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Category:NRC Preliminary Notification of Event/Occurrence
MONTHYEARPNO-III-23-001A, Update to Preliminary Notification of Event or Unusual Occurrence - PNO-III-23-0012023-07-21021 July 2023
PNO-III-23-001A: Update to Preliminary Notification of Event or Unusual Occurrence - PNO-III-23-001
PNO-III-23-001, Monticello Nuclear Plant Unplanned Shutdown Due to Increased Tritium Levels2023-03-27027 March 2023
PNO-III-23-001 Monticello Nuclear Plant Unplanned Shutdown Due to Increased Tritium Levels
PNO-III-19-003, Monticello Nuclear Generating Plant Expiration of Security Supervisor Union Contract2019-08-29029 August 2019
PNO-III-19-003: Monticello Nuclear Generating Plant Expiration of Security Supervisor Union Contract
PNO-III-15-010, A UPDATE-Monticello Automatic Scram Due to Reactor Protection System Signal2015-12-0303 December 2015
PNO-III-15-010A UPDATE-Monticello Automatic Scram Due to Reactor Protection System Signal
ML15331A3442015-11-27027 November 2015
PNO-III-15-010 - Monticello Automatic Scram Due to Reactor Protection System Signal
PNO-III-14-001, A - Update to Monticello Shutdown Due to Reactor Coolant System (RCS) Pressure Boundary Leakage in Excess of Technical Specification Limits2014-02-0707 February 2014
PNO-III-14-001-A - Update to Monticello Shutdown Due to Reactor Coolant System (RCS) Pressure Boundary Leakage in Excess of Technical Specification Limits
ML14022A0222014-01-21021 January 2014
PNO-III-14-001: Monticello Shutdown Due to RCS Pressure Boundary Leakage in Excess of Technical Specification Limits
ML12234A6372012-08-20020 August 2012
Update to Monticello Shutdown Due to Drywell Unidentified Leakage Above Technical Specification Limits
ML12229A3152012-08-16016 August 2012
PNO-lll-12-009 - Monticello Shutdown Due to Drywell Unidentified Leakage Above Technical Specification Limits
PNO-III-11-016, A - Monticello Shutdowngreater than 72 Hours Due to Actuation of Reactor Protection Relays Sensing Low Turbine Control Valve Hydraulic Pressure (Update)2011-12-12012 December 2011
PNO-III-11-016-A - Monticello Shutdowngreater than 72 Hours Due to Actuation of Reactor Protection Relays Sensing Low Turbine Control Valve Hydraulic Pressure (Update)
ML11327A0262011-11-22022 November 2011
PNO-III-11-016, Monticello - Shutdown Greater than 72 Hours Due to Actuation of Reactor Protection Relays Sensing Low Turbine Control Valve Hydraulic Pressure
PNO-III-11-015, A, Monticello - Unplanned Shutdown Greater than 72 Hours Due to a Loss of the Auxiliary Power Transformer (Update)2011-10-28028 October 2011
PNO-III-11-015A, Monticello - Unplanned Shutdown Greater than 72 Hours Due to a Loss of the Auxiliary Power Transformer (Update)
ML11298A0652011-10-25025 October 2011
PNO-III-11-015, Monticello - Unplanned Shutdown Greater than 72 Hours Due to a Loss of the Auxiliary Power Transformer
PNO-III-11-008, A - Monticello - Update to Monticello Shutdown Greater than 72 Hours Due to a Leaking Safety Relief Valve2011-06-29029 June 2011
PNO-III-11-008A - Monticello - Update to Monticello Shutdown Greater than 72 Hours Due to a Leaking Safety Relief Valve
ML11178A0192011-06-27027 June 2011
PNO-III-11-008, Monticello Shutdown Greater than 72 Hours Due to a Leaking Safety Relief Valve
PNO-III-08-009, A, Monticello - Unplanned Shutdown Greater than 72 Hours - Update2008-09-29029 September 2008
PNO-III-08-009A, Monticello - Unplanned Shutdown Greater than 72 Hours - Update
PNO-III-08-010, Monticello - Loss of Offsite Power2008-09-17017 September 2008
PNO-III-08-010: Monticello - Loss of Offsite Power
ML0825906682008-09-15015 September 2008
PNO-III-08-009, Monticello, Unplanned Shutdown Greater than 72 Hours
PNO-III-07-001, A - Monticello Reactor Shutdown Due to Turbine Control Valve Failure (Update)2007-01-22022 January 2007
PNO-III-07-001A - Monticello Reactor Shutdown Due to Turbine Control Valve Failure (Update)
ML0701202562007-01-12012 January 2007
PNO-III-07-001: Monticello Reactor Shutdown Due to Turbine Control Valve Failure (Event Notification EN 43088)
2023-07-21
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January 22, 2007 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE -- PNO-III-07-001A This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verification or evaluation, and is basically all that is known by the Region III staff on this date.
Facility Licensee Emergency Classification Monticello Notification of Unusual Event Nuclear Management Co. Alert Monticello, MN Site Area Emergency Docket: 50-263 General Emergency License: DPR-22 X Not Applicable
SUBJECT:
MONTICELLO REACTOR SHUTDOWN DUE TO TURBINE CONTROL VALVE FAILURE (UPDATE)
DESCRIPTION:
At 3:28 p.m. CST on January 10, 2007, the reactor shut down automatically from 90 percent power after all four turbine control valves unexpectedly opened. The open control valves caused a decrease in main steam line pressure which led to the automatic shutdown. All safety systems functioned as designed.
The licensee subsequently identified that welds on the supports for the turbine control valve actuator box had failed and that the box had shifted downward about 6 inches. The downward shift caused the control valves to open and overrode the signals from the pressure regulating system.
The licensee determined that the failure of the control valve support structure was caused by inadequate design of the structure combined with shortcomings in weld quality dating from original construction. The final failure occurred after a series of intermediate weld failures which caused loads to be redistributed to other portions of the support structure, eventually resulting in failure of the remaining welds. The licensee has redesigned the actuator box support structure and will complete the installation of the modified design prior to restart.
The licensee inspected the main steam lines, located beneath the actuator box, and found no damage to the piping. The licensee staff also inspected other support structures to determine whether conditions similar to those identified on the actuator box supports exist, and no deficiencies were identified.
The NRC resident inspectors, assisted by two inspection specialists from the Region III office, have reviewed the licensees modification to the actuator box support structure and the associated engineering design. The inspectors did not identify any issues during this review.
The resident inspectors will observe portions of the plant restart including the approach to criticality and the restart of the turbine.
The State of Minnesota has been informed.
This information has been discussed with licensee management and is current as of 11:30 a.m. CST, January 22, 2007.
CONTACTS:
Stuart Sheldon Nirodh Shah Bruce Burgess 630/829-9727 630/829-9821 630/829-9629
