05000321/LER-2025-002, Reactor Protection System Instrumentation for Turbine Control Valve Fast Closure Inoperable
| ML25353A533 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 12/19/2025 |
| From: | Busch M Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-25-0476 LER 2025-002-00 | |
| Download: ML25353A533 (0) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2) |
| 3212025002R00 - NRC Website | |
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Southern Nuclear Matt Busch Vice President Plant Hatch llalch Nuclear Plant 11028 !latch Parkway North Baxley, GA 31513 912 453 5859 tel 912 366 2077 fax NL-25-0476 December 19, 2025 Docket Nos.: 50-321 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant Licensee Event Report 2025-002-00 Unit 1 Reactor Protection System Instrumentation for Turbine Control Valve Fast Closure Inoperable Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(i)(B), 10 CFR 50.73(a)(2)(v)(A), and 10 CFR 50.73(a)(2)(vii), Southern Nuclear Operating Company hereby submits the enclosed Licensee Event Report.
This letter contains no NRC commitments. If you have any questions, please contact the Hatch Licensing Manager, Jimmy Collins, at 912.453.2342.
Respectfully submitted, Matt Busch Vice President - Hatch MSB/CJC Enclosure: LER 2025-002-00 Cc:
Regional Administrator, Region II NRR Project Manager - Hatch Senior Resident Inspector - Hatch RTYPE: CHA02.004
Edwin I. Hatch Nuclear Plant Licensee Event Report 2025-002-00 Unit 1 Reactor Protection System Instrumentation for Turbine Control Valve Fast Closure Inoperable Enclosure LER 2025-002-00
Abstract
With Unit 1 at 100-percent power on 10/22/2025 at 0918 EDT, after performance of a past operability evaluation, it was determined that three Reactor Protection System (RPS) pressure switches for the Turbine Control Valve (TCV) Fast Closure trip on low Electrohydraulic Control (EHC) oil pressure were likely inoperable longer than allowed by Technical Specifications (TS).
These three TCV RPS pressure switches failed TS Surveillances (SRs) on 4/5/2025 and 4/6/2025. Additionally, one of the same TCV RPS pressure switches failed a TS SR on 12/17 /25. The failures of the TCV RPS pressure switches are attributed to elevated ambient temperatures which degraded EHC oil locally at the pressure switches, impeding proper depressurization of the EHC sensing lines during TCV actuation. Corrective actions included purging the EHC sensing lines, replacing the fast acting solenoid for one of the TCVs, installing temporary fluid conditioning units, increasing the TCV SR frequency, which helps prevent fluid stagnation and flushes contaminants, reducing varnish buildup and sticking.
The event is reportable per 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by technical specifications, 10 CFR 50.73(a)(2)(v)(A) for a condition that could have prevented fulfillment of a safety function, and 10 CFR 50.73(a)(2)(vii) for a common cause inoperability of independent channels.
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EVENT DESCRIPTION
050 052 I
- 2. DOCKET NUMBER
- 3. LER NUMBER 00321 I
YEAR SEQUENTIAL REV NUMBER NO.
1 002 1-0 With Unit 1 at 1 OD-percent power on 10/22/2025 at 0918 EDT, after performance of a past operability evaluation, it was determined that three Reactor Protection System (RPS) (EIIS Code: JC) pressure switches (EIIS Code: PS) for the Turbine Control Valve (TCV) (EIIS Code: FCV) Fast Closure trip on low Electrohydraulic Control (EHC) (EIIS Code: TG) oil pressure were likely inoperable longer than allowed by Technical Specifications (TS). These three TCV RPS pressure switches failed TS SRs on 4/5/2025 and 4/6/2025. Additionally, one of the same RPS pressure switches failed a TS SR on 12/17/25.
EVENT CAUSE ANALYSIS
The failures of the TCV RPS pressure switches are attributed to elevated ambient temperatures which degraded EHC oil locally at the pressure switches. The degraded EHC oil prevented the TCV Fast Acting Solenoid (FAS) (EIIS Code: SOL) from fully shuttling which inhibited depressurization of the RPS pressure switch sensing line when the TCVs actuated.
Because the sensing line did not depressurize when the TCVs were actuated, the pressure switches were unable to generate the RPS reactor trip signal on low EHC oil pressure as required.
SAFETY ASSESSMENT AND REPORTABILITY
The RPS pressure switches associated with the TCV Fast Closure trip are credited in the Updated Final Safety Analysis Report (UFSAR) Chapter 15 for initiating a reactor trip during both the Turbine Trip and Generator Load Reject events.
For the Turbine Trip event, the UFSAR credits both the TCV RPS pressure switches and the Turbine Stop Valve (TSV)
(EIIS Code: ISV} RPS instrumentation for initiating a reactor trip. During the period when the TCV RPS pressure switches were inoperable, the TSV instrumentation remained operable; therefore, a Turbine Trip event would have resulted in a reactor trip.
For the Generator Load Reject event, the UFSAR credits only the TCV RPS pressure switches for initiating a reactor trip.
However, the UFSAR evaluates the condition when the reactor is not tripped by the TCV RPS instrumentation during a Generator Load Reject event. In such cases, a High Flux scram is credited to mitigate the event, concluding that no fuel damage would occur and that the event remains within acceptance criteria. Accordingly, there were no safety consequences as a result of the inoperability of the TCV RPS pressure switches.
Considering the failure history of the TCV RPS pressure switches, the simultaneous inoperability of multiple TCV RPS pressure switches, and since there is no other equipment in the same system as the TCV RPS pressure switches that would trip the reactor during a Generator Load Reject, this event is reportable per 10 CFR 50.73(a)(2)(i}(B) as a condition prohibited by TS and per 10 CFR 50.73(a)(2)(v)(A) as a condition that could have prevented fulfillment of a safety function.
Additionally, the event is also reportable per 10 CFR 50. 73(a}(2)(vii) due to degraded EHC oil creating a common cause condition that resulted in the inoperability of multiple, independent RPS channels.
CORRECTIVE ACTIONS
Corrective actions included purging the EHC sensing lines, replacing the fast acting solenoid for one of the TCVs, installing temporary fluid conditioning units, increasing the TCV SR frequency, which helps prevent fluid stagnation and flushes contaminants, reducing varnish buildup and sticking. Additional, planned corrective actions include replacing TCV insulation, replacing the remaining fast acting and test solenoids, and implementing a permanent EHC filtration upgrade.
PREVIOUS SIMILAR EVENTS
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