05000445/LER-2020-001, Main Feedwater Pump Failure to Trip
| ML21041A178 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 02/10/2021 |
| From: | Sewell S Luminant, Vistra Operating Co. (VistraOpCo) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CP-202100080, TXX-21048 LER 2020-001-00 | |
| Download: ML21041A178 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4452020001R00 - NRC Website | |
text
m Luminant CP-202100080 TXX-21048 February 10, 2021 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Steven K. Sewell Senior Director, Engineering & Regulatory Affairs
Subject:
Comanche Peak Nuclear Power Plant (CPNPP)
Docket No. 50-445 Main Feedwater Pump Failure To Trip Licensee Event Report 445/1-2020-001-00
Dear Sir or Madam:
Comanche Peak Nuclear Power Plant (Vistra Operations Company LLC)
P.O. Box 1002 6322 North FM 56 Glen Rose, TX 76043 T 254.897.6113 Ref 10 CFR50.73 Pursuant to 10CFR50.73, Vistra Operations Company LLC (Vistra OpCo) hereby submits the enclosed Licensee Event Report 445/1-2020-001-00, "Main Feedwater Pump Failure To Trip" for Comanche Peak Nuclear Power Plant (CPNPP), Unit 1.
This communication contains no new licensing basis commihnents regarding CPNPP Units 1 and 2.
Should you have any questions, please contact Garry Struble at (254) 897-6628 or garry.stru ble@luminant.com.
TXX-21048 Page 2 of 2 Sincerely, Enclosure: -
Comanche Peak Nuclear Power Plant Main Feedwater Pump Failure To Trip Licensee Event Report 445/1-2020-001-00 c (email) -
Scott Morris, Region IV [Scott.Morris@nrc.gov]
Dennis Galvin, NRR [Dennis.Galvin@nrc.gov]
John Ellegood, Senior Resident Inspector, CPNPP Uohn.Ellegood@nrc.gov]
Neil Day, Resident Inspector, CPNPP [Neil.Day@nrc.gov]
Abstract
During a plant shutdown for a planned refueling outage on October 10, 2020; manual trip, from the main control room of Main Feedwater Pump (MFP) 1A failed. Local trip of MFP 1A also failed. Non-licensed operators took local actions to secure MFP 1A.
The inability to trip MFP 1A led Operations to declare one of two inputs for automatic start of both Motor-Driven Auxiliary Feedwater Pumps (MDAFWP) inoperable in accordance with Technical Specification 3.3.2, "Engineered Safety Feature Actuation System (ESFAS) Instrumentation, Function 6.g, Trip of all Main Feedwater Pumps." The Auxiliary Feedwater (AFW) system remained operable.
All times listed in this report are Central Daylight Time (CDT).
I. DESCRIPTION OF REPORTABLE EVENT At 0945 on October 10, 2020, during a Unit 1 planned shutdown for refueling outage, MFP 1A failed to trip manually from the main control room and failed to trip locally at the pump. MFP 1A failure to trip led Operations to declare one of two input signals to ESFAS Instrumentation inoperable for Function 6.g, "Trip of all Main Feedwater Pumps" of Technical Specification 3.3.2, which uses a two of two logic to automatically start both MDAFW pumps when all (both) MFPs trip.
A. REPORTABLE EVENT CLASSIFICATION
The event is reportable in accordance with 10 CFR 50.73(a)(2)(vii), "Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system designed to:
(A) Shut down the reactor and maintain it in a safe shutdown condition; (B) Remove residual heat; (C) Control the release of radioactive material; or (D) Mitigate the consequences of an accident."
B. PLANT CONDITION PRIOR TO EVENT At 0945 on October 10, 2020, Comanche Peak Nuclear Power Plant, Unit 1 was operating in MODE 1 at approximately 50% rated thermal power.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE INOPERABLE AT THE START OF THE EVENT AND CONTRIBUTED TO THE EVENT There were no structures, systems, or components which were inoperable prior to the event that contributed to the event. A planned unit shutdown was in progress for a refueling outage.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES At 0945 on October 10, 2020, Comanche Peak Nuclear Power Plant, Unit 1 entered Technical Specification 3.3.2, Engineered Safety Feature Actuation System (ESFAS) Instrumentation when an attempt to trip MFP 1A from the main control room push-button failed. When MFP 1A did not trip non-licensed operators were dispatched to locally trip MFP 1A and it would not trip. MFP 1A steam supply valves were closed and trip oil pressure manually lowered to place the pump in a tripped state. Once MFP 1A was in a tripped status Technical Specification 3.3.2 was exited at 1053.
The failure of trip oil pressure to lower prevented making up one input to the two out of two logic required for MDAFWP automatic start. The actual ESFAS Instrumentation circuit for Function 6.g did not fail, but the non-safety MFP trip oil circuit prevented the signal needed to provide one of two trip inputs for automatic start the MDAFWPs.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR PROCEDURAL PERSONNEL ERROR Initial indication of the event was provided to the Control Room Operators when MFP 1A failed to trip when the trip push-button was depressed.
II. COMPONENT OR SYSTEM FAILURES A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE The cause of the event was failure of MFP 1A trip oil pressure to lower when the trip push-button was depressed. Trip oil pressure also did not lower when a local trip of MFP 1A was attempted. Non-licensed operators closed the steam supply valves to MFP 1A and manually lowered trip oil pressure to allow generation of one of two inputs required to automatically start the MDAFWPs from a trip of all MFPs.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT MFP 1A trip push-button was depressed and the pump did not trip followed by failure of the pump to trip locally. Through use of trouble shooting, engineering analysis, and test documentation review, plant staff identified that no actual Technical Specification component failed. However, the failure of MFP 1A to trip when required by manual action remotely and locally was considered as a failure of a non-safety system to provide a trip signal to the ESF.AS Instrumentation system.
There is no direct evidence of failure of components in the the oil system.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS This event did not involve systems or secondary functions which were affected by the possible failure of MFP 1A to trip.
D. FAILED COMPONENT INFORMATION
No specific component was determined to be failed.
Ill. ANALYSIS OF THE EVENT A. SAFETY SYSTEM RESPONSES THAT OCCURRED The ESFAS Instrumentation system performed as designed once MFP 1A was tripped through local actions that depressurized the pump trip oil. This event occurred during a normal plant shutdown and the MDAFW pumps were manually started in response to the planned reactor trip.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY The event herein did not involve the inoperability of any safety system component or system. This event involved a non-safety system, MFP 1A trip oil system failure to provide input into the ESFAS Instrumentation system.
MFP 1A trip oil system input to the ESFAS Instrumentation system was unavailable for approximately 18 minutes.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT A loss of normal feedwater is an ANS Condition II event (Faults of Moderate Frequency). The automatic start of both MDAFW pumps on a trip of all Main Feedwater Pumps is an anticipatory function that is accomplished manually if the automatic action fails. The reactor trip on low-low level in any steam generator provides the necessary protection against a loss of normal feedwater. No automatic safety functions were exercised and all plant safety systems responded as designed. This event had no impact on nuclear safety, reactor safety, radiological safety, environmental safety or the safety of the public.
Non-safety MFP trip oil system low pressure is associated with Function 6.g, "Trip of all Main Feedwater Pumps" in that low trip oil pressure on both MFPs provides an anticipatory automatic start of both MDAFWPs prior to receiving the automatic start of the MDAFWPs on low-low level in any steam generator. This event is reported under 50.73(a)(2)(vii) due to a one out of two input into ESFAS Instrumentation being unavailable. This event has been evaluated to not meet the definition of a safety system functional failure per 10 CFR 50.73(a)(2)(v).
IV. CAUSE OF THE EVENT
A definitive cause for the inability to trip MFP 1A was not identified. Inspection of MFP 1A trip oil system did not identify a component failure.
V. CORRECTIVE ACTIONS
A design modification to the MFP seal water system is in the Corrective Action Program (CAP) to minimize water intrusion into the oil system. During the fall 2020 Unit 1 outage, following the event lockout solenoid valve SV-13 was replaced. The major tear-down and inspection of MFP 1A did not identify any additional component issues. Internal and external operating experience identified the "sticking" of feedwater pump control solenoids and relays.
A new preventative maintenance action to cycle lockout solenoid valve SV-13 is in CAP to cycle the valve quarterly until water intrusion into the oil is corrected.
VI. PREVIOUS SIMILAR EVENTS
There have been no similar reportable events at Comanche Peak Nuclear Power Plant in the past three years. Page 4
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