Remote Dismantling of Activated Reactor Internals with Plasma Arc Torch

The decommissioning program of the Japan Power Demonstration Reactor (JPDR) has been carried out since 1981 in the Japan Atomic Energy Research Institute (JAERI) in order to develop techniques applicable to future commercial power reactor decommissioning. In this program, a technical development for an underwater plasma arc cutting system has been carried out for dismantling activated steel structures in the reactor pressure vessel (RPV). The major aim of the development was to establish a safe and reliable remote dismantling system for the objects which are hardly accessible by workers because the radioactivity of the objects was very high and, in addition, the objects were located in a limited working space. In particular, major emphasis was placed on the development of the underwater plasma arc cutting system to minimize worker radiation exposure. Until now, a part of the steel structures in the RPV has been dismantled underwater with the plasma arc torch operated by a developed general-purpose robotic manipulator. Through the dismantling of these steel structures (reactor internals), various kinds of knowledge and experience were obtained.