Abstract :
The objective of the present work is to study the kinetic (i.e., in absence of in-core feedbacks) response of the subcritical system to variation of the efficiency of the external neutron source. The particular class of the subcritical system with the intensity of the external source being intrinsically dependent on neutron production in the core (so-called coupled hybrid systems) is considered. The accelerator coupled system is taken as example, although this analysis may be expanded to other types of the coupled subcritical systems. Within the framework of a simple mathematical model of coupled system, an interpretation of the external coupled source as supplementary group of delayed neutrons is given. An auxiliary quantity – ‘source reactivity’ is introduced for convenience and a modified inhour equation for coupled systems is deduced. Analytical solution of the modified inhour equation is obtained in approximation of one group of delayed neutrons. The principal conclusion resulting from this analysis is as follows: the response of the coupled system to ‘source reactivity’ variation is intrinsically different from the response to core reactivity variation. Namely, there is no equivalent of prompt criticality (accompanied by drastic decrease of the reactor period) in the case of ‘source reactivity’ variation.
