Problems and Methods of Activation Calculations for Experimental and Next-Step Fusion Devices

Activation data are needed for many evaluations concerning fusion reactors and, in particular, safety and environmental impact assessments. A stepwise description of the activation analysis process is given. A neutron source description for one-dimensional neuronic models is compared with that for three-dimensional models. Concerning neutron flux calculations, the choice between one-dimensional deterministic codes and three-dimensional Monte-Carlo codes is examined, taking into account their interface with activation codes. A reliable inventory code and an updated activation library are essential to obtain good activation data: The problems in the modeling of either pulsed irradiation or operation at different flux levels are tackled. The analysis and comparison of activation calculations for two different machine concepts [the Next European Torus (NET)/International Thermonuclear Experimental Reactor (ITER) and Ignitor], are carried out, showing how pulsed irradiation affects the results in the two cases and the main differences between the two analyses. As an example of the application of inventory calculations, a classification of NET/ITER and Ignitor materials into waste categories is proposed and discussed.