05000324/LER-2014-001
| Brunswick Steam Electric Plant (Bsep), Unit 2 | |
| Event date: | 03-06-2014 |
|---|---|
| Report date: | 05-02-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| Initial Reporting | |
| ENS 49880 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 3242014001R00 - NRC Website | |
Energy Industry Identification System (ENS) codes are identified in the text as [XX].
Background
Initial Conditions At the time of this event, Unit 2 was at 100 percent of rated thermal power (RTP). There were no other structures, systems or components out of service that contributed to this event.
Reportability Criteria This condition is being reported in accordance with 10 CF: 50.73(a)(2)(v)(C), as an event or condition that could have prevented fulfillment of a safety function needed to control the release of radioactive material. Specifically, secondary containment [NG] was considered inoperable per Technical Specification (TS) requirements for approximately one to two minutes on March 5, 2014, when both the inner and outer secondary containment airlock doors (i.e., doors 2-RB2-D1- -EL050-301 and 2-RB2-DR-EL050-302), on the 53 foot elevation of the reactor building, had been simultaneously opened. The NRC was initially notified of this event on March 6, 2014 (i.e., Event Number 49880).
With both doors open, Surveillance Requirement 3.6.4.1.2 of Technical Specification (TS) 3.6.4.1, Secondary Containment, was not met, rendering secondary containment inoperable. In accordance with the guidance of NUREG-1022, Even': Reporting Guidelines 10 CFR 50.72 and 50.73, Revision 3, TS inoperability of a structure, system, or component with no redundant equipment in the same system operable constitutes an event that could have prevented the fulfillment of a safety function.
Event Description
At 1605 Eastern Standard Time (EST) on March 6, 2014, Operations determined that both the inner and outer secondary containment airlock doors, on the 50 foot elevation of the reactor building, had been simultaneously opened for approximately one to two minutes on March 5, 2014. This event occurred while an employee was exiting secondary containment. The inner door failed to latch and opened as the employee was opening the outer door. Upon recognition of the condition the employee took action to secure both doors.
Event Cause The root cause of this event is that the design of the secondary containment airlock door irrledocks is not robust enough to prevent inoperability of secondary containment.
Statements from personnel involved in the event and maintenance technicians who investigated afterwards clearly demonstrate that the interlock was physically actuating both during and after the evenL The interlock systems have known physical vulnerabilities and require mainte:ance of moving parts to guarantee proper function. It is possible for the door position switch or plunger Li stick in intern *tient cases, particularly if the door is experiencing heavy use during an outage. The interlock system, when actuating properly, ultimately relies on the door t. be in the fully closed and latched position in order for 1 Event Cause (continued) the plunger to be effective. The door may go out of alignment periodically due to heavy use, may not completely close under a high differential pressure, or may not be challenged by personnel; any of which potentially renders the plunger ineffective.
Safety Assessment The safety significance of this event was minimal. The principal functions of secondary containment are to minimize ground level release of airborne radioactive materials and to provide the means for a filtered and controlled elevated release of the reactor building atmosphere if an accident ; `muld occur. The safety objectivc of secondary containment is to limit the releaoe of radioactivity to the environs after an accident so that the resulting exposures are kept to a practical minimum and are within 10 CFR 50.0 7 and 10 CFR 100 values. The duration of a potential for releasc have occurred via the open airock doc rs was approximately one to two minutes. Throughout Lis time, secondary containment negative pressure was maintained.
Corrective Actions
Any changes to the corrective actions and schedules noted below will be made in accordance with the site's corrective action program.
The following corrective actions have been completed.
- The secondary containment airlock doors were cilsed to re-establish secondary containment.
- Video monitoring equipment was installed for Units 1 and 2 at the 20 foot personnel airlock doors were identified as emergency use only. These actions will remain in place until the newly designed interlocks for the airlock doors have beer installed.
The following corrective action to prevent recurrence (CAPR) is planned.
- Design and implement a new interlock for the Unit 1 and 2 secondary containment personnel airlock doors. This action is scheduled to be completed by December 30, 2014.
Previous Similar Events
A review of LERs for the past three years identified the following previous similar occurrence.
- LER 2-2013-005, dated December 19, 2013, repor;A a loss of secondary containment integrity due to gaps in the Unit 2 secondary containment airlock door ceals. Corrective actions included translating design basis requirements for sc ondary containment into acceptance criteria f.N.
the Unit 1 and Unit 2 secondary containment -ure boundary doors, as well as c.ornplMing procedure revisions to incorporate the acceptant_ 4eria. Since the causes of the events ‘,,,rc different, the actions from LER 2-2013-005 could not have reasonably been expected to p:
- eve the condition reported in LER 2-2014-001.
Li! Commitments No regulatory commitments are contained in this repo:L