April 21, 2014 

MEMORANDUM TO: Gregory Suber, Chief 

Low-Level Waste Branch 

Environmental Protection 

 and Performance Assessment Directorate 

Division of Waste Management 

 and Environmental Protection 

Office of Federal and State Materials 

 and Environmental Management Programs 

THRU: Christepher McKenney, Chief /RA/

Performance Assessment Branch 

Environmental Protection 

 and Performance Assessment Directorate 

Division of Waste Management 

 and Environmental Protection 

Office of Federal and State Materials 

 and Environmental Management Programs 

FROM: Christopher Grossman, Systems Performance Analyst /RA/ 

Performance Assessment Branch 

Environmental Protection 

 and Performance Assessment Directorate 

Division of Waste Management 

 and Environmental Protection 

SUBJECT: TECHNICAL REVIEW: U.S. DEPARTMENT OF ENERGY 

DOCUMENTATION RELATED TO FEATURES, EVENTS, AND 

PROCESSES IN THE F-AREA TANK FARM PERFORMANCE 

ASSESSMENT 

The U.S. Nuclear Regulatory Commission (NRC) staff has performed a technical review of the 

subject documents prepared by the U.S. Department of Energy (DOE) that address the NRC 

staff technical evaluation report comments related to the documentation of scenario analysis for 

the F-Area Tank Farm (FTF) Performance Assessment (SRS-REG-2007-00002, Rev. 1). This 

technical review memorandum supports Monitoring Factor 6.1, “Scenario Analysis” listed in the 

NRC staff’s FTF Monitoring Plan (available in the Agencywide Documents Access and 

Management System (ADAMS) Accession No. ML12212A192). 

CONTACT: Christopher Grossman, FSME/DWMEP 

 (301) 415-7658 
 2 

As described in the enclosure, DOE prepared an ex post facto analysis of features, events, and 

processes (FEPs) considered for the liquid waste performance assessments and an evaluation 

of the adequacy of the disposition of included FEPs in the FTF Performance Assessment. 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. 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. The questions and issues raised 

in the enclosure can be addressed as part of DOE’s performance assessment maintenance 

program or as part of special analyses for specific tank closures. 

Enclosure: 

Technical Review of Features, 

 Events, and Processes in the F-Area Tank 

 Farm Performance Assessment 
 2 

As described in the enclosure, DOE prepared an ex post facto analysis of features, events, and 

processes (FEPs) considered for the liquid waste performance assessments and an evaluation 

of the adequacy of the disposition of included FEPs in the FTF Performance Assessment. 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. 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. The questions and issues raised 

in the enclosure can be addressed as part of DOE’s performance assessment maintenance 

program or as part of special analyses for specific tank closures. 

Enclosure: 

Technical Review of Features, 

 Events, and Processes in the F-Area Tank 

 Farm Performance Assessment 

DISTRIBUTION (w/Enclosure): CBarr GAlexander LParks MFuhrmann/RES 

MFerdas/Region 1 MRoberts/Region 1 DPickett/CNWRA CDinwiddie/CNWRA 

WIR ServiceList WIR e-mail Contacts List 

ML13277A063 

OFC DWMEP:TR DWMEP:LA DWMEP: PM DWMEP:BC DWMEP:TR 

NAME CGrossman AWalker-Smith HFelsher CMcKenney CGrossman 

DATE 3/25/14 3/27/14 3/28/14 4/18/14 4/21/14 

OFFICIAL RECORD COPY
Enclosure 

Technical Review of Features, Events, and Processes in the F-Area 

Tank Farm Performance Assessment 

Date: March 25, 2014 

Reviewers:

Mr. Christopher Grossman and Ms. Cynthia Barr, U.S. Nuclear Regulatory Commission (NRC), 

And Ms.Cynthia Dinwiddie, Southwest Research Institute® 

Documents: 

SRR-CWDA-2012-00011. Hommel, S. “Features, Events, and Processes for Liquid Waste 

Performance Assessments.” Revision 0. Aiken, South Carolina: Savannah River Remediation, 

LLC. February 14, 2012. 

SRR-CWDA-2012-00022. Hommel, S. “Evaluation of Features, Events, and Processes in the 

F-Area Tank Farm Performance Assessment.” Revision 0. Aiken, South Carolina: Savannah 

River Remediation, LLC. February 15, 2012. 

Summary of Documents: 

The U.S. Department of Energy (DOE) prepared an ex post facto evaluation of features, events, 

and processes (FEPs) for the F-Area Tank Farm (FTF) Performance Assessment 

(SRS-REG-2007-00002, Rev 1). The aforementioned reports document the analysis which 

consisted of four steps: 

(Step 1) Implementation of FEPs in the FTF Performance Assessment; 

(Step 2) Identification of FEPs; 

(Step 3) Screening of FEPs; and 

(Step 4) Evaluation of FEPs included for consideration in the FTF Performance 

Assessment. 

Identification of FEPs:

Specifically, SRR-CWDA-2012-00011, Rev. 0 documents the methods used in identification of 

FEPs (i.e., Step 2) that could potentially affect the performance of Savannah River Site (SRS) 

liquid waste closure facilities and the criteria to screen FEPs (i.e., Step 3) for inclusion in or 

exclusion from the performance assessments (e.g., FTF Performance Assessment). 

SRR-CWDA-2012-00022, Rev. 0 documents a crosswalk that maps included FEPs to the FTF 

Performance Assessment (SRS-REG-2007-00002, Rev 1) and evaluates whether the FTF 

Performance Assessment appropriately incorporates included FEPs (Step 4). Implementation 

of FEPs in the FTF Performance Assessment was performed prior to Steps 2-4 during 

development of the FTF Performance Assessment (SRS-REG-2007-00002). 

The identification of FEPs (Step 2) included the compilation of FEPs from several domestic and 

international lists for radioactive waste management. Specifically, DOE compiled FEPs from the 

sources listed in Table 1. The compilation of FEPs from these sources resulted in a total of 
- 2 - 

1,383 FEPs including duplicates. DOE then proceeded to remove duplicates and combine 

similar FEPs, which resulted in 245 unique FEPs. DOE categorized the 245 unique FEPs into 

six groups and 32 associated subgroups that were used to perform the screening (Step 3) for 

the liquid waste performance assessments. See Table 2 for a listing of categories. DOE then 

reviewed the existing liquid waste performance assessments and identified 17 additional FEPs 

that were missing from the initial list, resulting in a total of 262 initial FEPs to be screened during 

Step 3. 

Table 1. Sources for Identification of Features, Events, and Processes 

for Savannah River Site Liquid Waste Performance 

Assessments

Source Document Number of 

FEPs 

Safety Assessment Methodologies for Near-Surface 

Disposal Facilities, Results of a Coordinated Research 

Project, Volume 1 [IAEA, 2004] 

141 

Features, Events, and Processes for the Disposal of Low 

Level Radioactive Waste FY2011 Status Report 

[FCRD-USED-2011-000297] 

449 

Features, Events, and Processes for the Total System 

Performance Assessment: Analyses 

[ANL-WIS-MD-000027 REV 0] 

374 

Deep Geologic Repository for OPG's Low and 

Intermediate Level Waste, Post-Closure Safety 

Assessment (Volume 1): Features, Events and Processes

[NWMO DGR-TR-2009-05] 

299 

Encyclopedia of Features, Events and Processes (FEPs) 

for the Swedish SFR and Spent Fuel Repositories 

[Miller et al., 2002] 

120 
- 3 - 

 

Table 2. Categories of Features, Events, and Processes for Liquid Waste Performance 

Assessment at the Savannah River Site 

Group Subgroup

1.0 Assessment Basis

1.1 General

1.2 Regulations and Controls

1.3 Models and Calculations

1.4 Other Assessment Factors

2.0 External Factors

2.1 Human Characteristics

2.2 Land and Water Management

2.3 Future Human Activity

2.4 Biological Factors

2.5 Geologic Features

2.6 Geologic Processes

2.7 Climate

2.8 Water Cycle

3.0 Closure System

3.1 General Closure System

3.2 Pre-Closure Activities

3.3 Closure System Components

3.4 Closure System Hydrology

3.5 Chemical Processes

3.6 Thermal Processes

3.7 Material Degradation

3.8 Other Closure System Factors

4.0 Contaminant Factors

4.1 Contaminant Description

4.2 Contaminant Properties

4.3 Concentrations

4.4 Exposure Factors

4.5 Other Contaminant Factors

5.0 Flow and Transport

5.1 Flow Factors

5.2 Hydraulic Effects on Flow

5.3 Release and Transport

6.0 Disruptive Events

6.1 Intrusions

6.2 Seismic Events

6.3 Igneous Events

6.4 Other Events
- 4 - 

Screening of FEPs:

DOE performed a qualitative screening (Step 3) of each of the 262 unique FEPs based on 

programmatic requirements, the perceived probability of occurrence within 10,000 years, and 

the perceived consequence relative to final performance assessment results and expected 

compliance. First, DOE reviewed the FEPs and identified 46 of the 262 FEPs that required 

inclusion for programmatic purposes, leaving 216 of the FEPs for further screening according to 

perceived probability and consequence. DOE assembled a team of nine subject matter experts 

to conduct the screening process considering perceived probability of occurrence and 

consequence in two phases. 

In the first phase of the screening, each team member independently assigned one of three 

values (i.e., 0, 1, or 2) for both perceived frequency within 10,000 years and perceived impact 

on release or dose. Table 3 provides a matrix of possible results from the assignments. FEPs 

were screened in/out during this phase based on whether there was unanimity amongst the 

team members on the ranking for the FEP being screened. For example, FEPs for which all

team members assigned perceived frequency values of 0 and impact values of 0 were screened 

out (i.e., excluded from consideration in the liquid waste performance assessments) without 

further consideration in the second screening phase. Likewise, FEPs for which all team 

members assigned a perceived frequency value of 2 and an impact value of 2 were screened in 

without further consideration in the second phase. FEPs for which the results of the first phase 

of screening did not result in unanimity were considered further in the second phase of 

screening. DOE reports that the first phase of screening resulted in five of the initial FEPs being 

screened out from further consideration in the liquid waste performance assessments. 

Likewise, DOE screened in 691

 FEPs for implementation in the liquid waste performance 

assessments. This left 142 FEPs for further consideration in the second phase of the screening 

process. 

In the second phase of the screening process, the team of nine subject matter experts 

discussed the remaining 142 FEPs from the first phase. In the second phase, the experts also 

reconsidered three FEPs that were screened out during the first phase (i.e., FEPs 6.4.08 

 

1

 DOE actually screens in 70 FEPs during the first phase of screening. However, DOE reconsiders FEP 

6.4.07 during the second phase and subsequently screens it out as discussed later, therefore, the count 

reported here does not reflect a screening decision on this FEP and it is counted in the quantity of FEPs 

considered further during the second phase (i.e., as part of the 142 FEPs considered during the second 

phase). 

Table 3. FEPs Screening Criteria Matrix† 

Frequency Beyond Extremely 

Unlikely 

Unlikely or Extremely 

Unlikely 

Anticipated, Expected, 

or Already Known to 

Exist or Occur 

Impact 0 1 2 

High 2 Considered Screened In Screened In 

Moderate 1 Screened Out Considered Considered 

Negligible 0 Screened Out Screened Out Screened Out 

†

 Adapted from Table 4.1-3 of SRR-CWDA-2012-00011, Rev. 0 
- 5 - 

through 6.4.10)2

 and one FEP that was screened in during the first phase (i.e., FEP 6.4.07). 

The discussions were reported to consider the probability and impact values for each FEP as 

well as available knowledge (or uncertainty) and synergism with other FEPs. The team 

evaluated these FEPs, screened them accordingly, and developed a justification for FEPs that 

were screened out. During the second phase, 27 FEPs were screened out3

 and 115 FEPs were 

screened in for implementation in the liquid waste performance assessments after discussion 

and evaluation by the team of subject matter experts. Table 4 summarizes the number of FEPs 

screened during each phase. In total, DOE screened in 230 FEPs for further consideration in 

the liquid waste performance assessments and screened out 32 FEPs from further 

consideration in the liquid waste performance assessments. 

Table 4. Number of FEPs Screened During Each 

Phase 

In Out 

Programmatic 46 0 

Phase 1 69 5 

Phase 2 115 27 

Total 230 32 

Evaluation of FEPs Implementation in Performance Assessment:

In Step 4, DOE provided a short technical basis for each FEP and a cross-walk to relevant FTF 

reference documents that address the relevant FEP. DOE notes that not all of the 230 FEPs 

that were screened in are explicitly implemented in the FTF Performance Assessment 

(SRS-REG-2007-00002, Rev. 1). Rather, DOE came to the conclusion that the FTF 

Performance Assessment appropriately considered the relevant FEPs either explicitly or 

implicitly. 

 

 

2

 DOE screens out FEPs 6.4.08 through 6.3.10 during the first phase. The second phase confirmed the 

decision to screen them out. Therefore, they are counted in the quantity of FEPs screened out during the 

first phase rather than in the quantity of FEPs considered/screened in the second phase. 

3

 The second phase of screening reversed the decision made during the first phase to screen in FEP 

6.4.07, therefore, it is accounted for in the quantity of FEPs that were screened out during the second

phase. Whereas, the decision made during the first phase to screen out FEPs 6.4.08 through 6.4.10 was 

reaffirmed, thus they are accounted for in the quantity screened out during the first phase. 
- 6 - 

NRC Evaluation: 

The NRC staff evaluated DOE’s methodology for identification of FEPs, screening of FEPs for 

further consideration, and implementation of FEPs in the FTF Performance Assessment 

(SRS-REG-2007-00002, Rev. 1). 

Identification of FEPs:

To review DOE’s identification of FEPs, the NRC staff used Section 4.1.1.3 of NUREG-1854 

(ML072360184) as well as Section 3.2.1 of NUREG-1573 (ML003770778). Also, the NRC staff 

consulted the list of FEPs for near-surface disposal of radioactive waste compiled by the 

International Atomic Energy Agency (IAEA, 2004) for comparison to DOE’s initial list of FEPs for 

liquid waste performance assessments to provide assurance that DOE’s list of FEPs was 

reasonably complete. The NRC staff found that nearly all the FEPs documented in IAEA (2004) 

were reasonably represented in the initial list of FEPs identified by DOE in 

SRR-CWDA-2012-00011, Rev. 0. The NRC staff notes that SRR-CWDA-2012-00011, Rev. 0 

does not appear to identify four FEPs related to climate change that are identified by IAEA 

(2004) and may be relevant to liquid waste tank closure at SRS over the time periods 

considered: 

• Hydrological/hydrogeological response to climate changes 

• Ecological response to climate changes 

• Human response to climate changes 

• Other geomorphological changes 

However, in response to an NRC request for additional information during the consultation on 

the draft Basis Document for the H-Area Tank Farm (HTF) (DOE/SRS-WD-20130-001, Rev. 0) 

regarding FEP screening, DOE provided a Microsoft® Excel spreadsheet, entitled 

“SRS_LW_FEPs_Rev0.xlsx” which identifies the four FEPs from IAEA (2004) and appears to 

roll them into DOE’s FEP 2.7.07, “Climate Change” although this consolidation is not 

transparent to NRC staff in SRR-CWDA-2012-00011, Rev. 0 (See response to CC-PA-1; 

SRR-CWDA-2013-00106, Rev. 1). Therefore, the NRC staff’s review of DOE’s identification of 

FEPs finds that DOE’s identification is adequate. 

Screening of FEPs:

To review DOE’s screening of FEPs, the NRC staff reviewed DOE’s screening methodology and 

its documented basis for excluding individual FEPs using the guidance in Section 4.1.1.3 of 

NUREG-1854 (ML072360184) and Section 3.2.1 of NUREG-1573 (ML003770778) to ensure 

that key FEPs have been included in the performance assessment. The NRC staff notes that 

criteria in 10 CFR Part 61 and NRC guidance on screening of FEPs for disposal of low-level 

radioactive waste are limited. The NRC staff does provide more extensive criteria and guidance 

for screening of FEPs for geologic disposal of high-level waste under 10 CFR Part 63. 

However, the approach envisioned under 10 CFR Part 63 places a numerical limit on the 

chance that a FEP might occur in a year, due to the higher hazard associated with geologic 

disposal of high-level radioactive waste. 
- 7 - 

DOE’s methodology considers: (i) the perceived likelihood of a FEP occurring within 10,000 

years and (ii) the perceived impact on release or dose. DOE’s emphasis on likelihood of 

occurrence and significance of the impact on release or dose is a reasonable approach to 

screen FEPs for further consideration in the liquid waste performance assessments. This 

emphasis is similar to the approach envisioned for 10 CFR Part 63, but focuses on qualitative 

judgments of perceived likelihoods and impacts rather than quantitative estimates. While 

quantification would enhance DOE’s approach, the NRC staff finds that DOE’s emphasis on 

likelihood and impact is reasonable, considering a graded approach, for screening of FEPs from 

a performance assessment for incidental wastes. DOE also provides documentation of which 

rationale is relied upon for the screening decision in the case of excluded FEPs. However, the 

NRC staff notes that the justification provided for excluding a number of FEPs during the second 

phase (See Table 4.3-1 of SRR-CWDA-2012-00011, Rev. 0) appears to mix the likelihood and 

impact criteria. For instance, FEP 2.6.03, Orogeny, is screened out with the following 

justification: 

This FEP is screened out based on the professional judgment of the FEPs 

Screening Team members that it would be beyond extremely unlikely for this to 

affect PA [performance assessment] results. 

The NRC staff finds this justification confusing as to whether the FEP is perceived as unlikely to 

occur during the 10,000 years, or unlikely to affect the results of the performance assessment. 

In some cases, the meanings could be equivalent, but not necessarily so, and this may lead to 

confusion and a loss of transparency. For transparency, DOE should clarify FEPs with the 

aforementioned justification. The clarification should identify that: (i) the FEP is perceived to be 

unlikely during the assessment period, (ii) the impact of the FEP is perceived to be insignificant 

according to DOE’s decision criteria, or (iii) the FEP is both perceived to be unlikely and its 

impact is insignificant. 

Next, NRC reviewed the qualifications of the team of nine members that performed the 

screening via expert judgment. The NRC staff notes that NUREG-1563 (ML033500190) 

recommends that subject matter experts, even for informal professional judgments be 

knowledgeable individuals, in engineering and science, who, by nature of their experience and 

academic achievement, can speak to the understanding of certain scientific laws and principles. 

The membership of DOE’s team minimally meets this requirement, however, the NRC staff 

notes that the expertise appears to be focused on performance assessment and appears to be 

limited in the areas of geosciences, corrosion, and cementitious materials behavior. Preferably, 

DOE should include subject matter experts in the specific engineering and scientific disciplines 

that are pertinent to the expert judgment being made, particularly for judgments regarding FEPs 

that are perceived to be more likely or have larger impacts. In some cases, subject matter 

experts may not be available due to the nature of the FEP or resource limitations. In these 

cases, DOE should document more clearly the specific expertise of the chosen experts and how 

their experience relates to the expert judgment being made. Regardless of whether appropriate 

subject matter experts are utilized, DOE should clearly document a transparent technical basis 

for the screening decision that also provides a traceable link to the information both considered 

and relied upon to arrive at the screening decision. 

 
- 8 - 

NUREG-1563 (ML033500190) also indicates that the NRC staff will accept for review the results 

of formal or informal judgment so long as the rationale associated with the judgment is 

adequate, transparent, and sufficiently documented. The NRC staff notes that documentation of 

an individual subject matter expert’s basis for judgment is not included from the first phase of 

the screening in which subject matter experts assign values for perceived likelihood and impact 

for each FEP. Further, documentation in SRR-CWDA-2012-00011, Rev. 0 of the discussions 

from the second phase of screening and why subject matter experts may have been swayed 

from initial opinions on the criteria to arrive at a consensus opinion are not provided. In 

response to an NRC request for additional information during the HTF consultation, DOE 

provided a Microsoft© Excel spreadsheet entitled “SRS-LW-FEPs_Rev0.xlsx” (See response to 

CC-PA-2; SRR-CWDA-2013-00106, Rev. 1). However, the DOE response provides sparse 

information regarding the rationales for individual subject matter expert’s judgments and little to 

no information on the data considered during the first phase of screening. Further, the response 

provides no information on why subject matter experts may have been swayed from initial 

opinions to arrive at a consensus in the second phase. DOE should enhance the transparency 

and traceability of the expert judgment process to be consistent with the guidance provided in 

NUREG-1563 (ML033500190) for informal expert judgment. Specifically, subject matter experts 

should provide reasoning for their judgments and the data, if any, from which those judgments 

are formed. Further, sufficient documentation should exist to allow external examination of what 

the judgments are, how the judgments are arrived at (i.e., their basis including supporting data), 

and how the judgments are used. 

Finally, the NRC staff has questions regarding the screening decisions for the following FEPs. 

The outstanding questions are identified with each FEP below: 

• 2.7.04, Acid Rain – (Excluded) It is not clear to the NRC staff why this is outside the 

scope of a liquid waste performance assessment. The NRC staff believes that 

information on existing pollution and its effects on performance of the closed tanks could 

be considered in the performance assessment should the anticipated impact be 

expected to be sufficiently significant. 

• 2.2.07, Pollution – (Excluded) It is not clear to the NRC staff why this is outside the 

scope of a liquid waste performance assessment. The NRC staff believes that 

information on existing pollution and its effects on performance of the closed tanks could 

be considered in the performance assessment should the anticipated impact be 

expected to be sufficiently significant. 

• 3.5.12, Chelating Agents Effects – (Excluded) It is not clear to the NRC staff how DOE 

considered the effects of chelating agents such as oxalates that result from the use of 

oxalic acid during tank cleaning on contaminant mobility. Other examples of chelating 

agents may include humic or fulvic acids in SRS soils or agents used in the solvent 

extraction processes from F and H canyons that remain in the waste stored at the FTF 

and HTF. 
- 9 - 

• 3.6.01, Thermal Processes and Conditions the Engineered System – (Excluded) It is not 

clear to NRC staff how DOE considered the effects of heat of hydration and its effects on 

changes to stresses that may change both hydrologic and mechanical properties of the 

engineered components. 

• 3.6.04, Thermo-Mechanical Stresses Alter Characteristics of Engineered Barrier System 

Components – (Excluded) See discussion for FEP 3.6.01 above. 

• 6.2.04, Seismicity Associated with Igneous Activity – (Excluded) It is not clear to the 

NRC staff whether the rationale for screening this FEP out is related to the subject of this 

particular FEP. The justification provided in Table 4.3-1 of SRR-CWDA-2012-00011, 

Rev. 0 for screening out this FEP indicates that the closure system does not have 

enough heat to significantly impact the results. This rationale appears unrelated to the 

subject of this particular FEP. 

Evaluation of FEPs Implementation in Performance Assessment:

The NRC staff also reviewed DOE’s evaluation of whether the FTF Performance Assessment 

appropriately incorporates FEPs that were screened for inclusion as documented in 

SRR-CWDA-2012-00022, Rev. 0. SRR-CWDA-2012-00022, Rev. 0 provides a cross-walk of 

each FEP to the relevant sections of the FTF Performance Assessment (SRS-REG-2007-

00002, Rev. 1) or supporting references and a summary of the DOE findings of whether 

included FEPs were appropriately incorporated in the performance assessment. The NRC 

staff’s review finds that the cross-walk has the potential to enhance transparency and 

traceability. However, NRC staff notes that many of the selected FEPs it reviewed are crosswalked to either an erroneous section of the FTF Performance Assessment or a section that 

provides only an example of where the particular FEP is implemented in the FTF Performance 

Assessment, and is generally not comprehensive. In some cases, the cross-walk does not link 

every instance or links to an erroneous instance where the implementation of the FEP is 

discussed, while in other cases, the level of detail that is provided by SRR-CWDA-2012-00022, 

Rev. 0 regarding the implementation of the FEP in the FTF Performance Assessment is 

inadequate. 

In the former case, NRC staff points to FEP 3.5.04, “Evolving Water Chemistry in the Far-Field” 

as an example. SRR-CWDA-2012-00022, Rev. 0 cross-walks implementation of this FEP to 

Section 5.2.1 of the FTF Performance Assessment (SRS-REG-2007-00002, Rev. 1). 

SRR-CWDA-2012-00022, Rev. 0 (see Table 3.0-1) indicates that the “Water chemistry evolution 

(such as Eh and pH transitioning) is a primary driver in changes to contaminant transport 

properties.” DOE appears to have confused its near-field modeling, which implicitly models Eh

and pH changes, with its far-field modeling, which does not appear to model pH and Eh

evolution when describing how this FEP is implemented in the FTF Performance Assessment. 

Further, NRC staff finds that the FTF Performance Assessment (SRS-REG-2007-00002, Rev. 

1) provides no discussion in Section 5.2.1 of how the evolution of water chemistry in the far-field 

is implemented in the performance assessment. Therefore, it appears that DOE does not 

consider the evolution of water chemistry in the far-field in its performance assessment even 

though it screens in this FEP. Other examples among the sampling of FEPs reviewed by NRC 

staff that are reportedly screened in, but in fact not implemented in the FTF Performance 

Assessment base case, or are cross-walked to erroneous sections are: FEP 3.5.11, “Reaction 
- 10 - 

Kinetics”, FEP 3.5.07, “Colloidal Generation”, and FEP 3.7.09, “Concrete Shrinkage/Expansion”. 

In the latter case described earlier regarding the level of detail, the NRC staff points to FEP 

3.4.04, “Resaturation and Desaturation” as an example. The NRC staff notes that this is a 

general FEP, but DOE appears to limit its consideration to the closure cap. DOE provides no 

documentation in SRR-CWDA-2012-00022, Rev. 0 regarding the consideration of resaturation 

and desaturation on other components of the FTF closure system such as the steel liner or 

cementitious materials. Given that some of the tanks at FTF are in the zone of fluctuation of the 

water table, for instance, would warrant implementation in the FTF Performance Assessment of 

processes affiliated with wet/dry cycling. Other examples among the sampling of FEPs 

reviewed by NRC staff that are considered in insufficient detail are: 

• FEP 1.3.12, “Model Confidence”, which only considers DOE’s benchmarking of FTF 

GoldSimTM and PORFLOWTM model results, rather than the more comprehensive effort 

to provide confidence in the output of the models via multiple lines of supporting 

evidence; 

• FEP 3.5.01, “Chemical/Geochemical Processes and Conditions”, which does not provide 

traceability to the various chemical/geochemical processes considered (e.g., oxalic acid 

impacts on waste release) in the FTF Performance Assessment; and 

• FEP 3.5.09, “Rind (Chemically Altered Zone) Forms in the Near-Field”, for which DOE 

provides limited discussion of chemically altered zones, other than soils impacted by 

cement leachate, such as weathering or coating of fracture surfaces. 

The result of these examples is a lack of transparency and traceability and reduced confidence 

that all relevant FEPs are included in the FTF Performance Assessment. The NRC staff 

recommends that DOE improve the transparency and traceability of its implementation of FEPs 

as described in SRR-CWDA-2012-00022, Rev. 0 to ensure comprehensive, accurate, and 

traceable links to clear descriptions of how included FEPs are actually implemented in the FTF 

Performance Assessment. 

Teleconference or Meeting: 

The NRC staff will follow-up on DOE’s plans to address the issues identified herein during future 

on-site observations. 

Follow-up Actions: 

The NRC staff will continue to monitor DOE’s identification, screening, and implementation of 

FEPs in the FTF Performance Assessment under Monitoring Factor 6.1, “Scenario Analysis” 

listed in the NRC staff’s FTF Monitoring Plan (ML12212A192) focusing on the technical 

concerns listed in this review report. 

Open Issues: 

There are currently no open issues. 
- 11 - 

Conclusions: 

DOE prepared an ex post facto analysis of FEPs considered for the liquid waste performance 

assessments and an evaluation of the adequacy of the disposition of included FEPs in the FTF 

Performance Assessment. DOE identifies, and NRC agrees, that this is not how the 

identification and screening of FEPs are typically performed for performance assessment. 

Rather, these steps should be employed early in the process to inform the development of a 

robust performance assessment, provide transparency and traceability for stakeholders, and 

ultimately provide confidence that the performance assessment is comprehensive. The NRC 

staff’s review of DOE’s identification of FEPs finds 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. 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; however, 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. The NRC staff believes that the 

questions and issues raised can be addressed as part of DOE’s performance assessment 

maintenance program or as part of special analyses for specific tank closures. 

 
- 12 - 

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