05000443/LER-2023-004, Manual Reactor Trip Due to Main Turbine Electro-Hydraulic Control Oil Level
| ML23270B916 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 09/27/2023 |
| From: | Strand D NextEra Energy Seabrook |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-2023-137 LER 2023-04-00 | |
| Download: ML23270B916 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4432023004R00 - NRC Website | |
text
September 27, 2023 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Re: Seabrook Station Docket No. 50-443 Reportable Event: 2023-04-00 Date of Event: July 30, 2023 NEXTera ENERGY~
SEABROOK Docket No. 50-443 L-2023-137 10 CFR 50.73 Manual Reactor Trip Due to Main Turbine Electro-Hydraulic Control Oil Level The attached Licensee Event Repo1t 2023-04 is being submitted pursuant to the requirements of IO 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 July 30, 2023, during normal operation, the electrical trip solenoid for an Electro-hydraulic control (EHC) header dump valve separated from the digital EHC system trip manifold assembly due to the failure of four cap screws on the manifold. This caused an EHC reservoir low level alarm. Operators manually actuated the Reactor Protection System (RPS) in accordance with procedure. Systems responded as expected to the plant trip including the actuation of the Emergency Feedwater (EFW)
System, upon low steam generator level. Forensic analysis concluded that the cap screws failed because the equipment manufacturer did not use parts specified by General Electric (GE) for the EHC system trip manifold assemblies. Corrective actions included replacement of the Main Turbine EHC trip manifold assembly. Additionally, both EHC and Feedwater dump valve assembly model work orders will be revised to ensure correct cap screws are installed. This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an actuation of the Reactor Protection System and Emergency Feedwater System.
Description
- 2. DOCKET NUMBER
- 3. LER NUMBER I
443 On July 30, 2023 at 1526 EDT, with Unit 1 in Mode 1 at 100 percent power, the reactor was manually tripped due to low main turbine EHC [EIIS: TG] fluid reservoir level. This alarm was ultimately caused by the separation of the electrical trip solenoid (EIIS: SOL] from the EHC header dump valve [EIIS: PCV], which led to an 80-psig decrease in hydraulic fluid header pressure. Operators manually tripped the reactor in accordance with procedures based on low EHC reservoir level.
The reactor trip was uncomplicated, with systems responding as expected. The actuation of the EFW [EIIS: BA] system iwas expected due to steam generator low level. This licensee event report is being reported pursuant to 10 CFR 50.73(a)
(2)(iv)(A) for actuation of the Reactor Protection System and Emergency Feedwater System. In addition, there were no inoperable Structures, Systems, or Components that contributed to this event.
Cause of the Event
Cap screws on the manifold failed because the equipment manufacturer did not use the parts specified by GE for EHC system trip manifold assemblies. The trip solenoid and associated sub-components, including the cap screws, were procured by Fluid Power Products. Metallurgical analysis was performed on the failed cap screws and confirmed the cap screws were consistent with alternate design ASTM A574 material but had zinc coating which causes low toughness and absorption of hydrogen into the screws. These incorrect parts were used in the assembly of the trip manifolds. The trip manifolds are sold as pre-fabricated assemblies along with the cap screws. Based on this, the most probable modes of failure were determined to be inadequate material and/or over torquing of the cap screws. No safety systems were affected as a result of this failure.
Safety Significance
There were no safety consequences. This condition had no actual safety consequences impacting plant or public safety.
The EHC system interfaces with the Turbine System [EIIS: TAJ and if EHC fluid pressure decreases enough, then steam inlet valves [EIIS: FCV] to the high and low pressure turbine (EIIS: TRB] will be closed, initiating a turbine trip and reactor trip. This event did not result in a safety system function failure.
Corrective Actions
Completed/Planned
- 1. Replaced the failed Main Turbine EHC trip manifold assembly with a new assembly ordered directly from GE.
- 2. Revise model work order for each EHC and Feedwater dump valve assembly to ensure correct cap screws are installed.
- 3. Replace ASTM A574 zinc plated screws on trip manifold assemblies, including Feedwater and EHC, with cap screws that comply with GE specifications.
Similar Events
A review of internal and external operating experience did not identify any previous events or conditions that involved the same underlying cause as this event. Page 2
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