Decommissioning the San Onofre Nuclear Generating Station

Grace Farley
March 18, 2017

Submitted as coursework for PH241, Stanford University, Winter 2017


Fig. 1: San Onofre Nuclear Generating Station, 2012. A landmark in the surrounding area. (Source: Wikimedia Commons)

The San Onofre Nuclear Generating Station is a nuclear power plant located on the coast of Southern California. The plant first opened in 1968, and remained open with three reactor units until 2013, when the plant was first closed. During its tenure, the San Onofre Nuclear Generating Station generated a good deal of power to the surrounding Southern California area. In the early 2000s, Edison commissioned a renovation project that replaced the steam generators with more improved and advanced Mitsubishi steam generators. This project was completed in 2011, and cost the company $671 million. [1]


In January 2012, the new tubing in the steam generators began to leak radiation. Despite the recent upgrades to the steam generators, this leak caused an immediate emergency shutdown to begin. Upon initial inspection, it was found that over 3,000 of the tubes that were recently installed just a year prior showed signs of premature wear. Spawning further investigation, many government and manufacturers sought out to discover the root cause of this failure. According to the Mitsubishi root cause analysis, void friction (a gas to liquid measurement) caused the tube wear on the alloy tubing to cause the leak. [2] The intense thermal and flow-induced vibration of the San Onofre Nuclear Generating Station was enough to expedite wear on the newly-installed tubes. In the aftermath of the radiation leak, numerous reports pointed to the fact that the generators would not have been licensed by the United States Nuclear Regulatory Commission, but the designs were implemented because there was no licensing review. [3] There were reports that Edison, the company that owned the majority of the power plant had expressed concerns in the past over the safety of the new generators, but many of these concerns were dismissed. These concerns were not reported to federal nuclear regulatory commissions, which could have potentially prevented the tubal wear. [3] Due to the potential for a further and even greater disaster, it was decided that the San Onofre Nuclear Generating Station be permanently retired. The plant was called to be decommissioned in June 2013.

Current State of Events

The San Onofre Nuclear Generating Station will take many years to fully decommission. There are still continuing debates for who is responsible for the decommissioning efforts, however, utility users will continue to pay $830 million a year for the plant to remain idle. [4] Given that 7 million people live within a 50 mile radius of the power plant, any further damage could have proven disastrous. [5] The failure in 2012 released a small amount of radioactive material to the environment, but future failures could have proven catastrophic. While natural gas emissions increased in California in part because of the San Onofre shutdown, ultimately the response from the federal government supported the decommissioning. The dismantling of the San Onofre Nuclear Generating Station could be a hallmark decision that may influence nuclear power globally.

© Grace Farley. 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] N. Groom, "California Moves to Open Probe into San Onofre Nuclear Shutdown, Reuters, 16 Oct 12.

[2] R. E. Lanz, "Mistubishi Heavy Industries - Request for Withholding Root Cause Analysis and Supplemental Technical Evaluation Report Information from Public Disclosure," U.S Nuclear Regulatory Commission, 6 Mar 13.

[3] J. McDonald, "It’s Not Just the Steam Generators That Failed," San Diego Union-Tribune, 30 jan 16.

[4] M. Lee, "A Year Off the Grid," San Diego Union-Tribune, 26 Jan 13.

[5] M. Walker, "Workers, Surfers, Pols React to San Onofre," San Diego Union-Tribune, 7 Jun 13.