05000424/LER-2012-003
| Vogtle Electric Generating Plant - Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4242012003R00 - NRC Website | |
A. REQUIREMENT FOR REPORT
This report is required per 10 CFR50.73(a)(2)(i)(B) based, in part, upon the 1A Engineered Safety Feature (ESF) Chiller being inoperable for a duration of greater than the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed by Technical Specification LCO 3.7_14 Condition A due to a failure to identify and respond to an out of specification operating parameter, Further, during the extended period during which the 1A ESF Chiller was inoperable (albeit unrecognized as inoperable), opposite train supported components as well as redundant room coolers on the Train B ESF Chiller and Room Cooler train were removed from service for unassociated activities which resulted in a number of occasions during which Technical Specification LCO 3.0.3 should have been applied. There were, therefore, periods of operation of the plant during which the applicabilities of two LCOs were inadvertently unrecognized thereby necessitating this report made pursuant to the requirements of 10 CFR50.73(a)(2)(i)(B).
B. UNIT STATUS AT TIME OF EVENT
During the period of the event the unit was in Mode 1 Other than described herein, there was no other inoperable equipment that contributed to the event.
C. DESCRIPTION OF EVENT
On August 17, 2012, a systems operator (SO) notified the Control Room the 1A ESF Chiller condenser pressure gauge indicated a vacuum of 12 inches of mercury with a vacuum of 15 inches of mercury specified on operating logs as the low vacuum limit. At the time, no procedural basis for this limit existed other than to document the reading in a condition report. The shift supervisor erroneously informed the SO that condenser pressure was one of the parameters which engineering personnel (Engineering) were monitoring and that a previous CR on this component existed. This misunderstanding was carried forward through subsequent shifts via the SO's log entry.
During the next five calendar days, the condenser vacuum continued to decrease to 4 inches of mercury and subsequently stabilized at this value for an additional four calendar days. On August 26, 2012, an Operations crew member questioned the off-normal parameter and initiated a CR. Engineering personnel, after consultation with the vendor, notified the Control Room the 1A ESF Chiller would not be able to perform its safety function under current conditions and the 1A ESF Chiller was promptly declared inoperable at 1437 on August 26, 2012. The 1A ESF Chiller was restored to operable and the LCO exited at 1930 on August 28, 2012.
Subsequent causal analysis of the event determined that the 1A ESF Chiller would be operable with respect to condenser vacuum provided condenser vacuum remained greater than or equal to 10 inches of mercury. Based on a review of operator rounds, the 1A ESF Chiller condenser vacuum decreased to less than 10 inches of mercury on August 19. 2012. An opportunity to recognize this operability limit was missed by not evaluating the out of specification parameter on August 17, 2012. The cause of the loss of condenser pressure was due to system in-leakage in conjunction with failure of the condenser purge compressor control circuit.
D. CAUSE OF EVENT
The underlying cause of the failure to comply with Technical Specification LCOs 3.7.14 and 3.0.3 event was a weakness in sensitivity to out of specification parameters by the shift supervisor, along with the associated failure to initiate a condition report documenting the out of specification parameter, as required by procedure. As a result of this error, the Operability Determination process was not conducted upon discovery of the condition, and the applicability of LCOs 3.7.14 and 3.0.3 was not recognized.
E, SAFETY ASSESSMENT During the period of time the 1A ESF Chiller was inoperable but prior to the time of discovery, scheduled maintenance activities were performed on redundant train B equipment. As a result, on two occasions both trains of ESF Chillers and ESF Room Coolers were rendered concurrently inoperable placing the plant in a condition for which the applicable LCOs were not met and LCO 3.0.3 applied. These periods were longer than allowed by LCO 3.0.3 for plant operation in Mode 1. In addition, scheduled maintenance activities were performed on equipment supported by the redundant ESF Chiller and ESF Room Cooler Train that would have resulted in a determination of a Loss of Safety Function (LOSF) had the actual status of the 1A ESF Chiller been recognized and a LOSF evaluation been performed.
The Essential Chilled Water System (ECWS) and ESF Room Coolers are not included in the Vogtle Probabilistic Risk Assessment (PRA) model due to their negligible impact on the reliability of PRA- credited functions as determined by room heat-up studies and the availability of alternate methods of room cooling. Based on a detailed review of Vogtle-specific room heat-up calculations and industry reference documents, it has been concluded that the ECWS-supported systems will be able to perform their safety function within the PRA credited mission time. In addition, a risk analysis of modeled components that were out of service during the period of inoperability of the 1A ESF Chiller was performed. The annualized increases in CDF and LERF were determined to be not significant.
F. CORRECTIVE ACTION
All Operations personnel were briefed on this event and reviewed the expectations for the performance of rounds. The event was entered into the plant's corrective action program and a causal analysis was completed. Procedures have been revised to strengthen the rigor and formality of supervisory review and oversight of operator rounds.
G. ADDITIONAL INFORMATION
1) Failed Components:
Unit 1 Train A ESF Chiller condenser purge compressor manufactured by Trane Company.
2) Previous Similar Events:
Although similar events related to monitoring of technical specification component parameters have been documented at Plant Vogtle, no similar occurrences of failure to initiate a condition report upon discovery were identified.
3) Energy Industry Identification System Code: Environmental Control Systems are coded by the area serviced. The 1A ESF Chiller served components in both the Auxiliary and Control Buildings.
The respective codes are: VF and VI.