Operations of the Diablo Canyon Power Plant

Kyra Carusa
December 2, 2017

Submitted as coursework for PH240, Stanford University, Fall 2017


Fig. 1: Diablo Canyon Power Plant from Port San Luis. (Source: Wikimedia Commons)

The Diablo Canyon Power Plant is an electricity-generating nuclear power plant located near Avila Beach in San Luis Obispo County, California. As of 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 and Electric. These twin 1,100 MWe reactors produce almost 18,000 GWh of electricity per year. Almost 8.6% of the electricity California use comes from this plant, supplying the electrical needs of more than 3 million people. [1]

Plant's Power Units

The plant is made up of two operational units and one cooling unit.

Unit One is a 1138 MWe pressurized water reactor supplied by Westinghouse. The unit became active May 7, 1985. The unit is licensed to operate until November 2, 2024. In 2006, Unit One generated electricity at a nominal capacity factor of 101.2 percent. [2]

Unit Two is a 1118 MWe pressurized water reactor supplied by Westinghouse. It went online on March 3, 1986 and is licensed to operate through August 26, 2025. In 2006, Unit Two generated electricity at a capacity factor of 88.2 percent. [2]

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.

Plant Operation Closing

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. The deal entails 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. Ultimately, the Diablo Canyon represents two opposing sides of an argument surrounding the idea of clean energy development and having a clean environment paired with projected growth. All of this needing to happen while keeping the California environment safe and clean. Though there are positions coming from both sides of the argument, the general stigma surrounding the use of nuclear energy in California is over powered by those who want to keep California a clean energy state. The major problems with the nuclear plant stem from the necessary precautions needed in case of natural disasters. Without complete confidence in plant safety, the surrounding terrain is vulnerable to massive disaster. Ultimately, PG&E has decided to shut the plant rather than take this risk. [3]

© Kyra Carusa. 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.


[1] K. Mayeda and K. Reiner, "Economic Benefit of Diablo Canyon Power Plant," Pacific Gas and Electric Company, June 2013.

[2] "State Nuclear Profiles 2010," U.S. Energy Information Administration, April 2012, p. 8.

[3] T. Hyman, "The Diablo Canyon Nuclear Power Plant," Physics 240, Stanford University, Fall 2016.