Diablo Canyon Power Plant

Diablo Canyon Power Plant

Diablo Canyon Power Plant
Location of Diablo Canyon Power Plant in California
Coordinates 35°12′39″N 120°51′22″W / 35.21083°N 120.85611°W / 35.21083; -120.85611Coordinates: 35°12′39″N 120°51′22″W / 35.21083°N 120.85611°W / 35.21083; -120.85611
Status Operational
Commission date Unit 1: May 7, 1985
Unit 2: March 13, 1986
Owner(s) Pacific Gas & Electric
Operator(s) Pacific Gas & Electric
Nuclear power station
Reactor type Pressurized water reactor
Reactor supplier Westinghouse
Cooling source North Pacific Ocean
Cooling towers no
Power generation
Units operational 1 x 1118 MW
1 x 1122 MW
PG&E Diablo Canyon
Diablo Canyon Power Plant, 2009 photo from offshore. The light beige domes are the containment structures for Unit 1 and 2 reactors. The brown building is the turbine building where electricity is generated and sent to the grid. In the foreground is the Administration Building (black and white stripes).

The Diablo Canyon Power Plant is an electricity-generating nuclear power plant near Avila Beach in San Luis Obispo County, California. After the permanent shutdown of the San Onofre Nuclear Generating Station in 2013 it is the only nuclear plant operational in the state. The plant has two Westinghouse-designed 4-loop pressurized-water nuclear reactors operated by Pacific Gas & Electric.

The facility is located on about 900 acres (360 ha) west of Avila Beach, California, of which about 12 acres form the power-producing portion of the plant. Together, the twin 1,100 MWe reactors produce about 18,000 GW·h of electricity annually, about 8.6% of the electricity California uses, supplying the electrical needs of more than 3 million people.[1] It was built less than a mile from the Shoreline fault line, which was not known to exist at the time of construction, and is located less than three miles from the Hosgri fault.[2][3][4][5][6][7]

The plant is located in Nuclear Regulatory Commission Region IV. In November 2009, PG&E applied to the Nuclear Regulatory Commission (NRC) for 20-year license renewals for both reactors.[8]

In June 2016, PG&E announced that it plans to close Diablo Canyon in 2025.[9] This will make California free of commercial nuclear power plants, but will mean the loss of 2240MW of carbon-free power.


Unit One

Unit One is a 1,122 MWe pressurized water reactor supplied by Westinghouse. It went online on May 7, 1985 and is licensed to operate through November 2, 2024.[10] In 2006, Unit One generated 9,944,983 MW·h of electricity, at a nominal capacity factor of 101.2 percent.

Unit Two

Unit Two is a 1,118 MWe pressurized water reactor supplied by Westinghouse. It went online on March 3, 1986 and is licensed to operate through August 20, 2025.[10] In 2006, Unit Two generated 8,520,000 MW·h of electricity, at a capacity factor of 88.2 percent.


The plant draws cooling water from the Pacific Ocean, and during heavy storm surges the units can be throttled back to prevent an excess of kelp from entering the cooling water intake. The plant utilizes once-through cooling for the condenser, which is returned to the Pacific Ocean at a temperature that is regulated to be no more than 20 degrees Fahrenheit warmer than ambient ocean temperatures, influencing an area only one-quarter (1/4) mile radius from the discharge of the plant.


Pacific Gas & Electric Company went through six years of hearings, referenda and litigation to have the Diablo Canyon plant approved. A principal concern about the plant is whether it can be sufficiently earthquake-proof. The site was deemed safe when construction started in 1968.

By the time of the plant's completion in 1973, a seismic fault, the Hosgri fault, had been discovered several miles offshore. This fault had a 7.1 magnitude quake 10 miles offshore on November 4, 1927, and thus was capable of generating forces equivalent to approximately 1/16 of those felt in the 1906 San Francisco earthquake.[11]

The company updated its plans and added structural supports designed to reinforce stability in case of earthquake. In September 1981, PG&E discovered that a single set of blueprints was used for these structural supports; workers were supposed to have reversed the plans when switching to the second reactor, but did not.[12] According to Charles Perrow, the result of the error was that "many parts were needlessly reinforced, while others, which should have been strengthened, were left untouched."[13] Nonetheless, on March 19, 1982 the Nuclear Regulatory Commission decided not to review its 1978 decision approving the plant's safety, despite these and other design errors.[14]

In response to concern that ground acceleration, or shaking, could cause spillage of submerged fuel rod assemblies which, upon exposure to air, could ignite, PG&E and NRC regulators insist that the foregoing scenario is anticipated and controlled for, and that there is no basis to anticipate spillage.[15] Additional seismic studies are in process, though completion of those studies is not a condition precedent to re-issuance of the operating licenses for the two onsite units.[16]

In October 2008, Unit 2 was taken offline for approximately two days due to a rapid influx of jellyfish at the intake.[17]

The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Diablo Canyon was 1 in 23,810, according to an NRC study published in August 2010.[18][19] In April 2011, in the wake of the Fukushima nuclear incident in Japan, PG&E asked the NRC not to issue license renewals until PG&E can complete new seismic studies, which are expected to take at least three years.[20][21]

In February 2013, Unit 2 was shut down for refueling and upgrading; Unit 1 beginning in April 2013.[22]

On June 24, 2013 at 9:20 PM PDT, Diablo Canyon experienced a loss of offsite power to the startup transformers of both units due to a failure on the 230 kV transmission system. At the time, none of the startup transformers were loaded as both units were online and their electrical systems were at the time being powered by the plant's turbine generators. However, as a precaution the emergency diesel generators started with no load during the outage in case either unit tripped offline while offsite power was unavailable. The electrical output of the plant via the 500 kV transmission system was not interrupted allowing both units to remain online during the outage.

Public participation and protest

Diablo Canyon was built and entered service despite legal challenges and civil disobedience from the anti-nuclear protesters of the Abalone Alliance.[23] Over a two-week period in 1981, 1,900 activists were arrested and sent to jail for protesting at Diablo Canyon Power Plant. It was the largest arrest total in the history of the U.S. anti-nuclear movement.[23]

In spring of 2011, State Senator Sam Blakeslee[24] and US Representative Lois Capps[25] both expressed concern for a renewed safety review. Speaking before the Senate Committee on Environment and Public Works, the congresswoman stated that she believed the "Nuclear Regulatory Commission should stay the license renewal process until the completion of independent, peer reviewed, advanced seismic studies of all faults in the area." The Alliance for Nuclear Responsibility began circulating a petition to similar effect,[26] going further and calling for an outright halt to relicensing. An array of San Luis Obispo-based anti-nuclear groups including Mothers for Peace also called for the closure of Diablo Canyon nuclear power plant.[27]

The Alliance for Nuclear Responsibility also works at the level of the California Public Utilities Commission and initiated a letter writing campaign to Governor Jerry Brown, which requests he "instruct the CPUC to rescind the Certificate of Public Convenience and Necessity for ... Diablo Canyon ... and allow them to operate conditionally only under the agreement by the utilities to immediately begin to fully comply with completion of the state-directed AB 1632 [seismic] studies."[28]

Post-Fukushima developments

Due to international reactions to the Fukushima Daiichi nuclear disaster, concerns have continued over the ongoing operations of Diablo Canyon, which like the reactors at Fukushima, is in an area prone to earthquakes and tsunami. The elevation of the Fukushima site is approximately 20 feet above sea level, while Diablo Canyon sits on a bluff 85 feet above sea level. According to Victor Dricks, senior public affairs officer for NRC Region IV,[29] the Commission conducted a nationwide review of nuclear power plants for their capacity to respond to earthquakes, power outages and other catastrophic events, and Diablo was found to have "a high level of preparedness and strong capability in terms of equipment and procedures to respond to severe events."

On June 2, 2011, the NRC announced that it would delay the environmental part of the re-licensing application but that it had completed the safety portion.[30] A few days later, the Atomic Safety Licensing Board indicated that it would defer adjustment of the adjudicatory schedule of the four contentions brought by SLOMFP, a community-based organization, accordingly. The ASLB made no findings regarding the merits of the contentions.[31] Both parties to the dispute claim these developments as victories: Pacific Gas and Electric[32] as well as San Luis Obispo Mothers for Peace.[33]

S. David Freeman, a former general manager of the Sacramento Municipal Utility District for four years, criticized the continued operation of Diablo Canyon, calling nuclear power the "most expensive and dangerous source of energy on Earth". According to Freeman, Diablo Canyon and the since-closed San Onofre nuclear plant are both "disasters waiting to happen: ageing, unreliable reactors sitting near earthquake fault zones on the fragile Pacific Coast, with millions or hundreds of thousands of Californians living nearby".[34]

Save Diablo Canyon campaign

In January 2016, several authors of the An Ecomodernist Manifesto – including Robert Stone, David Keith, Stewart Brand, Michael Shellenberger and Mark Lynas – as well as Kerry Emanuel, James Hansen, Steven Pinker, Stephen Tindale and Burton Richter; signed an open letter urging that the plant not be closed.[35] It was addressed to California Governor Jerry Brown, Tony Earley, CEO of Pacific Gas & Electric, and California state officials[36] and posted on their website.[37] They argued that Diablo is an asset for California in achieving global warming goals since it does not emit greenhouse gases which cause global warming like a natural gas power plant.[38]

Closure in 2024–2025

On June 21, 2016, PG&E announced a Joint Proposal with labor and environmental organizations to increase investment in energy efficiency, renewables and storage, while phasing out nuclear power. Specifically, the operating licenses for Diablo Canyon Units 1 and 2 will not be renewed. These are set to expire on November 2, 2024 and August 26, 2025 respectively.[39]


Overall, there are approximately 1200 employees of Pacific Gas and Electric and 200 employees of subcontractors at the Diablo Canyon site.[40] Several unions represent the workforce at Diablo, among them the International Brotherhood of Electrical Workers and the International Association of Machinists. Control Technicians and electricians who work for Crane Nuclear, one of many subcontractors, are represented by the IBEW Local 1245.[41] 1245 also represents PG&E meter readers, clerical workers, etc.[42] Local 639, which is involved with Diablo but is under "spring outage", also supports solar energy development as part of the overall energy industry portfolio.[43] This outage has been retracted as of June 10, 2011[44] The outages are routine for maintenance and the complex process of refueling, and created 1,000 temporary jobs, according to PG&E.[45] Other workers are represented by the Plumbers and Pipefitters.[46]


Earthquake protection

Diablo Canyon was originally designed to withstand a 6.75 magnitude earthquake from four faults, including the nearby San Andreas and Hosgri faults,[47] but was later upgraded to withstand a 7.5 magnitude quake.[48] It has redundant seismic monitoring and a safety system designed to shut it down promptly in the event of significant ground motion.

Independent Safety Committee

The Diablo Canyon Independent Safety Committee (DCISC) was established as a part of a settlement agreement entered into in June 1988 between the Division of Ratepayer Advocates of the California Public Utilities Commission (CPUC), the Attorney General for the State of California, and Pacific Gas and Electric Company (PG&E). It consists of three members, one each appointed by the Governor, the Attorney General and the Chairperson of the California Energy Commission. They serve staggered three-year terms. The committee has no authority to direct PG&E personnel.

Emergency planning

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.[49]

The 2010 U.S. population within 10 miles (16 km) of Diablo Canyon was 26,123, an increase of 50.2 percent in a decade, according to an analysis of U.S. Census data for msnbc.com. The 2010 U.S. population within 50 miles (80 km) was 465,521, an increase of 22.4 percent since 2000. Cities within 50 miles include San Luis Obispo (12 miles to city center) and Paso Robles (31 miles to city center).[50]

Emergency sirens were installed when the plant went operational. Federal law requires an early warning system that radiates out 10 miles from any nuclear facility. The county siren coverage goes farther, extending from Cayucos in the north down to upper Nipomo to the south. All businesses are required to have a siren information sticker in their business generally located within the restrooms. Schools, government offices, and any other public building will have a PAZ card (Protective Action Zone). These cards show the 12 zones of evacuation with zone one being the plant itself. The cards also show the direction of evacuation on the highways.

See also

Wikimedia Commons has media related to Diablo Canyon Power Plant.


  1. Economic Benefits of Diablo Canyon Power Plant, PG&E, June 2013
  2. Koenen, Leon (2011-03-25). "The Diablo Canyon Nuclear Power Plant, a 48-Year Odyssey | Environment | SoCal Focus". KCET. Retrieved 2011-06-10.
  3. "Is Diablo Canyon prepared for possible earthquake? | KSBY.com | San Luis Obispo, Santa Maria, Santa Barbara, Paso Robles". KSBY.com. 2011-03-14. Retrieved 2011-06-10.
  4. "California's Two Nuclear Plants Near Fault Lines, But Chris Wills with the California Geological Survey says the types of faults are different than the ones in Japan. - KTXL". Fox40.com. 2011-03-14. Retrieved 2011-06-10.
  5. "Newsom: Calif. Wouldn't Build Diablo Plant Today". Newsmax.com. 2011-03-17. Retrieved 2011-06-10.
  6. "Is California Underestimating Quake Threat To Nuclear Plants? | Capital Public Radio". CapRadio. 2011-03-25. Retrieved 2011-06-10.
  7. "Capps Testifies Before Senate About Diablo Canyon Safety | U.S. House of Representatives". U.S. House. 2011-04-12. Retrieved 2014-08-22.
  8. "Diablo Canyon - License Renewal Application". Operating Reactor Licensing. Nuclear Regulatory Commission (NRC). March 12, 2011. Retrieved 2011-04-19.
  9. Baker, David R. (June 21, 2016). "End of an atomic era: PG&E to close Diablo Canyon nuclear plant". San Francisco Chronicle. San Francisco, Calif. Retrieved June 21, 2016.
  10. 1 2 "California Nuclear Profile > Diablo Canyon Nuclear Power Plant". Energy Information Administration, U.S. Department of Energy (DOE). September 2010. Retrieved January 21, 2011.
  11. "Lompoc Earthquake (1927)". Southern California Earthquake Data Center. 2010. Retrieved November 2, 2010.
  12. Cummings, Judith (October 2, 1981). "Coast A-Plant Construction Error Tied to Missing Guide to Blueprint". The New York Times. p. 14. Retrieved August 31, 2016.
  13. Perrow, Charles, Normal Accidents (New York: Basic Books 1984) ISBN 0-465-05142-1 p. 37
  14. "U.S. Won't Review Diablo Plant Decision: Nuclear Board Upholds '78 Approval of Quake Design Standards". Los Angeles Times. March 20, 1982. p. A35.
  15. "Diablo Canyon Independent Safety Committee's Evaluation of Pressurized Thermal Shock and Seismic Interactions for a 20-Year License Extension at the Diablo Canyon Nuclear Power Plant". Diablo Canyon Independent Safety Committee. 2011. Retrieved March 18, 2011.
  16. "In The World of Nuclear Power Crisis". Life Magazine. May 1979. pp. 23–30. Retrieved July 14, 2010.
  17. "Current Event Notification Report". NRC. October 22, 2008. Retrieved July 14, 2010.
  18. Dedman, Bill (March 17, 2011). "What are the odds? US nuke plants ranked by quake risk". msnbc.com. Retrieved April 19, 2011.
  19. http://msnbcmedia.msn.com/i/msnbc/Sections/NEWS/quake%20nrc%20risk%20estimates.pdf
  20. Upton, John (March 17, 2011). "Seismic Uncertainty at Diablo Canyon". The Bay Citizen. Retrieved 2011-04-19.
  21. Casselman, Ben; Stephen Power (April 12, 2011). "Diablo Plant Delays License Bid for Quake Study". The Wall Street Journal. Retrieved 2011-04-19.
  22. David Sneed (4 February 2013). "Diablo Canyon reactor shut down for refueling, upgrades". San Luis Obispo Tribune. Retrieved 7 February 2013.
  23. 1 2 Wills, John (2006). Conservation Fallout: Nuclear Protest at Diablo Canyon. Reno: University of Nevada Press. ISBN 0-87417-680-8.
  24. "Blakeslee and Rachel Maddow discuss Diablo". Cal Coast News. 2011-03-25. Retrieved 2011-06-10.
  25. "Capps Testifies Before Senate About Diablo Canyon Safety | Congresswoman Lois Capps, Representing the 23rd District of California". Capps.house.gov. 2011-04-12. Retrieved 2011-06-10.
  26. http://a4nr.org/wp-content/uploads/2011/04/042211-A4NR-petition.pdf
  27. Hickey, Julia (April 17, 2001). "Anti-nuclear rally at Avila Beach". The Tribune.
  28. "a4nr.org". a4nr.org. Retrieved 2011-06-10.
  29. Dricks, Victor. "The Santa Barbara Independent The Eyes on Diablo". Independent.com. Retrieved 2011-06-10.
  30. http://pbadupws.nrc.gov/docs/ML1115/ML111530522.pdf
  31. http://pbadupws.nrc.gov/docs/ML1115/ML111580337.pdf
  32. Johns, Chris (2011-06-05). "Viewpoint: PG&E chief says it is committed to safety of Diablo | The Tribune &". Sanluisobispo.com. Retrieved 2011-06-10.
  33. "— Mothers For Peace". Mothersforpeace.org. Retrieved 2011-06-10.
  34. S. David Freeman (Jun 2, 2012). "Viewpoints: Time has come for California to embrace a nuclear-free future". Sacramento Bee.
  35. McDonnell, Tim (3 February 2016). "Closing This Nuclear Plant Could Cause an Environmental Disaster". Mother Jones. Foundation For National Progress. Retrieved 11 February 2016.
  36. "Open letter: Do the right thing — stand-up for California's largest source of clean energy". Save Diablo Canyon. Retrieved 11 February 2016.
  37. "Save Diablo Canyon". Save Diablo Canyon. Retrieved 21 June 2016.
  38. Baker, David R. (January 29, 2016). "Yes nukes! Conservationists rally to save state's nuclear plant". San Francisco Chronicle. San Francisco, Calif. Retrieved 27 June 2016.
  39. https://www.pge.com/en/about/newsroom/newsdetails/index.page?title=20160621_in_step_with_californias_evolving_energy_policy_pge_labor_and_environmental_groups_announce_proposal_to_increase_energy_efficiency_renewables_and_storage_while_phasing_out_nuclear_power_over_the_next_decade
  40. Public hearing minutes, Santa Barbara Board of Supervisors, Special NRC session of June 16, 2011
  41. http://www.ibew1245.com/Agreements/Crane_Nuclear_2009-2011.pdf
  42. http://www.ibew1245.com/ContractIndex/PT-002-01.htm
  43. http://www.ibew639.org/index.cfm
  44. http://www.pgecurrents.com/2011/06/10/diablo-canyon-power-plant-unit-returns-to-service-after-planned-outage/
  45. More than 1,000 temporary workers – a boost to the local economy – were brought in to work with PG&E employees to replace a portion of the reactor fuel and to perform maintenance and testing on plant system components that are inaccessible during regular plant operations.
  46. http://openjurist.org/874/f2d/816/huhn-ii-v-pullman-power-products-corporation
  47. "Energy: A Nuclear Horror". Time. February 9, 1976. Retrieved July 14, 2010.
  48. David Sneed (August 9, 2011). "Diablo Canyon workshop to focus on earthquakes". The San Luis Obispo Tribune.
  49. "NRC: Backgrounder on Emergency Preparedness at Nuclear Power Plants". Nrc.gov. Retrieved 2011-06-10.
  50. Bill Dedman, Nuclear neighbors: Population rises near US reactors, msnbc.com, April 14, 2011 http://www.msnbc.msn.com/id/42555888/ns/us_news-life/ Accessed May 1, 2011.

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