A report from the company that oversees the troubled San Onofre nuclear power plant estimates it could run safely at full power, but only for 11 months.
The California plant hasn't produced electricity since January 2012, when a tiny radiation leak led to the discovery of damaged tubes that carry radioactive water.
A consultant's study from Southern California Edison on Monday represents an attempt to answer regulators who are considering Edison's proposal to restart one reactor.
The restart plan calls for a trial run at reduced power, but Nuclear Regulatory Commission staff wanted Edison to show steam generator tubes don't break during "the full range" of conditions.
The report found it would be too risky to run at full power for more than 11 months.