Critical approach of energy accounting for fusion reactor

Energy investments for the construction and the maintenance of a typical commercial fusion reactor system over its lifetime are evaluated and compared with those for a power generating station using a fission reactor. The problem is studied in terms of net energy analysis, specifically with the direct estimation of the consumed energies for the production, handling and transport of the component parts and raw materials. Emphasis is placed on the study in the energy term of the handling of the radioactive wastes produced during and at the end of the lifetime of the reactor due to the decommissioning of the whole structure. Very clearly revealed is a distinct difference between the crucial factors in the energy investments for the fission and fusion reactors. The total energy investments occupy a considerable part of their energy output to be possibly a few tens percent. The result would be much more serious than that obtained previously. It also suggests that the treatment of the residual radioactive wastes could be the key problem for the fusion reactor to be a practical power station, otherwise one has to find somehow a scenario of an advanced fusion cycle other than DT reaction, which would reduce the induced radioactivities and resulted environmental pollution to a large extent. (author)