In 2016, PG&E announced that it plans to close the two Diablo Canyon reactors in 2024 and 2025, stating that because California's energy regulations give renewables priority over nuclear, the plant would likely only run half-time, making it uneconomical.

[8][9][10] In 2021 the California Energy Commission and CAISO warned that the state may have summer blackouts in future years as a result of Diablo's closure coinciding with the shutdown of four natural gas plants of 3.7GW total capacity, and the inability to rely on imported electricity during West-wide heat waves due to reduced hydroelectric capacity (from the decades-long drought) and the closure of coal plants.

Unlike evaporative cooling systems used at other plants, Diablo Canyon's OTC is designed so all water can be recycled, and to assure minimal impact on ocean ecosystems.

All thermal power stations in California using OTC systems for cooling employ various filtering capabilities to prevent larvae and other aquatic objects from being drawn into impacts with the grids on the intake tubes, known as entrainment.

[20] These upgrade cost estimates have been the subject of controversy and debate, with some arguing instead for construction of an artificial reef to better offset the environmental impact of diminished larvae spawning.

[24][25][26][27][28] This fault experienced a 7.1 magnitude quake 10 miles offshore on November 4, 1927, and thus is capable of generating forces equivalent to approximately 1⁄16 of those felt in the 1906 San Francisco earthquake.

In September 1981, PG&E discovered that a single set of blueprints was used for these structural supports; workers were supposed to have reversed the plans when switching to the second reactor, but did not.

[33] The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Diablo Canyon was 1 in 23,810, according to an NRC study published in August 2010.

[37][38] On June 24, 2013, at 9:20 PM PDT, Diablo Canyon experienced a loss of offsite power to the startup transformers of both units due to a failure on the 230 kV transmission system.

Diablo Canyon was built and entered service in the midst of legal challenges and civil disobedience from the anti-nuclear protesters of the Abalone Alliance.

[40][41] Speaking before the Senate Committee on Environment and Public Works, Representative Capps stated that she believed the "Nuclear Regulatory Commission should stay the license renewal process until the completion of independent, peer reviewed, advanced seismic studies of all faults in the area."

According to Victor Dricks, senior public affairs officer for NRC Region IV, the Commission conducted a nationwide review of nuclear power plants for their capacity to respond to earthquakes, power outages and other catastrophic events, and Diablo was found to have "a high level of preparedness and strong capability in terms of equipment and procedures to respond to severe events.

[45] A few days later, the Atomic Safety Licensing Board (ASLB) indicated that it would defer adjustment of the adjudicatory schedule of the four contentions brought by San Luis Obispo Mothers for Peace (SLOMFP), a community-based anti-nuclear organization, accordingly.

[46][47] S. David Freeman, a former general manager of the Sacramento Municipal Utility District for four years, criticized the continued operation of Diablo Canyon, calling nuclear power the "most expensive and dangerous source of energy on Earth."

According to Freeman, Diablo Canyon and the since-closed San Onofre nuclear plant are both "disasters waiting to happen: aging, unreliable reactors sitting near fault zones on the fragile Pacific Coast, with millions or hundreds of thousands of Californians living nearby.

[52] Lieutenant Governor Gavin Newsom, as a member of the State Lands Commission, was interested in moving the discussion along in part to allow for a slower, greener transition.

PG&E's application to close Diablo Canyon, including the Joint Proposal, was approved by the California Public Utilities Commission in January 2018.

[14] Steven Chu, energy secretary in the Obama administration, endorsed the study and said: “We are not in a position in the near-term future to go to 100% renewable energy, and there will be times when the wind doesn’t blow, the sun doesn’t shine and we will need some power that we can turn on and dispatch at will, and that leaves two choices: fossil fuel or nuclear" and he noted that countries that have shut down their nuclear plants have ended up using more fossil fuels.

)[11] In a November 2021 opinion article, the editorial board of The Washington Post said: "If the state is serious about achieving carbon neutrality over the next few decades — and it should be — it cannot start by shutting down a source of emissions-free energy that accounts for nearly 10 percent of its in-state electricity production.

A new report from experts at the Massachusetts Institute of Technology and Stanford University has made that point clearly: Closing down Diablo Canyon would be the definition of climate incoherence."

"[58] In February 2022 a group of 79 scientists published an open letter highlighting that the plant provides 18 TWh of low-carbon electricity annually and its closure is at odds with decarbonization goals.

[59] In response to these concerns, in August 2022 California Governor Gavin Newsom proposed providing PG&E with a $1.4 billion loan to support the continued operation of Diablo Canyon for another 5 to 10 years.

[61] PG&E is also expected to seek funding from a $6 billion federal program intended to support the continued operation of nuclear plants facing closure.

[67][68] The Department of Energy approved $1.1 billion in funding in November from the Civil Nuclear Credit program which was included in the Infrastructure Investment and Jobs Act.