05000313/LER-2024-002, ANO Unit 1 Inoperable Containment Isolation Boundary
| ML25037A301 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 02/06/2025 |
| From: | Keele R Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 1CAN022501 LER 2024-002-00 | |
| Download: ML25037A301 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3132024002R00 - NRC Website | |
text
entergy 1CAN022501 February 6, 2025 ATTN: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 Riley D. Keele, Jr.
Manager, Regulatory Assurance Arkansas Nuclear One Tel 479-858-7826 10 CFR 50.73
Subject:
Licensee Event Report 50-313/2024-002-00, Inoperable Containment Isolation Boundary Arkansas Nuclear One - Unit 1 NRC Docket No. 50-313 Renewed Facility Operating License No. DPR-51 Entergy Operations, Inc. (Entergy) submits the enclosed Licensee Event Report (LER) 50-313/2024-002-00 for Arkansas Nuclear One, Unit 1. This event is being reported in accordance with 1 O CFR 50.73(a)(2)(i)(B) as any operation or condition which was prohibited by the plant's Technical Specifications; 1 O CFR 50.73(a)(2)(ii)(B) as any event or condition that resulted in the condition of the nuclear power plant, including its principal safety barriers, being in an unanalyzed condition; and 1 O CFR 50.73(a)(2)(v) as any event or condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to (C) control the release of radioactive material or (D) mitigate the consequences of an accident.
The LER describes an inoperable Unit 1 containment isolation boundary and also provides justification why this will not be counted against the Nuclear Regulatory Commission (NRC)
Safety System Functional Failure (SSFF) performance indicator since a loss of safety function was determined to have not occurred.
This letter contains no new commitments and no revisions to existing commitments.
Should you have any questions concerning this issue, please contact Riley D. Keele Jr.,
Manager, Regulatory Assurance, at 479-858-7826.
1CAN022501 Page 2 of 2
Enclosure:
Licensee Event Report 50-313/2024-002-00 cc:
NRC Region IV Regional Administrator NRC Senior Resident Inspector - Arkansas Nuclear One NRC Project Manager - Arkansas Nuclear One Institute of Nuclear Power Operations (LEREvents@inpo.org)
Enclosure 1CAN022501 Licensee Event Report 50-313/2024-002-00
Abstract
On December 10, 2024, Arkansas Nuclear One, Unit 1 was at 67% power and in Mode 1 following a planned maintenance outage. At 0930 Central Standard Time (CST), Operations discovered the outside Breathing Air Reactor Building penetration manual isolation valve was open.
Prompt investigation determined the inside manual isolation valve was likely open as well. The mode of applicability for the Reactor Building Isolation Valves to be closed, Mode 4, was entered from Mode 5 at 0556 CST on December 8, 2024 without the appropriate controls in effect.
Discovery of this condition resulted in the Reactor Building being declared inoperable and a violation of Unit 1 Technical Specifications.
The Reactor Building was restored to operable status at 0950 CST on December 10, 2024, when the outside isolation valve was closed. The inside isolation valve was closed at 1345 CST on December 10, 2024, restoring full compliance with Unit 1 Technical Specifications.
There were no consequences to the general safety of the public, nuclear safety, industrial safety or radiological safety. No radiological releases occurred due to this event.
The NRC Senior Resident Inspector was informed of the event.
PLANT STATUS 050 052
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00313 NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 002 1-G At the time of the event, Arkansas Nuclear One, Unit 1 (ANO-1) was at 67% Rated Thermal Power and in Mode 1. There were no other structures, systems, or components that were inoperable at the time that contributed to the event.
EVENT DESCRIPTION
The Reactor Building (RB) [NH] isolation valves form part of the RB pressure boundary and are required to be operable per ANO-1 Technical Specifications (TS) in Modes 1-4. The operability requirements for the RB isolation valves ensure that the RB is isolated, providing assurance that the RB function assumed in the safety analysis will be maintained.
At 0930 on December 10, 2024, Operations discovered the outside isolation valve for the Breathing Air (BA) penetration to the Unit 1 Reactor Building was open. Operations entered TS 3.6.3 Condition A, Reactor Building Isolation Valves, due to one inoperable penetration isolation valve. It was quickly determined the inside isolation valve for this penetration was likely open as well so TS 3.6.3 Condition B was entered for two valves in a penetration flowpath inoperable. ANO Engineering provided input that this configuration (both the inside and outside penetration valves open) would exceed the overall Reactor Building leakage rate acceptance criteria and Operations entered TS 3.6.1 Condition A, Reactor Building, as required. Operations closed the inside and outside penetration isolation valves on December 10, 2024, and all TS conditions were exited at 1345.
Upon discovery of the open BA Valves, an Extent of Condition (EOC) was performed and an Instrument Air (IA) outside penetration valve (manual valve) was also found open. Unit 1 entered TS 3.6.3 Condition A for this penetration flowpath.
This valve is associated with the IA penetration to the Unit 1 Reactor Building Purge Valves. Closure of this valve also occurred on December 10, 2024 and TS 3.6.3 Condition A was exited at 1541.
On December 10, 2024, this event was reported per 10 CFR 50.72(b)(3)(ii)(B) as an event or condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety; and 10 CFR 50.72(b)(3)(v)
(C) and (D), as an event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to (C) control the release of radioactive material or (D) mitigate the consequences of an accident (EN 57 464 ).
This LER is being submitted in accordance with 10 CFR 50.73(a)(2)(i)(B) as any operation or condition which was prohibited by the plant's TS; 10 CFR 50.73(a)(2)(ii)(B) as any event or condition that resulted in the condition of the nuclear power plant, including its principal safety barriers, being in an unanalyzed condition; and 10 CFR 50.73(a)(2)(v) as any event or condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to (C) control the release of radioactive material or (D) mitigate the consequences of an accident.
SAFETY ASSESSMENT
The consequence of this event was operation of the plant in a condition prohibited by Unit 1 TS. There were no other actual consequences to general safety of the public, nuclear safety, industrial safety, and/or radiological safety for this event.
After discovery, the outside breathing air Reactor Building isolation valve was closed, isolating the penetration until the inside Reactor Building isolation valve was also closed, fully restoring compliance, and exiting the TS.
The Instrument Air Line penetration to the Reactor Building Purge Isolation Valves was operable due to the inside penetration valve remaining in its required configuration (closed). The outside isolation valve was closed after discovery as part of the extent of condition investigation.
The risk associated with this event is LOW.
050 052
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00313 NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 002 1-G The basis for this determination is the ANO-1 Large Early Release Frequency (LERF) Probabilistic Risk Assessment (PRA) does not include failures of piping less than 2 inches in diameter as contributors to LERF. The penetrations associated with this event are 1 inch in diameter. Additionally, another check valve outside of the Reactor Building in the Breathing Air penetration flowpath was identified that would have mitigated a potential radioactive release through the penetration. Subsequent testing of this valve resulted in minimal leakage and it would have assisted in maintaining the safety function of the Unit 1 Reactor Building. Because of this, it was determined that the safety function was not lost.
Due to the factors above contributing to the determination of a low safety risk related to this event, it will not be counted against the Nuclear Regulatory Commission (NRC) Safety System Functional Failure performance indicator since no loss of safety function occurred.
EVENT CAUSE(S)
The Direct Cause of this event was a series of lapses in Human Performance tools, Operator Fundamentals, and procedures that allowed this condition to exist.
The Root Cause of this event is inadequate procedure quality due to procedures associated with control of containment penetrations and Category E components contained misleading, interpretative, and incomplete information. Category E components are those in the flow path of safety-related systems that have a specified position for the system to perform its safety function, and whose misalignment could go undetected from the Control Room.
The first Contributing Cause of this event was that Operations performance standards were not commensurate with the risk associated with containment penetrations and Category E component configuration control.
The second Contributing Cause of this event is that management response to declining standards did not result in adequate plans to prevent or mitigate issues.
CORRECTIVE ACTIONS
Completed corrective actions include:
- 1. Closed the open Reactor Building isolation valves in both the Breathing Air and Instrument Air Line to Reactor Building Purge Valves penetrations.
- 2. Completed the ANO-1 Containment Closure Determination Sheet and verified ANO-1 accessible component positions were configured as required.
Proposed actions:
- 1. To address the Root Cause, two procedures will be revised to improve clarity on containment penetrations and Cat. E components. These procedures are scheduled to be revised by March 27, 2025.
- 2. To address the Contributing Causes, a corrective action plan has been developed with actions to reset and reinforce Operations performance standards, monitor Operations performance standards, reset and reinforce Operations Management ownership and engagement in improving performance standards, monitor Operations Management ownership and engagement in improving performance standards. This corrective action plan is in progress and scheduled for completion June 19, 2025.
CORRECTIVE ACTIONS (continued}
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YEAR SEQUENTIAL REV 120241 NUMBER NO.
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- 3. Additionally, an extent of cause review of additional procedures is in progress and revisions will be incorporated for any of these procedures where misleading, interpretative, or incomplete direction is identified. Completion of these extent of cause actions is scheduled for July 17, 2025.
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