05000281/LER-2002-002
| Document Number | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2812002002R00 - NRC Website | |
1.0 DESCRIPTION OF THE EVENT The purpose of the Surry Power Station Low Head Safety Injection (LHSI) [EIIS-BP] is to provide post accident cooling to ensure continued long-term cooling of the core. This is accomplished by two 100% LHSI Pumps [EllS-BP-P] taking suction from either the Refueling Water Storage Tank [EllS-BP-TIC] or the containment sump and injecting either directly to the Reactor Coolant System (RCS) [EIIS-AB] loops or to the suction of the High Head Safety Injection Pumps [EIIS-BQ-P].
On October 30, 2002, with Unit 2 operating at 100% reactor power, an operator taking normal daily logs noticed that valve [EIIS-BP-ISV] 2-SI-463, LHSI Pump 1A Seal Cooler Outlet, was not tie-wrapped open as required by procedure. The valve lineup procedure requires this quick throw valve to be tie-wrapped in the open position as a result of past instances that valves in the LHSI pump seal coolers were found out of position. In addition, valve 2-SI-463 was observed approximately 90% closed when it should have been fully open. Since this valve's position minimized the capability to provide seal cooling LHSI Pump 2-SI-P-1A, the pump was declared inoperable at 1708 hours0.0198 days <br />0.474 hours <br />0.00282 weeks <br />6.49894e-4 months <br />. During the time 2-SI-P-1A was inoperable, the #3 Emergency Diesel Generator [EIIS-EK] power supply for the redundant 2-SI-P-1B LHSI Pump was also inoperable due to preplanned maintenance and as a result, 2-S1-P-1B could-net be considered operable in accordance with Technical Specification 3.0.2. With both pumps declared inoperable, neither LHSI train was operable and a limiting condition of operation (LCO) to bring the unit to hot shutdown within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> was started in accordance with Technical Specification 3.0.2. At 1723 hours0.0199 days <br />0.479 hours <br />0.00285 weeks <br />6.556015e-4 months <br />, valve 2-SI-463 was opened and the 6-hour LCO was exited.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS A Probabilistic Risk Analysis was performed that considered the impact of extended unavailability of pump 2-SI-P-1A. An operator stated he remembered valve 2-S1-463 being tie-wrapped open on October 23, 2002 when taking normal daily founds. The risk over the 7-day interval between October 23, 2002 and the LHSI recovery on October 30, 2002 integrates to a core damage probability/year of 6.7E-8. This is below the 1.0E-6 threshold between green and white findings in the Significance Determination Process resulting in a very low le(tel of risk for Unit 2. A Probabilistic Risk Analysis was also performed based on pump 2-S1-P-1A assumed out of service and pump 2-SI-P-1B being inoperable for the period its emergency power supply was inoperable for preplanned
- maintenance. The risk integrates to a core damage probability/year of 7.4E-8 over the three-day span. This is below the 1.0E-6 threshold between green and white tindings in the Significance Determination Process and also results in a very low level of excess risk for Unit 2. Therefore, the health and safety of the public were not affected by this event.
U.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1)
SURRY POWER STATION
I � DOCKET I 05000 - 281 LER NUMBER 6) PAGE (3) 3.0 CAUSE The cause was not determined. A valve lineup had been performed on April 6, 2002. The valves were checked, verified open and tie-wrapped at that time. A search of the tag outs performed on 2-SI-P-1A was done and valve 2-SI-463 had not been tagged out since 1999. During operator rounds on October 23, 2002, it was observed that the tie-wraps were installed. Individuals that were in the area of the pump cubicle since October 23, 2002, were interviewed but no conclusive results were obtained from the interviews.
4.0 IMMEDIATE CORRECTIVE ACTION(S) A station corrective action system report was submitted for valve 2-SI-463, LHSI Pump 1A
- Seal Cooler Outlet, being approximately 90% closed, causing LHSI Pump 2-SI-P-1A to be declared inoperable. A 6-hour LCO was started IAW Technical Specification 3.0.2 due to the second LHSI pump being inoperable because its emergency power supply was inoperable. Valve 2-SI-463 was fully opened and the LCO was exited. A root cause evaluation was initiated. A tie-wrap was installed on 2-SI-463 to provide an additional measure of security.
5.0 ADDITIONAL CORRECTIVE ACTIONS Performed valve lineup verifications for Unit 2.0utside Recirculation Spray (ORS) pumps and Unit 1 LHSI and ORS pumps. Also performed a walkdown of both units Safeguards areas. No discrepancies were found.
6.0 ACTIONS TO PREVENT RECURRENCE "Latch Lock" handles will be installed on all quick throw valves in the LHSI, and ORS Pump seal cooling loops. The locking devices physically latch the hand wheel in place plus have a hole for installing a locking device. This hole will be tie-wrapped to provide an additional measure of security.
7.0 SIMILAR EVENTS The following Plant Issues were documented as part of the Station Corrective Action System:
Plant Issue S-1996-2213 documents valve 2-SI-159 on 2-SI-P-1A being out of position.
The corrective action was to perform the valve lineup.
NM FORM 366A (7-2000 U.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1) � DOCKET
SURRY POWER STATION
05000 - 281 LER NUMBER 6) � PAGE (3) NUMBER � NUMBER Plant Issue S-1998-0494 documents valve 2-SI-463 being out of position. The corrective action was to open the valve and verify the seal head tank valves on the other U2 LHSI and ORS pumps were lined up properly. In this case, it was determined that an outside contractor had been obtaining nameplate data from the LHSI pump motor and 2-SI-463 was in close proximity to this data. The positioning of the valve was consistent with being bumped by someone reviewing the pump name plate data.
Plant Issue S-1999-0736 documents valve 2-SI-469 being out of position. The corrective action was to tie wrap all of the valves for the LHSI and ORS pump seal cooling loops.
8.0 MANUFACTURER/MODEL NUMBER No component failure.
9.0 ADDITIONAL INFORMATION None