05000387/LER-2002-001
| Susquehanna Steam Electric Station - Unit 1 | |
| Event date: | 02-22-2002 |
|---|---|
| Report date: | 04-23-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3872002001R00 - NRC Website | |
EVENT DESCRIPTION
On February 22, 2002 with Unit 1 at 81% power and Unit 2 at 100% power, the 'B' Control Structure (CS) Chiller (EIIS: KM) tripped when an operator placed the chiller's handswitch from 'Auto' to 'Start' following an automatic start of the equipment. The 'B' chiller automatically started when the 'A' chiller tripped during post-maintenance testing.
Subsequent investigation revealed the following timeline of events on 2/22/2002:
- 11:50 - The 'A' CS chiller was started for post-maintenance testing. Testing was conducted throughout the afternoon.
- 18:37 - The 'A' CS Chiller tripped, and the 'B' Chiller auto-started according to plant design.
- 18:55 - A plant operator (Utility, Licensed) placed the 'B' Chiller circulating pump handswitch from 'Auto' to 'Start', per plant operating philosophy to match handswitch position to equipment status.
The "break-before-make" switch contacts momentarily interrupted power to the chiller auxiliaries, and the electrical breaker for the 'B' CS Equipment Fan tripped open. The 'B' chiller tripped due to the loss of the required permissive to have its associated equipment fan running.
- 19:01 - The breaker for the 'B' Equipment Fan was reset, the equipment fan and the 'B' chiller were restarted.
CAUSE OF EVENT
The cause of the 'B' CS Chiller trip was lack of specific procedural guidance for the operating condition.
Procedures for normal starting and stopping of the chillers result in the handswitch for the in-service chiller's circulating pump in the 'Start' position and the other chiller in 'Auto' for standby service or 'Stop' if removed from service. In the absence of procedural guidance after a chiller starts automatically, the operator placed the handswitch from 'Auto' to 'Start' to bring the equipment alignment within generic operating guidance. The handswitch "break-before-make" design imposed an additional start event on the equipment for this action. In this event, the high starting current did not trip the breaker on the first start, but the subsequent electrical transient during the switch alignment tripped the equipment fan supply breaker.
ANALYSIS / SAFETY SIGNIFICANCE
Based on the fact that neither of the two CS Chillers would have started if called upon for the six minutes between 18:55 - 19:01, the required cooling for Control Structure equipment would not have been present for those 6 minutes during an accident scenario. In addition, the ability to pressurize the CS envelope was lost for this same time period. This event is reportable as an event or condition that could have prevented fulfillment of a safety function per 10CFR50.73(a)(2)(v). Based upon the simplicity of resetting the electrical supply breaker, and the short amount of time that no chillers were available, this event resulted in very low safety significance. There were no actual adverse consequences to the health and safety of the public as a result of this event.
In accordance with guidance in NUREG-1022, Revision 2, the due date for this report is April 23, 2002.
CORRECTIVE ACTIONS
The appropriate operating procedure for the CS Chillers will be revised to provide guidance following an automatic start of the equipment to avoid similar operator-induced trips.
ADDITIONAL INFORMATION
Past Similar Events:
� None Failed Component:
� None