Calculation Method of Effective Delayed Neutron Fraction in Graphite-moderated Channel-type Molten Salt Reactor

The effective delayed neutron fraction (βeff) is an important reactor kinetics parameter. In liquidfueled molten salt reactor (MSR), the fuel flow leads to the redistribution of delayed neutron precursors (DNP) in the core, and results in part of DNP decay in the external loop, which bring differences from solidfueled reactors in the calculation method of βeff. In order to evaluate the reactivity loss caused by fuel flow, probe the flow behavior of the delayed neutrons driven by fuel salt, and provide a basis for design and safety analysis of the graphitemoderated channeltype MSRs, based on analytical and numerical methods, two mathematical models for calculating the βeff of graphitemoderated channeltype MSR were derived, and the loss in DNP fractions and the DNP distribution of the molten salt reactor experiment (MSRE) were obtained. Besides, the impacts of inlet flow and residence time of fuel in external loop on βeff were analyzed. The results show that both the two methods can provide a reliable description of DNP behavior. βeff decreases with the rise of inlet flow rate when the residence time of fuel in external loop is kept constant, and with the rise of residence time of fuel in external loop, βeff first decreases and then tends to be stable after 80 s when the inlet flow rate remains unchanged.