05000454/LER-2024-002, Reactor Vessel Closure Head Penetration 31 Degraded

Reactor Vessel Closure Head Penetration 31 Degraded

ML24312A225
Person / Time
Site:	Byron
Issue date:	11/07/2024
From:	Welt H Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
BYRON 2024-0055, 1 D.101, 5A.108 LER 2024-002-00
Download: ML24312A225 (1)

LER-2024-002, Reactor Vessel Closure Head Penetration 31 Degraded

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
4542024002R00 - NRC Website

text

l November 7, 2024 L TR:

BYRON 2024-0055 File:

1 D.101 5A.108 United States Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Byron Station, Unit 1 Renewed Facility Operating License No. NPF-37 NRC Docket No. STN 50-454 10CFR50.73 Subject:

Licensee Event Report (LER) No. 454-2024-002, "Reactor Vessel Closure Head Penetration 31 Degraded" Enclosed is Byron Station Licensee Event Report (LER) No. 454-2024-002 regarding Reactor Vessel Closure Head Penetration 31 Degraded. This condition is being submitted in accordance with 10 CFR 50.73, 11Licensee Event Report System."

There are no regulatory commitments in this report.

Should you have any questions concerning this submittal, please contact Ms. Zoe Cox, Regulatory Assurance Manager, at (779) 231-6606.

Respectfully,

~--

Harris Welt Site Vice President Byron Generating Station HW/DG/hh Enclosure:

LER 454-2024-002 cc:

Regional Administrator-NRC Region Ill NRC Senior Resident Inspector - Byron Generating Station

NRG FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2027 (04-02-2024)

1. Facility Name

[8J 050

2. Docket Number

3. Page Byron Station, Unit 1 052 05000454 1 OF 3

4. Title Reactor Vessel Closure Head Penetration 31 Degraded

5. Event Date

6. LER Number

7. Report Date

8. Other Facilities Involved Sequential Revision Facility Name Docket Number Month Day Year Year Number No.

Month Day Year N/A 050 N/A 09 13 2024 2024 002 00 11 07 2024 Facility Name2 Docket Number N/A 052 N/A

9. Operating Mode 110. Power Level 6

000

)

N/A NIA NIA

Abstract

On September 13, 2024 at 08:23 CDT, during a Liquid Penetrant (PT) examination on the seal weld repair known as Embedded Flaw Repair (EFR) of Control Rod Drive Mechanism (CROM) Penetration 31, four rounded indications were discovered that were determined to be unacceptable per the acceptance criteria in ASME Section Ill.

The cause of these indications is attributed to existing mechanical discontinuities/minor subsurface voids growing or opening to the weld surface due to thermal and/or pressure stresses during plant operation. The indications were reduced to an acceptable dimension by grinding/blending the indications to meet the applicable acceptance criteria in ASME Section Ill.

This event is reportable in accordance with 10 CFR 50.73(a)(2)(ii)(A), any event or condition that results in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded.

A.

Plant Operating Conditions Before the Event

Event Date:

September 13, 2024

2. DOCKET NUMBER YEAR 05000454 2024 -

3. LER NUMBER SEQUENTIAL NUMBER 002 REV NO.

00 Unit: 1 MODE: 6 Reactor Power: 000 percent Unit 1 Reactor Coolant System (RCS) [AB]:

Ambient temperature and depressurized No structures, systems or components were inoperable at the start of this event that contributed to the event.

B.

Description of the Event:

On September 13, 2024 at 08:23 CDT, a Liquid Penetrant (PT) examination on the seal weld repair known as the Embedded Flaw Repair (EFR) of Control Rod Drive Mechanism (CROM) Penetration 31 was performed.

During the PT examination, four unacceptable rounded indications were discovered on the EFR penetration.

Rounded indications that exceed 3/16 inches in any dimension are unacceptable per the acceptance criteria in ASME Section 111:

The first indication was a 1-inch rounded indication located at 20 degrees on the nozzle portion of the EFR and 0.5 inches below the transition of the head to the nozzle.

The second indication was a 1/4-inch rounded indication located at 180 degrees on the head portion of the EFR and 3.5 inches from the transition of the head to the nozzle.

The third indication was a 1/4-inch rounded indication located at 310 degrees on the nozzle portion of the EFR and 0.2 inches below the transition of the head to the nozzle.

The fourth indication was a 3/4-inch rounded indication location at 300 degrees on the EFR at the transition of the head to the nozzle.

Zero (0) degrees azimuth is the location at the outermost portion of the penetration on the flange side (downhill/outermost side). The transition is the point where the vertical portion of the nozzle meets the horizontal area of the reactor head.

This event is reportable in accordance with 10 CFR 50.73(a)(2)(ii)(A), any event or condition that results in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded, since the as-found indications did not meet the applicable acceptance criterion referenced in ASME Section Ill to remain in service without repair. This LER is being submitted in follow-up to ENS#57321 made on September 13, 2024 at 1254 CDT.

C.

Cause of Event

The cause of these indications is attributed to existing mechanical discontinuities/minor subsurface voids growing or opening to the weld surface due to thermal and/or pressure stresses during plant operation.

Unacceptable rounded indications have previously been identified on the EFR on CROM Penetration 31.

D. Safety Consequences

2. DOCKET NUMBER YEAR 05000454 2024 -

3. LER NUMBER SEQUENTIAL NUMBER 002 REV NO.

00 This condition had no actual safety consequences impacting plant or public safety.

Each unacceptable indication was identified in a timely manner during routine inspection activities and repaired prior to through-wall leakage occurring. None of the indications penetrated through the EFR. With these required inspections being performed at the required intervals, detected degradation that does not meet acceptance criteria will be repaired or evaluated prior to reaching any level of significance. This condition is limited to CROM Penetration 31 at Byron Station Unit 1.

Bare metal visual examination on the reactor vessel closure head did not detect any evidence of reactor coolant pressure boundary leakage. Based on the characteristics and dimensions of the unacceptable indications discovered during PT examination, there was no loss of safety function due to these indications.

E.

Corrective Actions

Corrective actions were completed to grind/blend the indications to remove or reduce the indication size to meet the applicable acceptance criteria in ASME Section Ill. Progressive PT examination was performed during the grinding/blending to determine if the indications met acceptance criteria. All four of the previously unacceptable indications were determined to meet acceptance criteria via PT examination.

F.

Previous Occurrences

Byron Station, Unit 1, Reactor Pressure Vessel Head Control Rod Drive Mechanism Penetration Nozzle Weld Repair Surface Indications, (LER 2012-004-00), November 12, 2012.

Byron Station, Unit 1, Liquid Penetrant Indications in Embedded Flaw Seal Weld Repair of Control Rod Drive Mechanism Penetration 31 during Refueling Outage (LER 2015-005-00), November 17, 2015.

Byron Station, Unit 1, Byron Station Unit 1 Volumetric and Surface Examinations of Reactor Pressure Vessel Penetration Nozzles Identify Indications Attributed to Primary Water Stress Corrosion Cracking and Minor Subsurface Void Enlargement from Operating Stresses (LER 2017-001-00), April 25, 2017.

A review of these LE Rs concluded that these events are similar; however, the causes and corrective actions taken would not have been expected to prevent this event from occurring.

G. Component Failure Data

Manufacturer Westinghouse Nomenclature Reactor Vessel Integrated Head Package Termination 1718E72 Mfg. Part No.

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