Abstract
Fast group constants sets are indispensable for the study of fast reactor physics. Many sets published abroad have been utilized in Japan. However, these published sets hove the shortcoming not having the effective elastic removal cross sections properly treated. For heavy nuclides, the resonance cross sections have been obtained on the assumption of constant collision density and isolated narrow resonance approximation. Mutual shielding and self overlapping effects are not taken into account. Nuclear data utilized are thought to be inaccurate.
Recent studies have resulted in gradual elimination of these shortcomings, and have aided in producing more reliable fast group constants. The present paper describes the current status of the theory and practical processes used for obtaining advanced fast reactor group constants sets.
