05000443/LER-2023-002, Automatic Actuation of Emergency Service Water During Testing Due to a Defective Relay
| ML23181A085 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 06/30/2023 |
| From: | Strand D NextEra Energy Seabrook |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-2023-085 LER 2023-002-00 | |
| Download: ML23181A085 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv), System Actuation |
| 4432023002R00 - NRC Website | |
text
..
June 30, 2023 U.S. Nuclear Regulato1y Commission Attn: Document Control Desk Washington, DC 20555 Re: Seabrook Station Docket No. 50-443 Reportable Event: 2023-002-00 Date of Event: May 2, 2023 NEXTera ENERGY. ---
SEABROOK Docket No. 50-443 L-2023-085 10 CFR 50.73 Automatic Actuation of Emergency Se1vice Water due to a Defective Relay The attached Licensee Event Report 2023-002 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 General Manager, Regulatory Affairs Attachment cc: Seabrook Station NRC Senior Resident Inspector Seabrook Station NRC Project Manager NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874
Abstract
On May 2, 2023, during planned Engineered Safety Features Actuation System Testing, a Tower Actuation (TA) signal occurred. The TA occurred due to the failure of the first level undervoltage load shedding scheme to shed loads from the 4KV bus prior to the Service Water (SW) Ocean Pumps coasting down following the opening of the 4KV supply breaker. With no power to the bus, and the SW Ocean Pumps breakers still closed, a low SW pump discharge pressure condition occurred, resulting in the TA logic being satisfied. Troubleshooting determined that a defective relay contact in the first level undervoltage load shedding scheme caused the failure. The relay was replaced, and the system was returned to service. There was minimal impact to the station due the unplanned actuation, therefore this event had no impact on the health and safety of the public. In addition, there were no other Structures, Systems, or Components (SSCs) that contributed to this event. This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A) for actuation of the emergency service water system that does not normally run that serves as the ultimate heat sink.
Description
I
- 2. DOCKET NUMBER
- 3. LER NUMBER 00443 I,..,
SEQUENTIAL REV NUMBER NO.
- 12023 I -I 002 1-0 On May 2, 2023, the plant was in Mode 5 at O percent power with coolant temperature less than 200 degress fahrenheit and depressurized, during planned Engineered Safety Features Actuation System (ESFAS) [EIIS: JE] testing, a Tower Actuation (TA) signal occurred. A TA signal is initiated to transfer Service Water (SW) (EIIS: Bl) from the ocean when one of two ocean pumps [EIIS: P] is running (in a train) with pump discharge pressure below the low pressure TA setpoint. The TA signal is time delayed by 3 seconds to prevent spurious operation.
During the planned ESFAS testing, the combination of a loss of offsite power to the 4 KV bus [EIIS: BU], and Safety Injection (SI) is simulated by simultaneous removal of the safeguards bus protection relay fuses [EIIS: FU], with the actuation of a SI signal. Removal of the bus protection fuses de-energizes both the first and second level undervoltage relay schemes, which also inputs to the Emergency Power Sequencer (EPS). The EPS opens the offsite power source breaker [EIIS: BKR] to the 4 KV bus. The undervoltage schemes shed the loads from the bus.
Troubleshooting determined that the load shedding did not occur at the expected time delay (1.2 seconds) associated with the first level undervoltage protection. Instead load shedding occurred at 6 seconds after the test initiation. Six seconds is the time delay associated with load shedding on a second level undervoltage relay actuation coincident with a SI signal present. The Ocean SW pumps remained connected to the 4KV bus for 6 seconds following initiation of the test. With the offsite power supply removed, the pumps coasted down resulting in discharge pressure continuing to decrease to the tower actuation setpoint prior to 6 seconds.
The Tower actuation occurred due to the failure of the first level undervoltage load shedding scheme to shed loads from the 4KV bus prior to the SW Ocean Pumps coasting down following the opening of the 4KV Bus supply breaker. With no power to the bus, and the SW Ocean Pump breakers still closed, combined with the subsequent low SW pump discharge pressure, the Tower Actuation logic was satisfied. Troubleshooting determined that a defective relay contact in the first level undervoltage load shedding scheme caused the failure. The relay was replaced, and the system was returned to service.
Cause of the Event
Complex troubleshooting was performed in accordance with station processes. As part of the troubleshooting, the cause of this event was determined to be a failure of a relay contact in the load shedding circuit. The relay was made by Westinghouse and is a time delay starting relay.
Analysis of the Event
This licensee event report is being reported pursuant of 10 CFR 50.73(a)(2)(iv) for actuation of emergency service water system that does not normally run and that serves as ultimate heat sinks. This event did not result in a Safety System Functional Failure.
Safety Significance
There were no safety consequences due to this event. This event had no impact on the health and safety of the public. In addition, there were no other Structures Systems or Components (SSCs) that contributed to this event.
Corrective Actions
I
- 2. DOCKET NUMBER
- 3. LER NUMBER 00443 YEAR SEQUENTIAL REV I 2023 I NUMBER NO.
- - I 002 I -G The defective relay was replaced and the testing was performed satisfactorily the next day.
Similar Events
A review of reportable events dating back 10 years, did not identify any previous events or conditions that involved the same underlying cause as this event. Page 3
of 3