Qualitative analysis of physical and mathematical approximations necessary for induced radioactivity calculations in fusion devices

When engineers and designers of fusion research and power reactors require information related to the induced radioactivity in the first wall, blanket and shield, they turn to one of many codes to generate a solution. Unfortunately, these codes all make physical and mathematical approximations in order to turn a functionally infinite and highly complicated problem into a more manageable, simple problem. This paper examines these approximations, namely, the handling of loops in the decay scheme, the truncation of the decay scheme, and the modeling of pulsed/intermittent operation histories, as physical approximations and the choice of a solution method as a mathematical approximation. The final recommendation is a code that uses an exact representation of the pulsing history, handles loops by unraveling, truncates the decay schemes with a relative sub-tree production rule modified by a stable truncation restriction and uses an adaptively chosen analytical or Laplace inverse mathematical solution method.