Report: Federal regulator blames San Onofre nuclear plant's tube troubles on design flaw

The San Onofre Nuclear Power Plant is seen on April 6, 2012.
The San Onofre Nuclear Power Plant is seen on April 6, 2012.
Grant Slater/KPCC

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After months of investigation, federal regulators have determined that design flaws appear to be the cause of excessive wear in tubing that carries radioactive water through Southern California's troubled San Onofre nuclear power plant, a top federal regulator said.

Regulators are scheduled to host a meeting at 6 p.m. Monday in San Juan Capistrano to talk about the plant's troubles, which has been idle since January, after a tube break in one of four steam generators released traces of radiation. A team of federal investigators was dispatched to the plant in March after the discovery that some tubes were so badly corroded that they could fail and possibly release radiation, a stunning finding inside the virtually new equipment.

Flaws in fabrication or installation were considered as possible sources of the rapid tube decay but "it looks primarily [like] we are pointed toward the design" of the heavily modified generators, Nuclear Regulatory Commission Regional Administrator Elmo Collins told the Associated Press in an interview Sunday.

Collins couldn't rule out that one or more of the generators, installed in a $670 million overhaul in 2009 and 2010, might have to be replaced.

Eight tubes failed during earlier pressure tests in the Unit 3 reactor and "we have not seen that in the industry before," Collins said.

"It's these four steam generators that either have, or are susceptible to, this type of problem," Collins said, referring to the unusual damage caused when alloy tubes vibrate and rattle against each other or brackets that hold them in place. So far, a fix has remained elusive.

"It's not too hard to frame up the problem," he added. "The answers are very difficult, or they already would have emerged."

The disclosure will rivet new attention on a series of alterations to the equipment design, including the decision to add 400 tubes to each generator and installing V-shaped supports that were intended to minimize tube wear and vibration.

Southern California Edison, which operates the plant, has said its own inspectors blame it on vibration and friction from bracing and adjacent tubes. But they have not been able to say why that is happening or how they’ll fix it. The Nuclear Regulatory Commission must approve any plans before the San Onofre nuclear plant is restarted. Edison officials said they will submit plans to the NRC to restart Unit 2 by the end of July. The company said it has no plans yet for restarting Unit 3.

Anti-nuclear activists, who want the plant shut down permanently, are planning a rally before the NRC meeting.

Friends of the Earth, which previously issued reports saying design modifications caused the problems, filed a legal petition asking the NRC to keep San Onofre offline until the company amends its license to reflect design changes.

“We’ll be announcing future plans to prevent the restart of the crippled reactors at the San Onofre Nuclear Generating Station prior to the meeting,” said Bill Walker Friends of the Earth, one of the groups.