05000482/LER-2006-002
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 4822006002R00 - NRC Website | |
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 to 10CFR50, Appendix R and the Wolf Creek Updated Safety Analysis Report 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, C-35.
In the event of a fire detection signal in any of the vital Class 1 E switchboard rooms, auxiliary contacts located in fire area C-35 will open, which will open contacts associated with the Class lE electrical equipment air conditioning units and stop the air conditioning units. Cables associated with the auxiliary contacts are run in fire area C-35 which, if damaged, could cause a spurious shutdown of the Class 1E air conditioning units.
The Class 1 E electrical equipment air conditioning units are included in the post fire safe shutdown (PFSSD) design to ensure adequate room cooling for the operating train of safety-related electrical equipment. The air conditioning units provide a support function for Class 1 E electrical equipment required for safe shutdown. The loss of the Class lE air conditioning units does not directly result in loss of capability to achieve and maintain safe shutdown in the event of a fire. Rather, room heating beyond design limits could reduce the life of electrical components within the switchgear.
Qualification data exists to show that some components within the switchgear will survive the expected room temperatures and be functional following a loss of room cooling. Data does not exist for each and every component within the switchgear, so a conclusive argument cannot be made regarding equipment functionality following a loss of room cooling. At that point, an eight-hour non-emergency report to the NRC Operations Center was made in accordance with 10 CFR 50.72(b)(3)(ii)(B).
Basis for Reportability:
The Wolf Creek commitment to 10CFR50, Appendix R, Section III.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 III.G.2, or else a diverse means of providing the safe shutdown capability exists and is unaffected by the fire.
Based on the event described above and the fact that Wolf Creek Nuclear Operating Corporation (WCNOC) does not have a diverse means in place for providing the safe shutdown capability required, 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 (EFHA) 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 continuous fire watch was established for fire area C-35. The continuous fire watch was reduced to an hourly fire watch after a temporary procedure change was completed to allow the use of a jumper to restore a Class 1 E air conditioning unit to service.
A modification will be made to install a handswitch in the control room (Panel RP068) to provide the control room operators the ability to bypass the fire isolation signal on the Train "A" Class lE electrical equipment air conditioning units. This modification and resulting changes to off-normal procedure OFN KC-016 will be completed by January 31, 2009.
Safety Significance:
This issue is of low safety significance due to the extremely conservative assumptions made for this failure to occur.
Loss of the Class lE electrical equipment air conditioning units does not automatically cause inoperability of the associated Class 1 E electrical equipment. There is reasonable assurance that safe shutdown can be achieved without Class 1 E electrical equipment room cooling. In addition, the combined fixed and allowed transient fire loading is low. Therefore, a fire with sufficient severity to cause damage to cables in area C-35 is not credible.
Operating Experience/Previous Events:
pump's capability to successfully inject borated water into the reactor. This condition was caused by the original EFHA having non-validated assumptions and being insufficiently documented.
Emergency Diesel Generator. This condition was caused by the original EFHA completed for the Wolf Creek Generating Station not identifying that field flashing may not be available if a fire occurs in the control room.