05000282/LER-2003-002
| Event date: | |
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| Report date: | |
| 2822003002R00 - NRC Website | |
EVENT DESCRIPTION
In August 2002, a Nuclear Management Company (NMC) evaluation of potential flow diversion (an ongoing assessment of the extent of a similar condition reported in LER 1-98-15) was in progress. At this point in the evaluation, NMC identified (as a conservative measure prior to completing the detailed evaluation) interim actions to preclude the potential for adversely affecting safe shutdown. Before the interim actions were implemented the potential existed for adverse effects on safe shutdown.
On March 26, 2003, with both units operating at 100% power, the completed evaluation determined that, absent compensatory measures, the ability to safely shutdown could have been adversely affected in two cases. In the first case, a fire postulated in certain Fire Areas (FA 13/18 — Control Room/Relay Room complex or FA 58/73 — 695' elevation of the Auxiliary Building) could result in a spurious start of a containment sprays (CS) pump2 and spurious opening of its associated discharge motor-operated valve3 (MOV), which would divert the sole credited source of reactor coolant system4 (RCS) makeup - the refueling water storage tanks (RWST) - into containment.
In the second case, the scavenging and combustion air dampers6 (CD-34136 and CD-34139) for the diesel-driven emergency cooling water? pumps (which are required to open when the associated pump operates) were found to be vulnerable to postulated fires in certain Fire Areas (FA 18 — Relay Room; FA 29 — Administrative Building, Electrical and Piping Room #1; FA 30 — Administrative Building, Electrical and Piping Room #2; FA 31 — Train A Hot Shutdown Panel and Air Compressor Room; FA 32 - Train B Hot Shutdown Panel and Air Compressor Room; FA 37 — Unit 1 480V Normal Switchgear Room; FA 38 — Unit 2 480V Normal Switchgear Room; FA 41B — Screenhouse BaSement; and FA 58 — 695' elevation of the Auxiliary Building.) Upon completing the evaluation, the interim actions implemented in August 2002 were assessed and found to be effective compensatory measures until corrective actions are completed.
1 EIIS System Code: BE 2 EIIS Component Identifier: P 3 EIIS Component Identifier: V 4 EIIS System Code: AB 5 EIIS Component Identifier: TK 6 ENS Component Identifier: DMP 7 EIIS System Code: BI Impact on Safety System Functional Failure Performance Indicator These conditions could not have (by themselves) prevented a safety function, because a postulated fire (in the fire areas of concern) would be required in addition to the as-found condition. Thus, this condition is not reportable per 10CFR 50.73 (a)(2)(v), and, therefore, does not impact the Safety System Functional Failure Performance Indicator.
Risk Significance A risk assessment (using the plant-specific probabilistic risk assessment (PRA) model) was completed to ascertain the risk significance of the as-found condition. The assessment assumed:
1. Fires do not start concurrently in more than one fire area at a time.
2. Operator actions to locally fail air to CD-34136 and CD-34139 following fires in areas where cables to these dampers are located were not modeled.
3. Automatic fire suppression in FA 31 and FA 32 was not credited.
4. Automatic CO2 fire suppression and fire brigade actions to suppress fires were not credited in FA 18.
5. 12 and 22 cooling water pumps are unavailable if their respective scavenging and combustion air damper (CD-34136 and CD-34139, respectively) does not open.
6. The possibility of a hot short causing spurious starting of a CS pump or spurious opening of the associated discharge valve is conservatively assumed to be 0.07.
7. Operator actions to stop flow diversion from the CS pumps into containment were not credited.
The results of the assessment indicate the resulting conditional core damage frequency (CCDF) for both units is 6.0E-07 per year. The conditional large early release frequency (CLERF) for the same events is 8.7E-08 per year for both units. The assumed time duration is one year, so the CCDF and CLERF are the same as the conditional core damage probability (CCDP) and conditional large early release probability (CLERP). Since CCDP is less than 1E-06 and CLERP is less than 1E-07, the events can be both be classified as non-risk significant.
CORRECTIVE ACTION
Immediate:
1. Prior to completing the evaluation of these conditions with respect to whether they potentially affected the ability to safely shutdown, interim actions were implemented as a conservative measure. These actions consisted of revising the plant procedures for responding to a catastrophic fire. The revisions included steps for the operators to verify that the Containment Spray pumps for the affected unit were de-energized at the breaker and steps for the operators to isolate air to CD-34136 and CD-34139 to fail the dampers open.
Subsequent:
2. Upon determining that these conditions did indeed have a potential to affect the ability to safely shutdown, the interim actions were evaluated as suitable compensatory measures.
These measures will remain in effect until planned corrective actions are completed.
Planned:
3. With the compensatory measures in place, the affected components are considered to be operable, but degraded. Actions to restore full operability of the affected components will be selected and completed.
FAILED COMPONENT IDENTIFICATION
None.
PREVIOUS SIMILAR EVENTS
A similar issue related to flow diversion was identified in LER 1-98-15. The current conditions were identified as a result of completing corrective actions associated with LER 1-98-15.