ENS 48565
ENS Event | |
|---|---|
22:09 Oct 8, 2012 | |
| Title | 60-Day Optional Telephonic Notification of Invalid System Actuation |
| Event Description | On October 8, 2012, at 1709 EDT, Unit 2 received a Reactor Auto SCRAM System 'B' Trip signal in the main control room. The power monitoring breaker in RPS panel 2C71P003D tripped, causing a half-SCRAM in conjunction with the automatic actuation of the Unit 2 standby gas treatment system (SGT) and isolation of CIVs [Containment Isolation Valves] in multiple systems, both of which are normal responses to this loss of the 'B' RPS bus. The crew entered the appropriate abnormal operating procedures and confirmed the actuations automatically occurred as required given the loss of the RPS bus. They investigated the 'B' RPS Motor/Generator (M/G) set, placed the 'B' RPS bus on its alternate supply, reset the SGT and CIV actuation logic, and returned the CIVs to their normal position.
Upon investigation, the 'B' RPS M/G set was found running with a steady output of 120 VAC. The breaker in RPS panel 2C71P003B stayed closed in. Further troubleshooting did not identify a cause for the failure of RPS breaker 2C71B003D. The breaker was replaced and the power monitoring relays were rebuilt. The 'B' MG Set was left running unloaded for 8 days with no trips observed. On October 26, 2012, approximately 20 seconds after returning the RPS 'B' M/G Set to service, RPS breaker 2C71B003D tripped again. At this time, investigators determined that 2C71B003B had no output voltage present when load was increased to 25 amps or greater. 2C71B003D tripped because 2C71B003B was not supplying load to it. A lug mounting screw was subsequently found to be loose on 2C71B003B. After tightening the screw, maintenance personnel determined that continuity existed and the 2C71B003B indicated closed with output voltage present as expected. Review of the six-month surveillances on 2C71B003B and the more-detailed 5-year surveillance that took place in August 2010 revealed no previous problems with the breaker. It is unknown when the lug mounting screw became loose or if repeated cycles of operation caused it to loosen. For broadness, thermography testing is being completed on 2C71P003 A, C, D, E, F and 1C71P003 A, B, C, D, E, F. When the second trip of 2C71B003D occurred on October 26, 2012, U1 SGT trains started and CIVs in multiple systems closed. This was an expected actuation with radiation monitor 2D11K634C already out of service and in the tripped condition at the time of the RPS 'B' trip. The RPS 'B' trip caused radiation monitor 2D11K634D to also trip thereby completing the logic to start U1 SGT trains and to close associated CIVs. The second event is included in this report since the failures are related as a result of having the same general cause and since they occurred over a reasonably short period of time. Because a malfunctioning subcomponent caused the loss of RPS 'B' rather than a valid CIV actuation signal, the resulting isolation of CIVs in multiple systems is considered an invalid actuation in both cases. Based on that information 10CFR50.73(a)(2)(iv) allows these events to be reported via a telephone notification within 60 days instead of submitting a written LER. The licensee will notify the NRC Resident Inspector. |
| Where | |
|---|---|
Hatch  Georgia (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation | |
| Time - Person (Reporting Time:+1409.42 h58.726 days <br />8.389 weeks <br />1.931 months <br />) | |
| Opened: | Kenny Hunter 16:34 Dec 6, 2012 |
| NRC Officer: | Donald Norwood |
| Last Updated: | Dec 6, 2012 |
| 48565 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (98 %) |
| After | Power Operation (98 %) |
WEEKMONTHYEARENS 568972023-11-02T01:11:0002 November 2023 01:11:00
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