Above: An independent spent fuel storage installation (ISFSI) for the storage of spent nuclear fuel at San Onofre Nuclear Generating Station. Photo courtesy of Southern California Edison/Mark Pettijohn
REGION — The Nuclear Regulatory Commission has given Southern California Edison the green light to resume dry storage operations at the decommissioning San Onofre nuclear plant, but it will be some time until the company can do so.
During a June 3 webinar, the NRC gave its basis for why Edison and its contractors could resume fuel-loading operations at the plant.
Linda Howell, acting director of NRC Region IV’s Division of Nuclear Materials Safety, said Edison told the agency it would take them several weeks before they could actually resume loading spent nuclear fuel.
Fuel transfer operations at San Onofre have been on hold since the Aug. 3, 2018, incident when a spent fuel canister got stuck during the downloading process into the cavity enclosure container.
Personnel was unaware the canister was stuck like that for nearly an hour and could have potentially fallen 17 to 18 feet if the metal ring it was stuck on fell or if it slipped off.
Howell recapped the sequence of events since the Aug. 3 incident, including its independent inspections of the loading process and Edison’s responses to those issues.
Edison was issued $116,000 penalty in March from the NRC for a “severity level II” violation, the second most important level in regards to safety for its failure to provide redundant drop protection.
Howell said a violation at this severity level has never been given to a spent fuel storage licensee before.
Edison also received a severity level III violation for failing to make a timely notification about the Aug. 3 incident to the NRC.
Edison told the NRC about the incident on Aug. 6, but was supposed to have made an event report within the first 24 hours after the incident.
Howell said Edison did not receive a civil penalty for the third-level violation because it was given “corrective action credit” after not being the subject of escalated enforcement within the past two years.
The NRC stated in its May 21 announcement to allow Edison to continue transferring the canisters after an “extensive review of technical data” submitted by the company about the possible effects of scratching on the canisters during loading operations.
Edison completed a visual assessment of eight canisters to examine any contact between the cask and canister during downloading using a robotic, specialized precision camera to measure surface defects, and a statistical evaluation was performed based on the wear marks observed for each canister.
“We’re comfortable with their conclusion on how the gouging occurred,” Howell said.
Some concerns regarding gouges to the canister walls question if the canisters are thick enough.
According to Edison, the canisters used at San Onofre are 0.125 inches thicker than standard Holtec canisters, meaning potential wear marks will still be well above the normal licensed value for a 0.50-inch thick canister wall.
Before Edison restarts its fuel transferring operations, it intends to perform a “thorough review to confirm all corrective actions developed over the last nine months.” Edison will commence with fuel transfer from one unit once those reviews are completed, and all fuel transfers are expected to be complete by early next year.
So far, 29 of 73 canisters have been loaded into the Holtec UMAX dry storage facility at San Onofre.
Howell said the NRC has been having weekly teleconferences with Edison to plan its own oversight and inspection activities during this process. The NRC intends to be on site to observe Edison’s review process and will eventually initiate frequent, unannounced inspections once transferring resumes.
Edison’s improvements to fuel transfer operations include new training requirements, the addition of a senior manager observation program and oversight personnel with specific fuel transfer experience, a strengthened corrective action program and a new equipment to monitor every step of the downloading process.