|Fig. 1: Diablo Canyon Nuclear Power Plant (Source: Wikimedia Commons)|
Historically, California has been a pioneer in harnessing nuclear energy. However, recent trends in sustainable energy and push for cleaner, safer options have resulted in the decommissioning of all of California's nuclear power plants, the last of which will close in August 2025.  Energy companies in California have chosen to move away from the Nuclear power of old and focus on developing more solar, wind and other clean power technologies. This transition to clean energy marks the end of an era of Nuclear power in California.
The Santa Susana Sodium Reactor Experimental (SRE) was the first Nuclear Power Plant in California. The plant was in operation from April 1957 to February 1964. The plant was located in near Moorpark in Ventura County and used sodium as a coolant rather than water. The plant produced a maximum of about 20 megawatts.. It was considered the country's first civilian nuclear plant and the first "commercial" nuclear power plant to provide electricity to the public by powering the near-by city of Moorpark in 1957. 
The Vallecitos Nuclear Power Plant near Pleasanton, CA operated from 1957 to 1967. This was a small, 30 megawatt power plant. Vallecitos Power Plant was the first privately funded plant to supply power in megawatt amounts to the electric utility grid. [3,4]
The Humboldt Bay Nuclear Power Plant was located in Eureka, CA and operated from August 1963 to July 1976. It was the seventh licensed nuclear plant in the United States. This plant closed following an earthquake as the necessary repairs were too costly. 
The Rancho Seco Nuclear Power Plant, located about 25 miles south of Sacramento, was in operation from April 1975 to June 1989. 
Located just north of San diego, the San Onofre Nuclear Generating Station went offline in January 2012 and was ordered by the Nuclear Regulatory Commission to stay offline while tubing wear issues were investigated. Plant owners announced in June 2013 that remaining Units 2 and 3 would be permanently retired. [4,5] The closure of San Onofre exemplifies why Nuclear energy is being phased out in California. High operating costs coupled with sub optimal output and hazardous waste sparked the closure of the plant. Closing costs alone amount to over $4.7 billion. 
The Diablo Canyon Nuclear Power Plant (Fig. 1), located in San Luis Obispo County, consists of two units. Unit 1 is a 1,073 megawatt (MW) pressurized water reactor which began commercial operation in May 1985. Unit 2 is a 1,087 MW pressurized water reactor that began commercial operation in March 1986.  The plant, built against a seaside cliff near Avila Beach, provides 2,160 megawatts of electricity for Central and Northern California enough to power more than 1.7 million homes.  After the shutdown of the San Onofre Nuclear Generating Station in 2012, the Diablo Canyon Power Plant supplied 100% of California's nuclear energy which amounts to 9.6% of California's total energy supply.  The Diablo Canyon Power Plant will be retired in 2025 after its current U.S. Nuclear Regulatory Commission operating licenses expire. 
Many of these plants were phased out for economic reasons, but more recent motivations for closing nuclear power plants stem from a desire to transition to more efficient, cleaner energy sources. Ultimately, this transition will benefit the environment, but a large source of electricity in California will be lost.
© Collin Riccitelli. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 I. Penn and S. Masunaga, "PG&E to Close Diablo Canyon, California's Last Nuclear Power Plant," Los Angeles Times, 21 Jun 16.
 A. Liang, "Nuclear Energy in California," Physics 241, Stanford University, Winter 2017.
 "Decommissioning Funding Plan," GE Hitachi Nuclear Energy Americas, LLC, 6 Feb 17.
 "Nuclear Power in California: Status Report," California Energy Commission, CEC-150-2006-001-F, March 2006.
 J. Mcdonald, "Who Pays for San Onofre Nuclear Plant's Early Closure? Negotiations Fall Apart," Los Angeles Times, 15 Aug 17.
 "2010 State Nuclear Profiles," U.S. Energy Information Administration, April 2012, p. 7.