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At 1830 (CST) on December 9, 2014 Door 410B, a HELB (High Energy Line Break) door between the east and west sides of the ground floor of the reactor building, was found closed. This door is one half of a pair of double doors that are normally open to provide a HELB energy and flooding release path to mitigate postulated HELB events. The closed HELB door has the potential to impact safe shutdown by exposing both divisions of safe shutdown components to unanalyzed environmental conditions. With the potential loss of both divisions of safe shutdown equipment, no safe shutdown path would exist. This condition is being reported as an unanalyzed condition as defined by (10 CFR) 50.72(b)(3)(ii)(B). The HELB door was immediately opened and returned to normal configuration. Door 410A remained open during the time that Door 410B was closed and provided an available, but not yet analyzed, release path that could have mitigated the consequences of this event. The health and safety of the general public was not impacted as a result of this condition. The NRC Resident Inspector has been notified.

• * * RETRACTION FROM JON LAUDENBACH TO CHARLES TEAL ON 1/30/15 AT 1513 EST * * *

Further analysis has determined that the condition did not significantly degrade plant safety. Door 410B in the Reactor Building was found closed. This door is one half of a pair of double door (Doors 410A and 410B) that normally open to provide a High Energy Line Break (HELB) energy and flooding release path to mitigate postulated HELB events. The condition of one half of the double door closed was not previously analyzed. A subsequent completed engineering evaluation analyzed this condition, Door 410B being closed and Door 410A being open, for the following environmental conditions: peak compartment temperatures, block wall differential pressure, radiation dose, and flooding. The environmental conditions found the Reactor Building in response to Door 410B being closed with 410A being open does not affect the operability of safety related equipment housed within the Reactor Building or the ability to safely shut-down the plant and maintain the plant shutdown condition following a HELB event. The NRC Resident Inspector has been notified. Notified R3DO (Dickson).

At 1258 CDT on 07/05/2012, Operations was notified that both panels of Door 45 (south doors for the reactor building railroad bay airlock) were blocked by a man lift. Blocking both doors represents an unanalyzed condition as a flow path through the door is assumed for pressure relief during postulated HELB events. The man lift was immediately removed correcting the situation and all work related to Door 45 was stopped. Door 45 was blocked for approximately 20 minutes. The NRC Resident Inspector has been notified.

• * * RETRACTION FROM BART BLAKESLEY TO DONALD NORWOOD AT 1605 EDT ON 8/31/2012 * * *

The purpose of this notification is to retract the previous Event Notification Report (#48072) made by the Monticello Nuclear Generating Plant on 7/5/2012. The initial report indicated that blocking both panels of the railroad bay doors by a man lift represented an unanalyzed condition, as a flow path through the door is assumed for pressure relief during postulated HELB events, and was reported in accordance with 10CFR50.72(b)(3)(ii)(B), Unanalyzed Condition. Since the initial report, Engineering has completed an evaluation that demonstrates equipment supporting safe shutdown would have been capable of performing their specified design function during postulated HELB events. Based on this analysis, the condition initially reported in EN #48072 did not result in an unanalyzed condition that significantly degraded plant safety and is therefore retracted. The NRC Resident Inspector has been informed of this retraction. Notified R3DO (Cameron).

On 8/6/09 at 0600 hours CDT the Monticello Nuclear Generating Plant's Technical Support Center uninterruptable power supply will be isolated to perform a planned maintenance activity. The maintenance activity requires implementation of compensatory measures to maintain TSC functions during the activity. The compensatory measures include having the Emergency Director report to the Control Room and co-locating the remaining TSC staff at the EOF should an event be declared requiring ERO activation. The ERO has previously successfully demonstrated the ability to implement these compensatory measures. The maintenance activity is scheduled to be completed with the TSC returned to full functionality by the end of the dayshift on 8/6/09. The Site Emergency Response Organization has been notified of the maintenance activity and instructed on the planned compensatory measures to be implemented during the activity. MNGP will notify the NRC upon completion of the activity restoring full TSC operability. This event is considered reportable per 10CFR50.72(b)(3)(iii). The licensee has notified the NRC Resident Inspector.

* * * UPDATE FROM D. BARNETT TO P. SNYDER AT 1943 ON 8/6/09 * * * 

On 8/6/09 at 1700 CDT the Monticello Nuclear Generating Plant's Technical Support Center was returned to service and declared functional. The Monticello Emergency Response Organization has been notified and the compensatory measures that were in effect have been terminated. The licensee has notified the NRC Resident Inspector. Notified R3DO (Skokowski).

At 1616 on 12/15/08, a plant heating boiler trip resulted in a loss of a reactor building ventilation. The loss of reactor building ventilation resulted in maximum average main steam chase temperatures greater than or equal to 165F. High energy line break (HELB) analysis of piping in the steam chase assumes an initial average temperature prior to the break of 165F. Temperature greater than or equal to 165F in the steam chase challenges EQ qualification of the piping analysis. Abnormal procedures for loss heating boiler and ventilation system failure were entered. C.3 (Shutdown) and C.5-1300 (secondary containment control) were also entered. The plant heating boiler was restarted and ventilation restored prior to power reduction. All systems have been returned to normal. The licensee notified the NRC Resident Inspector.

• * * RETRACTION PROVIDED FROM DAVID BARNETT TO JOE O'HARA AT 1158 ON 2/6/09 * * *

The licensee is retracting this report based on the following: Monticello is retracting the event reported based on further evaluation, which found that the issue was not an unanalyzed condition that seriously degraded plant safety. The investigation of the event found the peak temperature achieved was 167.2 degrees F and the condition lasted for approximately 11 minutes. Engineering review of Safety System Components found no impact on the equipment for the temperature reached, Additionally, revised High Energy Line Break (HELB) calculations performed with an initial average Steam Chase Room temperature of 180 degrees F before a HELB determined that Safety System components could perform their safety functions. The station has identified the cause for the event and corrective actions will be tracked in the station's corrective action program. Since there was no impact on the equipment in either Environmental Qualification (EQ) or safety function, the temperature of the event was less than the revised calculation temperature, and the unanalyzed condition that existed in the initial event notification report no longer exists and did not result in a condition that seriously degraded plant safety, this event can be retracted. The licensee informed the NRC Resident Inspector. Notified R3DO (Ring).