ML22272A033

Memo E-mail to File - Summary of August 29, 2022, Meeting with Dominion to Discuss Proposed Alternative Request Post-peening follow-up Volumetric Exam of RPV Head Penetration Nozzle

ML22272A033
Person / Time
Site:	Millstone
Issue date:	09/29/2022
From:	Richard Guzman NRC/NRR/DORL/LPL1
To:	Gonzales H NRC/NRR/DORL/LPL1
Guzman R
References
EPID L-2022-LRM-0058
Download: ML22272A033 (4)

Text

From: Richard Guzman To: Hipo Gonzalez Bcc: Richard Guzman

Subject:

Memo E-mail to File - Summary of August 29, 2022, Meeting with Dominion to Discuss Proposed Alternative Request, Post-Peening follow-up volumetric examination of RPVH Penetration Nozzle (EPID L:2022-LRM-0058)

Date: Thursday, September 29, 2022 9:44:00 AM

Hipo, For your information, shown below is a summary of the August 29, 2022, observation meeting with Dominion Energy Nuclear Connecticut, Inc. to discuss the licensees planned alternative request related to post-peening follow-up volumetric examination for the reactor pressure vessel head penetration nozzles at Millstone Power Station, Unit No. 3. This communication will be added to ADAMS as an official agency record and Listservd.

Please contact me if you have any questions regarding this meeting.

Rich Guzman Sr. PM, Division Operator Reactor Licensing Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Office: O-9C7 l Phone: (301) 415-1030 Richard.Guzman@nrc.gov CATEGORY 1 PUBLIC MEETING WITH DOMINION ENERGY NUCLEAR CONNECTICUT, INC. (DENC),

TO DISCUSS PROPOSED ALTERNATIVE REQUEST REGARDING POST-PEENING FOLLOW-UP VOLUMETRIC EXAMINATION OF REACTOR PRESSURE VESSEL HEAD PENETRATION NOZZLE MILLSTONE POWER STATION, UNIT NO. 3 PRE-APPLICATION MEETING MEETING

SUMMARY

AUGUST 29, 2022 DOCKET NO. 50-423 The U.S. Nuclear Regulatory Commission (NRC or the staff) and representatives of Dominion Energy Nuclear Connecticut, Inc. (DENC, the licensee) held a public meeting via teleconference call on August 29, 2022, to discuss the licensees planned alternative request for Millstone Power Station, Unit No. 3 (MPS3) related to post-peening follow-up volumetric examination for the reactor pressure vessel head penetration nozzles. The licensees meeting slides are available in ADAMS at Accession No. ML22236A060. The licensees presentation is summarized as follows:

Background

The licensee began the presentation with an overview of the background relative to the applicable NRC regulatory requirements as applied to Millstone 3. Per Section 50.55a(g)

(6)(ii)(D)(5) of Title 10 of the Code of Federal Regulations (10 CFR), a reactor pressure vessel (RPV) upper head with nozzles and J-groove welds mitigated by peening can obtain examination relief Code Case N-729-6 provided that the peening satisfies the performance criteria, qualification and examination requirements of MRP-335, Revision 3-A (MRP-335).

The licensee explained that for RPV heads with less than 8 years of effective degradation years (EDY) and free from pre-peening flaws, MRP-335 requires a follow-up volumetric examination in the second refueling outage following peening. For MPS3, the licensee peened the RPV head during the fall 2020 refueling outage; therefore, per the requirements of MRP-335, a follow-up examination is required during the fall 2023 refueling outage. The licensee stated that the RPV head operates at reactor cold-leg temperature and has experience less than 8 EDY. Additionally, previous exams have identified no indications attributed to primary water stress corrosion cracking (PWSCC).

Reason for the Proposed Alternative The licensee stated that pursuant to 10 CFR 50.55a(z)(1), it plans to request a one-time alternative to permit the volumetric examination for the subject nozzles to be deferred from fall 2023 to spring 2025. The proposed alternative would not change the visual examination frequency such that the bare metal visual examinations will be performed each RFO in accordance with MRP-335. Deferring this examination to the spring 2025 RFO would (1) alleviate scheduling and resource conflicts with the RPV hot leg dissimilar metal weld post-peening follow-up examinations, and (2) align with the RPVHPN post-peening follow-up examination frequency required by the vendor warranty.

Proposed Resolution of Issue The licensee provided the following as their technical justification for the proposed alternative relative to PWSCC:

• The pre-peening exam conducted in accordance with MRP-335 did not identify any indications of cracking attributed to PWSCC.

• The peening application met the requirements of MRP-335, without any deviations; if there was a flaw located within the region of compressive stress, PWSCC growth of the pre-existing flaw would be arrested.

• A calculation of re-inspection years for an unmitigated head (per Code Case N-729-

6) concluded that the next volumetric exam would not be required until the fall of 2026; use of re-inspection years for unmitigated heads is conservative to apply for a peened head, as peening reduces the likelihood of PWSCC.

The licensee also provided the following as their technical justification for the proposed alternative in terms of defense-in-depth:

• Bare metal visual exams conducted every RFO would provide defense-in-depth in the unlikely event of pressure boundary leakage.

• The boric acid corrosion program provides both detection and analysis of leakage of borated water inside containment.

• Millstone 3 Technical Specifications (TS 3.4.6.2) require online leakage detection and outline the actions required to maintain safe operability for reactor coolant system leakage greater than 1 gallon per minute (gpm).

• Millstone 3 also implements a 0.1 gpm action level on unidentified leakage,

consistent with WCAP-16465-NP.

Schedule The licensee stated their planned submittal is on track and projected for submission by end of September 2022. DENC intends to request an approval date of Sept 2023 (i.e., one year from the submission date) to support implementation by the MPS3 fall 2023 (3R22) outage.

Questions from the NRC Staff The staff did not have any questions for the licensee but provided several applications of similar proposed alternatives from recent precedented submittals for the licensees consideration. Specifically, the staff referenced an alternative request submitted for Byron and Braidwood Nuclear Generating Station based on a hardship justification. The submittal provided a technical basis with analysis that looked at changes to the stress profile of mis-flaws relative to the extent of flaw growth during the given period of extended operation.

The submittal included an assessment of their peening application and identified the potential affects and changes to the weld residual stress pattern and the extent of growth of the flaws. Additionally, the staff highlighted a precedent submittal for Wolf Creek Generating Station, Unit 1, in relation to the use of applying a hardship justification based on the post-peening follow-up examination frequency required by the vendor warranty. The licensee stated that they were aware of both precedents and would consider the associated NRC acceptance reviews, requests for additional information, and safety evaluations as it finalizes the MPS3 plant-specific submittal.

Conclusion DENC completed its presentation with no open/unanswered questions from the staff and summarized its conclusion by stating that relative to PWSCC considerations and defense-in-depth, there is technical justification for deferring the follow-up volumetric exam from fall 2023 (i.e., the second outage after peening) to spring 2025 (i.e., the third outage after peening) based on the following: (1) previous exams have identified no indications attributed to PWSCC, (2) the peening process met all MRP-335, Revision 3-A requirements, so PWSCC growth of shallow, pre-existing flaws would likely be arrested, (3) calculation of re-inspection years for an unmitigated head, which is conservative for a peened head, supports deferral, and (4) defense in depth is achieved through continued performance of the bare metal visual examination each RFO, boric acid corrosion control practices, and the plants online leak detection capabilities.

No decisions were made regarding the acceptability of the licensees proposed submittal.

There were no members of the public in attendance. To date, no public meeting feedback forms have been submitted through the NRC public meeting feedback system.

LIST OF ATTENDEES AUGUST 29, 2022, CATEGORY 1 PUBLIC MEETING WITH DOMINION ENERGY NUCLEAR CONNECTICUT, INC. (DENC),

TO DISCUSS PROPOSED ALTERNATIVE REQUEST POST-PEENING FOLLOW-UP VOLUMETRIC EXAMINATION OF

REACTOR PRESSURE VESSEL HEAD PENETRATION NOZZLE MILLSTONE POWER STATION, UNIT NO. 3 DOCKET NO. 50-423 ATTENDEE ORGANIZATION Richard Guzman U.S. Nuclear Regulatory Commission (NRC)

Jay Collins NRC Karen Sida NRC Neil Sheehan NRC Paul Cataldo NRC Nate Mentzer NRC Shayan Sinha DENC Craig Sly DENC Ethan Treptow DENC Timothy Olsowy DENC Daniel Beachy DENC Beth Haluska DENC Kevin Hacker DENC Janelle Madison DENC Brian Derreberry DENC