Influence of the photoneutrons on the kinetics of the beryllium reflected core of the Budapest research reactor

The Budapest Research Reactor contains beryllium in the reflector, accordingly this phenomenon is presumably smaller than that in the cores where photoneutrons emerge in the moderator. On the other hand, the space dependence of the kinetic processes is stronger. The dynamics of this core has been investigated by the code KIKO3D developed in KFKI Atomic Energy Research Institute. It is a nodal, three-dimensional coupled neutron physical - thermohydraulic code. The nodes in the fuel are represented by generalized response matrices while the absorbers and the reflector are described by precalculated albedo matrices depending on some parameters. The time - dependent equations are solved by the improved quasi - static method. The effect of the photoneutrons was neglected in the original form of KIKO3D. In the last years a more sophisticated version of the code was developed to include the effect of the photoneutrons with the help of modified albedo matrices for the reflector and with additional delayed neutron groups due to the (γ,n) reaction. The photoneutrons were treated by a modified form of the Monte Carlo code MCNP. (orig.)