ADAPTATION OF THE B1 LEAKAGE MODEL TO MONTE CARLO CRITICALITY CALCULATIONS

This paper presents an attempt to consistently adapt the B1 homogeneous leakage model within Monte Carlo criticality calculations based on the power iteration method. Unlike deterministic lattice codes, most of Monte Carlo-based reactor physics codes perform lattice calculations without introducing leakage models. The critical flux is however required to accurately compute homogenized cross sections and diffusion coefficients in the context of lattice physics computation. In our proposed approach, a fundamental mode approximation is introduced in the Monte Carlo K-effective power iteration method. Similarly to the deterministic implementation of the lattice code DRAGON (typically the collision probability method), B1 equations are solved at each cycle, leading to Monte Carlo estimates for the critical buckling B2 and for the group-dependent leakage rates. These leakage reactions are then introduced in the neutron random walk. This approach is discussed on legacy PWR pin cell cases, by direct comparison with results obtained by the collision probability method. This approach leads to consistent results between the Monte Carlo and the deterministic computational ways of the DRAGON code.