05000353/LER-2007-002

LER-2007-002, Automatic Actuation of Main Condenser Low Vacuum Isolation Logic During Refueling Outage

Docket Number
Event date:	03-12-2007
Report date:	05-11-2007
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation
Initial Reporting
ENS 43231	10 CFR 50.72(b)(3)(iv)(A), System Actuation
3532007002R00 - NRC Website

Unit Conditions Prior to the Event Unit 2 was in Operational Condition (OPCON) 4 (Cold Shutdown). There were no structures, systems or components out of service that contributed to this event.

Description of the Event

On Monday, March 12, 2007, Unit 2 was in OPCON 4 conducting 2R09 refueling outage activities. Operations personnel were performing the procedure for breaking main condenser vacuum [EIIS:SH] as scheduled. The main steam isolation valves (MSIVs) [EIIS:ISV] were manually closed in preparation for breaking main condenser vacuum. At 14:01 hours, the main condenser vacuum breakers were opened. Vacuum decreased to the low vacuum isolation setpoint and two of four channels (A and D) of the main condenser vacuum isolation logic actuated. There was no valve movement as a result of this isolation demand since the MSIVs were already closed. On Tuesday March 13, 2007, at 07:30 hours, Operations personnel identified that two channels of MSIV isolation logic had actuated and commenced an investigation.

The investigation determined that an Equipment Operator (EO) had been instructed to bypass the main condenser low vacuum isolation logic as required by the procedure for breaking main condenser vacuum (507.2.A). The EO was required to bypass four channels [EIIS:CHA] (A,B,C and D) of isolation logic using four key-lock switches [EIIS:HS]. However, the EO only bypassed two channels (B and C) of isolation logic using two key-lock switches. This resulted in actuation of A and D channels of MSIV isolation logic when vacuum was broken.

This event involved a valid automatic actuation of the main condenser low vacuum isolation logic for multiple main steam isolation valves. The 8-hour ENS notification (#43231) required by 10CFR50.72(b)(3)(iv) was performed on Tuesday, March 13, 2007 at 15:14 hours. � This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(iv).

Analysis of the Event

There were no actual safety consequences associated with this event. The potential safety consequences of this event were minimal as the event occurred after the system was properly removed from service and the safety function had already been completed (the MSIVs were closed as directed by procedure prior to breaking main condenser vacuum).

A weakness in the procedure for bypassing the main condenser low vacuum isolation contributed to the event. The procedure included two steps for bypassing the isolation logic. The first step directed bypassing the A and C channels. The second step directed bypassing the B and D channels. However, the EO only bypassed the B and C channels. The inclusion of these two actions in a single step is not in accordance with station guidance for procedure preparation.

Cause of the Event

The event was caused by a human performance deficiency regarding a failure to properly execute the procedure step that bypasses the main condenser low vacuum isolation prior to breaking main condenser vacuum. A contributing condition was a procedure weakness that involved two actions being directed in a single step.

Corrective Action Completed A stand down was conducted with Operations shift personnel to communicate the issue and reinforce standards.

The procedure for breaking main condenser vacuum was revised to provide an individual step for each low vacuum logic bypass switch.

Previous Similar Occurrences There was one previous similar occurrence of an automatic actuation of the main condenser low vacuum isolation logic when breaking main condenser vacuum. This event was reported in LER 2-89-014.