05000333/LER-2009-004
| James A. Fitzpatrick Nuclear Power Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3332009004R00 - NRC Website | |
BACKGROUND
On January 31st 2009, the Control Room Chiller Room to Control and Relay Room Fan Room door (70D0R-A 300-5) was found unlatched. The door was relatched and a condition report was entered to document the condition. Since there was no history of problems with this door and no work being performed in the area, this was considered to be an isolated event. The cause was attributed to human error, in that an individual failed to appropriately latch the door after passing through it. Based on normal operations rounds and routine entry into the area, it was considered that the door had not been unlatched for a significant period of time, compensatory measures were available, and the boundary was restored within the Technical Specification completion time for an inoperable control room envelope, therefore no report was required. Considering that there was no history of problems with this door, the relatching of the door and reemphasizing the expectation to insure that doors are properly latched after passing through them was considered to be adequate corrective action.
On March 3, 2009 work began to replace the single personnel access door to the Control Room Chiller Room with a double door to facilitate replacement of the control room chillers. The replacement was completed March 12, 2009. On March 19th, 2009, after the replacement of the Control Room Chiller Room door, door 70D0R-A 300-5 was found to be unlatched. This occurrence on March 19th was again attributed to human error since contract personnel were working in the area to replace ventilation equipment. Contract personnel working in the area were briefed at this time on the event and the need to insure the door was closed and latched.
Additionally, Operations personnel were briefed to increase their periodic rounds in the area to ensure the door was closed and latched. A condition report was written to document the occurrence.. This condition report was reviewed by the condition review group after the weekend on Monday March 23, 2009.
On March 23rd, door 70D0R-A-300-5 was again identified unlatched and was subsequently relatched. A condition report was not immediately written to document this occurrence. Then on March 24, 2009, the door was found unlatched for the third time since March 19th. At this time the control room envelope (CRE) boundary was declared inoperable, and TS 3.7.3 Condition B was entered at 1335 hours0.0155 days <br />0.371 hours <br />0.00221 weeks <br />5.079675e-4 months <br />, a new Condition Report was written, and the maintenance department initiated corrective maintenance on the door latching mechanism.
During the subsequent investigation, it was discovered that air flow changes in the area due to the other doors (Control Room Chiller Room Doors) being open to support ventilation equipment replacement, could cause door 70D0R-A-300-5 to become unlatched. Airflow changes could cause the subject door to slightly flex in its opening which in turn would relieve the latching force on the surface mounted friction latch. The latch was designed such that the handle represented a larger moment arm than the latching arm thus causing the latch to rotate open if the normal differential pressure across the door changed relieving the pressure on the latch. The replacement of the single chiller room door with a double door to facilitate replacement of the control room chillers may have contributed to the noted airflow changes. The area of the opening was significantly increased, therefore, the perturbation in the air flow was potentially greater. Although wear on the friction latch was identified as the mechanistic cause of the March 2009 occurrences, it is notable that other than an isolated occurrence in January 2009, there was no history of problems with 70D0R-A-300-5 becoming unlatched, until the Control Room Chiller Room door was replaced with a double door set and work requiring the opening of the double doors was in progress.
An engineering evaluation of the door configuration and Control Room Emergency Ventilation System (CREVAS) performance parameters determined that operability of the control room envelope integrity could not be assured. The engineering evaluation determined that the since the door could not be assured to maintain BACKGROUND (continued) integrity of the CRE as required by the Technical Specifications to mitigate the consequences of an accident (as discussed below), the deficiency is reportable under 10 CFR 50.73(a)(2)(v)(D). Because the Actions for Condition B require immediately establishing compensatory actions and the time that the subject door was unlatched is indeterminate, the condition also represents a violation of Technical Specifications and is reportable under 10 CFR 50.73(a)(2)(i)(B).
In the event of an accident involving a significant release of radioactive material (a release sufficient to cause the control room supply radiation monitor high alarm to annunciate), the control room ventilation system is manually placed in the isolate mode of operation. In the isolate mode, the inlet and exhaust motor operated dampers and valves close (the inlet bypass damper is also closed manually) and one of two redundant emergency ventilation supply fans with its associated filter train is placed in service. With the emergency supply fan in service, outside air is filtered by a filter train consisting of a pre-filter, high efficiency particulate air (HEPA) filter, two charcoal filters in series 'and a second HEPA filter. The emergency supply fan provides outside air to maintain acceptable air quality (replenish oxygen) and to ensure a positive pressure greater than or equal to 0.125 in. water gage is maintained within the control room. Air is exhausted from the space within the CRE by leakage through and from the CRE. (Some leakage through the CRE is required to allow supplying filtered outside air to the space.) Door 70D0R-A-300-5 is an element of the CRE. The CRE supports the ability of the control room ventilation system to maintain control room habitability following 'an accident. Engineering evaluation has shown that the CRE cannot be maintained if door 70D0R-A-300-5 is open.
EVENT DESCRIPTION
On March 24th CRE boundary door 70D0R-A-300-5 (Control Room Fan room to Control Room Chiller room) was discovered to be unlatched. The door was re-latched immediately, Technical Specification 3.7.3 Condition B for an inoperable Control Room Envelope was entered and the maintenance department was directed to begin trouble shooting and repair activities. During the trouble shooting it was determined that flexing the door a small amount would cause the door to unlatch.
Over the previous week there had been two other occurrences where the door was discovered unlatched.
Based on the discovery that wear on the latch contributed to the door becoming unlatched it was determined that the CRE boundary should have been considered inoperable on March 19th, 2009 and remained inoperable until the degraded latching mechanism was repaired. Since the immediate actions of Technical Specification 3.7.3 Condition B were not completed until March 24th the event is reportable under both 10 CFR 50.73(a)(2)(i)(B) (violation of Technical Specifications) and 10 CFR 50.73(a)(2)(v)(D) (Loss of a Safety Function).
EVENT ANALYSIS
Differential pressure between the control room and surrounding areas is measured during surveillance testing.
These measurements show that the control room ventilation equipment room is maintained at higher pressure than the chiller room with the system in isolate. These measurements also show that the control room chiller room is maintained at higher pressure than surrounding areas. If the door between the equipment and chiller rooms is unlatched, the door will open until a force balance between equipment room pressure and door closing force is achieved. This will result in lowering equipment room pressure and increasing chiller room pressure.
The redistribution of pressure has the potential to increase the leakage from the CRE with a consequent increase in the rate of unfiltered in-flow to the envelope. There is also a potential that the system will be unable to maintain the control room pressure at least 0.125 inches of water gage above the surrounding areas. Due to the potential increase in inleakage, there could be a negative effect on air quality in the CRE. There are proceduralized compensatory measures that would be implemented should the air quality in the control room deteriorate.
CAUSE OF EVENT
The door latch at the time of the event was a friction latch. The latch design was such that the door handle had a larger moment than the latch arm. When the latch became worn, the friction fit relaxed and the mechanism became susceptible to unlatching, due to vibration or pressure changes in the room.
EXTENT OF CONDITION
Door 70D0R-A-300-5 is a non-rated, commercial bi-parting swinging door that is normally held closed by a surface mounted friction latch. The extent of condition is limited to this door, because this is the only door provided with a friction style surface mounted latch. Therefore, the condition is unique and does not extend to other components.
FAILED COMPONENT IDENTIFICATION
The latch for the Control Room Fan room to Control Room Chiller room door, 70D0R-A-300-5.
CORRECTIVE ACTIONS
Immediate Corrective Action(s):
1) Control Room Envelope Boundary door 70D0R-A-300-5 latch was repaired. The latch mechanism was disassembled, fasteners tightened, lubricated, and restored. Door functionality was accepted by Operations.
Completed Corrective Action(s):
1) The surface mounted friction latch for Control Room Envelope Boundary door 70D0R-A-300-5 was replaced with a heavy-duty cylinder style lockset with a mortised style deadlocking latch.
With the door unlatched, the control room pressure could have maintained a higher pressure than in the surrounding area, however, the control room pressure might not have met the minimum 0.125 inches of water gage pressure requirement. Should there have been a need to isolate the CRE, any degradation in the CRE atmosphere could have been compensated for by using the breathing air manifold and self contained breathing apparatus staged in the Control Room. Therefore, this condition did not represent a significant safety issue.
SIMILAR EVENTS
No similar event has occurred at JAF during the past ten (10) years.
REFERENCES
JAF Condition Report CR-JAF-2009-00387 JAF Condition Report CR-JAF-2009-01021 JAF Condition Report CR-JAF-2009-01070.
NUREG-1022, Rev. 2, Section 3.2.7.
JAFNPP Technical Specification 3.7.3 JAFNPP Technical Specifications Bases B 3.7.3