More than half of the fuel assemblies from Fukushima Daiichi unit 4 have now been transferred to a central storage pool on the site. The remainder should be removed by the end of the year.
|A transportation cask is lowered into the fuel pool of unit 4 (Image: Tepco)
In an operation that began last November, Tokyo Electric Power Company (Tepco) has now removed 792 used fuel assemblies and 22 unused ones from the unit's fuel pool. At this rate of progress, the remaining 539 used and 180 unused assemblies stand to be moved before the end of the year in line with Tepco's published schedule.
The fuel assemblies in the storage pool are being removed one by one from storage racks and placed into a transportation cask. When the container is full it is sealed, lifted from the water by the main crane, placed on the service floor for decontamination and taken through a special route to a vehicle that moves it across the site to be unloaded at the site's shared storage facility. This process will be repeated until the pool is empty. Two containers are being used in relay and so far 37 cask transportations from unit 4 to the central storage pool have been made.
Unit 4 was off line for maintenance at the time of the 2011 accident with its full core load of fuel, as well as used fuel from previous operation, stored in a fuel pool at the top of the reactor building. Although this meant there was no possibility of a reactor accident at unit 4, there was a risk of the pool overheating. The stability of the pool was then reduced by major structural damage to the building caused by the ignition of hydrogen that leaked through ventilation systems shared with unit 3. The building has since been reinforced, and heavy debris and rubble has been removed from its roof. The fuel transfer operation is being managed within a new cover over the building which includes all the fuel handling equipment of a normal nuclear power plant.
Researched and written
by World Nuclear News