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

Point Beach GL 2004-02 Resolution Update NextEra Energy Point Beach, LLC (NextEra)

December 9, 2021

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 2

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 3

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 4

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 5

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 6

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 7

PBN Risk-Informed Approach 8

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 9

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 10

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 11

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 12

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 13

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 14

Submittal Content and Schedule

• Submittal will address the five principles from RG 1.174

• Submittal will include the following enclosures

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

- Enclosure 2: License amendment request (LAR) for implementation of risk-informed approach to address debris effects

- Enclosure 3: Updated GL 2004-02 responses following the NRC content guide (revision bars will be shown for technical changes from the 2017 GL submittal)

- Enclosure 4: Risk quantification and uncertainty analyses

- Enclosure 5: Defense in depth measures and safety margin

• NextEra is currently working on the submittal

• Projected date for submittal to the NRC: Spring 2022 15

Questions?