Photo: Fuel Handling Machine in Reactor 3. (8. 2015) [Link]
In order to remove the molten nuclear fuel (debris) from the Fukushima Nuclear Plant, TEPCO is considering a “submersion method” in which the entire reactor building is submerged in water. In this newly proposed method, the entire reactor building is enclosed in a structure like a huge water tank.
However this has not been implemented in the nuclear industry so far, thus, technical and cost issues remain uncertain. A person concerned pointed out that this is going to prolong the decommissioning process even longer and substantially affect the cost, which is currently estimated to be over 56 billion USD.
This new construction method uses a structure called a “hull structure” that is normally used to build ships and airplanes and is resistant to pressure and maintains durability. The entire reactor building, including the basement, will be enclosed to retain water inside, and debris will be removed from the top of the structure. This method is assumed to be applied to the worst damaged facility, reactor 3.
At the Fukushima nuclear plant, another plan that is to submerge only the primary containment vessel (PCV) was initially considered, however it was postponed due to the difficulty of repairing the severely damaged vessel as it will increase the radiation exposure of workers.
Regarding reactor 2, Tepco is currently planning to remove the molten fuel debris in the atmosphere.
Debris removal is the most difficult task in decommissioning the Fukushima nuclear plant. It is estimated that the total amount of debris from reactor 1 to 3 is approximately 880 tonnes. TEPCO and the national government plan to remove debris and complete decommissioning by 2051.