On Pseudo-Cross Sections for Neutron Escape from a Domain by a Physical Monte Carlo Simulation

The present work reports on a novel approach in the study of stationary neutron transport including escape from finite domains using a physical Monte Carlo simulation. The novelty is that escape is treated in an analogous way to the absorption reaction but outside the domain of interest and is quantified by an associated pseudo-cross section, which is the principal goal of this endeavour. Reaction rates determined by a physical Monte Carlo simulation were used to compute the space and energy-dependent pseudo-cross sections for neutron escape. As a case study we considered neutron transport in a spherical finite multiplicative medium of 76 cm diameter composed of 72% of water and 28% of uranium dioxide enriched to a 2.5% uranium-235 content. The simulation started with 2 × 104 neutrons. All determined distribution functions from the simulation were cast in analytical representation so that the escape cross section was also obtained by an analytical expression. Our results showed the perspectives that arise if simulations are performed with power computing resources so that the rich influence of the resonances and their effects on leakage may be evaluated in high fidelity.