The Public Utility Commission announced an agreement Thursday with Pacific Gas & Electric (PG&E) to close California’s last nuclear power plant reactors at Diablo Canyon by 2025.

California pioneered America’s effort to switch to clean and cheap nuclear power generation by switching on the Sodium Reactor Experiment near Alameda on July 12, 1957. Over the next four decades, eight more plants were approved at Bodega Bay, Diablo Canyon, Humboldt Bay, Rancho Seco, San Onofre, Stanislaus, Sundesert, and Vallecitos.

From 1995 to 2011, nuclear power was rated as having the cheapest electrical production cost at 2.19 cents per kilowatt hour. That compared to per kilowatt hour production costs of 3.29 cents for coal; 4.51 cents for natural gas; ad 21.56 cents for oil.

But a 2011 earthquake in Japan caused a massive tsunami that eventually led to multiple-core meltdowns at Tokyo Electric Power’s Fukushima Daiichi nuclear power plant. Japan’s Ministry of Economy, Trade and Industry estimated that the disaster costs of decommissioning, clean up, power replacement and economic loss added up to $188 billion.

With a moratorium already issued on requests to site any additional nuclear power plants until a permanent solution was found for radioactive waste disposal, the CPUC forced the shut-down of San Onofre Nuclear Generating Station in North San Diego County after Southern California Edison Co. (SCE) operators caused a radiation leak by pushing the one of its two reactors beyond its rated pressure and temperature.

SCE considered repairing the plant, but the CPUC agreed to a wildly lucrative deal that allowed the company to charge its customers $3.3 billion of the supposedly $4.7 billion in costs for the premature closure. It is believed SCE gained the valuable right to sell cap-and-trade greenhouse gas allowances due to the plant closing.

Based on the economics of San Onofre closing, PG&E announced on June 20, 2016 that it had begun negotiations with the CPUC to close both Diablo Canyon Power Plant reactors located at San Louis Obispo County’s Avila Beach by 2025.

Under a Joint Proposal with the International Brotherhood of Electrical Workers, Coalition of California Utility Employees, Friends of the Earth, Natural Resources Defense Council, Environment California, and Alliance for Nuclear Responsibility, PG&E requested $1.3 billion from ratepayers to replace 2,200-megawatts of nuclear powered electricity with a “greenhouse-gas free portfolio” consisting of energy efficiency, renewable energy sources, and storage.

CPUC announced on Jan. 11 that they had approved the plant closure, but only authorized PG&E to charge ratepayers an extra $241.2 million in costs associated with the premature plant closing — including $211.3 million to pay workers through 2025, $11.3 million for worker retraining, and $18.6 million license expenses. It is unknown if PG&E will also be able to sell huge cap-and-trade greenhouse gas allowances.

The once energy-rich California has managed to go from having among the cheapest commercial electrical power costs in the nation during the 1960s, to the most expensive in the continental United States at 15.98 cents per kilowatt hour as of October. The shutdown of the extremely low-cost Diablo Canyon Power Plant reactors is expected to increase California’s commercial, industrial and residential electrical costs.