Coupled sampling with the Monte Carlo method in neutron transport calculations

AbstractA scheme is devised which combines in a coupled manner the sampling from the transport equation and the adjoint transport equation to improve the sampling for a functional such as the space- and velocity-dependent neutron distribution due to a given source distribution. Specific use is made of sampling from the transport equation to construct a scheme for a near-optimal subsequent sampling from the adjoint equation, even when inelastic scattering is present. The energy-dependent reciprocity relation is utilized to relate the solution of the adjoint equation to that of the transport equation itself. This procedure may be expected to be advantageous when the phase-space volume contributing to the functional in the region of interest is smaller than that volume in the source region. Numerical results demonstrate that calculation times in two example problems can be significantly reduced with the coupled sampling approach.