LOS ANGELES (AP) — Federal regulators Wednesday rejected a request from two environmental groups to immediately shut down one of two reactors at California’s last nuclear power plant.

Friends of the Earth and Mothers for Peace said in a petition filed last month with the Nuclear Regulatory Commission that long-postponed tests needed to be conducted on critical machinery at the Diablo Canyon Nuclear Power Plant, located midway between Los Angeles and San Francisco. They argued the equipment could fail and cause a catastrophe.

In an order dated Tuesday, the NRC took no action on the request to immediately shut down the Unit 1 reactor and instead asked agency staff to review it.

The NRC also rejected a request to convene a hearing to reconsider a 2003 decision by staff to extend the testing schedule for the Unit 1 pressure vessel until 2025. The vessels are thick steel containers that hold nuclear fuel and cooling water in the reactors.

According to the groups, the last inspections on the vessel took place between 2003 and 2005. The utility postponed further testing in favor of using results from similar reactors to justify continued operations, they said.

The commission found there was no justification for a hearing.

The groups said in a statement that the decision showed “a complete lack of concern for the safety and security of the people living near” the plant, which started operating in the mid-1980s.

Operator Pacific Gas & Electric had said the plant was in “full compliance” with industry guidance and regulatory standards for monitoring and evaluating the safety of the reactor vessels.

The petition marked the latest development in a long fight over the operation and safety of the seaside plant, which sits on a bluff above the Pacific Ocean. In August, a state judge rejected a lawsuit filed by Friends of the Earth that sought to block PG&E from seeking to extend the operating life of the plant.

PG&E agreed in 2016 to shutter the plant by 2025, but at the direction of the state changed course and now intends to seek a longer operating run for the twin reactors. Democratic Gov. Gavin Newsom, who once was a leading voice to close the plant, said last year that Diablo Canyon’s power is needed beyond 2025 to ward off possible blackouts as California transitions to solar and other renewable energy sources.