05000382/LER-2006-001
| Waterford Steam Electric Station | |
| Event date: | 06-12-2006 |
|---|---|
| Report date: | 08-11-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor |
| 3822006001R00 - NRC Website | |
Waterford Steam Electric Station, Unit 3 05000 382 2006 -- 001 --�� �� 00 2� OF� 5
REPORTABLE OCCURRENCE
The condition, as described below, was reported to the NRC Operations Center on June 12, 2006 within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> of discovery, as a condition that could have prevented fulfillment of the safety function of structures or systems that are needed to shutdown the reactor and maintain it in a safe shutdown condition [10CFR50.72(b)(3)(vi)]. The condition, as reported, involved a preliminary analysis indicating non-feasible manual actions (due to potential for smoke in the fire area during a fire). The preliminary analysis also indicated the potential for damage to equipment in the room resulting from a potential hot gas layer, that could impact operability of safe shutdown equipment. Based on subsequent reviews, it has been determined that there were steps in an emergency operating procedure that would have been performed by the Control Room operators that would have been a concurrent success path to the non-feasible manual action that was required to be performed within 10 minutes. However, the condition remains reportable based on the preliminary analysis indications that there could be damage to redundant safe shutdown trains from a hot gas layer in the room. Further analysis is planned using more accurate fire modeling techniques to provide definitive information regarding potential damage to redundant safe shutdown trains. Therefore the condition is being reported herein under the 60 day reporting requirements of 10CFR50.73(a)(2)(v)(A).
INITIAL CONDITIONS
At the time of discovery, Waterford 3 was operating in Mode 1 at 100% Reactor Power. There were no plant systems, structures, or components out of service specific to the reported condition.
Waterford Steam Electric Station, Unit 3 05000 382 2006 -- 001 --��� � 00 3� OF� 5
EVENT DESCRIPTION
On June 12, 2006, while reviewing a preliminary analysis of feasibility of manual actions designated to be performed in a fire area (RAB 7), it was discovered that the actions were not feasible due to postulated environmental conditions (smoke) that could be present in the fire area during a fire in any adjacent zone of that fire area. The preliminary analysis indicated that the manual actions could not be performed within the time prescribed in the Post Fire Safe Shutdown Analysis. Furthermore, the preliminary analysis indicated that there could be damage to equipment in the room needed to achieve safe shutdown, due to a hot gas layer that could be present in the room. The subject fire area is subdivided into fire zones by part height fire walls. The fire zones share a common ceiling.
The room is a relay room, with the most fire sensitive equipment in the area being the relays [RLY].
Waterford 3 has an approved Appendix R deviation for the part height fire wall configuration.
Assuming a fire in Fire Area RAB 7, Operator entry into that same fire area is required to perform manual actions. Results of preliminary analysis using CFAST modeling techniques indicate that the conditions in Fire Zone RAB 7B rapidly exceed the habitability threshold. Conditions there do not moderate before ten minutes. Therefore, a manual action required to be performed in Fire Zone RAB 7B within 10 minutes became non-feasible. Further reviews, including circuit analysis, identified that steps in an existing approved Operator emergency operating procedure, performed concurrently from the Control Room, would have achieved the same desired result as the non feasible manual action. Therefore the non-feasible manual action was not required. However, as stated above, the preliminary analysis also indicated that there could be damage to equipment due to a hot gas layer that would be present throughout the room.
CAUSAL FACTORS
The condition was caused by an inadequate firewall design in the form of part height walls between fire zones in the affected fire area (RAB 7). The design allows smoke and hot gases that are products of a fire in one zone of the fire area to travel to the other zones of the fire area due to the common ceiling arrangement. This could result in damage to equipment in multiple zones of the fire area. The firewall design is included in Waterford 3's licensing basis in the form of a NRC approved Appendix R deviation. However, based on the preliminary analysis results, the wall design, in this specific application, appears to be inadequate to protect equipment. Additional analysis using a more robust fire modeling technique is being pursued to further evaluate the condition.
NRC FORM 366A (1.2001) U.S. NUCLEAR REGULATORY COMMISSION
2. DOCKET
CORRECTIVE ACTIONS
As an immediate action taken, a temporary compensatory action was initiated, establishing a fire watch in Fire Area RAB 7 in accordance with Section 3.7.11 of the Technical Requirements Manual (TRM). The fire watch is designated to detect a fire in the incipient stage. Special written instructions and equipment have been given to the fire watch to extinguish a fire in that area while it is in the incipient stage.
A project is currently in progress at Waterford 3 to convert to NFPA-805. The condition described herein will be evaluated in that NFPA conversion.
Corrective actions are being addressed under the plant corrective action program.
SAFETY SIGNIFICANCE
The computer based model results detailing the potential exposure of redundant safe shut down trains to a common fire (hot gas layer) are being validated via the use of a more robust fire model that accounts for fire attributes not normally considered using the CFAST model. The results of this model and additional engineering reviews may result in the retraction of this LER. The area of concern is a relay room with a combustible loading (area averaging method) of approximately 10 minutes. The area is a room not normally accessed by through traffic. In addition any hot work performed in the area, per station procedures, would require a fire watch. Thus the potential of a fire due to an outside ignition source and/or transient combustibles is very low. The area is provided with fire detection and automatic sprinkler systems which would further mitigate and potentially reduce the impact of a fire in the area. The more robust fire model currently being initiated will provide more details with respect to the true safety significance of this condition. To ensure operability, a fire watch has been established in Fire Area RAB 7, in accordance with Section 3.7.11 of the Technical Requirements Manual (TRM) as a compensatory measure. The fire watch is designated to detect a fire in the incipient stage. Special written instructions and equipment have been given to the fire watch to extinguish a fire in that area while it is in the incipient stage. This condition did not compromise the health and safety of the general public.
SIMILAR EVENTS
No similar events have been identified or reported at Waterford 3.
Waterford Steam Electric Station, Unit 3 05000 382 2006 -- 001 --��� � 00 5� OF� 5
ADDITIONAL INFORMATION
Energy Industry Identification System (EIIS) codes are identified in the text within brackets [ ].