ENS 47195
ENS Event | |
|---|---|
20:30 Aug 23, 2011 | |
| Title | Crefs Was Declared Inoperable |
| Event Description | This telephone report is being made in accordance with 10 CFR 50.72(b)(3)(v) as a loss of safety function for a single train safety system. On August 23, 2011 at 1530 CDT, the clevis pin that connects the valve with the air operator was found not fully inserted on the Control Room HVAC Emergency Bypass System Inlet Valve, HV-AO-271 AV. This valve is normally closed and opens in response to a Group 6 isolation signal to align the Control Room Emergency Filtration System) (CREFS) to outside air. A retaining clip at one end of the pin was found to be missing, allowing the pin to partially back out of the clevis. The pin was found engaged with half of the clevis. This condition resulted in declaring CREFS inoperable at 15:30 CDT, and CNS entered LCO 3.7.4 Condition A which requires the CREF system to be restored to OPERABLE status in 7 days. The cause of the displaced clevis pin is under investigation.
The licensee has notified the NRC Resident Inspector.
This notification is being made to retract Event Notification EN# 47195 which reported a loss of safety function for a single train safety system due to the unplanned inoperability of the Control Room Emergency Filtration System (CREFS). CREFS was declared inoperable on August 23, 2011 per LCO 3.7.4 due to finding a clevis pin not fully inserted on the valve operator for the Control Room HVAC Emergency Bypass System Inlet Valve IIV-AOV-271AV. This normally closed valve opens on a Primary Containment Group 6 Isolation signal to align CREFS to outside air. The retaining clip at one end of the pin was found missing which allowed the pin to partially back out of the clevis. Cooper Nuclear Station (CNS) recently completed its trouble shooting of the as-found condition of the pin and a subsequent evaluation of its ability to withstand seismic loading. CNS determined that CREFS would have been able to fulfill its safety function. The clevis pin was shown via testing to remain engaged when the valve was stroked. The seismic evaluation showed that the maximum seismic force is less than one-tenth of the estimated force required to remove the pin, and consequently it is not credible that the pin would have become disengaged in a seismic event. CREFS did not lose the ability to perform its safety function. The NRC Resident Inspector has been notified. Notified the R4DO (Walker). |
| Where | |
|---|---|
Cooper  Nebraska (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+2.67 h0.111 days <br />0.0159 weeks <br />0.00366 months <br />) | |
| Opened: | Steve Wheeler 23:10 Aug 23, 2011 |
| NRC Officer: | John Knoke |
| Last Updated: | Sep 20, 2011 |
| 47195 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |