05000316/LER-2002-004
| Donald C. Cook Nuclear Plant Unit 2 | |
| Event date: | 01-19-2002 |
|---|---|
| Report date: | 12-13-2002 |
| Initial Reporting | |
| 3162002004R02 - NRC Website | |
Donald C. Cook Nuclear Plant Unit 2 05000-316 . NUMBER 17. TEXT (If more space Is required, use additional copies of NRC Form (366A) Conditions Prior to Event Unit 1 - 100 percent power Unit 2 - 22 percent power
Description of Event
At 00:01 hours on 01/19/02, in preparation for a Unit 2 refueling outage, Operations shift personnel initiated a planned manual reactor trip of Unit 2 from 22% power per Procedure 02-OHP-4021-001-003, Revision 15, "Power Reduction." Shortly thereafter, an automatic start of the turbine driven auxiliary feedwater pump (TDAFP) [BA] occurred as a result of valid low-low level indication in two of four Steam Generators.
The automatic start of the TDAFP was not specifically called out as an expected occurrence after manual reactor trip from 22% power in procedure 02-0HP-4021-001-003.
The reactor trip setpoint had been selected to avoid challenging ESF equipment (i.e., auto start of the TDAFP) both by industry benchmarking and validation in the plant simulator. However, based on simulator response, it was recognized that conditions may be possible where a start of the TDAFP could occur. During simulator training the operating crew had noted that steam generator levels had dropped to within a few percent of the TDAFP auto-start setpoint. Prior to the conduct of the unit shutdown, a pre-job briefing was held with the operating crew. During this pre-job briefing the potential for a TDAFP auto-start was discussed.
The automatic start of the TDAFP was determined to be an "unanticipated" engineered safety feature (ESF) [JEJ actuation, in accordance with the guidance contained in NUREG-1022, Revision 2, Paragraph 3.2.6.
Steam generator levels rapidly recovered. Operators secured the TDAFP and throttled flows from the motor driven auxiliary feedwater pumps in accordance with plant procedures for reactor trip response and recovery. Reactor Coolant System (RCS) [AB] cooldown and depressurization proceeded normally. During the trip, pressurizer level shrank lower than procedurally anticipated, resulting in a reactor coolant system letdown isolation. The operating crew recovered from the letdown isolation in accordance with approved plant procedures.
At 07:56 on.01/19/02, the Shift Manager made an eight hour, non-emergency notification to the NRC (EN# 38640) in accordance with 10 CFR 50.72(b)(3)(iv)(A) for an unanticipated ESF actuation.
Previous Similar Events
None.
revised to reduce the planned power level trip set 17% power.
revised to reduce the planned power level trip set 17% power.
004 02 2002 17. TEXT (If more space Is required, use additional copies of NRC Form (366A)
Cause of Event
With regard to the operational aspects of this event, it was acknowledged that a planned trip should not challenge the engineered safety features equipment to automatically start.
The manual trip set point of 22% reactor power was based on industry benchmarking of similar design/size units. Following the start of the TDAFP during reactor shutdown, CNP learned, based on additional benchmarking, that lowering the established manual trip set point to 17% reactor power was prudent. The lower manual trip set point minimizes the amount of shrinkage within the steam generators, thus providing adequate margin to prevent a start of the TDAFP. CNP has determined that the cause of this event was the establishment of a manual reactor trip set point in the station shutdown procedure that challenged the TDAFP to automatically start.
Analysis of Event
Although the automatic start of the TDAFP was not expected to occur after a manual reactor trip from 22% power, the system performed as designed.
There were no actual nuclear, radiological, or industrial safety consequences as a result of this event.
Corrective Action