ML20170B021

NRC Pre-Submittal Meeting Byron Unit 2 One-Time Deferral of Reactor Pressure Vessel Head Penetration Nozzle (Rpvhpn) Inspections

ML20170B021
Person / Time
Site:	Calvert Cliffs, Dresden, Peach Bottom, Nine Mile Point, Byron, Three Mile Island, Braidwood, Limerick, Ginna, Clinton, Quad Cities, FitzPatrick, LaSalle
Issue date:	06/23/2020
From:	Getchius W, Render D, Simpson L, White G Dominion Engineering, Exelon Generation Co, Exelon Nuclear
To:	Joel Wiebe Office of Nuclear Reactor Regulation
Purnell B
References
Download: ML20170B021 (17)

Text

NRC Pre-Submittal Meeting Byron Unit 2 One-Time Deferral of Reactor Pressure Vessel Head Penetration Nozzle (RPVHPN)

Inspections Diane Render, Exelon Glenn White, Dominion Engineering, Inc.

Jamie Getchius, Exelon Lisa Simpson, Exelon June 23, 2020 1

Agenda

• Introductions and Opening Remarks

• Objectives and Scope

• Primary Water Stress Corrosion Cracking (PWSCC) and Peening History

• Authorized and Proposed Inspection Schedule

• Proposed Relief Request (RR)

• Technical Basis for RR

• COVID-19 Risk During Byron Unit 2 RPVHPN Inspections

• Timeline for Submittal

• Summary 2

Objectives and Scope Objectives:

• Present Exelons proposed RR for one-time deferral of follow-up inspection for RPVHPNs for Byron Unit 2

• After this deferral, the approved volumetric examination frequency per MRP-335, Revision 3-A, Table 4-3, Item No.

B4.60, will be followed Scope:

• RPVHPN Numbers 1 through 78 and the vent penetration nozzle

• Proposed alternative only applies to the volumetric examination of the Byron Unit 2 RPVHPNs currently scheduled for the Fall 2020 (B2R22) refueling outage 3

PWSCC History

• The Byron Unit 2 RPV head is a B&W-fabricated T-Cold head with the RPVHPNs fabricated using material supplied by B&W Tubular Products

• Inspections to date have identified flaws in two nozzles (Spring 2007, Fall 2014)

• Each flaw was located on the nozzle OD at the weld toe

• Exelon repaired the two flaws by implementing an embedded flaw weld overlay Elevation of Remaining Primary Upper Tip Vertical Outage Outage Flaw Depth, a Depth-to- Length 2c Aspect Above As-Built Ligament to Detected Number Pen. # Orient. (in.) Thick., a/t (in.) Ratio, 2c/a Weld Toe (in.) Leakage (in.)

Spring B2R13 68 Axial 0.304 47% 0.60 2.0 0.50 1.22 2007 Fall 2014 B2R18 6 Axial 0.222 34% 0.52 2.4 0.60 0.96 4

Peening History

• In Spring 2016, Exelon pursued proactive RPVHPN peening with Framatome (formerly AREVA NP) to improve RPVHPN integrity and mitigate PWSCC

• Peening of 9 nozzles was not initially completed. These nozzles were re-peened in Fall 2017, one cycle (N+1) after the majority of nozzles were peened

• All nozzles have now been successfully peened to MRP-335, Revision 3-A requirements

• Relief has been granted to align the N+3 follow up inspection for the 70 nozzles peened in Spring 2016 with the N+2 follow up inspection for the 9 nozzles peened in Fall 2017 5

Authorized and Proposed Inspection Schedule Authorized Inspection Schedule:

2016 2017 2018 2019 2020 2021 2022 Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall B2R19 B2R20 B2R21 B2R22 B2R23 N+0 (70) N+1 (70)1 N+2 (70)2 N+3 (70) N+4 (70)

Byron Unit 2 B2R20 B2R21 B2R22 B2R23 N+0 (9) N+1 (9) N+2 (9) N+3 (9)

Notes:

1. Skip Byron Unit 2 N+1 - RR I4R-14 authorized 9/19/2017 (ML17249A241)

2. Align N+2/N+3 - RR I4R-16 authorized 2/25/2019 (ML19035A294)

Proposed Inspection Schedule:

2016 2017 2018 2019 2020 2021 2022 Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall B2R19 B2R20 B2R21 B2R22 B2R23 N+0 (70) N+1 (70) N+2 (70) N+3 (70)1 N+4 (70)

Byron OneTime Unit 2 B2R20 B2R21 B2R22 Deferral B2R23 N+0 (9) N+1 (9) N+2 (9)1 N+3 (9)

Notes:

1. Proposed Byron Unit 2 RR to defer inspections by one outage, resulting in:

a. N+4 (nominal 6.0 years) for 70 RPVHPNs

b. N+3 (nominal 4.5 years) for 9 RPVHPNs 6

Proposed Relief Request

• Exelon is developing a RR due to uncertainty of specialty vendor work force availability and to limit risk of exposure to site/local supplemental workers resulting from COVID-19 pandemic for upcoming Byron Unit 2 Outage (B2R22)

• The relief will protect the health and safety of plant personnel while maintaining responsibilities to support critical infrastructure

• Requesting one-time alternative to defer RPVHPN volumetric examinations by one outage, i.e., from October 2020 to April 2022

(~18 months)

• One-time alternative will be requested in accordance with 10 CFR 50.55a(z)(2) - Hardship without a compensating increase in quality and safety 7

Technical Basis for RR

• Previously detected indications at Byron Unit 2 show large remaining margin against a through-wall condition and pressure boundary leakage

• For the two previously repaired nozzles, plant experience has shown the embedded flaw repair to be a reliable approach, as long as consideration is given to ensuring the overlay covers all of the susceptible material

• Axial cracking within the nozzle does not represent a credible rupture concern

• Visual examinations (VEs) will identify boric acid corrosion before it becomes a safety concern

• Large margins exist in the time until circumferential cracking within the nozzle tube could produce nozzle ejection 8

Technical Basis for RR

• A PWSCC crack growth analysis specific to the Byron Unit 2 CRDM nozzles, which was previously submitted to NRC in 2007, determined the amount of time needed for a postulated flaw to result in a potential leak path

• Temperature conservatively assumed to be 558°F versus the current Byron Unit 2 head temperature of 549°F

• Considers axial flaws on the nozzle OD and ID, as well as on uphill and downhill sides

• Flaws were postulated with an initial depth (a/t = 0.12) slightly greater than the detectability limit for ultrasonic testing volumetric examinations (a/t = 0.10) typically applied

• Bounding time to leakage was found to be 6.9 calendar years

• Results show leakage due to base metal cracking is unlikely under the proposed alternative (up to 6.0 year interval between examinations)

• No credit taken for peening mitigation 9

Technical Basis for RR

• Proposed alternative of up to 6.0 years remains more frequent than requirements for unmitigated heads without previously detected PWSCC (the shorter of 8 calendar years or RIY (reinspection years)

= 2.25)

• Required interval would be 8 years for an unmitigated head without previously detected PWSCC and operating at 549°F

• Under the proposed alternative, defense in depth is maintained in the unlikely case that leakage were to occur due to base metal cracking

• Sensitive direct VEs shall be performed for evidence of leakage during the Fall 2020 (B2R22) refueling outage

• A leak or increase in radiation levels within containment would be detected during operation if a substantial leak were to develop 10

COVID-19 Risk During Byron Unit 2 RPVHPN Inspections

• January 27, 2020: Determination Public Health Emergency (PHE) exists Nationwide (PHE renewed April 21, 2020)

• March 9, 2020: Illinois declared disaster proclamation over Coronavirus outbreak

• May 5, 2020: Governor of Illinois announced a five-phase plan to reopen the State of Illinois, using health statistics and health care capacity

• As of June 18, Ogle County, the county in which Byron is located, and North-Central Region of Illinois are currently in Phase 3 of the plan

• Current limit on gatherings is 10 people

• Face coverings and social distancing are required

• To reach the fifth and final phase, a vaccine or highly effective treatment or herd immunity would need to be established

• Exelon is adhering to State and Centers for Disease Control and 11 Prevention (CDC) recommendations to keep employees safe

COVID-19 Risk During Byron Unit 2 RPVHPN Inspections

• Exelon does not have the internal capability and equipment to perform these inspections

• These examinations must be performed by one of the two qualified vendors in the U.S.

• 24 individuals from across the U.S. required to mobilize on-site to support B2R22 RPVHPN inspections

• Appropriate precautions will be taken based on lessons learned (e.g., individuals traveling alone, driving instead of flying, and staying in individual hotel rooms)

• Framatome has formalized the above precautions via company policy as a mitigation measure for COVID-19

• The potential remains for the introduction and spread of COVID-19 to Byron by vendor nondestructive examination (NDE) personnel who recently traveled from other areas of the country 12

COVID-19 Risk During Byron Unit 2 RPVHPN Inspections

• Industry vendors are supporting multiple overlapping outages (low bench strength) and maintain unique and complex qualifications

• The nature of the work prevents meeting CDC recommendations for social distancing by maintaining at least six feet from other personnel to limit the spread of the virus

• Mitigation strategies do not eliminate the time that social distancing is not maintained

• These individuals will wear the approved personal protective equipment (PPE) for COVID-19 in accordance with Exelon policy

• Exelon believes that additional PPE has potential to add individual effort to activities that increase human performance and safety risk

• Discussions with vendor yielded no additional or new technology to conduct the RPVHPN inspections 13

COVID-19 Risk During Byron Unit 2 RPVHPN Inspections

• Exelon has assessed the possibility of some of the personnel who normally support the examination on-site instead providing support remotely by data transmittal

• The savings in personnel from this approach would only be expected to reduce the number of personnel traveling to the site by 3 - 4 employees (of the 24 individual required to mobilize)

• This benefit is offset by the risk of slow data transmittal or interruptions, which would prolong the amount of time personnel to stay on site and delay the completion of the examination

• Exelon is contingency planning in case some of its workforce becomes unavailable due to the COVID-19 outbreak

• With the current work scope and potential loss of personnel, there is a potential that the company may not be able to complete the refueling outage in a timely manner, negatively impacting critical infrastructure 14

Timeline for Submittal

• Submittal of RR targeted by mid-July

• Byron Unit 2 Outage (B2R22) begins in early October

• Changes to the schedule will be communicated to Office of Nuclear Reactor Regulation (NRR) Project Manager

• Requested approval date will be September 1, 2020 15

Summary

• Relief approval would mitigate COVID-19 risk for upcoming Byron Unit 2 Outage (B2R22)

• Performance of a volumetric examination of the Byron Unit 2 RPVHPNs during B2R22 would result in hardship without a compensating increase in the level of quality and safety in accordance with 10 CFR 50.55a(z)(2)

• The proposed alternative provides reasonable assurance of structural integrity, with a technical basis that conservatively does not credit the peening mitigation:

• Large margins against nozzle ejection

• VEs performed each refueling outage address the concern for boric acid corrosion

• Deterministic crack growth analyses specific to Byron Unit 2 show that leakage is unlikely due to base metal cracking

• Defense in depth is maintained by the VEs and the online leak detection capability 16

Questions?

17