ML20161A170
| ML20161A170 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-019-00 | |
| Download: ML20161A170 (1) | |
Text
LER 271/82-019 Event
Description:
Trip with HPCI Inoperable Date of Event:
August 19, 1982 Plant:
Vermont Yankee Summary On August 19, 1982 with the plant operating at 100% power, the high-pressure coolant injection (HPCI) governor valve opened once for timing but did not open on system initiation during a monthly HPCI valve and pump operability test. Alternative testing was started. Investigation revealed that the failure of the governor valve to open on system initiation was due to a faulty ramp generator. The ramp generator was replaced and calibrated, and HPCI was returned to service.
A plant trip occurred four days prior to the discovery of the faulty HPCI governor. Assuming that the governor fault was present during the trip, this event was modeled as a transient with HPCI failed. The branch probability for HPCI was set to failed, and the non-recovery probability for HPCI was set to 1.0 to reflect the fact that operators most likely would not have been able to repair the HPCI within the allowable recovery time.
The estimated conditional core damage probability for this event is 6.1x10-6. The dominant sequence involves the observed transient, failure of the power conversion system, two relief valves sticking open, the failure of HPCI, and failure of the automatic depressurization system.