05000278/LER-2006-001
| Peach Bottom Atomic Power Station Unit 3 | |
| Event date: | |
|---|---|
| Report date: | |
| 2782006001R00 - NRC Website | |
Unit Conditions at the Time of the Event Unit 3 was in Mode 1 and operating at approximately 100% rated thermal power when the Technical Specification non-compliance was discovered on 4/6/06. The High Pressure Coolant Injection (HPCI) (EIIS:
BJ) system was inoperable as a result of the performance of a planned Logic System Functional Test (LSFT) and other unplanned maintenance involving a logic relay concern discovered during the LSFT. HPCI was inoperable since 4/5/06 at approximately 0824 hours0.00954 days <br />0.229 hours <br />0.00136 weeks <br />3.13532e-4 months <br />. There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
On 4/6/06 at approximately 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br />, Licensed Operations personnel declared an air-operated Primary Containment Isolation Valve (EIIS:ISV) associated with the HPCI Turbine Exhaust Drain Line inoperable in accordance with Technical Specification Limiting Condition for Operation (LCO) 3.6.1.3, Primary Containment Isolation Valves (PCIVs). This declaration was based on questions raised by an NRC Resident Inspector performing an in-plant observation of the position status of the HPCI Turbine Exhaust Line Inboard Isolation Valve (A0-137). The NRC Resident Inspector reported to station Operations personnel in the Main Control Room that the AO-137 appeared to not be fully closed as determined by a local observation of the actual valve stem position. This was discovered while HPCI was removed from service for a Logic System Functional Test (LSFT) and repair / replacement of a relay (unrelated to A0-137).
In accordance with Technical Specification LCO 3.6.1.3, the affected penetration flow path was isolated within the required 4-hour completion time. It was discovered during maintenance of the AO-137 on 4/7/06 at approximately 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br /> that the drain / test connection valves (HV-3-23C-31191 and HV-3-23C-31192) for the penetration were also leaking through the valve seats. It was subsequently determined that foreign material was lodged in the valve seats not allowing the AO-137 and associated drain / test connection valves to fully close.
Technical Specification LCO 3.6.1.3 concerning PCIVs is applicable in Mode 1. Prior to discovery of this condition, HPCI was last operated on 3/23/06 for a quarterly pump, valve and flow test. Therefore, the AO- 137 valve inoperability is judged to have existed since a time at or before the previous HPCI operation.
Technical Specification LCO 3.6.1.3 Required Action A.1 requires that the affected containment penetration(s) for an inoperable PCIV be isolated within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Because this action was not performed until 4/6/06 when the condition was discovered, this event was determined to be a condition prohibited by the Technical Specifications in accordance with 10 CFR 50.73 (a)(2)(i)(B).
Repairs were performed to AO-137 and the associated test taps and these components were returned to an operable status on 4/7/06 by approximately 2316 hours0.0268 days <br />0.643 hours <br />0.00383 weeks <br />8.81238e-4 months <br />.
Analysis of the Event
There were no actual safety consequences associated with this event.
A0-137 is a normally open 2" air-operated valve located in the drain line connected to the HPCI Turbine Exhaust Line. The function of the drain line is to maintain the HPCI Exhaust Line free of condensate. This function is not a credited safety function for HPCI operability. However, this normally open valve performs an active safety function in the closed position. This valve is credited as one of the redundant containment isolation barrier for containment penetrations N-214 and N-217B. These containment penetrations are associated with the Suppression Pool. This valve automatically closes in response to Primary Containment Isolation System signals associated with conditions necessary to isolate the HPCI system (e.g. high system area temperatures, high HPCI Steam Line flow).
HV-3-23C-31191 and 31192 are normally closed 1" drain / test connection valves upstream of A0-137 that performs a passive containment isolation function for the same penetrations as AO-137.
Primary Containment Isolation Valve AO-137 was inoperable for a minimum time period of 15 days (i.e. the time period between the last HPCI operation on 3/23/06 and the return to operable status on 4/7/06). The last assurance of the valve being leak-tight was on 9/30/05 when the valve was leak tested with satisfactory results during the P3R15 Refueling Outage.
The redundant containment penetration barriers for the associated N-214 and N-217B containment penetrations were operable during the period of exposure. Therefore, the Primary Containment Isolation safety function was met throughout the period of non-compliance.
This event was not determined to be risk significant.
Cause of the Event
The cause of the failure of the PCIVs to properly close was due to foreign material found in the seating areas of the valves. Foreign material was discovered in the AO-137 valve seating area. This foreign material consisted of metallic fragments. Evidence of plug, stem, and seat damage as a result of contact with the foreign material items existed. A foreign material inspection was performed between A0-137 and the upstream hand valve HV-3-23C-31158 and the downstream valve (AO-138). HV-3-23C-31191 and 31192 were also disassembled and inspected and similar foreign material was identified and removed. HV-3-23C- 31191 and downstream drain valve HV-3-23C-31192 were repaired and leak tested satisfactorily.
Preliminarily, it is believed that the foreign material was primarily introduced into the system as a result of historical system component failures (e.g. failure of exhaust line rupture disks in the 1980s). Further review and potential additional causes are being evaluated in accordance with the Corrective Action Program.
Corrective Actions
Foreign material was removed from the internals of the A0-137 PCIV and associated test taps. The valves were repaired and appropriate valve leak-tightness was verified as part of an as-left local leak rate test.
A foreign material inspection was performed within the attached piping to the AO-137 valve. No additional foreign material was identified.
Additional corrective actions including extent of condition evaluations are being evaluated in accordance with the Corrective Action Program. Pending further piping inspections for foreign material, proper stroke operation of the AO-137 valve is being performed after each HPCI system operation.
Previous Similar Occurrences There was one previous LER identified concerning a condition prohibited by Technical Specifications condition where foreign material was found in the AO-137 valve on the HPCI system. Corrective actions associated with LER 2-04-02 involved removal of foreign material and extent of condition examinations for Unit 2.
Foreign material searches performed during the last Unit 3 Refueling Outage (P3R15) did not detect the foreign material that migrated into the PCIVs discussed in this report.