The closure of California’s last nuclear power plant would cost Pacific Gas and Electric Co. customers $112.5 million annually under a regulatory settlement the utility recently reached with various groups.

PG&E customers would pay through 2027 to shut down the Diablo Canyon plant in San Luis Obispo County if the five-member California Public Utilities Commission signs off on the settlement. The entire closure would cost an estimated $3.9 billion, about $1 billion less than PG&E originally sought.

Monthly bills for the average PG&E customer would rise 59 cents under terms of the deal, or $7.08 per year, according to company spokeswoman Hillary Bouchenot. PG&E has already set aside about $3 billion in customer money to fund the plant’s decommissioning, Bouchenot said in an email.

The settlement proposal was filed with the commission on Friday, supported by PG&E, The Utility Reform Network consumer group, the Alliance for Nuclear Responsibility, the commission’s public advocates office and other groups.

In a statement on Monday, the alliance credited itself with reducing the amount of time it should take to transfer nuclear waste from fuel pools into dry cask storage. The company had planned to keep spent fuel in the pools for seven years after shutting down the plant, but as a result of the deal it will now look for companies that can transfer the waste in four years, the alliance said.

“Given PG&E’s woeful corporate safety record, this added measure of enhanced safety regarding the vulnerable spent fuel pools is a big victory for Californians,” said Rochelle Becker, the alliance’s executive director, in the statement.

Becker said her group is “pleased that our multi-year pursuit of those concerns will also keep costs lower for ratepayers as we bear witness to the end of nuclear power in our state.”

Assemblyman Jordan Cunningham, R-Templeton (San Luis Obispo County), has proposed a state constitutional amendment that would keep Diablo Canyon open. But the amendment faces long odds because it would reclassify nuclear power as renewable energy — a tough political sell in a state that has turned away from plants like Diablo Canyon.

Nick Mirman, Cunningham’s chief of staff, said in an email Monday that the lawmaker’s office is still waiting to hear whether the Legislature will hold a hearing on the proposed amendment.

In December, PG&E reached a different proposed settlement as part of its three-year general rate case. That settlement, which must also still be approved by the state utility commissioners, would raise the bill for a typical electric and gas customer by 3.4%.

J.D. Morris is a San Francisco Chronicle staff writer. Email: jd.morris@sfchronicle.com Twitter: @thejdmorris