Text

NEI Slides for Reg Policies and Practices Subcommittee on Construction Permit PRA Interim Staff Guidance - May 21, 2025
	ML25136A375
Person / Time
Site:	Nuclear Energy Institute
Issue date:	05/16/2025
From:	; Nuclear Energy Institute
To:	; Advisory Committee on Reactor Safeguards
References
	Download: ML25136A375 (1)
	v • d • e

©2025 Nuclear Energy Institute 2 February 2025 NEI Comments By Federal Register (FR) notice (90 FR 4806) dated January 16, 2025, the Nuclear Regulatory Commission (NRC) requested comments on draft Interim Staff Guidance (ISG) document, Content of Risk Assessment and Severe Accident Information in Light-Water Power Reactor Construction Permit Applications.

NEI Provided Comment on February 18, 2025 7 of 9 comment were accepted or partially accepted in updated ISG provided for this meeting NEI is focused on consistency in the level of detail required for CP PRA information and specifically RG 1.253, which includes an Appendix A on CP PRA Guidance for non-LWRs.

NEI also sought consistency with the Part 53 Rulemaking which intends to be Technology-Inclusive as well as the ADVANCE Act

A.3.2 the CP applicant should:

1. Identify all radiological sources, hazards, and POSs by performing a comprehensive and systematic search.

2. Disposition the search results by a combination of PRA logic modeling, acceptable screening methods, risk-informed supplemental evaluations, and crediting design-basis hazard levels (DBHLs).

A.3.3 Regarding PRA acceptability, the minimum scope of the CP PRA logic model should include the internal events hazard group for the reactor in the at-power POS.

A.3.7 The CP applicant may disposition certain hazards by crediting DBHLs in lieu of explicitly modeling these hazards in the PRA or accounting for them through a risk-informed supplementary evaluation.

A.3.6 Regarding PRA acceptability, risk-informed supplemental evaluations may be used to disposition certain radiological sources, hazards, or POSs. NUREG-1855, Revision 1, Guidance on the Treatment of Uncertainties Associated with PRAs in Risk-Informed Decisionmaking (Ref. A-19), provides a generally acceptable approach for developing risk-informed supplemental evaluations. Section 1.3 of NUREG-1855 notes that the process described in NUREG-1855 is applicable to non-LWRs and reactors in the design stage; however, the screening criteria and the specific sources of uncertainty may not be applicable. Consequently, non-LWR CP applicants who use the guidance in NUREG-1855 to develop risk-informed supplemental evaluations should (1) describe and justify the use of reactor technology-specific screening criteria, and (2) explain how specific sources of uncertainty were identified and addressed.

©2025 Nuclear Energy Institute 5 SRM-SECY-23-0021 Consistency SRM-SECY-23-0021 - Proposed Rule: Risk-Informed, Technology-Inclusive Regulatory Framework for Advanced Reactors (bold is emphasis added by NEI)

Screening tools and bounding or simplified methods may be used for any mode or hazard, provided that the applicant provides an acceptable technical basis. As with all risk-informed methodologies, treatment of uncertainties should be addressed.

The staff should not apply consensus probabilistic risk assessment (PRA) standards as a strict checklist of requirements for Part 53 PRA acceptability determinations. Rather, the staff should allow PRA acceptability determinations for Part 53 applications to be appropriately flexible, considering how PRA insights are relied upon to support the licensing application, together with factors such as safety margin, simplicity of design, and treatment of uncertainties.

The staff should revise the proposed rule or preamble, as appropriate, to convey this point and also seek specific comment in the Federal Register Notice (FRN) for the Part 53 proposed rule on PRA acceptability for Part 53 applications in order to develop guidance.

These requirements [53.415 and 53.510] would support either traditional deterministic approaches for determining and protecting against external hazards or probabilistic approaches that are being developed for seismic and some other external hazards.

The analyses required for this demonstration would be described in proposed § 53.450(e),

which would require that those events be identified and assessed using a PRA methodology in combination with other generally accepted approaches for systematically evaluating engineered systems Existing processes for defining the scope and capability of a PRA supporting an application offer flexibility in determining the degree to which the PRA needs to be developed and may be informed by other factors such as design complexity and the needed degree of realism and level of detail, consistent with the use of the PRA and substance of the application. Such processes are currently available for appropriately defining the scope of the PRA and determining applicability of supporting requirements in consensus PRA standards needed to satisfy the proposed regulatory requirements for the specific uses of analyses under § 53.450(b).

©2025 Nuclear Energy Institute 7 ADVANCE Act Consistency Section 208 - Regulatory Requirements for Micro-reactors The Commission shalldevelop risk-informed and performance-based strategies and guidance to license and regulate micro-reactorsincluding strategies and guidance for(E) risk analysis methods, including alternatives to probabilistic risk assessments;

Comments 1 & 2 -Clarification on ISG Scope was addressed

Comments 3 - Clarification on needs for CPA acceptance vs CP issuance was addressed

Comment 4 - Changes to risk assessment was not addressed. NEI comment still stands, given hazards PRAs may be undeveloped, relative risk insights may be masked by modelling limitations and provide limited value.

Comment 5 - Hazard risk evaluation requirements. This is inconsistent with RG 1.253, SRM-SECY-23-0021 and Part 53. LWRs should not be held to a higher standard than non-LWRs

Comment 6 - Use of PRA in establishing Licensing Basis Events (LBEs) was addressed.

Comment 7 - Supporting Requirements was addressed

Comment 8 - Hazards PRA at CP stage was partially addressed, see comment 5.

Comment 9 - Consistency with RG 1.253 was partially addressed, see comment 5. Guidance in this ISG should be clear that traditional hazard design is sufficient for a CPA consistent with RG 1.253, SRM-SECY-23-0021 and Part 53.

Consistent with RG 1.253, CP applicant may disposition certain hazards by crediting DBHLs in lieu of explicitly modeling these hazards in the PRA or accounting for them through a risk-informed supplementary evaluation. The ISG for hazard supplemental evaluations goes well beyond the requirements on RG 1.253. No risk-informed supplemental evaluation should be required for a CPA if traditional Hazard Design is applied.

Low Power and Shutdown risk evaluation guidance and the discussion of POS remains too stringent for a construction permit PRA.

- POS should not have to facilitate realistic estimation of CDF and LRF if lower modes can conservatively be shown to not be risk-significant.

- Qualitative arguments for why lower modes should be bounded by full power operation should be sufficient for a CP. Anything else is not consistent with the SRP which requires certain LPSD events to be addressed deterministically.

©2025 Nuclear Energy Institute 10 Proposed Resolution Amend the ISG in a way that aligns with RG 1.253, Part 53 and the ADVANCE Act. For hazards and lower modes of operation, three options should be acceptable for a CP PRA.

1) PRA

2) Risk-Informed Supplemental Evaluation following guidance in ISG

3) Traditional Analysis credited as a supplemental evaluation: Hazard Analysis following RG 1.59, RG 1.76, etc. Lower Modes assessed in accordance with SRP Chapter 15

©2023 Nuclear Energy Institute 11 ACRS - Advisory Committee on Reactor Safeguards CP - Construction Permit CPA - Construction Permit Application DBHL - Design Basis Hazard Level FR - Federal Register ISG - Interim Staff Guidance LBE - Licensing Basis Event LWR - Light-Water Reactor NEI - Nuclear Energy Institute Non-LWR - Non-Light-Water Reactor NRC - Nuclear Regulatory Commission POS - Plant Operating State PRA - Probabilistic Risk Assessment SE - Supplemental Evaluation SRM - Staff Requirements Memorandum TICAP - Technology Inclusive Content of Application TI-RIPB - Technology Inclusive Risk-Informed Performance-Based Acronym List

ML25136A375

Text

Navigation menu

Search