ENS 46563
ENS Event | |
|---|---|
23:31 Jan 18, 2011 | |
| Title | Both Loops of Low Pressure Coolant Injection Inoperable |
| Event Description | This condition is being reported in accordance with 10CFR50.72(b)(3)(v) as a condition that could have prevented fulfillment of a safety function.
On 1/18/2011 at 1731 CST, it was discovered that the open position indication light for RR-MO-53A, Reactor Recirculation [RR] Pump A discharge valve operator, was de-energized. The RR-MO-53A operator is powered by a 250 VDC motor with 125VDC control power. Investigations revealed that the 125 VDC control power circuit fuses for the valve operator were open. RR-MO-53A must close at a reactor pressure of 199 to 221 psig to allow Residual Heat Removal [RHR] Loop A to inject to the reactor during a LOCA involving Reactor Recirculation Loop B. This condition rendered RHR Loop A Low Pressure Coolant Injection [LPCI] function inoperable. At the time of discovery, RHR Loop B LPCI function was inoperable for planned maintenance. This maintenance was being performed on the service water side of the RHR heat exchanger, RHR-MO-25B, RHR Loop B Injection Outboard Isolation valve operator, RHR pump B motor, and RHR-MO-39B, Suppression Chamber Cooling Loop B Outboard Isolation valve operator. As specified by the Required Action for LCO 3.5.1 Condition H, two or more low pressure ECCS injection/spray subsystems inoperable, LCO 3.0.3 was immediately entered. LCO 3.0.3 requires the plant to be shutdown to Mode 2 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />. Preparations to commence plant shutdown were initiated in parallel with investigations to determine the cause of the open control power fuses. Subsequent troubleshooting revealed a failed light socket caused the fuses to open. The fuses were replaced and the circuit tested satisfactorily. At 1915 CST on 1/18/2011, RHR Loop A LPCI was declared Operable and LCO 3.0.3 was exited. The plant shutdown procedure was terminated prior to any power reduction occurring. Initial review of this condition for immediate reportability under 50.72(b)(3)(v), Condition that Prevents Fulfillment of a Safety Function, concluded the condition was not reportable based on the availability of Core Spray Pump A [CS-P-A], Core Spray Pump B [CS-P-B ], and RHR Pump D [RHR-P-D]. Procedure 2.0.11.1, Safety Function Determination Program, states that Emergency Core Cooling System [ECCS] Safety Function is maintained if three low pressure ECCS Injection/Spray pumps remain operable. CS-P-A, CS-P-B and RHR-P-D all were operable at the time of discovery of the condition. RHR Pump B was restored to available at 1510. The maintenance on RHR Loop B did not remove RHR-P-D from service and an injection path was available at time of discovery of LPCI Loop A inoperable as RHR-MO-25B, RHR Loop B Injection Outboard Isolation valve, post work testing had been completed and the injection capability restored at 1701. Subsequent review determined that the reportability decision under 50.72(b)(3)(v) as a Condition that Prevents Fulfillment of a Safety Function should be based on safety function at the system level, rather than at the ECCS function level. The decision to report the simultaneous inoperability of both RHR LPCI Loops under 50.72(b)(3)(v) was made at 1549 on 1/21/2011. The licensee has notified the NRC Resident Inspector. |
| Where | |
|---|---|
Cooper  Nebraska (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| LER: | 05000298/LER-2011-001 Regarding Both Loops of Residual Heat Removal Inoperable Results in Loss of Safety Function |
| Time - Person (Reporting Time:+71.48 h2.978 days <br />0.425 weeks <br />0.0979 months <br />) | |
| Opened: | John Myers 23:00 Jan 21, 2011 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Jan 21, 2011 |
| 46563 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |