Clearance considerations for slightly-irradiated components of fusion power plants

Abstract

The development of commercial fusion plants includes the demonstration that the waste burden for future generations would be avoided. In order to minimize the radioactive material requiring long-term storage, maximum emphasis should be placed on recycling and clearance, avoiding geologic disposal. Clearance is the most desirable option for components like the vessel, shield, magnets and bioshield, which make up a great part of the mass and are only mildly irradiated. Recently, the International Atomic Energy Agency, the US Nuclear Regulatory Commission and other institutions have revised clearance guidelines for nuclear applications. In this paper, the implications of these new standards, particularly for slightly irradiated fusion materials, are considered. The amount of clearable materials is lower and/or the cooling period is longer than previously estimated. It becomes more evident now that improvements to the clearance data are needed to include many missing fusion-specific nuclides, and that the control and measurement of impurity levels, even for materials subjected to low-neutron exposure, is important. Segregation of components into more basic parts also plays a key role in minimizing the amount of waste. Finally, the issue of public acceptability of cleared materials is discussed since the unrestricted release of radioactive materials to the market is still controversial, despite the extremely low level of activity (⩽10 µSv/y)—way below the natural background.