21 octobre 2013
Le 21 octobre, il y a eu interruption de l’arrêt automatique d’urgence du réacteur. Cet arrêt d’urgence s’est seulement effectué à moitié car plusieurs problèmes sont survenus. L’équipe de maintenance a remis en service les nombreuses parties de circuits défaillantes et a réenclenché le demi arrêt d’urgence restant à effectuer. Des investigations supplémentaires ont montré des problèmes de mauvaises soudures au niveau d’un relais qui avait été remplacé, ainsi que des défauts au niveau du relais lui-même.
Type : BWR Mark 1 - Puissance : 2 804 MWTh - Première divergence : 07 1978
Available in english only.
Event Number : 49641
Facility : HATCH - State : GA - Unit : [2] - GE-4,[2] Event Date : 10/21/2013 - Event Time : 04:19
Emergency Class : NON EMERGENCY 10 CFR Section : 50.73(a)(1) - INVALID SPECIF SYSTEM ACTUATION
Initial PWR : 100 %
Event Text
60 OPTIONAL REPORT - INVALID PARTIAL REACTOR PROTECTION SYSTEM ACTUATION
"Invalid partial Reactor Protection System (RPS) actuation results in ; Closure of Containment Isolation Valves (CIVs) in multiple systems, including isolation of the Reactor Water Clean-Up (RWCU) System.
"On October 21, 2013, at 0419 EST, Unit 2 received a Reactor Auto SCRAM System ’B’ trip signal in the main control room. Initial investigations at the local RPS Motor-Generator (MG) set room discovered breaker 52-3D tripped in cabinet 2C71-P003D. This resulted in a half-scram and the closure of CIVs in multiple systems, including closure of the RWCU system outboard isolation valve, 2G31-F004. These trips are normal responses to the loss of the ’B’ RPS. The operating crew entered abnormal operating procedures, including those for loss of RPS and for loss of the RWCU system, and confirmed that all isolations and trips occurred as expected. Additionally, the crew restored the ’B’ RPS bus from its alternate source, reset the half scram, returned the CIVs to their normal positions, and placed RWCU in service.
"Upon investigation, the determination was made that the trip and reset setpoints for under-voltage relay 2C71 -K752D had drifted. Consequently, once the drift reached the trip setpoints during the event, breaker 52-3D tripped, resulting in the loss of the ’B’ RPS bus. Because a malfunctioning subcomponent caused the partial RPS trip rather than a valid CIV actuation signal, the resulting isolation is considered an invalid actuation.
"Further evaluation into the cause of the drift revealed solder joint cracks in the relay circuit board and an inadequate previous refurbishment of the subject relay. The drifting relay was removed and a refurbished relay was installed in location 2C71-K752D. Plans are to replace both units’ RPS Power Monitoring relays with a different design. Until that design change is implemented, the frequency of calibration for these relays is being increased from every 182 days to every 91 days."
The licensee has notified the NRC Resident Inspector.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2013/20131218en.html
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