ML22277A656
| ML22277A656 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 10/06/2022 |
| From: | Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation |
| Thomas V, 301-415-5897 | |
| References | |
| Download: ML22277A656 (21) | |
Text
Browns Ferry Nuclear Plant (BFN) Subsequent License Renewal Application (SLRA) -
Severe Accident Mitigation Alternatives (SAMA) Analysis October 6, 2022
Introduction Pete Donahue - Director, Subsequent License Renewal (SLR)
Bill Baker - Senior Program Manager, SLR Plant Operations Ashley Michael - Senior Program Manager, SLR Mechanical Systems Nick Lovelace - Jensen Hughes - PRA 2
Dan Green - SLR Licensing Manager Dan Kearnaghan - Manager Nuclear Power Group Probabilistic Risk Assessment (PRA)
Projects Bill Victor - Senior Program Manager, Corporate Nuclear Licensing Joe Bashore - SLR Environmental Lead Beau Eckermann - Program Manager, Fleet Licensing Gerry Kindred - Senior Program Manager, PRA
Agenda Introduction P. Donahue
Background
J. Bashore/D. Kearnaghan Model Development N. Lovelace SAMA Results N. Lovelace Next Steps for Potentially Cost-Beneficial SAMAs J. Bashore SLRA Environmental Report Contents - SAMA J. Bashore Questions/Comments P. Donahue 3
Overview of SAMA Process N. Lovelace
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Background===
4 Purpose of Analysis of Severe Accident Mitigation Alternatives (SAMAs)
Identify design alternatives, procedural modifications, or training activities that are costbeneficial and further reduce risks of severe accidents Analysis of SAMAs includes identification and evaluation of alternatives that reduce risk from severe accident by
Preventing substantial core damage (preventing a severe accident) or
Limiting releases from containment in event substantial core damage occurs (mitigating impacts of a severe accident)
In accordance with 10 Code of Federal Regulations (CFR) 51.53(c)(3)(ii)(L) and Table B1 of Appendix B to 10 CFR Part 51, Subpart A
License Renewal Environmental Reports (ERs) must provide consideration of alternatives to mitigate severe accidents
If NRC staff has not previously considered such alternatives for applicants plant in an Environment Impact Statement (EIS) or related supplement or in an Environmental Assessment (EA)
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Background===
(continued) 5 Nuclear Regulatory Commission (NRC) staff previously considered alternatives to mitigate severe accidents for BFN in Supplemental EIS for License Renewal
Supplement 21 Regarding Browns Ferry Nuclear Plant Units 1, 2, and 3, to Generic EIS for License Renewal of Nuclear Plants (NUREG-1437) dated June 2005 Since that time, BFN Units 1, 2 and 3 and associated PRA models have undergone many modifications/changes Because of extent of changes to BFN Units 1, 2 and 3 and associated PRA models, TVA has determined that it would be more efficient to perform a full SAMA analysis rather than using Nuclear Energy Institute (NEI) 17-04, Model SLR New and Significant Assessment Approach for SAMA
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Background===
(continued) 6 BFN Modifications For example:
Numerous modifications to Unit 1 to support recovery to operating status
Extended Power Uprate (EPU) and Maximum Extended Load Line Limit Analysis Plus (MELLLA+) for Units 1, 2, and 3
Numerous modifications for compliance with BFN National Fire Protection Association (NFPA) 805 analyses
Diverse and Flexible Coping Strategies (FLEX) modifications
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Background===
(continued) 7 PRA Model Note: Previously submitted SAMA evaluation performed with RISKMAN model PRA model completely re-built using CAFTA software to meet Regulatory Guide 1.200
Substantial update to PRA internal events and internal flooding model Modeling changes
PRA updated to model current as-built, as-operated plant Extended Power Uprate
Several different analyses conducted to reflect EPU Fire PRA and seismic PRA models developed for BFN Modeling Updates from Internal and Industry Peer Reviews
PRA model refined by incorporation of latest state of knowledge and recommendations from Internal and Industry Peer Reviews
All Finding Level Facts & Observations (F&Os) have been closed using applicable NEI guidance Creation of One-Top Multi-Hazard Model (OTMHM)
Internal events, internal flood, fire and seismic PRA models integrated to create one-top model
Model Development 8
Level 1, 2, and 3 Models Level 1 PRA model: One-Top Multi-Hazard Model (OTMHM)
Includes internal events, internal flood, fire, and seismic Level 2 analysis uses Containment Event Tree (CET) to analyze all core damage sequences identified in Level 1 analysis
Results include each sequences release frequency, magnitude, and timing
Level 2 bins:
High-Early Release (H-E), High-Intermediate Release (H-I), High-Late Release (H-L),
Medium-Early Release (M-E), Medium-Intermediate Release (M-I),
Low-Intermediate Release (L-I), Low Low-Intermediate Release (LL-I),
Containment Intact (Intact)
Model Development (continued) 9 Level 1, 2, and 3 Models Level 3 PRA model created for BFN using Windows MELCOR Accident Consequences Code System (WinMACCS)
Site-specific meteorological, population, and economic data to estimate each accident consequences population dose and offsite economic costs
Used to estimate accident consequences in terms of population dose and offsite economic costs for 50 miles around BFN
Risks in terms of population dose risk and offsite economic cost risk also estimated in this analysis
Calculated as product of WinMACCS consequence and frequency of different postulated accidental releases based on Level 2 analysis
Overview of SAMA Process NEI 05-01 Methodology NEI 05-01, Severe, Accident Mitigation Alternatives (SAMA) Analysis Guidance Document, guidance used for all three BFN units
Guidance in NEI 17-04, Model SLR New and Significant Assessment Approach for SAMA, not used since full SAMA analysis performed
except for SAMA candidate identification Analytical Steps Involved:
- 1. Identification of Potential SAMA Candidates
Potential SAMA candidates were identified from following sources, based on NEI 05-01 and NEI 17-04 in relation to potentially cost beneficial SAMAs from other BWR plants
SAMA analyses for other BWR plants; (NEI 17-04 includes review of SAMAs identified as potentially cost beneficial for other industry plants that have been determined to be applicable, but not already implemented at the analyzed plant)
NRC and industry documentation discussing potential plant improvements; and
BFN updated PRA model lists of risk significant contributors (Including internal flood, fire, and seismic hazards) 10
Overview of SAMA Process (continued)
NEI 05-01 Methodology
- 2. Preliminary Screening (Phase I)
Potential SAMA candidate was screened out if:
It modified features not applicable to BFN;
It had already been implemented at BFN; or
It was similar and could be combined with another SAMA candidates
- 3. Final Screening and Cost-Benefit Evaluation (Phase II)
Cost-benefit analysis was performed for each SAMA candidate remaining after preliminary screening
Benefit of implementing a SAMA candidate was estimated in terms of averted consequences
- 4. Sensitivity Analyses
Two sensitivity cases
Instead of using a 20-year license renewal period, the full period is used (31 years for Unit 1, 32 years for Unit 2, and 34 years for Unit 3)
Conservative discount rate (3% instead of 7%)
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Overview of SAMA Process (continued)
Phase II Analysis Result of implementation of each SAMA candidate would be change in severe accident risk (change in frequency of severe accidents or change in frequency of subsequent release to environment)
Calculate baseline risk and cost
Calculate each SAMAs risk and cost
Calculate each SAMAs benefit 12
Overview of SAMA Process (continued)
Phase II Analysis: Severe Accident Risk After baseline risk is calculated, severe accident risk after implementation of each SAMA candidate is calculated
Level 2 PRA model was modified to reflect maximum benefit of each improvement
Generally, maximum benefit of a SAMA candidate was determined with bounding modeling assumption
For example, if objective of SAMA candidate was to reduce the likelihood of a certain failure mode, then eliminating the failure mode from PRA would bound the benefit, even though SAMA candidate would not be expected to be 100% effective in eliminating the failure
Severe accident impacts were calculated based on:
Offsite exposure costs (monetary value of dose consequences to offsite population);
Offsite economic costs (monetary value of damage to offsite property);
Onsite exposure costs (monetary value of dose to workers); and
Onsite economic costs (monetary value of damage to onsite property)
Results of Level 2 model were combined with Level 3 model to calculate post-SAMA costs
These values are subtracted to calculate SAMA benefit 13
Overview of SAMA Process (continued)
Phase II Analysis: Cost/Benefit Analysis Cost/Benefit Analysis of each SAMA performed
Estimate each SAMAs cost
Expected cost of enhancement to implement each SAMA established from existing estimates of similar modifications combined with engineering judgment
Compare each SAMAs cost estimate to benefit calculations
To assess viability of each SAMA considered for final cost-benefit evaluation, cost of implementing that SAMA was estimated and compared with estimated benefit
If cost of implementation was greater than attainable benefit of a particular SAMA, then modification was not considered economically viable and was eliminated from further consideration 14
SAMA Results Overall Results Identification of Potential SAMA Candidates: 298 SAMA candidates
Evaluation addressed 298 SAMA candidates for mitigating severe accident impacts Preliminary Screening (Phase I): 229 screened, 69 remain
Eliminated 229 SAMA candidates from further consideration
Based on either inapplicability to BFNs design, or features that had already been incorporated into BFNs current design, procedures, or programs Final Screening and Cost-Benefit Evaluation (Phase II): 63 screened, 6 remain
Additional 63 SAMA candidates were eliminated because their cost was expected to exceed their benefit
Six SAMAs found to be potentially cost-beneficial for mitigating consequences of severe accident at BFN Sensitivity Analyses: No additional cost-beneficial SAMAs
Sensitivity studies indicated results of analysis would not change for conditions analyzed 15
SAMA Results Resulting Potentially Cost-Beneficial SAMAs (based on conservative calculations)
SAMA 64: Enhance procedures for actions on loss of heating, ventilation and air conditioning (HVAC) (Units 1, 2, and 3)
SAMA 65: Add emergency diesel generator building high temperature alarm or redundant louver and thermostat (Unit 3)
SAMA 148: Install inter-unit control rod drive (CRD) system cross-tie as potential means of recovering from loss of CRD at a given unit (Unit 1)
SAMA 149: Diverse emergency diesel generator HVAC logic. (Units 1, 2, and 3)
SAMA 150: Provide diverse swing emergency diesel generator air start compressor (Units 1, 2, and 3)
SAMA 157: Add automatic fire suppression system (Fire Compartment 13 -
Electrical Board Room 3A) (Unit 3)
Note: None of these SAMAs are related to adequately managing effects of aging during subsequent period of extended operation 16
Next Steps for Potentially Cost-Beneficial SAMAs Potentially Cost-Beneficial SAMAs SAMA analysis is conservative and is not a complete engineering project cost-benefit analysis - does not estimate all benefits or costs of a SAMA For example:
May not consider increases or decreases in maintenance or operation costs following SAMA implementation
May not consider possible adverse consequences of the changes.
Although none of these potentially cost-beneficial SAMAs are related to adequately managing effects of aging during the subsequent period of extended operation, the following actions are being taken:
Condition Report initiated within Corrective Action Program to investigate more detailed cost analysis and potentially implement these cost-beneficial SAMAs
Knowledgeable AE for BFN currently working on more accurate minimum cost estimates for these SAMAs
Resulting SAMAs determined to be cost effective to be processed through BFN Plant Health Committee for further consideration 17
SLRA Environmental Report Contents -
SAMA SLRA ER Contents - SAMA SLRA ER Section 4.15, Severe Accident Mitigation Alternatives
Description of Methodology including:
Establishing Baseline Consequences of Severe Accidents
Identifying SAMA Candidates
Phase I Preliminary Screening
Phase II Final Screening and Cost Benefit Evaluation
Sensitivity Analyses
Tables with Potentially Cost-Beneficial SAMAs and Bases for Conclusion SLRA ER Appendix E.1, Evaluation of BFN PRA Model
Description of BFN PRA Level 1, 2, and 3 analyses, uncertainty, and PRA model peer review SLRA ER Appendix E.2, Evaluation of BFN SAMA Candidates
Description of generation of initial list of potential SAMA candidates, screening methods, and analysis of remaining SAMA candidates BFN SLRA currently scheduled for submittal by end of 2023 Note: Supporting Engineering Documents/Calculations available on BFN SLR online reference portal for NRC review/audit 18
Abbreviations List 19 BFN Browns Ferry Nuclear Plant L-I Low-Intermediate Release CET Containment Event Tree LL-I Low Low-Intermediate Release CFR Code of Federal Regulations M-E Medium-Early Release CRD Control Rod Drive M-I Medium-Intermediate Release EA Environmental Assessment MELLLA+
Maximum Extended Load Line Limit Analysis Plus EIS Environmental Impact Statement NEI Nuclear Energy Institute EPU Extended Power Uprate NFPA National Fire Protection Association ER Environmental Report NRC Nuclear Regulatory Commission F&Os Facts & Observations OTMHM One-Top Multi-Hazard Model FLEX Diverse and Flexible Coping Strategies PRA Probabilistic Risk Assessment H-E High-Early Release SAMA Severe Accident Mitigation Alternatives H-I High-Intermediate Release SLR SLR - Subsequent License Renewal H-L High-Late Release (H-L)
SLRA Subsequent License Renewal Application HVAC Heating, Ventilation and Air Conditioning WinMACCSS Windows MELCOR Accident Consequences Code System
Questions/
Comments 20