05000280/LER-2009-002
| Surry Power Station, Unit 1 | |
| Event date: | 09-24-2009 |
|---|---|
| Report date: | 11-23-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2802009002R00 - NRC Website | |
1.0 DESCRIPTION OF THE EVENT During system walk downs on September 24, 2009, with Units 1 and 2 at 100% power, it was discovered that the three emergency service water pump (ESWP) oil cooler [EllS—BI, HX] outlet lines were not sealed where they passed through the base plates to prevent pump house water intrusion. Gaps approximately 1/8 inch to 1/4 inch were noted between the 3/4 inch outlet lines and the holes in the base plates. The total open area, as a result of these gaps, was approximately 1.5 square inches. The ESW pump house is located on the James River and provides cooling water to the intake canal. The pump house may be subjected to hurricane induced tidal surges.
The Updated Final Safety Analysis Report (UFSAR) states that the ESW pump house is built to limit water ingress during a storm surge associated with a probable maximum hurricane. The pump house is elevated and, during routine operations, the building is accessible and ventilation is open.� By design, prior to arrival of a hurricane, site procedures require installing flood protection barriers on the ESW pump house doors and intake louver openings to ensure the building is water tight.
A maximum storm surge associated with a probable maximum hurricane is 22.7 feet above mean sea level (MSL), however, the highest water level of record is approximately 8.6 feet above MSL. Given that the pump base plates are at an elevation of approximately 18 feet above MSL, there was no imminent hurricane threat to the station, and the allowance for manual preparatory actions including sealing the gaps, the ESWPs were considered operable. However, without prior knowledge of the need to seal the gaps, the pumps may have been impacted by water ingress from a storm surge greater than 18 feet.
With the penetrations not sealed, the pump house would be susceptible to flooding during a storm surge greater than 18 feet above MSL and could affect the operability of the ESW pumps. Technical Specification (TS) 3.14.A.4 requires three ESW pumps to be operable.
Therefore, with the operability of the ESW pumps potentially affected during a hurricane surge, this report is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B), any event or condition which was prohibited by TSs.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS The ESW pump house is located on the James River and may be subjected to hurricane induced tidal surges. However, the highest water level of record was 8.6 feet above MSL, and the pump base plates are at an elevation of approximately 18 feet above MSL.
Therefore, there is significant margin from potential water intrusion.
Procedures require that two hours prior to a hurricane reaching the site, the units are to be shutdown and the reactor coolant temperature brought to less than or equal to 345 degrees F. Decay heat will be removed using the Circulating Water (CW)/ Service Water (SW) systems. With a loss of offsite power, the diesel driven ESW pumps will provide cooling water to remove decay heat and bring the units to cold shutdown condition. If the ESW pumps are affected by water ingress, sufficient cooling water will be available in the intake canal until the water ingress can be mitigated. Prior to a hurricane reaching the site, procedures require intake canal level to be brought to 28-30 feet to ensure that sufficient driving head is available to provide heat removal capability. Therefore, additional cooling water will be available.
Also, if a storm surge greater than 8 feet above MSL is projected and hurricane force winds are expected within four hours, procedures require an operator to be stationed at the ESW pump house and to start the three ESWPs. Maintenance personnel are also assigned to the ESW pump house area to seal the pump house and provide maintenance support. With personnel stationed and materials available in the area, water ingress caused by the gaps in the pump base plates could have been identified and mitigated.
This issue was determined to be of very low risk significance; therefore, the health and safety of the public were not affected.
In accordance with design basis criteria and the UFSAR, the station is not required to withstand a design basis accident (DBA) during a probable maximum hurricane.
Therefore, the ESWP oil coolers outlet lines unsealed penetrations had no impact on the capability of the ESWPs to perform their design function during a DBA.
3.0 CAUSE OF THE EVENT An evaluation found that the apparent cause of the gaps in the penetration seals for the three ESWP oil coolers outlet lines was inadequate maintenance procedural guidance.
The drawing for the ESWPs shows the base plate with a 3/4 inch drilled and tapped hole for the outlet line of the oil cooler. The piping was originally threaded into the penetration holes in the pump base plates, in lieu of passing through open holes. The cause evaluation identified that in the 1990's, this configuration was changed due to maintenance on the pumps and use of a spare angle drive and resulted in the use of the threaded interfaces being discontinued. Procedural guidance did not ensure that the pump base plate penetrations were sealed and the watertight configuration maintained.
4.0 IMMEDIATE CORRECTIVE ACTION(S) When the penetration sealing concern was identified, station operations personnel then became aware of the need to seal the gap in addition to other preparatory actions that are required if a hurricane approaches the site. Based upon this information, the ESWPs were determined to be operable. The penetrations were sealed on September 25, 2009.
5.0 ADDITIONAL CORRECTIVE ACTIONS An extent of condition walk down was performed at the ESW pump house and no other water ingress gaps were identified.
6.0 ACTIONS TO PREVENT RECURRENCE The maintenance procedure has been revised to require the penetrations through the pump base plate to be sealed if maintenance is performed.
7.0 SIMILAR EVENTS None 8.0 ADDITIONAL INFORMATION None �