Tokyo Electric Power Co (Tepco) on 15 April began removing used nuclear fuel rods from unit 3 of the Fukushima Daiichi NPP, using remote-controlled cranes. Tepco, said it had successfully removed the first four of 566 fuel assemblies from the unit’s used fuel pool, which 18 metres (60 feet) above ground level. The assemblies were placed in a specially designed steel cask for transfer to a truck on the ground, which will transfer the casks to a central storage pool.
The fuel removal was originally scheduled to start in late 2014 but was postponed multiple times. In 2014, Tepco completed fuel removal work from the pool linked unit 4, which was offline for regular checks at the time of the accident and had all of its fuel stored in the pool. Unlike units 1-3, it did not suffer a meltdown. The work at unit 3 is more complicated because of the damage it suffered in the 2011 disaster, when a hydrogen explosion resulted in the used fuel pool being covered in debris, including a crane. The damage and debris removal, and a series of malfunctions of the devices necessary for the operation, delayed work at unit 3 for four years. The high levels of radiation at the site means all the cranes moving the transportation casks carrying the rods, which each weigh about 45 tonnes, must be operated remotely.
Tepco said it plans to remove seven fresh fuel rods from the reactor’s pool, where a total of 514 used and 52 fresh fuel rods are stored, and transfer them to another storage pool on the premises later this month. After removing the seven fresh fuel rods that pose a relatively low risk, removal work will be intensified, possibly in June, when the storage pool to which the fuel will be transferred undergoes a regular check as is required by law. The fuel removal operation in unit 3 is expected to be completed in 2020, with units 1 and 2 set to be cleared of fuel in 2023. There an estimated 1,573 fuel rods at the Fukushima Daiichi NPP.
Meanwhile, Japan’s Hitachi-GE Nuclear Energy and the International Research Institute for Decommissioning have jointly developed a series of submersible devices which will be used to investigate the interior of the primary containment vessel (PVC) of unit 1, the Japan Atomic Industrial Forum said. They will be used to inspect the pressure containment vessel in anticipation of the removal of fuel debris from the melted core. Initial investigations of the PCV in March 2017 revealed sediment accumulating in water at the base of the vessel. Jaif said the submersibles will be used for 3D mapping of sediment, taking samples of sediment and looking for fuel debris.
