The divide over Diablo

Greens battle greens over the fate of California’s last nuke plant.

In 1966, when Pacific Gas & Electric proposed building a two-reactor nuclear plant at Diablo Canyon on California’s Central Coast, it sparked a bitter fight within the Sierra Club, which was then the nation’s most powerful environmental group.

The Sierra Club’s director, David Brower, opposed the project because it would industrialize a relatively undisturbed stretch of coastline. But board president William Siri — who had worked on the Manhattan Project — supported it, arguing that building one big nuclear plant on the coast would keep coal plants and hydroelectricity dams out of wildlands. “Nuclear power is one of the chief long-term hopes for conservation,” he wrote.


The Sierra Club’s membership sided with Siri and nuclear power, and in 1968 the Atomic Energy Commission approved construction of the Diablo Canyon Power Plant on yak titʸu titʸu yak tiłhini Northern Chumash ancestral land. Brower left the Sierra Club and, in 1969, started Friends of the Earth, where he continued to fight power plants of every kind. But neither he nor a growing No Nukes movement could stop Diablo Canyon, which began churning out electricity in 1985.

Now, with its license set to expire and the reactors to retire in 2025, Diablo Canyon is again causing rifts within the environmental community. One side wants to keep it running for at least five more years to avoid more fossil fuel burning, and the other side wants to see the plant shut down as planned.

The fight over Diablo Canyon exemplifies a new era of environmental conflicts, as a faction determined to cut carbon emissions at any cost goes head-to-head with another that’s equally determined to protect ecosystems, tribal lands and front-line communities from the on-the-ground impacts of low-emissions technologies.

It’s a bit confusing, for sure, so here’s the Diablo Canyon meltdown … er, breakdown … I mean, rundown:  

THE PLANT: Diablo Canyon Power Plant has been California’s sole nuclear plant since San Onofre Nuclear Generating Station shut down in 2011. Its two reactors comprise the Western Grids third-largest generator after Arizonas Palo Verde nuclear plant and Washingtons Grand Coulee Dam.

Generating Capacity: 2,323 megawatts

Annual Electricity Output: 16.5 million megawatt hours in 2020 (enough to power about 1.6 million homes).

Began Operations: 1985. Its 40-year operating license with the Nuclear Regulatory Commission expires in 2025.

Machines stand inside the Pacific Gas and Electric Co. (PG&E) Diablo Canyon nuclear power plant in Avila Beach, California.
David Paul Morris/Bloomberg via Getty Images


In 2016, PG&E announced it was dropping efforts to relicense Diablo Canyon. It would be far too expensive to retrofit the aging plant with a cooling system that complied with a new state ban on once-through cooling systems that suck water from the ocean, killing fish in the process, and spit it back into the ocean at warmer temperatures. Plus, with the price of renewables dropping, it just wasn’t worth it to keep the plant running. And while a nuclear plant provides a huge amount of steady, round-the-clock power, it lacks flexibility. Output can’t be quickly ramped up or down to handle the fluctuations in electricity inherent in today’s power grid.

“I just don’t see that this plant is going to survive beyond 2024, 2025. And there is a compelling argument as to why it shouldn’t.”
— then Lt. Gov. Gavin Newsom in 2015

Besides, the company was up against not only Friends of the Earth, Mothers for Peace and the Natural Resources Defense Council, but also then-Gov. Jerry Brown — who had rallied against the plant’s construction in the 1970s — and his lieutenant governor, Gavin Newsom. “I don’t think that PG&E, in its quiet moments, would disagree that this may not have been the ideal site for a plant,” Newsom said at a 2015 meeting of the State Lands Commission. “I just don’t see that this plant is going to survive beyond 2024, 2025. And there is a compelling argument as to why it shouldn’t.”

Newsom’s words turned out to be prescient: The utility announced it would shutter the two reactors when their licenses expired in 2024 and 2025, respectively, following a plan endorsed by greens and unions that would provide a just transition” for the community and the workers, and replace lost power capacity with low-carbon sources other than natural gas. Brown signed off on the plan in 2018, sealing the deal.


Then, in mid-August 2020, an intense heat wave moved into California. Electricity demand exceeded available supplies, and grid operators were forced to implement rolling blackouts. Not only did the outages leave Californians without air-conditioning when they needed it most, but they also raised doubts about the state’s growing reliance on wind and solar power: If renewables couldn’t keep the lights on with Diablo Canyon running, what would happen after the huge nuclear plant shut down?

A growing group of pro-nuclear eco-modernists, who believe atomic fission is the only way to avoid a climate catastrophe, took those concerns and ran with them. Their position, summed up by the motto, “Split, don’t emit,” is similar to Siri’s back in the 1960s: More nuclear power means less fossil fuels and, for that matter, fewer ecosystem-harming utility-scale solar installations in the desert.

Their position was fortified by a report put out by MIT and Stanford researchers last year that found keeping Diablo Canyon running would save billions of dollars in capital costs for building out renewables, avoid greenhouse gas emissions and help stabilize the grid. The researchers noted it would take 90,000 acres of solar panels to replace the plant’s output. Newsom — rumored to have presidential ambitions — joined the pro-nuclear camp, urging PG&E to go for a portion of $6 billion the Biden administration committed to keeping old nuclear plants running. He also asked state lawmakers to relax environmental laws and financially support efforts to keep the plant going until 2030.

THOSE WHO WANT IT TO CLOSE ON SCHEDULE: Friends of the Earth, NRDC, Environment California, Mothers for Peace, Union of Concerned Scientists, Environmental Working Group, Sierra Club California and various other environmental and anti-nuclear organizations.  


  • Safety: Nuclear fission is very powerful, and with great power comes great danger. While catastrophic accidents at nuclear reactors are rare, when they do happen, they can be very bad, as Chernobyl and Fukushima illustrate. Diablo Canyon was built to withstand earthquakes from a seismic fault-line about three miles offshore. But in 2008, a new fault, just 2,000 feet away, was discovered, raising fears that a quake could damage aging safety and cooling mechanisms and lead to a meltdown. Safety concerns were exacerbated earlier this year when federal investigators found that inspectors had overlooked severe corrosion that led to a leak in a cooling system pipe.

  • Waste: Each of Diablo Canyon’s two reactors kick out about 80 tons of high-level radioactive waste when the old fuel rods are traded out for new ones every one to three years. The waste contains plutonium-239, which can be enriched to become the fissile material in a nuclear weapon or simply used in a “dirty bomb” as is. In the absence of a permanent national depository, PG&E must store this waste on site. Given the utility’s safety record — it is responsible for sparking deadly wildfires and gas pipeline explosions — critics aren’t too keen on letting it oversee a bunch of hazardous material.

  • Uranium’s Deadly Legacy: Nuclear reactors are fueled by uranium that must be mined and processed, an energy- and waste-intensive process that can be dangerous for miners, millers and any people who live nearby. Cold War-era uranium production for weapons and power sickened thousands of Indigenous workers and residents on the Colorado Plateau and scarred the landscape. Many of the abandoned sites have yet to be reclaimed and continue to do harm, even as the industry looks to bring mining back to Utah, Arizona, Colorado and Wyoming.

  • Economics/Reliability: Nuclear power is expensive and, like coal, is becoming less and less cost-competitive with other forms of power, such as wind, solar and natural gas. And it is not as reliable as it is made out to be: A pipeline leak forced the plant’s shutdown for eight days in July 2020, even as extreme heat strained the grid, and equipment malfunctions caused it to go down again three months later.

  • Unnecessary: California has added significant amounts of solar and wind and energy storage to its grid since 2020 and continues to deploy resources rapidly. This spring, the grid ran entirely on renewables for a short period of time, and during the Labor Day weekend heat wave, batteries kicked out about 2 gigawatts of power — equivalent to Diablo Canyon’s output — to stave off rolling outages.

  • Cooling System: Each day, Diablo Canyon sucks up about 2.5 billion gallons of ocean water to generate steam and cool the reactors, before spitting it — 20 degrees warmer — back into the Pacific. The water intake kills thousands of fish each year and sometimes other sea animals. The warm water discharges are also changing the marine ecosystem in Diablo Cove, driving out the bull kelp and having a detrimental effect on abalone.

    Aerial view of the Diablo Canyon Nuclear Power Plant which sits on the edge of the Pacific Ocean at Avila Beach in San Luis Obispo County, California.
    Mark Ralston/AFP via Getty Images

THOSE WHO WANT TO KEEP IT OPEN: California Gov. Gavin Newsom, former energy secretaries Ernest Moniz and Steven Chu, Mothers for Nuclear, Breakthrough Institute, Generation Atomic, Carbon Free California and social media influencer and Brazilian model Isodope.  


  • Economics: Shutting down Diablo Canyon would eliminate about 1,400 high-paying jobs, a $226 million payroll and $26.5 million in annual tax revenue (although these losses would be mitigated by the just transition plans).

  • Grid Stability: Climate change-exacerbated heat is driving up electricity demand as air-conditioners work overtime to keep homes habitable even as it diminishes supplies by draining reservoirs and reducing hydropower production. The supply-demand imbalance will only get worse as the climate warms and homes and transportation are electrified. Shutting down Diablo Canyon would rob the grid of a critical baseload power source.

  • Emissions: If Diablo Canyon were to shut down today, grid operators would be forced to rely on natural gas generation to replace the lost power. That would result in more greenhouse gas emissions and other air pollution from the plants, along with emissions and other impacts from natural gas extraction and transportation.

  • Desalination: One of the main drawbacks of Diablo Canyon is that it can’t be turned down when solar power floods the grid in the middle of the afternoon. The aforementioned 2021 Stanford and MIT report proposed solving this problem by using power from Diablo Canyon to run an ocean-water desalination plant and for “pink” hydrogen production during times when solar output is high and power demand low. That would require constructing desalination and hydrogen production plants, costing billions of dollars, however, which would not make economic sense if Diablo Canyon remains open only until 2030, as Newsom proposes.


At the end of August, California lawmakers voted to lend PG&E $1.4 billion to keep the plant running and to continue to exempt it from the once-through cooling ban until 2030. Less than a week later, PG&E, which had remained on the fence about whether it even wanted to keep the plant open, formally applied with the Energy Department for nuclear plant bailout subsidies.

“I’m extremely pleased to see California extending the operation of Diablo Canyon,” said Kathryn Huff, who leads the department’s Office of Nuclear Energy, in a statement. “These reactors critically underpin our nation’s decarbonization goals and their 24/7 power will support grid stability for consumers in the state during our transition to net zero.”

Still, Diablo Canyon’s reprieve is not a done deal: PG&E must first renew its license or get an extension from the federal Nuclear Regulatory Commission. And that will provide plenty of opportunity for both pro-nuclear climate hawks and anti-nuclear environmentalists to be heard — and for the divide between them to grow into an even deeper abyss.

“The rush by lawmakers and Gov. Newsom to keep Diablo Canyon running is dangerous and dumb and will only set back California’s drive to make solar and wind the prevailing sources of electricity in the state,” said Environmental Working Group President Ken Cook in a statement. “EWG will explore every available opportunity — administratively, legally and policy-wise — to prevent the extended operation of Diablo Canyon.”

Jonathan Thompson is a contributing editor at High Country News. He is the author of Sagebrush Empire: How a Remote Utah County Became the Battlefront of American Public Lands. 

Note: This story was updated to reflect that Diablo supplied about 2 gigawatts of power over Labor Day weekend, not 2 megawatts.