Edison unit says San Onofre nuclear restart safe at lower output

HOUSTON, March 18 Mon Mar 18, 2013 5:05pm EDT

HOUSTON, March 18 (Reuters) - Southern California Edison, operator of the shuttered San Onofre nuclear plant in California, submitted additional analysis to nuclear regulators to demonstrate that the 1,070-megawatt Unit 2 can be restarted safely, the utility said on Monday.

Both reactors at the 2,150-megawatt San Onofre nuclear station, owned by Edison International and Sempra Energy , have been shut for more than one year following the discovery of excessive wear that prematurely damaged thousands of tightly packed tubes inside large steam generators that were installed in the reactors in 2010 and 2011. Each reactor has two steam generators.

Loss of the plant's output has strained Southern California's power grid and state agencies are planning for a second summer without the plant. {ID:nL1N0B7IM7]

Staff of the U.S. Nuclear Regulatory Commission is reviewing a plan by Southern California Edison (SCE) to restart Unit 2 by running the unit at 70 percent of capacity for five months, then shutting it to inspect for additional wear on damaged tubes.

SCE said running the plant at a reduced power will prevent the conditions that caused premature tube wear in San Onofre Unit 3 and indications of wear in Unit 2.

The NRC staff and SCE have disagreed on whether the utility's plan to operate Unit 2 at a reduced rate complies with technical specifications in the unit's operating license.

Even though SCE said it will only operate the reactor at 70 percent power, the NRC staff said the license requires that steam generator tubes be able to operate safely "over the full range of normal operating conditions," including full power.

Last month, SCE agreed to supply additional analysis to show that the tubes will retain structural integrity when the unit is running at 100 percent power.

SCE said its new assessment, performed by Intertek APTECH of Sunnyvale, California, showed that Unit 2 "could operate at full power for 11 months with full tube integrity."

"This evaluation confirms the structural integrity of the Unit 2 steam generators at 100 percent power, as requested by the NRC," said Pete Dietrich, SCE's chief nuclear officer, in a statement.

"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," Dietrich said.

A nuclear engineer hired by Friends of the Earth, an anti-nuclear environmental group, said the SCE report was not convincing.

There "remain enormous uncertainties with predicting tube wear and this report is not convincing that they know enough to allow restart," said John Large, a London-based consultant.

The NRC is reviewing SCE's filing and had no immediate comment. A decision on whether or not San Onofre 2 can restart may come in May or June, according to an NRC website.