ML25054A001

March 6, 2025, Public Meeting on Between NRC and EPRI on EPRI TR 3002025288, Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components, Requests for Additional Information

ML25054A001
Person / Time
Site:	Electric Power Research Institute
Issue date:	03/06/2025
From:	Licensing Processes Branch
To:
References
EPRI TR 3002025288, EPID L-2023-TOP-0031 pre-app, EPID L-2023-TOP-0045 pre-fee
Download: ML25054A001 (17)

Text

Public Meeting on EPRI TR 3002025288 Review Request for Additional Information March 6, 2025

2 PURPOSE Discuss status of the review and request for additional information (ADAMS Accession No. ML24352A469) associated with the NRC review of EPRI TR 3002025288, Enhanced Risk-Informed Categorization Methodology for Pressure Boundary Components.

Methodology for Pressure Boundary Components

3 OUTLINE

• Status of the review

• High impact technical issues

• Discussion of RAI-01

• Discussion of RAI-02

• Discussion of RAI-06

• Discussion of RAI-09

• Conclusions

4 STATUS OF REVIEW Staff audit was highly successful and answered many staff questions.

The staff understands that relative to the ANO precedent, the TR:

• Methodology designates more SSCs as LSS

• Methodology is easier and less resource dependent for licensees to implement

5 HIGH IMPACT TECHNICAL ISSUES Methodology allows designation of a number of potentially high-consequence SSCs as LSS and there is a large degree of uncertainty associated with the failure rates of certain non-code repairs that could be implemented after categorization.

• Most RAIs relate to this issue.

Methodology allows categorization of passive SSCs without categorization of active functions/SSCs dependent on passive integrity

6 RAI-1 Discussion LSS LSS CCDP CDF HSS or LSS with defined minimum treatment or additional justification (e.g., follow specific nationally-recognized standards)

HSS or LSS with defined minimum treatment or additional justification (e.g., follow specific nationally-recognized standards)

HSS HSS The audit found many SSCs with internal flooding CCDPs >1x10-4 and <1x10-2 Using CCDP instead of CDFxCCDP has many advantages:

• No change expected due to treatment or operating experience

• Lower uncertainty Figure 1 - CCDP Threshold Consequence Chart

7 RAI-2 Discussion By categorizing only passive components in each system, it could create a situation where the alternative treatment for a passive LSS SSC adversely affects an active function/SSC.

Potential impacts on active system categorization should be explicitly addressed:

To maintain level of reliability of the entire SSC per 10 CFR 50.69(c)(1)(iv) and 50.69(e)(3).

Reasonable confidence that RISC-3 SSCs remain capable to performing their safety-related function per 10 CFR 50.69(d)(2).

Consistent with active system categorization process in NEI 00-04.

8 RAI-6 Discussion

• Methodology lists several degradations mechanisms for which robust programs must be implemented as prerequisites to the methodology.

• Methodology does not have actionable requirements concerning these programs (e.g., permissive language and no definition of robust). Applicant presented examples of robust programs during audit but did not propose revisions.

9 RAI-9 Discussion

• Methodology relies on an uncertainty factor without sufficient evidence that the uncertainty factor is appropriate.

• Uncertainty factor used is appropriate to address tail uncertainty, whereas in methodology distribution uncertainty is paramount.

10 UNCERTAINTY ANALYSIS (RAI-09)

Tail Uncertainty (proposed factor)

Distribution Uncertainty (proposal reality)

C&S compliant pipe (Section III, B31.1, etc.)

Component of unknown reliability and no minimum treatment

11 CONCLUSION

• Audit was a major success.

• Number of technical issues considerably reduced from acceptance review.

• Some high-impact technical issues remain to be managed.

• Staff is confident resolution could be achieved while retaining substantial value for methodology.

12 RAI-03, -04, 05, -07, AND -08 ADDITIONAL RAIs

13

SUMMARY

OF RAI-3

• This RAI is related to the risk thresholds in Criteria 11-13 and how uncertainty is addressed. It also includes questions as to how the methodology preserves defense-in-depth, maintains safety margins, accounts for recovery actions (e.g., FLEX) and addresses seismic risk.

• Applicant proposed some draft revisions to TR as part of the audit. Additional justification/clarification is needed.

14

SUMMARY

OF RAI-4

• It is unclear how the methodology, whether independently or in conjunction with the guidance in NEI 00-04, requires assessment of shutdown operations and external events, for potential impact on the categorization of passive components. If addressed by the IDP, explain how this is communicated and what guidance is available for the IDP.

• Applicant provided additional information in Attachment 2 of Supplement 2. This issue was discussed further during the audit and the applicant communicated that additional justification / references to guidance could be provided.

15

SUMMARY

OF RAI-05

• Methodology does not limit applicability to designs for which it was verified. Applicant concurred with staff during audit that methodology is not appropriate for unverified designs (e.g., AP1000, NuScale US600).

• Applicant did not provide proposed revisions to TR.

16

SUMMARY

OF RAI-07

• Methodology discusses relying on industry guidance in Section 4.2 under Criteria 11-13 but used permissive and unclear language. Applicant agreed during audit that this language could more clearly refer to prerequisite 4.1.1.

• Applicant did not provide proposed revisions to TR.

17

SUMMARY

OF RAI-08

• Methodology criteria 1 lacked clarity concerning components that can be isolated from the RCS by two valves in series. Applicant agreed during audit that this could be more clearly worded.

• Applicant did not provide proposed revisions to TR.