MULTIGROUP CALCULATIONS OF EFFECTIVE NEUTRON FRACTION $beta$eff' PROMPT NEUTRON LIFETIME lp' AND RELATED KINETICS PARAMETERS FOR LARGE, FAST, PLUTONIUM-FUELED REACTORS

Large, plutonium-fueled, fast reactors will have a different kinetic behavior than fast reactors fueled with U/sup 235/, due to the much smaller delayed-neutron fraction emitted in the fissioning of plutonium. The fissioning of Pu/sup 240/, Pu/sup 241/, Pu/sup 242/, and especially U/sup 238/, which emit mor e delayed neutrons per fission than Pu/sup 239/, introduces a considerable increase in BETA /sub eff/ over that for a hypothetical pure Pu/sup 239/ reactor. The cases considered are 800-, 1500-, and 2500-liter cores fueled with plutonium of different isotopic content, which lead to effective delayed-neutron fractions of approximately one-half the values of similar U/sup 235/-U/sup 238/-fueled fast reactors. The energy spectrum and the number of fissions weighted with their importance are recorded in order to reason physically on the obtained parameters. (auth