In this research, effective delayed neutron fraction (βeff) and neutron generation time (Λ) of the Tehran Research Reactor (TRR) are calculated for different uranium enrichments from 14.84 w/o to 96.56 w/o U235 in two states of the TRR, (cold fuel, clad and coolant temperature of 20 °C; and hot fuel, clad and coolant temperature of 65, 49 and 44 °C, respectively) using the MTR_PC computer code. Comparative analysis shows that both βeff and Λ increase as fuel enrichment decreases. However, variation rate of βeff is not the same in two conditions. βeff in the hot state is larger than those calculated in the cold state when fuel enrichment goes more than 83.91%, while the situation is reverse for enrichment less than that. The obtained neutron generation time shows normal behavior for all different fuel enrichments. The variables involved in kinetics parameters calculations (i.e., neutron fission cross section, fuel enrichment, etc.) are investigated theoretically to confirm the results of calculations in cold and hot states. Variations of βeff and Λ with fuel burnup are studied too.

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