One of the two reactors at the darkened San Onofre nuclear plant could be restarted at full power and operate safely for almost a year, Southern California Edison officials said Monday.
The utility said its analysis confirms that it would be safe to fire up one of the reactors, but that out of an abundance of caution, Edison is proposing running the unit at only 70%.
The plant has been shut down 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 plant were showing signs of unusual 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 generator would then be powered down and inspected.
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 to speculation that Edison could be asked 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 — and not the full power allowed under the plant’s license.
That assertion drew an outcry from environmental activists, led by Friends of the Earth, who have been pushing the NRC to require a license amendment — which could require public hearings and substantially delay the restart process — before making a decision on the restart proposal.
John Large, a consultant to Friends of the Earth, said the analysis, if correct, shows the plant’s life span to be limited, but added: “There remain enormous uncertainties with predicting tube wear, and this report is not convincing that they know enough to allow restart.”
Edison officials said requesting a restart at reduced power was a conservative measure. The company provided an analysis showing that the generator could operate at full power for 11 months without a tube rupture.
“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.