05000483/LER-2002-010
| Callaway Plant Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 4832002000R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
This event has been classified as reportable under 10CFR50.73(a)(2)(ii)(B), an unanalyzed condition that could significantly degrade plant safety.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
Callaway Plant was in Mode 1 at 100 percent power.
C. STATUS OF STRUCTURES, SYSTEMS OR COMPONENTS THAT WERE INOPERABLE AT THE START
OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT
"A" Train Ultimate Heat Sink sump heater, SEFO2A, was discovered grounded during daily shift inspections, which resulted in an extent of condition review that identified the reportable fire protection separation issue.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES
On 6/25/02, with Callaway Plant in Mode 1 at 100 percent power, a Non-Licensed Operator (NLO) was testing the "A" Train Ultimate Heat Sink (UHS) sump heater, SEFO2A. When the NLO energized SEFO2A, the motor control center (MCC) feeder breaker, NG0705, tripped. Investigation revealed that SEFO2A was grounded and that its feeder breaker over current protection was not properly coordinated with the upstream MCC feeder breaker ground fault protection. The next closest breaker with ground fault protection was NG0705.
An extent of condition review was completed that revealed the potential for Safety Related components and electrical load centers to experience a common cause failure due to the miscoordination if a fire were to occur in the 1974' Auxiliary Building Fire Area A-1. Safety related MCC's NGO I A and NGO2A (opposite trains) could experience a fire induced ground fault condition due to cable damage on downstream loads. This ground fault condition could cause the loss of either or both NGO1A and NGO2A which supply post fire safe shutdown equipment like "A" and "B" Residual Heat Removal (RHR) pump room coolers. It was concluded this scenario could impact post fire safe shutdown equipment.
In addition, it was identified that cables in Fire Area A-1 for the "A" and "B" Residual Heat Removal (RHR) pump room coolers, which are post fire safe shutdown equipment, have less than 20 feet of horizontal separation and do not meet the separation commitments documented in FSAR Table 9.5E-1.
The following compensatory actions have been taken:
- An hourly firewatch was established for the affected area on 7/2/02 as the evaluations were completed.
- Circuit Breakers associated with Essential Service Water Sump Heaters have been isolated, pending completion of a design change to address electrical coordination consistent with the FSAR.
- An Operations Night Order detailing actions to be taken to restore NGOI A and/or NGO2A if a fire were to occur that affected these load centers. Actions include measures to isolate faulted circuits.
- Revisions to Fire Area Pre-plans have incorporated the guidance of the Operations Night Order.
E. METHOD OF DISCOVERY OF EACH COMPONENT, SYSTEM FAILURE, OR PROCEDURAL ERROR
The fire protection separation violation of FSAR Table 9.5E-1 commitments was discovered during an extent of condition review related to the ground fault failure of UHS sump heater SEFO2A.
H. E EVENT DRIVEN INFORMATION
A. SAFETY SYSTEMS THAT RESPONDED
Not Applicable for this event.
B. DURATION OF SAFETY SYSTEM INOPERABILITY
Not Applicable for this event C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.
A risk evaluation was performed of the potential impact for a fire in area A-1. Assuming that both MCC's NGO1A and NGO2A would fail, the probability of mitigation failure results in a less than 1E-6/year increase in the core damage frequency for Fire Area A-1. This results in a classification of very low risk significance.
III. CAUSE OF THE EVENT
The fire protection separation issue is the result of changes to industry interpretations of cable fault assumption requirements, associated with the fire protection program, since initial construction design.
IV. CORRECTIVE ACTIONS
The following compensatory actions have been taken:
- An hourly firewatch was established for the affected area on 7/2/02 as the evaluations were completed.
- Circuit Breakers associated with Essential Service Water Sump Heaters have been isolated, pending completion of a design change to address electrical coordination consistent with the FSAR.
- An Operations Night Order detailing actions to be taken to restore NGOI A and/or NGO2A if a fire were to occur that affected these load centers. Actions include measures to isolate faulted circuits.
Revisions to Fire Area Pre-plans have incorporated the guidance of the Operations Night Order.
Addition of fire wrap material and/or cable re-routing is being evaluated to address the cable separation issue concerning the cables for the "A" and "B" RI-IR pump room coolers.
V. P PREVIOUS SIMILAR EVENTS A review of Callaway Action Request System (CARS) documents from the last three years revealed two CARs that dealt with a cable separation issue. These were CARs:
200002070 — concern with separation of redundant equipment trains in fire areas.
200203631 — addresses separation issue involving cables associated with potential for Refueling Water Storage Tank (RWST) drain down to containment A review of LERs over the last three-year period identified one LER. It was LER 2002-006-00 and documented the potential for drain down of the RWST to containment as identified in CAR 200203631.
VI. � ADDITIONAL INFORMATION are from the IEEE Standard 805-1984 and IEEE Standard 803A-1984 The system and component codes listed below respectively.