LOS ANGELES — Federal regulators signaled Wednesday that running California's San Onofre nuclear power plant at reduced power would not pose a significant safety risk – a key step toward a possible restart of one of the idled reactors.
The preliminary ruling from Nuclear Regulatory Commission staff represents a victory for operator Southern California Edison, which is pushing for a restart by June and has argued for months that the Unit 2 reactor is safe to run at lower power.
But Sen. Barbara Boxer, D-Calif., called plans to restart the plant before an investigation is complete "dangerous and premature."
"It makes absolutely no sense to even consider taking any steps to reopen San Onofre until these investigations look at every aspect of reopening the plant," Boxer said in a statement.
Rep. Ed Markey, D-Mass., said in a statement issued jointly with Boxer's that the commission was showing "blatant disregard for the safety of tens of millions of people."
The plant between Los Angeles and San Diego has not produced electricity since January 2012, after a small radiation leak led to the discovery of unusual damage to hundreds of tubes that carry radioactive water.
Edison has asked the NRC to change the seaside plant's operating rules to permit the single reactor to run at no more than 70 percent power, down from the now-required 100 percent. Company engineers believe the lower power will stop the excessive tube wear that sidelined San Onofre more than a year ago.
Edison submitted the filing after the NRC staff raised questions about the plant's ability to operate at full throttle.
In the tentative ruling, the NRC staff reviewed a company analysis and agreed that running the reactor at no more than 70 percent power would not significantly increase the risk of any accident.
The issue represents one of a series of regulatory steps Edison faces before being allowed to fire up the reactor.
Critics of the nuclear power industry warned that the agency was inviting disaster, and they claim that Edison is trying to ram through a restart without sufficient public input.
"This is outrageous," said Shaun Burnie of Friends of the Earth, a group that has been challenging the proposed restart. "This is one very seriously flawed process."
The agency said it is seeking public comments for 30 days on this proposed ruling, which will be considered in the decision.
Members of the public can request a hearing on the change in operating rules, technically known as a license amendment. However, environmentalists have argued that if NRC staff finds there is no significant hazard in a restart, the hearing can be held after the amendment is approved, making it essentially meaningless.
Edison submitted its formal request to run Unit 2 at lower power on Monday. The company did not immediately respond to a request for comment.
Company officials are also preparing long-range plans under which the plant might run for years, even though some of Edison's own research has suggested tube damage could cut short its life span.
Precise projections about the future are dependent on a restart. Edison engineers need to study how the reactor behaves at 70 percent power before being able to sharpen longer-range calculations.
The plant could be started then shut down as many as five times during a trial run to assess its operation and safety.
An earlier Edison analysis concluded the Unit 2 reactor could run at 100 percent power, but the research also found the risk of a tube break could reach unacceptable levels after 11 months.
The NRC has promised a transparent review.
The problems at San Onofre focus on its steam generators, which were installed in a $670 million overhaul in 2009 and 2010.
The future of the heavily damaged Unit 3 reactor, where the radiation leak occurred after a tube break last year, is not clear. Edison has said that because of manufacturing differences, Unit 2's generators did not suffer the extent of deep tube wear witnessed in its sister plant.
Decaying generator tubes helped push San Onofre's Unit 1 reactor into retirement in 1992, even though it was designed to run until 2004.
San Onofre is owned by SCE, San Diego Gas & Electric and the city of Riverside.