Engineers at the Vermont Yankee plant informed the US Nuclear Regulatory Commission (NRC) on 21 April that they were unable to account for two pieces of spent fuel. The pieces, which are about the thickness of a pencil, one about 18cm long, the other 43cm long, had defective cladding and were removed from a fuel assembly in 1979. According to plant documentation, shortly after their removal from the reactor, the rods were placed in a special stainless steel container in the spent fuel pool. However, a recent examination of the contents determined the rod segments were not in their documented location.
The plant’s operator, Entergy, will now have to conduct an exhaustive search and analysis of the possible pathways the fuel may have taken. At the end of April, technicians at the plant lowered a self-propelled remote control camera into the spent fuel pool – which is some 12m deep and contains over 2750 fuel assemblies – to inspect the pool floor. Technicians from ROV Technologies are manoeuvring the 7.5cm-high motorised crawling device in the space under the spent fuel storage racks. Video data from the cameras is being analysed by plant engineers and by state and federal regulators.
Vermont Yankee’s investigation also includes a thorough review of shipping and storage records as far back as 1979 when the fuel segments were originally removed from the reactor. The record review will address the possibility that the segments were shipped in shielded containers to other facilities licensed to handle radioactive waste.
The NRC said the situation “does not pose a threat to public health and safety as it is highly unlikely that the material is in the public domain.” The NRC will “look over the shoulder of the utility” as it conducts the search, which could take weeks. Region 1 inspector Todd Jackson has been sent to Vermont Yankee for an indefinite period, according to NRC spokesman Neil Sheehan.
In June 2000, two fuel rods from Millstone 1 were found to be missing. In that case, a search involving up to 25 workers and running until October 2001 failed to locate the fuel and the operators were fined $288,000 by the NRC. The most likely explanation is that the fuel was mistakenly cut up and sent for disposal with low-level waste.
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