[en] The decommissioning of a reactor plant differs from that of other facilities in that radioactive materials due to neutron irradiation remain in the concrete etc. structural materials. This presents technical difficulties in its dismantling, raising the cost. In the Japan Atomic Energy Research Institute, the dismantling of Japan Power Demonstration Reactor is to start in fiscal 1986. The techniques of dismantling its concrete structures are being developed; which will be employed in the decommissioning of JPDR. As such, there are the following : (1) Controlled blasting method - by the explosive energy of powder, cracks are made in a concrete structure. (2) Mechanical cutting - A concrete structure is cut into pieces with a diamond blade or bit. (3) Water jet cutting - A concrete structure with iron reinforcement is cut off with an abrasive-containing high-pressure water jet. (Mori, K.)