CAPISTRANO BEACH, Calif. — 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 California’s troubled San Onofre nuclear power plant, a top federal regulator said.
The twin-reactor plant between Los Angeles and San Diego has been idle since January, after a tube break in one of four, massive 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 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.
It’s possible operator Southern California Edison could face penalties stemming from the federal investigation, Collins said.
The generators were designed to meet a federal test to qualify as “in-kind,” or essentially identical, replacements for the original generators, which would allow them to be installed without prior approval from federal regulators.
An environmental group, Friends of the Earth, has claimed Edison misled the NRC about the changes that it has identified as the likely culprit in excessive tube wear. The federal agency previously disputed that charge, but Collins said that’s under review as part of the investigation.
Inside the guts of the machinery, the original steam generators and the replacements “look substantially different,” Collins added.
The NRC is scheduled to discuss its findings Monday evening at a meeting near the plant.
Collins said safety would remain the first consideration at San Onofre. About 7.4 million Californians live within 50 miles of San Onofre, which can power 1.4 million homes.
“These are significant technical issues. They are not resolved yet,” Collins said.
Cracked and corroded generator tubing has vexed the nation’s nuclear industry for years.
Decaying generator tubes helped push San Onofre’s Unit 1 reactor into retirement in 1992, even though it was designed to run until 2004. The following year, the Trojan nuclear plant, near Portland, Ore., was shuttered because of microscopic cracks in steam generator tubes, cutting years off its expected lifespan. Westinghouse Electric Corp. weathered a legal battle with five utilities in the 1990s that wanted the company to replace steam generators it manufactured for the Beaver Valley nuclear power plant in Pennsylvania after tubing corroded.
The Associated Press