Federal officials investigating the cause of excessive tube wear in replacement steam generators at the San Onofre Nuclear Generating Station, which led to a small radiation leak in January, say there was approval of design changes to the generators before they were put into service.
“Anything that has been installed … all of that was reviewed by the NRC prior to install,” said Lara Uselding, a spokeswoman for the United States Nuclear Regulatory Commission.
Yet neither the government nor the plant's operator, Southern California Edison, has made public any evidence that three key changes a nuclear expert claims caused the leak were reviewed by the NRC.
These changes, including the addition of almost 400 tubes per generator, aren't mentioned in official inspection reports provided by the NRC. And so far the agency won't say whether it reviewed and approved those changes before the generators were installed or whether it has any records that refer to the modifications.
The new generators were installed in 2010 and 2011.
“There’s not an answer for you,” Uselding told the Voice of OC. "Because of an ongoing inspection on that right now, you’re going to have to wait."
The NRC is reviewing "the design changes to ensure they were properly reviewed and approved," she said.
Edison said early this month that it would provide a timeline of when it told regulators about specific changes, but the company hasn't responded several follow-up queries.
Nonetheless, the changes — which include the additional tubes, removal of a "stay cylinder" structural component and welding of a ring to restrict water flow into the generator — have all been documented in a trade journal article co-authored by a San Onofre engineer.
Nuclear expert Arnie Gundersen, who was hired by the environmental group Friends of the Earth to study the radiation leak, has concluded that it was caused by those design changes. NRC officials, however, say they have more investigating to do before identifying the ultimate cause.
The leak posed no threat to workers or the public, the officials say.
Under federal law, a nuclear plant's operator is responsible for evaluating proposed design changes to the plant. A thorough review by the NRC, which regulates nuclear plant safety in the United States, typically isn't required unless the company running the plant determines that the changes bring an added safety risk.
In the case of San Onofre's replacement steam generators, Edison determined that the design changes did not pose an added safety risk, according to Uselding.
The new generators, however, developed problems. Tubes vibrated and rubbed against each other, wearing them down at an extremely rapid rate, according to Edison and the NRC. They were supposed to last decades, but in just a year, the tubes in Unit 3 had worn down so much that a break occurred, causing the small radioactive leak on Jan. 31.
Edison and the NRC shut down the plant and are investigating the leak's cause. They haven't yet commented on what they believe was responsible for the excessive vibration.
Gundersen, who served on a state panel overseeing the Vermont Yankee Nuclear Power Station, has declared the three changes as responsible for the leak. In his reports, he also alleges that Edison improperly claimed that the changes were "like for like" replacements to avoid independent analysis by the government.
Edison has issued a broad denial of Gundersen's assertion that it misrepresented the changes.
"At all times during the steam generator replacement process, and the ongoing outages in Unit 2 and 3, SCE has provided open and transparent information to the Nuclear Regulatory Commission," the company asserted in a recent statement.
Edison didn't respond to a request last week for the date it first informed the NRC about the three changes. The company also said on April 6 that it would provide the timing for when it notified the NRC of specific changes but hasn't responded to several queries in the weeks since.
Clarification: This article has been amended to more clearly reflect the U.S. Nuclear Regulatory Commission's position that it did not approve all design changes to the replacement steam generators at the San Onofre Nuclear Generating Station because the plant's operator, Southern California Edison, determined that the changes did not pose an added safety risk.