05000336/LER-2008-002

LER-2008-002, Unplanned LCO Entry - Three Charging Pumps Aligned for Injection With the Reactor Coolant System Temperature Less than 300 Degrees F.

Docket Number
Event date:	04-13-2008
Report date:	06-11-2007
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3362008002R00 - NRC Website

1. Event Description:

Technical Specification (TS) 3.1.1.3.b (Reactivity Control Systems - Boron Dilution) states a maximum of two charging pumps [P] shall be capable of injecting into the Reactor Coolant System (RCS) [AB] whenever the temperature of one or more of the Reactor Coolant System (RCS) cold legs is less than 300 degrees F. With more than two charging pumps capable of injecting into the RCS and the temperature of one or more of the RCS cold legs less than 300 degrees F, take immediate action to comply with TS 3.1.1.3.b. This Technical Specification allows a maximum of two charging pumps to be OPERABLE when RCS cold leg temperature is less than 300 degrees F, thus ensuring the maximum dilution flow rate assumed in the boration analysis is not exceeded.

On April 13, 2008 at 0805 with the plant shut down in MODE 6, while performing control room operator rounds, a Licensed Operator identified three charging pumps were aligned so they were capable of injection with the RCS temperature less than 300 degrees F. TS Action Statement 3.1.1.3.b was immediately entered and then exited when the swing charging pump was made incapable of injecting. The plant was in the prohibited configuration for approximately six hours. With the plant in the prohibited configuration there was no impact on reactivity since primary make-up water had been isolated and tagged. Additionally low temperature overpressure protection (LTOP) conditions were not applicable because the reactor vessel head was removed.

Since the plant was in a configuration not allowed by the Technical Specifications, this event is reportable in accordance with 10CFR50.73(a)(2)(i)(B) as any operation or condition prohibited by the plant's Technical Specifications.

2. Cause:

A Root Cause Evaluation was conducted. The cause of this event was determined to be inadequate configuration control because the tag for the charging pump removed from service to comply with the Boron Dilution TS 3.1.1.3.b. did not provide adequate guidance. To ensure the third charging pump is not capable of injecting into the RCS, it is electrically isolated. The underlying basis for tagging and removing one of the charging pumps from service was not clearly indicated on the tag for the charging pump removed from service to comply with TS 3.1.1.3.b. Subsequent reconfiguration of the charging system was not prevented when subsequent work activities to support electrical work activities in the outage aligned three charging pumps so they were capable of injection with the RCS temperature less than 300 degrees F.

3. Assessment of Safety Consequences:

This event is judged to be of very low safety significance. In accordance with TS 3.1.1.3, with the cold leg temperature less than 300 degrees F, a configuration with a maximum of two charging pumps capable of injecting into the RCS is permitted. This specification limits the maximum number of charging pumps assumed to deliver un-borated water to the RCS in the FSAR Chapter 14 Boron Dilution Event Analysis. In MODE 6, the Technical Specifications require the RCS boron concentration must be maintained so Keff is less than or equal to 0.95. During the time when all three charging pumps were available in MODE 6, no actual event occurred resulting in a reduction in the RCS boron concentration. Additionally primary make-up water had been isolated and tagged. This event occurred prior to core offload. The procedurally required boron concentration during this timeframe was 2097 ppm. This boron concentration is adequate to maintain Keff less than or equal to 0.95 following the core reload with new fuel in the reactor vessel and all control element assemblies withdrawn.

During this event, the actual RCS boron concentration was approximately 2240 ppm. Prior to core offload (end of Cycle 18 conditions), the required RCS boron concentration to maintain Keff less than or equal to 0.95 is 1133 ppm with all control element assemblies withdrawn. Since all control element assemblies were inserted during this event, the required boron concentration to maintain Keff less than or equal to 0.95 is even further reduced. Given the above factors, with three charging pumps operating, the time to decrease the RCS boron concentration from 2240 ppm to the point the reactor becomes critical would be considerably longer than 30 minutes, and bounded by the existing FSAR Chapter 14 boron dilution analyses.

4. Corrective Action:

Upon discovery of the condition where three charging pumps were aligned so they were capable of injection with the RCS temperature less than 300 degrees F, TS Action Statement 3.1.1.3.b was immediately entered and then exited when the swing charging pump was made incapable of injection into the RCS. The plant was in the prohibited configuration for approximately six hours.

Additional corrective actions to address this event will be evaluated in accordance with the station's Corrective Action Program.

5. Previous Occurrences:

No previous similar events/conditions were identified.

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].