Preparatory Activities of the Fugen Decommissioning

Advanced Thermal Reactor “Fugen” is a 165MWe, heavy water moderated, light-water cooled, pressure-tube type reactor. In February 1998, the Atomic Energy Commission of Japan decided to end the mission of ATR development and introduced a new policy that development and research of decommissioning of Fugen should be promoted in order to carry out the decommissioning smoothly after the shutdown. The Fugen NPS has shut down permanently in March 2003, and based on the report titled Activities of Fugen NPS after permanent shutdown, “Fugen” has been preparing for the project, including necessary development of technologies. The development of decommissioning for “Fugen” is divided into two areas. One area is developement of unique technology for dismantling special components such as the reactor core and the heavy water system. Another area is improvement and enhancement of existing technologies. Especially the former area requires effort and comprises development of the reactor dismantlement, tritium decontamination of heavy water system and engineering support systems. The concrete activities are as follows: The density and amount of radioactive nuclides in all equipment or concrete including the reactor core need to be evaluated for the decommissioning. To prepare for decommissioning, analysis, measurement and evaluation of the neutron flux density have been executed during reactor operation. Special dismantling process is necessary for the heavy water system and the reactor that are unique to Fugen. Some studies and tests are going on for the safe dismantling based on existing technologies and their combination. It is important to execute the decommissioning economically and rationally. Therefore, systems engineering approach is necessary in order to optimize the work load, exposure dose, waste mass and cost by selecting appropriate dismantling process at the planning stage of the decommissioning. For this reason, in order to make a decommissioning plan efficiently, we have been developing an Engineering Support System for decommissioning by adopting new information technologies such as three-dimensional- (3D-) CAD system and virtual reality (VR) system. Moreover, the technical results of technology development and decommissioning activity should be organized and opened to the public so that they can contribute to other decommissioning projects. For this purpose, information exchange and co-operation with domestic and international organizations are underway.