05000325/LER-2009-001
| Brunswick Steam Electric Plant (Bsep) | |
| Event date: | 01-21-2009 |
|---|---|
| Report date: | 03-22-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 44793 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3252009001R00 - 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 and Unit 2 were in Mode 1, operating at approximately 100 percent of Rated Thermal Power (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 of structures or systems that are needed to mitigate the consequences of an accident. The NRC was initially notified of this event on January 21, 2009 (i.e., Event Number 44793).
Event Description
The BSEP Control Building Heating, Ventilation and Air Conditioning (HVAC) Control Air system includes two safety-related instrument air compressors. These air compressors provide control air for the Control Building HVAC pneumatic controllers. If all control air is lost, the Control Room isolation dampers fail closed, rendering the Control Room Emergency Ventilation (CREV) system [VI] inoperable.
Also, the control room Air Conditioning (AC) subsystems are lost.
On January 21, 2009, at approximately 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br /> Eastern Standard Time (EST), a loss of Control Building Heating, Ventilation and Air Conditioning (HVAC) control air occurred. As a result, the two Control Room Emergency Ventilation subsystems required by Technical Specification (TS) 3.7.3, "Control Room Emergency Ventilation (CREV) System," and the three Control Room Air Conditioning subsystems required by TS 3.7.4, "Control Room Air Conditioning (AC) System," became inoperable. Because BSEP has a shared control room (CR), Unit 1 and Unit 2 entered TS 3.7.3 Required Action C.1, for two CREV subsystems inoperable (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 />) and TS 3.7.4, Required Action E.1, for three Control Room AC subsystems inoperable (i.e., enter Limiting Condition for Operation (LCO) 3.0.3 immediately).
Trouble shooting activities were initiated and it was determined that air pressure downstream of the instrument air dryer (i.e., 2-VA-INST-AIR-DRYER) was 0 psig. Appropriate pressure (i.e., 80 pisg) was verified at the two safety related instrument air compressors and 0 psig at the regulators which supplies air to the Control Room AC dampers. This was indicative of blockage either in the air dryer or moisture trap for the dryer. The moisture trap contained water and was not blocked. Therefore, it was concluded that the condensate within the cooling coil had frozen. After disconnecting the inlet and outlet lines to the dryer in an attempt to clear the lines, the air lines to the dryer were reconnected and pressure downstream of the Event Description (continued) dryer recovered to approximately 20 psig. Over a period of several minutes, pressure gradually recovered to between 80 and 100 psig air at the regulators.
Operability of the Control Room AC subsystems and CREV subsystems was restored and related LCOs, including TS 3.0.3, were exited at 1429 hours0.0165 days <br />0.397 hours <br />0.00236 weeks <br />5.437345e-4 months <br /> following the restoration of Control Building HVAC control air.
Event Cause The direct cause of the loss of control air to the control room ventilation system was blockage of air flow through the Control Building instrument air dryer due to freezing of condensate within the cooling coil.
The freezing was due to the failure to incorporate system operating parameters for temperature into the operating procedures associated with the Control Building HVAC system.
The control building instrument air dryer is located in the mechanical equipment room on the 70-foot elevation of the Control Building. Existing plant documentation provided information regarding the need to maintain the temperature in this room above 32 degrees F to support proper operation of equipment located in the room. However, existing plant procedures did not adequately ensure this would occur.
Low temperature in the mechanical equipment room (i.e., less than or equal to 45 degrees F) is annunciated in the Control Room. Procedure 2APP-UA-14, "Annunciator Procedure for Panel UA-14," directs Operations to perform cold weather operation checks in accordance with procedure 001-01.03, "Non- Routine Activities," if outside temperature is less than or equal to 40 degrees F and temperature forecast predicts freezing. For the 70-foot elevation of the Control Building, 001-01.03 directed operators to provide supplemental heating to maintain temperature above 32 degrees F in the vicinity of the chlorine detectors. However, these detectors are no longer used because water treatment was converted from chlorine to sodium hypochlorite in October 2007. Based upon the temperatures that occurred prior to the event, supplemental heating was not provided during the cold weather that occurred in January 2009. It has been concluded that, prior to abandoning use of the chlorine detectors, the existing room heaters, in conjunction with the supplemental heating implemented to maintain chlorine detector operability, likely provided sufficient heat in the mechanical equipment room to prevent failure of the instrument air system.
No procedural guidance existed to ensure instrument air dryer operability in the event of cold weather.
Safety Assessment The safety significance of this event is considered minimal. The condition existed for approximately 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 29 minutes. Plant staff took immediate action to return the equipment to service. For the brief time the Control Room AC and CREV systems were inoperable, performance of plant personnel and equipment in the Control Room was not adversely affected. The loss of CREV created a condition where positive pressure could not be maintained. There was no nuclear or industrial safety consequence from this event.
Corrective Actions
Corrective Actions to Prevent Recurrence
- Procedure 201-03.4.3, "Unit 2 Turbine Building Auxiliary Operator Daily Check Sheets," has been revised to include the necessary information to ensure the proper operation of the Control Building HVAC system during cold weather conditions. This procedure change was issued on March 6, 2009.
- The following procedures will be revised to include the necessary information to ensure the proper operation of the Control Building HVAC system during cold weather conditions.
o 2APP-UA-14, "Annunciator Procedure for Panel UA-14" This procedure change is currently scheduled to be completed by August 26, 2009.
o 001701.03, "Non-Routine Activities" This procedure change is currently scheduled to be completed by August 26, 2009.
o 00P-37, "Control Building Ventilation Systein Operating Procedure" This procedure change is currently scheduled to be completed by August 27, 2009.
Additional Corrective Actions
- Operability of the Control Room AC subsystems and CREV subsystems was restored at 1429 hours0.0165 days <br />0.397 hours <br />0.00236 weeks <br />5.437345e-4 months <br /> on January 21, 2009, following the restoration of Control Building HVAC control air.
- As an interim action, a portable heater was installed in the vicinity of the Control Building instrument air dryer. In addition, Operations established temperature monitoring of the Control Building mechanical equipment room, once per shift, to verify the temperature is 50 degrees F or higher. If the temperature is below 50 degrees F, the portable heater will be started.
Previous Similar Events
A review of LERs and corrective action program condition reports for the past three years identified the following similar events.
- LER 1-2006-001, dated March 9, 2006, "Control Rodin Emergency Ventilation (CREV) and Air Conditioning (AC) Inoperable Due to Loss of Control Air," documents an event where the CREV and AC systems were declared inoperable for Unit 1 and 2 due to the Control Building Instrument Air compressor failing to maintain pressure. The root cause of the event was determined to be ineffective condition monitoring of compressor oil pressure to detect hydraulic unloader Previous Similar Events (continued) degradation. The corrective actions to prevent recurrence associated with LER 1-2006-001 addressed the oil pressure trending and monitoring, and could not have reasonably been expected to prevent the condition reported in this LER.
- LER 1-2008-002 dated August 4, 2008, "Loss of Two Control Room Air Conditioning (AC) Subsystems," documents an event where the two operating Control Room AC subsystems tripped while replacing solenoid valves for the Control Building supply/exhaust fan dampers. The root cause of this event was determined to be a reliance on an Engineering Change calculation which did not adequately consider the impact of system material condition and resulted in an inadequate assessment of risk. The corrective actions to prevent recurrence revised the Preventive Maintenance (PM) tasks to use a Temporary Modification to keep the air conditioners running without requiring instrument air whenever the Control Room AC system solenoid valves are being replaced. The corrective actions associated with LER 1-2008-002 could not have reasonably been expected to prevent the condition reported in this LER.
- LER 1-2008-004, dated August 18, 2008, "Control Room Emergency Ventilation (CREV) Subsystems Inoperable Due to Failure to Isolate," documents an event where the failure of the Control Room washroom exhaust fan and damper to isolate resulted in the CREV system inoperable. The cause of this event was determined to be failure to identify appropriate PM routes for the CREV system components. The corrective actions to prevent recurrence developed PM tasks for the Control Building ventilation system dampers, actuators, limit switches, and relays. The corrective actions associated with LER.
Commitments No regulatory commitments are contained in this report.