|SAFETY EQUIPMENT FAILURE OF THE CRITICALITY ALARM SYSTEM |
"SNM-124 Section 12.6.4 requires that criticality alarm system detector pairs must generate an alarm signal when both detectors in a pair exceed their trip point, or when one detector is in a fault condition while the other exceeds the alarm trip point.
"During testing, 2 of 18 detector pairs did not generate an alarm signal in all modes as discussed above.
"In the event of a criticality, 2 detector pairs may not have generated an alarm signal.
"During 27 December 2007 through 29 December 2007, a programmable logic controller (PLC) monitoring system was attached to the critical alarm system components. On 29 December 2007, all detector pairs were satisfactorily tested that they would generate an alarm signal when required.
"During 31 December 2007 until 5 January 2008, limited SNM operations were conducted at the plant. Suspect equipment faults occurred during the time frame from 29 December 2007 to 5 January 2008 due to unknown cause.
"Troubleshooting revealed an equipment fault in each detector pair that failed during testing. These faults have been corrected and the detector pairs satisfactorily retested."
The two (2) affected detector pairs are located in the NDA North & South and Building 311 North & South. There were no recorded trouble alarms generated by the operable detector in the affected areas during the week when the system was not functioning properly. Also, there is no indication of tampering in that the fault was identified as loose wiring/connections inside locked cabinets accessible to authorized personnel only.
The licensee informed the NRC Resident Inspector.