US NRC to inspect San Onofre after incident involving used fuel

28 August 2018

The US Nuclear Regulatory Commission (NRC) announced on 24 August that it will conduct a special inspection at the site of the San Onofre Nuclear Generating Station (Songs), after a near-accident occurred on 3 August during the transfer of highly radioactive used fuel. NRC inspectors will review what happened when a canister loaded with used fuel became jammed while being lowered into a storage vault. It narrowly avoided being dropped 18 feet. The incident was revealed during a community engagement panel by safety inspector David Fitch. Tom Palmisano, chief nuclear officer of Southern California Edison (SCE), described the event as “a serious near miss.”

The San Diego Union Tribune on 13 August quoted officials as saying that "performance errors" by workers from contractor Holtec International had resulted in a canister containing nuclear waste catching the inner ring of a Cavity Enclosure Container on one of the pads at a newly constructed storage site.

SCE stated in press releases and at public meetings that Holtec’s HI-STORM UMAX canisters can withstand a 25-foot drop, but NRC said in its announcement that this has not been evaluated in its safety practices. The canisters can weigh between 50 and 100 tons, according to documents from SCE and Holtec. “It was estimated that the canister could have experienced an approximately 17-18 foot drop into the storage vault if the canister had slipped off the metal flange or if the metal flange failed,” NRC stated. “This load drop accident is not a condition analyzed in the dry fuel storage system’s Final Safety Analysis Report (FSAR).”

Since February, operators of the plant have been transferring canisters from wet storage to a newly constructed dry storage facility at the plant, which is in the process of being decommissioned. Those transfers have now been put on hold, Edison officials said. "At no point during this incident was there a risk to employee or public safety, and immediate lessons learned have already been integrated into our process," Edison officials said in a statement.

During an earlier incident in March involving the transfer of used fuel, when the shims (small pins that help ensure the natural, cooling flow of air in a canister) in one canister were found damaged or broken. SCE officials said the canister did not reach levels of critical heat within the canister. However, work was delayed for 10 days. Holtec and an independent engineering firm assured SCE that the canister's integrity was sound, officials said.

The plant holds 3.55 million pounds of used fuel. There are already 51 other canisters built by Areva in dry storage at the shuttered nuclear power plant from a unit that was decommissioned decades ago. A second dry storage installation, recently constructed and approved by the California Coastal Commission (CCC), is in the process of transferring 73 canisters from pool storage. So far 29 have been transferred. SCE still plans to have the remaining 44 canisters in dry storage by mid-2019.

Southern California residents held a meeting on 7 August to protest against plans to demolish the shuttered plant. Songs was closed in 2012 after reactor coolant leaked from an 11-month-old steam generator, releasing 82 gallons of radioactive coolant a day. Edison alerted the public to a “possible leak” and responded to a Nuclear Regulatory Commission report with confirmation that a “barely measurable” amount of radioactivity was released into the atmosphere.

CCC has issued a permit to Southern California Edison to store used fuel in canisters buried under the beach next to the shuttered plant. This year, Edison began the process and is a third of the way through burying the canisters. But to complete decommissioning, CCC needs to issue a final permit. This depends on approval of a recently released 706-page environmental impact report (EIR) by the California State Lands Commission. Among significant “unavoidable impacts” outlined in the EIR, however, are potential release of radiological materials and impacts on air quality. The public comment period on the EIR runs until 28 August and a tentative commission meeting to approve it is scheduled for 11 December in San Diego.



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