Treatment of neutron streaming through cavities in SN-transport and diffusion calculations

For the improved treatment of neutron streaming through cavities under consideration of interactions with surrounding materials a new method has been developed. The basic idea is an analytic or Monte Carlo-treatment of the integral transport equation for the cavity and a SN- or diffusion solution in surrounding materials. The solutions for cavity and surrounding materials will be coupled via boundary conditions of the PL-approximation to the transport equation. For problems in which the SN-method shows strongly ray-effects the improvement will be demonstrated. For application of diffusion theory the reactivity worth of a control rod bank inserted into the cavity of a high temperature pebble bed reactor is calculated