05000416/LER-2017-007
| 02-05-2018 | At approximately 0918 hours0.0106 days <br />0.255 hours <br />0.00152 weeks <br />3.49299e-4 months <br /> on Tuesday, December 12, 2017, while operating in MODE 1 at approximately 18 percent power, the Grand Gulf Nuclear Station (GGNS) experienced a loss of the Engineered Safety Features (ESF) Transformer 11 which was powering the Division 1 ESF bus. Subsequently, the station experienced an automatic start of the Division 1 Emergency Diesel Generator and the partial isolation of the primary and secondary containment buildings. Both of these events were expectedand as designed. The direct cause of ESF actuations was the loss of ESF Transformer 11. The cause of the transformer loss is under investigation at this time and this licensee event , report will supplemented upon completion of GGNS's causal analysis.
Additionally, GGNS experiented an unrelated isolation of the Reactor Core Isolation Cooling System upon restoration of power. The isolation of the Reactor Core Isolatigh Cooling System did not result in a loss of safety function. The cause of this isolation is under investigation and will be documented in accordance with the.GGNS corrective action program. This event is reportable to the NRC in accordanCe with 10 CFR 50.72(b)(3)(iv) and 10 CFR 50.73(a)(2)(iv)(A) as an event or condition resulting in a valid actuation of a ESF system. Grand Gulf Nuclear Station, Unit 1 05000 416 . NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/3112020 (4-2017) Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Information Services Branch (T-2 so RkG,„ LICENSEE EVENT REPORT (LER)
ContentsDESCRIPTIONAt approximately 0918 hours0.0106 days <br />0.255 hours <br />0.00152 weeks <br />3.49299e-4 months <br /> on Tuesday, December 12, 2017, while operating in MODE 1 at approximately 18 percent power, the Grand Gulf Nuclear Station (GGNS) experienced a loss of the Engineered Safety Features (ESF) Transformer 11 [EB] which was powering the Division 1 ESF bus [EA]: The transformer experienced an instantaneous ground resulting in a transformer lockout and loss of power to the ESF bus. Subsequently, the station experienced an automatic start of the Division 1 Emergency Diesel Generator [EK] and the partial isolation of the primary and secondary containment buildings. Both of the system actuations were expected responses to a loss of ESF bus and both systems responded as designed. The direct cause of ESF actuations was the loss of ESF Transformer 11. Additionally, GGNS experienced an unrelated isolation of the Reactor Core Isolation Cooling System [BN] upon restoration of power. The' isolation of the. Reactor Core Isolation Cooling System did not result in a loss of safety function. The cause of this isolation is under investigation and will be documented in accordance with the GGNS corrective action program. REPORTABI LITYThis event is reportable to the NRC in accordance with 10 CFR 50.72(b)(3)(iv)(A) and 10 CFR 50.73(a)(2)(iv)(A) as an event or condition resulting in a valid actuation of a ESF system. The 10 CFR 50.72 reporting requirements were met with the completion of Emergency Notification System (ENS) Notificatibn 53115, at 1740 hpurs eastern standard time on December 12, 2017. CAUSEDirect Cause: The direct cause of the ESF actuation was the loss of ESF Transformer 11 and the opening of the transformer feeder breaker due to an instantaneous ground. Apparent Cause: The most probable cause is a ground on one of the feeder cables to ESF Transformer 11. However, the investigation and causal analysis is ongoing at this time and this licensee event report will be supplemented upon completion of the GGNS causal analysis. NRC FORM(6-2016) 366A U.S. NUCLEAR. REGULATORY COMMISSION LICENSEE. EVENT REPORT (LER)
2. DOCKET 3. LER NUMBER 05000.416 CORRECTIVE ACTIONSSpare Essential Transformer 21 was placed into service and normal power was restored. The investigation and causal analysis is ongoing and this licensee event report will be supplemented upon completion of GGNS's causal analysis. The planned corrective actions will be included in the corrective action program and may be changed in accordance with the program.
SAFETY SIGNIFICANCEThere were no nuclear safety consequences or radiological consequences as a result of this event. No Technical Specification Safety Limits were violated. Upon the loss of Engineered Safety Feature Transformer 11 all required accident mitigation ESF components responded as designed. The isolation of the Reactor Core Isolation Cooling System, although unexpected, did not adversely impact the plant's ability to respond to the event. PREVIOUSLY SIMILAR EVENTSProtective Relaying Circuitry on the "B" Main Transformer Transformer Wiring Entergy has reviewed the events listed in the licensee event reports (LER) documented above to determine if the corrective actions should have prevented the event documented in this LER. Based on a preliminary evaluation it has been concluded the established corrective actions would not have prevent this event. Entergy's investigation into the cause of this event and the development of corrective actions to preclude recurrence are ongoing. This section will be supplemented at the conclusion of this effort. |
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| Grand Gulf Nuclear Station, Unit 1 | |
| Event date: | 12-12-2017 |
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| Report date: | 02-05-2018 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4162017007R00 - NRC Website | |
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