Monte Carlo algorithm for buckling search and neutron leakage-corrected calculations

A Monte Carlo algorithm has been developed for taking into account neutron leakage effect specified by a buckling. The algorithm enables one to perform buckling search mode eigenvalue calculations where the buckling is treated as an eigenvalue. For introducing neutron leakage effect, the spatial dependence of neutron flux is approximated by a single Fourier mode. The particle weight is generally a complex number. The imaginary part, however, vanishes and only the real part needs to be treated if symmetry exists with respect to the direction represented by the buckling and the scattering and fission neutron emission are isotropic. The algorithm has been verified by comparing bucklings obtained by buckling search mode eigenvalue calculations with those by the diffusion approximation and the B1 method. The newly developed algorithm can also be applied to leakage-corrected Monte Carlo calculations, generating leakage-corrected neutron spectra and flux distributions. Although this paper has presented only one-group calculations, the algorithm can contribute to the generation of leakage-corrected group constants based on Monte Carlo calculation techniques.

► A Mont Carlo method is developed for including neutron leakage effect.
► The effect is specified by a buckling.
► The method enables one to perform buckling search mode eigenvalue calculations.
► The imaginary part of a weight vanishes if symmetry exists for buckling direction.
► The method is verified by comparing bucklings with the ones by diffusion theory.