Used fuel transfers to resume at San Onofre

22 May 2019

Fuel transfer operations at the shut down San Onofre nuclear power plant in California can resume following approval by the US Nuclear Regulatory Commission (NRC). Such operations were suspended following an incident last August during the lowering of a used fuel canister into a storage vault.

The on-site dry storage facility at San Onofre (Image: SCE)

Southern California Edison (SCE) retired the two-unit San Onofre Nuclear Generating Station - also known as SONGS - in June 2013 after a contractor provided faulty steam generators. The plant is now undergoing decommissioning. Located on the Pacific coast of California, in the northwestern corner of San Diego County, the plant is owned by Edison International, parent of SCE, with 78.2%, San Diego Gas & Electric Company, 20%, and the City of Riverside Utilities Department, 1.8%.

On 3 August 2018, workers were transferring a multipurpose canister containing used nuclear fuel from San Onofre's storage pool to a HI-STORM UMAX dry cask storage facility. As the canister was being lowered from the transport cask into the underground storage vault, it became stuck on the gusset or inner ring assembly near the top of the vault's inner liner, known as the "divider shell". The plant personnel believed the canister had been fully inserted, because the rigging that supported the canister had gone slack. After a radiation protection technician registered radiation readings higher than expected for a properly loaded cask, the workers performing the operation realised the problem. They then corrected the canister's alignment and successfully completed the operation. SCE stopped all canister-loading activities and subsequently notified the NRC.

The interior of the storage vault (Image: NRC)

The failure of lifting equipment placed the canister in what the NRC calls "an unanalysed condition", and created the possibility of a "load drop event"," as the canister could have fallen 18 feet (5.5 meters) into the storage vault if it had slipped off of the inner ring assembly.

The NRC began a special on-site inspection at San Onofre on 10 September. The inspection team investigated the "near miss" drop event, interviewed personnel involved, and observed equipment operation and preliminary corrective actions put in place to prevent recurrence of the event.

The NRC yesterday said it has now determined that fuel loading at San Onofre can be safely resumed. The regulator said it made its determination following the extensive review of technical data submitted by SCE regarding the possible effects of scratching on used fuel canisters during fuel loading operations.

In a statement, SCE said that since the incident the company and its contractors have performed a comprehensive review of used fuel transfer operations and created "a more robust programme through better procedures, better training, and more intrusive oversight". This includes the addition of cameras and load monitoring equipment. "We have demonstrated these improvements are effective and sustainable through numerous dry runs, regulatory inspections and independent reviews," it said.

SCE stated, "The ultimate decision on when fuel transfer operations will resume will be made following a careful review of operational readiness by SCE and our contractor. SCE will continue to provide timely updates to the community and our stakeholders as we move through this process."

Researched and written by World Nuclear News