05000443/LER-2023-005, Auxiliary Feedwater System Inoperable
| ML23354A067 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 12/20/2023 |
| From: | Strand D NextEra Energy Seabrook |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-2023-171 LER 2023-05-00 | |
| Download: ML23354A067 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 4432023005R00 - NRC Website | |
text
December 20, 2023
L-2023-171 10 CFR 50.73 Attention: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Seabrook Station Docket No. 50-443 Reportable Event: 2023-05-00 Date of Event: November 7, 2023
Subject: Auxiliary Feedwater System Inoperable
The attached Licensee Event Report 2023-05-00 is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event. If you have any questions, please contact Mr. Kenneth Mack, Fleet Licensing Manager, at 561-904-3635.
Respectfully,
Dianne Strand 1) \\.---- -s '~..
General Manager Regulatory Affairs N extEra Energy
Attachment
cc: Seabrook Station NRC Senior Resident Inspector Seabrook Station NRC Project Manager
Abstract
On November 07, 2023, during normal operation, Seabrook Station declared the Auxiliary Feedwater System inoperable because control power to the 'B' train Emergency Feedwater (EFW) flow control valve, which supplies the 'D' Steam Generator (SG), was lost. The 'B' transformer providing control power to the EFW circuit was identified as the failure mechanism. Failure of any of the eight EFW flow control valves to meet its Surveillance Requirements will render all EFW pumps inoperable per Technical Specifications.
This event is reportable in accordance with 10 CFR 50.73(a)(2)(v)(B) as any 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 remove residual heat.
Description
On November 07, 2023 at 1200 EST, with Unit 1 in MODE 1 at 100 percent power, it was discovered that the red open lights for the 'B' train Emergency Feedwater (EFW) flow control valve [BA, FCV] 1-FW-FV-4244B were not illuminated on the Main Control Board (MCB) or on the Remote Shutdown System (RSS) panel. Loss of control power to the flow control valve represents a failure to meet Technical Specification (TS) Surveillance Requirement (SR) 4.7.1.2.1.c, which required declaring the Emergency Feedwater Pumps [BA, P] inoperable. Consequently, this event was reportable pursuant to 10 CFR 50.73(a)(2)(v)(B) as a condition that could have prevented the fulfillment of a safety function needed to remove residual heat.
Cause of the Event
The loss of control power to the flow control valve was a result of a failed transformer in the motor control center. Without control power, the automatic high-flow isolation design function was challenged. In the supply line to the D Steam Generator (SG), two flow control valves are arranged in series, each powered from separate 120V sources. Train B control power was lost but train A control power remained available. Train 'A' control power preserved the EFW system's capability to supply all of the SGs or to isolate a supply line. Upon transformer and fuse replacement, the EFW system was declared operable.
Analysis of the Event
The EFW system is comprised of two 100% capacity pumps (one motor-driven and one turbine-driven). Both pumps discharge to a common header which feeds four branch lines to the SGs. Each branch line includes a manual gate isolation valve, two motor-operated flow control valves, a flow venturi and a flow orifice. The flow control valves are normally open while in operation and closed in the event of a pipe break. Each branch line has two flow control valves in series and they are powered from separate trains. Each of these valves are also provided with a handwheel to allow for manual operation. The EFW system has sufficient redundancy to maintain its safety-related functions under all credible accident conditions.
Technical Specification Surveillance Requirement (SR) 4.7.1.2.1.c. to verify that each automatic valve in the flow path actuates to its correct position upon receipt of an EFS actuation test signal, was not met. The TS rendered the EFW system inoperable but redundancy allowed for the system to retain its safety functions.
Safety Significance
This event was of very low safety significance because the flow control valves are arranged in series, with separate control power sources, assuring that the system's safety functions would have been met. There were no adverse effects to the health and safety of the public, nuclear safety, industrial safety, or radiological safety. The station remained in steady-state power operation.
Corrective Actions
The failed transformer was replaced.
Failed Component:
Gould ITE Machine Tool Transformer, 0.100 kVA 480/120V
Safety System Functional Failure Consideration:
This event required reporting under the criterion of 10 CFR 50.73(a)(2)(v)(B) because of the failure to meet the TS SR.
However system redundancy preserved the EFW system safety functions. Consequently, this event will not be included in the Station's Performance Indicator (PI) reporting in accordance with NEI 99-02.
Similar Events
Seabrook Station has experienced no similar events in the past three years.