ML21336A797

GL 2004-02 Resolution Update - NextEra Energy Point Beach, LLC - December 9, 2021 (Slides)

ML21336A797
Person / Time
Site:	Point Beach
Issue date:	12/09/2021
From:	Point Beach
To:	Booma Venkataraman NRC/NRR/DORL/LPL3
Venkataraman B
References
Download: ML21336A797 (16)

Text

NextEra Energy Point Beach, LLC (NextEra)

Point Beach GL 2004-02 Resolution Update December 9, 2021

2 Meeting Agenda Overview of Plant Layout and Strainer Configuration Overview of Risk-Informed Resolution Approach Risk and Uncertainty Quantification Content of Submittal Current Status and Submittal Schedule Meeting Objectives Communicate current status of PBN response to GL 2004-02 Obtain staff feedback on the overall risk-informed resolution path

3 PBN Plant Layout Westinghouse 2-loop pressurized water reactor (PWR) with large dry containment Two redundant emergency core cooling system (ECCS) and containment spray (CS) trains Each train has a high-head safety injection (SI) pump, residual heat removal (RHR) pump, and CS pump During recirculation, the CS and SI pumps take suction from the RHR pump discharge

4 Sump Strainer Arrangement Unit 1 Unit 2

• PCI Sure-Flow strainers

• Vertical disk modules around a core tube

• Surface area of 1904.6 ft2 per train

5 Background

Previous GL Response submitted to the NRC in 2017 (ML17363A253)

NRC performed an audit of the submittal in January 2019 and issued an audit report in December 2019 with several questions PBN was able to address all questions from the audit report except for Mineral Wool cassettes having a lower destruction pressure than assumed NextEra conducted an alternative analysis for PBN to determine the best path for closeout of GL 2004-02 The selected option was the use of a risk-informed resolution approach

6 Overview of Risk-Informed Approach PBNs risk-informed approach is similar to Vogtle Overall evaluation based on models that have been used in the past and accepted by the NRC for GSl-191 resolution Screening of break scenarios and high likelihood equipment configurations Multiple breaks postulated at each Class 1 weld within first isolation valve on primary loop NARWHAL software evaluated each primary side break to determine if it would result in strainer failures due to effects of debris In-vessel downstream effects analyzed in a bounding evaluation outside of NARWHAL

7 Overview of Risk-Informed Approach Conditional failure probabilities (CFPs) calculated for each equipment lineup and PRA break size category Change in core damage frequency (CDF) calculated outside PRA model using LOCA frequencies and equipment failure probabilities Change in large early release frequency (LERF) calculated from conditional large early release probability for a large LOCA given core damage Risk contribution of secondary side breaks evaluated conservatively assuming all breaks fail the strainers due to effects of debris The total CDF and LERF values are obtained from the PBN PRA model Risk quantification results compared with RG 1.174 acceptance guidelines

8 PBN Risk-Informed Approach

9 Revision to Debris Generation Calculations ZOI size for mineral wool increased to 5.4D Mineral wool insulation is similar to K-Wool, which is classified as unjacketed mineral wool with wire mesh reinforcement in NEI 04-07 K-Wool went through air jet impact testing and was assigned a ZOI size of 5.4D per NEI 04-07 SE Tested K-Wool had wire mesh lining and fabric cover Mineral wool insulation at PBN is encapsulated in stainless steel cassettes All mineral wool within the 5.4D ZOI is assumed to be fines Shown to be more conservative than using 17D ZOI and LDFG size distribution This assumption is similar to that used by Surry and North Anna

10 Acceptance Criteria for Risk Quantification NARWHAL software used to evaluate strainer performance Strainer head loss vs. pump NPSH margin and strainer structural margin NPSHr adjusted for degasification using RG 1.82 methodology Gas voids from degasification or flashing compared with acceptance limits Debris loads of a break compared with debris limits Head loss compared with acceptance criterion for partially submerged strainer Bounding analyses were performed for the following acceptance criteria Upstream blockage does not prevent water from reaching sump Pump performance not affected by air intrusion from vortexing Penetrated debris within ex-vessel wear and blockage limits In-vessel fiber load within WCAP-17788 limit for Westinghouse two-loop plant

11 Evaluation of In-Vessel Downstream Effects In-vessel downstream effects was analyzed outside of NARWHAL following latest NRC review guidance Determined total in-vessel fiber load for the bounding hot leg break using WCAP-17788 methodology Maximum total in-vessel fiber load is ~85 g/FA, which is less than the limit in WCAP-17788 for Westinghouse 2-loop plants Boric acid precipitation is mitigated by starting an SI pump ~3-5 hours after the accident to supply flow to the cold legs and reactor core inlet PBN meets the requirements in the NRC review guide on in-vessel effects In-vessel effects have no contribution to the risk quantification

12 Risk Quantification Results Risk quantification results for base case:

CDF on the order of 1E-08 /yr LERF less than 1E-10 /yr Total CDF and LERF were based on PBN PRA model of record for internal and external events Total CDF less than 1E-04 /yr Total LERF on the order of 1E-6 /yr Risk increase due to strainer and reactor failures caused by LOCA-generated debris is within Region III of RG 1.174 guideline

13 Uncertainty Evaluation Following the guidance in NUREG-1855, uncertainty evaluation addresses parametric uncertainty, model uncertainty and completeness uncertainty Parametric uncertainty analyzed by rerunning base case model and shifting all input parameters that are not bounding to the more conservative direction Parametric uncertainty cases showed increase in CDF but the result is well within Region III of RG 1.174 guideline Model uncertainty quantified by replacing each non-consensus model with an alternative model Four model uncertainty scenarios were analyzed All model uncertainty cases showed results within RG 1.174 Region III Completeness uncertainty qualitatively determined to be low, given over four decades of industry and NRC research and analysis in this area

14 PBN PRA Model Status Internal events and fire PRA models developed and maintained in accordance with RG 1.200, Revision 2 Recent NRC approved applications TS Initiative 5.b - Surveillance Frequency Control Program 10 CFR 50.69 NFPA-805 The open peer review facts and observations (F&Os) were determined to have no significant impact on the risk-informed resolution of GL 2004-02 The relevant PRA model assumptions were reviewed and none of the assumptions are key sources of uncertainty for the risk-informed resolution of GL 2004-02

15 Submittal Content and Schedule Submittal will address the five principles from RG 1.174 Submittal will include the following enclosures

- : Request for exemption from the requirement of using deterministic methodology in 10 CFR 50.46(a)(1)

- : License amendment request (LAR) for implementation of risk-informed approach to address debris effects

- : Updated GL 2004-02 responses following the NRC content guide (revision bars will be shown for technical changes from the 2017 GL submittal)

- : Risk quantification and uncertainty analyses

- : Defense in depth measures and safety margin NextEra is currently working on the submittal Projected date for submittal to the NRC: Spring 2022

Questions?