ML23037A812

Summary of the January 19, 2023, Public Meeting with EPRI and Stakeholders to Discuss Use of the Extremely Low Probability of Rupture Code for LOCA Frequency Estimates

ML23037A812
Person / Time
Issue date:	02/07/2023
From:	Nellis C NRC/RES/DE
To:	Raj Iyengar NRC/RES/DE
References
Download: ML23037A812 (7)

Text

February 7, 2023 MEMORANDUM TO: Raj M. Iyengar, Chief Reactor Engineering Branch Division of Engineering Office of Nuclear Regulatory Research Signed by Nellis, Chris FROM: Christopher Nellis, Reactor Engineer on 02/07/23 Reactor Engineering Branch Division of Engineering Office of Nuclear Regulatory Research

SUMMARY

OF THE JANUARY 19, 2023 PUBLIC MEETING WITH EPRI AND STAKEHOLDERS TO DISCUSS USE OF THE EXTREMELY LOW PROBABILITY OF RUPTURE CODE FOR LOSS-OF-COOLANT ACCIDENT FREQUENCY ESTIMATES The U.S. Nuclear Regulatory Commission (NRC) staff held a meeting on January 19, 2023, with representatives of the Electric Power Research Institute (EPRI) to discuss technical aspects concerning use of the Extremely Low Probability of Rupture (xLPR) probabilistic fracture mechanics (PFM) code to inform loss-of-coolant accident (LOCA) frequency estimates and related regulatory applications.

The agenda and slide presentations for the meeting are available in the NRCs Agencywide Documents Access and Management System under Accession Numbers ML22363A572 and ML23019A148, respectively. Enclosed is a list of the meeting participants.

A summary of the meeting's discussions follows by agenda topic.

1. Review of June 14, 2022, Public Meeting on Use of xLPR for LOCA Frequency Estimates The NRC staff reviewed the topics discussed at a public meeting held previously on June 14, 2022 (ML22173A222). The benefits of using the xLPR code to estimate loss-of-coolant accident frequencies from piping integrity failures were reiterated. The staff highlighted how the topics from that meeting related to the present discussions.

CONTACT: Christopher Nellis, RES/DE/REB (301)-415-5973

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2. Scope Change on Work Using the xLPR Code to Develop LOCA Frequency Estimates An EPRI representative discussed the original scope of an EPRI project aimed to broadly compare LOCA frequencies from NUREG-1829 with those generated from the xLPR code that would support EPRIs proposed alternative licensing strategy (ALS) for high burnup fuels. The EPRI representative informed the NRC staff that further development of the ALS has narrowed the scope of line sizes that needed to be analyzed. The new scope was highlighted to provide context for the subsequent agenda topic, which presented results of the study.

3. Updates on Full-Scope Study Using the xLPR Code to Develop LOCA Frequency Estimates An EPRI contractor detailed results from EPRIs study using the xLPR code to develop LOCA frequency estimates with xLPRs probability of rupture output used as a surrogate for LOCA frequencies. EPRI found that, when crediting in-service inspection (ISI) and leak-rate detection (LRD), the probabilities of rupture as calculated by the xLPR code were on the same order of magnitude as the LOCA frequency estimates from NUREG-1829. The probability of rupture with ISI and LRD was zero for almost all the cases considered, except in a few sensitivity studies that were not representative of typical plant conditions and operations. However, these cases are planned to be further investigated by the EPRI contractor as they can provide a supporting basis for ALS applications. In cases analyzing the time between 1 gallon per minute (gpm) detectable leakage and rupture (i.e., the lapse time), the minimum was found to be at least 14 months for all base cases and at least 1 month for all sensitivity study cases. As the simulation timestep used in these evaluations was 1 month, the EPRI contractor indicated that it would rerun the limiting sensitivity study cases with a shorter timestep.

The NRC staff suggested additional sensitivity studies that could be of value.

4. Treatment of Non-xLPR-Modeled Failures As related to ALS initiatives, an EPRI contractor reviewed contributions to LOCAs by non-piping related failures such as bolted components and component bodies as well as piping failure contributions that are not modeled by the xLPR code. He stated that, for piping in the small to intermediate range, fuel cladding burst is not expected using conventional LOCA analysis. However, leak-before-break analysis should also be applied to large-bore piping to evaluate associated failure frequencies or demonstrate an acceptable margin. Failure of non-piping components cannot cause a leak rate larger than the failure of the pipes they are connected to. The EPRI contractor also stated that Regulatory Guide 1.45, Revision 1 Guidance on Monitoring and Responding to Reactor Coolant System Leakage (ML073200271) was reviewed to describe the anticipated timeframe of operator actions in response to an unidentified leak.

5. Use Cases for LOCA Frequency Estimates Representatives from the NRC staff and EPRI reviewed applicable use cases for xLPR-generated LOCA frequency estimates. An EPRI representative described a roadmap for

3 R. Iyengar finding opportunities to use the xLPR code by compiling a list of regulatory requirements and licensing and design bases that use LOCA frequency estimates.

He described plans to perform risk-benefit analyses to identify which would be the most promising to pursue. An EPRI report on the outcome of these analyses is planned to be published in 2023. The NRC staff reviewed the NRCs core regulatory processes and discussed how LOCA frequency estimates are used as input in its standardized plant analysis risk models.

6. Perspectives on EPRI Pilot Study Using the xLPR Code to Develop LOCA Frequency Estimates The NRC staff presented its perspectives on EPRIs pilot study to investigate use of the xLPR code for developing LOCA frequency estimates, which was introduced at the June 14, 2022, public meeting. Overall, the staff was satisfied with the sample size but suggested increasing it for certain analyses. The NRC staff also cautioned against treating rupture probabilities as a direct equivalent to LOCA frequencies at 80 years of plant operation. Additional recommendations were provided to check for non-conservatisms in post-processing and treatment of weld residual stress uncertainties.

7. Updates to Example xLPR LOCA Frequency Estimates Compared to NUREG-1829 Expert Elicitation Results The NRC staff provided updates on work it presented at the June 14, 2022, public meeting comparing xLPR LOCA frequency results to those in NUREG-1829. The NRC staff provided more details on the progression from leak to LOCAs to rupture for the previously completed analyses for small, medium, and large breaks. When developing LOCA frequencies with LRD, the staff found no occurrences of LOCA when simulating 100,000 realizations. A statistical extrapolation method was explored to estimate sample sizes for cases with extremely low probabilities.

4 R. Iyengar Participant List JANUARY 19, 2023, PUBLIC MEETING WITH EPRI AND STAKEHOLDERS TO DISCUSS USE OF THE EXTREMELY LOW PROBABILITY OF RUPTURE CODE FOR LOSS-OF-COOLANTACCIDENT FREQUENCY ESTIMATES Name Organization Matthew Homiack NRC Christopher Nellis NRC Donald Palmrose NRC Michael Benson NRC Seung Min NRC Lois James NRC Joseph Messina NRC Kevin Heller NRC MJ Ross-Lee NRC Elijah Dickson NRC David Dijamco NRC Cory Parker NRC Chris Van Wert NRC Cindy Rosales-Cooper NRC Kristy Bucholtz NRC Josh Whitman NRC Varoujan Kalikian NRC Joseph Bass NRC David Rudland NRC Scott Krepel NRC Daniel King NRC Stewart Bailey NRC John Tsao NRC Raj Iyengar NRC Tony Nakanishi NRC Nathan Glunt EPRI Craig Harrington EPRI Fred Smith EPRI Kurshad Muftuoglu EPRI Cecile Dame MPR Associates Storm Kauffman MPR Associates Gideon Schmidt Dominion Engineering, Inc.

Markus Burkardt Dominion Engineering, Inc.

5 R. Iyengar Cedric Sallaberry Engineering Mechanics Corporation of Columbus DJ Shim EPRI Aylin Kucuk EPRI Zhegang Ma Idaho National Laboratory Jay Leininger PowerLein LLC Brian Mount Dominion Energy Don Algama U.S. Department of Energy Jeffrey Kobelak Westinghouse

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SUMMARY

OF THE JANUARY 19, 2023, PUBLIC MEETING WITH EPRI AND STAKEHOLDERS TO DISCUSS USE OF THE XLPR CODE FOR LOCA ACCIDENT FREQUENCY ESTIMATES DATE February 7, 2023 DISTRIBUTION:

RTregoning, RES/DE RIyengar, RES/DE/CIB JMcKirgan, RES/DE MHomiack, RES/DE/CIB NChandran, RES/DE/REB DDijamco, NRR/DNRL/NVIB SMin, NRR/DNRL/NPHP VKalikian, NRR/DNRL/NPHP AHiser, NRR/DNRL DRudland, NRR/DNRL ABuford, NRR/DNRL/NVIB MMitchell, NRR/DNRL/NPHP BThomson, NRR/DNRL BSmith, NRR/DNRL MBenson, RES/DE/CIB CParker, NRR/DNRL/NVIB MHaywood, OCHCO/ADHRTD/NRANB JMessina, NRR/DSS/SFNB JTsao, NRR/DNRL/NPHP KBucholtz, NRR/DRA/APOB MWentzel, NRR/DANU/UTB2 AHeller, NRR/DSS/SFNB AKock, NRR CFairbanks, NRR/DNRL/NVIB OYee, NRR/DNRL/NVIB JDean, NRR/DSS/SFNB JMedoff, NRR/DNRL/NVIB JDonoghue, NRR/DSS MReisi-Fard, RES/DRA JWhitman, NRR/DSS/SFNB JLehning, NRR/DSS/SFNB CMoyer, RES/DE/CMB ADAMS Accession No.: ML23037A812

OFFICE RES/DE/REB NAME CNellis CN DATE Feb 7, 2023 OFFICIAL RECORD COPY