Event Notification Report for November 15, 2002

24-HOUR NRC BULLETIN 91-01 CRITICALITY CONTROL ISSUE AT PADUCAH

"At 0315 on 11-15-02, the Plant Shift Superintendent (PSS) was notified that the pressure chart recorder for the C-333 'C' surge drum bank had failed, violating an SRI in NCSE.016. As a result of this failure, the shiftly pressure checks performed prior to this discovery were performed using a failed AQ-NCS pressure instrument and therefore were not valid. The purpose of this pressure check is to identify if wet air inleakage has begun on the surge drum bank. Following identification and remediation of failure, pressure checks were performed and it was determined that no wet air inleakage had occurred and double contingency was restored.

"The NRC Resident Inspector has been notified of this event.

"SAFETY SIGNIFICANCE: Although pressure readings were taken using a failed AQ-NCS pressure instrument, there are several important mitigating factors. First the integrity of the drum bank has been maintained. Second, the drum contained non-fissile material. Third, the UF6 has maintained in the gas phase. Because the drum contained non-fissile material, the NCS controls were not necessary to prevent a criticality from occurring.

"POTENTIAL CRITICALITY PATHWAYS: These drums are used to store gases. Therefore, in order for a criticality to be possible, the drum would have to contain fissile UF6. Wet air would have to react with any UF6 in the drum. Wet air inleakage would have to occur over a long period of time in order to create a large mass of UO2F2 and then sufficiently moderate the material.

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

"ESTIMATED AMOUNT, ENRICHMENT, FORM OF LICENSED MATERIAL: Drum bank contains gaseous UF6 enriched to [ ].

"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 maintaining the integrity of the surge drum against wet air inleakage. This integrity is insured by an SRI for the unlikely breach of the surge drum system. Structural integrity of the drum is intact, therefore this SRI was maintained.

"The second leg of double contingency is based performance of shiftly checks using an AQ-NCS instrument as an indication of wet air inleakage. The required checks were performed using a failed instrument. Since a failed instrument was used, the shiftly checks were invalid resulting in a loss of this control. Since there are two controls on one parameter, double contingency was not maintained.

"Even though moderation control was maintained, double contingency is based on two controls on moderation. Therefore double contingency was not maintained. The drum contained a non-fissile material. It should be noted that a second parameter, assay (not controlled in the NCSA), was maintained since the drum bank contained non-fissile material.

"CORRECTIVE ACTIONS TO RESTORE SAFETY SYSTEMS IMPLEMENTATION: Approximately one hour after discovery, AQ-NCS Instrumentation was connected to surge drum manifold and pressure was verified to less than NCS limit. Readings are being obtained from this instrumentation pending calibration of recorder.

"DESCRIPTION OF OCCURRENCE: The pressure chart recorder for the C-333 'C' surge drum bank failed, violating an SRI in NCSE.016. As a result of this failure the shiftly pressure checks were performed using a failed AQ-NCS pressure instrument and therefore were not valid. The purpose of the pressure check is to identify if wet air inleakage has begun on the surge drum bank.

"It is important to note that an AQ-NCS pressure instrument was subsequently connected to the system and pressure readings have been taken. The pressure readings indicate there has been no wet air inleakage. Double contingency has been restored since the ability to read pressure in the surge drum bank using a properly operating AQ-NCS pressure instrument has been restored

"NUCLEAR CRITICALITY SAFETY CONTROLS INVOLVED AND THEIR IMPACT ON DOUBLE CONTINGENCY: Double contingency is maintained by implementing two controls on moderation.

"The first leg of double contingency is based on maintaining the integrity of the surge drum system against wet air inleakage. This integrity is assured by an SRI for the unlikely breach of the surge drum system. Structural integrity of the drum is intact, therefore this SRI is maintained.

"The second leg of double contingency is based on the performance of shiftly pressure checks using an AQ-NCS instrument as an indication of wet air inleakage. The required checks were performed using a failed instrument. Since a failed instrument was used, the shiftly checks were invalid resulting in a loss of this control. Since there are two controls on one parameter, double contingency was not maintained.

"Even though moderation control was maintained; double contingency is based on two controls on moderation. Therefore double contingency was not maintained. The drum contained non-fissile material. It should be noted that a second parameter (not controlled in the NCSA) was maintained since the drum contained non-fissile material.

"Potential Critical Pathways: These drums are used to store gases. Therefore, in order for a criticality to be possible, the drum would have to contain fissile UF6. Wet air would have to react with any UF6 in the drum. The leak would have to occur over a long period of time in order to create a large mass of UO2F2 and then sufficiently moderate the material.

"Safety Significance: Although pressure readings were taken using a failed AQ-NCS pressure instrument, there are several important mitigating factors. First the integrity of the drum bank has been maintained. Second, the drum contained non-fissile material. Third, the uranium has been maintained in the gas phase. Because the drum contained non-fissile material, the NCS controls were not necessary to prevent a criticality from occurring."

UNIT 3 EXPERIENCED AN AUTOMATIC REACTOR TRIP DUE TO A GENERATOR LOCKOUT

"At 0957 EST, 345 Kv Breaker 3 failed open resulting in breakers 1, 5 and 6 opening. This electrically isolated Unit 3 resulting in the Main Generator primary and backup lockout relays (86P and 86 Bu) tripping. This resulted in an immediate reactor trip. All equipment operated as expected with the following exceptions:

1. 32 Source Range failed to come on scale as required

2. 34 Circulating Water Pump transferred to standby drive when normal drive tripped

3. 36 Circulating Water Pump tripped

"The plant is stable in mode 3. Post trip review is in progress and will be completed prior to restart. The Public Service Commission has been notified."

There was no maintenance or other activities in progress in the switchyard at the time the 345 Kv Breaker 3 catastrophically failed. Unit 3 is currently removing decay heat via the steam dump bypass to the main condenser. Both motor driven auxiliary feedwater pumps autostarted and are in-service. The steam generator atmospheric dumps may have lifted during the transient. There is no known primary-secondary tube leakage. The licensee notified the NRC resident inspector and plans on issuing a press release.

MANUAL REACTOR TRIP DUE TO HIGH FEEDWATER HEATER LEVEL

"While reducing power for a planned refueling outage, at 2020, U1 reactor was manually tripped at 12% power due to Hi Hi Level in 13 'A' Feedwater heater. An existing problem with an extraction bellows in 13 'A' Feedwater heater had been previously identified and contingency plans were in place for monitoring the level during the load decrease. Levels were being monitored locally by Engineering and Operations during the load decrease in anticipation of level control problems. Control Room Operators made the decision as planned, to manually trip the reactor per annunciator response procedures, when it was determined that level in 13 'A' Feedwater heater could not be reduced. During performance of reactor trip recovery procedures, 11 Turbine Driven Auxiliary Feedwater Pump auto started when the running Main Feedwater Pump was secured. 11 Turbine Driven Aux Feedwater Pump was secured and Steam Generator levels are being maintained with 12 Motor Driven Aux Feedwater Pump."

Additionally, the Licensee stated that all control rods properly inserted into the core and that all safety systems responded as required.

The Licensee notified the NRC Resident Inspector.