05000352/LER-2012-009
| Limerick Generating Station, Unit 1 | |
| Event date: | 10-03-2012 |
|---|---|
| Report date: | 12-03-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3522012009R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 1 and Unit 2 were in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power. There were no structures, systems or components out of service that contributed to this event.
Description of the Event
On Wednesday, October 3, 2012, Unit 1 and Unit 2 were operating at 100% power and a detailed logic and cable routing review for the Multiple Spurious Operations (MSO) 5f scenario was in progress. The review identified that a D22 Emergency Diesel Generator (EDG) (EIIS:EK) output breaker (EIIS:BKR) control cable (EIIS:CBL) could fail due to postulated fire damage in fire area 067W. At 1710 hours0.0198 days <br />0.475 hours <br />0.00283 weeks <br />6.50655e-4 months <br />, an initial fire watch was performed in the affected area. At 1742 hours0.0202 days <br />0.484 hours <br />0.00288 weeks <br />6.62831e-4 months <br />, the control room supervisor (CRS) posted an hourly fire watch in the affected area.
On Saturday, November 3, 2012, the affected EDG breaker was rewired, to eliminate the condition and the fire watch was terminated.
During closure reviews for the MSO project, to confirm MSO scenario resolution, detailed reviews of all applicable MSO fire scenarios were completed and no additional FSSD issues were identified.
An 8-hour NRC ENS notification was required by 10CFR50.72(b)(3)(ii)(B) since this event involved an unanalyzed condition that significantly degraded plant safety. The ENS notification (48372) was completed on Wednesday, October 3, 2012, at 2022 EDT. This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(ii)(B) due to the unanalyzed condition.
The NRC ENS submitted at the time of the event also conservatively listed 10CFR50.72(b)(3)(ii)(A) as a reporting criterion. It was later determined that the condition of the nuclear power plant, including its principle safety barriers, was not seriously degraded by this event. There was no degradation of fuel cladding, primary coolant boundary, or primary containment as a result of this event.
Therefore, the prior ENS report related to this criterion is being retracted.
Analysis of the Event
There was no actual safety consequence associated with this event.
The potential safety consequences of this event could have been significant since the inadvertent closure of an EDG output breaker could result in unavailability of the single credited 4 kV safeguard power source during a fire in the affected fire area.
This postulated spurious EDG output breaker closure could open the credited offsite source breaker on overcurrent and lockout the credited 4kV bus. The existing fire safe shutdown analysis should have identified that this cable needed to be protected in order to credit the 4kV safeguard bus in fire area 067W.
reactor enclosure safeguard systems access area on the 217 foot elevation. This fire area credits FSSD Method C. If the credited 4kV safeguard bus fails due to a single spurious fire induced D22 EDG output breaker closure, it will prevent the "2B" low pressure coolant injection (LPCI) system injection which is credited approximately 20-25 minutes into the post fire event for reactor pressure vessel (RPV) inventory control and cooling.
This event resulted in a non compliance with the current FSSD analysis documented in the fire protection evaluation report and fire protection program which is the current licensing basis (CLB).
The CLB assumes a single spurious actuation of safe shutdown components during any single deterministic fire event for plant areas as documented in the Limerick UFSAR FPER section 9A.5. The identified error could result in a single spurious actuation that could impact the ability to safely shutdown.
Cause of the Event
The event was caused by an error during the FSSD analysis.
Corrective Action Completed The D22 EDG output breaker control logic was rewired to eliminate the deficiency.
Previous Similar Occurrences There is no previous similar occurrence of a FSSD analysis error that resulted in an unanalyzed condition that significantly degraded plant safety during the past 5 years.