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| Entered date | Event description | |
|---|---|---|
| ENS 48341 | 25 September 2012 15:11:00 | During maintenance on 4160V Bus 12 ammeter, a Bus 12 lockout occurred. The station power was from 1R Reserve transformer for work on the 2R Auxiliary transformer. Net effect was Bus 12 locked out, removing power from 12 Reactor Feed Pump and 12 Reactor Recirculation pump. Reactor level lowered to +23 inches then began to rise. With both Main Feed Reg Valves in AUTO, the level transient reached +48 inches, the Reactor Water Level Hi Hi setpoint. The Main Turbine and 11 Reactor Feed Pump tripped as designed, and a Reactor SCRAM occurred. Reactor water level began to drop, and C.4.A Abnormal Procedure for SCRAM was used to restart 11 Reactor Feed Pump and recover water level. Minimum water level reached was -26 inches. Reactor Low Level SCRAM signal and Group 2 Primary Containment isolation occurred at +9 inches as designed, No Safety Relief valves lifted during this transient. High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC) did not receive an initiation signal due to not reaching their setpoints. There were no Emergency Core Cooling Systems initiation setpoints reached. Prior to the event, both divisions of Standby Liquid Control were inoperable as part of planned maintenance. All control rods fully inserted. Decay heat is being removed through the turbine bypass to the main condenser. The plant is in a normal shutdown electrical lineup and stable in Mode 3. The licensee has notified the NRC Resident Inspector and will notify the State and local governments. |
| ENS 47909 | 8 May 2012 17:06:00 | At 0900 (CDT) on May 8, 2012, it was determined that Monticello Nuclear Generating Plant did not meet Technical Specification Limiting Condition for Operation 3.3.8.1 because the requirement of Table 3.3.8.1-1 for the 4.16 KV Essential Bus Degraded Voltage time delay transfer to the Emergency Diesel Generators (EDGs) of 9.2 seconds could not be met under all postulated conditions. The degraded transfer scheme has the ability to transfer to an intermediate offsite source (1AR) which under a degraded voltage condition, coincident with an accident, would delay the transfer to the EDGs an additional 5 seconds. Both EDGs were subsequently declared inoperable. As an interim action 1AR transformer has been removed from service. This eliminates the unanalyzed condition, restores Technical Specification compliance, and restores both EDGs to an operable condition. Additionally this event is being reported under criteria 10 CFR 50.72(b)(3)(v)(D) - Accident Mitigation. The NRC Resident Inspector has been notified. |
| ENS 47725 | 8 March 2012 13:40:00 | At 0954 on 3/8/12 Xcel Energy notified the Minnesota Pollution Control Agency of an Amertap ball release exceeding 1.5 barrels per agreement. Three barrels of Amertap balls are unaccounted for. Plant operational personnel are inspecting the site water system for unaccounted Amertap balls. A survey of the river performed by personnel only produced 4 of the missing balls. The licensee notified the NRC Resident Inspector. |
| ENS 46394 | 4 November 2010 17:22:00 | On November 4, 2010, at 11:28 AM both doors in airlock 124 from secondary containment to access control were simultaneously open for a period <5 seconds. The doors were immediately closed. This condition resulted in an unplanned entry into Technical Specification 3.6.4.1.A for secondary containment. The condition could have prevented the Standby Gas Treatment System from developing a negative pressure within secondary containment following a design basis accident. This negative pressure is required to prevent ground consequences following an accident. The Standby Gas Treatment System remained operable throughout the event. The licensee was decreasing power at the time of the report for a condition unrelated to the report. The licensee will notify the Minnesota Duty Officer. The licensee notified the NRC Resident Inspector. |
| ENS 46113 | 21 July 2010 11:39:00 | At 0816 (CDT) on 7/21/2010, the Monticello Nuclear Power Generating Plant (MNGP) received a report from the Sherburne County Sheriff Dispatcher that there had been an inadvertent manual initiation of Emergency Preparedness sirens in the county while performing siren testing. All plant conditions/parameters are normal. A total of 48 emergency sirens were on for approximately 1 minute before being secured. The inadvertent initiation of the sirens was determined to be reportable under 10 CFR 50.72(b)(2)(xi), 'News Release or Notification of Other Government Agency.' Sherburne County, the State of Minnesota, and the site NRC Resident Inspector have been notified. |