The cover building of Fukushima Daiichi 4 is being kitted out for the removal of used reactor fuel. The main crane and the fuel handling machine are in place.
|The service floor of Fukushima Daiichi 4 is restored to an operational state. Painted green are the rail-mounted fuel handling machine and the larger ceiling crane beyond
Within the new structure built over the badly damaged reactor building of unit 4, Tepco has been installing equipment that will allow the transfer of used nuclear fuel for long-term storage elsewhere. Underwater inspections in the pond have shown most of the fuel to be undamaged, but the pond contains a lot of dust and debris which will complicate operations. The cover is fitted with air filters that will prevent any release of radioactivity as the fuel is moved.
Transport containers will be placed in the empty and undamaged reactor vessel and the fuel will be transferred to them underwater using the fuel handling machine. The used fuel will eventually be placed in the site's shared used fuel pool, which was undamaged by the natural disasters two years ago.
Removal of fuel from unit 4's storage pool is one of the highest decommissioning priorities at the site. The reactor was off line for maintenance when the earthquake and tsunami struck on 11 March 2011. Its full core load of fuel, plus used fuel from previous operation, was being 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.
Researched and written
by World Nuclear News