05000368/LER-2021-002, Material Defect in Primary Coolant System That Cannot Be Found Acceptable Under American Society of Mechanical Engineers Section XI
| ML21336A340 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 12/01/2021 |
| From: | Keele R Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2CAN122101 LER 2021-002-00 | |
| Download: ML21336A340 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded |
| 3682021002R00 - NRC Website | |
text
2CAN122101 10 CFR 50.73 December 1, 2021 ATTN: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Entergy - Licensee Event Report 50-368/2021-002-00, Material Defect in Primary Coolant System that Cannot be Found Acceptable Under American Society of Mechanical EngineersSection XI Arkansas Nuclear One - Unit 2 NRC Docket No. 50-368 Renewed Facility Operating License No. NPF-6 Entergy Operations, Inc. (Entergy) submits the enclosed Licensee Event Report (LER) 50-368/2021-002-00 for Arkansas Nuclear One, Unit 2. This event is reportable in accordance with 10 CFR 50.73(a)(2)(ii)(A) as any event or condition that resulted in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded. The LER describes a Reactor Pressure Vessel Closure Head Penetration Nozzle in-service test indication resulting in a material defect in the primary coolant system that could not be found acceptable under ASME Section XI.
This letter contains no new regulatory commitments.
Should you have any questions concerning this issue, please contact Riley D. Keele Jr.,
Manager, Regulatory Assurance, at 479-858-7826.
Respectfully, ORIGINAL SIGNED BY RILEY D. KEELE, JR.
Riley D. Keele, Jr.
RDK/mkh Enclosure: Licensee Event Report 50-368/2021-002-00 Entergy Operations, Inc.
Arkansas Nuclear One 1448 S.R. 333 Russellville, AR 72802 Tel 479-858-7826 Riley D. Keele, Jr.
Manager, Regulatory Assurance
2CAN122101 Page 2 of 2 cc:
NRC Region IV Regional Administrator NRC Senior Resident Inspector - Arkansas Nuclear One NRC Project Manager - Arkansas Nuclear One
Enclosure to 2CAN122101 Licensee Event Report 50-368/2021-002-00
Abstract
Arkansas Nuclear One, Unit 2 0368 3
Material Defect in Primary Coolant System that Cannot be Found Acceptable Under American Society of Mechanical EngineersSection XI 10 04 2021 2021 002 00 12 01 2021 N/A N/A N/A N/A 6
0
Riley D. Keele / Manager, Regulatory Assurance (479) 858-7826 B
On October 3, 2021, Arkansas Nuclear One, Unit 2 was shut down in Mode 6 for a scheduled refueling outage. The reactor vessel closure head (RVCH) was being examined in accordance with the Inservice Inspection Program. Ultrasonic (UT) examination identified an indication that was not acceptable under American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel code requirements. The RVCH Control Element Drive Mechanism (CEDM) Nozzle 46 was found to contain a surface-connected flaw. On October 4, 2021, it was determined that the indication did not meet the acceptable limits as defined in ASME Code Case N-729-6.
A half-nozzle repair was completed on November 20, 2021 to correct the identified condition on CEDM Nozzle 46. This event is reportable in accordance with 10 CFR 50.73(a)(2)(ii)(A) as any event or condition that resulted in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded. Page of 05000-
- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
Materials Reliability Program RVCH Penetration Safety Assessment for U.S. Pressurized Water Reactor Plants (MRP 110) was performed by the industry, and it was demonstrated that there is significant margin against nozzle ejection due to circumferential cracking because of the time required for a circumferential crack to grow to the critical size, which is typically at least 330 degrees. Likewise, the safety assessment also demonstrated that periodic BMV examination of the top surface of the RVCH performed at appropriate intervals (each refueling outage for ANO-2) provides assurance against significant wastage of the low-alloy steel head material, even given the assumption of a leaking nozzle.
EVENT CAUSE(S)
The ANO-2 RVCH penetrations are constructed of Inconel Alloy 600 material which is susceptible to PWSCC, resulting in a flaw in RVCH Nozzle 46.
CORRECTIVE ACTIONS
Half-nozzle repair was performed to correct the identified condition on CEDM Nozzle 46. The half-nozzle repair involved machining away the lower section of the nozzle which contained the flaws, then welding the remaining portion of the nozzle to the RVCH to form the new pressure boundary. The new weld also attached a replacement lower nozzle that provided a means for re-attaching the guide cone.
Examinations documented in ANO2-RR-21-002 Request for Additional Information response (ML21312A017) required by ASME Code Case N-729-6 have been performed satisfactorily on Nozzle 46.
PREVIOUS SIMILAR EVENTS
None.
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