Powering the Golden State: Diablo Canyon’s Role in California’s Energy Evolution

Powering the Golden State: Diablo Canyon’s Role in California’s Energy Evolution

California stands at a crossroads in its energy future, where the balance between innovation, sustainability, and reliability is more crucial than ever. Central to this discussion is the Diablo Canyon Power Plant (DCPP), California’s last nuclear power facility, whose fate highlights the challenges and opportunities of transitioning to clean energy. This blog explores the intricate dynamics of nuclear energy, the history and potential future of DCPP, and the diverse perspectives that shape its significant debate.

 Photo courtesy of PG&E Social Media

Photo courtesy of PG&E Social Media

The Role of Nuclear Energy and Diablo Canyon Power Plant

Nuclear energy is a powerful source of electricity, generated through the process of nuclear fission. In this process, uranium atoms are split in a nuclear reactor, releasing a significant amount of heat. This heat is then used to produce steam, which drives turbines to generate electricity. Unlike fossil fuels, nuclear power plants operate with a significant environmental advantage during the electricity generation process, as they produce no greenhouse gas emissions. This contrasts sharply with fossil fuel-based electricity generation, which releases carbon dioxide and other pollutants that contribute to climate change and air pollution. Nuclear energy also helps maintain a stable and constant power supply without the need for energy storage, unlike solar and wind energy. These characteristics position nuclear energy as a significant player in the mix of energy sources aimed at reducing our carbon footprints and combat climate change.

In California, nuclear energy has played a vital role in meeting the state’s electricity needs. Among the nuclear power plants in California, DCPP stands out. Located near Avila Beach in San Luis Obispo County, DCPP is not only the state’s last operating nuclear power plant, but also its largest. Owned and operated by Pacific Gas and Electric Company (PG&E) since 1985, DCPP plays a key role in California’s energy infrastructure, providing about 18,000 gigawatt-hours (GWh) of electricity annually. This contribution represents approximately nine percent of California’s in-state generation, establishing DCPP as a critical source of reliable, carbon-free electricity, and contributing to California’s diverse energy portfolio.

Decommissioning vs. Extension

The discussion around decommissioning DCPP began seriously in 2016 when PG&E, the plant’s operator, announced plans to close the facility by 2025. This decision was driven by energy demand projections that indicated the plant’s continued operation was not necessary to meet future energy requirements. Coupled with a commitment to align with California’s state policy favoring renewable energy sources, this decision reflected a shift towards meeting the state’s electricity needs through increased investment in renewables. The plan for a phased shutdown was part of an agreement with several environmental and labor groups, aiming to facilitate a smooth transition to renewable energy without compromising grid reliability or increasing emissions. This plan was formally approved in January 2018 by the California Public Utilities Commission (CPUC) and PG&E withdrew its application to the NRC for a licensing extension in February 2018.

However in 2022, the conversation took a significant turn. California was faced with the escalating challenges of climate change, including severe droughts and extreme temperature fluctuations, which greatly increased electricity demand, posing serious threats to the state’s energy reliability. Simultaneously, global supply chain disruptions, along with delays in interconnection and permitting, hindered the roll-out of renewable energy projects. These difficulties created a gap between the immediate energy demand and the available supply from renewables, highlighting the need for DCPP’s continued operation to address reliability risks during peak demand times. Consequently, California officials expressed support for extending DCPP’s operational life. On September 2, 2022 Governor Newsom signed Senate Bill 846 into law, providing a path for extended operations of DCPP through 2030. This shift was influenced by concerns over energy reliability and the ambitious goals to transition to clean energy. The proposal to extend the plant’s life beyond its scheduled closure sought to ensure a stable electricity supply while the state ramps up renewable energy capacity. The California Energy Commission’s Vice Chair Siva Gunda explains: “An extension would allow more time for additional clean energy projects to come on-line as we work on the long-term transition away from fossil fuels”.

The U.S. Nuclear Regulatory Commission (NRC) is currently evaluating a License Renewal Application submitted by PG&E for DCPP. This application, submitted in November 2023, seeks a 20-year extension for the operation of the plant. Following the submission, the NRC confirmed in December 2023 that the application meets the necessary criteria to proceed with a comprehensive safety and environmental review. This process, which includes the preparation of an Environmental Impact Statement, is expected to be completed in approximately 20 months.

 Photo courtesy of PG&E Social Media

Photo courtesy of PG&E Social Media

Key Players in Diablo Canyon’s Future

The decision-making process regarding the future of DCPP involves several key stakeholders, each with distinct roles and perspectives. At the heart of this process is the NRC, the federal body responsible for overseeing nuclear power plants’ safety and licensing. The NRC’s approval is essential for any plans to extend DCPP’s operational life, making their evaluations and requirements a central aspect of the discussion.

Another vital player is the CPUC, which has a crucial role in evaluating the implications of extending the plant’s operation, especially regarding how it impacts electricity rates and infrastructure planning. The CPUC’s decisions are pivotal for ensuring that California’s energy policies align with both environmental goals and the need for a stable power supply.

Other key state agencies play important roles in regulating DCPP, each focusing on distinct aspects of its operation. The California Energy Commission (CEC) evaluates the plant’s importance for energy reliability and emission goals. The California State Lands Commission (CSLC) manages land leases, ensuring environmental compliance. The California Coastal Commission (CCC) oversees adherence to coastal policies, safeguarding environmental and public access. The California State Water Resources Control Board regulates water use, particularly for cooling, to meet state conservation standards. Collectively, these agencies ensure that DCPP operates in line with California’s energy, environmental, and water management policies, providing a layered state oversight alongside federal regulation.

PG&E is integral to assessing the plant’s ongoing operation, focusing on safety, feasibility, and economic factors while engaging with regulators and the community for license extension efforts. The Diablo Canyon Independent Safety Committee (DCISC) complements these efforts by providing critical oversight on nuclear safety, through regular reviews, inspections, and recommendations to uphold stringent safety standards. San Luis Obispo County also addresses local governance, emergency preparedness, and community welfare concerns, acting as a liaison between the plant and the residents.

Environmental groups and community stakeholders also play a significant role in this process. They bring important concerns to the table, including safety, environmental impact, and the transition to renewable energy sources. Their input ensures that a wide range of perspectives are considered in the decision-making process, aiming for a balance between reliable energy, environmental protection, and public health and safety.

Beyond 2025: The Nuclear Energy Extension Debate

> Opposition Viewpoint

(1) The proximity of DCPP to thirteen known fault lines, including two considered active and major, has intensified concerns about the plant’s seismic safety, underscored by critics as an unacceptable threat to public safety and the environment. Recent analyses suggest that seismic risks to DCPP are significantly greater than PG&E’s estimates, raising alarms over the potential for earthquake-caused accidents during extended operation. Additionally, issues of reactor embrittlement, particularly in Unit 1’s reactor pressure vessel pose serious risks. This embrittlement could compromise the reactor’s integrity, with PG&E and regulatory bodies yet to fully address these concerns or update seismic studies with the latest data.

(2) The issue of radioactive waste management is also a significant argument against the plant’s extension. Nuclear power generation produces high-level waste that requires long-term, secure storage solutions, which are yet to be fully resolved at a national level. Continuing to operate DCPP worsens the challenge of managing and storing radioactive waste safely, especially as the infrastructure ages, posing environmental and public health risks for generations. Additionally, the plant’s once-through cooling system poses a threat to marine ecosystems, potentially affecting local biodiversity and the health of aquatic environments.

(3) Opponents of the license extension also argue for an accelerated shift towards renewable energy, challenging the assertion that DCPP is crucial for grid reliability. Expert analysis suggests California has ample renewable, storage, and demand response capacities that can maintain grid reliability without DCPP—even during extreme weather events. Moreover, DCPP’s inflexible, continuous operation could ironically heighten blackout risks by necessitating large reserves to cover its potential sudden outage, thus straining the California Independent System Operator (CASIO)’s ability to manage grid stability. This reliance on a large, inflexible power source restricts the integration of more adaptable solutions, such as renewables paired with energy storage and demand response programs, which are pivotal for a resilient energy system. Advocates highlight that shifting towards these diversified, flexible resources promises not just to uphold but enhance grid reliability, offering a sustainable path forward in line with California’s clean energy goals.

(4) Financial considerations are also central to the debate on extending DCPP’s license, with concerns about the cost-effectiveness and impact on Californians’ utility bills. The CPUC’s projections suggest the costs of running DCPP for an additional 5 years could exceed $6 billion, translating to an important burden spread to non-PG&E ratepayers. This financial outlay could detract from investments in less costly, more flexible renewable resources, which are essential for California’s clean energy future.

> In Favor of Extension

(1) DCPP is a cornerstone of California’s energy landscape, supplying around 17% of the state’s zero-carbon electricity and supporting the state’s climate goals by operating without emitting carbon emissions. This clean energy source is pivotal in California’s strategy to achieve 100% renewable and carbon-free electricity by 2045. Its around-the-clock electricity generation provides a steady, reliable power supply that complements the intermittent nature of renewable sources such as solar and wind, without the need for storage solutions. This capability not only helps to stabilize energy prices by hedging against the volatility of other energy sources but also ensures that California’s energy needs are continuously met, even during high demand or when renewable energy production is low.

(2) The economic benefits of DCPP, especially to its surrounding communities, are significant. As San Luis Obispo County’s largest private employer, DCPP supports over 1,300 nuclear professionals and contributes more than $15 million in property taxes, benefiting local schools and communities. The continuation of DCPP’s operations aligns with supporting local economies, preserving jobs, and facilitating a smoother transition to renewable energy sources, providing time to develop and implement strategies to mitigate potential economic impacts on the community.

(3) In response to concerns about seismic safety and radioactive waste management, PG&E has undertaken extensive measures to ensure the plant’s safety and compliance. An updated seismic assessment conducted as required by Senate Bill 846 and validated by independent experts has reaffirmed DCPP’s resilience to seismic events, with PG&E’s ongoing Long-Term Seismic Program ensuring the facility remains seismically secure. Regarding radioactive waste, PG&E assures there is ample capacity for storing spent fuel safely and securely, with plans in place to accommodate additional waste if necessary.

(4) Countering arguments on grid reliability and financial considerations, PG&E references CEC report emphasizing the challenges of rapidly integrating new clean energy resources. DCPP’s role is deemed valuable until sufficient replacement resources are operational, ensuring a stable transition toward California’s clean energy future. They emphasize that no supply resources available before the planned 2025 retirement could replicate DCPP’s contribution of 18,000 GWh per year to California’s energy mix. PG&E is also addressing the economic aspects of DCPP’s extension, ensuring cost recovery and minimizing impacts on customers through strategic filings and leveraging funds from the U.S. Department of Energy Civil Nuclear Credit Program to support the transition to extended operations.


For those interested in learning more about DCPP and staying up to date with the ongoing discussions about the plant’s future, several resources are available:

  • The NRC’s License Renewable Application process and schedule is available here.
  • The County of San Luis Obispo’s Planning and Building Department provides updated information here.
  • The Diablo Canyon Decommissioning Engagement Panel provides detailed reports, related meetings and events information here.
  • PG&E’s website contains additional information regarding DCPP’s status and future.
  • Mothers for Peace is a non-profit organization and a legal intervenor challenging the NRC and PG&E on DCPP’s safety issues. They discuss the dangers of extending the operations of DCPP. Learn more here.
  • The CEC discusses the economic benefits of DCPP here, and analyzes the need of DCPP to support grid reliability here.


The debate over Diablo Canyon Power Plant’s future is complex, involving a delicate balance between ensuring energy reliability, addressing climate change, safeguarding public safety, managing nuclear waste, and embracing the transition to clean energy. As California navigates these challenges, the decision on DCPP will require careful consideration of both the immediate and long-term implications for the state’s energy landscape, environmental goals, and community well-being.