A panel of three federal administrative law judges has announced it is delaying Diablo Canyon nuclear power plant’s license renewal until at least December 2015.

The Nuclear Regulatory Commission’s Atomic Safety and Licensing Board on Tuesday put NRC staff and PG&E on notice that it cannot make a decision on license renewal until detailed seismic studies of faults around the plant are complete and ordered the utility to submit monthly reports starting in July on the status of those studies.

The ruling confirmed a decision last week by the NRC to delay license renewal until seismic studies are done and added new reporting requirements.

It also recognized that the state Coastal Commission has a role in license renewal. That agency must certify that the renewal is consistent with the state Coastal Zone Management Act.

The ASLB is a judicial panel assigned by the NRC to settle protests filed against license renewal. That process includes holding trial-like adjudicatory hearings.

License renewal cannot move forward until those hearings are complete, and the board has postponed them until the seismic studies are complete.

“The schedule submitted by staff on June 1, 2011, fails — probably because of uncertainties in the PG&E schedule — to provide this board with necessary information to permit establishment of a meaningful adjudicatory schedule,” the board ruled.

The ruling also acknowledges that the state has an independent peer review role in license renewal. Early on in the process, the state Energy Commission and state Sen. Sam Blakeslee, R-San Luis Obispo, requested completion of seismic studies.

“PG&E should have never filed this relicensing application in 2009 in defiance of the state’s requests; they should have done the studies first,” said Rochelle Becker with the San Luis Obispo-based Alliance for Nuclear Responsibility.

The ruling is the latest in a series of NRC decisions regarding PG&E’s plans to extend the operating life of Diablo Canyon by 20 years. Many local elected officials have criticized the move as premature until the utility completes detailed studies of the earthquake faults near the plant.

Earlier this year, PG&E sent a letter to the NRC requesting that no final decision be made on license renewal until the seismic studies are done. Last week, the NRC granted that request.

The NRC has already made substantial progress in processing the renewal application, including completing one of two necessary parts, a safety review, said Lara Uselding, NRC spokeswoman. The other part, an environmental review, is now on hold pending completion of the seismic studies.

“This ruling is the ASLB telling the NRC, ‘Keep us posted,’ and telling PG&E, ‘Keep us updated on the seismic studies,’ ” Uselding said.

Local antinuclear activists and Rep. Lois Capps, D-Santa Barbara, have praised the ruling as a meaningful step forward. They had denounced previous decisions as disingenuous because they allowed the renewal process to continue with only a final decision delayed.

“The ASLB’s order is wise and responsible,” said Capps in a letter to the NRC. “It fully recognizes that the NRC relicensing process for Diablo Canyon cannot continue until California’s significant seismic concerns are studied and resolved.”

Pressure on PG&E and the NRC to delay license renewal grew exponentially after a March 11 massive earthquake and subsequent tsunamis in Japan that crippled a large nuclear power plant there, causing radiation releases.

“This more realistic schedule is especially important in light of the Fukushima catastrophe,” said Jane Swanson, spokeswoman for the antinuclear group San Luis Obispo Mothers for Peace. “It provides four-plus years to examine and apply the lessons yet to be learned from the Fukushima disaster.”