Optimized broad energy group structures for radiation transport in air and in LWR-shields

Basic ideas of the automatic group collapsing scheme AGRUKO are briefly described. The errors introduced by the collapsing process are controlled by criteria, which are constructed by the sensitivity profiles and the required target accuracies of the specific shielding type configurations. The group widths are optimized to reduce the calculation time with respect to the fine group calculations. Optimized group structures were generated for two rather different shielding benchmarks: Neutron and gamma transport in a LWR-shield and in air using a fusion source respectively. In the case of the LWR-shield the 100/20 groups EURLIB-3 structure was collapsed to 45/16 and 15/5 groups. In the case of the ''air'' problem the original 22/18 groups were collapsed to 4/8 groups. The accuracies achieved were in general within the required accuracies for the targets thermal flux (activation), radiation damage, radiation heating and dose rates. Because the broad group structures were optimized in view of basic physical and numerical principles, they are nearly free from arbitrary assumptions as constant lethargy width e.g. Therefore they may be recommended for further use in the field of more complex transport calculations or cross section adjustment procedures. (Auth.)