Calculation and Analysis of Effective Delayed Neutron Fraction β_eff in MSR

The effective delayed neutron fraction(β_eff) plays an extremely important role in the dynamics behavior of the reactors. In molten salt reactors（MSRs）, because of the adoption of the fluid fuel, the calculation of the β_eff is different with that in the traditional solid-fuel reactor. This work concentrates on the calculation of the β_eff in MSRs. The β_eff of the MOSART was calculated and the effect of external-loop transit time and inlet velocity on the β_eff is analyzed in detail in this paper. The results indicate that the increasing of the external-transit time decreases the β_eff, and the increasing of the inlet-velocity also decreases the β_eff.