Adjoint neutron flux calculations with Tripoli-4®: Verification and comparison to deterministic codes

The possibility of computing adjoint-weighted scores by Monte Carlo methods is a subject of active research. In this respect, a major breakthrough has been achieved thanks to the rediscovery of the so-called Iterated Fission Probability (IFP) method, which basically maps the calculation of the adjoint neutron flux into that of the neutron importance function. Based on IFP, we have recently developed the calculation of effective kinetics parameters and sensitivity coefficients to integral reactor responses in the Monte Carlo production code Tripoli-4®. In view of the next release of the code, we have added a new routine allowing for the calculation of the adjoint angular flux (and more generally adjoint-weighted sources) in eigenvalue problems, which can be useful for code-code comparisons with respect to deterministic solvers. In this work we analyse the behaviour of the adjoint angular flux as a function of space, energy and angle for a few benchmark configurations, ranging from mono-kinetic transport in one-dimensional systems to continuous-energy transport in fuel assemblies. The Monte Carlo adjoint flux profiles are contrasted to reference curves, where available, and to simulation results obtained from ERANOS and APOLLO2 deterministic codes.