Most Californians share an interest in clean, sustainable energy for California and are probably pleased to see the expansion of wind and solar energy in California. Since 2001, California has almost completely eliminated coal-fired power plants, increased wind power from 1% to 5% of total generation and increased solar power from almost nothing to 11% of total generation. These are all climate achievements to be celebrated, but California will lose its single largest source of low-carbon electricity if residents do not act soon.

Nuclear power’s historical role in California 

In 2011, San Onofre Nuclear Generating Station (SONGS) was shuttered permanently due to safety concerns, leaving Diablo Canyon Nuclear Power Plant (Diablo Canyon) as the only remaining nuclear generating station in California. This prevented California from reducing its reliance on natural gas, and indeed contributed to California getting 40-41% of its electricity from natural gas in 2012-2015 (compared to 31% in 2011 and 38% in 2012).

While SONGS had equipment malfunctions and documented mismanagement that were legitimate causes for concern, Diablo Canyon is still reliably generating 6-7% of California’s electricity per year and has not had any major safety problems in its entire 37-year history. Diablo Canyon is an economical source of green energy and would require minimal maintenance and refitting to remain in compliance with US regulations. PG&E had originally applied to renew Diablo Canyon’s license until 2045, but it withdrew its application in 2018 due to pressure from environmental organizations.

Unless Diablo Canyon’s license is renewed, Diablo Canyon will be decommissioned starting in 2024. (Editor’s Note: This proposal to extend operations until 2030 did move forward with approval from the state Legislature.)

Should Diablo Canyon continue to operate? 

While new nuclear power plants are very expensive to build, an existing nuclear power plant with no outstanding safety concerns can be a clean, affordable electricity source, because the annual cost of operation after construction is low, safety risks are minimal, and greenhouse gas emissions are almost nonexistent. Furthermore, decommissioning a large nuclear power plant can cost billions of dollars, and should therefore be delayed as much as practicable. Diablo Canyon could probably continue to operate safely well into the 2040’s, and possibly into the 2060’s. 

Natural gas is the only viable alternative to nuclear power as a source of base load electricity in California, and gas-burning power plants produce large amounts of CO2 (several million excess tons CO2 equivalent per year for a Diablo Canyon-equivalent amount of natural gas production). Wind and solar are safer and arguably more environmentally friendly than nuclear, but California does not presently have enough electricity storage to allow those to serve as alternatives to Diablo Canyon for base load demand, nor is it expected to have enough renewable generation to make up for the energy shortfall by 2025. Most realistic scenarios in which Diablo Canyon is closed in 2024 involve California compensating with increased use of natural gas. For this reason, many scientists believe that shutting down Diablo Canyon would be unwise.

Proposed 10-year life extension 

Governor Gavin Newsom proposed a 5-year extension of Diablo Canyon’s life to 2030 and an optional further extension to 2035, for an added cost of $1.4 billion. (Editor’s Note: The state legislature voted to approve this expenditure just before the 2022 legislative session closed on August 31.)  

The mere fact that a life extension is being entertained seems to make it more likely that Diablo Canyon won’t close in 2025. However, some scientists are concerned about whether Diablo Canyon would need seismic retrofitting, while writers at media outlets like the Los Angeles Times point to the logistical difficulties of changing course on a decision that was made in 2016. John Laird, the state legislator representing the district that contains Diablo Canyon, also raised concerns about the prudence of extending Diablo Canyon’s life. However, with hydroelectric power imperiled by the ongoing drought and a slow rollout of solar power, many legislators are likely to agree with Newsom. 

The economics of extending Diablo Canyon’s life 

While the proposed $1.4 billion for a 10-year life extension is certainly a lot of money, it is important to compare this cost to the costs of feasible alternatives. The cost-per-megawatt-hour matrix (cost/MWh) below shows how the cost/MWh of a Diablo Canyon life extension would compare to an equivalent amount of utility-scale solar generation. The matrix includes assumptions ranging from the expected cost/MWh at the top left (no cost overruns and historical levels of production) to massive cost overruns and very low production on the bottom right. It is important to emphasize that, based on historical precedent, even 80% production (the second row) would be extremely low for Diablo Canyon, and so even the second row represents a near-worst-case scenario for the power plant. 

Solar power is already very cheap and is getting cheaper all the time, but as this matrix shows, even if solar got much cheaper than it is today ($28-$41/MWh), there is a wide range of scenarios in which a 10-year extension for Diablo Canyon would still be cheaper than replacing it entirely with solar power. For example, two projects approved this year would add 465 MW of solar and 400 MW of battery power in the California desert at a cost of $689 million. By comparison, Diablo Canyon generates about 2240 MW except for about 4 weeks per year when it’s being refueled. Furthermore, it is important to emphasize that California most likely won’t replace Diablo Canyon’s generation with 100% renewables, but rather natural gas, because it will take years to build enough renewable capacity to compensate for the loss of Diablo Canyon. 

Solar panel arrays form a canopy at a construction site in Fort Hunter Liggett, Calif., March 12, 2013. The construction site is for phase 1 and 2 of a solar microgrid project at the installation, managed by the U.S. Army Corps of Engineers Sacramento District. (U.S. Army/John Prettyman via Bay City News)

Clock is ticking on Diablo extension 

Diablo Canyon nuclear power plant has been a linchpin of California’s electricity generation since it opened in 1986. Despite the large initial investment in its construction, the added cost per year of continuing to operate Diablo Canyon’s is very low. That said, the falling price of renewable alternatives will eventually make it uneconomical to operate. Safety, especially safety against earthquakes, may be an issue, but PG&E and the Nuclear Regulatory Commission don’t believe so. The California legislature must weigh the pros and cons of operating Diablo Canyon and decide by the end of August whether Diablo Canyon can continue to live past its currently scheduled end of life in 2025.