05000352/LER-2012-003
| Limerick Generating Station, Unit 1 | |
| Event date: | 05-02-2012 |
|---|---|
| Report date: | 05-21-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 47888 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3522012003R01 - NRC Website | |
Unit Conditions Prior to the Event Unit 1 was 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. The 1A exhaust fan was unavailable for automatic start on loss of the 1B or 1C exhaust fan.
Description of the Event
On Wednesday, May 2, 2012, Limerick Unit 1 was operating at approximately 100% power. At 0718 hours0.00831 days <br />0.199 hours <br />0.00119 weeks <br />2.73199e-4 months <br />, the Unit 1 reactor enclosure ventilation system (EIIS:VA) tripped which resulted in a low delta pressure condition in reactor enclosure secondary containment (EIIS:NH). A valid manual initiation of the secondary containment isolation system was performed as directed by procedure.
The actuation resulted in closure of primary containment isolation valves (PCIVs) (EIIS:ISV) in the instrument gas system. Containment atmospheric control (CAC) PCIVs that were in their normally closed position also received a closure demand.
The initial investigation did not identify the cause of the ventilation system trip. The isolation signal was reset, the affected PCIVs were restored to the pre-event positions, and the ventilation system was restored to service. Temporary instrumentation was installed on the reactor enclosure ventilation system to monitor the system performance. Additional investigation and troubleshooting, identified the cause of the ventilation system trip was the degraded performance of the reactor enclosure equipment compartment exhaust (REECE) flow transmitter.
An 8-hour NRC ENS notification was required by 10CFR50.72(b)(3)(iv)(A) for a valid manual actuation of the primary containment isolation system. The ENS notification (#47888) was completed on Wednesday, May 2, 2012 at 1315 EDT. This event affected primary containment isolation valves in more than one system.
Therefore, this LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(iv)(A).
Analysis of the Event
There was no actual safety consequence associated with this event.
The potential safety consequences of this event were minimal. The primary containment isolation system operated as designed and closed PCIVs in the instrument gas system. The low delta pressure condition in the reactor enclosure did not result in degradation of secondary containment integrity other than a brief period of operation with a low delta pressure condition. Normal reactor enclosure secondary containment delta pressure was restored when the standby gas treatment system (SGTS) and reactor enclosure recirculation system (RERS) automatically started as a result of the manual initiation of the reactor enclosure secondary containment isolation.
Per UFSAR 9.4.2.1.3, safety-related equipment in the reactor enclosure is designed to perform safety functions under the environmental conditions resulting from a loss of the normal ventilation system. Per TS 3.6.5.1.1 Reactor Enclosure Secondary Containment Integrity surveillance requires pressure within the reactor enclosure secondary containment to be maintained greater than or equal to 0.25 inch of vacuum water gauge.
Cause of the Event
The cause of the event was a trip of the reactor enclosure ventilation system that resulted in a low reactor enclosure secondary containment delta pressure condition and alarm (EIIS: ALM). The operators initiated a "B" manual secondary containment isolation as directed by the alarm procedure. The cause of the ventilation system trip was degraded performance of the reactor enclosure equipment compartment exhaust (REECE) flow transmitter.
Corrective Action Completed The degraded REECE flow transmitter was replaced and the system was tested successfully.
The reactor enclosure ventilation system was restored to service and continues to operate normally.
Previous Similar Occurrences There were no recent previous similar occurrences of reactor enclosure ventilation system trips that resulted in manual actuation of the primary containment isolation system.