ENS 46604
ENS Event | |
|---|---|
12:38 Dec 20, 2010 | |
| Title | Fuse Failure Causes Low Pressure Core Spray to Be Inoperable |
| Event Description | On December 20, 2010, the low pressure core spray (LPCS) system was declared inoperable due to loss of power to the LPCS minimum flow valve. The minimum flow valve supports operability by providing a flow path to prevent pump damage during situations where the LPCS pump has been started in response to a transient, but reactor vessel pressure is not low enough to allow LPCS injection. The power loss was caused by the clearing of all 3 line power fuses for the motor starter for the minimum flow valve. An apparent cause evaluation concluded that the most likely cause of the fuses clearing was a random fuse failure of one of the fuses at less than design amperage attributable to a defect in the fuse solder joint.
The Technical Specification (TS) Required Action for LCO 3.5.1 Condition A, one low pressure ECCS injection/spray subsystems inoperable, was complied with by restoring the LPCS system to operable within the allowed completion time. The safety functions for LPCS are to provide inventory makeup and spray cooling during large breaks in the reactor coolant system that uncover the core. All remaining ECCS subsystems were operable and at no time did this event result in the loss of a safety function. The low pressure injection function was not challenged due to all three loops of the Residual Heat Removal (RHR) system Low Pressure Coolant Injection (LPCI) mode being operable while the core spray function was satisfied by the operable High Pressure Core Spray (HPCS) system. This event is being reported under 10 CFR 50.72(b)(3)(v)(D) as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident tor a single train system. Historically, LPCS inoperabilities at Columbia (including initial review of this event) were not considered to be a single train system for reportability purposes. The basis for the historical consideration was assessment of LPCS inoperabilities consistent with the plant safety analysis and the associated system and safety function groupings which do not single out LPCS as a single train system. There are two pertinent groupings in the safety analyses which are aligned with the credited safety functions of LPCS. The two groupings are the low pressure injection system function (combined with LPCI), and a core spray system function (combined with HPCS). Industry precedent has been consistent with the historical position. However, recent NRC interpretations have considered safety function at the lowest system level which result in LPCS being considered as a single train performing a safety function in scope of the reportability rules in 10 CFR 50.72 and 50.73. A Licensee Event Report will be submitted for this event. As a result of the recent interpretation with regard to LPCS, a review of prior LPCS inoperabilities within the past three years is being performed to determine if the reporting criteria were met during prior events. If necessary, additional 10 CFR 50.72 and 10 CPR 50.73 notifications/reports will be made on prior LPCS inoperabilities . The licensee will notify the NRC Resident Inspector. |
| Where | |
|---|---|
Columbia Generating Station  Washington (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| LER: | 05000397/LER-2010-002 |
| Time - Person (Reporting Time:+1208.28 h50.345 days <br />7.192 weeks <br />1.655 months <br />) | |
| Opened: | Matt Hummer 20:55 Feb 8, 2011 |
| NRC Officer: | Mark Abramovitz |
| Last Updated: | Feb 8, 2011 |
| 46604 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |