NEUTRON LIFE CYCLEDOE-HDBK-1019/2-93Reactor Theory (Nuclear Parameters)Neutron Life Cycle Summary (Cont.)The thermal utilization factor can be calculated from the macroscopic cross sectionfor absorption of reactor materials using Equation (3-1).f SUaSUaSmaSpaThe reproduction factor can be calculated based on the characteristics of the reactorfuel using Equation (3-2).h NU235sU235fnU235NU235sU235aNU238sU238aThe number of neutrons present at any point in the neutron life cycle can becalculated as the product of the number of neutrons present at the start of thegeneration and all the factors preceding that point in the life cycle.The thermal utilization factor is effected by the enrichment of uranium-235, theamount of neutron poisons, and the moderator-to-fuel ratio.The reproduction factor is effected by the enrichment of uranium-235.The resonance escape probability is effected by the enrichment of uranium-235, thetemperature of the fuel, and the temperature of the moderator.An increase in moderator temperature will have the following effects.Increase the thermal utilization factorDecrease resonance escape probabilityDecrease fast non-leakage probabilityDecrease thermal non-leakage probabilityNP-03Rev. 0Page 16
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