05000251/LER-2013-001
| Docket Number | |
| Event date: | 3-23-2013 |
|---|---|
| Report date: | 5-22-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2512013001R00 - NRC Website | |
DESCRIPTION OF THE EVENT
On March 23, 2013 at approximately 2245, with Unit 4 in Mode 5, while restoring Residual Heat Removal (RHR) System [BP] interlocks, RHR loop suction stop valve [BP, ISV] MOV-4-750 commenced closing. The MOV-4-750 breaker [BP, ISV, BKR] was promptly opened and the valve was deenergized in an intermediate position. RHR pump [BP, P] operation and flow were verified stable.
Following the event, it was determined that MOV-4-750 commenced closing because an isolation signal was present. The isolation signal was present because control power was removed from the instrumentation due to two lifted leads [CBL4]. The lifted leads also removed control power to the pressure comparator [AB, PIC] circuit for power operated relief valve (PORV) [AB, RV] PCV-4-456 rendering it inoperable.
In Mode 5, Technical Specification (TS) Limiting Condition for Operation 3.4.9.3 for Overpressure Mitigating Systems (OMS) requires high pressure safety injection [BQ] flow paths to be isolated, and either two operable PORVs or a Reactor Coolant System (RCS) [AB] vent path of at least 2.20 square inches. With one PORV inoperable, TS 3.4.9.3, Action c, requires operability to be restored within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or a vent path established within the next 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. The removed pressurizer safety valve [AB, PZR, RV] providing the vent path was installed on March 10, 2013 at approximately 1020. Control power to PCV-4-456 was removed on or about February 23, 2013. Control power was restored and PCV-4-456 declared operable at approximately 2145 on March 24, 2013. As a result, one PORV was inoperable for a period of approximately 14 days and 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> without the required RCS vent path exceeding the total allowed outage time of 32 hours3.703704e-4 days <br />0.00889 hours <br />5.291005e-5 weeks <br />1.2176e-5 months <br />.
Because one PORV was inoperable for a time greater than allowed by the TS without a RCS vent path, this event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS.
CAUSE OF THE EVENT
The root cause is inadequate procedure compliance by supplemental personnel during performance of a modification. Also, the review to establish PORV operability for OMS credited a Surveillance Requirement (SR) that was current but performed prior to the lifting of the leads.
ANALYSIS OF THE EVENT
The OMS is designed to protect the RCS from over-pressurization due to the start of an idle reactor coolant pump [AB, P] with steam generator [SB, SG] water temperature 50°F above RCS cold leg temperature, or a single high head safety injection (HHSI) pump injecting into a water solid RCS.
The OMS system was placed in service on March 9, 2013 using the normal operating procedure. The procedure checks switch, valve and nitrogen alignment, and also checks if SRs are current. Performance of the surveillance procedure would have identified the issue with OMS operability due to the lifted leads.
However, the surveillance procedure had been satisfactorily completed on February 16, 2013 and the SR was current at the time OMS was placed in service.
The leads were lifted by supplemental personnel during the performance of an engineering change, were not controlled, and were not relanded.
ANALYSIS OF SAFETY SIGNIFICANCE
During the period one PORV was inoperable (PCV-4-456) a second PORV (PCV-4-455C) was operable and available in the event the OMS was required. Furthermore, HHSI isolation was maintained through clearance and procedural control. As such, the Unit 4 RCS was protected from an inadvertent overpressure event. As a result, the safety significance of this event is very low.
CORRECTIVE ACTIONS
Corrective actions are documented in AR 1868533 and include the following:
1. Update site training for supplemental personnel to better emphasize the importance of configuration management and the procedural controls employed to maintain it.
2. Revise the alarm response procedure for a related annunciator to include a check that fuses for OMS PORVs are installed and control power to pressure comparators is in service.
3. Verify status of PORV actuation instrumentation prior to declaring OMS operable.
FAILED COMPONENTS IDENTIFIED: None PREVIOUS SIMILAR EVENTS: None
ADDITIONAL INFORMATION
component function identifier (if appropriate)].