05000338/LER-2009-001
| Document Numbersequential . Revmonth Day ' Year Year Month Day Year | |
| Event date: | 10-13-2009 |
|---|---|
| Report date: | 12-14-2009 |
| 3382009001R00 - NRC Website | |
1.0 DESCRIPTION OF THE EVENT On August 27, 2009, the Service Water Valve House (SWVH) missile shield door tornado design basis was questioned with regards to the locking pins not being engaged on the east missile shield door. The door was only secured with a security hasp and lock due to binding concerns with the locking pins. The design specification for the steel swing tornado missile door at the SWVH requires the door to be designed to withstand the larger of a rebound effect of 25 percent of the design missile impact load or an external pressure drop of 3.0 psi in 3 seconds. The initial engineering evaluation noted the security hasp and lock would likely be overstressed during the 25 percent rebound effect of a design missile impact, and may not withstand subsequent tornado missiles. At that time the SWVH east missile shield door (EllS System — BI, Component — BLDG DR) was secured using the installed locking pins, fulfilling the tornado design basis requirements, and posted to not use for routine access until it was repaired. Signs were posted to inform personnel to use the SWVH west missile door as the normal ingress and egress for the SWVH. The SWVH east missile shield door locking pins were repaired and the door was returned to service on October 9, 2009.
On October 13, 2009, an engineering evaluation confirmed the SWVH east missile shield door could not have performed its design function during a design basis tornado event.
The retaining eye of the hasp would not be capable of meeting the design loading and the door would swing outward in a tornado missile event. As such, the SWVH east missile door should have been considered inoperable. During severe weather a subsequent tornado missile could have entered the SWVH and disabled the electric power supply to the Service Water (SW) motor operated valves (MOV). This condition could have prevented the SW System from providing adequate cooling to the Recirculation Spray Heat Exchangers (EllS System — BE, Component - HX) (RSHX) during an accident.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS The station entered the abnormal procedure for severe weather conditions multiple times when the SWVH east missile shield door should have been considered inoperable. The weather conditions during these entries were not severe enough to require the SWVH missile shield doors be locked closed. A sufficient number of SW spray arrays were verified to be in operation during each entry into the severe weather condition such that the heat transfer between SW and RSHX would have been adequate to mitigate the consequences of an accident had a tornado missile struck and disabled power to the SW MOVs.
This event is reportable pursuant to 10 CFR 50.73 (a)(2)(v)(D) for a condition that could have prevented the SW System from performing its safety function to mitigate the consequences of an accident.
3.0 CAUSE During certain severe weather conditions an abnormal procedure (AP) directs closure of missile shield doors throughout the station. The SWVH missile shield doors were not _ included in the AP. Had a condition occurred which required the missile shield doors to be closed and locked the SWVH missile shield doors would not have been verified in the required configuration.
The SWVH missile shield doors are the only missile shield barriers onsite with a swing door. All other missile shield doors are a rolling/sliding design. It was not understood that while the SWVH missile shield doors were fully closed and locked with the security hasp that they would not perform their tornado design function when the locking pins were not engaged. None of the other rolling/sliding missile barrier doors have this unique locking pin design. This knowledge deficiency along with the absence of SWVH missile shield door verification in the abnormal procedure was determined to be the cause.
4.0 IMMEDIATE CORRECTIVE ACTION(S) Upon identification of the deviating condition the SWVH missile shield door locking pins were engaged and the door was posted to prevent its use for routine access.
Subsequently, repairs to the SWVH missile shield door locking pins were completed and the door was returned to service.
5.0 ADDITIONAL CORRECTIVE ACTIONS The abnormal procedure was revised to include verification of the SWVH missile shield doors and require all equipment in the areas affected by an inoperable missile shield door be declared inoperable and associated actions entered.
Training is being provided regarding the knowledge deficiency for safety functions the missile shield barriers are required to maintain. A table is being developed for inclusion in the Technical Requirements Manual that will list missile shield doors and the required compensatory actions.
6.0 ACTIONS TO PREVENT RECURRENCE The actions taken regarding abnormal procedure revision, personnel training and inclusion of a missile shield door list in the TRM will prevent recurrence.
7.0 SIMILAR EVENTS None.
8.0 ADDITIONAL INFORMATION Component information:
Mark Number� 1-BLD-MBAR-WV26-2 Manufacturer� Mosier, Inc.
Model Number� B-960000 1/2 Description� Service Water Valve House Steel Swing Door (Missile Barrier) �