Application of forward and adjoint Monte Carlo coupling technique to detector system designs

A forward and adjoint Monte Carlo coupling technique has been developed for analyzing neutron streaming in a system with large geometry. Particles (neutron and adjoint particle) are scored by surface type estimators such as the next event surface crossing estimator and the boundary crossing estimator. The detector response is calculated by folding the calculated neutron and adjoint angular fluxes. The reliability and efficiency of this method were studied by solving a sample problem of neutron streaming through narrow sodium pipe embedded in an iron shield. This method gave a figure of merit several times better than the conventional method. The applicability of the method to detector system design has been demonstrated by calculating the signal to noise ratio for a delayed neutron failed fuel element detection system located behind a concrete reactor shield. This method has the advantage of identifying the spatial channels for neutron streaming. (author)