Loose bolt causes minor delay in fuel transfer at San Onfre

2 April 2018


The US works crews transferring used fuel at Edison’s San Onofre nuclear station from cooling pools into dry storage discovered a loose bolt inside one of the canisters on 5 March, prompting Southern California Edison to stop the work for ten days.

The free piece of the bolt, about 4 inches by half an inch, was discovered in one of 43 canisters that featured a new design aimed at improving storage capability. The bolt was part of a redesigned system called a shim that seeks to improve the balance and storage of the used assemblies. The work resumed using 30 other canisters that do not include the new design. Edison, which had already filled four of the newly designed canisters with waste, is unable to check whether those casks have the same flaw. The utility said the free part was found while a fifth canister was being filled with spent fuel assemblies.

Edison acknowledged the incident at a meeting on 22 March.

The canisters were designed and built by Holtec International which altered the design midway through the fabrication process. Forty-three of the 73 cask feature an amended shim-basket element, which is designed to support spent fuel assemblies for improved storage and transport. Holtec said on 23 March that it is investigating what happened, and checking if other canisters might be vulnerable to the same weakness that caused the bolt to break. Analyses have shown that the loose bolt does not impact the safety or performance of the dry storage system, Holtec project manager Fred Bidrawn told US press.

The San Onofre plant has been undergoing decommissioning since 2013. Under current plans, Edison is to transfer the used  fuel assemblies from cooling pools to dry storage canisters, which will be placed adjacent to the beach. The transfer process began in January even though Edison agreed, last summer, to settle a lawsuit by exploring ways to move the nuclear waste away from the beach.



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