The Nuclear Regulatory Commission held its first public webinar Thursday to take questions about a near miss accident at the San Onofre nuclear power plant.
NRC investigators were frank about the cause of the incident.
A stainless steel canister weighing about 50 tons and loaded with 37 radioactive spent fuel rods nearly fell 18 feet into a concrete bunker while being transferred from spent fuel pools into dry cask storage. The storage system was designed by Holtec International.
The incident happened Aug. 3 and was revealed publicly by a whistle blower.
NRC Investigator Erik Simpson said two of the operators involved in lowering a canister into a bunker were performing the operation for the first time. He said they ignored important cues.
“This violation revolves around inattentiveness,” Simpson said. “They weren’t paying attention to what they were doing, so instead of paying attention and getting that round peg lined up just so and into the hole, they fell asleep at the switch.”
Simpson said there were no supervisors observing the operation at the time, though oversight was fine when he visited the site before the transfer of radioactive spent fuel began.
“They’re going to have their best performers out there because nobody wants to fail in front of the NRC,” he said. “When we were out there observing dry runs, there was everyone and their mother out there watching these operations, but once we left, oversight falls off, instead of having two people up in the manned basket, now you have one.”
Troy Pruit is director of Nuclear Safety in District Four, which covers San Onofre. He said the NRC does not require licensees — in this case, Southern California Edison — to analyze the consequences of a canister “drop,” because they are required to have cables attached to the canister that prevent it from dropping.
“Their license requires that they provide redundant drop protection throughout the movement of a canister,” Pruit said. “And that’s what makes this event so serious."
Photographs show the cable coiled loosely around the top of the canister.
“I don’t think anybody has analyzed trying to pull a canister from a drop out of the bottom of a vault, I don’t think it’s been done,” Pruit said. “And again, the NRC does not require that type of analysis. What we do require is redundant load protection features.”
A second violation was Edison’s failure to report the incident within 24 hours.
Southern California Edison put out a statement following the webinar:
"SCE’s findings, developed through rigorous evaluations, match many of the commission’s findings. SCE will not restart spent fuel transfer operations until satisfied all corrective actions are in place and proven effective, the public has been briefed, and the commission has completed its onsite inspection actions," the statement read. "SCE will update the community at the next Community Engagement Panel public meeting Nov. 29."
Pruit said 500 people signed up for the webinar. The three-hour hearing will be transcribed and put on the NRC website in the coming weeks. Civil penalties could be imposed next year.
