRC staff 

recommended that DOE include subject matter experts on the screening team in the specific 
3-42

engineering and scientific disciplines that are pertinent to the professional judgments being 

made. NRC staff also recommended that DOE improve the transparency and traceability of its 

implementation of FEPs (SRR–CWDA–2012–00044) to ensure comprehensive, accurate, and 

traceable links to clear descriptions of how included FEPs are actually implemented in the HTF 

PA. NRC will close this MF when DOE demonstrates that all risk-significant FEPs have been 

(or will be under another MF) adequately evaluated in PA documentation.

3.6.2 Monitoring Factor 6.2: Model and Parameter Support

As documented in NRC’s TERs (ML112371751, ML14094A496), NRC staff provided a number 

of recommendations regarding the technical bases for model selection and justification of 

parameter ranges and distributions. NRC staff will review DOE’s PA revisions to evaluate the 

selection of models and justification of parameters. Specifically, NRC staff will examine 

information DOE generates, including experimental and site characterization data and 

information from literature, to support model selection and justify parameters. NRC staff also 

will review DOE methods to characterize data and model uncertainty and propagate the 

uncertainty through the PAs. NRC staff will use a graded approach to focus on aspects of most 

importance to demonstrating compliance with the POs. This MF can be closed when DOE 

provides sufficient information to support risk-significant models and/or model parameters listed 

in Appendix A related to MF 6.2.

3.6.3 Monitoring Factor 6.3: Tank Farm PA Revisions

It is anticipated that DOE will update its current Tank Farm PAs (SRS–REG–2007–00002, 

SRR–CWDA–2010–00128) in the future, to incorporate new and significant information 

collected since preparation of the PAs. NRC staff will review the revised PAs and issue a TER 

documenting the results of its review. NRC anticipates results of the review, as documented in 

NRC’s TER, will be used by NRC to update this monitoring plan in the future. NRC staff will pay 

special attention to supporting documentation generated since the last PA revision, including 

results of experiments, analog studies, models, and peer reviews conducted to support the key 

MAs listed in this monitoring plan, as well as lower priority items listed under MA 6, “PA 

Maintenance.” Evaluation of revisions to the Tank Farm PAs is considered critical to NRC 

staff’s execution of its monitoring responsibilities to assess compliance of DOE disposal actions 

with the POs in 10 CFR Part 61, Subpart C. The Tank Farm PAs and special analyses provide 

the technical support for DOE’s demonstration of compliance with the POs in 10 CFR Part 61, 

Subpart C. 

Closure of the Group of Monitoring Factors Under MA 6-PA Maintenance

NRC staff expects the PA Maintenance MA will remain active until all technical issues have 

been resolved (or are deemed unnecessary to the compliance demonstration) and possibly for 

the entire duration over which DOE performs maintenance activities related to the Tank Farm 

PAs. Alternatively, NRC staff could close this group of MFs if it determines DOE’s PA 

maintenance program is sufficient to evaluate new and significant information related to tank

farm compliance with 10 CFR 61.41 in the future.
4-1

4 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.42

Design, operation, and closure of the land disposal facility must ensure protection of any 

individual inadvertently intruding into the disposal site and occupying the site or contacting the 

waste at any time after active institutional controls over the disposal site are removed.

Protection of individuals from inadvertent intrusion considers the potential risks to individuals 

who are unknowingly exposed to radiation from disposed waste while engaging in normal 

activities while occupying the site. Generally, compliance with the waste classification system at 

10 CFR 61.55 ensures protection of inadvertent intruders. However, for waste streams that 

were not considered in the development of 10 CFR Part 61 in NUREG–0945 (ML052590184), 

such as the residual waste projected to remain in the tank farms, it would be prudent to assess 

the performance of the disposal facility to limit radiological exposures to inadvertent intruders to 

demonstrate compliance with the PO. 

Exposures to radiation can be through direct contact with the waste or indirect exposure to the 

radiation from buried waste while onsite. Direct contact could occur as a result of an activity 

that disturbs the waste zone directly. Examples of activities that could lead to direct contact of 

radioactivity by an inadvertent intruder include excavation during dwelling construction and well 

drilling. DOE rules out excavation for dwelling construction in its PA because DOE assumes a 

minimum of 3-m [10-ft] clean cover is present and most residential dwellings disturb less than 3

m [10 ft] of soil. Although well drilling was considered a potential direct intrusion event in DOE’s 

PA, well drilling into an HLW tank was considered unlikely in DOE’s PA, given the presence of 

multiple redundant barriers, such as the closure cap, tank grout, and steel liner, that would 

make drilling more difficult and, based on regional experience, would likely alert a driller 

accustomed to drilling into softer materials to the potential hazards of the disposal facility. 

Instead, DOE considered intrusion into transfer lines more likely. Nonetheless, because tank

farm waste is located several meters below grade underneath a closure cap, DOE also 

considers exposures resulting from indirect contact with contaminated onsite groundwater as a 

more likely exposure scenario for an inadvertent intruder. The basis for the 10 CFR 61.42 

compliance demonstrations is therefore calculations of potential dose to a well driller who 

intrudes into the tank farm transfer lines and the potential dose to a groundwater receptor. 

Because 10 CFR Part 61 relies on the waste classification system to ensure protection of 

inadvertent intruders, the regulation does not specify a time period for an assessment. LLW

and WIR guidance found in NUREG–1573 and NUREG–1854 suggest a 10,000-year period of 

performance is generally sufficient for demonstration of compliance with 10 CFR 61.41. 

Likewise, the NRC staff considers this time period appropriate for assessment of compliance 

with 10 CFR 61.42. However, longer evaluation periods may be necessary to capture the peak 

dose and provide insights on facility (natural and engineered) performance for certain long-lived 

wastes. 

To determine the dose to a potential receptor, DOE also must select a POC. NRC assumes in 

the development of 10 CFR Part 61 in NUREG–0945, Final Environmental Impact Statement on 

10 CFR Part 61, Licensing Requirements for Land Disposal of Radioactive Waste, Volume 1, 

Summary and Main Report (ML052590184) the intruder excavated into a disposal cell or 

extracted water from a well located at the boundary of the disposal area after the end of the 

institutional control period. DOE assumes the inadvertent intruder installs a well located 1 m 

from the boundary of the disposal facility (see Figures 3-2 and Figure 3-3). In the HTF PA

(SRR–CWDA–2010–00128), DOE also evaluates several additional compliance points next to 

tank sources within the tank farm boundary (see Figure 3-3).
4-2

Because the groundwater pathway is evaluated for both the 10 CFR 61.41 and 61.42 POs, with 

the only difference being the POC (100 m [330 ft] versus 1 m [3.28 ft], respectively) and the 

allowable dose (0.25 mSv/yr [25 mrem/yr] versus 5.0 mSv/yr [500 mrem/yr]), each MA that is 

important for demonstrating compliance with 10 CFR 61.41 also is important for demonstrating 

compliance with 10 CFR 61.42. In general, NRC staff expects that compliance with the 

10 CFR 61.41 PO will be bounding for the 10 CFR 61.42 evaluations. This is true for long-lived 

radionuclides because the factor difference between the dose standards (20 times higher for the 

10 CFR 61.42 evaluations) is greater than the difference in concentrations between the 1-m 

[3.28 ft] and 100-m [328 ft] POCs for most key radionuclides. This generalization would not be 

true for relatively short-lived radionuclides such as Cs-137 and Sr-90 whose concentrations 

drop off substantially with distance from the source to the 100-m [328 ft] POC. Additionally, 

because in some cases DOE relies on timing of the peak dose to demonstrate compliance with

the POs, the 10 CFR 61.42 compliance demonstration could be bounding for those 

radionuclides whose travel times are assumed to be prolonged between the 1 m [3.28 ft] and 

100-m [328 ft] POCs (e.g., Pu-239). Finally, because 10 CFR 61.41 does not consider a direct 

intrusion case (e.g., intrusion into the transfer lines), constituents important to the 10 CFR 61.42 

evaluations may not be important for the 10 CFR 61.41 evaluations and will be highlighted in 

MA 1, “Residual Inventory.”

1

 In general, NRC staff considers MA and MA factors discussed in 

Chapter 3 with respect to 10 CFR 61.41 applicable to 10 CFR 61.42 discussed in Chapter 4 and 

will not be repeated. However, special considerations are discussed below for each MA.

MA 1, “Inventory” 

Monitoring Factor 1.1: Final Inventory and Risk Estimates

(Additional Considerations)

In the FTF PA (SRS–REG–2007–00002), DOE evaluates a well driller scenario in which a 

worker is acutely exposed to radioactivity during construction of a well that intersects a 8 cm

[3-in] transfer line and a resident is chronically exposed to contaminated drill cuttings brought to 

the surface following well construction. The FTF PA indicates that primary radionuclides 

contributing to dose in the acute intruder exposure scenario are Cs-137/Ba-137m. DOE also 

reports a peak 10,000-year dose for the chronic intruder of 0.73 mSv/yr [73 mrem/yr] with the 

most important pathway being ingestion of vegetables contaminated with drill cuttings at the 

time of intrusion at 100 years. The primary radionuclides contributing to dose within 

10,000 years are Sr-90/Y-90 and Cs-137/Ba-137m. The peak 20,000-year dose for the chronic 

intruder is slightly higher at 0.75 mSv/yr [75 mrem/yr] due to groundwater-dependent pathways; 

the majority of the dose is from vegetable and water ingestion from Np-237. Results of the 

probabilistic analysis show the potential for doses in excess of the 5 mSv/yr [500 mrem/yr]

applied dose standard for 10 CFR 61.42. Sensitivity analysis indicated the potential for other 

radionuclides in addition to Np-237 to dominate the groundwater-dependent pathway dose.2

 

Other potentially important radionuclides from the groundwater pathway include Th-229 and 

U-233, although DOE indicated its plans to eliminate these two radionuclides from the list of 

highly radioactive radionuclides (HRRs) that is used to identify constituents in the waste residue 

 

1In general, groundwater-dependent scenarios dominate the intruder dose; however, groundwater-independent 

scenario doses and key radionuclides are listed for completeness.

2The peak of the mean dose in the probabilistic analysis is 6.4 mSv/yr [640 mrem/yr]. DOE performed a sensitivity 

analysis and identified Pu inventory, Pu and Tc solubility limits, Pu sand Kd, steel liner failure times, and aquifer 

thickness as important to peak intruder dose from groundwater-dependent pathways.
4-3

to be sampled by DOE, following cleaning, based on low inventories of these two radionuclides 

in cleaned Tanks 18F and 19F. 

In the HTF PA (SRR–CWDA–2010–00128), DOE also evaluates the same well driller scenario 

evaluated in the FTF PA. Most of the dose to the acute well driller is from key radionuclide Cs137, with Sr-90, Pu-238, and Am-241 also contributing less significantly to peak dose. With 

respect to groundwater-dependent pathway peak dose (0.51 mSv/yr or [51 mrem/yr]) within 

10,000 years,

3 primary radionuclides include Ra-226, U-234, and U-233. At the end of the 

institutional control period (at 100 years), the dose (0.4 mSv/yr or [40 mrem/yr]) is dominated by 

water-independent pathways or dose attributable to direct exposure from the drill cuttings. The 

primary radionuclides contributing to peak dose at 100 years are Sr-90/Y-90.

NRC staff noted in the HTF TER (ML14094A514) that differences in the timing of the peak dose 

between the deterministic and probabilistic analysis4 may be important to the compliance 

demonstration (i.e., doses may be above the PO within the compliance period considering

uncertainty in the timing of the peak dose). Additionally, based on DOE’s response to a request 

for additional information, the intruder dose could be above the 10 CFR 61.42 PO for alternative 

cases(i.e., Case E results indicate a peak chronic intruder dose of 10 mSv/yr [1,000 mrem/yr] at 

around 2,000 years). The peak Case E dose is attributed to Np-237. Because Np-237 has a 

relatively high solubility under oxidizing conditions and high mobility in the natural environment, 

only the tank basemats provide a significant barrier to Np-237 release when the system 

becomes oxidized. Therefore, when the attenuating properties of the basemat are degraded in 

Case E, the Np-237 dose is significantly greater than in the compliance case, Case A.

Also, for HTF, the NRC staff believes the potential dose contributions of short-lived 

radionuclides in the annuli of the tanks, such as Cs-137 and Sr-90, may not have been fully 

evaluated by DOE in alternative cases. Of particular concern to the NRC staff is the 

risk-significant inventory of Sr-90 located in HTF tank annuli, such as Tanks 9H, 10H, 14H, and 

16H. Evidence of the potential risk significance of Sr-90 in primary tank waste is found in 

alternative case results performed for the 10 CFR 61.41 evaluation. In its HTF TER

(ML14094A496), NRC staff also expressed concern with the selection of the 1-m compliance 

boundary in the HTF PA. Because DOE evaluated compliance points next to tank sources, 

NRC staff was able to evaluate the potential impact of selection of the compliance boundary on 

intruder dose results [e.g., the highest intruder dose associated with an evaluation point next to 

Tank 12H was a factor of five times higher than the highest intruder dose reported for any

location along the 1-m [3.28 ft] boundary].

NRC staff will review special analyses prepared for each cleaned tank to ensure intruder risks 

reported in the tank farm PAs are appropriately assessed and evaluated under MF 1.1, paying 

special attention to the key radionuclides and technical issues discussed in this section. This 

MF can be closed after NRC staff reviews each special analysis developed by DOE for the tank 

farms and concludes that DOE has adequately evaluated risk to the inadvertent intruder.

 

3The dose is significantly higher in the 20,000-year time period; however, no information was provided on key 

radionuclides during this time period.

4Probabilistic analysis results presented in the HTF PA indicate a peak of the mean dose of 7.6 mSv/yr 

[760 mrem/yr]. Sensitivity analysis results show (1) the importance of the aquifer in which the well is completed and 

(2)Tc related parameters important to dose.
4-4

Monitoring Factor 1.2: Residual Waste Sampling (Additional Considerations)

DOE’s conclusion that inventories of Th-229 and U-233, which may be important to the 

10 CFR 61.42 analysis, were overestimated in the FTF PA, is based on analyses of these 

radionuclides in cleaned Tanks 18F and 19F. However, NRC indicated in the technical 

evaluation report for FTF (ML112371751) that unless DOE can show that final inventories in 

other tanks are similar to final inventories in Tanks 18F and 19F, DOE should continue to 

characterize samples for these radionuclides. With respect to HTF, U-233 is considered to be a 

key radionuclide because H-Canyon processing of Th-232 targets irradiated for the production 

of U-233 led to a significantly greater expected inventory of U-233 in HTF compared to FTF 

(factor of 108 times higher inventory of U-233 is expected in HTF compared to FTF according to 

SRNL–STI–2012–00479). Based on process knowledge and sampling, DOE could provide 

additional information to eliminate U-233 from consideration as a key radionuclide at FTF.

NRC staff will review sampling and analysis plans to ensure all HRRs are sampled or a basis for 

exclusion of an HRR is provided. This MF can be closed when NRC concludes that DOE has 

provided sufficient information to support its list of HRRs and has addressed the other technical 

issues identified in Section 3.1.2.

Monitoring Factor 1.3: Residual Waste Volume

There are no special considerations under MF 1.3 for the 10 CFR 61.42 analyses.

Monitoring Factor 1.4: Ancillary Equipment Inventory

Short-lived radionuclides Sr-90/Y-90 and Cs-137/Ba-137 that may not be considered important 

by DOE to the 10 CFR 61.41 evaluation could be more important for the 10 CFR 61.42 analysis, 

because the 10 CFR 61.42 analysis considers direct intrusion into the tank farm transfer lines at 

100 years, when these radionuclides may still be present in risk-significant quantities.

5

 In fact, 

the dose at 100 years for the chronic intruder scenario is 0.73 mSv/yr [73 mrem/yr] at FTF and 

0.40 mSv/yr [40 mrem/yr] at HTF due primarily to relatively short-lived radionuclides Sr-90/Y-90 

and Cs-137/Ba-137m. However, because the estimated does is significantly below the 

5-mSv/yr [500-mrem/yr] applied dose standard, inventory of these radionuclides could 

potentially be higher, while still maintaining compliance with the dose standard. NRC staff 

should ensure risks associated with these relatively short-lived radionuclides are bounded by 

the PAs or a special analysis is performed to assess the increased risk associated with a higher 

than assumed inventory, once final estimates of transfer line inventories are assessed through 

additional characterization. DOE indicated in response to an NRC comment (SRR–CWDA–

2009–00054) its intent to verify PA assumptions regarding transfer line inventories and listed 

this activity under Section 8.2, “Further Work,” in its FTF and HTF PAs (SRS–REG–2007–

00002, and SRR–CWDA–2010–00128). NRC staff will monitor DOE’s efforts in this area to 

ensure the assumed transfer line inventories are sufficiently bounding or that increased risk is 

 

5The 10 CFR 61.41 analyses are dominated by groundwater-dependent pathways and in most cases risk-significant 

releases from tank farm components are not assumed to occur for hundreds to thousands of years, allowing sufficient 

time for decay of relatively short-lived radionuclides, such as Cs-137 and Sr-90. In HTF, NRC staff is concerned that 

risk-significant releases of short-lived radionuclides could occur in tanks with liners that are assumed to be initially 

failed and that have a significant inventory in the annulus.
4-5

assessed. This MF can be closed when NRC staff concludes that DOE has adequately 

assessed the risk associated with transfer lines.

Monitoring Factor 1.5: Waste Removal (As It Impacts ALARA)

MF 1.5 related to ALARA does not apply to the 10 CFR 61.42 evaluations.

MA 2, “Waste Release”

Monitoring Factor 2.1: Solubility-Limiting Phases/Limits and Validation

There are no special considerations under MF 2.1 for the 10 CFR 61.42 analyses.

Monitoring Factor 2.2: Chemical Transition Times

There are no special considerations under MF 2.2 for the 10 CFR 61.42 analyses.

MA 3, “Cementitious Material Performance”

Monitoring Factor 3.1: Hydraulic Performance of Concrete Vault and Annulus 

(As it Relates to Steel Liner Corrosion and Waste Release)

(Additional Considerations)

Because DOE relies on grouted tanks and vaults in the tank farm PAs to deter inadvertent 

intrusion into the HLW tanks,

6 NRC staff will perform routine monitoring of DOE’s reliance on 

cementitious materials to ensure tank farm PA assumptions regarding the ability of the tank 

vaults to serve as a recognizable and durable barrier to intrusion are valid. This MF will be 

reviewed in conjunction with MF 3.4 and can be closed following closure of tanks at FTF 

and HTF.

Monitoring Factor 3.2: Groundwater Conditioning via Reducing Grout

There are no special considerations under MF 3.2 for the 10 CFR 61.42 analyses.

Monitoring Factor 3.3: Shrinkage and Cracking of Reducing Grout

There are no special considerations under MF 3.3 for the 10 CFR 61.42 analyses.

Monitoring Factors 3.4: Grout Performance (Additional Considerations)

Because DOE relies on the grouted tanks and vaults in the tank farm PAs to deter inadvertent 

intrusion into the HLW tanks,

7 grouting activities under MA 3, “Cementitious Materials 

Performance,” will also be monitored under 10 CFR 61.42. NRC will perform routine monitoring 

of DOE’s use of grout materials to stabilize HLW tanks to ensure tank farm PA assumptions 

 

6DOE only considers intrusion into the HLW tanks in sensitivity analyses due to assumed robustness of the grouted 

tank and vault system.

7DOE only considers intrusion into the HLW tanks in sensitivity analyses due to assumed robustness of the grouted 

tank and vault system.
4-6

regarding the ability of the grouted tank and vaults to serve as a recognizable and durable 

barrier to intrusion remain valid. This MF will be reviewed in conjunction with MF 3.1 and can 

be closed following closure of tanks at FTF and HTF.

Monitoring Factor 3.5: Vault and Annulus Sorption

There are no special considerations under MF 3.5 for the 10 CFR 61.42 analyses.

Monitoring Factor 3.6: Waste Stabilization (As it Impacts ALARA)

MF 3.6 related to ALARA does not apply to the 10 CFR 61.42 evaluations (there are no ALARA 

provisions in 10 CFR 61.42).

MA 4, “Natural System Performance”

Monitoring Factor 4.1: Natural Attenuation of Key Radionuclides

(Additional Considerations)

Due to potential reliance on travel time of Pu to the 100-m [328 ft] POC for the 10 CFR 61.41 

analyses, NRC will specifically consider whether the shorter distance and travel time to the 1-m 

[3.28 ft] POC for the 10 CFR 61.42 analyses make compliance with the latter PO bounding. As 

discussed in Section 3.4.1, NRC staff has concerns with the Kd averaging approach used by 

DOE that tends to delay travel times to the 10 CFR 61.41 and 61.42 POCs. NRC staff will 

review information generated by DOE and perform independent modeling to assess whether 

more mobile forms of Pu, if evaluated explicitly in DOE’s PA modeling, could reach the 

inadvertent intruder POC within 10,000 years. This MF can be closed when NRC staff 

concludes that DOE has adequately assessed the timing and magnitude of Pu-239 release and

transport to the 1-m [3.28 ft] POC.

Monitoring Factor 4.2: Calcareous Zone Characterization

There are no special considerations under MF 4.2 for the 10 CFR 61.42 analyses.

Monitoring Factor 4.3: Environmental Monitoring

There are no special considerations under MF 4.3 for the 10 CFR 61.42 analyses.

MA 5, “Closure Cap Performance”

Monitoring Factor 5.1: Long-Term Hydraulic Performance

There are no special considerations under MF 5.1 for the 10 CFR 61.42 analyses. 

Monitoring Factor 5.2: Long-Term Erosion Protection Design

(Additional Considerations)

DOE relies on the erosion barrier to maintain a minimum 3-m [10-ft] clean cover to prevent 

intrusion into Tank Farm waste (DOE/SRS–WD–2012–001 and DOE/SRS–WD–2014–001), 

thereby eliminating certain shallow intrusion scenarios from analysis in DOE’s PAs (SRS–REG–

2007–00002 and SRR–CWDA–2010–00128). DOE also considers the erosion barrier part of a 
4-7

system of durable engineered barriers that would cause a regional driller not accustomed to 

encountering hard materials to change location. For these reasons, NRC will specifically 

monitor use of the engineered closure cap as a barrier to intrusion. This MF can be closed after 

construction of the closure cap.

Monitoring Factor 5.3: Closure Cap Functions that Maintain Doses ALARA

MF 5.3 related to ALARA does not apply to the 10 CFR 61.42 evaluations.

MA 6, “Performance Assessment Maintenance”

Monitoring Factor 6.1: Scenario Analysis (Additional Considerations)

NRC will pay particular attention to DOE’s consideration of various scenarios related to 

inadvertent intrusion in its tank farm PAs. NRC will also evaluate DOE’s consideration of FEPs

related to inadvertent intrusion. In a technical review report (ML13277A063), NRC evaluated 

DOE’s FEPs analysis (SRR–CWDA–2012–00011) and crosswalk of the FEPs analysis to the 

FTF PA (SRR–CWDA–2012–00022). In the HTF TER (ML14094A496), NRC also evaluated 

SRR–CWDA–2012–00044, which crosswalks the FEPs described in SRR–CWDA–2012–

00011, to the HTF PA. NRC staff can close this MF when it concludes that DOE has 

adequately addressed exposure scenarios and FEPs related to inadvertent intrusion in its PA 

documentation.

Monitoring Factor 6.2: Model and Parameter Support

There are no special considerations under MF 6.2 for the 10 CFR 61.42 analyses. 

Monitoring Factor 6.3: Tank Farm PA Revisions 

(Additional Considerations)

NRC will evaluate any revisions to the tank farm PAs to ensure inadvertent intrusion into tank 

farm components were properly evaluated in the 10 CFR 61.42 analyses. Evaluation of 

revisions to the tank farm PAs is considered critical to NRC staff’s execution of its monitoring 

responsibilities to assess compliance of DOE disposal actions with the POs in 10 CFR Part 61, 

Subpart C. The tank farm PAs and special analyses provide the technical support for DOE’s 

demonstrations of compliance with the POs in 10 CFR Part 61, Subpart C. This MF can be 

closed when NRC staff concludes that DOE has adequately evaluated FEPs and scenarios 

related to inadvertent intrusion in its PA documentation and that its PA maintenance program is 

sufficient to evaluate new and significant information related to inadvertent intrusion in the

future. 
5-1

5 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.43

Operations at the land disposal facility must be conducted in compliance with the standards for

radiation protection set out in Part 20 of this chapter, except for releases of radioactivity in

effluents from the land disposal facility, which shall be governed by 10 CFR 61.41 of this part. 

Every reasonable effort shall be made to maintain radiation exposures as low as is reasonably

achievable.

The NRC interprets the term “operations” as those DOE activities related to waste retrieval 

(i.e., heel removal), grouting, stabilization, observation, maintenance, or other similar activities. 

NRC intends to evaluate this PO from the time that DOE issues its final waste determination 

until the end of the institutional control period. For workers performing activities 

(e.g., construction and maintenance of closure caps) at the tank farms on the larger 

DOE-controlled site and under DOE’s radiation protection program, the 50-mSv/yr [5-rem/yr]

radiation worker dose limit applies. For members of the public who may visit the site prior to the 

end of the institutional control period,

1 including workers performing limited activities not covered 

under a DOE radiation protection program, the 1-mSv/yr [100-mrem/yr] dose limit for members 

of the public applies from sources other than effluents.

2

 10 CFR 20.1101(d) further specifies 

that the maximum annual dose that a member of the public can receive from airborne emissions 

is 0.10 mSv [10 mrem/yr]. DOE also must demonstrate that dose in any one hour in an 

unrestricted areas is less than 0.02 mSv [2 mrem]. 

DOE has a radiation protection program to ensure protection of individuals during operations. In 

DOE’s 2010 FTF waste determination and 2014 HTF waste determination (DOE/SRS–WD–

2012–001 and DOE/SRS–WD–2014–001), DOE provided a crosswalk of the relevant DOE 

regulation or limit consistent with that provided in 10 CFR 20 to demonstrate that the DOE 

regulation provides an equivalent level of protection. 

During operations associated with tank farm disposal at the SRS, the primary pathway of 

concern will be through the air. No significant releases to the subsurface or surface water from 

the waste in the tank farm tanks are expected during the time of operations. Additionally, the 

release of radionuclides from the tank farms to the subsurface is being monitored in 

assessments of compliance with 10 CFR 61.41 (Chapter 3) and 10 CFR 61.42 (Chapter 4). Any 

leaching of contaminants from the vaults observed while the tank farms are still in operation 

may indicate the ability of the waste form to retain the radionuclides is less than expected and 

that 10 CFR 61.41 and 10 CFR 61.42 may not be met.

Importance of MA 7, “Protection of Individuals During Operations”

The NDAA requires NRC, in coordination with the State of South Carolina, to monitor DOE

disposal actions to assess compliance with the POs in 10 CFR Part 61, Subpart C. 10 CFR 

61.43 is related to protection of individuals during operations, including workers and members of 

the public. NRC expects the following DOE activities to incur the largest risks to workers and 

members of the public during tank farm closure operations: (i) tank cleaning, (ii) waste 

 

1The 10 CFR 61.42 performance objective, related to protection of individuals from inadvertent intrusion, provides 

standards to protect individuals who may occupy the site following the institutional control period.

2The public dose limit is 1 mSv/yr [100 mrem/yr]. However, 10 CFR 61.43 indicates that effluents will be addressed 

under 10 CFR 61.41. The 10 CFR 61.41 dose based standard is 0.25 mSv/yr [25 mrem/yr]. The point of compliance 

during active disposal facility operations under 10 CFR 61.41 is the larger SRS site boundary.
5-2

sampling, (iii) waste stabilization, and (iv) other maintenance activities. Tank cleaning activities 

could include use of high pressure water that has the potential to lead to releases or 

radioactivity into secondary containment and the environment. Waste sampling may lead to 

significant exposures to workers collecting and processing samples. Radioactivity also may be 

released to the tank vapor space during tank grouting activities. Modification and maintenance

of tank equipment and ventilation systems during tank cleaning, sampling, grouting, and other 

tank farm activities are expected to incur worker dose. Therefore, NRC may observe installation 

and removal of equipment from HLW tanks during an onsite observation, as practical.

NRC Monitoring Under MA7, “Protection of Individuals During Operations”

NRC staff has developed the following MFs related to protection of individuals during

operations:

• MF 7.1 “Protection of Workers During Operations”

• MF 7.2 “Air Monitoring”

• MF 7.3 “ALARA”

Monitoring Factor 7.1: Protection of Workers During

Operations

Compliance with the dose requirements for protection of individuals during operations is 

expected to be assessed by NRC through the use of dosimetry and the monitoring of radiation 

data and radiation records. NRC staff should review, on at least an annual basis, DOE reports 

and records that are related to dose during waste disposal operations to assess whether doses 

are within the limits found in 10 CFR Part 20 and are ALARA. 

NRC staff should periodically confirm programs and policies presented in the waste 

determination (DOE/SRS–WD–2012–001) continue to be in effect during the operational period. 

In particular, NRC staff should verify personnel involved in waste disposal operations are

provided dosimetry and are familiar with requirements of the radiation protection program. NRC 

will leverage staff in its Region I office with experience in radiation protection inspections to 

support onsite observations in this area. Any NRC staff participating in an onsite observation 

should abide by DOE’s onsite radiation protection program requirements, as well as obtain 

dosimetry from NRC’s Office of Administration, if not already assigned, prior to the onsite 

observation.

This factor will be closed at the end of the assumed 100-year institutional control period or after 

operational doses are expected to be reduced to non-risk-significant levels following tank 

closure activities. 

Monitoring Factor 7.2: Air Monitoring 

DOE monitors air quality at SRS using air sampling stations located at the site boundary as well 

as in other locations throughout the site. NRC staff should review air monitoring data to 

determine whether activity released in the air, as a result of tank farm disposal facility activities,

could cause a member of the public located at the SRS site boundary to receive an annual dose 

of greater than 0.10 mSv/yr [10 mrem/yr] through the air pathway. 
5-3

NRC staff should periodically confirm the air monitoring program continues to adequately

assess the risk of tank farm operations. As part of this review, NRC staff should evaluate 

whether sampling locations and sampling methodologies are adequate to assess airborne 

emissions from the tank farms or rely on independent verification from the SCDHEC. NRC staff 

expects the dose from airborne emissions to be small. If the airborne emissions dose becomes 

more risk significant, then NRC staff will need to evaluate the air monitoring program in greater 

detail.

This factor will be closed at the end of the assumed 100-year institutional control period or when 

operational doses are expected to be reduced to non-risk-significant levels following tank 

closure activities.

Monitoring Factor 7.3: As Low As Is Reasonably Achievable

The NRC regulation at 10 CFR 20.1003 defines ALARA in relevant part:

ALARA ... means making every reasonable effort to maintain exposures to radiation as far below the 

dose limits ... as is practical consistent with the purpose for which the ... activity is undertaken, taking into 

account the state of technology, the economics of improvements in relation to state of technology, the 

economics of improvements in relation to benefits to the public health and safety, and other societal and 

socioeconomic considerations, and in relation to utilization of nuclear energy and licensed materials in the 

public interest.

10 CFR 835 and relevant DOE Orders, which establish DOE regulatory and contractual 

requirements for DOE facilities and activities, establish a definition of ALARA that is similar to 

the definition at 10 CFR 20.1003. DOE regulation at 10 CFR 835.2 defines ALARA as “... the 

approach to radiation protection to manage and control exposures (both individual and 

collective) to the work force and to the general public to as low as is reasonable, taking into 

account social, technical, economic, practical, and public policy considerations.”

Furthermore, the DOE regulation at 10 CFR 835.101(c) requires the contents of each radiation 

protection program (RPP) to include formal plans and measures for applying the ALARA 

process to occupational exposure. As such, NRC staff’s monitoring of ALARA under 

10 CFR 61.43 will be carried out through monitoring of the Radiation Protection Program and 

related activities.

NRC staff should periodically (or at the appropriate time relevant to each measure) review 

documents associated with the following measures for ensuring ALARA: (i) a documented RPP;

(ii) a Documented Safety Analysis; (iii) radiological design for protection of occupational workers 

and the public; (iv) regulatory and contractual enforcement mechanisms; (v) access controls, 

training, and dosimetry; and (vi) occupational radiation exposure history. These measures are 

described in the waste determination or basis documents (DOE/SRS–WD–2012–001 and 

DOE/SRS–WD–2014–001).

This factor will be closed at the end of an assumed 100-year institutional control period or when 

operational doses are expected to be reduced to non-risk-significant levels following tank 

closure activities.
6-1

6 MONITORING TO ASSESS COMPLIANCE WITH 10 CFR 61.44

The disposal facility must be sited, designed, used, operated, and closed to achieve long-term 

stability of the disposal site and to eliminate, to the extent practicable, the need for ongoing 

active maintenance of the disposal site following closure so that only surveillance, monitoring, or 

minor custodial care are required.

These requirements relate to both stability of the disposal site and control of releases within 

acceptable limits. Ensuring site stability helps to minimize the access of water to the residual 

waste by helping to maintain the performance of the closure cap. In addition, site stability is 

important in protecting against inadvertent intrusion. 

The MA for site stability includes FEPs that are external to the individual disposal facility 

components (e.g., settlement of the subsurface) that may impact individual barrier performance. 

FEPs that are internal to the individual components (e.g., grout shrinkage, erosion of the topsoil 

layer) are discussed under the relevant POs and MAs. 

Importance of MA 8, “Site Stability”

Site stability is an integral aspect to limiting the infiltration through the disposal site and in 

maintaining an adequate barrier to intrusion. The key attributes responsible for providing 

stability of the tank farms are the grouting of the HLW tanks and annular spaces and the erosion 

protection designs associated with the closure cap. The DOE assumes that tank grout used to 

fill the tanks will create a solid monolith with little void space and eliminate differential settlement 

due to structural collapse of the tanks.

Site stability could be affected by settlement. Settlement could lead to cracking of the vault 

concrete and tank grout. Cracking is not expected to result in significant structural tank 

collapse; however, the integrity of the vault concrete and tank grout is important to steel liner 

performance and waste release, as discussed under MF 3.1. Settlement may impact the 

hydraulic performance of the closure cap due to (i) modifications of the closure cap slope and 

surface drainage patterns and (ii) disruption to closure cap components (e.g., HDPE/GCL 

composite layer, foundation layer, lateral drainage layer). The erosion protection design is 

important in maintaining a minimum of 3 m [10 ft] of clean material above the tanks and 

significant ancillary equipment, which is discussed in Chapter 4. 

NRC Monitoring Under MA 8, “Site Stability”

Because other MFs related to site stability are discussed in the preceding chapters, monitoring 

activities to assess compliance with 10 CFR 61.44 will focus on settlement.

Monitoring Factor 8.1: Settlement 

Settlement could result from (i) increase in overburden from the tank grout and closure cap and 

(ii) the ongoing dissolution of calcareous sediment in the lower portion of the UTRA (i.e., the 

Santee Formation). Increased loading resulting from the increase in overburden may lead to

compression of subsurface layers and consequently, differential settlement. Differential 

settlement has the potential to disrupt the HDPE/GCL composite layer, which acts as a 

significant barrier to infiltration in the early part of the performance period. Hydraulic isolation of 

the residual waste during this period is important in the retention of short-lived radionuclides 

before significant decay. Differential settlement may also affect the continuity and therefore 
6-2

performance of the foundation layer and lateral drainage layer, both of which act as long-term 

barriers to infiltration. DOE should account for the potential effects of the additional overburden 

of the engineered barriers on site stability. Technical reviews and onsite observations of 

settlement will be conducted by the NRC staff to assess compliance with 10 CFR 61.44. 

Reviews will focus on (i) settlement data collected during closure operations of the tank farms,

(ii) settlement data collected from analogous sites, and (iii) updated settlement modeling 

investigations. 

In addition to settlement from loading, settlement may result from the dissolution of calcareous 

sediment. Elevated bicarbonate ion concentrations and relatively high pH groundwater in and 

near the Santee Formation suggests ongoing dissolution of the calcareous zones within the 

lower zone of the UTRA (U.S. Army Corps of Engineers, 1952). Although dissolution of 

calcareous sediment may be a very slow process, DOE has not demonstrated that dissolution 

will be insignificant to site stability throughout the performance period. Such dissolution 

previously has created a soil structure that is characterized by arching, underconsolidation, and 

historic, periodic collapses. The U.S. Army Corps of Engineers (1952) identified seven surface 

depressions (i.e., Carolina Bays) thought to be sinks within F-Area, including one sink located 

within the 100-m [330-ft] compliance boundary. In H-Area, several depressions are outlined as 

potential sinks. However, the authors noted that the amount of drilling in H-Area was insufficient 

to interpret the geology in detail. DOE’s calculations do not account for the stability of 

calcareous soft zones in the Santee Formation, given the additional overburden that is to be 

contributed by waste-stabilizing grout and the engineered closure cap, or for additional 

subsidence that could occur as a result of future dissolution of subsurface material during the 

performance period. DOE should account for the potential effects of future dissolution of 

calcareous zones on ground subsidence over the long-term period of performance or 

demonstrate that future dissolution of calcareous sediment will be insignificant to site 

performance. Technical reviews related to the risk significance of calcareous zones will be 

conducted to assess compliance with 10 CFR 61.44. Reviews will focus on (i) processes that 

have resulted in the formation of sinks at the SRS and specifically at the tank farms at the 

General Separations Area, (ii) the potential for these processes to affect site stability throughout 

the performance period, and (iii) the potential dose consequences from subsidence related to 

dissolution of calcareous sediment. DOE stated that it will consider static-loading-induced 

settlement, seismically induced liquefaction and subsequent settlement, and seismically induced 

slope instability in the final design of the closure cap. NRC staff will review DOE’s consideration 

of these processes as information is made available. 

Compliance or noncompliance with the PO for 10 CFR 61.44 is associated with the status of the 

aforementioned monitoring activities. If surveillance, monitoring, and custodial care are carried 

out after closure, NRC staff expects DOE to inform it of changes to features in the immediate 

area that might affect site stability. These changes may include (i) vegetation denudation at the 

surface due to fires or storms; (ii) erosion features caused by extreme precipitation events or 

long-term processes; or (iii) visible surface changes due to significant biotic intrusion, 

earthquakes, or other geological processes.

Closure of MA, 8 “Site Stability”

To assess compliance with 10 CFR 61.44, NRC staff will visually observe the facility for obvious 

signs of degeneration of the facility. For example, evidence of ponded water on the cap surface 

may be a sign of differential settlement. Surface fractures may be evidence of underlying 

displacement. NRC staff also may plan site visits to observe the facility after severe weather 

events (e.g., storms, tornados) to ascertain how well the facility can withstand these events. 
6-3

DOE is expected to carry out an active maintenance program for the facility through the end of 

the institutional control period; therefore, DOE should repair any obvious signs of facility 

degradation. However, such degradation can provide insights into potential long-term facility 

performance. NRC staff should also discuss any maintenance activities that are performed at 

the disposal facility (e.g., repairs to engineered surface barriers) with SCDHEC. This monitoring 

activity is expected to remain open indefinitely.
7-1

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8-1

8 LIST OF CONTRIBUTORS

U.S. Nuclear Regulatory Commission

James Shaffner

(Project Manager)

Project Manager–Low-Level Radioactive Waste (LLRW)

M.S., Civil Engineering, University of Maryland

B.S., Civil Engineering, Drexel University

30 years’ experience in LLRW management

Cynthia S. Barr

(Technical Lead)

Sr. Systems Performance Analyst

M.S., Environmental Systems Engineering, Clemson University

B.S., Mathematics, College of Charleston

B.A., Political Science, College of Charleston

17 years’ experience in nuclear environmental analysis and risk

assessment

Christopher Grossman

(Technical Co-Lead)

Systems Performance Analyst

M.S., Environmental Engineering and Science, Clemson 

University

B.S., Civil Engineering, Purdue University

13 years’ experience in radioactive waste management and 

performance assessment

Mark Fuhrmann Geochemist

Ph.D., Geochemistry, State University of New York at Stony Brook

M.S., Geology, Adelphi University

B.S., Marine Science, State University of New York, Empire 

College

30 years’ experience in geochemistry of contaminants

George Alexander Systems Performance Analyst

Ph.D., Energy and Geo-Environmental Engineering, Pennsylvania 

State University

M.S., Energy and Geo-Environmental Engineering, Pennsylvania 

State University

B.S., Geo-Environmental Engineering, Pennsylvania State 

University

7 years’ experience in radioactive waste management and 

performance assessment

Leah Parks Systems Performance Analyst

Ph.D., Environmental Management, Vanderbilt University

M.S., Environmental Engineering, Vanderbilt University

B.S., Systems and Information Engineering, University of Virginia

7 years’ experience in radioactive waste management and 

performance assessment
8-2

Southwest Research Institute®

Center for Nuclear Waste Regulatory Analyses

Roberto T. Pabalan Former Institute Scientist49

Ph.D., Geochemistry and Mineralogy, Pennsylvania State 

University

B.S., Geology, University of the Philippines

35 years’ experience in geology and geochemistry

25 years’ experience in nuclear waste management applications

Southwest Research Institute®

Center for Nuclear Waste Regulatory Analyses

David A. Pickett Sr. Program Manager (geochemistry, radionuclide release, and

transport)

Ph.D., Geology, California Institute of Technology

M.S., Geology, California Institute of Technology

B.A., Geology, Rice University

21 years’ experience in nuclear waste disposal analyses

Cynthia Dinwiddie, P.G. Principal Engineer (near-field hydrology and far-field 

hydrogeology)

Ph.D., Environmental Engineering and Science, Clemson 

University

M.S., Environmental Systems Engineering, Clemson University

B.S.E., Mechanical Engineering, Walla Walla College

14 years’ experience in nuclear waste disposal analyses

Gary R. Walter Staff Scientist (hydrology, hydrogeology, and environmental risk

assessment)

Ph.D., Hydrology, University of Arizona

M.A., Geology, University of Missouri–Columbia

B.A., Chinese and Sociology, University of Kansas

35 years’ consulting experience

10 years’ experience in nuclear waste management

Biswajit Dasgupta Staff Engineer (structural/geotechnical engineering and risk

assessment)

Ph.D., Structural Engineering, University of Minnesota

M. Tech., Structural Engineering, Indian Institute of Technology, 

Mumbai, India

B. Tech., Civil Engineering, Indian Institute of Technology, 

Kharagpur, India

15 years’ experience in nuclear waste disposal analyses

 

49Currently with the U.S. Nuclear Waste Technical Review Board.
APPENDIX A

CROSSWALK OF CONSULTATIVE RECOMMENDATIONS

TO MONITORING FACTORS LISTED IN THIS PLAN
A–1

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

MA 1, “Inventory”

1 10 CFR 61.41

10 CFR 61.42

In the FTF and HTF TERs, NRC 

recommended that DOE sample each tank 

following waste retrieval operations for the 

purpose of developing a final inventory.

Factors 1.1—Final 

Inventory and Risk 

Estimates

Factor 1.2—Residual 

Waste Sampling

Medium to High Risk

Medium Difficulty

As tanks are cleaned 

and sampled

FTF TER pgs. 107, 178

HTF TER pgs. xx, 4-36, 

4-168

2 10 CFR 61.41

10 CFR 61.42

Including ALARA

In the FTF TER, NRC recommended that 

DOE better explain intratank waste variability 

that influences waste characterization and 

uncertainty evaluation. NRC’s comments 

were expressed in the context of Tank 18F

sampling, but also pertain to future 

characterization of other tanks. Specifically, 

NRC commented on (i) lack of explanation 

regarding differences between past and 

current sample variability, (ii) potential lack of 

consideration and explanation of the 

unexpectedly high tank wall concentrations 

for Pu-238, and (iii) lack of basis for 

assumptions regarding normality of sample 

concentrations and volume estimates when 

calculating inventory multiplier to be used in 

the probabilistic analysis.

Factor 1.2—Residual 

Waste Sampling

(This recommendation 

is also related to Factor 

6.2, Model and 

Parameter Support)

Medium Risk

Medium Difficulty

As tanks are sampled 

and special analyses 

are prepared

FTF TER pgs. 46, 47, 

48, 127

3 10 CFR 61.41

10 CFR 61.42

In the TERs for FTF and HTF, NRC staff 

recommended that DOE continue to evaluate 

its HRR list and provide sufficient justification 

for any changes as additional information 

becomes available. The HRR list should be 

evaluated especially where it is used to inform 

decisions, such as the selection of 

radionuclides characterized in residual waste, 

selection of treatment technologies, and the 

screening of radionuclides for the purpose of 

detailed PA calculations.

Factor 1.1 – Final 

Inventory and Risk 

Estimates 

Factor 1.2—Residual 

Waste Sampling

Low to Medium

Risk

Low Difficulty

When developing HRR 

list and when 

characterizing residuals

FTF TER pg. 51

HTF TER pgs. xvii, 3-

20, 3-30, 3-31, 3-55

4 10 CFR 61.41

10 CFR 61.42

Including ALARA

In the FTF TER, NRC recommended that 

DOE consider improvements to residual 

material mapping and consideration of 

uncertainty in volume estimates. 

Factor 1.3—Residual 

Waste Volume

Medium Risk 

Medium Difficulty

1 to 5 Years

FTF TER pgs. 43, 48, 

79

HTF TER pgs. xvii, 3-

21, 3-25, 3-55
A–

2

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

In the HTF TER, NRC staff repeated 

recommendations related to volume 

estimations from the Inventory TRR 

(ML13085A291) for FTF Tanks 5F and 6F

(see Table B–1). 

Next tank mapping

5 10 CFR 61.41

10 CFR 61.42

In the HTF TER, the NRC staff repeated 

recommendations from the Inventory TRR 

(ML13085A291) for Tanks 5F and 6F related 

to sampling. 

Factor 1.2—Residual 

Waste Sampling

Low to Medium

Risk

Low Difficulty

When characterizing 

residuals

HTF TER pg. 3-26

6 10 CFR 61.41

10 CFR 61.42

Including ALARA

DOE indicates, in response to NRC comment 

(SRR–CWDA–2009–00054, Rev. 0), its intent 

to verify PA assumptions regarding transfer 

line inventories consistent with Section 8.2, 

“Further Work,” in DOE’s PAs (SRS–REG–

2007–00002, Rev. 1 and SRR–CWDA–2010–

00128, Rev. 1).

Factor 1.4—Ancillary 

Equipment Inventory

Low to Medium Risk

Low Difficulty

1 to 5 Years

FTF TER pg. 49

HTF TER pg. 3-24

7 10 CFR 61.41

10 CFR 61.42

In the HTF TER, NRC staff recommended 

that DOE revise its annulus inventory 

assumptions in the HTF PA if plans to clean 

the annuli of Tanks 9H, 10H, and 

14H change.

Factor 1.1—Final 

Inventory and Risk 

Estimates

Low to Medium Risk

Low Difficulty

HTF TER pg. 3-24 

8 Criterion 2—

Removal to the 

Maximum Extent 

Practical

10 CFR 61.41 

ALARA

In the FTF TER, NRC recommended DOE 

more fully evaluate costs and benefits of 

additional HRR removal, including 

(i) consideration of benefits of additional HRR 

removal over longer performance periods 

(and considering uncertainty in the timing of 

peak doses), (ii) justification for assumptions 

regarding alternative cleaning technology 

effectiveness, and (iii) comparison of costs 

and benefits of additional HRR removal to 

similar DOE activities. 

In the HTF TER, NRC indicated that DOE 

provide a clear linkage between the Criterion 

2 evaluation and the PA results, including 

consideration of the long-term risks 

associated with the HTF facility, and indicated 

Factor 1.5—Waste 

Removal As It Pertains 

to ALARA

Medium Risk

Medium Difficulty

As tanks are cleaned

FTF TER pgs. 80, 81

HTF TER pgs. xviii, 3-

52, 3-56
A–

3

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

that sufficient detail was not provided in the 

waste determination to ensure consistent 

format and appropriate content for future costbenefit analyses.

9 Criterion 2—

Removal to the 

Maximum Extent 

Practical

10 CFR 61.41 

ALARA

In the HTF TER, NRC staff indicated that it 

does not have confidence that DOE has 

adequately evaluated the risk associated with 

the projected inventory of the Tank 16H

annulus. The NRC staff recommended that 

DOE evaluate a waste release scenario due 

to groundwater in-leakage into and out of the 

annular region and contacting the highsolubility waste in the annuli of those tanks.

Factor 1.5—Waste 

Removal As It Pertains 

to ALARA

HTF TER pgs. 3-51, 3-

54

MA 2, “Waste Release”

10 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC recommended DOE 

perform experiments to verify validity of 

Geochemist’s Workbench calculations used to 

determine solubility-limiting phases, solubility 

limits, and chemical transition times. These 

experiments should study (i) pH and Eh 

evolution of the grout pore water over time, 

(ii) controlling solubility-limiting phases, and 

(iii) static and dynamic leach tests to study the 

mobility of HRRs, including consideration of 

alteration of tank residuals following chemical 

cleaning with reagents, such as oxalic acid.

In the HTF TER, NRC staff reiterates its FTF 

recommendation that DOE conduct waste 

release experiments to (i) distinguish between 

releases from high solubility compounds and 

low solubility compounds via semi-dynamic 

leach tests and (ii) determine constant 

concentrations of elements of concern under 

conditions of exposure to local groundwater 

and grout leachate via static tests.

Factor 2.1—SolubilityLimiting Phases/Limits 

and Validation

Factor 2.2—Chemical 

Transition Times

High Risk

Medium to High 

Difficulty

Short to 

Intermediate Term

FTF TER pgs. 134, 178

HTF TER pgs. xx, 4-22, 

4-84, 4-157, 4-167

11 10 CFR 61.41

10 CFR 61.42

The NRC staff recommends that DOE include 

dissolved oxygen concentrations in its 

modeling that are consistent with 

measurements of unimpacted groundwater 

across SRS or collect additional dissolved 

Factor 2.2—Chemical 

Transition Times and 

Validation

Medium to High Risk

Low to Medium 

Difficulty

HTF TER pg. 4-76
A–

4

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

oxygen measurements within the HTF at 

locations and elevations that are in closer 

proximity to the tanks.

Intermediate Term

MA 3, “Cementitious Material Performance”

12 10 CFR 61.41

10 CFR 61.42

In the HTF TER, NRC staff indicated that 

DOE should conduct a more comprehensive 

analysis of contaminant release from the 

annular regions of Types I and II tanks. Dose 

projections from the potential release of the

radionuclides in the annuli and sand pads are 

likely to be very sensitive to several key 

assumptions, which should be well supported. 

These assumptions include, but are not 

limited to, (i) the assumed release scenario; 

(ii) the chemical composition of the infiltrating 

water; (iii) the volumetric flow rate through 

grouted tanks, including shrinkage gaps and 

cracks; and (iv) the solubility of the annulus 

and sand pad waste. NRC staff also 

indicated that if the possibility of rise and fall 

of the water table in the vicinity of the Types I 

and II tanks cannot be excluded, DOE should 

evaluate a scenario where water drains from 

any gaps in the annulus and sand pad 

regions.

Factor 3.1—Hydraulic 

Performance of 

Concrete Vault and 

Annulus (As it Relates 

to Steel Liner Corrosion 

and Waste Release)

Factor 3.2—

Groundwater 

Conditioning via 

Reducing Grout

Factor 3.3—Shrinkage 

and Cracking of 

Reducing Grout

Factor 3.5—Vault and 

Annulus Sorption

Medium to High Risk 

Significance 

Medium Difficulty

Short and Intermediate 

Term

HTF TER pgs. xx, 4-75, 

4-82, 4-85, 4-168, 5-1

13 10 CFR 61.41

10 CFR 61.42

In the FTF and HTF TERs, NRC staff 

recommended that DOE consider uncertainty 

in initial conditions and performance lifetime 

of concrete vaults, because they impact 

uncertainty in the calculated steel liner failure 

times.

Factor 3.1—Hydraulic 

Performance of 

Concrete Vault and 

Annulus (as it relates to 

steel liner corrosion and 

waste release)

Medium to High Risk

Medium Difficulty

Long-Term Activity 

(need contingent on 

other factors)

FTF TER pgs. 120–128

HTF TER pg. 4-58

14 10 CFR 61.41

10 CFR 61.42

In the FTF and HTF TERs, NRC 

recommended DOE obtain greater support for 

its assumption regarding flow through the 

tank grout (i.e., fracture versus matrix) flow as 

it impacts the timing of chemical transition or 

time to release of HRRs at risk-significant 

solubility. If found to be risk significant, DOE 

should consider the appropriateness of using 

moisture characteristic curves for matrix 

Factor 3.2—

Groundwater 

Conditioning via 

Reducing Grout

Factor 3.3—Shrinkage 

and Cracking of 

Reducing Grout

Medium to High Risk

Medium to High 

Difficulty

Intermediate to 

Long-Term (need 

contingent on other 

factors)

FTF TER pgs. 126–127

HTF TER pgs.4-62, 4-

75–4-76
A–

5

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

materials to simulate fracture flow.

In the HTF TER, NRC staff recommended 

that DOE provide more support for the 

assumption that the engineered system will 

not interfere with the ability of the overlying 

grout to sufficiently condition the infiltrating 

water for the fully and partially submerged

tanks.

MA 3, “Cementitious Material Performance”

15 10 CFR 61.41

10 CFR 61.42

In the FTF and HTF TERs, NRC staff 

commented that given the wide range of 

values in the literature, NRC recommends 

DOE obtain additional support for basemat 

Kds for Pu and Np, including consideration of 

solubility affects from previous evaluations 

and representativeness of experimentally 

derived values for aged concrete.

DOE should continue to evaluate the 

appropriateness of selected transport 

parameters (e.g., cementitious material and 

soil Kds) and the selection of sorption models 

during the monitoring period.

Factor 3.5—Vault and 

Annulus Sorption

Medium to High Risk

Medium to High 

Difficulty

Intermediate Term

FTF TER pgs. 128, 178

HTF TER pgs. xx,4-79, 

4-83, 4-85, 4-168

MA 4, “Natural System Performance”

16 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC recommended DOE 

evaluate appropriateness of averaging Kds of 

multiple oxidation states to simulate the 

transport of Pu in the natural system.

Consistent with the recommendation in the 

FTF TER, in the HTF TER, NRC staff 

indicated that a more accurate representation 

of the transport of multivalent plutonium would 

be to treat the two species separately, 

assuming the oxidation state distribution 

could be reasonably quantified. 

In the HTF TER, NRC staff also questioned 

the basis for the sandy sediment Kd for 

plutonium of 650 mL/g derived from SRNL–

Factor 4.1—Natural 

Attenuation of Key 

Radionuclides

Medium to High Risk

Short-Term

Intermediate Term

FTF TER pg. 129

HTF TER pgs. xx, 4-80, 

4-114
A–

6

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

STI–2011–00672, as well as the cement 

leachate factors that were derived based on 

Hanford data (SRNL–STI–2009–00473)..

17 10 CFR 61.41

10 CFR 61.42

In the FTF and HTF TERs, NRC 

recommended that DOE continue to evaluate 

significance of calcareous zone dissolution on 

FTF flow and transport, including conduct of 

tracer studies and field mapping of seepage 

locations along Upper Three Runs Creek. 

Site-specific Kds may also need to be 

developed for the UTRA-LZ.

Factor 4.2—Calcareous 

Zone Characterization

Factor 6.2—Model and 

Parameter Support

Medium Risk

Low to Medium 

Difficulty

Next PA Updatem

(Long Term)

FTF TER pgs. 146, 147, 

149, 150, 178

HTF TER pgs. 4-115, 4-

105

MA 5, “Closure Cap Performance”

18 10 CFR 61.41

10 CFR 61.42

10 CFR 61.44

In the FTF and HTF TERs, NRC 

recommended DOE provide additional model 

support for (i) the long-term hydraulic 

conductivity of the upper foundation layer and 

lateral drainage layer and (ii) the long-term 

erosion of the topsoil layer. 

Factor 5.1—Long-Term 

Hydraulic Performance 

of the Closure Cap

Factor 5.2—Long-Term 

Erosion Protection 

Design

Low to Medium Risk

Medium Difficulty

Long-Term Activity

FTF TER pgs. 104, 105 

HTF TER pg. 4-33

19 10 CFR 61.41

10 CFR 61.42

10 CFR 61.44

In the FTF and HTF TERs, NRC 

recommended DOE conduct a preliminary 

evaluation of erosion protection designs (e.g., 

assessment of an acceptable rock source, 

and the ability of an integrated drainage 

system to accommodate design features) 

prior to completing the final closure cap 

design.

Factor 5.1—Long-Term 

Hydraulic Performance 

of the Closure Cap

Factor 5.2—Long-Term 

Erosion Protection 

Design

Low to Medium Risk

Low Difficulty

Intermediate to LongTerm Activity

FTF TER pgs. 104, 105

HTF TER pg. 4-34

MA 6, “Performance Assessment Maintenance”

20 10 CFR 61.41

10 CFR 61.42

As documented in the FTF TER, DOE will 

explain the differences in the inventory lists 

for tanks versus ancillary equipment in future 

PA documentation. DOE made this 

commitment in an NRC/DOE teleconference 

on the FTF RAIs held on June 28, 2011 

(ML111920367).

Factor 6.2—Model and 

Parameter Support

Low Risk

Low Difficulty

Next PA Update

FTF TER pg. 49

21 10 CFR 61.41

10 CFR 61.42

In the HTF TER, NRC staff repeated an FTF 

technical review report (ML13273A299) 

comment indicating that DOE should provide 

a stronger technical basis for the projected 

inventory multipliers used in the probabilistic 

analysis. Given the significant fraction of the 

Tank 5F and 6F radionuclide inventories that 

Factor 6.2—Model and 

Parameter Support

Low Risk

Low Difficulty

Next PA Update

HTF TER pgs. 3-21
A–

7

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

were underestimated, it was not clear to the 

NRC staff that the inventory multipliers should 

be biased at 100 times less and only 10 times 

higher. NRC staff went on to state that DOE 

should analyze trends in projections versus 

actual inventories by radionuclide to update 

the multiplier assumptions for the probabilistic 

analysis.

22 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC staff recommended 

DOE perform a systematic scenario analysis 

in which FEPs are identified, screened, and 

dispositioned using transparent and traceable 

documentation of the FEPs considered, the 

screening arguments, and how FEPs are

implemented in the models to support future 

waste determination efforts. DOE performed 

a FEPs analysis to support the final waste 

determination for FTF. NRC staff reviewed 

the FEPs analysis and documented the 

results of its review in a technical review 

report (ML13277A063; see also Table B–1)

In the HTF TER, similar to the findings in the 

technical review report for FTF, NRC staff 

recommended that DOE include subject 

matter experts on the screening team in the 

specific engineering and scientific disciplines 

that are pertinent to the professional 

judgments being made. NRC staff noted that 

the screening documentation could be more 

transparent. The NRC staff also 

recommended that DOE improve the 

transparency and traceability of its 

implementation of FEPs to ensure 

comprehensive, accurate, and traceable links 

to clear descriptions of how included FEPs 

are actually implemented in the HTF PA.

Factor 6.1—Scenario 

Analysis

Low to Medium Risk

Medium Difficulty

Next PA Update

FTF TER pgs. 12, 14, 

92, 93, 95, and 178

HTF TER pgs. 4-18–4-

21, and 4-24

23 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC staff recommended 

DOE consider uncertainty in steel liner 

performance, including more aggressive 

service conditions and corrosion mechanisms 

Factor 6.2—Model and 

Parameter Support

Medium to High Risk

Medium to High 

Difficulty

FTF TER pg. 121

HTF TER pgs. 4-58, 4-

60
A–

8

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

than assumed in the PA, as well as a patch 

model for waste release, if deemed to be risk 

significant.

In the HTF TER, similar to previous FTF 

consultative comments, NRC staff also 

questioned DOE’s assumed time-invarient 

oxygen diffusivity of 10−6 cm2/s given 

expected degradation of concrete vaults over 

time and potential presence of bypassing 

pathways through the system.

Long-Term Activity 

(need contingent on 

other factors)

24 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC recommended DOE 

obtain additional support for probabilistic 

parameter distributions, including solubility 

limiting phases, cement Kds (based on 

sediment variability), chemical transition 

times, basemat bypass, and configuration

probability.

In the HTF TER, NRC staff recommended 

DOE incorporate in probability distributions 

“pessimistic” values that exceed base case 

solubility limits and that DOE obtain support 

for the solubilities and probability

assignments.

Factor 6.2—Model and 

Parameter Support

Medium Risk

Medium to High 

Difficulty

Intermediate-Term

FTF TER pgs. 130–132

HTF TER pg. 4-73

25 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC recommended DOE 

acquire FTF specific data to support material 

property assignments, including hydraulic 

conductivity, moisture characteristic curves, 

and Kds.

Factor 6.2—Model and 

Parameter Support

Low to Medium Risk

Medium Difficulty

Long-Term

FTF TER pgs. 128–129

26 10 CFR 61.41

10 CFR 61.42

10 CFR 61.44

In the HTF TER, NRC staff recommended 

that DOE provide additional model support to 

understand the effects of perimeter infiltration 

and focused infiltration in the drainage valley 

between the East and West Caps on nearfield and far-field groundwater flow patterns 

and radionuclide transport. The analysis 

should include appropriate refinement of the 

grid cells receiving recharge and a wellsupported value for the diversion of flow.

Factor 6.2—Model and 

Parameter Support 

Low Risk Significance

Medium Difficulty

Prior to final closure

HTF TER pgs. 4-31, 4-

33–4-34

27 10 CFR 61.41 In the FTF TER, NRC staff indicated that it Factor 6.2—Model and Low to Medium Risk FTF TER pg. 127
A–

9

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

10 CFR 61.42 would monitor DOE’s efforts to study the 

impact of cement leachate on radionuclide 

mobility.

NRC reviewed cement leachate factors 

utilized in the HTF PA and listed several 

technical concerns in the HTF TER, most 

notably the lack of site-specific information 

and basis for some of the factors.

Parameter Support

Medium Difficulty

Long-Term

HTF TER pg. 4-80

28 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC staff recommended that 

DOE address the significant amount of 

dispersion evident in its near-field and far-field 

PORFLOW models, including evaluation of 

the need for mesh refinement to ensure that 

contaminant plumes are not artificially 

dispersed over the volume of the cells in the 

far-field model. Nonphysical dispersion may 

be attributable to large changes in adjacent 

element size and large differences in element 

sizes between the vadose zone and far-field 

models. DOE should evaluate the adequacy 

of the time discretization of the model(s) for 

high mobility constituents such as Tc-99.

Factor 6.2—Model and 

Parameter Support

Medium Risk

Low to Medium 

Difficulty

Next PA Update

FTF TER pgs. 149–150

29 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC recommended that 

DOE evaluate the appropriateness of the 

assumed level of physical dispersion in the 

FTF model (i.e., dispersivities).

Factor 6.2—Model and 

Parameter Support

Medium Risk

Low to Medium 

Difficulty

Next PA Update

FTF TER pgs. 149, 178

30 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC staff recommended 

DOE provide greater transparency and 

traceability of far-field model calibration, 

including consideration of more extensive 

calibration focused strictly on the area of

interest.

In the HTF TER, NRC staff made 

recommendations similar to those in the FTF 

TER, but more strongly indicated that the 

model may not be sufficiently calibrated local 

to HTF, and recommended specifically that 

Factor 6.2—Model and 

Parameter Support

Medium Risk

Medium to High 

Difficulty

Next PA Update

FTF TER pg. 178

HTF TER pgs. xx, 4-

107–111, 4-115, 4-168
A–10

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

DOE study uncertainty in calibration targets 

and provide support for hydraulic conductivity 

assignments (Kh was artificially lowered in 

elliptical regions during the calibration 

process), including consideration of 

conducting pumping tests to provide support 

for the model and model parameters.

31 10 CFR 61.41

10 CFR 61.42

NRC staff indicated in the FTF TER that 

Gordon Aquifer concentrations should not be 

used to demonstrate compliance with the POs 

if higher concentrations are observed in 

another aquifer that can support groundwaterdependent pathways. These statements 

were repeated in the HTF TER.

Factor 6.2—Model and 

Parameter Support

Medium Risk

Low Difficulty

Next PA Update

FTF TER pgs. 147–148

HTF TER pg. 4-113

32 10 CFR 61.41

10 CFR 61.42

In the HTF TER, NRC staff recommended 

that DOE evaluate the compliance boundary 

and loading of the contaminant source cells 

(i.e., tank cells in the far-field model) to 

ensure that the dose estimates are not 

significantly underestimated. 

Factor 6.2—Model and 

Parameter Support

Low to Medium Risk

Low Difficulty

Next PA Update

HTF TER pg. 4-115

33 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC recommended DOE 

evaluate plant transfer factor uncertainty in 

future updates to its PA. DOE should 

consider the appropriateness of excluding 

common vegetable types in its assignment of 

plant transfer factors (DOE only considers 

root vegetable data) based on production 

data rather than household data that might be 

more appropriate for a resident gardener.

In the HTF TER, NRC staff indicated that 

DOE addressed the use of root vegetable 

transfer factors; however, uncertainty in plant 

transfer factors was not addressed.

Factor 6.2—Model and 

Parameter Support

Low to Medium Risk

Medium difficulty

Next PA Update

FTF TER pg. 153

HTF TER pg. 4-117

34 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC staff recommended that 

DOE evaluate the appropriateness of 

assumptions related to drinking water 

consumption in future updates to its PA, such 

as partitioning consumption rates based on 

use of both bottled and community water. 

Biosphere parameters should be reasonably 

Factor 6.2—Model and 

Parameter Support

Low to Medium Risk

Low Difficulty

Next PA Update

FTF TER pgs. 153–154

HTF TER pg. 4-117
A–11

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

conservative and reflect the behavior of the 

average member of the critical group. NRC 

staff reiterated the FTF TER recommendation 

in the HTF TER.

35 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC staff indicated that DOE 

better assess uncertainty in the timing of peak 

dose, given the inherent level of uncertainty 

associated with predicting doses over tens of 

thousands of years. Additionally, NRC staff 

indicated that key parameters, such as steel 

liner failure times and chemical transition 

times, may be overly constrained.

Factor 6.2—Model and 

Parameter Support

Medium to High Risk

Medium Difficulty

Next PA Update

FTF TER pgs. 167, 168, 

169

36 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC staff recommended 

DOE provide additional support for the 

likelihood of its base case or expected Case 

A. 

In the HTF TER, NRC staff went on to state 

the NRC staff thinks that additional 

information is needed to support the 

compliance case, Case A. Ideally, supporting 

information would be in the form of additional 

experimental or field data, natural analogs, 

peer review, expert elicitation, and other 

forms of model support. NRC staff stated that 

without this additional model support, it would 

be difficult to argue the relative likelihood of 

the base case compared to alternative cases.

Additionally, NRC staff indicated that the 

uncertainty analysis results not be used to 

demonstrate compliance with the POs 

because (i) there is limited support for the 

base case and (ii) there is limited support for 

the assignment of the likelihood of alternative 

cases and consequently, the averaging of 

alternative cases in the “All Cases” model. 

NRC staff recommended that DOE present 

the results of alternative cases individually 

and provide qualitative information regarding 

the likelihood of alternative cases.

Factor 6.2—Model and 

Parameter Support

Medium to High Risk

Medium to High 

Difficulty

Next PA Update

FTF TER pgs. 167, 168, 

170

HTF TER pgs. 4-157, 4-

161
A–12

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

Finally, NRC staff indicated that DOE should 

use the results of its probabilistic analysis to 

inform areas where additional model support 

is needed.

37 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC staff recommended 

DOE improve transparency and 

documentation of its benchmarking process. 

NRC recommends DOE apply a more 

methodical and systematic approach to the 

benchmarking process in future updates to its 

PA. In the HTF TER, NRC staff also noted 

that DOE could improve its benchmarking 

process.

Factor 6.2—Model and 

Parameter Support

Medium Risk

Medium Difficulty

Next PA Update

FTF TER pg. 171

HTF TER pg. 4-166

38 10 CFR 61.42 In the HTF TER, NRC staff noted that due to 

significant differences between the GoldSimTM

and PORFLOWTM modeling results, the NRC 

staff plans to continue to evaluate the 

PORFLOWTM modeling assumptions and 

results for the compliance case (Case A) 

during the monitoring period to provide 

confidence that the timing of peak dose is not 

artificially delayed. This applies to the 

inadvertent intruder analysis.

Factor 6.2—Model and 

Parameter Support

Medium Risk 

Medium Difficulty

Next PA Update

HTF TER pg. 4-125

39 10 CFR 61.41

10 CFR 61.42

In the FTF TER, NRC staff suggested that 

DOE consider consistency between the 

plotting interval and calculation time step size. 

DOE should also correct errors in its 

probabilistic assessment (e.g., porosity of 1 × -20). 

Factor 6.2—Model and 

Parameter Support

Low to Medium Risk

Low Difficulty

Next PA Update

FTF TER pgs. 147–148

40 10 CFR 61.41

10 CFR 61.42

NRC made a general comment that DOE 

could improve its parameter distribution 

assignments, hybrid modeling approach, 

benchmarking process, and evaluation and 

interpretation of probabilistic modeling results. 

With respect to parameter distributions, NRC 

included several items in its open items 

database (see Appendix B in ML12212A192), 

most of which are listed in other 

recommendations, with the exception of 

probability of basemat bypass flow.

Factor 6.2—Model and 

Parameter Support

Medium Risk

Medium Difficulty

Next PA Update

FTF TER pg. 177
A–13

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

MA 7, “Protection of Individuals During Operations”

41 10 CFR 61.43 DOE can demonstrate compliance with

protection of individuals during operations.

DOE provides adequate information that

individuals will be protected during

operations.

Factor 7.1—Protection 

of Workers During 

Operations 

Factor 7.2—Air 

Monitoring

Low Risk

Low to Medium 

Difficulty

Ongoing

FTF TER pg. 174

HTF TER pg. 4-161

MA 8, “Site Stability”

42 10 CFR 61.44 In the FTF and HTF TERs, NRC staff 

recommended DOE continue to evaluate 

closure cap settlement and stability, including 

consideration of (i) increased overburden from 

the tank grout and closure cap on settlement 

and (ii) potential for subsidence associated 

with ongoing dissolution of calcareous 

sediment in the Santee Formation.

Factor 8.1—Settlement Medium Risk

Medium to High 

Difficulty

Intermediate-Term

FTF TER pg. 176

HTF TER pg. 4-164

43 10 CFR 61.41

10 CFR 61.42

10 CFR 61.44

In the FTF and HTF TERs, NRC staff 

concluded that assumed long-term 

compressive strength of the grout monolith is 

not adequately supported and may be 

optimistic based on observations of vault 

cracks, discussed in TER Section 4.2.9.1 

(ML112371751). While cracking of the vault 

concrete and tank grout is not expected to 

result in significant structural tank collapse, 

the integrity of the vault concrete and tank 

grout is important to steel liner performance 

and waste release.

Factor 8.1—Settlement Medium Risk

Medium to High 

Difficulty

Intermediate-Term

FTF TER pg. 175

HTF TER pg. 4-163

Other TER Recommendations

44 Criterion 2—

Technology 

Selection

In the FTF TER, NRC staff recommended

DOE specifically consider and evaluate HRR 

removal in its technology selection and 

effectiveness evaluations consistent with the 

NDAA.

In the HTF TER, NRC staff recommended

that DOE provide more emphasis on removal 

of HRR in its technology selection process 

and provide a clear linkage between the HTF 

PA results, including information regarding the

TER 

Recommendation Only

NA FTF TER pgs. 55, 56, 

79

HTF TER pg. xviii

HTF TER pgs. 3-55, 3-

38
A–14

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

long-term risks associated with the HTF 

facility, and the demonstration that HRRs 

have been removed to the MEP per Criterion 

2.

45 Criterion 2—

Technology 

Selection

In the FTF TER, NRC staff recommended

DOE continuously evaluate new technologies, 

participate in technology exchanges, and not 

default to previous evaluations for technology

selection.

In the HTF TER, NRC staff recommended

that DOE continue evaluating new 

technologies for future use as tank closure 

progresses, especially if previously used 

technologies are no longer practical to use. 

Furthermore, for those tanks in which 

conditions are dissimilar (e.g., Tank 48), the 

NRC staff would expect DOE to reevaluate 

technologies as opposed to relying on 

previously performed technology evaluations.

The NRC staff also recommended that DOE 

continue its efforts to participate in technology 

exchanges so that it can stay informed of 

potential new cleaning technologies. New 

technologies or improvements to current 

technologies should be fully considered in the 

selection process for future tank cleaning. 

DOE should try to optimize operational 

parameters for existing technologies and 

technologies to be developed in the future to 

ensure that removal of HRRs is not hampered 

or made more difficult because of poor 

planning or lack of investment in waste 

characterization.

TER 

Recommendation Only

NA FTF TER pgs. 77, 78, 

79

HTF TER pgs. xviii, 3-

55, 3-37, 3-38, 3-49, 3-

51, 3-52

46 Criterion 2 –

Technology 

Implementation and 

Optimization

In the HTF TER, NRC staff indicated that 

DOE’s approach to optimization of technology 

through sampling and monitoring during 

cleaning should be documented.

The NRC staff also recommended that DOE 

TER 

Recommendation Only

NA HTF TER pgs. 3-49, 

xviii, 3-56
A–15

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

consider how it might better assess and 

optimize the effectiveness of selected 

technologies (e.g., obtain better baseline 

information).

47 Criterion 2 –

Technology 

Implementation and 

Optimization

In the HTF TER, NRC staff noted that, 

although the results from mapping contain 

uncertainties, performing the tank mapping 

methodology during multiple cleaning phases 

will provide additional information on the 

effectiveness of specific technologies. As 

such, the NRC staff recommended that DOE 

perform the tank mapping consistently and as 

frequently as practical throughout the 

cleaning process.

TER 

Recommendation Only

NA HTF TER pg. 3-49

48 Criterion 2 –

Technology 

Implementation and 

Optimization

In the HTF TER, NRC staff recommended 

that DOE should obtain better baseline 

information from which it could better assess 

oxalic acid effectiveness.

TER 

Recommendation Only

NA HTF TER pgs. 3-49, 3-

51

49 Criterion 2 –

Technology 

Implementation and 

Optimization

In the HTF TER, NRC staff supported DOE’s 

efforts to re-evaluate oxalic acid cleaning 

against downstream impacts to determine the 

future role of oxalic acid cleaning, as opposed 

to relying on previous evaluations of oxalic 

acid technology.

TER 

Recommendation Only

NA HTF TER pg. 3-51

50 Criterion 2 –

Technology 

Implementation and 

Optimization

In the HTF TER, NRC staff noted that each 

final characterization should be accompanied 

by a Technical Task Request and a Quality 

Assurance and Quality Control Plan.

TER 

Recommendation Only

NA (HTF TER pg. 3-51)

51 Criterion 2 –

Technology 

Implementation and 

Optimization

In the HTF TER, NRC staff indicated that to 

help overcome the limitations encountered 

with cleaning Tanks 5F and 6F for the 

cleaning of future tanks, the NRC staff 

recommends that DOE evaluate the 

effectiveness of the SMPs with respect to bulk 

sludge removal versus residual heel removal. 

The NRC staff also recommends that DOE 

compare the efficiency and effectiveness of 

the SMP to previously used technologies or 

readily available technologies.

TER 

Recommendation Only

NA HTF TER pg. 3-50

52 Criterion 2—

Removal to the 

In the FTF TER, the NRC staff recommended 

that DOE include more specificity in its 

TER 

Recommendation Only

NA FTF TER pgs. 77, 79–

80
A–16

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

Maximum Extent 

Practical

Criterion 2 –

Technology 

Implementation and 

Optimization

process for determining HRRs are removed to 

the maximum extent practical, including 

(i) defining the term end states versus 

removal goals and (ii) clarifying when 

conditions are sufficiently similar to warrant 

use of a previous technology evaluation. 

NRC staff also recommended that DOE 

continue to better define the documented 

process to be used to demonstrate removal to 

the MEP to ensure consistent (nonarbitrary) 

application of the criterion.

In the HTF TER, NRC staff noted that 

Appendix B of the draft basis for the waste 

determination for HTF (DOE/SRS–WD–2013–

001, Rev. 0) outlines a general approach to 

demonstrate that the HRRs will be removed to 

the MEP. However, DOE could still improve 

the standardization of metrics for determining 

that the anticipated end states have been 

reached.

HTF TER pgs. xviii, 3-

51

53 Criterion 2—

Removal to the 

Maximum Extent 

Practical

In the HTF TER, NRC staff noted that if oxalic 

acid is not available to be used for cleaning 

future tanks and a technology with similar 

proven effectiveness is not used as an 

alternative, DOE may need to reconsider the 

validity of assuming that the cooling coil and 

tank wall surface inventory is negligible.

TER 

Recommendation Only

NA HTF TER pgs. 3-21, 3-

56

54 Criterion 3—Waste 

Classification

In the HTF TER, NRC staff recommended 

that DOE should develop separate sitespecific factors for risk-significant annular 

waste versus tank waste sources in the 

future. Annular and tank sources would then 

be separately compared to adjusted waste 

classification concentration limits to determine 

the classification of HTF components.

TER 

Recommendation Only

NA HTF TER pg. 4-7

55 Criterion 2—

Removal to the 

Maximum Extent 

Practical

In the FTF TER, NRC recommended DOE 

more fully evaluate or document its 

consideration of alternatives to additional 

HRR removal, including (i) modifications to 

existing technologies (e.g., upgraded Mantis 

TER 

Recommendation Only

NA FTF TER pgs. 79, 81
A–17

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

or enhanced chemical cleaning); 

(ii) modification to tank system components 

(e.g., installation of new risers or removal of 

equipment from existing risers); (iii) sequential 

cleaning (e.g., sequencing of mechanical and 

chemical technologies in Tank 18F); and (iv) 

alternative cleaning technologies (e.g., 

alternative reagents to leach HRRs out of 

residual heels).

56 Criterion 2—

Removal to the 

Maximum Extent 

Practical

Criterion 2 –

Technology 

Implementation and 

Optimization

In the FTF TER, NRC recommended that 

DOE better quantify technology effectiveness. 

For example, DOE should better characterize 

waste and residual tank inventory prior to 

deployment of cleaning technologies to better 

assess effectiveness.

In the HTF TER, NRC staff recommended

that, to the extent practical, DOE consider 

obtaining data on HRR inventories prior to 

and following major cleaning campaigns 

(e.g., before and after treatment of Type I 

tanks with oxalic acid) to provide 

effectiveness measurements for chemical 

cleaning and mechanical feed-and-bleed.

TER 

Recommendation Only

NA FTF TER pgs. 77, 79

HTF TER pg. 3-51

57 Criterion 2—

Removal to the 

Maximum Extent 

Practical

In the HTF TER, NRC staff noted that given 

the potential risk significance of the waste 

remaining in the Tank 16H annulus, the NRC 

staff recommends that DOE more fully 

evaluate the practicality of additional 

radionuclide removal from the Tank 16H

annulus versus the long-term benefit of 

reduced risk considering uncertainty in the 

releases of radionuclides from the Tank 16H

annulus. While DOE’s HTF PA demonstrates 

that the risk from waste remaining in the 

annulus is reasonable, alternative waste 

release models may lead to higher risk 

estimates.

NRC staff went on to note that at this stage, 

DOE has provided a rough order of 

TER 

Recommendation Only

HTF TER pgs. xviii, 3-

56
A–18

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

magnitude cost-benefit analysis of additional 

HRR removal from the Tank 16H annulus to 

the NRC staff (U–ESR–H–00107, Rev. 0). 

The NRC staff acknowledges that DOE is still 

preparing the final removal report and 

recommends that DOE provide a more 

detailed cost benefit analysis to support the 

Criterion 2 demonstration for Tank 16H in the 

final removal report. NRC staff indicated that 

it would like to obtain a copy of the final 

removal report when it is complete.

58 Criterion 2 –

Technology 

Implementation and 

Optimization

In the HTF TER, NRC staff noted that DOE 

improved the operating plan for Tank 12H by 

requiring the availability of the transfer receipt 

tank to be confirmed prior to acid addition. 

The NRC staff encourages DOE to continue 

to analyze the lessons learned from these

prior cleaning campaigns to prevent 

limitations of the liquid waste system from 

unexpectedly influencing the effectiveness of 

future cleaning campaigns.

TER 

Recommendation Only

HTF TER pgs. xviii, 3-

52

*The table is organized by Monitoring Area. The crosswalk from the consultative recommendation/comment to MFs is provided in the column “Monitoring 

Factor.”

†NRC notes that NRC monitoring pertains to assessment of compliance with the POs in 10 CFR Part 61, Subpart C. Thus, comments or recommendations 

related to the NDAA criterion that waste has had HRR removed to the maximum extent practical or what NRC refers to as Criterion 2 under the NDAA is only 

monitored if the same comment or recommendation applies to the ability of the disposal facility to meet Criterion 3: compliance with the POs in 10 CFR Part 61, 

Subpart C, including the ALARA requirements found in 10 CFR 61.41 and 61.43. If Criterion 2 recommendations in NRC’s TER are not tied to Criterion 3, such 

as ALARA, then the TER recommendations are not carried forward into monitoring.

ALARA–As Low As Is Reasonably Achievable, CFR–Code of Federal Regulations, DOE–The U.S. Department of Energy, FEP–Features, Events and 

Processes, FTF–F-Tank Farm, HRR–Highly Radioactive Radionuclide, HTF–H-Tank Farm, Kd–Distribution Coefficient, Kh–Hydraulic Conductivity, MEP–

Maximum Extent Practical, NDAA–Ronald Reagan National Defense Authorization Act of 2005, NRC–The U.S. Nuclear Regulatory Commission, PA–

Performance Assessment, PO–Performance Objective, RAI–Request for Additional Information, SMP–Submersible Mixing Pump, SRS–Savannah River Site, 

TER–Technical Evaluation Report, TRR–Technical Review Report, UTRA–Upper Three Rivers Aquifer, 

References:

DOE/SRS–WD–2013–001, Rev. 0. “Draft Basis for Section 3116 Determination for Closure of H-Tank Farm at the Savannah River Site.” Washington, DC: 

U.S. Department of Energy. 2013.

SRR–CWDA–2009–00054. “Comment Response Matrix for Nuclear Regulatory Commission (NRC) Comments on the F-Tank Farm Performance 
A–19

Table A–1. Crosswalk Between Consultative Review Comments, Recommendations, and Monitoring Areas/Factors*

ID

Performance 

Objective Recommendation or Comment Monitoring Factor†

Risk, Difficulty, and 

Timing Ranking TER Page No.

Assessment.” Aiken, South Carolina: Savannah River Remediation, LLC, Closure and Waste Disposal Authority. 2010.

SRS–REG–2007–00002. Rev. 1. “Performance Assessment for the F-Tank Farm at the Savannah River Site.” Aiken, South Carolina: Savannah River 

Remediation, LLC, Closure and Waste Disposal Authority. 2010.

SRNL–STI–2011–00672, Rev. 0. “Variability of Kds Values in Cementitious Materials and Sediments.” Almond, P.M., D.I. Kaplan, and E.P. Shine. Aiken, South 

Carolina: Savannah River National Laboratory. 2012.

SRNL–STI–2009–00473. “Geochemical Data Package for Performance Assessment Calculations Related to the Savannah River Site, Savannah River National 

Laboratory.” Aiken, South Carolina: Savannah River Site. 2010.

Shaffner, J. “Summary of Teleconference Between U.S. Nuclear Regulatory Commission Staff and U.S. Department of Energy Representatives Concerning 

Responses to RAIs Related to Closure of F-Tank Farm, Savannah River Site.” Memorandum to File PROJ0734. ML111920367. Washington, DC: U.S. 

Nuclear Regulatory Commission. 2011.

ML112371751. “Technical Evaluation Report for F-Area Tank Farm Facility, Savannah River Site, South Carolina—Final Report.” Washington, DC: 

U.S. Nuclear Regulatory Commission. 2011.

ML12212A192. “U.S. Nuclear Regulatory Commission Plan for Monitoring Disposal Actions Taken by the U.S. Department of Energy at the Savannah River 

Site F-Area Tank Farm Facility in Accordance With the National Defense Authorization Act for Fiscal Year 2005.” Washington DC: U.S. Nuclear Regulatory 

Commission. 2013.

ML13277A063. “Technical Review: U.S. Department of Energy Documentation Related to Features, Events, and Processes in the F-Area Tank Farm 

Performance Assessment.” Memorandum from C. Grossman (NRC) to G. Suber (NRC). Washington, DC: U.S. Nuclear Regulatory Commission. 2014.

ML14094A496. “Technical Evaluation Report for H-Area Tank Farm Facility, Savannah River Site, South Carolina—Final Report.” Washington, DC: U.S. 

Nuclear Regulatory Commission. 2014.

U–ESR–H–00107. Rev. 0. "Tank 16H: Preliminary Evaluation of Cessation of Annulus Waste Removal Activites.” Aiken, South Carolina: Savannah River 

Remediation, LLC, Closure and Waste Disposal Authority. 2013.
A–20

Table A–2. Crosswalk of DOE’s Performance Assessment Maintenance Items to Monitoring Factors in This Plan

DOE PA 

Maintenance

Program Section 

(s)

DOE PA Maintenance

Program Title

Monitoring Factor

3.1.1 

4.1.1

Maintain F- and H-Area Tank Farm 

Performance Assessment Control 

through Unreviewed Waste 

Management Question Process

This general technical support activity can support any monitoring factor listed

in this plan but is not specific to any single monitoring factor or set of 

monitoring factors.

3.1.2

4.1.2

Prepare Annual Performance 

Assessment Maintenance Program 

Implementation Plan

This general technical support activity can support any monitoring factor listed

in this plan but is not specific to any single monitoring factor or set of 

monitoring factors.

3.1.3

4.1.3

Provide General Technical Support on 

F-and H-Area Tank Farm Performance 

Assessment Issues

This general technical support activity can support any monitoring factor listed

in this plan but is not specific to any single monitoring factor or set of 

monitoring factors.

3.1.4

4.1.4

Develop and Maintain Performance 

Assessment Model Archive and Revision 

Control 

Facilitates NRC staff’s review of the PAs.

3.2.2

4.2.2

F- or H-Area Tank Farm Special 

Analyses

Monitoring Factor 1.1, Final Inventory and Risk Estimates

Monitoring Factor 1.4, Ancillary Equipment Inventory

3.2.1

4.2.3

Prepare Out-Year F- or H-Area Tank 

Farm Performance Assessment 

Revisions

Monitoring Factor 6.1, Scenario Analysis

Monitoring Factor 6.2, Model and Parameter Support

Monitoring Factor 6.3, F-Tank Farm Performance Assessment Revisions

3.3.2

4.3.1

To Be Determined Out-Year HTF 

Testing & Research Activities

No specific plans listed in SRR–CWDA–2014–00108), but could include:

Monitoring Factor 2.2, Chemical Transition Times

Monitoring Factor 3.2, Groundwater Conditioning via Reducing Grout

Monitoring Factor 3.3, Shrinkage and Cracking of Reducing Grout

Monitoring Factor 3.5, Vault and Annulus Sorption

Monitoring Factor 4.1, Natural Attenuation of Key Radionuclides

Monitoring Factor 4.2, Calcareous Zone Characterization

Monitoring Factor 5.1, Long-Term Hydraulic Performance

Monitoring Factor 5.2, Long-Term Erosion Protection Design 

Monitoring Factor 6.1, Scenario Analysis

Monitoring Factor 6.2, Model and Parameter Support

Monitoring Factor 8.1, Settlement

3.3.1.1 Waste Release Studies Monitoring Factor 2.1, Solubility Limiting Phases/Limits and Validation

2.3.1.1 Measurement of Distribution Coefficients 

in SRS Subsurface Sediments

Monitoring Factor 4.1, Natural Attenuation of Key Radionuclides

Monitoring Factor 6.2, Model and Parameter Support
A–21

Table A–2. Crosswalk of DOE’s Performance Assessment Maintenance Items to Monitoring Factors in This Plan

DOE PA 

Maintenance

Program Section 

(s)

DOE PA Maintenance

Program Title

Monitoring Factor

2.3.2.2 Long-Term Radiological Lysimeter 

Program

Monitoring Factor 3.5, Vault and Annulus Sorption

Monitoring Factor 4.1, Natural Attenuation of Key Radionuclides

2.3.2.1 Measurement of Unsaturated 

Permeability of Fractured Saltstone

Monitoring Factor 3.2, Groundwater Conditioning via Reducing Grout 

Monitoring Factor 3.3, Shrinkage and Cracking of Reducing Grout

2.3.2.3 Studies Related to Cementitious 

Materials Degradation Due to Radiation

Damage

Monitoring Factor 3.4, Grout Performance

2.3.2.4 Closure Cap Drainage Layer Long-Term 

Performance

Monitoring Factor 5.1, Long-Term Hydraulic Performance of the

Closure Cap

Monitoring Factor 5.2, Long-Term Erosion Protection Design

Monitoring Factor 5.3, Closure Cap Functions That Maintain

Doses ALARA

ALARA–As Low As Is Reasonably Achievable, DOE–U.S. Department of Energy, PA–Performance Assessment, HTF–H-Tank Farm, NRC–U.S. Nuclear 

Regulatory Commission

Reference:

SRR–CWDA–2014–00108, Rev. 0. “Savannah River Site Liquid Waste Facilities Performance Assessment Maintenance Program, FY2015 Implementation 

Plan.” Aiken, South Carolina: Savannah River Remediation, Savannah River Site. January 2015.
APPENDIX B

CROSSWALK BETWEEN TECHNICAL REVIEW REPORTS AND 

MONITORING FACTORS
B

–1

Table B–1. Crosswalk Between Technical Review Report Findings and Monitoring Factors

ID Technical Review Report (TRR) Finding TRR Monitoring Factor Related Monitoring Factor

New Monitoring 

Factor

Tanks 18F and 19F Special Analysis (ML13100A230)

1 Although the Tanks 18F and 19F Special Analysis presented 

useful information on the impact of changes to solubility and Kd

on the results of the analysis, the uncertainty and sensitivity 

analysis was not comprehensive and primarily focused on factors 

that served to decrease the risk. For example, the impact of 

preferential flow through cracks and fractures resulting in faster 

chemical transition times, water table rise,

1 and existence of 

more mobile forms of Pu were not considered in the analysis. 

DOE should provide sufficient information to support its base 

case (or rule out these processes) or provide adequate 

representations of these processes in performance assessment 

calculations used to support the compliance demonstration. 

Furthermore, updated geochemical modeling for Pu showed that 

Pu could be released much earlier than assumed in the FTF PA, 

upon transition to Oxidized Region II. Experimental support for 

updated solubility modeling is also needed. The TRR also 

expressed potential issues with the Pu Kd analysis, SRNL–STI–

2011–00672. Issues with the Pu Kd analysis were more fully 

discussed in the HTF TER (ML14094A496).

Monitoring Factor 1.1, 

“Final Inventory and Risk 

Estimates” 

Monitoring Factor 2.1,

“Solubility Limiting 

Phases/Limits and Validation”

Monitoring Factor 2.2, 

“Chemical Transition Times”

Monitoring Factor 3.1, 

“Hydraulic Performance of 

Concrete Vault and Annulus”

Monitoring Factor 3.2, 

“Groundwater Conditioning

via Reducing Grout”

Monitoring Factor 3.3, 

“Shrinkage and Cracking of 

Reducing Grout”

Monitoring Factor 4.1, 

“Natural Attenuation of Key 

Radionuclides” 2

Monitoring Factor 4.3, 

“Environmental Monitoring”

Tanks 5F and 6F Special Analysis (ML13273A299)

2 DOE should evaluate whether it has appropriately managed 

inventory uncertainty.

DOE should provide a stronger technical basis for projected 

inventory multipliers.

Additional information related to the Niobium distribution 

coefficient, or Kd, is needed to have reasonable assurance that 

DOE disposal actions at the FTF will meet the POs in 10 CFR 

Part 61, Subpart C.

Monitoring Factor 1.1, 

“Final Inventory and Risk 

Estimates”

Monitoring Factor 4.1, 

“Natural Attenuation of Key 

Radionuclides”2

See Monitoring Factors listed 

under ID 1

Old Monitoring 

Factor 4.1, “Natural 

Attenuation of Pu” 

will be expanded to 

include natural 

attenuation or Kd for 

Nb and other key

radionuclides.

 

1With respect to water table rise, NRC staff was concerned with both (i) accelerated corrosion of the steel liner and (ii) early release from Tank 18. Accelerated 

corrosion from water table rise is considered in Monitoring Factor 3.1, “Concrete Vault Performance.” Early release from the tanks due to water table rise is 

considered under Monitoring Factor 3.2, “Groundwater Conditioning.”

2 MF 4.1 in the FTF Monitoring Plan was named, “Natural Attenuation of Pu”. MF 4.1 has been broadened to include other key radionuclides.
B

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Table B–1. Crosswalk Between Technical Review Report Findings and Monitoring Factors

ID Technical Review Report (TRR) Finding TRR Monitoring Factor Related Monitoring Factor

New Monitoring 

Factor

Finally, technical concerns identified in the NRC staff’s review of 

the Tanks 18F and 19F Special Analysis (ML13100A230) are 

also applicable to the Tanks 5 and 6 Special Analysis and are 

not repeated in this report.

Tanks 5F and 6F Final Inventory Development (ML13085A291)

3 With regard to sample analysis, NRC staff identified the following 

issues:

DOE should consider, in its tank sampling design, historical 

information on tank waste receipts and information related to the 

alteration and redistribution of waste due to cleaning operations 

that may impact horizontal and vertical waste heterogeneity.

 DOE should evaluate the option to composite samples within 

segments (or strata) to preserve information about segment (or 

strata) variance.

 DOE should evaluate and present information on the relative 

contributions of various forms of uncertainty in its estimation of 

mean tank concentrations.

 DOE should clarify the statistical approach used to estimate 

the UCL95 (e.g., treatment of all nine measurements as 

independent when computing the UCL95).

 DOE should also consider how it can better assure sample 

representativeness by improving tank sampling designs, 

collection tools, and instructions.

Alternatively, DOE could manage sampling and analysis 

uncertainty through use of estimates that clearly err on the side 

of higher inventories. These technical concerns do not need to 

be addressed until the next tank sampling effort is conducted.

Ancillary equipment inventory verification and support for 

changes to the HRR list were also mentioned. 

Tanks 5F and 6F Final Inventory Development (continued’)

With regard to volume estimation, NRC staff identified the 

following issues:

 DOE should better understand the accuracy of mapping team 

height estimates through additional field validation activities for a 

range of solid material heights.

Monitoring Factor 1.2, 

“Residual Waste

Sampling”

Monitoring Factor 1.3, 

“Residual Waste Volume”

Monitoring Factor 1.1, “Final 

Inventory and Risk Estimates”

Monitoring Factor 1.4, 

“Ancillary Equipment 

Inventory”

Issues in red text in 

column 2 are 

incorporated into 

Monitoring Factor 

1.2, “Residual Waste 

Sampling,” or 

Monitoring Factor 

1.3, “Residual Waste 

Volume.” These 

issues are also 

discussed in the HTF 

TER.
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Table B–1. Crosswalk Between Technical Review Report Findings and Monitoring Factors

ID Technical Review Report (TRR) Finding TRR Monitoring Factor Related Monitoring Factor

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Factor

 DOE should clearly communicate how it determines the size of 

areas to be mapped and how it manages uncertainty related to 

height estimates for discretized areas in its deterministic 

analysis. Likewise, DOE should clarify how it represents 

uncertainty in the assignment of high and low end heights to 

these areas (e.g., does it use a height that is clearly below/above 

the nonuniform surface of the delineated areas?).

 DOE should consider uncertainty in the volume estimates 

resulting from the transfer of data from photographic and video

evidence to hand-contoured maps (and then to Excel 

spreadsheets with a finer discretization).

 DOE should be more transparent with respect to its approach 

to (i) mapping annular volumes including use of a crawler to 

inspect internal surfaces and (ii) estimating residual waste 

volumes in ventilation ducts. DOE should consider uncertainty in 

annulus volume estimates.

Alternatively, volume mapping uncertainty could be managed 

through use of estimates that

clearly err on the side of higher volumes.

NRC staff will monitor DOE’s visual inspection of internal 

surfaces to ensure no significant inventory is overlooked (e.g., 

Pu-238 on the walls of Tank 18F).

Cost Benefit Analysis for Tanks 18F and 19F (ML13080A401)

4  NRC staff notes that many additional costs were due to the 

length of time that had passed between the decision to cease 

removal activities and the time at which the cost-benefit analysis 

was performed. DOE does not expect this lapse in time for 

future cost-benefit analysis for other tanks.

 NRC staff also noted issues with the collective dose 

comparison, which only included 1 person for 50 years, although 

NRC also noted problems with use of collective dose.

 NRC staff questioned DOE’s criteria that additional waste 

removal be more cost beneficial than other similar DOE 

activities.

 NRC staff also questioned DOE’s separate consideration of 

cost and benefit uncertainty in its sensitivity analysis (cumulative 

impact of uncertainty in the costs and benefits was not 

Monitoring Factor 1.5, 

“Waste Removal (As It 

Impacts ALARA)”

NRC staff has been 

reviewing closure 

module 

documentation early 

on in the process, 

alleviating concerns 

with escalation of 

costs due to timing 

of the analysis. NRC 

will continue to 

monitor DOE 

documentation that 

supports ALARA 

criteria.
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Table B–1. Crosswalk Between Technical Review Report Findings and Monitoring Factors

ID Technical Review Report (TRR) Finding TRR Monitoring Factor Related Monitoring Factor

New Monitoring 

Factor

considered). Additionally, higher removal rates (e.g., 75 

percent) could have been evaluated in sensitivity analysis.

Finally, NRC staff inquired about DOE plans to perform costbenefit analyses in the future. NRC will continue to monitor 

DOE’s process for optimizing waste removal as it impacts the 

ALARA criteria in 10 CFR 61.41, as tank farm closure 

progresses.

Waste Release and Solubility Documentation (ML12272A082)

5 Given the risk significance of the solubility of plutonium and 

consistent with previous NRC recommendations, as well as 

recommendations made by DOE's plutonium solubility peer 

review group (Cantrell, et al., 2011) and other DOE experts, 

NRC continues to believe that experimental verification of 

modeled plutonium solubility under a range of chemical 

conditions potentially relevant to the contaminated zone should 

be undertaken.

NRC staff identified two follow-up actions:

 DOE should provide additional information to support 

assumptions regarding longevity of reducing conditions in the 

contaminated zone. Recent studies (Cantrell and Williams, 

2012) suggest that the reducing capacity of the tank grout could 

be depleted much earlier than assumed in the FTF PA (SRS–

REG–2007–00002) and in more recent Pu solubility modeling 

performed for Tank 18F (Denham, 2012). Uncertainty in the 

normative mineralogy assumed in geochemical modeling should 

be considered under this action.

 DOE should provide additional support for the assumption that 

the Eh of infiltrating water will remain below a critical threshold 

at which Pu solubility will increase to a risk-significant value 

(e.g., updated geochemical modeling indicates a dramatic 

increase in Pu solubility occurs at Eh greater than +0.45 V). 

Uncertainty in the critical threshold and the Eh of infiltrating 

groundwater should be considered under this action.

Monitoring Factor 2.1, 

“Solubility Limiting

Phases/Limits”

Monitoring Factor 2.2, 

“Chemical Transition Times” 

Issues in red text in 

column 2 are 

incorporated into 

Monitoring Factor 

2.1, “Solubility 

Limiting 

Phases/Limits and 

Validation,” and 

Monitoring Factor 

2.2, “Chemical 

Transition Times”

Tanks 18F and 19F Grout Documentation (ML13269A365)
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Table B–1. Crosswalk Between Technical Review Report Findings and Monitoring Factors

ID Technical Review Report (TRR) Finding TRR Monitoring Factor Related Monitoring Factor

New Monitoring 

Factor

6 DOE has not provided sufficient information to rule out 

preferential pathways in its reference case. NRC staff expects 

DOE to provide additional information related to the extent and 

performance impact of shrinkage. During the review of the tank 

grouting video, NRC staff has observed potential segregation of 

tank grout that could enhance the extent of shrinkage along the 

periphery of the Type IV tanks (i.e., along the tank walls). NRC 

staff also expects DOE to provide additional information on the 

potential for thermal cracking of the grout monolith for Tanks 18F 

and 19F. The NRC staff will continue to evaluate the potential 

for shrinkage- and cracking-induced preferential flow through the 

tank grout under Monitoring Factor 3.3, “Shrinkage and 

Cracking” (see ML12212A192).

NRC also continues to monitor the potential for segregation of 

emplaced grout and its impacts on flow through the grout 

monolith and waste release under Monitoring Factor 3.4, “Grout 

Performance.”3

The NRC staff will also continue to monitor void volumes in the 

emplaced grout to the extent information is available (Monitoring 

Factor 3.4, “Grout Performance”),4 the importance of alkali-silica 

reactivity on cementitious material degradation (Monitoring 

Factor 3.3, “Shrinkage and Cracking”), and the impact of 

limestone additions to the grout mix on pH buffering of water 

contacting the emplaced grout (Monitoring Factor 3.4, “Grout 

Performance”).5

Monitoring Factor 3.3, 

“Shrinkage and Cracking fo 

Reducing Grout,” and 

Monitoring Factor 3.4, 

“Grout Performance”

Monitoring Factor 3.2, 

“Groundwater Conditioning

via Reducing Grout”

Monitoring Factor 8.1, 

“Settlement”

Monitoring Factor 2.2, 

“Chemical Transition Times”

Issues in red text in 

column 2 are 

incorporated into 

Monitoring Factor 

3.2, “Groundwater 

Conditioning via 

Reducing Grout,” 

Monitoring Factor 

8.1 “Settlement,” and 

Monitoring Factor 

2.2, “Chemical 

Transition Times”

Tanks 5F and 6F Grout Documentation (ML14342A784)

7 DOE has not provided sufficient information and testing to 

exclude from its reference case preferential flow through the tank 

grout monolith.

During its review of tank grouting video, NRC staff observed 

potential bleedwater segregation of tank grout during placement

Monitoring

Factor 3.3, “Shrinkage and 

Cracking of Reducing 

Grout,” and

Monitoring Factor 3.4, 

“Grout Performance”

Monitoring Factor 3.2, 

“Groundwater Conditioning

via Reducing Grout”

Monitoring Factor 8.1, 

“Settlement”

Issues in red text in 

column 2 are 

incorporated into 

Monitoring Factor 

3.2, “Groundwater 

Conditioning via 

 

3The impact of segregation on the flow through the monolith is also closely related to Monitoring Factor 3.2, “Groundwater Conditioning.” 4Void volume is also important for site stability (Monitoring Factor 8.1, “Settlement”). 5Limestone addition is also important to chemical transition times (Monitoring Factor 2.2, “Chemical Transition Times”).
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Table B–1. Crosswalk Between Technical Review Report Findings and Monitoring Factors

ID Technical Review Report (TRR) Finding TRR Monitoring Factor Related Monitoring Factor

New Monitoring 

Factor

that could result in inhomogeneity of the monolith, which can 

affect flow patterns. 6

The NRC staff will continue to evaluate the potential for 

shrinkage- and cracking-induced preferential flow through the 

tank grout under Monitoring Factor 3.3, “Shrinkage and 

Cracking.”

The NRC staff will also continue to monitor void volumes in the 

waste tanks to the extent that information is available (Monitoring 

Factor 3.4, “Grout Performance”); 7 the importance of alkali–silica 

reactivity on cementitious material degradation (Monitoring 

Factor 3.3, “Shrinkage and Cracking”); and the impact of 

limestone additions to the grout mix on pH buffering of water 

contacting the emplaced grout (Monitoring Factor 3.4, “Grout 

Performance”). 8

Monitoring Factor 2.2, 

“Chemical Transition Times”

Reducing Grout,” 

Monitoring Factor 

8.1 “Settlement,” and 

Monitoring Factor 

2.2, “Chemical 

Transition Times”

Environmental Monitoring (ML12272A124)

8 NRC staff concluded the following:

1. DOE has performed environmental monitoring at the FTF that 

provides useful information on the hydrogeological system at 

FTF. This information can also be used to better understand 

contaminant flow and transport and validate DOE Performance 

Assessment models.

2. Uncertainty exists in the source of contaminant plumes 

detected via the FTF monitoring well network. Reducing this 

uncertainty will be important to better understanding 

contaminant flow and transport processes operable at the FTF.

3. Progress has been made on development of cement leachate 

factors used to account for the impact of cement leaching on 

natural system sorption; however, additional information is 

needed to support factors for key radio-elements such as 

Neptunium (Np), Plutonium (Pu), and Uranium (U).

4. Progress has been made on development of site-specific Kds 

for Niobium (Nb); however, additional information is needed to 

Monitoring Factor 4.1, 

“Natural Attenuation

of Key Radionuclides,” and 

Monitoring Factor 4.3, 

“Environmental Monitoring”

Issues in red text in 

column 2 are 

incorporated into 

Monitoring Factors 

4.1, “Natural 

Attenuation of Key 

Radionuclides,” and 

4.3 “Environmental 

Monitoring”

 

6The impact of segregation on the flow through the monolith is also closely related to Monitoring Factor 3.2, “Groundwater Conditioning.” 7Void volume is also important for site stability (Monitoring Factor 8.1, “Settlement”).

8Limestone addition is also important to chemical transition times (Monitoring Factor 2.2, “Chemical Transition Times”).
B

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Table B–1. Crosswalk Between Technical Review Report Findings and Monitoring Factors

ID Technical Review Report (TRR) Finding TRR Monitoring Factor Related Monitoring Factor

New Monitoring 

Factor

support Kd values used in performance assessment 

calculations.

5. Little progress has been made to address the technical issue 

associated with the Pu Kd averaging approach used in tank farm 

performance assessment calculations. DOE should address this 

technical issue in the future.

Follow-up actions include the following:

1. The NRC staff will continue to monitor the ability of the tank 

farm monitoring well network to detect releases from the tank 

farm facilities following closure. DOE could (i) evaluate the 

monitoring well network by performing an analysis of the 

centerline of plumes emanating from tank sources should 

releases occur in the future and (ii) provide input on optimal well 

locations to ensure that future releases from the tank farm 

facility would be detected.

2. The NRC staff will continue to evaluate the source of elevated 

Technetium (Tc)-99 levels in well FTF 28. It is not clear that 

releases from the F-Area Inactive Process Sewer Line could 

migrate vertically to the lower zone of the Upper Three Runs 

Aquifer in such a short distance from the source. This evaluation 

is important to ensure that the hydrogeological system at FTF is 

well understood and that releases from the tanks could be 

detected by the monitoring well network. DOE could provide 

additional support for the source of contamination detected at 

well FTF 28 by performing particle tracking to better understand 

contaminant plume trajectories. DOE could also perform a more 

formal statistical analysis of FTF and Western Groundwater 

Operable Unit well data to correlate contaminant concentrations 

associated with various sources.

3. The NRC staff will continue to monitor the Kd averaging 

approach used to simulate Pu transport in the natural system at 

FTF. DOE could address the issue by modeling explicitly more 

mobile and less mobile forms of Pu in future performance 

assessment calculations.

4. The NRC staff will continue to monitor support for cement 

leachate factors developed for Pu (and other constituents). 

DOE could provide support for cement leachate factors by 

performing site-specific analyses.

5. The NRC staff will continue to monitor the basis for selection 

of the Nb distribution coefficient or Kd value of 160 L/kg used in 

the Tanks 5F and 6F Special Analysis. DOE could address the 
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Table B–1. Crosswalk Between Technical Review Report Findings and Monitoring Factors

ID Technical Review Report (TRR) Finding TRR Monitoring Factor Related Monitoring Factor

New Monitoring 

Factor

technical issues by verifying the batch experiments did not 

exceed solubility limits and are representative of conditions at 

FTF (e.g., plot solid phase versus aqueous phase concentration 

or Kd versus concentration; evaluate Kd for FTF aquifer soils) or 

perform additional experiments to verify the Nb Kd.

Review of Features, Events, and Processes (ML13277A063)

9 The NRC staff’s review of the DOE screening methodology finds 

that DOE properly focused on likelihood and impact as criteria 

for screening, but identifies several concerns with DOE’s 

screening of FEPs, including the membership of the FEPs 

screening team and the documentation of each subject matter 

expert’s basis for judgment. The NRC staff’s review also 

identifies questions with the screening process for selected 

FEPs. Finally, the NRC staff’s review finds that DOE’s 

crosswalk of included FEPs has the potential to enhance 

transparency and traceability, while NRC staff identifies multiple 

examples where transparency and traceability are reduced, 

which results in a loss of confidence that all relevant FEPs are 

adequately considered in the FTF Performance Assessment.

Monitoring Factor 6.1, 

“Scenario Analysis”

Issues in red text in 

column 2 are 

incorporated into 

Monitoring Factor 

6.1, “Scenario 

Analysis”

ALARA–As Low As Is Reasonably Achievable, CFR–Code of Federal Regulations, DOE–U.S. Department of Energy, Eh–Oxidation-Reduction Potential, FEP–

Features, Events, and Processes, FTF–F-Tank Farm, HRR–Highly Radioactive Radionuclides, Kd–Distribution Coefficient, NRC–U.S. Nuclear Regulatory 

Commission, PA–Performance Assessment, pH–Hydrogen Ion Activity, PO–Performance Objective, TER–Technical Evaluation Report, TRR–Technical Review 

Report, UCL95–95th Percentile Upper Confidence Limit.

References:

ML12212A192. “U.S. Nuclear Regulatory Commission Plan for Monitoring Disposal Actions Taken by the U.S. Department of Energy at the Savannah River Site 

F-Area Tank Farm Facility in Accordance With the National Defense Authorization Act for Fiscal Year 2005.” Washington DC: U.S. Nuclear Regulatory 

Commission. 2013.

ML13080A401. “Technical Review Updated Cost-Benefit Analysis for Removal of Additional Highly Radioactive Radionuclides from Tank 18.” Memorandum from 

L. Parks (NRC) to G. Suber (NRC) thru C. McKenney (NRC). Washington, DC: U.S. Nuclear Regulatory Commission. March 2013.

ML13100A230. “Technical Review of Tank 18 and 19 Special Analysis for the Performance Assessment for the F-Tank Farm at the Savannah River Site, SRRCWDA-2010-00124, Rev. 0, February 2012 (DOCKET NO. PROJ0734).” Memorandum from C. Barr (NRC) to G. Suber (NRC) thru C. McKenney (NRC). 

Washington, DC: U.S. Nuclear Regulatory Commission. April 2013.

ML12272A082. “Technical Review: Waste Release and Solubility Related Documents Prepared by United States Department of Energy to Support Final Basis 

Section 3116 Determination for the F-Area Tank Farm Facility at Savannah River Site.” Memorandum from G. Alexander (NRC) to J. Jesse (NRC) thru C. 

McKenney (NRC). Washington DC: U.S. Nuclear Regulatory Commission. May 2013.
B

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Table B–1. Crosswalk Between Technical Review Report Findings and Monitoring Factors

ID Technical Review Report (TRR) Finding TRR Monitoring Factor Related Monitoring Factor

New Monitoring 

Factor

ML13085A291. “Tehnical Review of Final Inventory Documentation for Tanks 5 and 6 at F-Tank Farm, Savannah River Site, (Project No. PROJ-0734).” 

Memorandum from C. Barr (NRC) to G. Suber (NRC) thru C. McKenney (NRC). Washington, DC: U.S. Nuclear Regulatory Commission. September 2013.

ML13273A299. “Technical Review of Tanks 5 and 6 Special Analysis at F-Tank Farm Facility, Savannah River Site (Project No. PROJ0734).” Memorandum from 

C. Barr (NRC) to G. Suber (NRC) thru C. McKenney (NRC). Washington, DC: U.S. Nuclear Regulatory Commission. October 2013.

ML13269A365. “Technical Review: U.S. Department of Energy Documentation Related to Tanks 18F and 19F Final Configurations with an Emphasis on Grouting 

from Recommendations and Testing to Final Specifications and Procedures (Project No. PROJ0734).” Memorandum from C. Grossman (NRC) to G. Suber (NRC) 

thru C. McKenney (NRC). Washington, DC: U.S. Nuclear Regulatory Commission. October 2013.

ML14342A784. “Technical Review: U.S. Department of Energy Documentation Related to Tanks 5F and 6F Final Configurations with an Emphasis on Grouting 

from Recommendations and Testing to Final Specifications and Procedures (Project No. PROJ0734)”. Memorandum from L. Parks (NRC) to G. Suber (NRC) thru 

C. McKenney (NRC). Washington, DC: U.S. Nuclear Regulatory Commission. December 2014.

ML13277A063. “Technical Review: U.S. Department of Energy Documentation Related to Features, Events, and Processes in the F-Area Tank Farm 

Performance Assessment.” Memorandum from C. Grossman (NRC) to G. Suber (NRC) thru C. McKenney (NRC). Washington, DC: U.S. Nuclear Regulatory 

Commission. April 2014.

ML12272A124. “Technical Review of Environmental Monitoring and Site-Specific Distribution Coefficient Reports.” Memorandum from C. Barr (NRC) to G. Suber 

(NRC) thru C. McKenney (NRC). Washington, DC: U.S. Nuclear Regulatory Commission. March 2015.
APPENDIX C

MA 2, “WASTE RELEASE”
C–1

APPENDIX C

MA 2, “WASTE RELEASE”

The DOE relies on solubility controls in the residual waste to constrain aqueous phase 

concentrations of HRRs released from the residual waste remaining in the primary liners of the 

waste tanks and associated groundwater doses to a potential receptor. In DOE’s FTF and HTF

PAs, solubility-limiting phases and the resulting solubility limits are often a function of the 

chemical environment in the contaminated zone. The chemical environment of the 

contaminated zone is affected by chemical conditioning afforded by the overlying reducing grout

used to fill the tanks following closure, which is intended to ensure a relatively high pH and low 

Eh chemical environment in the contaminated zone for thousands to tens of thousands of years, 

thereby delaying significant release of key HRRs beyond the 10,000-year compliance period.

1

In its TERs (ML112371751, ML14094A496) the NRC staff presented a number of observations 

and recommendations. NRC staff’s primary recommendation related to Criterion 3, as stated in 

the FTF TER2 Executive Summary, is as follows:

NRC staff recommends DOE conduct waste release experiments to increase support for 

key modeling assumptions related to (i) the evolution of pH and Eh in the grouted tank 

system over time, (ii) identification of HRR association with solid phases comprising the 

residual wastes, and (iii) expected solubility of HRRs under a range of environmental or 

service conditions that the residual wastes in the contaminated zone are expected to be 

exposed to over time. Implementation of this recommendation is deemed crucial for 

NRC staff to have reasonable assurance that the POs in 10 CFR Part 61, Subpart C,

can be met. 

As a result, NRC staff has identified the following MFs related to waste release:

• MF 2.1 “Solubility-Limiting Phases/Limits and Validation” (see Section 3.2.1)

• MF 2.2 “Chemical Transition Times” (see Section 3.2.2)

Because chemical transitions to risk-significant solubilities for HRRs could lead to exceedance 

of the 0.25 mSv/yr [25 mrem/yr] 10 CFR 61.41 dose standard (or 5 mSv/yr applied dose 

standard for 10 CFR 61.42) during the compliance period, the timing of chemical transitions 

could be important to compliance. Therefore, both (i) the nature of flow through the tank grout 

(e.g., fracture versus matrix flow) that dictates the reactive surface area and amount of grout 

available to condition infiltrating water and (ii) the assumed rate of change of Eh and pH3 may 

 

1In contrast to the FTF PA and based on updated solubility modeling, the HTF PA assumes that solubility of many 

HRRs remains at non-risk-significant values into perpetuity. DOE evaluates the impact of higher HRR solubility upon 

transition to Oxidized Regions II or III in uncertainty and sensitivity analysis in the HTF PA. 2In HTF TER, the NRC staff reiterated the FTF recommendation that DOE conduct waste release experiments.

3In the FTF PA, a risk-significant increase in solubility of Tc and Pu occurred upon transition to Oxidized Region III. 

In the Tanks 18F and 19F Special Analysis and HTF PA reference cases, DOE assumes that Pu solubility remains at 

non-risk-significant values for all chemical states; or assumes Pu solubility increases to a risk-significant value upon 

transition to Oxidized Region II in sensitivity analysis cases. In the HTF PA, DOE assumes that Tc remains at a low 

solubility phase for all chemical conditions or increases to a risk-significant value upon transition to Oxidized 

Regions II or III in sensitivity analysis. In general, the updated geochemical modeling results in the HTF PA indicate 

that HRR solubility is generally not sensitive to the transition from Oxidized Region II to Oxidized Region III. 

However, if future revisions to the HTF PA and updated geochemical modeling indicate that the solubility of certain 
C–2

also be important to the compliance demonstration. Uncertainty related to flow through the tank 

grout is considered under MA 3, “Cementitious Material Performance,” and MF 3.2,

“Groundwater Conditioning via Reducing Grout,” which is concerned with the hydraulic (rather 

than the chemical) performance of cementitious materials mitigating tank farm releases and 

doses.

Other NRC staff TER recommendations related to waste release are binned under PA 

maintenance activities under MA 6 until overall facility performance is better understood and 

constrained. Should the results of the experiments indicate less than favorable performance, 

NRC staff expects DOE to assess the impact on the results of the PAs. NRC staff also will 

assess the need for additional experiments, data collection, and modeling to provide support for 

key barriers in DOE’s PAs that might serve to mitigate underperformance of chemical barriers. 

If the results of the experiments show that key radionuclides are strongly retained in the residual 

waste, NRC staff expects other MAs or MA components will become less important and may be 

closed as monitoring progresses.

Since preparation of the FTF PA, DOE performed additional analysis to study potential solubility 

of Pu in Tank 18 to support the final waste determination and closure of the tank (SRNL–STI–

2012–00404). The analysis indicates that Pu may be present in the tank waste waters at risksignificant concentrations for what DOE describes as “conservative” or higher Eh conditions, or 

that Pu also can be relatively insoluble at what DOE describes as more “realistic” or lower Eh 

conditions. These results are important, as they show that peak doses could either be similar to 

those doses reported in DOE’s FTF PA (i.e., hundreds of mrem/yr) or that the peak doses from 

Pu could be insignificant. However, only through additional analyses and experimental 

validation can DOE confirm the geochemical modeling results and present a more accurate 

measure of risk. It also is important to note that if higher Eh conditions prevail, DOE models 

predict releases from the tanks much earlier in time. In Figure 3-5, a green dashed line that 

dissects the tank grout and contaminated zone chemical barriers4 at around 10,000 years for 

Type IV FTF tanks (including Tank 18)5 marks the first chemical transition from reducing to 

oxidizing conditions, corresponding to the time at which Pu is expected to be released at 

risk-significant rates based on DOE’s updated solubility modeling. Potential risk-significant 

release of Pu-239 at higher solubility may occur much earlier in time based on results of the 

updated solubility modeling compared to what was assumed in DOE’s FTF PA (i.e., Pu-239 was 

previously assumed to be released at risk-significant rates only after the second chemical 

transition to lower pH marked with a red dashed line after 30,000 years in Figure 3-5). If 

performance of the tank grout, steel liner, or basemat is slightly less than assumed in DOE’s 

base case scenario, then release of Pu-239 into the surrounding environment could occur within 

the 10,000-year period of performance.

In 2011, NRC staff recommended in its FTF TER (ML112371751) that DOE initiate discussions 

with NRC staff regarding implementation of waste release experiments for Tank 18F as soon as 

practical, given the overall risk-significance of the tank in the FTF PA and DOE’s plans to close 

Tank 18F in CY 2012. After issuance of NRC staff’s FTF TER, DOE convened a peer review 

group, which documented its recommendations with respect to Pu solubility experiments in 

LA–UR–2012–00079. In the report, the peer review group recommended, consistent with NRC 

 

radionuclides is sensitive to pH, DOE may need to provide additional support for the chemical transition times to 

Oxidized Region III conditions.

4Tank grout and contaminated zone chemical barriers are combined and shown in purple in Figure 3-5. 5Type IV tanks are illustrated in the bottom set of three panels in Figure 3-5.
C–3

staff’s TER recommendations, that DOE update its geochemical modeling and validate 

modeling results with follow-up experiments. The peer review report, however, suggested that 

validation experiments could occur after tank grouting had been completed. Consistent with the 

peer review group recommendation, DOE decided to grout the tanks and perform follow-up 

experiments to study waste release later (SRR–CWDA–2012–00020). DOE developed an 

experimental plan to provide additional information and model support for the closure of 

Tank 18F. The task is intended to provide additional information regarding the residual waste

solubility assumptions used in the FTF and HTF PA waste release models. DOE plans to 

perform the task in two phases. The first phase involved development of a test plan and 

methods, which are documented in SRNL–RP–2013–00203, as updated in SRNL–RP–2013–

00203 and the second phase involves experiments with actual Tank 18F waste residuals. NRC 

staff commented on (ML15153A384) DOE’s experimental plan (SRNL–RP–2013–00203) and 

discussed the research with DOE at the March 2014 Onsite Observation Visit (ML14106A573). 

The research is ongoing with testing currently limited to surrogate samples (SRNL–STI–2014–

00456). One of the key findings of this research is that the pore-water Eh in these studies is 

inconsistent with the values assumed in the PA waste release modeling. This may be an 

experimental artifact (e.g., insufficient equilibration time). NRC staff commented that the 

assumed Eh and pH values in the field are uncertain and that this uncertainty should be 

considered in the design of the experiments (i.e., pH and Eh endpoints should be investigated in 

the experiments to determine whether the HRRs could be at a risk-significant solubility; if the

solubility at the endpoint is risk significant, then DOE should investigate the critical threshold 

where solubility increases to risk-significant values).

Monitoring Factor 2.1—Solubility-Limiting Phases/Limits and Validation

The key radio-elements that are expected to significantly contribute to receptor dose and are

sensitive to solubility limits are Tc, Np, and Pu. As discussed in the NRC staff’s TERs

(ML112371751, ML14094A496), DOE models solubility limits for these elements in the DOE

PAs for pure phases and, in some cases,

6 as coprecipitates with iron oxyhydroxide minerals in 

the residual waste. NRC staff will, therefore, emphasize these elements in monitoring how DOE 

treats its concentration-limited release in the PAs.

As mentioned previously, NRC staff’s primary recommendation in its TERs (ML112371751,

ML14094A496) was that DOE conduct waste release experiments to increase support for key 

modeling assumptions. Accordingly, NRC staff will monitor experiments conducted by DOE to 

address the primary recommendation. With respect to the experiments, DOE should develop a 

plan to analyze key radio-elements that rely on solubility for control, such as Pu, Tc, and Np. 

The experiments should consider the effects of reagents (e.g., oxalic acid) used to remove 

radionuclides from the tank residue, including formation of new compounds that may alter 

leachability of key radionuclides. DOE should determine the number of samples to be analyzed 

from each waste tank based on characterization results that show the homogeneity or lack 

thereof of residual waste remaining in the tanks. 

 

6In the FTF PA, iron coprecipitation is used to calculate solubility limits for uranium (U), Tc, and Pu in both the 

deterministic and probabilistic models. In the HTF PA, iron coprecipitation is used to calculate solubility limits for Tc 

in both the deterministic and probabilistic models. For U, Np, and Pu, the iron coprecipitation model is not used to 

calculate solubility limits in the HTF PA deterministic models, but it is used to calculate solubility limits for establishing 

probability distributions and also used in sensitivity analyses.
C–4

In the FTF TER, NRC staff recommended DOE perform experiments for residual waste from 

Tank 18F in the short term and, based on the results of the first set of experiments and 

expected intertank variability, determine the need for additional experiments for remaining 

tanks. Decisions on additional experiments should be based on expected tank risk; HRRs 

targeted for these studies should be those that are the largest risk drivers and for which the 

reliance on chemical retention is greatest. The experiments should be representative of the 

final chemical and physical form of the waste (e.g., should reflect postchemical treatment for 

those tanks where chemical cleaning is selected as the preferred technology).

DOE should conduct tests recommended by the peer review group (LA–UR–2012–00079) using 

archived samples of Tank 18F heels or additional samples that were obtained before grouting 

commenced. As mentioned earlier, DOE has developed an experimental plan to provide 

additional information and model support for the closure of Tank 18F. The proposed task is 

intended to provide additional information regarding the residual waste solubility assumptions 

used in the FTF and HTF PA waste release models. The need for this information is important, 

especially when considering waste reactions with water and the subsequent interactions of this 

leachate with soil underlying the tanks. 

The remainder of this section will address, in turn, each of the three elements for which waste

release is most significant to calculated dose. The Pu section exceeds the others in length 

mainly because recent information has become available that warrants discussion; the DOE 

efforts that led to much of the new information were expanded in the HTF PA (i.e., updated 

geochemical modeling) and provide relevant data for Tc and Np.

Technetium

In the FTF PA, solubility limits of Tc are controlled by coprecipitation with iron oxides for 

Reduced Region II and Oxidized Region II; however, no solubility limit is placed on Tc under 

Oxidized Region III. In the HTF PA, technetium coprecipitates with iron oxides, which limits its 

solubility in all chemical conditions modeled. NRC staff still has questions regarding the 

applicability of the iron coprecipitation model for Tc. It appears these concerns will be moot if 

the tank Tc-99 inventories are reduced enough by cleaning, such that the Tc solubility limit is 

not risk significant. If Tc-99 tank inventories continue to be sufficiently low, NRC staff may not 

need to monitor Tc solubility limit issues.

Neptunium

NRC staff’s FTF TER (ML112371751) observed that Np pure-phase solubilities used in the PA 

appeared reasonable. These solubility values have the potential to be risk-significant if release 

and chemical transitions occur before 10,000 years. In the HTF TER, (ML14094A496) NRC 

staff observed that while the solubilities used in the HTF PA were considerably lower than in the 

FTF PA,

7 they appeared reasonable considering that DOE uses a thermodynamic database 

based on the well-established Nuclear Energy Agency (NEA) data compilation. However, DOE 

model results in Figure 24 of SRNL–STI–2012–00404 show that the neptunium solubility limit is 

 

7Np solubility limits range from 2 × 10−6 to 1 × 10−9 mol/L in the HTF PA (SRR–CWDA–2010–00128, Table 4.2-11) 

compared to 1.1 × 10−4 mol/L to 1.6 × 10−9 mol/L in the FTF PA (SRS–REG–2007–00002, Table 4.2-10).
C–5

sensitive to Eh for Oxidized Regions II and III. The solubility value of over an order of 

magnitude higher is possible if Eh is 400 mV rather than 290 mV (i.e., 3 × 10−5 mol/L 

versus 2 × 10−6 mol/L). 

DOE assumes the basemat is quite effective in limiting Np release in its PAs. Accordingly, 

monitoring activities concerning the Np Kds in the basemat are discussed under MA 3, 

“Cementitious Materials Performance,” as well as those concerned with by-pass flow through 

the basemat, which are discussed further under MA 6, “PA Maintenance.”

Plutonium

Pu release and, therefore, dose are highly sensitive to the contamination zone solubility limit. 

The DOE plot seen in Figure C–1 shows that, if timing is disregarded, any Pu solubility limit 

above 1 × 10−10 mol/L could yield doses that exceed the 10 CFR 61.41 compliance limit at FTF. 

Independent NRC staff analyses corroborate DOE’s sensitivity analysis results and show that 

peak release rates (and therefore doses) are relatively insensitive to solubility at higher solubility 

levels but that, at some threshold value, tank waste solubility becomes increasingly controlling 

with respect to peak release and dose. Because NRC staff remains unconvinced of the timing 

of release, owing to uncertainty in chemical transition times and potential for tank grout bypass, 

a solubility limit exceeding 1 × 10−10 mol/L, under any set of chemical conditions, has the 

potential to lead to an unacceptable dose at FTF within 10,000 years. Because Pu solubility is 

highly dependent on assumptions regarding any solubility limiting pure Pu phases, 

recommended waste release studies discussed earlier are particularly critical for Pu.

Table C–1 also shows that a Pu solubility at the source of less than 1 × 10−10 mol/L is not likely 

to be risk significant for FTF, considering minimal credit for the performance of other FTF 

barriers [i.e., 1 × 10−12 mol/L could easily be reduced by two orders of magnitude, which is a 

minimal amount of credit for the performance of engineered and natural FTF barriers (see Table 

3-1)]. The concentrations were calculated based on the DOE-calculated pathway dose 

conversion factor for Pu-239 used in the FTF PA, which provides the dose to groundwater 

concentration ratio for this key radionuclide.

DOE convened a peer review group to assess recommendations and comments NRC staff 

made in its FTF TER (ML112371751), specifically with regard to the technical justification for the 

assumptions and technical bases for modeling Pu release from tank residual wastes. Much of 

this effort focused on the solid phases of Pu in the waste and the modeling activities associated 

with assessing solubility of those phases. The peer review group’s report points out the DOE 

analysis of chemistry in the tanks only provides “possible clues as to the potential nature of Pu 

speciation in the precipitates and residues left in the tank after extensive cleaning” (LA–UR–

2012–00079). In addition, the report states, “There is no real understanding of the nature of Pu 

speciation in tank precipitates” (LA–UR–2012–00079, p. 8). The peer review team’s findings 

are based on several days of discussions with Savannah River Site (SRS) personnel. The peer 

review report states that, to provide a stronger scientific foundation to justify the use of 

geochemical modeling in the tank closure PA, validation and verification of the model and 

assumptions are required.
C–6

Figure C–1. Revised Tank 18F/Tank 19F Special Analysis (SRR–CWDA–2010–00124, 

Figure 6.3-23) Showing the Sensitivity of Calculated Dose to the Plutonium 

Solubility at the Waste Residue

Table C–1. Risk-Significant Concentrations of Pu-239 in the Environment Based on 

DOE FTF PA Modeling

Standard Concentration (pCi/L)

Concentration 

(mol/L)

Intruder 5 mSv/yr 1,100 7 × 10−11

Member of the Public 0.25 mSv/yr 55 4 × 10−12

Pathway Dose Conversion Factor = 4.5 × 10−3 mSv/yr per pCi/L

Specific Activity = 0.063 Ci/g

1 pCi/L = 3.7 × 10−02 Bq/pCi

PU = Plutonium, DOE = U.S. Department of Energy, FTF F-Area Tank Farm, PA= Performance Assessment
C–7

With respect to tank waste residues, the peer review group recommended:

• Spectroscopic analyses [e.g., Extended X-Ray Absorption Fine Structure or (EXAFS)] of Pu 

and other metals in the waste residues.

• Leach tests that use leachant solutions representative of aged as well as fresh grout and 

deionized water. The recommended leach tests would include the following features:

• Chemical analysis including all major ions, pH, alkalinity, Eh, and appropriate trace 

components (e.g., Pu, Fe, and sulfide).

• Solids characterization after leaching, because new phases may have precipitated or 

some phases may have dissolved completely.

• Geochemical modeling with the leachate data as input, in order to validate and verify 

the solubility model and certain assumptions used in the model.

In addition to these peer review group recommendations, SRNL–STI–2012–00106 recommends

that if the presence of PuO(CO3)(am,hyd) is confirmed by x-ray absorption analysis, 

experiments be conducted to determine whether Pu carbonates can be transformed back 

intoPuO2(am,hyd) upon contact with grout. This is important because observed Pu 

concentrations in the Tank 18F were risk significant (1 x 10−8 mol/L) and could lead to peak 

doses similar to the larger doses in the FTF PA (3–5 mSv/yr [300–500 mrem/yr]).

Many of the tests that were recommended by the peer review group are consistent with NRC’s 

TER (ML112371751) recommendations. DOE has identified an experimental plan and begun 

testing of surrogate samples, prior to testing actual waste samples, to provide additional 

information and model support for the closure of Tank 18F (SRNL–RP–2013–00203). The 

proposed task is intended to provide additional information regarding the residual waste

solubility assumptions used in the FTF and HTF PA waste release models. Although DOE has 

performed some preliminary work, DOE has not yet adequately characterized tank waste 

residues, especially with respect to the forms and behavior of the transuranic elements, to allow 

reasonable assurance that releases from the tanks have been appropriately modeled. The 

complex behavior of Pu and the variety of tank configurations, materials, and potential pathways 

for water to short-circuit closure conditions suggest DOE should conduct carefully considered 

leaching studies coupled to site-specific soil interaction analysis. Specifically, DOE should 

conduct leaching studies to ascertain maximum solubilities and leach rates of key radionuclides 

from the tank heels. These tests should represent different scenarios of waste-grout 

interactions that control factors such as pH and speciation. DOE could use leachate from the 

experiments to define site-specific Kds values, based on waste-specific releases to support the 

cement leachate factors derived from the literature (see Section 3.4.1).

SRNL–STI–2012–00106 provides a discussion of the possible solid phases and aqueous 

species in which Pu may reside in residual SRS tank wastes, based on observations of 

Tank 18F residues, the tank operational history, and the literature. A variety of metals, including 

Pu, that precipitate from solution as acidic residues from spent fuel dissolution are made 

alkaline by addition of NaOH. SRNL–STI–2012–00106 describes three forms that the Pu may 

take if it co-precipitates with other, much more abundant metals, such as iron and aluminum: (i)

Pu substitution for another metal in a crystal lattice, (ii) physical occlusion into a mass of 

precipitated material without becoming part of the structure, and (iii) adsorption onto surfaces of 

the material. In each of these cases, Pu would be expected to be uniformly dispersed in the 
C–8

solid. However, recent Scanning Electron Microscopy (SEM) analyses of a single Tank 18F

waste sample (SRNL–L3100–2012–00017) show Pu present as discrete, small (<1 μm) 

particles that are not evenly distributed within the precipitated matrix. The Pu mass represented 

by these particles seems to be smaller than total Pu in the sample, suggesting that some Pu 

also is co-precipitated. Perhaps more importantly, the concentrations of Pu in Tank 18F waste 

liquids (1 × 10-8 mol/L and 3 × 10-8 mol/L) were “well above the predicted solubilities for 

PuO2(am,hyd) and co-precipitated Pu(IV)” (less than 2 × 10-9 mol/L) (SRNL–STI–2012–00106).

Further, SRNL-STI-2012-00106 discusses how the speciation of Pu in the waste may be 

impacted by changes in pH and ingress of CO2, resulting from continual active ventilation of the 

tanks to control hydrogen accumulation. The presence of CO2 gas over a strongly alkaline 

solution will result in accumulation of carbonates in solution, inducing the formation of 

PuO(CO3)xH2O(solid) or Pu(OH)2(CO3)(solid) in the presence of aqueous Pu carbonate species. In 

fact, carbonate concentrations of about 0.04 mol/L were measured in the aqueous phase of 

Tank 18F heels. A recent X-Ray Diffraction (XRD) analysis of Tank 18F heels shows the 

presence of Na4UO2(CO3)3 and calcite at about 10 percent of the crystalline solid phase 

material (SRNL–L3100–2012–00017). The presence of these solids and the measured 

aqueous carbonate concentrations strongly suggests that some Pu in the heels is in a 

carbonate form. These observations have important implications for how Pu solubility is 

modeled, because the solubility limits for these carbonate phases could differ substantially from 

the hydrated Pu oxides used in DOE models. If Pu is present as a carbonate solid, then at pH 

9.8, Pu solubilities of around 1 × 10-6 mol/L can be expected (SRNL-STI-2012-00106). In 

addition, these observations mean that at least some of the Pu in the aqueous phase will be 

negatively charged carbonate complexes, which will have very low Kds values. Higher solubility 

and lower Kd could lead to an exceedance of the performance objective within the period of 

compliance (i.e., increase the magnitude of peak dose and lead to earlier peak doses within the 

compliance period).

In the recent special analyses for Tanks 18F and 19F (SRR–CWDA–2010–00124), DOE 

assumes that reaction of Pu carbonate species with the high pH of the grout will convert all Pu 

to the lower-solubility phases Pu(OH)4(am) or PuO2(am, hyd). Presumably, this would take place 

with free alkaline water released during grout setting or with water that percolated from the 

surface through the grout. In many release scenarios, water in the system will be alkaline 

before it contacts the waste residue. This seems reasonable for many situations. However, 

there are several important processes that may preclude the conditioning of water entering the 

contamination zone. Based on information presented in the PA, the Pu Peer Review Report, 

and SRNL-STI-2012-00106, there are potential radionuclide release scenarios that may lead to 

greater leach rates than expected from the PA.

The recent analysis of one sample of tank residue by SEM and XRD has altered the conceptual 

model presented in the PA. From SRNL-STI-2012-00106, it is reasonable to think that Pu may 

be present in at least three forms in the heels, and the higher than expected concentrations of 

aqueous Pu highlight this point. This illustrates the importance of doing a characterization of the 

waste, as outlined above. Other radio-elements that cannot be detected by the solid phase 

analytical techniques may be better characterized by the leach tests. Moreover, release rates of 

Pu and other related elements as well as their speciation can be used by DOE to validate 

modeling of this system.

In summary, DOE should characterize tank heels as recommended in NRC’s TER 

(ML112371751) and by the DOE peer review group. These analyses, to be conducted on 

multiple samples, include: XRD; SEM/Energy Dispersive Spectroscopy (EDS); synchrotron-
C–9

based studies, such as X-Ray Absorption Near Edge Structure (XANES); synchrotron 

microprobe; and EXAFS for selected materials. Leach tests need to be conducted under 

differing environmental conditions. Analyses of the leachates should attempt to determine the 

aqueous speciation of Pu. Tests need to be conducted to assess the ability of fluids from the 

grout to transform Pu carbonate solids to Pu(OH)4(am) or PuO2(am, hyd).

Monitoring Factor 2.2—Chemical Transition Times

DOE relies on geochemical modeling to estimate the time at which two key chemical transitions 

take place (i) transition from reduced to oxidized conditions reflected in an increase in Eh and

(ii) transition from relatively high to relatively low pH reflected in a decrease in pH. In

Section 4.2.9.3 of its TERs (ML112371751; ML14094A496), NRC staff discussed its concerns 

with the geochemical modeling results, which may be attributable to assumptions such as the 

solid phases that comprise the tank grout, the characteristics of the infiltrating groundwater, 

uncertainties in the thermodynamic data used in the modeling, or assumptions regarding the 

ability of grout components to react with and condition infiltrating groundwater. As illustrated in 

Figure C–2 (ML112371751, Figure 4-5), NRC staff questioned the shape of the pH vs. time 

curve generated, using the results of DOE’s geochemical modeling. The experimental data 

presented in Figure C–2 suggest that DOE’s conceptual model or modeling results related to 

chemical transition times may be flawed. DOE acknowledges that the shape of the curve is a 

limitation of the geochemical model (ML12236A370). As a consequence of this model 

simplification, the pH is overestimated at some times and underestimated at other times. 

However, DOE also discusses that the solubility of key radionuclides is not significantly 

sensitive to these slight variations in pH for the HTF PA. Because of its importance for the FTF 

PA and because of its potential importance should concerns regarding radionuclide solubility 

limits discussed under Monitoring Factor 2.1 lead to changes in solubility limits for key 

radionuclides in the HTF PA, the NRC staff will continue to evaluate information related to 

chemical transitions and groundwater conditions during monitoring.

Chemical transition times also are dependent on the nature of flow through the grouted tanks. If

flow is primarily through cracks, only a small fraction of the total mass of tank grout may come 

into contact with infiltrating water over time, thereby limiting the effective reductive and buffering 

capacity of the tank grout and hastening chemical transitions to higher solubility. MF 3.2—

Groundwater Conditioning and MF 3.3—Shrinkage and Cracking, discussed in Sections 3.3.2 

and 3.3.3 and Appendix D is concerned with the potential for preferential pathways to form that

by-pass the tank grout, limit groundwater conditioning, and lead to faster chemical transition

times.

In addition to these aforementioned concerns, in a technical review report on waste release 

([ML12272A082) and the HTF TER (ML14094A496), the NRC staff discussed various research 

that raises additional questions regarding the ability of the grout to condition the contaminated 

zone because of (i) the relative rate of flow versus the rate of chemical reaction, (ii) formation of 

a passivation layer along the flow paths, and (iii) the potential for the early release of soluble 

reduced sulfur phases (e.g., CaS). In light of this research, NRC staff identified in a TRR on
C–10

Figure C–2. Experimental Versus Modeled Change in pH Versus Displaced Pore 

Volumes (Dimensionless Time) (ML112371751, Figure 4-5; BNL-82395)

waste release documentation (ML12272A082) that DOE has not to date provided adequate 

support for assumptions regarding the longevity of reducing conditions.

For these reasons, NRC staff does not believe a compelling case has been made yet that waste 

release will be limited to times after the 10,000-year compliance demonstration period. For the 

purposes of waste release, NRC staff assumes releases and chemical transitions can occur 

before 10,000 years. Until DOE resolves questions of the timing of release and chemical 

transitions, the compliance demonstration will depend on whether the highest solubility limits 

identified as a result of monitoring DOE activities under MF 2.1 will lead to doses that meet or 

exceed the dose limits in 10 CFR 61.41 and 61.42.

Since preparation of DOE’s FTF PA and NRC’s FTF TER (ML112371751), DOE has performed 

additional modeling (SRNL-STI-2012-00404, Rev. 0) that updates the chemical transition times 

presented in DOE’s HTF PA. Table 3-2 of this monitoring plan summarizes the differences in 

chemical transition times between the FTF and HTF PAs that resulted from DOE’s additional 

modeling. As part of this MF, NRC will review information provided in the updated solubility 

report as a technical review activity. However, DOE should perform experiments to validate 

results of the updated geochemical modeling. As NRC staff has expertise in design and 

implementation of relevant experiments, DOE should discuss with NRC staff its plans to ensure 

that experiments are designed to optimize their usefulness in supporting the 10 CFR 61.41 

compliance demonstration. NRC staff also may observe DOE experiments related to this MF in 

conjunction with an onsite observation. This MF will be closed when DOE completes 

experiments to study the evolution of pH and Eh in the tank grout over time to provide more 

accurate estimates of chemical transition times to higher solubility.
C–11

In addition to concerns regarding geochemical modeling results that show the evolution of pH 

and Eh over time, NRC staff also is concerned that the reducing capacity of the tank grout may 

not be readily transferable to the waste zone; DOE PA modeling assumes the waste zone 

remains in a reduced state for thousands of years (see purple barrier to the left of the green 

dashed line in Figure 3-5), based on conditioning from the overlying grout. NRC will, therefore, 

monitor the ability of tank grout to maintain reducing conditions in the waste zone through 

experimentation or other support. 

References

ML112371751. “Technical Evaluation Report for F-Area Tank Farm Facility, Savannah River 

Site, South Carolina—Final Report.” Washington, DC: U.S. Nuclear Regulatory Commission. 

2011.

ML14094A496. “Technical Evaluation Report for H-Area Tank Farm Facility, Savannah River 

Site, South Carolina—Final Report.” Washington, DC: U.S. Nuclear Regulatory Commission. 

2014.

ML12236A370. Shaffner, J. “Summary of Telephone Conference Call Held on July 26, 2012, 

Between the U.S. Nuclear Regulatory Commission Staff and Department of Energy 

Representatives Concerning Requests for Additional Information/Clarification Pertaining to the 

Residual Waste Solubility Related to Removal of Highly Radioactive Radionuclides from Tank 

18, F Area Tank Farm. Note to File PROJ0734. Washington, DC: U.S. Nuclear Regulatory 

Commission. September 7, 2012.

ML12272A082. “Technical Review: Waste Release and Solubility Related Documents 

Prepared by United States Department of Energy to Support Final Basis Section 3116 

Determination for the F-Area Tank Farm Facility at Savannah River Site.” Memorandum from 

G. Alexander (NRC) to J. Jesse (NRC). Washington DC: U.S. Nuclear Regulatory 

Commission. 2013.

ML15153A384. “NRC Staff Comments on SRNL-STI-2013-00203, Rev. 0.” Washington DC: 

U.S. Nuclear Regulatory Commission. Email from H. Felsher (NRC) to S. Ross and L. Suttora 

(DOE) on November 18, 2013.

SRNL–L3100–2012–00017, Rev 0. Hay, M.S., P.E. O’Rourke, and H.M. Ajo. “Summary of 

XRD and SEM Analysis of Tank 18 Samples.” Memorandum (February 23) to F.M. Pennebaker 

(NRC). Aiken, South Carolina. Savannah River National Laboratory. 2012.

SRNL–RP–2013–00203. Rev. 0, Hobbs, D.T., Taylor-Pashow, K.M.L., Roberts, K.A., and 

Langton, C.A. “Task Technical and Quality Assurance Plan for Determining the Radionuclide 

Release from Tank Waste Residual Solids.” Aiken, South Carolina: Savannah River National 

Laboratory. June 2013.

SRNL–RP–2013–00203, Rev. 1, Hobbs, D.T., Taylor-Pashow, K.M.L., Roberts, K.A., and 

Langton, C.A. “Task Technical and Quality Assurance Plan for Determining the Radionuclide 

Release from Tank Waste Residual Solids.” Aiken, South Carolina: Savannah River National 

Laboratory. April 2014.
C–12

SRNL–STI–2012–00106. Hobbs, D.T. “Form and Aging of Plutonium in Savannah River Site 

Waste Tank 18, Savannah River National Laboratory.” Aiken, South Carolina: Savannah River 

Nuclear Solutions, LLC. 2012.

SRNL–STI–2012–00404, Rev. 0. Denham, M. and Millings, M. “Evolution of Chemical 

Conditions and Estimated Solubility Controls on Radionuclides in the Residual Waste Layer 

During Post-Closure Aging of High-Level Waste Tank.” Aiken, South Carolina: Savannah River 

National Laboratory. 2012.

SRNL–STI–2014–00456. Miller, D.H., Roberts, K.A., Taylor-Pashow, K.M.L., and 

D.T. Hobbs. Determining the Release of Radionuclides from Tank Waste Residual Solids.

Aiken, South Carolina: Savannah River National Laboratory. September 2014.

SRR–CWDA–2010–00124, Rev. 0. “Tank 18/Tank 19 Special Analysis for the Performance 

Assessment for the F-Tank Farm at the Savannah River Site.” Aiken, South Carolina: 

Savannah River Remediation, LLC. 2012.

SRR–CWDA–2010–00128, Rev. 1. “Performance Assessment for the H-Area Tank Farm at the 

Savannah River Site.” Aiken, South Carolina: Savannah River Remediation, LLC, Closure and 

Waste Disposal Authority. 2012.

SRR–CWDA–2012–00020, Rev. 0. “Savannah River Site Liquid Waste Facilities Performance 

Assessment Maintenance Program, FY2012 Implementation Plan.” Aiken, South Carolina: 

Savannah River Remediation, LLC. 2012.

SRS–REG–2007–00002, Rev. 1. “Performance Assessment for the F-Tank Farm at the 

Savannah River Site.” Aiken, South Carolina: Savannah River Remediation, LLC, Closure and 

Waste Disposal Authority. 2010.
APPENDIX D

MA 3, “CEMENTITIOUS MATERIAL PERFORMANCE”
D–1

MA 3, “CEMENTITIOUS MATERIAL PERFORMANCE”

DOE relies on the cementitious vault materials to (i) limit flow and transport of deleterious

species into the vault or key radionuclides out of the vault; (ii) condition the chemistry of the 

water contacting the residual waste, thereby limiting dissolution of radionuclides associated with 

the residual waste (see MA 2 for a discussion of dissolution of residual waste); (iii) retard 

radionuclide transport through the vault via interactions with cementitious grout and vault 

materials; and (iv) stabilize waste residuals. These capabilities are directly dependent upon the

chemical and hydraulic performance of the cementitious materials. The NRC has identified the 

following MFs related to the capabilities of the cementitious materials to limit or mitigate 

releases from the tank farms:

• MF 3.1 “Hydraulic Performance of Concrete Vault and Annulus (As It Relates to Steel Liner 

Corrosion and Waste Release)”

• MF 3.2 “Groundwater Conditioning via Reducing Grout”

• MF 3.3 “Shrinkage and Cracking of Reducing Grout”

• MF 3.4 “Grout Performance”

• MF 3.5 “Vault and Annulus Sorption”

• MF 3.6 “Waste Stabilization (As It Pertains to ALARA)”

MA 3, “Cementitious Material Performance,” MF 3.2—“Groundwater Conditioning via Reducing 

Grout,” focuses on the nature of flow or the hydraulic performance of the tank and vault grout, 

while technical uncertainties related to the geochemical modeling performed to estimate the 

extent to which groundwater is conditioned by the tank grout and geochemical changes over 

time is addressed under MA 2, “Waste Release,” MF 2.2—“Chemical Transition Times.” Both 

MFs, however, pertain to the rate at which grout degradation proceeds and leads to changes in 

the chemistry of the infiltrating water over time and are therefore closely related. 

Other NRC TER recommendations related to cementitious material or steel liner1 performance 

are binned by NRC under PA maintenance activities under MA 6 until NRC obtains a better 

understanding of overall tank farm facility performance. Should the results of experiments 

conducted under MA 2, “Waste Release,” or MA 3, “Cementitious Material Performance,” 

indicate less than favorable results, NRC staff expects DOE to assess the impact on the results 

of the PAs. NRC staff also will assess the need for additional experiments, data collection, and 

modeling to provide support for key barriers in DOE’s PAs that might serve to mitigate 

underperformance of chemical and hydraulic barriers. If the results of waste release 

experiments show key radionuclides are strongly retained in the residual waste, NRC staff 

expects other MAs or MA components, including MA 3, “Cementitious Material Performance,” 

will become less important and may be closed as monitoring progresses.

 

1Steel liner performance is indirectly related to cementitious material performance under MF 3.1— •Hydraulic 

Performance of Concrete Vault and Annulus (As It Relates to Steel Liner Corrosion and Waste Release).
D–2

MF 3.1—Hydraulic Performance of Concrete Vault and Annulus (As It Relates to 

Steel Liner Corrosion and Waste Release)

DOE relies on steel liners to limit water flow to the residual waste remaining in many of the 

tanks.

2

 DOE’s steel liner corrosion modeling relies on concrete vaults, which enclose the HLW

tanks, as barriers to fluid flow. DOE assumes the cementitious materials surrounding the steel 

liners will provide a passive chemical environment that will limit corrosion to a low general 

corrosion rate (1 μm/yr [0.04 mil/yr] in the base case scenario) prior to carbonation- or chlorideinduced steel depassivation that can lead to higher corrosion rates. Because chemical species 

that induce corrosion (i.e., water, chloride, carbon dioxide, and oxygen) need to be transported 

through the cementitious materials, NRC staff finds that the uncertainty in steel tank liner 

longevity is related primarily to the hydraulic properties of the cementitious materials and their 

effect on the persistence of a chemical and physical environment that will limit corrosion of the 

steel liner.

DOE’s corrosion analyses use diffusion coefficients of carbon dioxide, chloride, and oxygen 

applicable to intact concrete to model the transport of these species through the concrete vault. 

Although earlier corrosion initiation times and significantly higher corrosion rates could result if 

higher diffusion coefficients are assumed, higher diffusion coefficient values are only applied by 

DOE in limited cases in its probabilistic assessments (i.e., higher diffusion coefficients are not 

considered in the base case assessments). Also, DOE assumes concrete vault degradation 

starts once carbonation reaches one-half the concrete thickness, even though steel 

reinforcements typically have only a few inches of concrete cover (i.e., steel reinforcement is 

located much closer to the vault surface than one-half the concrete vault thickness). Although 

rebar corrosion-induced cracking of concrete would be delayed relative to carbonation of the 

concrete cover, initiation of concrete vault degradation may initiate sooner than assumed in 

DOE’s concrete degradation analysis. 

Additionally, although groundwater in-leakage into the concrete vaults is evident at the SRS

site,

3 DOE does not consider this phenomenon an important factor that could influence the 

expected performance of the concrete vaults and steel liner. DOE projects the steel liners for 

39 of 51 tanks fail after 10,000 years in the PA reference cases. DOE assumes the steel liners 

of one Type I and three Type II tanks at HTF are failed initially because of the number of 

observations of leak sites on their primary liners. While the liners of these tanks do not provide 

a significant barrier to waste release in the HTF PA, other assumptions (e.g., solubilitycontrolling phases and associated solubilities) ensure significant releases of key radionuclides 

are delayed beyond 10,000 years. Should these other assumptions prove incorrect, the risk 

significance of early liner failure should become evident. 

The steel liners of eight Type IV tanks are projected by DOE to fail in the DOE PAs after 

3,600 years. These tanks provide a rather significant early barrier to waste release should other 

model assumptions prove incorrect. Because Type IV tank bottoms at FTF are near the water 

table, NRC staff also is concerned that intermittent flooding of the tank bottoms due to water 

 

2DOE assumes Type I Tank 12H and Type II Tanks 14H, 15H, and 16H are initially failed at HTF because of a 

significant number of leaksites. Although some tanks at FTF have leaksites (C–ESR–G–00003), DOE does not 

assume any FTF tanks are initially failed in its PA. In an onsite observation visit in March 2014, DOE clarified that the 

logic used to determine that tanks were initially failed in the HTF PA was not used for the FTF PA (ML14106A573). If 

the same logic was applied, DOE may have assumed that some FTF tank liners were initially failed.

3See DP-1358 and SRR–ESH–2013–00078, for example.
D–3

table fluctuations over the long period of performance could (i) expose the tank liners 

periodically to corrosive environments and (ii) cause contaminants exiting the basemat to be 

released directly into the saturated zone. The contaminated zones of Type IV tanks at HTF also 

appear to be within the zone of water fluctuation (SRNL–STI–2010–00128). DOE also notes in 

SRNL–STI–2012–00079 that given the close proximity of Type I FTF tanks to the water table, 

the likelihood that groundwater could come in contact with the grouted tanks is high because the

average depth to water ranges from 0.3 to 2 m [1 to 6 ft]. These concerns about periodically 

exposing the tank liners to corrosive environments and release of contaminants directly to the 

saturated zone are also applicable to Type II tanks at HTF, which are partially submerged in the 

water table. Furthermore, Type II tanks at HTF are projected in DOE’s PA to have a significant 

annuluar inventory. DOE should more fully evaluate the potential effect of water in-leakage and 

drainage on waste release for those tanks that are partially submerged or whose tank bottoms 

are located in the zone of water table fluctuation. 

DOE’s lack of consideration of flow through preferential pathways through the concrete vault 

and annulus in the FTF and HTF reference cases may lead to an underestimate of dose. 

Consideration of preferential pathways through the system may increase release rates for waste 

located in both the primary liner and in the annuli of certain tanks. For example, simulated 

limited flow through preferential pathways in DOE’s models may lead to unrealistic estimates of 

the degree of retention in the cementitious materials compared to what may actually occur in the 

real system if a greater quantity of flow bypasses the attenuating properties of the concrete 

vaults. For example, NRC staff indicated in the HTF TER that for HTF Type I and II tanks with 

residual waste in their annular regions (including the sandpads beneath the liners of Type II 

tanks), DOE has not adequately evaluated the risk from annular or sand pad releases through 

preferential pathways through the annuli and concrete vault. 

Given the potential risk significance of the steel liner barrier and retention of contaminants in the 

concrete vault, DOE should provide additional support for the assumptions used in its base case 

assessment that concrete vaults will remain an effective fluid flow barrier that prevents exposure 

of the tanks to corrosive conditions for thousands to tens of thousands of years and limits the 

releases of contaminants initially present in the annuli of certain tanks, most notably certain 

Type I and II tanks at HTF. A peer review panel that evaluated the DOE PA modeling of waste 

release and transport noted that fracturing of the cement-based material with preferential flow 

through cracks would appear to be a more likely scenario that should be evaluated 

(LA-UR-2012-00079). While referring to the waste release model, this statement by the peer 

review panel would also apply to cementitious material and steel liner degradation models, and 

suggests that relatively slow carbonation of cement-based material via matrix diffusion of carbon 

dioxide may lead to an underestimate of cement and steel liner failure times.

In its HTF TER (ML14094A496), NRC staff also questioned DOE’s assumption of low corrosion 

rates, because oxidation and reduction reactions that control corrosion could be 

macroscopically separated. Metal locations where oxygen reduction occurs can be physically 

separated from locations where iron is oxidized and dissolved if the two locations are electrically 

connected. In other words, limited supply and transport of oxygen to the liner surface may not 

necessarily limit corrosion rates.

NRC staff will review reports, analog studies, and other information used to support DOE’s 

assumption regarding initial conditions and performance of the concrete vaults. For example, 

NRC staff will review annual tank inspection reports that provide information regarding 

trenching, scarifying, and cracking of the concrete vaults, as well as information about 

groundwater intrusion into the tank vaults. NRC staff will review reports related to previous 
D–4

events that led to potential releases for groundwater in-leakage through joints or cracks in the 

concrete vaults. Analog studies could include review and evaluation of information obtained 

from West Valley or other analog sites to better understand the potential for and rates of 

corrosion of HLW tanks/components, as well as mitigative design measures. As part of this MF, 

NRC staff also will consider the potential for earlier steel liner failure than assumed in DOE’s PA 

for many of the tanks due to corrosion of steel components (e.g., rebar) in the concrete vaults 

that are close to the vault surface and due to corrosion resulting from macroscopically

separated electrochemical reaction sites. NRC staff will also consider the potential for earlier 

waste release from the annular regions of Types I and II HTF tanks than assumed in DOE’s PA 

due to flow through preferential pathways.

If DOE performs additional modeling or experiments to study the potential for transport of 

deleterious species into the tank vaults and subsequent corrosion of the steel liners or tanks, 

NRC staff will review the documentation or provide input on the design and results of the 

experiments. Experiments to study steel liner corrosion are expected to be relatively difficult to 

implement with unknown benefit compared to other experimental investigations recommended 

in NRC’s TERs (ML112371751, ML14094A496) and discussed in this monitoring plan. 

Therefore, these experiments are not considered a high priority by NRC staff at this time. NRC 

staff will assume the steel liners will not be effective at mitigating releases for the long periods of 

time typically relied on for performance in the PAs and will investigate the support for the 

performance of other barriers to ensure that the POs can be met. Should results of other 

investigations indicate that tank farm barriers relied on in DOE’s reference (or best estimate) PA 

cases are not expected to perform as well as assumed, then more thought will be given to 

methods for obtaining additional support for steel liner performance assumptions, including use 

of a patch model that could simulate such processes as partial failure and slower release rates 

from the tanks.

If DOE performs additional modeling or experiments to study the potential for early release of 

residual waste from the tank vaults through preferential pathways, NRC staff will review the 

documentation or provide input on the design and results of experiments. Experiments are 

expected to be difficult to implement because many parts of the concrete vaults and annuli are 

not presently observable and their present condition is uncertain. However, modeling of waste 

release from preferential pathways may demonstrate that the performance objectives can be 

met even with earlier release through preferential pathways. For example, NRC staff 

recommended in the HTF TER (ML14094A496) that DOE conduct a more comprehensive 

analysis of the potential release of radionuclides from the annuli and sand pads of Types I and II 

tanks. To address NRC staff’s concerns, DOE considered an alternative scenario that included 

a preferential pathway (e.g., construction joint) through the Tank 16H vault in a Special Analysis 

(SRR–CWDA–2014–00106). NRC staff is in the process of evaluating the Special Analysis and 

will present its review findings in a technical review report to be issued later in FY2015.

NRC staff may conduct technical review activities listed previously in conjunction with onsite 

observations that could help inform its assessment of the concrete vaults as a hydraulic barrier 

mitigating steel liner corrosion and waste release. If DOE conducts experiments to provide 

additional support for concrete vaults as effective hydraulic barriers, NRC staff may observe 

these experiments at SRS facilities. 
D–5

MF 3.2—Groundwater Conditioning via Reducing Grout

The hydraulic performance of the tank grout is important to DOE’s compliance demonstration 

because it both limits infiltration and delays chemical transition times to higher solubility, thereby 

reducing and delaying waste release from the contaminated zone4 for long periods of time. The 

transitions in chemical conditions in the grout and residual waste that generally lead to higher 

solubility are directly dependent on how water flows through the grouted tanks and, potentially, 

from below the tanks. NRC staff has unresolved technical concerns regarding the potential for 

the existence or creation of fast flow paths through the grouted tanks. The potential for 

relatively rapid chemical modifications along these flow paths, and consequent chemical 

transitions, have not been ruled out. For example, water may flow along cracks relatively 

rapidly and react with the grout lining the crack walls. This may lead to a chemical environment 

for percolating water that is quite different from that for water permeating through the bulk grout 

(e.g., lower pH, higher Eh, and higher aqueous carbonate—as a result of calcification of the 

crack walls).

In addition to flow through preferential pathways, water table rise could lead to a scenario where 

residual waste comes into contact with unconditioned groundwater that has not significantly 

interacted with the reducing grout that lies above the waste residue. As stated previously, water 

table rise above the bottom of the tanks is primarily a concern for Type IV tanks at FTF and 

HTF, as well as Type II tanks at HTF that are partially submerged in the water table.

For Type I tanks at HTF, DOE does consider a large fraction of unconditioned water flowing 

horizontally into the tank system mixing with a small fraction of conditioned groundwater flowing 

vertically through the reducing tank grout located above the contaminated zone in its base 

case.

5

 However, the level of conditioning afforded by the small quantity of water assumed to 

flow vertically through the reducing HTF Type I tank grout is nonetheless quite significant. The 

number of pore water exchanges needed for each chemical transition is actually higher for Type 

I tanks compared to other HTF tanks (see Table 3-2). This counterintuitive result occurs 

primarily due to assumptions regarding the chemistry of the saturated groundwater that is 

assumed to flow into the tank (i.e., low Dissolved Oxygen or DO).6

 With regard to flow 

assumptions, NRC staff also thinks DOE should provide more support for its assumptions that 

the engineered system will not interfere with the ability of the reducing grout to sufficiently 

condition the infiltrating water for fully submerged tanks.

The lack of characterization of the waste, and especially the transuranic elements in it, make the 

impacts associated with a water table rise scenario uncertain. NRC staff will evaluate the 

likelihood and assumptions of these scenarios under this monitoring factor through review of 

historical water table data, groundwater chemistry data, and observations of the conditions and 

 

4DOE assumes that residual waste in the annular regions of HTF Types I and II tanks is soluble, although chemical 

transition times affect the Kds or desorption rates for waste located in annuli of Type I tanks (annular waste is loaded 

in the reducing tank grout that will be used to fill the annuli of Type I tanks). 5DOE assumes a ratio of 90- percent unconditioned groundwater and 10-percent conditioned infiltrating water 

contacting the contaminated zone.

6While DOE reports low DO of the unconditioned groundwater as the cause of the longer chemical transition times in 

SRNL–STI–2012–00404, Table 4.2-8 in the HTF TER indicates that Eh is used in the geochemical modeling to 

estimate chemical transition times. Because NRC staff analysis of water table well data used in the modeling 

indicates that Eh and DO may not be well correlated, NRC staff plan to follow up on the effect of Eh and DO on the 

chemical transition times in DOE’s geochemical modeling in a future TRR.
D–6

performance of the concrete vaults and other engineered barriers installed during monitoring to 

affect the flow of water through the tanks.

NRC staff is concerned with DOE’s PA assumptions regarding the transition from reduced to

oxidized conditions. For example, it is not clear to NRC staff that infiltrating groundwater will, in 

fact, be conditioned to low Eh by the tank grout. Under contract with the NRC, CNWRA has 

collected experimental data relevant to the saltstone disposal facility. These data indicate that 

even if a significant portion of the system remains in a reduced state, minimal interaction 

between infiltrating groundwater and the reduced inner pore space of the waste form may occur,

such that the Eh of the groundwater is more reflective of the incoming groundwater chemistry, 

rather than a groundwater conditioned by the waste form grout (Pabalan, et. al., 2012). 

Because flow rates used in CNWRA experiments are higher than might occur in the real 

system, it is possible that the experimental conditions might not be representative of the real 

system. Therefore, DOE should undertake experiments using grout formulations consistent with 

those used or planned for the tanks to confirm PA assumptions regarding groundwater 

conditioning and chemical transition times that are important to compliance demonstration. 

NRC staff will also evaluate data collected from lysimeter studies conducted at SRS, primarily to 

support the saltstone disposal facility PA, to see whether the data could help corroborate PA 

assumptions regarding the extent of groundwater conditioning. For example, the extent to 

which infiltrating water is conditioned by saltstone waste form present in the lysimeters may be 

used to support assumptions regarding conditioning of infiltrating water by tank grout.

Another DOE PA scenario is characterized by preferential pathways through the grout, along 

either cracks or shrinkage voids along the tank margins. In reality, carbonation of the grout can 

be expected to be relatively rapid along the preferential pathways. These calcite/aragonite 

coatings may inhibit conditioning of ingress water by the grout, such that the pH of the water is 

more likely conditioned by calcite rather than the grout hydroxide. In addition, the reducing 

capacity of the grout could decline relatively rapidly along these preferential pathways. DOE 

evaluated the performance impact of preferential pathways in alternative cases in the PAs.7

 

Case G from the FTF PA, developed in response to NRC Requests for Information (RAIs), also 

addressed other potential issues with DOE’s base case analysis. In all FTF PA cases, peak 

doses were in the range of a few mSv/yr (hundreds of mrem/yr) from Pu-239 

(SRS-REG-2007-00002, SRR-CWDA-2009-00054). The primary difference between these 

cases was the timing of the peak dose. Because Case G also considered an earlier transition to 

higher solubility-limiting phases, this scenario resulted in peak doses that exceeded the dose 

standard in 10 CFR 61.41 within 10,000 years. Likewise, Case E from the HTF PA also 

evaluated the impact of preferential pathways. This scenario also resulted in peak doses that 

exceeded the dose standard in 10 CFR 61.41 within 10,000 years. Therefore, if Cases G of the 

FTF PA and E of the HTF PA are found to be more likely than assumed by DOE, the extent to 

which groundwater is conditioned under this scenario may become important to the compliance 

demonstration and will be evaluated under this MF. 

 

7In the FTF PA or RAI responses, DOE evaluated the impact of preferential pathways in Cases C, D, and G. In the 

HTF PA, DOE evaluated the impact of preferential pathways in Cases B–E.
D–7

MF 3.3—Shrinkage and Cracking of Reducing Grout

As discussed in the preceding section, the hydraulic performance of the tank grout is important 

to DOE’s compliance demonstration because it both limits infiltration and delays chemical 

transition times to higher solubility chemical conditions, thereby reducing and delaying waste 

release from the contaminated zone for long periods of time. An important factor in the 

longevity of the chemical barrier performance within the nonsubmerged tanks is the DOE 

assumption that the infiltrate reaching the contaminated zone does not bypass the waste tank 

grout (via fast flow pathways). Instead, downward flow through the grout remains relatively 

uniform and significant across the plane of the contaminated surface. DOE should provide 

additional support for this assumption. NRC staff is concerned that in actual field conditions, 

only a fraction of the grout components may be accessible for reaction with the infiltrate, 

particularly if flow occurs through preferential fast pathways. Preferential fast flow pathways 

could include shrinkage gaps that form:

• Between the tank grout and steel liner;

• Between the tank grout and internal fixtures;

• At lift interfaces; or

• In between individual grout flow lobes, including the pseudo-cracks formed at internal

fixtures where grout split by an obstacle into two lobes merges back together to form a 

vertical seam on the trailing edge of the obstacle.

CNWRA observed many of these listed features through an independent, NRC-funded study of 

large grout monoliths (Walter and Dinwiddie, 2008; Walter, et al., 2009; Walter, et al., 2010; 

Dinwiddie, et al., 2011; Dinwiddie, et al., 2012). The study is providing information to help 

assess the robustness of DOE assumptions regarding the nature of flow through the tank grout 

that affects the calculated chemical transition times. NRC conducts these analyses to 

independently inform its review rather than make conclusive findings because NRC recognizes 

these studies cannot fully duplicate conditions in waste tanks at SRS. DOE should consider 

conducting its own grout studies and inspections of the distribution, consistency, flowability, and 

topography of the grout, as it is placed in the tanks, as well as measurement of the in-place 

physical properties of the grout, including vertical distribution and temporal evolution of grout 

density, porosity, and permeability. These activities could provide the information necessary to 

support key PA modeling assumptions.

DOE also should consider design measures to minimize the occurrence of negative features, 

events, or processes related to grout placement. For example, DOE should consider removal of 

in-tank equipment that could lead to development of shrinkage-induced annuli around 

equipment or corrosion of steel components and associated cracking due to corrosion product 

expansion. DOE also should ensure the ability of the tank grout to fill all void spaces (i.e., grout 

should be self-leveling) to minimize imperfectly bonded grout seams and voids that may form in 

between grout pours. DOE should research and evaluate shrinkage-compensating agents for 

use in its grout formulations to minimize shrinkage, shrinkage gap formation, and creation of

annuli and void space within the tank grout, as recommended in SRNL-STI-2011-00551.

Preferential fast flow pathways also include cracks that form due to thermal or mechanical 

stresses (e.g., those due to settlement or corrosion product expansion from steel component 

corrosion). NRC will request information regarding thermal gradients generated during tank 
D–8

grout curing and evaluate potential for thermal cracking in a future technical review activity or 

onsite observation. In its technical reviews of the final configurations for Tanks 18F/19F; and 

Tanks 5F/6F at FTF, NRC staff noted that a more detailed thermal analysis that considers the 

specific grout pour sequence and geometry to determine the impact on grout porosity, hydration 

products, and the potential for thermal cracking of the tank ground would improve model support 

(ML13269A365; ML14342A784). Cracking due to settlement is discussed in Section 6.2.

NRC staff also is concerned with potential formation of cracks in the tank grout due to alkalisilica reaction (ASR). ASR is a process whereby reactive aggregates break down under 

exposure to the highly alkaline pore solution in concrete, which can result in significant 

expansion and, in some cases, cracking of concrete. This concern arose because the grout 

being used to fill Tanks 18F and 19F included 3/8-inch granite “pea gravel” as an aggregate, 

instead of using only sand aggregate, as described in the DOE’s FTF PA document 

(SRS-REG-2007-00002), and because of recent observations of concrete cracking at the 

Seabrook Nuclear Power Plant in Seabrook, New Hampshire. In that facility, granite aggregates 

also were used in the concrete mix. ASR is a slow process, and its occurrence at Seabrook 

became evident only decades after the plant was constructed. Grout fill mix in Tanks 18F and 

19F contained less Portland cement than the concrete mix used at Seabrook and likely would 

be less susceptible to ASR. Nevertheless, NRC staff is concerned that DOE’s criterion for 

acceptance of vendor-supplied granite aggregate relies on short-term alkali reactivity tests 

(ASTM C–1260), which is unlikely to predict the occurrence of ASR over the very long period of 

performance for compliance with PO 61.41. NRC staff first raised the ASR technical issue with 

DOE in an onsite observation (ML12191A210). NRC staff also discussed this issue in its 

technical review reports for Tanks 18F/19F grouting, and Tank 5F/6F grouting (ML13269A365

and ML14342A784). NRC staff will continue to discuss this issue with DOE and evaluate the 

potential for ASR to negatively impact tank farm performance in future technical review activities

or onsite observations.

NRC staff will review grout formulations, calculations, research, test methods, and results to 

ensure the disposal facility is designed to minimize fast flow path development. NRC staff may 

conduct technical reviews in conjunction with onsite observations that could include such 

activities as video inspections of grout pours, observations of grout tests, and inspections of test

specimens.

MF 3.4—Grout Performance

During onsite observations, NRC staff will verify the actual grout formulation DOE uses is

consistent with performance assumptions in the PAs (SRS–REG–2007–00002,

SRR–CWDA–2010–00128) and design specifications assumed in the final waste determinations 

(DOE/SRS–WD–2012–001, DOE/SRS–WD–2014–001). DOE should evaluate significant 

deviations from the design specifications to ensure expected grout performance will not be 

negatively affected. In addition, NRC staff will evaluate DOE’s program for sampling, testing, 

and accepting grout materials to ensure materials conform to DOE specifications and national 

standards, such as ASTM C–989. The verification program should incorporate a

comprehensive record-keeping system to include, for example, (i) plant operation records;

(ii) vendor-provided test reports on the grout components; (iii) as-received acceptance test 

reports on bleed, slump, and/or flow of each grout batch (e.g., ASTM C–232, ASTM C–143, 

ASTM C–1611) and records of any additional water or other components added onsite to meet 

the acceptance criterion prior to emplacement; (iv) DOE laboratory test results of composite or 

grab samples; and (v) certification of shipping records. As part of its evaluation, NRC staff 

expressed concern about the use of commercially available Portland cements in Tanks 18F/19F 
D–9

and 5F/6F because up to 5-wt% substitution with limestone can occur that could lower the pH 

buffering capacity of the grout and the observations of bleedwater segregation that could 

potentially impact hydraulic properties and grout quality and affect the timing of release of key 

radionuclides (ML13269A365; ML14342A784). 

Also, NRC staff will evaluate the adequacy of the verification program pertaining to DOE’s 

supply of grout components, such as blast furnace slag. NRC staff’s evaluation will be based, 

to the extent practicable, on direct observation of ongoing activities and interviews with key DOE 

personnel. The review will evaluate certain aspects of the program:

• Representativeness of the samples collected

• Adequacy of the analytical equipment

• Calibration of the analytical equipment

• Adequacy of verification records

To minimize degradation in the quality and chemical reactivity of the slag and Portland cement, 

DOE must store the material in weather-tight silos or bins to prevent contact with moisture. 

During onsite observations, NRC staff will examine silos or bins for storage of the slag and 

cementitious materials. In addition to the grout formulation, curing conditions are expected to 

have a significant effect on the short- and long-term performance of the emplaced grout. 

Numerous studies have shown that improper curing results in a variety of undesirable effects, 

such as lower strength, high permeability, and several types of cracking. For example, early 

age cracking could occur due to thermal and self-dessication stresses and uneven lift 

topography. DOE streamed live video (over the internet) of the initial grout pours into Tank 18F, 

which provided important information regarding grout flowability and non-self-leveling grout 

behavior. The technology needed to observe most stages of grout emplacement has thus been 

proven, and DOE should continue to use this technology during grout emplacement. NRC will 

review video footage of grout emplacement activities to (i) provide confidence that grout 

behavior during emplacement is understood and (ii) incorporate this information into NRC 

reviews of PA updates. NRC staff performing onsite observations will verify grout placement is 

conducted under proper temperature and humidity conditions or that steps are taken to ensure 

proper curing of the grout. NRC staff will also evaluate DOE’s efforts to ensure that grout is 

able to flow into voids within the tanks and remaining equipment so that no risk-significant void 

space remains in the grouted tanks and vaults.

MF 3.5—Vault and Annulus Sorption

An additional NRC concern pertains to the hydraulic and chemical performance of the concrete 

vault walls and floor, which NRC considers an important barrier to radionuclide release. Despite 

the relatively short transport pathway, sorption onto the concrete attenuates release of HRRs, 

such as isotopes of Np and Pu, by orders of magnitude in DOE’s PAs. DOE barrier analyses 

indicate the presence of a fast flow path through the basemat causes a more rapid release of 

contaminants. This effect is more evident for Pu because of its high sorption coefficient in 

oxidized concrete. Notwithstanding results of the barrier analyses, a fast flow path through the 

basemat is not considered a likely scenario in the DOE PA base cases. DOE needs to provide 

support for its base case assumption that the basemat will remain intact. In particular, the 
D–10

basemat underneath Type IV tanks is only 10 cm [4 in] thick and could be susceptible to 

cracking due to stress imposed by the mass of emplaced grout.

Additionally, the concrete vaults and reducing annular grout were shown in the HTF PA to be a 

potentially significant barrier to waste release. NRC staff will review studies and information 

regarding the sorptive capacity of these cementitious materials in attenuating releases from the 

vaults, as well as the chemical transition times of these cementitious materials as they affect 

sorption that may be important to the compliance demonstration.

References

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Information (Rev. 11)”. Aiken, South Carolina: Savannah River Remediation LLC. 

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Dinwiddie, C.L., D.R. Bannon, M.K. Todt, G.R. Walter, and M.M. Roberts. “Draft Fiscal Year 

2012 Meso- and Intermediate-Scale Grout Monolith Test Bed Experiments: Results and 

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D–11

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Waterways Experiment Station, U.S. Army Corps of Engineers. 1952.

Walter, G.R., C.L. Dinwiddie, D. Bannon, G. Frels, and G. Bird. “Intermediate Scale Grout

Monolith and Additional Mesoscale Grout Monolith Experiments: Results and 

Recommendations. San Antonio, Texas: Center for Nuclear Waste Regulatory Analyses. 

2010.

Walter, G.R., C.L. Dinwiddie, E.J. Beverly, D. Bannon, D. Waiting, and G. Bird. “Mesoscale 

Grout Monolith Experiments: Results and Recommendations.” San Antonio, Texas: Center for 

Nuclear Regulatory Analyses. 2009.
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Walter, G.R. and C.L. Dinwiddie. “Conceptual Design for Small-Scale Grout Monolith Tests.” 

San Antonio, Texas: Center for Nuclear Waste Regulatory Analyses. 2008.
APPENDIX E

MA 4, “NATURAL SYSTEM PERFORMANCE”
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APPENDIX E

MA 4, “NATURAL SYSTEM PERFORMANCE”

MF 4.1—Natural Attenuation of Key Radionuclides

The choice of appropriate distribution coefficient (Kd) values for radionuclides in the natural 

system is very important to PA analyses and has been the subject of considerable effort at SRS. 

As radionuclides are leached from the waste and released to the soil, sorption in the natural 

system will be a critical barrier that will depend on a number of factors, including pH, ionic 

strength of the solution, speciation of the radionuclides, and their oxidation state(s). 

In the FTF PA (SRS–REG–2007–00002), Pu is one of the most important radionuclides 

contributing to peak dose. For oxidized forms of Pu (V/VI), the “best” value for Kds is 16 mL/g. 

For reduced forms of Pu (III/IV), the best value for Kds is 300. Because Pu can exist in several 

redox states at the same time, a combination best value was suggested as 290 mL/g. These 

values were taken from SRNL–STI–2009–00473 as the best estimates for sandy sediment. As 

explained in the report, the combination value is a hybrid that is taken to describe fractions of Pu 

in two different oxidation states: 95 percent of reduced Pu (III/IV) and 10 percent oxidized (V/VI) 

[sic]. 

Subsequent to preparation of the DOE’s FTF PA (SRS–REG–2007–00002), Section 6.3.5.3.4 of 

the Tanks 18F and 19F Special Analyses (SRR–CWDA–2010–00124) explains that Pu Kds

values were reevaluated. Section 6.3.6.1 of the special analyses (SRR–CWDA–2010–00124) 

considers the impact of the new Kds values on the deterministic model results. A statistical 

analysis of 65 Kds values (SRNL–STI–2011–00672) taken from many areas and materials 

around the SRS was conducted in an attempt to reexamine Kds from a site-wide perspective. 

SRNL–STI–2011–00672 only grossly considers chemistry in evaluating Kds for FTF (e.g., pH is 

binned into two categories—greater or less than 7—and Pu redox state is not considered). 

SRNL–STI–2011–00672 recommends a Kd value of 650 L/kg for FTF based on the following: 

(i) information from a modeling analysis (Demirkanli, et al., 2007) of long-term lysimeter studies 

(Kaplan, et al, 2006) indicates that a Kd of 1,800 L/kg should be used and (ii) the statistical 

analysis shows that the 290 L/kg value used in the FTF PA is in the lower quantile. The 

sediment in the lysimeter appears to have had more clay in it than typically found at FTF, and so 

the 1,800 L/kg value was lowered to 650 L/kg. This value, in turn, was increased for the near 

field of the tanks, using a factor of two recommended in SRNL–STI–2009–00473 to account for 

greater adsorption due to elevated pH resulting from grout component leaching. Technical 

issues associated with DOE’s development of the Pu Kds are discussed in an NRC staff 

technical review report (ML12272A124). 

The work to analyze and model results of the SRS Pu lysimeters has led to a model in which a 

reduction rate and an oxidation rate drive concentrations of different Pu redox states at any 

given time (SRNL–STI–2009–00473; Kaplan, et al., 2006; Demirkanli, et al., 2007). This leads 

to a small fraction of mobile Pu and a large fraction of relatively recalcitrant Pu. To reproduce 

the profiles in the lysimeters, the two rates and the retardation factor needed to be adjusted. In 

lysimeters containing reduced Pu sources, a retardation factor of 15 was used for Pu in the 

small, mobile fraction, while a retardation factor of 10,000 was used for the larger fraction. Even 

with the high retardation of the large fraction, modeling was not able to capture the overall Pu 

distribution in the lysimeter by using a single species retardation factor (Demirkanli, et al., 2007). 

A small, mobile fraction was needed to mimic the soil profile of Pu below the source.
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The long-term lysimeter experiments conducted at SRS and other work referenced in Kaplan et 

al. (2006) show that although most Pu is in the (IV) state, there is a small component that at 

times is in a much more mobile form. In fact, most Pu that is in solution (albeit a very small 

concentration) is in the Pu (V) form. Even PuO2(s), which had been considered a stable form of 

Pu (IV), has been shown to oxidize in the presence of water, forming a substantial fraction 

(27 percent) of Pu (VI) (Haschke, et al., 2000). In SRS sediment, it is thought that Pu cycles 

repeatedly through the Pu (IV) and Pu (V) oxidation states in response to wet/dry cycles 

(WSRC–MS–2003–00889).

From SRNL–STI–2009–00473 the best Kd value for sandy soil for Pu (V/VI) is 16 mL/g, while for 

Pu (III/IV) the best value is 300 L/kg. Recognizing that Pu chemistry is especially complex and 

disproportionation presents a difficult problem, NRC staff suggests that averaging Kd values for 

different oxidation states is not appropriate, even if values are weighted for proportions of 

different redox states. 

A potential additional complication is the possibility that Pu (III) can be produced by certain 

common Fe (II) species, and that the Pu (III) form can be more soluble or mobile than Pu (IV). 

The finding by Felmy, et al. (2011) that Pu (IV) can be reduced to Pu (III) by Fe (II) and that the 

presence of certain Fe (III) minerals increases the reaction rate suggests that for long times a 

single Kds, steady-state adsorption model may not be appropriate. For the SRS lysimeters 

containing sources of reduced Pu, XANES showed that in the soil, Pu was distributed as 

follows: approximately 37 percent Pu (III), 67 percent Pu (IV), 0 percent Pu (V), and 0 percent 

Pu (VI) (Kaplan, et al., 2007). This distribution was essentially the same for both the Pu (III) and

Pu (IV) lysimeters. In both cases, most Pu remained very close to the source over 11 years;

however, a small but measurable quantity of Pu in the sediment had migrated to a maximum of 

15 cm [5.9 in] from the source, giving a concentration of about 1 pCi/g. XANES is not sensitive 

to species that are less than about 5 percent abundance, so even if some Pu (V) were present,

it would almost certainly not be observed. From the evidence based on research at SRS, it is 

apparent that in the presence of reduced Pu, some small fraction can be oxidized, enter 

solution, and become relatively mobile. This is probably an ephemeral process, with Pu (IV) 

and Pu (V) switching back and forth, but always heavily dominated by Pu (IV). Factors such as 

complexation of the aqueous phase and possibly microbiological activity will potentially 

influence this distribution in a currently unknown way.

SRNL–STI–2012–00106 provides a discussion of the possible solid phases and aqueous 

species in which Pu may reside in residual tank wastes. Recent SEM analysis (of a single 

waste sample) is reported (Hay, et al., 2012) to show Pu present as discrete, small (<1 um) 

particles that are currently not characterized. The mass of these particles seems to be smaller 

than total Pu in the sample, suggesting that some Pu also is coprecipitated. Further, the 

formation of PuO(CO3)xH2O(solid) or Pu(OH)2(CO3)(solid) in the presence of aqueous Pu carbonate 

species in the tank heels is viewed as a likely possibility. In fact, carbonate concentrations of 

about 0.04 M were measured in the aqueous phase of Tank 18F heels. Recently, XRD analysis 

of Tank 18F heels shows the presence of Na4UO2(CO3)3 and calcite at about 10 percent of the 

crystalline solid phase material (SRNL–L3100–2012–00017). The presence of these solids and 

the measured aqueous carbonate concentrations strongly suggests that some Pu in the heels is 

in a carbonate form. If Pu is present as a carbonate solid, then at pH 9.8, relatively high Pu 

solubilities of around 1 × 10−6 mol/L can be expected. Hobbs suggests that the OH ̅ from the 

grout, in contact with the heels, should convert the carbonate to less soluble Pu(OH)4(am) or 

PuO2(am, hyd). However, it is not clear whether this process does in fact take place; Hobbs 

recommends experiments to verify the transformation. These observations suggest that at least 

some of the Pu in the aqueous phase in the heels will be negatively charged carbonate 
E–3

complexes of higher solubility. SRNL–STI–2012–00106 reported that Pu(OH)2(CO3)2

−2 was the 

dominant solution Pu species between pH 9.4 and 10.1, while Pu(OH4)(CO3)2

−4 was the 

dominant Pu solution species when pH was between 12 and 13. If these species are present in 

leachate from the grouted tanks, then very low Kds values can be expected. The stability of 

these species under high pH and varying redox conditions is not clear. 

Therefore, based on the information presented previously, NRC staff will monitor DOE’s efforts 

to conduct transport modeling that explicitly accounts for the multiple oxidation states of Pu that 

may be present or may form during transport through the FTF far field. Kds for Pu should be 

developed based on sorption studies relevant to FTF (i.e., based on sorption to sediments 

encountered during transport from the FTF tanks to various points of compliance and 

considering important changes to geochemical conditions that may occur over space and time).

As expressed in the HTF TER (ML14094A496), NRC staff has technical issues associated with 

the cement leachate factors applied in the HTF Performance Assessment (SRR–CWDA–2010–

00128, Table 4.2-25). The cement leachate factors are used to account for the effect of high pH 

leachate on the ability of natural soils to sorb key radionuclides also present in the leachate. 

The cement leachate factors used in the HTF PA are based on information provided in SRNL–

STI–2009–00473 and Hanford site data. As stated in the HTF TER, because the Hanford site 

geological and geochemical environment contrasts sharply with SRS, using Hanford site data to 

calculate the factors for SRS is not justified without an element-by-element analysis of the 

chemical processes affecting sorption. Element-specific considerations were applied to some 

but not all key radionuclides when deriving cement leachate factors. With respect to uranium 

and neptunium, DOE uses cement leachate factors for sand greater than 1, and DOE selected a 

value of 0.9 for Pu, which is higher than the value of 0.25 used in the Hanford study. Selection 

of the Pu and U cement leachate factors is based on solubility arguments. However, sorption 

describes a different natural attenuation mechanism, which is different than solubility 

constraints, and solubility limits may not be appropriate for application in the natural 

environment. Furthermore, the sorption behavior of actinides at high pH in the unsaturated 

zone may be strongly dependent on the presence of carbonate species. Sorption may 

decrease in the presence of elevated pH if high carbonate concentrations exist in the natural 

environment.

NRC staff recently issued a technical review report (ML12272A124) related to MF 4.1, “Natural 

Attenuation of Pu,” and MF 4.3, “Environmental Monitoring,” listed in NRC staff’s FTF Monitoring 

Plan (ML12212A192). The NRC staff listed a few follow-up actions that were not included in the 

original FTF monitoring plan, including the following:

• The NRC staff will continue to monitor support for cement leachate factors developed for Pu 

(and other constituents). DOE could provide support for cement leachate factors by 

performing site-specific analyses (this issue will be addressed under MF 4.1, “Natural 

Attenuation of Key Radionuclides”).

• The NRC staff will continue to monitor the basis for selection of the Nb distribution 

coefficient or Kd value of 160 L/kg used in the Tanks 5F and 6F Special Analysis. DOE 

could address the technical issues by verifying that the batch experiments did not exceed 

solubility limits and are representative of conditions at FTF (e.g., plot solid phase versus 

aqueous phase concentration or Kd versus concentration; evaluate Kd for FTF aquifer soils) 

or performing additional experiments to verify the Nb Kd (this issue will be addressed under 

MF 4.1, “Natural Attenuation of Key Radionuclides”).
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• The NRC staff will continue to monitor the ability of the tank farm monitoring well network to 

detect releases from the tank farm facilities following closure. DOE could evaluate the 

monitoring well network by performing an analysis of the centerline of plumes emanating 

from tank sources should releases occur in the future and providing input on optimal well 

locations to ensure that future releases from the tank farm facility would be detected (this

issue will be addressed under MF 4.3, “Environmental Monitoring”).

• The NRC staff will continue to evaluate the source of elevated Tc-99 levels in well FTF 28. 

It is not clear that releases from the F-Area Inactive Process Sewer Line could migrate 

vertically to the lower zone of the UTRA in such a short distance from the source. This 

evaluation is important to ensure that the hydrogeological system at FTF is well understood 

and that releases from the tanks could be detected by the monitoring well network. DOE 

could provide additional support for the source of contamination detected at well FTF 28 by 

performing particle tracking to better understand contaminant plume trajectories. DOE could 

also perform a more formal statistical analysis of FTF and Western Groundwater Operable 

Unit well data to correlate contaminant concentrations associated with various sources (this 

issue will be addressed under MF 4.3, “Environmental Monitoring,” and MF 6.2, “Model and 

Parameter Support”).

References

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Plutonium Transport in the Savannah River Site Vadose Zone.” Vadose Zone Journal. Vol.6. 

pp. 344–353. 2007.

Felmy, A., D.A. Moore, K.M. Rosso, O. Qafoku, D. Rai, E.C. Bock, and E.S. Ilton. 

“Heterogenous Reduction of PuO2 With Fe(II): Importance of the Fe(III) Reaction Product.” 

Environmental Science and Technology. Vol. 45. pp. 3,952–3,958. 2011.

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