Millstone Nuclear Power Plant

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Millstone Nuclear Power Plant
HD.6D.129 (10821944423).jpg
Millstone Nuclear Power Plant
Millstone Nuclear Power Plant is located in Connecticut
Millstone Nuclear Power Plant
Location of Millstone Nuclear Power Plant in Connecticut
Country United States
Location Waterford, Connecticut
Coordinates 41°18′43″N 72°10′7″W / 41.31194°N 72.16861°W / 41.31194; -72.16861Coordinates: 41°18′43″N 72°10′7″W / 41.31194°N 72.16861°W / 41.31194; -72.16861
Status Operational
Commission date Unit 2: December 26, 1975
Unit 3: April 23, 1986
Construction cost Unit 2: $424 million
Unit 3: $3.77 billion
Operator(s) Dominion Resources
Nuclear power station
Reactor type PWR
Reactor supplier Unit 2: Combustion Engineering
Unit 3:Westinghouse
Cooling source Long Island Sound
Cooling towers no
Power generation
Units operational Unit 2: 882 MW
Unit 3: 1,155 MW
Units decommissioned Unit 1
Nameplate capacity 2,037 MW
Average generation 16,385 GWh

The Millstone Nuclear Power Station is the only nuclear power generation site in Connecticut and the only multi unit nuclear plant in New England. It is located at a former quarry (from which it takes its name) in Waterford.

Following a Time magazine cover story on safety issues at Millstone, all three units were shut down. Units two and three were restarted and are still operating at a combined output rating of 2020 electrical megawatts, or MWe; unit one did not restart, permanently ceasing operations in July 1998.


The Millstone site covers about 500 acres (2 km²).[1] The power generation complex was built by a consortium of utilities, using Niantic Bay (which is connected to Long Island Sound and the Atlantic Ocean) as a source of coolant water.

Since opening in the 1970s, the plant has had numerous safety-related shutdowns and at times been placed on enhanced examination status by the Nuclear Regulatory Commission.[2][3]

In 1999 Northeast Utilities, the plant's operator at the time, agreed to pay $10 million USD in fines for 25 counts of lying to federal investigators and for having falsified environmental reports. Its subsidiary, Northeast Nuclear Energy Company, paid an additional $5 million for having made 19 false statements to federal regulators regarding the promotion of unqualified plant operators between 1992 and 1996.[4][5]

Millstone Units 2 and 3, both pressurized water reactors (one from Westinghouse and one from Combustion Engineering), were sold to Dominon Resources by Northeast Utilities in 2000 and continue to operate.

On November 28, 2005, after a 22-month application and evaluation process, Millstone was granted a 20-year license extension for both units 2 and 3 by the NRC.[6]

Licensing history and milestones[edit]

Work being performed on the containment structure at the Millstone Nuclear Power Plant.

Unit 1[edit]

Millstone 1 was a General Electric boiling water reactor, producing 660 MWe, shut down in November 1995 before being permanently closed in July 1998.

  • Construction permit issued: May 19, 1966[7]
  • Final safety analysis report filed: November 1, 1968
  • Provisional operating license issued: October 7, 1970[8][1]
  • Full term operating license issued: October 31, 1986
  • Full power license: October 7, 1970[1]
  • Initial criticality: October 26, 1970[9]
  • Synchronized to the grid: November 1970
  • Commercial operation: December 28, 1970
  • 100% power: January 6, 1971
  • The U.S. Nuclear Regulatory Commission began a safety investigation relating to refueling procedures, based on information provided by George Galatis, a senior nuclear engineer, 1995.[10]
  • Leaking valve forced shutdown multiple equipment failures detected: February 20, 1996
  • Permanently ceased operations: July 21, 1998[11]

Unit 2[edit]

Millstone 2 is a combustion engineering plant built in the 1970s, and has a maximum power output of 2700 thermal megawatts, or MWth (870 MWe). It has 2 steam generators, and 4 reactor cooling pumps. It is 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 filed: August 15, 1972
  • Full term operating licensing issued: September 26, 1975
  • Full power license: September 26, 1975
  • Initial criticality: January 17, 1975[9]
  • 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[edit]

Millstone 3 is a Westinghouse plant that started operating in 1986, and has a maximum power output of 3411 MWth (1150 MWe). In the summer of 2008, the NRC approved a power uprate for Unit 3 that increased its electrical output 7.006% to 3650 MWth (1230 MWe). The increase took effect by the end of 2008.[12]

  • Construction permit issued: August 9, 1974[1]
  • Initial criticality: January 23, 1986
  • Commercial operation: April 23, 1986
  • Operating license expires: November 25, 2025
  • Extended operating license expires: November 25, 2045

Safety and environmental events[edit]


In the summer of 1971, more than 2 million menhaden fish were killed on the intake screens of the plant's cooling system.[13][14][15]


In April 1972, 20-30,000 menhaden fish died when they were trapped in an intake lagoon that formed part of the cooling system.[16][17]

Over five days in 1972, the plant's primary cooling system[18] killed an estimated 150 million Atlantic fingerling menhaden.[19][20]


In December 1977, two hydrogen explosions occurred at the plant.[21][22] The second explosion injured one man, who required hospitalization.[23]


Between May and July 1978, the containment dome of Millstone unit 2 was periodically purged of its atmosphere in order to reduce radioactivity levels inside the dome.[24]


In October 1990, operator error during a routine test caused a shutdown of unit 2.[2] In September 1991, twenty reactor operators failed required licensing examinations. The shortfall of licensed operators necessitated a shutdown of unit 1 until March 1992.[2]


The U.S. Nuclear Regulatory Commission began a safety investigation relating to refueling procedures at Millstone unit 1, based on information provided by George Galatis, a senior nuclear engineer, in 1995.[25]


On February 26, 1996, a leaking valve forced the shutdown of units 1 and 2. Multiple equipment failures were found.[26][27] Time magazine featured the plant on its cover, calling its operator a "rogue utility", and the Nuclear Regulatory Commission singled out millstone for additional attention.[28][3][2]

Also in 1996, the plant released one gallon per hour of hydrazine into Long Island Sound. The plant's operators were convicted in 1999 for falsifying environmental records related to the hydrazine release.[5]

Following the Time article and the subsequent shutdown of all reactors, unit 2 restarted May 11, 1999 and unit 3 restarted July 1, 1998. Unit 1 was never restarted as the cost of remedying numerous safety issues was too high.[29]


In 2002 Millstone's operators were fined $288,000 USD for failing to have properly accounted for two uranium fuel rod components that had been misplaced 30 years earlier in 1972.[30]


On April 17, 2005, Millstone unit 3 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 on the board.[31] In response to this event, Millstone implemented a procedure to inspect for these whiskers at every refueling outage, or 18 months.[32]


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.[33]

On December 21, 2009 the Unit 3 reactor tripped and shut down for longer than 72 hours.[34]

On July 27, 2009, the Unit 2 reactor tripped and shut down for longer than 72 hours.

On August 9, 2013, the Unit 3 reactor trip and shut down due to a malfunction.


In 2016, unit 3 was shutdown following a hydrogen gas leak.[35]

Surrounding population[edit]

The Nuclear Regulatory Commission defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of 10 miles (16 km), concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about 50 miles (80 km), concerned primarily with ingestion of food and liquid contaminated by radioactivity.[36]

The 2010 U.S. population within 10 miles (16 km) of Millstone was 123,482, an increase of 29.5 percent in a decade, according to an analysis of U.S. Census data for The 2010 U.S. population within 50 miles (80 km) was 2,996,756, an increase of 9.5 percent since 2000. Cities within 50 miles include Hartford (41 miles to city center).[37]

Seismic risk[edit]

The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Millstone was Reactor 2: 1 in 90,909; Reactor 3: 1 in 66,667, according to an NRC study published in August 2010.[38][39]


  1. ^ a b c d Millstone Nuclear Power Station Unit 3, Operation: Environmental Impact Statement. 1985. pp. 19–. 
  2. ^ a b c d Paul W. MacAvoy; Jean W. Rosenthal (2005). Corporate Profit and Nuclear Safety: Strategy at Northeast Utilities in the 1990s. Princeton University Press. pp. 48–. ISBN 0-691-11994-5. 
  3. ^ a b National Academy of Engineering (16 September 2004). Accident Precursor Analysis and Management: Reducing Technological Risk Through Diligence. National Academies Press. pp. 24–. ISBN 978-0-309-09216-6. 
  4. ^ Hechinger, John. "Northeast Utilities Pleads Guilty To Polluting at Millstone Plant". The Wall Street Journal. Retrieved 18 December 2016. 
  5. ^ a b Allen, Mike. "A Record U.S. Fine at a Connecticut Nuclear Plant". The New York Times. Retrieved 18 December 2016. 
  6. ^ NRC Renews Millstone Nuclear Power Station Operating Licenses For An Additional 20 Years
  7. ^ Millstone Nuclear Power Station, Unit 2, Construction: Environmental Impact Statement. 1973. 
  8. ^ Transactions of the American Nuclear Society. Academic Press. 1972. 
  9. ^ a b Janette Sherman (1 May 2014). Life's Delicate Balance: Causes and Prevention of Breast Cancer. Taylor & Francis. pp. 73–. ISBN 978-1-135-91406-6. 
  10. ^ NRC Failure to Adequately Regulate - Millstone Unit 1, 1995
  11. ^ "Millstone - Unit 1". US NRC. Retrieved 17 December 2016. 
  12. ^ [1]
  13. ^ Douglas Dixon; John A. Veil; Joe Wisniewski (12 August 2005). Defining and Assessing Adverse Environmental Impact from Power Plant Impingement and Entrainment of Aquatic Organisms: Symposium in Conjunction with the Annual Meeting of the American Fisheries Society, 2001, in Phoenix, Arizona, USA. CRC Press. pp. 215–. ISBN 978-0-203-97119-2. 
  14. ^ Atlantic Generating Station Units 1-2, Construction: Environmental Impact Statement. 1976. pp. 5–. 
  15. ^ New England Power Units 1-2, Construction Permit: Environmental Impact Statement. 1979. pp. 5–. 
  16. ^ "Metropolitan Briefs: Inquiry Ends at Atomic Plant". New York Times. Retrieved 17 December 2016. 
  17. ^ Millstone Nuclear Power Station Unit 3, Operation: Environmental Impact Statement. 1985. pp. 5–. 
  18. ^ G.F. Hewitt; John G. Collier (1 June 2000). Introduction to Nuclear Power, Second Edition. CRC Press. pp. 144–. ISBN 978-1-56032-454-6. 
  19. ^ Michael J. Kennish (11 October 1996). Practical Handbook of Estuarine and Marine Pollution. CRC Press. pp. 484–. ISBN 978-0-8493-8424-0. 
  20. ^ Millstone Nuclear Power Station: Unit 1, Northeast Nuclear Energy Company (formerly The Millstone Point Company). U.S. Atomic Energy Commission, Division of Technical Information Extension. 1974. 
  21. ^ Licensee Contractor and Vendor Inspection Status Report. Office of Inspection and Enforcement, Nuclear Regulatory Commission. 1978. 
  22. ^ Mother Jones (January 1979). Mother Jones Magazine. Mother Jones. pp. 18–. ISSN 0362-8841. 
  23. ^ "Bulletin 78-03: Potential Explosive Gas Mixture Accumulations Associated With BWR Offgas System Operations". Nuclear Regulatory Commission. Retrieved 17 December 2016. 
  24. ^ Federal Register. Office of the Federal Register, National Archives and Records Service, General Services Administration. 1978. 
  25. ^ NRC Failure to Adequately Regulate - Millsone Unit 1, 1995
  26. ^ Benjamin K. Sovacool; Scott Victor Valentine (16 May 2012). The National Politics of Nuclear Power: Economics, Security, and Governance. Routledge. pp. 260–. ISBN 978-1-136-29437-2. 
  27. ^ United States. Congress. House. Committee on Commerce. Subcommittee on Energy and Power (1996). Oversight hearing on the Nuclear Regulatory Commission: hearing before the Subcommittee on Energy and Power of the Committee on Commerce, House of Representatives, One Hundred Fourth Congress, second session, September 5, 1996. U.S. Government Printing Office. ISBN 978-0-16-053701-1. 
  28. ^ TIME. 1996. 
  29. ^ Lochbaum, David. "Longstanding Nuclear Safety Impairments". Union of Concerned Scientists. Retrieved 18 December 2016. 
  30. ^ Nuclear Regulatory Commission NRC needs to do more to ensure that power plants are effectively controlling spent nuclear fuel: report to Congressional requesters. United States Government Accountability Office. pp. 11–12. ISBN 978-1-4289-3176-3. 
  31. ^ John X. Wang (25 July 2012). Green Electronics Manufacturing: Creating Environmental Sensible Products. CRC Press. pp. 29–. ISBN 978-1-4398-2669-0. 
  32. ^ Reactor Shutdown: Dominion Learns Big Lesson From A Tiny ‘tin Whisker'
  33. ^
  34. ^ "Preliminary Notification of Event or Unusual Occurrence -- PNO-I-09-007" (PDF). Retrieved 18 December 2016. 
  35. ^ "Millstone Reactor Shuts Down Due to Hydrogen Gas Leak". Retrieved 17 December 2016. 
  36. ^
  37. ^ Bill Dedman, Nuclear neighbors: Population rises near US reactors,, April 14, 2011 Accessed May 1, 2011.
  38. ^ Bill Dedman, "What are the odds? US nuke plants ranked by quake risk,", March 17, 2011 Accessed April 19, 2011.
  39. ^

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