The premature shutdown of Diablo Canyon units 1 and 2 will "inflict grave harm to California's economy and environment," according to the American Nuclear Society (ANS). The closure of California's last remaining nuclear power plant will cause more grid instability and rolling blackouts for the state because Diablo Canyon reliably supplies about 10% of in-state power, it says. Former US energy secretaries Steven Chu and Ernest Moniz have also called for the decision to shut down the plant to be reassessed.

Diablo Canyon (Image: US Nuclear Regulatory Commission/PG&E)

Pacific Gas and Electric Company in August 2016 announced plans to retire Diablo Canyon's two pressurised water reactors at the end of their current 40-year operating licences, which expire in November 2024 for unit 1 and August 2025 for unit 2. The state's Public Utilities Commission in January 2018 approved a multiparty settlement to fully and permanently shut the plant down when unit 2's operating licence expires.

"Along with further weakening California's fragile power grid, the premature closure of Diablo Canyon will deprive California of its largest carbon-free energy resource and worsen the state's growing dependency on electricity from out-of-state fossil power plants," ANS President Steven Nesbit and Executive Director/CEO Craig Piercy said in a 24 November statement. "The premature loss of Diablo Canyon will result in millions of tonnes of additional greenhouse gas emissions per year, ruining state and federal plans for decarbonisation."

While solar, wind, geothermal and battery storage will play an important role in any decarbonisation plan for California, they say the state will need every clean energy resource that it has - including nuclear - to meet its climate goals.

"Intermittent sources alone cannot replace Diablo Canyon's reliable 24/7 production of dispatchable carbon-free electricity for Californians. If the planned closure goes ahead, Diablo Canyon's carbon-free electricity would be replaced by carbon-emitting natural gas- and coal-fired generation.

"Without Diablo Canyon, California will be forced to depend on the charity of neighbouring regions to make up for shortfalls in power supplies, including meeting demand after sunset when solar resources become unavailable. Given the inevitable potential for conditions limiting the availability of out-of-state energy, including the current drought impacting hydropower sources throughout the western United States, that is not a prudent situation."

Nesbit and Piercy note the decision to shut down the Diablo Canyon units was made several years ago and that circumstances have since changed. "The clean energy imperative is even stronger, and the importance of Diablo Canyon to the reliability of California's current and future supply of carbon-free electricity is undeniable. It is time to revisit outdated decisions made in the last decade in the light of today's facts and prepare for the continued operation of Diablo Canyon. ANS calls upon Governor Gavin Newsom to reconsider the decision and keep Diablo Canyon online."

All zero-carbon energy sources needed

The continued operation of Diablo Canyon was also called for by former US energy secretaries Steven Chu and Ernest Moniz in a joint Op-Ed published in the Los Angeles Times on 21 November. "Reconsidering the future of Diablo Canyon is now urgently needed in advancing the public good," they said.

"Without nuclear power, even as deployment of renewable power expands, California will have to increase reliance on gas-fired peaker plants (power plants that run when energy demand peaks) at a time when we need all the clean power we can produce."

Chu and Moniz referred to a new report by authors from Stanford University (where Chu is professor of physics and molecular and cellular physiology), the Massachusetts Institute of Technology (where Moniz is professor of physics and engineering systems emeritus) and LucidCatalyst. The study reassesses Diablo Canyon's potential value for helping California meet the challenges of climate change by providing clean, safe and reliable electricity, as well as its potential for powering water desalination and hydrogen fuel production.

The MIT-Stanford study found that keeping Diablo Canyon in operation until 2035 would reduce carbon emissions from the electricity sector by 11% annually compared with 2017 levels and would save ratepayers an estimated USD2.6 billion to 2035 and up to USD21 billion by 2045. It also would alleviate the need to develop 90,000 acres of land for renewable energy production just to replace the facility's capacity.

"We need to increase renewables at a massive scale, but that will take decades, so any zero-carbon source we retire today will set us back years on the zero-carbon journey," the Op-Ed said. "This is not an either/or situation: California needs both Diablo Canyon and renewables to significantly reduce emissions over the next two decades.

"The challenges here in California and globally are bigger than ever and the window of opportunity to mitigate climate change is closing fast. Extending the license of Diablo Canyon buys critical time for the innovation needed to reach net-zero emissions.

"Revisiting the decision to close Diablo Canyon will involve many stakeholders, including federal regulators needed to permit restart of the licence extension process. But that dialogue needs to happen because the stakes are so high. Reimagining Diablo Canyon's role in California's energy future is an opportunity we cannot afford to ignore."

Researched and written by World Nuclear News