COUPLED DIFFUSION-TRANSPORT CALCULATIONS OF FUSION-REACTOR ACTIVATIONS

The computer time saving attainable by solving the transport equation for the higher neutron energy groups and the diffusion equation for th e lower energy groups was investigated for fusion reactor safety appli cations. For the ARIES-I design considered, it was found that coupled diffusion-transport solutions can provide the activation rates in all the zones excluding the shield to within 2.5 % and 5 % when the transi tion to the diffusion approximation is, respectively, at 1.4 MeV and 8 .8 MeV. The corresponding saving in CPU time relative to an all-transp ort solution is 31 % and 43 %. For the low order transport approximati on used, this CPU time is significantly shorter than that required by ONEDANT, with its built-in diffusion synthetic acceleration.