05000397/LER-2005-002
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| 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 |
| Initial Reporting | |
| ENS 41499 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3972005002R00 - NRC Website | |
Plant Condition The plant was operating in Mode 1 at 100 percent power at the time of this event.
Event Description
At 0943 PST on March 16, 2005, the High Pressure Core Spray (HPCS) pump [BG-P]was___ —taken out.of.service for-mainte-naridetFigiaidite-the source of an identified motor [MO] oil leak. During the course of this inspection, cracks in the HPCS pump motor upper air deflector were discovered. Energy Northwest personnel determined this constituted a condition that could have prevented the fulfillment of a safety function and was reported under 10 CFR 50.72(b)(3)(v)(D) (refer to event number 41499). Accordingly, this LER is provided in accordance with 10 CFR 50.73(a)(2)(v)(D) and as operations prohibited by the Technical Specifications in accordance with 10 CFR 50.73(a)(2)(i)(B).
Immediate Corrective Action Corrective actions were taken to restore the HPCS system to an operable status within the 14-day completion time provided in the Columbia Technical Specifications. The degraded air deflector was removed and replaced.
To address the extent of condition for air deflector degradation, Energy Northwest reviewed the systems containing large vertical squirrel-cage induction style motors in safety related applications. Energy Northwest determined the design of the HPCS upper air deflector was unique with respect to other safety related motors for several reasons. Based on this determination, no immediate action for these other motors was deemed necessary.
Cause-- The root cause for the degraded air deflector is that critical dimensions were not maintained during the motor reassembly process in 1992 which led to clearance deficiencies between the motor rotor/fan assembly and the air deflector. Lack of detailed design drawings that included critical dimensions led to:
- Incorrect planning for reassembly
- Incorrect upper thrust bearing endplay (work order steps for a different bearing assembly was used)
- Assembly methods that allowed excessive rotor overall travel that caused an up-thrust impact to the air-deflector and caused deformation, dimpling and displacement (air deflector not in rabbet groove) A significant contributing cause for the degraded air deflector is less than adequate control of critical dimensions during the manufacturing process which led to parts that did not meet manufacturer dimensional specifications.
Assessment of Safety Consequences
HPCS is a part of the Emergency Core Cooling System (ECCS). Its purpose is to supply water to the reactor vessel over a wide range of accident conditions. For small-break Loss of Coolant Accidents (LOCAs) that do not result in rapid reactor depressurization, the system is designed to maintain reactor water level. For large breaks, the system provides core spray cooling. The ECCS has built-in redundancy, and is comprised of High Pressure Core Spray (HPCS), Low Pressure Core Spray (LPCS) [BM], Low Pressure Coolant Injection (LPCI) [BO] mode of the Residual Heat Removal (RHR) [BO] system and the Automatic Depressurization System (ADS). Failure of the HPCS is bounded within the ECCS single failure analysis.
The condition described in this report did not result in actual failure of HPCS during an event - when-itsas-required-to-operate.--The.HPCS motorand.pump.have been-successfully tested` and run numerous times since 1992 when the air deflector replacement was performed as discussed in the root cause analysis. The ability and duration of the system to perform its safety function in the as-found condition is the subject of a separate evaluation.
This event did not adversely affect the health and safety of either the public or plant personnel. If the failure of HPCS had occurred during an actual event, the ECCS is designed to accommodate this failure and the ECCS safety function could still be performed.
This event is reportable under 10 CFR 50.73(a)(2)(v)(D), "Any 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." There were no structures, systems or components that were inoperable at the start of the event that contributed to the event.
- 4 A- identify other industry experience in the area of failed air deflectors and oil leaks. For these searches, there were no recent similar events identified. However, a similar event involving the air deflector was reported for Columbia in 1992 (refer to LER 92-025). The conditions associated with the 1992 event and the corrective actions taken were reviewed in detail as part of the root cause investigation of this current failure.
--The root cause analysis and corrective actions from this previous event did not prevent recurrence. This root cause analysis did not identify specific procedural or work instruction flaws or weaknesses. It also did not consider that the repair and reassembly performed in 1992 could be subjected to the same causes that resulted in the cracked air deflector at that time. The corrective actions included a review of the applicable procedures. This procedure review did not identify specific deficiencies in procedures involved in repairing the HPCS pump motor that can result in excessive uplift movement and forces. Since this procedure review did not detect any flaws or weaknesses in the applicable procedures, no procedure changes were made.
EIIS information denoted as rxxl 26158 R2