Three tubes failed a pressure test Wednesday at the San Onofre Nuclear Generating Station's closed Unit 3, prompting the U.S. Nuclear Regulatory Commission to send a special team from its Maryland headquarters to find out why, officials said Thursday.
“The public should not be concerned,” said NRC spokeswoman Lara Uselding in a telephone interview. “The plant is safely shut down.”
Unit 3 has been closed down since Jan. 31 following a tube leak in one relatively new generator.
“Steam generators do experience some wear during the first year of operation, but the level of tube wear at Unit 3 is unusual,” the NRC asserted in a news release Thursday.
After the January leak, NRC officials said there was no danger to the public or employees. They have been trying to determine whether the tube failed because of its design, manufacture, installation, use, maintenance or testing.
The NRC reported that on Wednesday three more tubes in Unit 3 “failed a pressure test indicating they would be more likely to rupture during certain plant events that affect the pressure inside the steam generator.”
The NRC described the tests as pumping water into a tube, then increasing the water pressure while monitors evaluate the soundness of the tubes.
“The integrity of steam generator tubes is important, because the tubes provide an additional barrier inside the containment building to prevent a radioactive steam release,” according to the news release.
The roughly 40-year-old plant just south of San Clemente is operated by Southern California Edison. A special "augmented inspection team" from the NRC’s Rockville, Md., headquarters is headed to San Onofre to help research the cause of the tube leaks.
The special teams are “used when the NRC wants to promptly review the circumstances surrounding a significant issue,” stated NRC Region IV Administrator Elmo E. Collins in the news release. “We want to make sure we understand the cause of the degraded steam generator tubes and take appropriate actions based on our inspection results.”
When the review is completed within the next few weeks, the NRC team will hold a public meeting to discuss the issue, the news release announced.
Public interest in any safety issue at San Onofre and other nuclear power plants was heightened after the meltdown a year ago this week of three reactors at Japan’s Fukushima nuclear plant after a massive earthquake and tsunami.
After the March 11, 2011, natural disaster, the worst in Japan’s history, public fears mounted because government officials were not forthcoming about the seriousness of radiation problems at the nuclear plant, according to numerous news reports.
A Los Angeles Times article on the anniversary of the disaster speculated that that worse than the wreckage caused by earthquake and tsunami, “a more insidious legacy may be a shaken trust — in their government, in their source of energy, and even in the food that sustains them.”
Last month, residents of San Clemente urged local government officials to make independent radiation monitoring information available to the public in real time.