05000423/LER-2014-004
| Docket Number | |
| Event date: | 12-12-2014 |
|---|---|
| Report date: | 02-09-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 50676 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 4232014004R00 - NRC Website | |
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1. EVENT DESCRIPTION:
On December 12, 2014, with Millstone Power Station Unit 3 (MPS3) at 100% power and in operating mode 1, an operator discovered a door for the MPS3 East Motor Control Center Rod Control area would not latch upon exit from the room. Upon discovery of the door not properly latching, the door was declared non-functional. Since this door is a dual train High Energy Line Break (HELB) boundary door, it affected the operability of both trains of 480 volt safety related switch gear. Plant Technical Specification (TS) 3.0.3 was entered. The latching mechanism was manually manipulated and lubricated by maintenance personnel. Proper operation of the door was restored within 35 minutes of being identified not functioning properly and TS 3.0.3 was exited. This door was then tested over a dozen times without failure.
On January 15, 2015, with MPS3 at 100% power and in operating mode 1, an individual processed through the door normally and upon checking the door after passage the worker noted the door did not latch. The Control Room was promptly notified. The door was repaired and retested satisfactorily. The door was inoperable for approximately 19 minutes. TS 3.0.3 was entered and exited appropriately.
These events were reported to the NRC pursuant to 10 CFR 50.72(b)(3)(D), (NRC event # 50676 and 50737 respectively) as a condition that could have prevented the fulfillment of a safety function for systems needed to mitigate the consequences of an accident. These events are also being reported pursuant to 10 CFR 50.73(a)(2)(v)(D), as a condition that could have prevented the fulfillment of a safety function for systems needed to mitigate the consequences of an accident.
BACKGROUND:
This door fulfills the requirements of a Security Door, Technical Requirement Manual Fire Door, CO2 Door, Dual Train Protection Door, and a HELB Door. It is a key card actuated door with a crash bar on one side and a thumb latch on the other side. The door is part of the HELB barrier for the A and B 480 volt switchgear.
2. CAUSE:
The door passage mechanism consists of a crash bar on one side of the door and a lockset thumb piece, connected to the latch mechanism in the lockset, on the other side. Utilizing the thumb piece/crash bar causes the lock-set latch to retract into the lockset, unlocking the latch from behind the strike. When the strike is activated by the personnel security key card, the strike releases the latch. Personnel are then required to simply push the door open. Once the door is opened, the strike resets to its original locked position. The door then closes and latches. The door is now locked in the closed position preventing the door from opening. After the door is unlocked utilizing the security key card, if personnel accessing the door use the crash bar or the thumb piece to open the door, instead of simply pushing the door open, the lockset latch sometimes retracts far enough into the lockset to jam inside the lockset and fails to return to its normal position, behind the strike, thus leaving the door unlatched. The use of the crash bar/thumb piece is intended for emergency use only and not intended for normal passage.
Although no definite failure mechanism was identified, there have been several occasions where a security door lockset has been jammed due to usage of the emergency use only door hardware (crash bar/thumb piece).
3. ASSESSMENT OF SAFETY CONSEQUENCES:
Given the low likelihood of an Auxiliary Building HELB occurring during either time the door was not properly latched (35 minutes on December 12, 2014 and 19 minutes on January 15, 2015), the consequences of these events are of very low safety significance.
4. CORRECTIVE ACTION:
In both cases the door latching mechanism was manually manipulated and lubricated by maintenance personnel. The door was then tested several times satisfactorily. Additional inspection did not find any additional foreign material in the lockset mechanism.
Additionally, management has issued a special communication to remind plant personnel that security doors should only be pushed or pulled and not to use the crash bar or door thumb piece/knob/lever except for an emergency. Additional corrective actions are being taken in accordance with the station's corrective action program.
5. PREVIOUS OCCURRENCES:
MPS2 2011-005-00, Enclosure Building Rendered Inoperable Due to Degraded Door Seal.
6. Energy Industry Identification System (EIIS) codes
- Door — DR
- Switchgear — SWGR