05000280/LER-2015-001
| Surry Power Station, Unit 1 | |
| Event date: | 01-27-2015 |
|---|---|
| Report date: | 3-30-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vi) 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2802015001R00 - NRC Website | |
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
1.0 DESCRIPTION OF THE EVENT On January 27, 2015, with Units 1 and 2 operating at 100 percent power, it was identified that the sliding missile shields [EIIS XX-DR] for the four Main Steam Valve House (MSVH) access doors were not included in the Abnormal Environmental Conditions procedure to be closed upon the threat of high winds in the event of a hurricane or tornado watch or warning.
The shields are necessary to meet the design function of the MSVH for protection of the equipment inside the MSVH (e.g., auxiliary feedwater pumps [EIIS BA-P] or other safety- related components in the Main Steam (MS) [EIIS SB] and Auxiliary Feedwater (AFW) [EIIS BA] systems) from high wind generated missiles. These shields are normally maintained open and must be closed upon the threat of high winds from a hurricane or tornado in order to perform their design function. This issue was discovered during a procedure revision walk-through.
There have been approximately ten instances in the past three years when the Abnormal Environmental Conditions procedure was entered and it was determined that closure of sliding missile shields would have been appropriate due to local weather conditions. During these times, a missile could have penetrated the unprotected access doors and interacted with the auxiliary feedwater pumps or other safety-related components in the MS and AFW systems located inside the MSVH. 10 CFR 50.73(a)(2)(vi) includes events caused by procedural inadequacies. Since the Abnormal Environmental Conditions procedure did not ensure sliding missile shield closure, a missile could have prevented the AFW and/or MS system from performing their safety functions and is therefore reportable pursuant 10 CFR 50.73(a)(2)(v).
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS The MSVH sliding missile shields are part of the Class 1 structure designed to protect safety-related components inside the MSVH from the effects of tornados and high winds. If the doors are not closed upon the threat of high winds, the potential exists for a tornado- generated missile to disable a combination of MS lines and AFW trains which would challenge the ability to remove decay heat. Contingencies exist in Surry's function restoration procedures to provide alternate means of Decay Heat Removal, such as establishing Bleed and Feed Cooling or operation of the AFW crosstie from the other Unit.
Based on an assessment of this event, the increase in risk was determined to be of low significance due to the low probability of a missile entering the MSVH and disabling Surry's ability to remove decay heat. As a result, the health and safety of the public were not affected.
Surry Power Station 05000 - 280 3.0 CAUSE The Main Steam Valve House sliding missile shields were not included in original version of the Abnormal Environmental Conditions procedure. No documentation could be identified that indicated the reason these doors were not included in the procedure. No similar procedure could be identified to exist prior to issuance of the original revision of the current procedure.
4.0 IMMEDIATE CORRECTIVE ACTION(S) The abnormal environmental conditions procedure has been revised to include the four MSVH sliding missile shields in the list of sliding missile shields to be closed upon the threat of high winds.
5.0 ADDITIONAL CORRECTIVE ACTIONS An extent of condition review was completed and verified that the station sliding missile shields are included in the Abnormal Environmental Condition procedure.
6.0 ACTIONS TO PREVENT RECURRENCE No additional actions are required.
7.0 SIMILAR EVENTS None 8.0 MANUFACTURER/MODEL NUMBER Not applicable 9.0 ADDITIONAL INFORMATION None