ML24311A187

V.C. Summer EDG SDP for Nextera RUG Meeting - 11.7.2024 - Rev. 0

ML24311A187
Person / Time
Site:	Summer
Issue date:	11/07/2024
From:	Shane Sandal NRC/RGN-II/DORS, NRC/NRR/DRA/APOB
To:
References
Download: ML24311A187 (8)

Text

Significance Determination Process Risk Evaluation for V.C. Summer A EDG Fuel Line Leak November 7, 2024 Shane Sandal Senior Reactor Analyst Region II, Division of Operating Reactor Safety Technical Support Assessment Branch

2 Condition Summary

• The V.C. Summer A-train EDG experienced a fuel header through-wall leak discovered during a surveillance test.

• The crack size and associated leak rate increased until the surveillance test was terminated approximately six hours into a planned 24-hour run.

• Exposure period of 162-days (run-time failure analysis)

3 Detailed Risk Evaluation

• The component run time failure approach discussed in Section 2.5 of Volume 1 of the RASP manual was used to evaluate the condition exposure time

• Based on the run history of the A-train EDG, a condition exposure period of 162 days, divided into six separate run intervals (including repair time) was used for the analysis

• FLEX mitigating strategies and equipment were credited in the analysis

4 Preliminary Risk Results

• Preliminary risk results indicated the potential for E-05 risk and the NRC choice letter was issued as a preliminary Yellow

• SPAR model Fire sequences were dominant in the estimates

• At the time the DRE was completed, the site was working on a thermohydraulic analysis to determine if AFW would be capable of removing enough heat prior to the estimated run time failure of the A-train EDG (post LOOP) to allow sufficient time for implementation of FLEX Phase 2 mitigating strategies

5 Regulatory Conference

• Regulatory conference was conducted to discuss new information that was developed after the choice letter was issued

• That information included (in part):

1) Refined FIRE PRA model to include FLEX strategies

2) Results of impact of TH analysis on time to CD

3) Updated HRA (derived from TH analysis results) for operator actions

6 Final Significance

• Reviewed updates made to the fire PRA, development of sequence timelines based on TH, and the HRA for operator actions necessary for event mitigation

• The updated analysis was only applicable to the specific plant conditions and expected failure mechanism that was assessed for this finding

• The new risk evaluation results were consistent with NRC SPAR model preliminary risk results for those sequences that included credit for FLEX mitigation

• Final significance determined to be a White finding (ML23342A000)

7 Important Take-Aways

• Adjustments that were made to the PRA model were supported by TH analysis

• The TH analysis was considered in the derivation of applicable HRA

• As always, early and continued periodic communication between SRA and site PRA risk analysts was important in refinement of the risk estimates

Questions Shane Sandal Senior Reactor Analyst U.S. NRC (404) 997-4513 shane.sandal@nrc.gov