Forward-Adjoint Monte Carlo Coupling with No Statistical Error Propagation

Methods for coupling multiple forward and adjoint radiation transport Monte Carlo calculations with no statistical error propagation are presented. Correlated forward and adjoint particle histories are uniformly initialized on arbitrarily placed intermediate source boundaries throughout the calculational system. In applying the method to multilegged duct streaming problems, these source boundaries are placed at the duct leg intersections. The necessary forward and adjoint fluxes for the coupling procedure are each computed from an opposite-mode calculation. The no-error-propagation feature is the result of an exact correlation of all phase-space variables for coupled forward-adjoint particle histories at each boundary. For ducts of more than two legs, next-event estimation between forward and adjoint collision sites across arbitrarily placed intermediate scoring boundaries is necessary to achieve the variable correlation. Comparison of calculational results between the coupled and standard methods for two- and three-legged ducts are presented.