05000263/LER-2009-005

LER-2009-005,

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
2632009005R01 - NRC Website

Event Description

Door-18 [DR], Turbine Building 911' East Door of Condenser Area (Inside), was discovered in the closed position by an operator on 8/20/09 during performance of the Turbine Building East 0800 operator rounds. The normally open position of the door is necessary to maintain the plant in the configuration required by the plant's High Energy Line Break (HELB) analysis. The closed door resulted in entering TS LCO 3.0.3 for plant shutdown. The door was subsequently opened to restore the HELB energy release path. The TS LCO 3.0.3 was exited. A fire impairment was initiated for the non-functional fire door. At 15:00 on 8/20/09 a new fusible link (identical to the failed link) was installed and the fire protection impairment was exited.

Event Analysis

The event was reported to the NRC on August 20, 2009 under 10 CFR 50.72(b)(3)(ii)(B) - Degraded or Unanalyzed Condition and 10 CFR 50.72(b)(3)(v) — Event or Condition that could have prevented Fulfillment of a Safety Function. A Licensee Event Report is required for this event under 10 CFR 50.73(a)(2)(ii)(B) — Degraded or Unanalyzed Condition.

In the August 20, 2009 event notification to the NRC under 10 CFR 50.72, the station reported a potential Safety System functional failure. A detailed evaluation performed by the station determined that the station would have maintained at least one source of off-site power and no safety function failure would have occurred due to the postulated event.

Therefore the station is not reporting a failure to fulfill a safety function in this LER.

Safety Significance

On August 20, 2009, fire/HELB Door-18 was found to be in the closed position due to a failed fusible link. This condition existed for a maximum of approximately one day, subjecting the lower (Division I) 4KV [EA] switchgear [SWGR] to failure due to flooding in the event of a feedwater [SJ] HELB in the east Turbine Building 911' elevation. Both divisions of 4KV switchgear were originally declared inoperable as a result of the failed fusible link. Division I 4KV switchgear was considered inoperable due to the potential HELB flooding vulnerability described above. Division ll 4KV switchgear was initially considered inoperable since severe flooding of the lower 4KV switchgear room could potentially lead to a loss of offsite power to both divisions of 4KV, leaving only the Emergency Diesel Generator (EDG) [EK] as the sole source of power to the Division II essential safety systems. Under the HELB requirements the EDG cannot be counted upon due to the need to assume a concurrent single active failure.

Risk of core damage or large early release from this event at Monticello is a small fraction of a HELB event probability, considering there is significant and redundant capability to perform all critical safety functions given the loss of equipment resulting from the HELB event and coincident barrier failure. Unless the Division II EDG experiences a random failure, a full complement of Emergency Core Cooling System (ECCS) [BM] equipment is available to recover from the HELB event. Even with a randornfailure of this EDG, leading to a Station.

Blackout, Monticello has both high pressure and low pressure injection capability to safely accommodate a loss of all AC power.

In conclusion, the safety significance in terms of reactor safety and radiological release to the environment from door-18 being in the closed position for approximately one day is considered to be very low.

Cause

The root cause of the door-18 fusible link failure was due to cyclic overload caused by repeated door over travel. Causal Factors:

■ Door closer design allows excessive force on the fusible link.

■ Installation made the door closer more susceptible to over travel.

■ The narrow vestibule precludes setting of the door hold open position such that the door is out of traffic (normal hold open position should be 100 -140°) Corrective Action The following corrective actions have been taken or are being tracked under AR01194446:

• The failed fusible link was replaced.

• The site is investigating alternative HELB door configurations for modification to handle the worst case flooding loads and door 18 will be placed in a shut configuration. If this solution is found not to be practical, the door 18 closer will be evaluated to determine if a model less susceptible to link failure can be obtained.

Failed Component Identification Lewis C. Norton (LCN) series 4010, model 4011 Door Closer Catalog Id.: 6559286 Door Fusible Link Arm model 4010-3049FL

Previous Similar Events

fusible link was shorter than required and therefore resulted in the failure. A different link of the correct size was installed.