05000334/LER-2024-002, Automatic Reactor Trip Due to Low Reactor Coolant Flow Caused by Transformer Overexcitation Protection Relay Actuation
| ML24163A306 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 06/11/2024 |
| From: | Blair B Vistra Operations Company |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-24-114 LER 2024-002-00 | |
| Download: ML24163A306 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B)(1) 10 CFR 50.73(a)(2)(iv)(B)(6) 10 CFR 50.73(a)(2)(iv)(B)(8) |
| 3342024002R00 - NRC Website | |
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L-24-114 June 11, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
SUBJECT:
Beaver Valley Power Station, Unit Nos. 1 Docket No. 50-334, License No. DPR-66 LER 2024-002-00 Beaver Valley Power Station Barry N. Blair Site Vice President P.O. Box4 Shippingport, PA 15077 10 CFR 50.73 Enclosed is Licensee Event Report (LER) 2024-002-00, "Automatic Reactor Trip Due to Low Reactor Coolant Flow Caused by Transformer Overexcitation Protection Relay Actuation." This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A), 10 CFR 50.73(a)(2)(iv)(B)(1), 10 CFR 50.73(a)(2)(iv)(B)(6), and 10 CFR
- 50. 73(a)(2)(iv)(B)(8).
There are no regulatory commitments contained in this submittal. If there are any questions or if additional information is required, please contact Ms. Hope Gilliam, Manager, Regulatory Compliance, at 724-682-4224.
Beaver Valley Power Station Unit No. 1 L-24-114 Page 2 Enclosure: Beaver Valley Power Station, Unit No. 1 LER 2024-002-00 cc: NRC Region I Administrator NRC Senior Resident Inspector NRC Project Manager INPO Records Center (via INPO Industry Reporting and Information System)
BRP/DEP
Enclosure L-24-114 Beaver Valley Power Station, Unit No. 1 LER 2024-002-00
Abstract
At 0035 on April 13, 2024, with Beaver Valley Power Station, Unit No. 1 (BVPS-1) at 97 percent power in Mode 1, the reactor automatically tripped due to reactor coolant pump (RCP) low flow. The cause of the RCP low flow was the loss of power to the 4KV bus caused by the 1A System Station Service Transformer (SSST) overexcitation protection relay. Prior to the reactor trip, the 4KV bus 1A had completed its transfer to onsite power and was setup for auto bus transfer when the SSST 1A overexcitation protection relay actuated. The reactor trip led to a turbine trip and loss of power to the Unit Station Service Transformer (USST), which resulted in loss of the 1A bus and 1AE emergency bus. This caused an auto-start of the Train A 1-1 Emergency Diesel Generator (EDG). The cause is the procedure used to make the transfer did not preclude operation of the plant in such a way that the SSST 1A overexcitation relay actuated.
This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in an automatic reactor trip by the reactor protection system, 10 CFR 50.73(a)(2)(iv)(B)(1), the automatic actuation of the auxiliary feedwater system, 10 CFR 50.73(a)(2)(iv)(B)(6), and the automatic actuation of the EDG, 10 CFR 50.73(a)(2)(iv)(B)(8).
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- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
052 050This event was reported to the NRC per 10 CFR 50.72 (b)(2)(iv)(B) and 10 CFR 50.72 (b)(3)(iv)(A) at 0355 on April 13, 2024 (Event Notification 57075).
CAUSE OF THE EVENT
The cause is procedure 1OM-36.4.A did not preclude operation of the plant in such a way that the SSST 1A overexcitation protection relay actuated. The SSST voltage was raised to the maximum value allowed by approved plant procedure.
Upon separating the SSST from the bus to complete the transfer, the voltage increased further, resulting in the actuation of the SSST overexcitation protection relay and subsequent trip of the SSST. This caused the loss of the 4KV bus 1B, which resulted in de-energizing the 'B' RCP and subsequent reactor trip.
ANALYSIS OF EVENT
The event is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in an automatic reactor trip by the reactor protection system, 10 CFR 50.73(a)(2)(iv)(B)(1), the automatic actuation of the auxiliary feedwater system, 10 CFR 50.73(a)(2)(iv)(B)(6) and the automatic actuation of the EDG, 10 CFR 50.73(a)(2)(iv)(B)(8).
The plant risk associated with the BVPS-1 reactor trip on April 13, 2024, is considered to be very low. This is based on the change in average core damage frequency derived using the conditional core damage probability and change in average large early release frequency derived using conditional large early release probability for the event. Therefore, this event had very low safety significance.
CORRECTIVE ACTIONS
An evaluation was completed to identify appropriate changes to procedure 1OM-36.4.A to preclude the overexcitation protection from operating during transfers from the SSST to the USST. A limited use procedure change was used for the remainder of 1R29.
Procedure 1OM-36.4.A will be permanently revised to incorporate the recommendations identified in the completed evaluation.
PREVIOUS SIMILAR EVENTS
LER 2017-003-00, Beaver Valley Unit 1 Reactor Trip due to Turbine Trip and Automatic Initiation of the Auxiliary Feedwater System. The turbine trip was initiated by a main unit generator overcurrent protection trip. The cause of this event was foreign material located in the 'B' phase bus duct.
LER 2014-001-01, Beaver Valley Unit 1 Trip due to Main Unit Transformer Failure. The cause of this event was an internal winding fault in the 'B' phase windings.
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Beaver Valley Power Station, Unit 1 334 2024 002 00