05000301/LER-2011-001
| Point Beach Nuclear Plant | |
| Event date: | 02-27-2011 |
|---|---|
| Report date: | 04-22-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3012011001R00 - NRC Website | |
Event Description
B train SI pump (2P-15B) [B[], had rotated and the oil had drained out. The B train SI pump was immediately declared inoperable. At the time of the event, the A train of SI was out of service for performance of a routine inservice test. Because both trains of SI were inoperable, [CO 3.0.3 was entered.
Upon completion of the A train inservice test, Unit 2 exited LCO 3.0.3 at 2211 CST.
This licensee event report is being submitted in accordance with 10 CFR 50.73(a)(2)(v)(D), 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. This event is classified as a safety system functional failure per NEI 99-02.
Cause of the Event
The root cause of the event was a 1995 modification to the SI pump oiler which introduced a latent design/configuration flaw. The flaw made the oilers susceptible to failure as a result of an inadvertent bumping event. There is no definitive time when the B SI pump oiler was rotated other than the time of discovery at 2159 on February 27, 2011, and there is no conclusive indication that the discrepancy existed prior to the discovery.
Analysis of the Event
The SI system is part of the emergency core cooling system (ECCS). Its primary purpose is to automatically deliver borated cooling water to the reactor core in the event of a loss of coolant accident (LOCA). The SI system will also insert negative reactivity into the core in the form of borated water during an uncontrolled plant cool down following a main steam line break or an accidental steam release.
The design basis of the ECCS is to provide two independent trains of ECCS for accident mitigation. During the 12-minute period that 2P-15A was out of service for inservice testing and 2P-15B was inoperable, high head safety injection could not be automatically initiated.
Analysis of Safety Significance Following a large-break loss of coolant accident (LOCA), the reactor coolant system (RCS) would be depressurized and voided of coolant rapidly and a high flow rate is required to quickly recover the exposed fuel rods and limit possible core damage. To achieve this objective, one residual heat removal (RHR) pump (high flow, low head) was available to deliver borated water to the core during the period both SI pumps were out of service.
During the time both trains of SI were inoperable, the delta core damage frequency (CDF) and delta large early release frequency (LERF) were below the annual cumulative probabilities. Therefore, the safety significance of the event is low.
Corrective Actions
The immediate corrective action included restoration of the oiler to the vertical position, refilling the oiler with oil, performing 5-minute pump run.
In addition to the above, the SI pump oiler assemblies for both units will be redesigned to reduce the possibility of an accidental misalignment. This action is being tracked to completion in the corrective action program (CAP).
Similar Events None
Failed Components
None