Event Notification Report for June 09, 2002

NRC BULLETIN 91-01 CRITICALITY CONTROLS AT PADUCAH PLANT

"At 0045 CDT, on 6-10-02 The Plant Shift Superintendent (PSS) was notified that a violation of criticality controls had been discovered in the C-337 process building. C-337 Unit #2 Cell #2 was isolated from the cascade and in the process of being evacuated without an independent verification that a known R-114 coolant leak did not exist, in violation of NCSA CAS-002. The building Front Line Manager checked documentation to see if any other evolutions had taken place without completing this verification. C-337 Unit #1 Cell #2 was also discovered isolated and evacuated to a UF6 negative without an independent verification that a known R-114 coolant leak did not exist, in violation of NCSA CAS-002. The purpose of this check is to determine actions when transitioning to different moderation controls, i.e. removal of fluorinating environment to R-114 and RCW controls. The subject independent verification and coolant sampling were subsequently performed with successful results. These actions re-established double contingency within four hours of the time of discovery. Due to the loss of double contingency and the re-establishment of NCS controls, this event is being report as a 24-Hr. Event Report. The NRC Resident inspector has been notified of this event.

"SAFETY SIGNIFICANCE: Significant R-114 leaks to process gas systems should be readily apparent, however no checks for leaks were performed. Both controls were violated and double contingency was not maintained.

"POTENTIAL CRITICALITY PATHWAYS INVOLVED: In order for a criticality to occur, an R-114 leak to the process gas system would have to occur. In addition, the R-114 would have to contain an unacceptable amount of moisture and the moisture would have to be absorbed in a deposit of unsafe mass.

"CONTROLLED PARAMETERS: Double contingency is maintained by implementing two controls on moderation.

"NUCLEAR CRITICALITY SAFETY CONTROL(S) OR CONTROL SYSTEM(s) AND DESCRIPTION OF THE FAILURES OR DEFICIENCIES: The first leg of double contingency is based on ensuring wet R-114 coolant does not moderate existing uranium deposits. NCSA CAS.002 requires that prior to the initial evacuation of UF6, a check be made to determine if a known R-114 to process leak exists. This check was not performed and the control was violated. Until the check was performed successfully, the process condition was not maintained and double contingency was not maintained. The second leg of double contingency is based on independent verification that a known R-114 leak into the process gas system does not exist. This independent check was not performed violating the control. Until the check was independently performed successfully, the process condition was not maintained and double contingency was not maintained. Since double contingency is based on two controls on one parameter and both controls were violated, double contingency was not maintained."

The NRC Resident Inspector was notified of this event.