Improvements of NET/ITER shielding to limit short-term radioactivity in magnet materials

The problem of neutron-induced radioactivity in magnet structural materials for fusion reactors is examined. Two near-term reactor designs (NET-DN and ITER) are considered. Long-term activation of these materials is low enough to permit their recycling after less than 25 years of intermediate decay. Short-term radioactivity, on the other hand, requires the remote handling of these components for relatively long periods after shutdown. To permit a nearly immediate direct handling, activation of magnet structural materials must be reduced. For this purpose, two possible actions are considered: Materials selection and improvement of the shielding. All the candidate materials for structural use in magnet components have a comparable activation behaviour. As far as the improvement of the shielding is concerned, the most interesting problem turns out to be the modification of the inboard shield in ITER. With some slight modifications, the goal of the direct handling for magnet materials is eventually reached. Finally, the activation of magnet materials in a next-step machine like DEMO is briefly examined.