05000269/LER-2022-001, Ultrasonic Examination Indications Identifies Degraded Reactor Coolant System Pressure Boundary

Ultrasonic Examination Indications Identifies Degraded Reactor Coolant System Pressure Boundary

ML22355A448
Person / Time
Site:	Oconee
Issue date:	12/21/2022
From:	Snider S Duke Energy Carolinas
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
RA-22-0609 LER 2022-001-00
Download: ML22355A448 (1)

LER-2022-001, Ultrasonic Examination Indications Identifies Degraded Reactor Coolant System Pressure Boundary

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
2692022001R00 - NRC Website

text

Steven M. Snider Vice President Oconee Nuclear Station

Duke Energy ON01SC l 7800 Rochester Hwy Seneca, SC 29672

o.864.873.3478 f: 864.873.5791 Steve.Snider@duke-energy.com

RA-22-0609

December 21, 2022 10 CFR 50.73

Attn: Document Control Desk U. S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2746

Duke Energy Carolinas, LLC Oconee Nuclear Station Unit 1 Docket Number: 50-269 Renewed Operating Licenses: DPR-38

Subject: Licensee Event Report 269/2022-001, Revision 00 - Unit 1 Ultrasonic Examination Indications Identifies Degraded Reactor Coolant System Pressure Boundary

Licensee Event Report 269/2022-001, Revision 00, is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.

There are no regulatory commitments associated with this LER.

There are no unresolved corrective actions necessary to restore compliance with NRC requirements.

If there are questions, or further information is needed, contact Sam Adams, Regulatory Affairs, at (864) 873-3348.

Sincerely,

Steven M. Snider Vice President Oconee Nuclear Station

Enclosure: Licensee Event Report 269/2022-001 Rev.00

RA-22-0609 December 21, 2022 Page 2

cc (w/Enclosure):

Ms. Laura Dudes, Administrator, Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE, Suite 1200 Atlanta, GA 30303-1257

Mr. Shawn Williams, Project Manager U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop O-08B1A Rockville, MD 20852-2738

Mr. Jared Nadel NRC Senior Resident Inspector Oconee Nuclear Station

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO.3150-0104 EXPIRES: 08/31/2023 (08-2020)

Oconee Nuclear Station Unit 1 0500000269 1 OF4

4. Title Ultrasonic Examination Indication Identifies Degraded Reactor Coolant System Pressure Boundary

5. Event Date 6. LER Number 7. Report Date 8. Other Facilities Involved Sequential Rev Facility Name Docket Number Month Day Year Year Number No. Month Day Year NA 05000 11 01 2022 2022 001 00 12 21 2022 Facility Name Docket Number NA 05000

9. Operating Mode 03 31 2025 Date) No

Abstract (Limit to 1400 spaces, i.e., approximately 14 single-spaced typewritten lines)

At 1433 Eastern Daylight Time on 11/1/2022, during the Oconee Nuclear Station (ONS) Unit 1 refueling outage, it was determined that the results of a planned ultrasonic examination (UT) performed on a Reactor Coolant System (RCS) pressure boundary weld (specifically the 1B2 High Pressure Injection (HPI) pipe to safe end weld) did not meet applicable acceptance standards. The examination was scheduled and performed as part of the ONS Augmented In-Service Inspection (ISI) Program.

The cause of the indication is unknown at the time of this report.

Units 2 and 3 were not affected by this event.

This event was reported to the NRC on November 1, 2022, in Event Notification 56197, as an 8-hour non-emergency notification under 10 CFR 50.72(b)(3)(ii)(A) - Degraded Condition. The event is also reportable under 10 CFR 50.73(a)(2)(ii)(A) as a degradation of a principal safety barrier.

NRC FORM 366 (08-2020)

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].

BACKGROUND

At the time that the indication on the 1B2 HPI Injection Line was identified, Unit 1 was in a refueling outage in Mode 6. No significant structures, systems or components were out of service at the time of this event that contributed to the event.

During normal operation, the HPI System [EIIS:BG] controls the RCS [EIIS:AB] inventory, provides the seal water for the Reactor Coolant Pumps (RCP) [EIIS:P], and recirculates RCS letdown for water quality maintenance and reactor coolant boric acid concentration control. The discharge of the HPI pumps connects to a nozzle on each of the four reactor inlet pipes downstream of the RCPs. The reactor coolant which is letdown is normally returned to the RCS through two of these nozzles (1A1 and 1A2).

During emergency operation, the HPI system supplies borated water from the Borated Water Storage Tank (BWST) to the RCS and the RCP seals. Three parallel HPI pumps have the capability to take suction from the BWST and discharge through two redundant flow headers into the RCS, utilizing four injection lines (two per header). The stainless steel HPI injection lines terminate at injection nozzle [EIIS:NZL] assemblies located on each of the reactor inlet pipes downstream of the RCPs. Each nozzle assembly consists of a carbon steel nozzle (stainless steel clad on the inside), to which a stainless-steel safe end is welded. The HPI piping is welded to the other end of the safe end. Inside the safe end is a stainless-steel thermal sleeve, which extends into the main RCS flow path.

EVENT DESCRIPTION

On 11/1/2022, Unit 1 was in a refueling outage in Mode 6 when a planned UT examination of component 1RC-201-121 (Pipe to Safe End Weld) was being performed, an ID connected, axially oriented indication was observed. The indication was located near the weld centerline and extended approximately 0.6 inches towards the safe end and 0.4 inches towards the piping side of the weld, for an overall length of approximately 1 inch. After initial detection, an additional team was sent out to further characterize the indication. The indication was confirmed and sizing techniques determined that the indication measured to be approximately 0.200 inches thru-wall height. When applying the flaw evaluation criteria of IWB-3514-2 in ASME Section XI 2007, 2008 Addendum, the resulting a/t % was determined to be greater than 50% which exceeded the allowable a/t % thereby preventing the flaw from being evaluated as acceptable for continued use.

Given the inability for continued use with the flaw present, the decision was made to install a weld overlay over the indication, in accordance with ASME Section XI Appendix Q, under the Engineering Change (EC) process, to allow operation for up to one cycle. The initial EC was completed to install the weld overlay and allow for startup and 90 days of operation of the plant with the weld overlay installed. That EC will be revised to allow operation for the entire cycle with the weld overlay installed. Additionally, thermocouples were installed on the 1B1 and 1B2 HPI nozzles, to support cause determination, as they are both emergency injection nozzles with similar baseline conditions. The thermocouple data will continue to be monitored during the remaining cycle.

Units 2 and 3 were not affected by this event.

Reportability

This event was reported to the NRC on November 1, 2022, in Event Notification 56197, as an 8-hour non-emergency notification under 10 CFR 50.72(b)(3)(ii)(A) - Degraded Condition. The event is also reportable under 10 CFR 50.73(a)(2)(ii)(A) as a degradation of a principal safety barrier.NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

Oconee Nuclear Station Unit 1 0500000269 NUMBER NO.

2022 001 00

CAUSAL FACTORS

An Investigation Team was assembled and a fault matrix was assembled to systematically identify and support or refute any potential causes. However, a definitive cause cannot be determined until the indication can be cut out for metallurgical analysis and evaluation. This will not happen until the next Unit 1 refueling outage in the Fall of 2024. A supplemental report will be provided when the cause is determined.

CORRECTIVE ACTIONS

Immediate:

1. Implemented Temporary EC to install weld-overlay and allow operation for 90 days.

2. Thermocouples were installed on the 1B1 and 1B2 HPI nozzles for temperature monitoring to support cause determination.

Planned:

1. Revise EC to allow operation for a full cycle with the weld overlay installed.

2. Continue to monitor data from the installed thermocouples for the duration of the cycle.

3. Cut out the indication during the next Unit 1 refueling outage and send it to the Metallurgy Lab for testing

4. Review the Metallurgy test results and take follow-on actions as appropriate.

SAFETY ANALYSIS

This condition had no effect on the health and safety of the public. The indication discovered on the 1B2 pipe to safe-end weld was identified and addressed (via the weld overlay) in a timely manner. The indication was identified as part of a required periodic inspection and did not penetrate through the weld. The frequency of the required inspections would ensure degradation was detected before it reached any level of significance. There were no actual safety consequences for the event. This event is not considered an event or condition that could have prevented fulfillment of a safety function.

ADDITIONAL INFORMATION

A review of Duke Energys Corrective Action Program identified 1 related Oconee LER since 2013 that involved similar underlying concerns or reasons as this event.

A thru-wall leak occurred at this weld location in November 2013 (ONS LER 2013-004-01, ML15055A597). The circumferential flaw that eventually propagated thru-wall was caused by mechanical high cycle fatigue loading.

Inadequate oversight of the augmented examination program was also found causal, leading to incomplete examination of this weld. The previous ultrasonic examinations performed on this weld failed to identify the existing flaw, which allowed it to continue growing until the thru-wall leak developed. As a result, weld inspection frequency was increased to every refueling outage. Improvements to NDE procedures were also made to increase weld coverage and oversight. NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

Oconee Nuclear Station Unit 1 0500000269 NUMBER NO.

2022 001 00

These changes were effective in identifying the current axial weld indication prior to it growing thru-wall. Past indications in this and similar HPI nozzle welds have been circumferential. The axial nature of the current flaw suggests a different loading mechanism. Therefore, this is not a recurring event.

This event is considered INPO IRIS Reportable. There were no releases of radioactive materials, radiation exposures or personnel injuries associated with this event.