05000354/LER-2023-002, Shutdown Margin Less than Expected Resulting in a Condition Prohibited by Technical Specifications
| ML23293A002 | |
| Person / Time | |
|---|---|
| Site: | Hope Creek  |
| Issue date: | 10/20/2023 |
| From: | Agster T Public Service Enterprise Group |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NPF-057 LER 2023-002-00 | |
| Download: ML23293A002 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3542023002R00 - NRC Website | |
text
PSEG Nuclear LLC P,O, Box 236, Hancocks Brid9e, New Jersey 08038,0236 LR-N23-0067 October 20, 2023 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington DC 20555-001
Subject:
Hope Creek Generating Station Renewed Facility Operating License No. NPF-57 Docket No. 50-354 Licensee Event Report 2023-002-00 10 CFR 50.73 Shutdown Margin Less Than Expected Resulting in a Condition Prohibited by Technical Specifications In accordance with 10 CFR 50.73(a)(2)(i)(B), PSEG Nuclear LLC is submitting Licensee Event Report (LER) number 2023-002-00.
There are no regulatory commitments contained in this letter.
If you have any questions or require additional information, please contact Mr. Harry Balian at (856) 339-2173.
Sincerely, Thomas R. Agster Plant Manager Hope Creek Generating Station Attachment: Licensee Event Report 2023-002-00
October 20, 2023 10 CFR 50.73 Page 2 LR-N23-0067 cc: USNRC Regional Administrator - Region 1 USNRC NRR Project Manager - Hope Creek USNRC Senior Resident Inspector - Hope Creek NJ Department of Environmental Protection, Bureau of Nuclear Engineering President & Chief Nuclear Officer, PSEG Nuclear Site Vice President, Hope Creek Plant Manager, Hope Creek Vice President, PSEG Nuclear Engineering Executive Director Regulatory Affairs & Nuclear Oversight Director Site Regulatory Compliance Manager, Nuclear Oversight Corporate Commitment Coordinator, PSEG Nuclear Records Management (Record Type 3E.111)
Abstract
On May 4, 2023, during reactor start-up following a maintenance outage, nuclear instrumentation readings (Source Range Monitor (SRM)) were observed to be rapidly rising during withdrawal of a control rod blade (CRB). The Reactor Operator was directed to re-insert the CRB. Nuclear instrumentation readings stabilized and began to lower when the CRB was re-inserted.
The Operating Crew subsequently performed a reactor shutdown by fully inserting all CRBs.
The start-up was re-commenced on May 5, 2023 with an adjusted start-up sequence. The start-up was successfully completed with normal responses from nuclear instrumentation. Subsequent collection of data determined that there had been a loss of reactivity worth in two CRBs.
On August 21, 2023, Hope Creek Generating Station received the results of a Shutdown Margin (SDM) Analysis performed by Global Nuclear Fuel (GNF). The analysis determined that with the reduced reactivity worth of the two CRBs, the calculated SDM for the current fuel cycle was lower than expected, and less than required by Technical Specification 3.1.1, Shutdown Margin, during the early portion of the fuel cycle. This condition is reportable under 10 CFR 50.73(a)(2)(i)(B).
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I IDENTIFICATION OF OCCURRENCE Event Date: May 4, 2023 Discovery Date: August 21, 2023 CONDITIONS PRIOR TO OCCURRENCE At the time of the unexpected increase in SRM readings, May 4, 2023, Hope Creek was in Operational Condition (OPCON) 2, Start-up, 0 percent power, with the reactor subcritical. No other structures, systems or components that could have contributed to the event were inoperable at the time of the event.
When the analysis from Global Nuclear Fuel (GNF) was accepted, August 21, 2023, Hope Creek was in OPCON 1, Power Operation, at 100 percent rated thermal power.
DESCRIPTION OF OCCURRENCE During reactor start-up following a maintenance outage, nuclear instrumentation readings (Source Range Monitor (SRM)) were observed by the Reactor Operator to be rapidly rising during continuous withdrawal of a CRB. The Reactor Operator was directed to re-insert the CRB. Nuclear instrumentation readings stabilized and began to lower when the CRB was re-inserted.
The Operating Crew subsequently performed a reactor shutdown by fully inserting all CRBs.
An initial investigation did not reveal any errors in sequence development, Estimated Critical Positions (ECP), or CRB reactivity worth calculations. These items were independently checked by the fuel vendor. However, the start-up sequence was revised and a second start-up proceeded without any issue.
Evaluation of Local Power Range Monitor (LPRM) responses and Traversing Incore Probe (TIP) data later determined that there was a loss of reactivity worth in two CRBs. Initially four CRBs were inserted to ensure shutdown margin requirements were met. After a calculation performed by GNF, three of the CRBs were withdrawn, leaving one inserted.
GNF was engaged to perform a Shutdown Margin (SDM) analysis of the Cycle 25 reactor core. The analysis concluded that the minimum SDM at Beginning of Cycle (BOC) 25 was below the Technical Specification limit of 0.38% delta k/k. Cycle 25 began on October 28, 2022 with reactor start-up from refuel outage R24. This condition existed until core average exposure reached approximately 500 Megawatt-Days per Short Ton (MWD/ST) on November 21, 2022. At that time, the SDM was determined to have been greater than 0.38% delta k/k and therefore compliance with Technical Specifications was restored.
CAUSE OF EVENT
A Root Cause Evaluation (RCE) was conducted. The Direct Cause of the event was determined to be a reduction of boron-10 in two (2) CRBs, reducing the reactivity worth of these two CRBs. The Root Cause was determined to be that established procedural and administrative criteria for CRB management was ineffective at identifying mechanical end of life.
As part of the Extent of Condition review, PSEG identified indications of reduced reactivity worth for two CRBs discharged during the last refueling outage, R24. This was documented in the Corrective Action Program. Visual inspection of the two CRBs was completed and assessment is on-going as part of the Corrective Actions for this event.
SAFETY CONSEQUENCES AND IMPLICATIONS
Shutdown Margin (SDM) is defined in Hope Creek Technical Specifications (HCTS) as the amount of reactivity by which the reactor is subcritical or would be subcritical throughout the cycle assuming that:
a. The reactor is xenon free; b. The moderator temperature is greater than or equal to 68 degrees F, corresponding to the most reactive state; and c. All CRBs are fully inserted except for the single CRB of highest reactivity worth, which is assumed to be fully withdrawn.
With CRBs not capable of being fully inserted, the reactivity worth of these CRBs must be accounted for in the determination of SDM.
HCTS 3.1.1 requires that the SDM be equal to or greater than 0.38% delta k/k with the highest worth CRB analytically determined. The GNF analysis determined that the actual SDM due to the reduction in boron concentration in the two CRBs was less than required. The Technical Specification minimum SDM was restored when the core average exposure reached 500 Megawatt-Days per Standard Ton (MWD/ST) on November 21, 2022, approximately 24 days into the fuel cycle. At that time, the SDM was above 0.38% delta k/k.
Although the SDM was determined to be less than required by HCTS, it was calculated as positive (greater than zero) throughout the period of non-compliance. While there is inherent uncertainty in SDM calculations, a positive value for SDM indicates that the reactor would have been able to be shutdown under all operating conditions, including transients and postulated accidents, during the time of non-compliance. A Technical Evaluation was performed to assess the conditions that existed during the first part of fuel cycle 25 and determined that conditions were sufficient to ensure the reactor could have been shutdown.
On April 30, 2023, a reactor shutdown was conducted in order to perform maintenance activities. During that shutdown all CRBs fully inserted demonstrating the capability to insert all CRBs during the affected period of time.
Based on the analysis conducted by GNF and the Technical Evaluation performed by the station, there were no Safety Consequences as a result of the condition.
PREVIOUS EVENTS A review of Hope Creek LERs for the past three years was conducted. No previous LERs for Shutdown Margin were identified during that period.
CORRECTIVE ACTIONS
1.
The affected CRBs will be replaced during the next refueling outage.
2.
Visual inspection of the affected CRBs will be performed.
3.
Extent of condition testing was performed on similar CRBs.
4.
The associated procedures will be revised to include appropriate end of life criteria based on internal and external OE for CRBs currently installed at Hope Creek.
5.
A recurring task will be created to perform visual inspection of this model of CRB to confirm no indications of cracking and verify that appropriate criteria have been developed.
COMMITMENTS
There are no regulatory commitments contained in this LER.Page 3 of 3