By John Stang
Holtec International is studying why an aluminum pin broke off inside a cask designed to store spent nuclear fuel at the San Onofre Nuclear Generating Station (SONGS) in California.
Tom Palmisano, vice president and chief nuclear officer at SONGS for majority owner Southern California Edison (SCE), briefed the public on the matter at a Thursday meeting of the SONGS Community Engagement Panel in Laguna Hills, Calif.
“They (Holtec) have stepped up. … Commercially, it’s Holtec’s responsibility. But we’re not saying its Holtec’s problem. It’s our problem,” Palmisano said.
Holtec, a New Jersey based energy technology company, is SCE’s contractor for relocation and dry storage of spent fuel from reactor Units 2 and 3 at the nuclear plant, which closed permanently in 2013.
Right now, roughly one-third of SONGS’ 3.55 million pounds of spent reactor fuel is already held in 51 canisters in an on-site independent spent fuel storage installation. That radioactive waste is from the plant’s reactor Unit 1, which shut down in 1992. Last year, Southern California Edison built a new dry storage site for another 73 canisters of fuel from Units 2 and 3. Relocation of this material is underway and is expected to be complete in mid-2019.
Of the 73 Holtec-built canisters, 30 are of an older design and 43 are of a newer design. So far, four huge canisters of the newer design have been used to move the fuel to dry storage about 100 feet from the Pacific Ocean. Before used fuel assemblies were put in a fifth canister, workers found a broken pin in the container, Palmisano said.
The interior of Holtec’s spent fuel canister has 37 long rectangular chambers that each hold up to 37 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 is one of many in each canister to hold the shims in place.
“It was found that the separated bolt was limited to a basket within a canister that was subject to a certain process during manufacturing that is not common to all canisters,” Holtec said in a statement Friday. “Investigation of baskets that were not subjected to this specific manufacturing process show no evidence of the bolt separation. Analyses demonstrate that the separation of the bolt does not impact the safety of the basket or the performance of the dry storage system in storage or transportation.”
Upon finding the broken pin, SONGS switched to using the 30 older-design casks, Palmisano said. The 39 remaining newer casks have been shipped back to Holtec for analysis of what went wrong in the canister with the broken pin, he said.
Southern California Edison double-checked the four canisters that have been moved to the storage pad, Palmisano added: “We’re satisfied the four canisters are safe.”
One audience member at the meeting asked if San Onofre is the first nuclear site to use this new type of cask. No answer was given at the meeting.
CEP Chairman David Victor requested that Palmisano provide an update on the situation at the panel’s next quarterly meeting.
