ML25134A166

ACRS Presentation Slides - Draft Final ISG - Content of Risk Assessment and Severe Accident Information in Light-Water Power Reactor Construction Permit Applications

ML25134A166
Person / Time
Issue date:	05/21/2025
From:	NRC/NRR/DNRL/NLIB
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References
DRA-ISG-2024-XX
Download: ML25134A166 (1)

Text

Draft DRA-ISG-2024-XX, Content of Risk Assessment and Severe Accident Information in Light-Water Power Reactor Construction Permit Applications NRC Staff Presentation to ACRS May 21, 2025

Introductions

• Malcolm Patterson, NRR/DRA

• Keith Tetter, NRR/DRA

• Marie Pohida, NRR/DRA

• Michael Swim, NRR DRA

• Steven Alferink, NRR/DRA

• Marty Stutzke, NRR/DANU

• Jeffery Wood, RES/DRA

• Anders Gilbertson, NRR/DANU

• Hanh Phan, NRR/DANU Presenting Staff Contributing Staff India Banks Project Manager, NRR/DNRL Stacey Rosenberg Co-author, NRR/DRA Alissa Neuhausen Co-author, NRR/DRA

Need for the Effort

• Planned use of 10 CFR Part 50 from near-term applicants

• Staff identified a gap in available regulatory guidance for risk insights and severe accident information in LWR CP applications

• No construction permit applications for nearly 40 years

• Past construction permit applications pre-dated agencys key PRA-related actions

• Three Mile Island Action Plan

• Generic Letter 88-20

• Commissions Policy Statements on Severe Accidents and PRA

• Use of PRA at the design stage

Overview This ISG clarifies the scope and depth of the staff review of the description of risk assessment and severe accident information in the PSAR

• SRM-SECY-22-0052:

• Operating license applicants required to submit a description of the plant-specific PRA and its results

• Construction permit applicants are not required to submit a description of the plant-specific PRA and its results

• Many designers of new LWRs are using risk assessment to support risk-informed design decisions

Objective of the Guidance

• Scope of information for risk insights and severe accident information in an LWR CPA commensurate with:

• Design readiness at time of CPA submission

• Use of risk insights and information in CPA (e.g., identifying licensing basis events)

• Increase consistency in content for LWR CPAs and predictability of staff review

• Overcome misconception that construction permit applicants must meet endorsed PRA standards

Development Approach Information sources such as:

Regulatory Guide 1.70 Regulatory Guide 1.200 Standard Review Plan for Chapter 19 DC/COL-ISG-028 DNRL-ISG-22-001 Internal deliberations

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Collaboration with non-LWR efforts Determine scope of information to support staff review and findings Guidance document Staff initiated public meetings Design-specific pre-application meetings

Internal Collaboration and External Outreach

• Conducted three public meetings (March & July 2023, January 2024)

• About 40 people participated in each meeting, including new LWR designers

• External stakeholders voiced support for this guidance at the first meeting

• Staff addressed stakeholder feedback on guidance topics

• Advanced reactor staff and new reactor licensing staff contributed to the development of white paper

• Open communication and sharing of similarities or differences in efforts

• Leveraged work on DG-1404, Revision 1 (proposed new RG 1.253)

Applicability

• CP applications for LWR designs that do not use licensing modernization project (LMP) framework

• Considers the role of risk assessment and severe accident analysis at time an application is submitted

• Scope and technical acceptability of CP application PRA depend on intended use of information and level of design maturity

Guidance Content - PSAR Information

• Scope of information is scaled down compared to DC or COL applications

• Considers design description requirements in 10 CFR 50.34

• Guidelines are presented as bulleted list for each topic

• To assist PSAR preparation, it can be used as a checklist

• Information identified for inclusion in PSAR is primarily

• descriptions, including justifications

• identification of assumptions and limitations

• summary of results and risk insights

• Level of detail is not prescribed to accommodate variation in design maturity

Scope - Internal Events

Scope - Hazards

Technical Elements

• DC/COL-ISG-028 provides staff positions and clarifications on supporting requirements in (ASME/ANS) RA-Sa-2009 (PRA Standard) that are not applicable or cannot be achieved as written for the DC and COL application stages

• Staff considers this as an approach for a CP application

• For the CP application, consistent with DC/COL-ISG-028, Capability Category I of an NRC-endorsed PRA standard is acceptable for PRAs

Seismic - PRA or Alternative Risk Evaluation

• Applicant can use site-specific response spectra

• Identification of site-specific seismic-induced initiating events (e.g., slope stability, liquefaction, dam failure)

• Applicant can use design response spectra representative of an envelope of multiple sites

• Demonstration that the site is bounded by the design response spectrum

• Applicant can use a seismic PRA

• Description of probabilistic seismic hazard analysis performed to develop the site-specific seismic hazard curves and any changes to the seismic hazard curves used in the seismic PRA

• Identification of site-specific seismic-induced initiating events

Guidance Content - Non-Seismic Hazards 14 Conservative Estimate of Risk Screen hazard from assessment Can hazard be screened on site-specific basis*?

PRA YES NO OR

• Re-evaluate at OL stage to account for design changes during construction.

Low Power and Shutdown

• A low-power and shutdown (LPSD) PRA or an alternative risk evaluation is acceptable for a CP application

• Description of any analysis performed to screen POSs from inclusion in the LPSD PRA, including identification of any design features relied on for the screening

Self-Assessment/Peer Review

• PRA self-assessment is acceptable for assessing the technical adequacy

• Certain PRA elements may not be applicable or met at this stage

• PSAR to include:

• Description of PRA self-assessment

• Summary of any limitations arising from maturity of the design

• Staff would accept peer review in accordance with RG 1.200 (would provide additional confidence in PRA results)

Configuration Control Configuration control program information provides confidence in the applicants ability to track assumptions and changes, including:

• identification of PRA technical elements (RG 1.200) that are not met or not applicable, an explanation for the reason for each

• a description of the process to track assumptions and monitor inputs

• a description of how new information will be collected and included consistent with the as-built, as-to-be-operated plant design

Severe Accidents PSAR should include:

• a description and analysis of design features for the prevention and mitigation of severe accidents

• a description of improvements to plant design, operations, or maintenance that prevent or reduce the possibility, likelihood, or consequence of the identified severe accident

RTNSS

• The RTNSS process applies to those non-safety-related SSCs (in designs with passive safety systems) that perform risk-significant functions and, therefore, are candidates for regulatory oversight

• A RTNSS evaluation is not required at CP application stage

• An applicant may choose to provide a RTNSS evaluation at CP application

Public Comments and Resolution Twelve comments received (9 from NEI and 3 from NuScale)

• Staff agreed with 5 comments and made changes to the ISG

• NRC-2024-0217-DRAFT-0001-1/2/6/7

• NRC-2024-0217-DRAFT-0002-3

• Staff partially agreed with 3 comments and made changes to the ISG

• NRC-2024-0217-DRAFT-0001-3/8/9

• Staff disagreed with 4 comments and made no changes to the ISG

• NRC-2024-0217-DRAFT-0001-4/5

• NRC-2024-0217-DRAFT-0002-1/2

Changes to Address Public Comments (1/7)

• Two comments requested additional clarity on the guidance document

• Acceptability of the descriptions of PRA information or the PRA model information and results provided in the PSAR

• Information required to be in the PSAR or available in separate source documents and analyses supporting the CPA

• The ISG provides guidance on the staff review of descriptions provided in the PSAR

• The draft ISG provides guidance on the PRA information required for a construction permit application (CPA) submittal if PRA information is used in the submittal

Changes to Address Public Comments (2/7)

• Five comments requested clarity or adjustments to the minimum elements and scope of the PRA

• Some elements may not be available

• Discussion of intermediate preliminary results may not be appropriate

• Use of PRA should not be required to determine licensing-basis events

• There may be hazards for which PRA does not offer additional insights at the CP stage

• Not appropriate for this ISG to suggest that hazard risk evaluations are required

• Staff modified the ISG to state that staff should review the applicants justification that the scope and level of detail of any PRA or alternative risk evaluation are consistent with the intended uses of the information... The staff should review the applicants plan for assessing any risk contributors not addressed by a PRA or alternative risk evaluation

Changes to Address Public Comments (3/7)

• One comment stated that the hazard assessment requirements appear to go beyond traditional design requirements for SR SSCs

• This draft ISG does not provide guidance on design requirements or propose alternate design requirements

• The PRA or alternative risk evaluations should be consistent with the design and assumptions

Changes to Address Public Comments (4/7)

• One comment requested clarification that supporting requirements may not be applicable or may not be reviewed

• For consistency with the existing discussion on page 5 of the ISG, staff reiterated on page 8 that the staff review should consider that all supporting requirements endorsed in industry standards may not be applicable at the CP stage

Changes to Address Public Comments (5/7)

• One comment requested references for alternative risk evaluations

• Staff is not endorsing particular alternative risk evaluation methods in this guidance document

• If the method can be justified to be applicable for its use, the staff will review the description provided in the CPA as described in this ISG

Changes to Address Public Comments (6/7)

• One comment requested a change to a statement included in the ISG on passive safety system reliability

• This statement is consistent with SRP Section 19.0

• This statement tells staff why this portion of the review may be important

• An applicant can justify on a case-by-case basis that this is not an important element for their design

Changes to Address Public Comments (7/7)

• One comment requested that the guidance clarify that some cases may result in the identification of no RTNSS non-safety-related SSCs

• The staff clarified in the ISG that RTNSS SSCs may not be identified for all designs following the RTNSS process

• The staff guidance includes reviewing the RTNSS process that determines that no RTNSS SSCs are identified

• The staff clarified that RTNSS SSCs may not be identified in the CPA depending on the use of the PRA and risk assessments and may be determined for the operating license application

Acronyms COL Combined operating license POS Plant operating state CP/CPA Construction permit/application PRA Probabilistic risk assessment DC Design certification PSAR Preliminary safety analysis report ISG Interim Staff Guidance RG Regulatory Guide LMP Licensing Modernization Project RTNSS Regulatory Treatment of Non-Safey Systems LPSD Low power and shutdown SRM Staff Requirements Memorandum LWR Light-water reactor SRP Standard Review Plan OL Operating license SSCs Structures, systems, and components