Southern California Edison submitted an analysis to federal regulators showing that one of the two reactor units at the shuttered San Onofre nuclear plant could operate safely at full power for almost a year.
The plant has been shuttered since a steam generator tube in the plant's Unit 3 sprung a small leak on Jan. 31, 2012, releasing a small amount of radioactive steam.
The incident led to the discovery that thousands of tubes in the recently replaced steam generators in both units of the nuclear plant were showing signs of wear.
Eight tubes in Unit 3 failed pressure tests, meaning they could have ruptured under some circumstances.
Unit 2 showed less wear overall and less of a particularly unusual type of wear caused by tubes banging against adjacent tubes. Officials attributed the difference between the two units to slight manufacturing differences in the support structures.
Edison has proposed to restart that unit at 70% power for five months, saying that running at reduced power would alleviate the conditions that led to the tube wear.
The U.S. Nuclear Regulatory Commission, which is still reviewing the restart proposal, asked Edison to show proof that the unit could operate at its full licensed power without danger of a tube rupture, leading many observers to speculate that the agency might require Edison to obtain a license amendment to run at 70% power.
The company previously argued that technical specifications governing tube integrity required it to demonstrate safety at the power level the plant would be operating at -- 70% in this case -- not the full power allowed under the plant's license.
That assertion drew an outcry from activists, led by the environmental group Friends of the Earth, who have been pushing the Nuclear Regulatory Commission to require a license amendment -- which could require public hearings and substantially delay the restart process -- before making a decision on the restart proposal.
Edison officials said requesting a restart at reduced power was a conservative measure. The company provided an analysis, completed by Intertek APTECH, showing that the generator could operate at full power for 11 months without a tube rupture. The analysis focused on the possibility of unusual tube-to-tube wear.
"While we have no intent to restart Unit 2 at full power, this demonstrates the amount of safety margin we have built into our analyses," Pete Dietrich, Edison's senior vice president and chief nuclear officer, said in a statement.
This story was reported by Times Staff Writer Abby Sewell.