05000446/LER-2025-003, Failure of Turbine Electrohydraulic Control System Results in Manual Trip of Unit 2 and Actuation of the Auxiliary Feedwater System
| ML25317A742 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 11/13/2025 |
| From: | Christopher Jackson Vistra Operations Company |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| CP-202500332, TXX-25058 LER 2025-003-00 | |
| Download: ML25317A742 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4462025003R00 - NRC Website | |
text
CP-202500332 TXX-25058 November 13, 2025 co U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 C
Pl K UCLI
Subject:
Comanche Peak Nuclear Power Plant (CPNPP)
Docket No. 50-446 POWE AT Comanche Peak Nuclear Power Plant Christopher J_ Jackson Nuclear Site Vice President Vislra Operations Company LLC P.O. Box 1002 6322 North FM 56 Glen Rose, TX 76043 Office: 254.897.6411 Ref 10 CFR 50.73 Failure of Turbine Electrohydraulic Control Results in Manual Trip of Unit 2 and Actuation of the Auxiliary Feedwater System Licensee Event Report 2-25-003-00
Dear Sir or Madam:
Attached is a Licensee Event Report (LER) 2-25-003-00, "Failure of Turbine Electrohydraulic Control Results in Manual Trip of Unit 2 and Actuation of the Auxiliary Feedwater System" for Comanche Peak Nuclear Power Plant (CPNPP) Unit 2.
This communication contains no new commitments regarding CPNPP Units 1 or 2.
Should you have any questions, please contact Marianne Burnett at (254) 897 - 5424 or marian ne. burnett@vistracorp.com.
Attachment:
Abstract
Comanche Peak Nuclear Power Plant, Unit 2 00446 5
Failure of Turbine Electrohydraulic Control System Results in Manual Trip of Unit 2 and Actuation of the Auxiliary Feedwater System 09 14 2025 2025 003 00 11 13 2025 1
100 Marianne Burnett 254 - 897 - 5424 B
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On September 14, 2025, Unit 2 experienced a loss of Electrohydraulic Control Channel 2 (EHC2) on the main turbine control system causing main steam control valves to fully open. The on-shift operating crew observed increasing steam flow as well as a step change in turbine load. Manual attempts to lower turbine load with the control system were unsuccessful. Operators manually tripped the reactor placing the unit in MODE 3, resulting in an automatic actuation of the Auxiliary Feedwater System (AFW). All safety systems responded as expected. The event was initially reported via EN 57929.
EHC1 previously failed in April 2025 creating a single-point vulnerability. A preliminary investigation has identified the cause of the event to be a result of a "system fault reset", which prevented a "run-to-failure" of EHC2. Immediate corrective actions were completed at the time of the forced outage when EHC1 and EHC2 components were replaced. This event is reportable per 10 CFR 50.73(a)(2)(iv)(A).
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Summary of the event, including dates and approximate times.
On September 14, 2025 at 20:13:27, the on-shift operating crew observed an increase in the steam flow. Subsequently, turbine power alarms [JA] were received, noting turbine power greater than 103 percent. By 20:14:38, the Operator initiated a runback to reduce turbine load to the load setpoint. No change in reactor power was observed. Runback was repeated three more times (20:14:59, 20:18:43, and 20:19:04) before the reactor was manually tripped at 20:19:21 entering MODE 3 to maintain reactor power at values less than design limits. The Auxiliary Feedwater (AFW) Pumps [BA, P] started as expected due to the steam generator Low-Low levels post-trip. The duration of the forced outage was approximately 66 hours7.638889e-4 days <br />0.0183 hours <br />1.09127e-4 weeks <br />2.5113e-5 months <br />. MODE 1 was reentered on September 17, 2025 at 14:08.
Ongoing load transients have been observed noting issues with the EHC system. Two concurrent alarms were received on September 14, 2025 at 20:15 related to a malfunction of EHC Channel 2 (EHC2). A failure of EHC2 resulted in the main turbine control valves (MCV) opening and the turbine power increasing.
During the forced outage, the following components were replaced in the EHC system for both channels: capacitor modules [JJ, CAP], amplifiers [JJ, AMP], proportional valves [JJ, V], and hydraulic converters [JJ, CNV].
E. The method of discovery of each component or system failure, or procedural personnel error.
The failure was self-revealing as the operating crew received alarms noting the increase in turbine power.
II. COMPONENT OR SYSTEM FAILURES.
A. Cause of each component or system failure.
A Preliminary Apparent Cause Analysis identified that a "system fault reset", completed at the time EHC1 was isolated and brought out of service in April 2025, blocked a "run-to-failure" status for EHC2. When EHC2 failed, it turned off, resulting in turbine MCV to fully open. This same analysis identified that incorrect vendor guidance, limited expertise by CPNPP personnel, risk-averse decision making, and acceptance of long-standing equipment issues played critical roles in the failure of EHC2 leading to the manual trip of Unit 2.
Forensic evaluation by the vendor is in progress.
B. Failure mode, mechanism, and effects of each failed component.
EHC1 was out of service creating a single point vulnerability at the time of the event. Failure of EHC2 resulted in an increase in turbine power that could not be manually controlled by the operator. As a result, Unit 2 was manually tripped.
C. Systems or secondary functions that were affected by failure of component with multiple functions.
EHC system failure did not affect other systems or secondary functions.
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- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
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V. CORRECTIVE ACTIONS
Immediate corrective actions during the forced outage focused on replacing EHC components including capacitor modules, amplifiers, proportional valves, and hydraulic converters.
VI. SIMILAR EVENTS
No licensee reportable events related to the failure of the EHC system have been documented in the last three years.
While multiple issues with the EHC system have been documented using the Corrective Action Program (CAP) at CPNPP over the last three years, none have resulted in a complete failure of the system. These previous issues led to the preliminary investigations determination of the contributing causes and long term corrective actions.
CPNPP is tracking all adverse trends using the CAP.
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