05000353/LER-2013-002
| Limerick Generating Station, Unit 2 | |
| Event date: | 09-03-2013 |
|---|---|
| Report date: | 10-31-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| Initial Reporting | |
| ENS 49318 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 3532013002R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 2 was in Operational Condition (OPCON) 1 (Power Operation) at 100% power. The affected local airlock door (EIIS:DR) open indicating light (EIIS:IL) was non-functional prior to the event.
There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
On Tuesday, September 3, 2013, Limerick Unit 2 was operating at 100% power. At 0646 hours0.00748 days <br />0.179 hours <br />0.00107 weeks <br />2.45803e-4 months <br />, the reactor enclosure low delta pressure alarm (EIIS:ALM) actuated and reactor enclosure pressure was observed at 0.18 inch of vacuum water gauge and recovered to a normal pressure of 0.33 inch of vacuum water gauge.
An investigation identified that workers in the reactor enclosure (EIIS:NH) were moving equipment through an airlock. An unplanned opening of both airlock doors occurred when the workers opened both doors for approximately 5 seconds. The affected blue light magnetic switch was replaced and the door open indicating light was restored to a functional status on September 5, 2013.
Technical Specification (TS) 3.6.5.1.1 Reactor Enclosure Secondary Containment Integrity surveillance requirement 4.6.5.1.1.a requires verification that reactor enclosure pressure is greater than or equal to 0.25 inch of vacuum water gauge which is performed on a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> frequency. The TS surveillance requirement 4.6.5.1.1.b.2 requires at least one door in each access to the reactor enclosure be verified closed which is performed on a 31 day frequency. TS 3.6.5.1.1 is applicable in operational conditions (OPCON) 1, 2 and 3.
An 8-hour NRC ENS notification was required by 10CFR50.72(b)(3)(v)(C) for a condition that at the time of discovery could have prevented fulfillment of a safety function of structures or systems needed to control the release of radioactive material.
The ENS notification (#49318) was completed on Tuesday, September 3, 2013, at 1410 hours0.0163 days <br />0.392 hours <br />0.00233 weeks <br />5.36505e-4 months <br /> ET. This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(v)(C).
Analysis of the Event
There was no actual safety consequence associated with this event.
The potential safety consequences of this event were minimal. Both doors on the airlock were open simultaneously for approximately 5 seconds.
Each reactor enclosure airlock is equipped with door open indicating lights which are used to locally verify the door status. If both doors are opened simultaneously a local alarm is actuated. If both doors remain open for greater than 10 seconds an alarm is actuated in the main control room and operators are dispatched to verify the airlock doors are closed.
UFSAR 6.2.3.2.1 describes the secondary containment design. The reactor enclosure secondary containment (Zones I and II) are designed to limit the inleakage to 200% of their zone free volume per day, and the refueling area secondary containment (Zone III) is designed to limit the inleakage to 50% of its zone free volume per day. These inleakage rates are based on a negative interior pressure of 0.25 in wg, while operating the standby gas treatment system (SGTS). Following a LOCA the affected zone is maintained at this negative pressure by operation of the SGTS.
Cause of the Event
This event was caused by a non-functional airlock door open indicating light not providing the correct door status.
Corrective Action Completed The non-functional door open indicating light magnetic switch has been replaced.
A review was conducted and no other non-functional door open indicating lights were identified.
Corrective Action Planned A periodic routine test of the airlock door open indicating lights will be implemented to identify non-functional door open indicating lights.
Previous Similar Occurrences There have been multiple previous similar occurrences in the prior three years based on a review of the operator logs. The events were identified by an actuation of the airlock seal open alarm which indicates that both airlock doors were open for a period exceeding 10 seconds.
Component Data Component Number Component Name Manufacturer Model Number Door-560 Reactor Enclosure Fan Room Door Woolley 7790 DWG/HW SET B