The Dependence of Neutron-Induced Radioactivity in Fusion Reactors on Geometric Design Parameters^a

Although the neutron-induced activation in a fusion reactor is a non-linear problem whose solution requires the use of neutron transport codes and neutron activation and decay codes, a number of simple arguments can be made which give useful scaling laws for the total radioactivity in a fusion reactor (these were reported earlier in Ref. 1). Because these laws rely heavily on assumptions of linearity and the smallness of second-order effects, we have compared them to the results of computer experiments designed to investigate their validity over the range of operating parameters typical of fusion reactors. The parameters that were varied for comparison of activation and decay were

• reactor power level,
• first wall thickness,
• neutron source distribution (point or homogeneous),
• first wall radius, and
• reactor configuration (spherical or cylindrical).

In addition, we have investigated

• the total radioactivity of the first wall compared to that of a structural wall located behind a lithium blanket,
• the effect of protecting the first wall with a thick liquid lithium wall (as in the case of liquid-metal-wall ICF reactors),
• the effect on total radioactivity due to neutron collisions in a typically dense ICF fusion plasma, and
• the effect on total radioactivity of the neutron flux reflected from the blanket.