ML24257A148
| ML24257A148 | |
| Person / Time | |
|---|---|
| Issue date: | 09/18/2024 |
| From: | Meena Khanna NRC/NRR/DRA |
| To: | |
| References | |
| Download: ML24257A148 (1) | |
Text
Public Workshop Subsequent License Renewal Postulated Accident/SAMA Environmental Rulemaking Implementation September 18, 2024 ADAMS Accession No. ML24257A148
NRC Opening Remarks Meena Khanna, Acting Director Division of Risk Assessment Office of Nuclear Reactor Regulation 2
Workshop Agenda
- Subsequent License Renewal Postulated Accident/
SAMA Environmental Rulemaking Implementation
- Break
- External Presentations
- Discussion/Q&A 3
Subsequent License Renewal Postulated Accident/SAMA Environmental Rulemaking Implementation Jerry Dozier, Sr. Reliability and Risk Analyst 4
Outline
- Postulated Accident/Rules basis and changes
- Design Basis Accidents (DBA)
- Severe Accidents (Probability Weighted Consequences (PWC))
- SAMA (mitigation)
- Category 1
- Disposition of new information regarding severe accidents and SAMA 5
Postulated Accident/SAMA Rule Changes
- Postulated Accident Rules from Table B-1
- Design Basis Accidents (No change)
- Severe Accident (Category (Cat) 2 to Cat 1) (functional equivalent of Cat 1, if previous SAMA or SAMDA performed)
- Mitigation (Cat 2 to Cat 1)
Design-Basis Accidents
- Impacts from DBAs would not be affected by changes in plant environment because such impacts (1) are based on calculated radioactive releases that are not expected to change; (2) are not affected by plant environment because they are evaluated for the hypothetical maximally exposed individual; and (3) have been previously determined acceptable (NRC 1996, NRC 2013). The maximally exposed individual is a hypothetical individual who, because of proximity, activities, or living habits, could potentially receive the maximum possible dose of radiation or of a hazardous chemical from a given event or process (2024 GEIS page J-22). Section 4.9.1.2 of the 2024 LR GEIS describes the Environmental Consequences of Postulated Accidents. Section 4.9.1.2.1 of the 2024 LR GEIS describes DBAs and concluded:
- The findings in the 1996 LR GEIS and 2013 LR GEIS remain valid. Therefore, the environmental impacts of design-basis accidents are SMALL for all plants during the initial LR and SLR terms and the issue is Category 1.
7
10 CFR 50.67 Accident Source Term (AST)
- The Site-Specific accident source term (AST) analysis demonstrates with reasonable assurance that DBA analyses results meet the following 10 CFR 50.67 acceptance criteria:
- (i) An individual located at any point on the boundary of the exclusion area for any 2-hour period following the onset of the postulated fission product release, would not receive a radiation dose in excess of 0.25 Sv (25 rem) total effective dose equivalent (TEDE).
- (ii) An individual located at any point on the outer boundary of the low population zone, who is exposed to the radioactive cloud resulting from the postulated fission product release (during the entire period of its passage), would not receive a radiation dose in excess of 0.25 Sv (25 rem) total effective dose equivalent (TEDE).
- (iii) Adequate radiation protection is provided to permit access to and occupancy of the control room under accident conditions without personnel receiving radiation exposures in excess of 0.05 Sv (5 rem) total effective dose equivalent (TEDE) for the duration of the accident.
8
10 CFR 51, Appendix B, Table B Summary of Findings on NEPA Issues for License Renewal (old severe accident rule)
- The probability-weighted consequences of atmospheric releases, fallout onto open bodies of water, releases to groundwater, and societal and economic impacts from severe accidents are small for all plants. However, alternatives to mitigate severe accidents must be considered for all plants that have not considered such alternatives.
9
NEW SLR Severe Accident/SAMA Rule The 10 CFR 51, Appendix B, Table B-1 summary of environmental impact relating to Severe Accidents and SAMA states:
- SMALL (Category 1). The probability-weighted consequences of atmospheric releases, fallout onto open bodies of water, releases to groundwater, and societal and economic impacts from severe accidents are small for all plants. Severe accident mitigation alternatives do not warrant further plant-specific analysis because the demonstrated reductions in population dose risk and continued severe accident regulatory improvements substantially reduce the likelihood of finding cost-effective significant plant improvements.
10
High Level Basis for New Severe Accident/SAMA Rule
- PWX of Severe Accident
- Table E.3-1 (PWC and PDR)
- Potential underestimation of risk and reasonable assurance of adequate protection covered in design basis with AST
- PWC now Category 1 instead of just functional equivalent of Category 1 if a SAMA/SAMDA was done previously
- Acknowledgement of Regulatory initiatives and mitigation outside of License renewal (mitigation) 11
12
Table E.3-1
- Column 6 provides PDR calculated in Plant LR app
- Column 7 provides margin to PDR calculated in 1996 for each plant (most plants have significant margin) 13
Severe Accident PWC
- Plant-Specific Severe Accidents Probability Weighted Consequences calculated to be smaller for all plants than predicted in the 1996 GEIS estimate using a Level III PRA (and documented in Table E.3-1)(All NRC approved)
- 2024 LR GEIS Section E.3.1 to E.3.8 (Internal Events, External Events, Source Term, Power uprates, Higher Fuel Burnup, Low Power and Shutdown, Additional Units etc.) only relate to how new information might impact the SMALL determination (for NRC generically and later for SLR applicant)
- In the Appendix E update, staff provide a generic factor for impact typically based on a mean CDF (SLR applicants provide info for their plant and staff determine specific factors) using each of the sections in Appendix E 14
Appendix E Update Includes SAMA PRA Results and Trends
- Population Dose risk (Site specific Level 3 Substantial decrease (from the predictive 1996 studies)
- External Events considered in SAMA Level III (significant reduction in population dose). However, some specific external hazards CDF increased (example Seismic)
- Other areas minor increase (burnup, uprates) or assumed to stay the same (SFP, BEIR VII) relative to orders of magnitude decreases in other areas (Source Term, Internal Events) 15
PWC in an SLR ER
- Table E.3-1 provides the PDR in person rem/yr. A factor that provides the ratio or factor decrease in PDR is calculated and provided in the last column of Table E.3-1. (Most plants have considerable margin)
- New information (IE, EE, power uprate) is evaluated to determine impact on risk (typically CDF) and a factor is given (up or down)
- Simply, NRC (or the applicant during SLR) looks at the new ups and downs to make final determination regarding N&S both in the GEIS and the SLR application 16
Quick Terminology Note The initial license renewal SAMA analysis is more precisely a plant -specific severe accident probability-weighted consequence analysis (considering Level 1, 2, 3 and external events PRA) with consideration of plant-specific cost beneficial mitigations (SAMAs) 17
Severe Accident Mitigation (NEPA)
- 1989 Limerick Court Case (Starting point for SAMAs/SAMDAs)
- 1996 GEIS and Rulemaking (Most Mitigation expected on Safety Side)
- 2nd Limerick Court Orders (New and Significant related to SAMA )
18
1996 GEIS and Rulemaking (NEPA)
- The original Commission in 1989 envisioned that risk improvements would be made by the severe accident program (which included IPE, IPEEE, containment improvement program, etc). Many improvements were made.
19
2013 LR GEIS Major Plant Modification
... the NRC expects that a site-specific consideration of severe accident mitigation for license renewal will only identify procedural and programmatic improvements (and perhaps minor hardware changes) as being cost-beneficial in reducing severe accident risk or consequence.
NUREG-1437, Generic Environmental Impact Statement for License Renewal of Nuclear Plants 20
2024 GEIS Regarding Mitigation
- As discussed in greater detail in Section E.4 of the 2024 LR GEIS, in light of these studies and severe accident initiatives outside of license renewal, the Commission stated that it did not expect future SAMA analyses to uncover major plant design changes or modifications that will prove to be costbeneficial (61 FR 28467, 28481; June 5, 1996).
The NRCs experience in reviewing SAMA analyses in plant-specific license renewal proceedings has confirmed this prediction. These plant-specific reviews further illustrate the magnitude of mitigation as a result of the agencys ongoing and robust safety oversight.
21
New and Significant Related to SAMA (2nd Limerick Orders and Court Case)
- Determination that Severe accidents are functional equivalent of Category 1, if previous SAMA/SAMDA performed and confirmation that staff need to look at New and Significant information related to SAMA 22
Insights from SAMA Evaluations Considerations:
- Internal Event CDFs from operating plants are trending lower
- Past regulatory programs address several known severe accident weaknesses
- SAMAs typically address one cut set, while risk is generally driven by multiple contributors
- Implementation costs are high for design retrofits Therefore,
- It is difficult to identify additional changes that substantially reduce risk and are cost-beneficial
- Cost-beneficial changes are usually limited to procedural changes, training, and limited hardware changes 23
Dispositioning New Information using Population Dose Risk 24
Primary Comparison Factors 25 Population Dose Risk
26 Level 1 PRA results in Core Damage Frequency (CDF)
Level 3 PRA results in Population Dose Risk (PDR) or probability weighted consequences to the public and environment
Disposition of Changes to Facilities using PDR
- Site specific population dose risk values from a Level 3 PRA consequence analysis have been determined and NRC reviewed these in the initial license renewal for the entire operational fleet
- Examples of new information dispositioned for its significance included:
Internal Events, External Events, Source Term, Power uprates, Higher Fuel Burnup, Low Power and Shutdown, Additional Units
- Comparison was made of impact of the dispositioned item to the PDR margin specified in Table E.3-1 of the 2024 LR GEIS 27
Category 1 in the 2024 LR GEIS
- Category 1: For the issue, the analysis reported in the Generic Environmental Impact Statement has shown:
- (1) the environmental impacts associated with the issue have been determined to apply either to all plants or, for some issues, to plants having a specific type of cooling system or other specified plant or site characteristics;
- (2) a single significance level (i.e., small, moderate, or large) has been assigned to the impacts (except for collective off-site radiological impacts from the fuel cycle and from high-level waste and spent fuel);
and
- (3) mitigation of adverse impacts associated with the issue has been considered in the analysis and it has been determined that additional plant-specific mitigation measures are likely not to be sufficiently beneficial to warrant implementation.
28
Category 1 in the 2024 LR GEIS (Contd)
- The license renewal applicant is not required to assess the environmental impacts of Category 1 issues listed in Table B-1, unless the applicant is aware of new and significant information that would change the conclusions in the LR GEIS. (Pages 1-15 2024 LR GEIS) 29
2024 LR GEIS Category 1 Regarding Mitigation
- Consistent with the NRC's current NEPA practice, an applicant must include alternatives to reduce or mitigate adverse environmental impacts in its environmental report. However, for license renewal, the Commission has generically considered mitigation for environmental issues associated with renewal and has concluded that no additional site-specific consideration of mitigation is necessary for many issues.
The Commission's consideration of mitigation for each issue included identification of current activities that adequately mitigate impacts and an assessment as to whether certain impacts are so insignificant that mitigation is not warranted. The Commission has considered mitigation for all impacts designated as Category 1 in Table B-1. Therefore, a license renewal applicant need not address mitigation for Category 1 issues in Table B-1.
30
Definition of Significance NEI 17-04 and CLI 13-07
- Limerick response to RAI regarding new and significant related to SAMA was the basis for NEI 17-04 definition of significance
- Since the definition of significant is not well established in the context of SAMA analysis, a review of PRA standards and relevant guidance documents has been performed to develop a basis for what is significant in the SAMA context. For the reasons stated below, Limerick has selected a 50% reduction in the maximum averted cost-risk (MACR) as the threshold for what may be significant.
- Since that time, significance has been defined elsewhere in guidance and regulations 31
Significance Definitions
- NUREG BR-0058 was updated to better define significant improvement (pages 2-18 to 2-19, primarily 1E-5)
- Guidance For Determination Of Appropriate Regulatory Action Based On Seismic PRA (ML17146A200)
- NEPA does not provide quantitative value 32
Significance in 2024 LR GEIS
- The NRC has established three significance levels for potential impacts:
SMALL, MODERATE, and LARGE. The three significance levels are presented in a footnote to Table B-1 of 10 CFR Part 51, Appendix B to Subpart A. (2024 GEIS pg. xxxvi)
- The significance level for Design Basis, Severe Accidents, and SAMA were considered SMALL
- SMALL: Environmental effects are not detectable or are so minor that they will neither destabilize nor noticeably alter any important attribute of the resource. For the purposes of assessing radiological impacts, the Commission has concluded that those impacts that do not exceed permissible levels in the Commissions regulations are considered SMALL.
33
Break 34
External Presentations 35
Discussion 36
- AST Accident Source Term
- CDF Core Damage Frequency
- DBA Design Basis Accidents
- GEIS Generic Environmental Impact Statement
- IPE Individual Plant Examinations
- IPEEE Individual Plant Examination of External Events
- NEPA National Environmental Policy Act
- PDR Population Dose Risk
- PWC Probability Weighted Consequences
- SAMA Severe Accident Mitigation Alternatives
- SAMDA Severe Accident Mitigation Design Alternatives