05000313/LER-2024-001, Source Range Nuclear Instrument Failure Resulting in Condition Prohibited by Technical Specifications
| ML24183A214 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 07/01/2024 |
| From: | Keele R Entergy Nuclear Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 1CAN072402 LER 2024-001-00 | |
| Download: ML24183A214 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3132024001R00 - NRC Website | |
text
- ) entergy 1CAN072402 July 1, 2024 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 50-313/2024-001-00, Source Range Nuclear Instrument Failure Resulting in Condition Prohibited by Technical Specifications Arkansas Nuclear One - Unit 1 NRC Docket No. 50-313 Renewed Facility Operating License No. DPR-51 In accordance with the reporting requirements of 10 CFR 50.73, attached is the Licensee Event Report concerning the Arkansas Nuclear One, Unit 1, Source Range Nuclear Instrument failure that resulted in a condition prohibited by Technical Specifications.
This letter contains no new regulatory commitments.
Should you have any questions or require additional information, please contact Riley Keele, Manager, Regulatory Assurance, at (479) 858-7826.
Respectfully, R~~
RDK/bka
Enclosure:
Licensee Event Report 50-313/2024-001-00 Entergy Operations, Inc. 1448 S.R 333 Russellville, AR 72802
1CAN072402 Page 2 of 2 cc:
NRC Region IV Regional Administrator NRC Senior Resident Inspector - Arkansas Nuclear One NRC Project Manager - Arkansas Nuclear One Designated Arkansas State Official Institute of Nuclear Power Operations
ENCLOSURE 1CAN072402 Licensee Event Report 50-313/2024-001-00
Abstract
On May 6, 2024, at approximately 1604 Central Daylight Savings Time (CDT), Arkansas Nuclear One, Unit 1 (ANO-1) started reactor core reload during Refueling Outage 31 (1R31). On May 7, 2024, at approximately 1846 CDT ANO-1 entered Technical Specification (TS) Limiting Condition for Operation (LCO) 3.9.2 "Nuclear Instrumentation" due to having one required source range neutron flux monitor inoperable during core alterations. ANO-1 immediately secured core alterations and suspended operations that could cause introduction of positive reactivity to the Reactor Coolant System (RCS) as required by TS 3.9.2 actions A.1 and A.2. On May 8, 2024, at approximately 0440 CDT the source range neutron flux monitor was declared operable after power supply replacement and completion of source range calibration, at which time reactor core reload activities recommenced.
The cause of this event was a failed power supply to the source range neutron flux monitor.
There were no consequences to the safety of the general public, nuclear safety, industrial safety or radiological safety. No radiological releases occurred due to this event.
PLANT STATUS 050 052
- 2. DOCKET NUMBER
- 3. LER NUMBER I
00313 NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 001 1-0 Arkansas Nuclear One, Unit 1 (ANO-1) was in Mode 6 "Refueling" Operation during Refueling Outage 31 (1R31) when this condition was discovered.
EVENT DESCRIPTION
On May 6, 2024, at approximately 1604 Central Daylight Savings Time (CDT), ANO-1 started reactor core reload during 1 R31. On May 7, 2024, at approximately 1846 CDT ANO-1 entered Technical Specification (TS) Limiting Condition for Operation (LCO) 3.9.2 "Nuclear Instrumentation" due to having one required source range neutron flux monitor inoperable during core alterations. ANO-1 immediately secured core alterations and suspended operations that could cause introduction of positive reactivity to the Reactor Coolant System (RCS) as required by TS 3.9.2 actions A.1 and A.2. On May 8. 2024, at approximately 0440 CDT the source range neutron flux monitor was declared operable after power supply [JX] replacement and completion of source range calibration, at which time reactor core reload activities recommenced.
No radiological releases occurred due to this event.
This report is made in accordance with 10 CFR 50.73(a)(2)(i)(B), "any operation or condition which was prohibited by the plant's TS."
SAFETY ASSESSMENT
Core alterations were immediately secured when it was identified that the source range neutron flux monitor was inoperable. All operations that could cause introduction of positive reactivity to the RCS were immediately secured.
ANO-1 was in Mode 6 "Refueling" Operation with the fuel transfer canal boron concentration at 2427 parts per million boron (ppmB) versus the Cycle 32 Core Operating Limits Report (COLR) required minimum boron concentration of 2266 ppmB. Additionally, one source range neutron flux monitor was available to monitor for an increase in count rates during the time that the other monitor was unavailable. Given that core alterations were secured when it was identified that the source range neutron flux monitor was inoperable, one of the two required source range neutron flux monitors remained operable and the boron concentration was maintained such that an inadvertent reactor criticality could not occur, the safety significance of this event is determined to be minimal. This condition did not result in actual consequences to safety of the general public, nuclear safety, industrial safety or radiological safety.
EVENT CAUSE(S)
- 2. DOCKET NUMBER I
00313
- 3. LER NUMBER NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 001 1-G While returning fuel assemblies to the reactor for 1 R31 reload, it was identified that the source range neutron flux monitor was not responding as expected. Further inspection determined the source range neutron flux monitor had failed low.
The actual time of failure could not be determined; however, through post event trend analysis it was determined that fuel assemblies were moved while the source range neutron flux monitor was failed. This is a violation of TS 3.9.2 that requires two source range neutron flux monitors during fuel movement.
The direct cause of the source range neutron flux monitor failure was a failed power supply [JX]. The primary cause of the failure to identify the inoperable source range neutron flux monitor was the failure of the local indication light on the source range neutron flux monitor cabinet and the failure of the control room annunciator. In this event, neither of these instruments performed their functions correctly and did not provide a reliable status of the source range neutron flux monitor operability. At this time it is unknown why these instruments did not function properly and this has been entered into the corrective action program (CAP), further troubleshooting is ongoing to determine the cause.
A contributing cause of this event was the procedure to perform functionality checks for the source range neutron flux monitor was inadequate to ensure that core reload prerequisite checks would identify voltage issues with both source range neutron flux monitors.
CORRECTIVE ACTIONS
This event was entered into the station's CAP.
The initial corrective action to be implemented to address the direct cause was to replace the failed power supply [JX] and verify operability of the source range neutron flux monitor prior to resuming core reload.
A corrective action is planned to address the primary cause of the failure to identify the inoperable source range neutron flux monitor which includes revision of the appropriate procedure to ensure that core reload prerequisite checks will identify voltage issues with both source range neutron flux monitors. Corrective action(s) are planned to identify the cause and resolve the condition of the failure of the local indication light on the source range neutron flux monitor cabinet and the failure of the control room annunciator to alarm as designed. Additionally, a corrective action is planned to add a step to the appropriate procedure to require the control room staff to monitor Plant Data Server points during core reload to provide early indication of source range neutron flux monitor issues.
PREVIOUS SIMILAR EVENTS
ANO-1 LER 2005-002-00, "Movement of Irradiated Fuel Assemblies with one Channel of Source Range Instrumentation Inoperable due to a Power Supply Failure Resulted in Operation Prohibited by Technical Specifications", ADAMS Accession No. ML060380523, 1CAN010602, dated January 27, 2006, was identified. A casual factor of this event was identified as the design of the source range instrumentation not providing sufficient continuous functional monitoring capability for detection and annunciation of a channel failure during core alterations when indicated count rates are at the low end of the scale. Page 3
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