05000482/LER-2005-005
| Wolf Creek Generating Station | |
| Event date: | 09-29-2005 |
|---|---|
| Report date: | 11-28-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 4822005005R00 - NRC Website | |
Background:
The centrifugal charging pumps (CCPs) [EDS Code: P] are used to inject borated water into the reactor to maintain reactor water inventory, maintain shutdown reactivity margin, and maintain a flow of cooling water to the reactor coolant pump (RCP) seals to prevent damage to the seals. The Volume Control Tank (VCT) provides suction to the CCPs through valves BGLCV112B and C. A fire could cause the VCT outlet valves to fail to close, allowing the VCT hydrogen cover gas to enter the suction of the CCPs. This has the potential to damage the CCPs and cause the loss of high head safety injection.
Plant Conditions Prior to the Event:
MODE —1 Power — 100 percent Normal Operating Temperature and Pressure
Event Description:
The compliance strategy for post fire safe shutdown (PFSSD) at the Wolf Creek Generating Station is being reviewed to validate and rebaseline the analysis. The validation project has reconstituted a complete set of data for components/equipment and cables credited for coping with a "post-fire safe shutdown scenario" in accordance with our commitments to10CFR50, Appendix R and the Wolf Creek Updated Safety Analysis Report (USAR) Appendix 9.5B Fire Hazard Analyses in selected areas. The event identified by this LER was found during the re-validation of the fire area, A-8.
The Wolf Creek commitment to 10CFR50, Appendix R, Section 111.G states the following:
Redundant trains of systems required to achieve and maintain hot standby are separated by 3-hour rated fire barriers, or the equivalent provided by 111.G.2, or else a diverse means of providing the safe shutdown capability exists and is unaffected by the fire.
Diverse means has been interpreted by Wolf Creek to mean manual operator actions which are deemed feasible.
One operator outside the control room who is not on the fire brigade was assumed to be available to perform diverse means actions. It was also assumed that one of the four available operators in the control room could exit the control room temporarily to perform some actions.
Due to the unpredictable nature of fire and the unknown point of origin, several Train A components in fire area A-8 including the Train A motor driven auxiliary feedwater pump, are affected.
Because of the number of time-critical actions that could be required to mitigate a design-basis fire in area A-8, the available operations staff may be challenged if all spurious actuations occur at nearly the same time. Specifically, the VCT outlet valves (BGLCV112B and C) may fail to close. This could allow the hydrogen cover gas from the VCT to enter the CCPs, damage the pumps, and cause the loss of high head safety injection.
Basis for Reportability:
A fire in Fire Area A-8 has the potential to damage the centrifugal charging pumps and cause a loss of the capability to borate the reactor. Based on this information, WCNOC made an eight hour Emergency Notification System call in accordance with 10 CFR 50.72(b)(3)(ii)(B).
This condition is also reportable pursuant to 10 CFR 50.73(a)(2)(ii)(B) for any event or condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety.
Root Cause:
This is a historical problem rooted in changes to the standards over time, and in non-validated assumptions made by the Architect-Engineer for their Electrical Fire Hazards Analysis at the time of construction and insufficiently documented at that time. Due to the historical nature of these facts, a specific root cause cannot be determined.
Corrective Actions:
A detailed evaluation of fire area A-8 will be completed to identify any additional components that fail to meet WCGS commitments to Appendix R. Corrective measures will be determined as needed. Any necessary design change package(s) will be developed and implemented.
The current validation effort is currently being re-assessed to determine if any additional fire areas should be reviewed.
Safety Significance:
This issue is of low safety significance due to the extreme conservative assumptions made for all of these failures to occur. There is a low loading of self-sustaining combustibles located in fire area A-8. A fire of the severity required to damage components and cables located over 80 feet apart is only postulated. The assumption that all of the spurious maloperations occur at time zero is also postulated since affected components and cables are located at various distances from one another. The reactor trip function will work correctly and the primary system can be isolated. The reported condition is outside Wolf Creek's licensing basis for protection of components required for safe shutdown following a fire since all mitigating actions may not be complete before damage occurs to the charging pumps.
Operating Experience/Previous Events:
control tank. In the event of a fire, a potential existed for gas intrusion into the suction of the centrifugal charging pump. While corrective actions have been taken to address these conditions, an additional corrective action for LER 1999-009-00 was to validate the post fire safe shutdown analysis and to provide necessary correction to the Updated Safety Analysis Report (USAR). The validation consists of two phases: phase one reverified the design criteria and phase two completes the post-fire safe shutdown analysis review.
LERs 2002-004-00, 01, and 02 identified cable separation issues during the phase two portion of the validation process.