Secondary Containment Degredation at Millstone

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Power Reactor Event Number: 47496
Region: 1 State: CT
Unit: [ ] [2] [ ]
RX Type: [1] GE-3,[2] CE,[3] W-4-LP
Notification Date: 12/03/2011
Notification Time: 16:53 [ET]
Event Date: 12/03/2011
Event Time: 12:35 [EST]
Last Update Date: 12/03/2011
Emergency Class: NON EMERGENCY
10 CFR Section:
50.72(b)(3)(v)(C) – POT UNCNTRL RAD REL
Person (Organization):


Unit SCRAM Code RX CRIT Initial PWR Initial RX Mode Current PWR Current RX Mode
2 N Y 100 Power Operation 100 Power Operation

Event Text


“On December 3, 2011 during operator rounds, it was discovered that an Enclosure Building (secondary containment) door sweep had failed and was not providing an adequate seal.

“Technical Specification (TS), ‘Secondary Containment Enclosure Building’, is applicable in Modes 1,2,3, and 4 was entered at 1235 [EST]. Since secondary containment was rendered inoperable, Dominion is reporting this as a condition that could have prevented the fulfillment of the safety function to control the release of radioactive material. The door has subsequently been repaired, the Enclosure Building declared OPERABLE and the TS Action Statement exited at 1524 [EST]. Further engineering review will be conducted to more fully evaluate the impact on radiological controls.

“This condition is being reported pursuant to 10 CFR 50.72(b)(3)(v)(C).”

The licensee has notified the Connecticut Department of Environmental Protection, surrounding towns and the NRC Resident Inspector.

The Millstone Nuclear Power Station is the only nuclear power generation site in Connecticut. It is located at a former quarry (from which it takes its name) in Waterford. Of the three reactors built here, units two and three are still operating at a combined output rating of 2020 MWe.

Unit 1

Millstone 1 was a General Electric boiling water reactor, producing 660 MWe, shut down in November 1995 before being permanently closed in July 1998. On February 20, 1996 a leaking valve forced the shutdown of this unit, and unit 2; multiple equipment failures were found.

  • Construction Permit Issued: May 19, 1966
  • Final Safety Analysis Report (FSAR) Filed: November 1, 1968
  • Provisional Operating License Issued: October 7, 1970
  • Full Term Operating License Issued: October 31, 1986
  • Full Power License: October 7, 1970
  • Initial Criticality: October 26, 1970
  • Synchronized to the Grid: November 1970
  • Commercial Operation: December 28, 1970
  • 100% Power: January 6, 1971
  • Leaking valve forced shutdown multiple equipment failures detected: February 20, 1996
  • Permanently Ceased Operations: July 21, 1998

Unit 2

Millstone 2 is a Combustion Engineering plant built in the 1970s, and has a maximum power output of 2700 MWth (870 MWe). It has 2 steam generators, and 4 reactor cooling pumps (RCP). It is currently undergoing an upgrade to its safe shutdown system which already met NRC standards. During its refueling outage in October 2006, the operator installed a new pressurizer.

  • Construction Permit Issued: December 11, 1970
  • Final Safety Analysis Report (FSAR) Filed: August 15, 1972
  • Full Term Operating Licensing Issued: September 26, 1975
  • Full Power License: September 26, 1975
  • Initial Criticality: October 17, 1975
  • Commercial Operation: December 26, 1975
  • 100% Power: March 20, 1976
  • “Stretch Power”: June 25, 1979
  • Operating License Extension Requested: December 22, 1986
  • Operating License Extension Issued: January 12, 1988
  • Full Term Operating License Expires: December 11, 2010
  • Operating License Expires: July 31, 2015
  • Extended Operating License Expires: July 31, 2035

Unit 3

Millstone 3 is a Westinghouse plant that started operating in 1986, and has a maximum power output of 3411 MWth (1150 MWe). Recently, the NRC approved a power uprate for Unit 3 that will increase its electrical output 7.006% to 3650 MWth (1230 MWe). The increase will take effect by the end of 2008.

  • Construction Permit Issued: August 9, 1974
  • Initial Criticality: January 23, 1986
  • Commercial Operation: April 23, 1986
  • Operating License Expires: November 25, 2025
  • Extended Operating License Expires: November 25, 2045


On February 26, 1996, A leaking valve forced the shutdown of units 1 and 2, multiple equipment failures were found.

On April 17, 2005, Millstone plant safely shut down without incident when a circuit board monitoring a steam pressure line short-circuited, which caused the board to malfunction and indicate an unsafe drop in pressure in the reactor’s steam system, when in reality there was no drop in steam pressure. The cause was attributed to “tin whiskers“. In response to this event, Millstone implemented a procedure to inspect for these whiskers at every refueling outage, or 18 months. David Lochbaum, a scientist affiliated with the Union of Concerned Scientists, while remaining critical of the processes leading to the discovery of the whiskers, praised Millstone for its handling of the situation.[7]

In September, 2009, unit-2 shut down when an electrical storm caused power fluctuations. When workers tried to restart the unit, they discovered a small leak in the reactor coolant pump. [8]

12/21/2009 Millstone Unit 3 Reactor Trip and Shutdown Greater Than 72 Hours.

07/27/2009 Millstone Unit 2 Reactor Trip and Shutdown Greater Than 72 Hours

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