05000387/LER-2002-003
| Susquehanna Steam Electric Station - Unit 1 | |
| Event date: | 03-04-2002 |
|---|---|
| Report date: | 05-03-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3872002003R00 - NRC Website | |
EVENT DESCRIPTION
On March 4, 2002 at 01:20 with Unit 1 in Mode 4 at 0% power for a refueling and inspection outage, an Instrumentation and Control Technician (non-licensed, utility) performing a 24 month logic system functional test observed that Anticipated Transient Without Scram (ATWS) Recirculation Pump Trip (RPT) 4.16 kV breaker 1A20502 (EIIS Code: EB) did not trip as required. Investigation by Electrical Maintenance personnel (non-licensed, utility) identified that the Truck Operated Cell (TOC) switch contact 52-H2 in the rear of the associated 4.16 kV switchgear cubicle had failed to make-up properly.
The TOC had excessive drive shaft and gear rotary motion, which allowed the TOC to over-travel when the breaker was "racked-in". This condition resulted in less than adequate contact 52-H2 make-up to trip the breaker on an AWTS - RPT instrumentation signal. The condition only affected the 52-H2 contact.
Electrical Maintenance personnel "racked-out" breaker 1A20502 and returned it to the "racked-in" position. Contact 52-H2 was checked for proper continuity and the logic system functional test was then completed successfully. The TOC was then subsequently replaced with a design less susceptible to over-travel.
An investigation of the as-found condition by Engineering personnel (non-licensed, utility) determined that the degraded condition of contact 52-H2 had only affected the breakers ability to trip on an ATWS- RPT instrumentation input signal. All other required functions of 1A20502 would have performed as designed. The condition of contact 52-H2 may have existed since the last time the breaker had been Technical Specification (TS) Basis for the ATWS - RPT Instrumentation (EIIS Code: JD) requires that instrument channels associated with a breaker that is incapable of operating be declared inoperable.
The 'B' and 'D' ATWS-RPT instrumentation channels (Division 2 trip system) are associated with breaker 1A20502 and therefore should have been declared inoperable since the Spring of 2000. With the Division 2 trip system of ATWS-RPT inoperable and the Unit in Mode 1, Unit 1 Technical Specification (TS) 3.3.4.2 required actions were not completed since the condition of the TOC was not known.
CAUSE OF EVENT
The failure of breaker 1A20502 to trip on an ATWS-RPT instrumentation input signal was attributed to inadequate make-up of TOC switch contact 52-H2 in the rear of the associated 4.16 kV switchgear cubicle. The TOC had excessive drive shaft and gear rotary motion, which allowed the TOC to over- travel when the breaker was "racked-in". This condition resulted in less than adequate contact 52-H2 make-up, and the inability to trip the breaker on an AWTS - RPT instrumentation signal.
An investigation of the event showed that contact 52-H2 is not visible (blind) when the breaker is in the "racked-in" position and there is no lamp indication to verify correct contact alignment. Additionally, there is no specific written guidance concerning verification of contact 52-H2 position.
ANALYSIS / SAFETY SIGNIFICANCE
This event is reportable as a condition prohibited by the Technical Specifications per 10CFR50.73(a)(2)(i)(B) in that Unit 1 was in a condition prohibited by the Technical Specification 3.3.4.2.
Specifically, the Division 2 trip system for the ATWS-RPT instrumentation was apparently inoperable for approximately two years while Unit 1 was in Mode 1. This time period exceeded that allowable by the Technical Specifications. However, due to redundancy in the design, both Reactor Recirculation Pumps would have tripped as required during an actual ATWS event. There are two ATWS-RPT breakers in series provided for each of the two Reactor Recirculation Pumps. A trip of either breaker in the series will trip the associated Reactor Recirculation Pump. The Division 1 trip system trips one of the two breakers for each Reactor Recirculation Pump and Division 2 trips the other breaker for each Reactor Recirculation Pump. Redundancy and diversity were reduced, but the ability to perform the safety function remained.
In addition, the degraded condition of contact 52-H2 had only affected the breaker's ability to trip on an ATWS-RPT instrumentation input signal. All other required functions of 1A20502 would have performed as designed. This event did not constitute a loss of safety function. 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 May 3, 2002.
CORRECTIVE ACTIONS
Corrective actions that have been completed:
- The TOC switch associated with 4.16 kV breaker 1A20502 was replaced with a design less susceptible to over-travel and subsequently tested satisfactorily.
- All other Unit 1 and Unit 2 52-H2 contacts on ATWS-RPT breakers were checked for proper contact make-up and found satisfactory.
Corrective actions to be completed:
- Identify other 4.16 kV breaker cubicles that have "blind" TOC contacts and determine where verification of contact alignment is necessary.
- Establish and implement written guidance for monitoring the necessary "blind" TOC contact make- up after a breaker is "racked-in".
- Establish training for monitoring the necessary "blind" TOC contact make-up for Operations and Maintenance personnel involved with 4.16 kV breaker manipulations.
- Station personnel are still evaluating additional corrective actions. An update to this report will be made if additional corrective actions are specified.
ADDITIONAL INFORMATION
Past Similar Events:
� None Failed Component:
� 4.16 kV Breaker 1A20502 TOC Manufacturer: � Westinghouse Model: � 50DHP250