The difference between the original and new style of spent fuel canister deployed at the San Onofre Nuclear Generating Station (SONGS) in California is effectively a minor tweak, manufacturer Holtec International said in response to concerns about a broken bolt found in the newer version of the container.
The New Jersey energy technology company issued a white paper after utility Southern California Edison from March 5 to 15 suspended transfer of spent fuel from wet to dry storage at the retired nuclear power plant. The stoppage was ordered following discovery of the broken pin in one of the Holtec canisters being used for the work.
“All of the safety criteria in the SONGS (interim dry storage facility) are fulfilled even if one postulates that every bolt (all 88 bolts in the canister) were somehow to vanish from the canister,” according to the white paper.
Of the 73 Holtec-built canisters in use for the waste transfer, 30 are of an older design and 43 are of a newer design. Through March 5, four huge canisters of the newer design had been used. Before spent fuel assemblies were placed in a fifth canister, workers found a broken pin in the bottom of the container. The remaining 39 newer canisters have been recalled. Work resumed on March 15 with only the old-design canisters, and a fifth canister has been moved to the dry storage facility since then.
The broken bolt came from a manufacturing process “that is not common to all canisters,” Holtec said.
The interior of Holtec’s spent fuel canister has 37 long rectangular chambers that each hold up to 37 spent fuel assemblies. “Basket shims” are placed around the interior of a canister’s walls to keep the long rectangular chambers in place and enable circulation of helium used to cool the fuel assemblies. The broken pin was one of 88 in each canister to hold the shims in place.
