05000325/LER-2012-007
| Brunswick Steam Electric Plant (Bsep), Unit 1 | |
| Event date: | 12-14-2012 |
|---|---|
| Report date: | 04-11-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 48596 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3252012007R01 - NRC Website | |
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
Introduction Initial Conditions At the time of the event, Unit 1 was in Mode 1, at approximately 100 percent of rated thermal power (RTP) and Unit 2 was in Mode 1 at approximately 93 percent of RTP.
Reportability Criteria This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), as an event or condition that could have prevented the fulfillment of the safety function that is needed to mitigate the consequences of an accident. The NRC was initially notified of this event on December 14, 2012 (i.e., Event Number 48596).
Event Description
On December 14, 2012, a modification to upgrade the Control Building [CB] fire detection system was in progress. This modification required smoke detectors to be inoperable and, in accordance with Technical Requirements Manual (TRM) Section 3.12, "CREV System Instrumentation," Condition F.1, the 2A subsystem of the Control Room Emergency Ventilation (CREV) system [VI] was placed in the radiation/smoke protection mode. This action prevented an auto-start of the 2B CREV subsystem and, as such, TS 3.7.3 Condition A was entered to restore the 2B CREV subsystem to operable status within 7 days.
At approximately 1306 hours0.0151 days <br />0.363 hours <br />0.00216 weeks <br />4.96933e-4 months <br /> Eastern Standard Time (EST), during jumper installation to isolate a fire detector, electrical continuity was lost. This resulted in an invalid charcoal fire signal being sent to the 2A CREV subsystem circuitry; shutting down the operating 2A CREV subsystem. With 2A CREV subsystem shut down due to the signal, both the 2A and 2B CREV subsystems were inoperable and TS 3.7.3 Required Action C.1 (i.e., be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />) applied for both Unit 1 and Unit 2.
TS 3.7.3 Required Action C.1 was exited within approximately two minutes by restarting the 2A CREV subsystem.
Event Cause The direct cause of the loss of the CREV function was an invalid charcoal fire signal caused by a loss of electrical continuity that occurred during jumper installation which shut down the operable 2A CREV subsystem. The apparent cause of the event was inadequate documentation and communication of the required system alignment.
As planned, implementation of the modification resulted in loss of Smoke Detection capability for a very short period of time. Per, Condition F of TRM 3.12, this would require the CREV system to be placed in the radiation/smoke protection mode of operation with a Completion Time of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. It was assumed that the duration of this condition would be less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and that the Required Compensatory Measure would not be implemented. This assumption was not clearly documented or communicated. Ultimately, this Event Cause (continued) led to parallel versus sequential scheduling of the tasks in Progress Reporter (i.e., the scheduling tool used at BSEP) and the decision to place the 2A CREV subsystem in the radiation/smoke protection mode of operation in support of the modification without recognizing the inconsistency or properly risk assessing the potential impact of the inconsistency on 2A CREV subsystem operability.
Safety Assessment The safety significance of this condition is considered minimal. The CREV function was only inoperable for approximately two minutes. Although considered inoperable, the 2B CREV subsystem remained available and could have been placed in service at any time by alternating the A and B subsystem control switches.
Corrective Actions
Any changes to the corrective actions or schedules noted below will be handled in accordance with the site's Corrective Action Program.
The following corrective action has been completed.
The Major Projects planning template, controlled by WO Planner Guide for Projects, Revision 4, dated April 10, 2013, has been be revised to require a brief summary of the (1) equipment impact, (2) plant impact, and (3) potential plant impact resulting from the work. The summary of each topic shall include a discussion of any assumption used to support the conclusion.
Previous Similar Events
A review of LERs and corrective action program condition reports for the past three years identified the following previous similar occurrences.
Conditioning due to a Control Building instrument air dryer failure. The failure of the Control Building instrument air dryer was due to low refrigerant pressure leading to ice blockage of the instrument air supply line. Corrective actions included replacing the instrument air dryer and a procedure revision to bypass the dryer when low refrigerant pressure conditions exist. The actions from LER 1-2011-003 could not have reasonably been expected to prevent the condition reported in LER 1-2012-007.
Emergency Bus E-7 main feeder breaker. The cause was determined to be a spurious actuation of the solid state trip unit on the E-7 breaker. The corrective action was to replace the E-7 breaker. The actions from LER 1-2011-001 could not have reasonably been expected to prevent the condition reported in LER 1-2012-007.
Previous Similar Events (continued) Conditioning due to blockage of air flow through the Control Building instrument air dryer due to freezing of condensate within the cooling coil. The corrective actions to prevent recurrence included procedure revisions to ensure proper operation of the Control Building Heating Ventilation and Air Conditioning system during cold weather operation. The actions from Commitments No regulatory commitments are contained in this report.