ICONE19-44125 A NEW MODELING OF VOLATILE DELAYED NEUTRON PRECURSORS AND ITS IMPACTS ON DYNAMIC NEUTRONICS CALCULATIONS OF DISRUPTIVE FAST REACTOR CORE

The effect of volatile precursor loss from core during core disruptive accidents was studied. Firstly, volatile precursors were specified, and delayed neutron parameters in 6 groups, half-life and delayed neutron yield, were newly evaluated with distinction of volatile and non-volatile precursors. Secondly, impact of the precursor loss to dynamic neutronics calculation was investigated based on the point neutron kinetic approximation. A set of new point neutron kinetic equations were derived taking into consideration of the precursor loss from the core, and several findings were derived from the equations. One of them is that the precursor loss has such an effect that as if negative reactivity was induced to the system, which has not been mentioned as far as the authors know. Lastly, the impact of the precursor loss to reactor power transitions was evaluated by numerical experiments under a typical condition with and without Doppler feedback effect. The results show that the relevant effect depends strongly on the existence of Doppler feedback. It was found that in actual cases, accuracy requirement on precursor loss rate is not so crucial.