Revisiting the Clio perturbative approach for analyzing systems in fundamental mode conditions

The Clio perturbative approach is a powerful tool available in the APOLLO2 lattice code for performing a detailed reactivity analysis between two heterogeneous systems in fundamental mode conditions. It is possible to compute group wise and isotope wise reactivity effects due to a modification in one of the two systems. This modification can be related to isotopic composition, temperature, cross-section uncertainties, or even a swap of solution algorithm. The Clio perturbative approach is an exact method based on the knowledge of the adjoint flux of the unperturbed system. Our contribution consists in a new normalization scheme for distributing the group wise reactivity effects due to the leakage term of the transport equation in a way that is consistent to both the direct and adjoint equations. (author)