Combining the tone’s and subgroup models for reference LWR self-shielding calculations in apollo3®

International audienceThe new deterministic platform APOLLO3 ® offers three different self-shielding models:-the Sanchez-Coste model currently used in APOLLO2 for Light Water Reactors production calculations,-the subgroup method of ECCO used for Fast Reactors applications,-the recently implemented Tone method specifically dedicated to Fast Reactors calculations. The Sanchez-Coste method is based on an equivalence in dilution and lies on some hypothesis (pure elastic scattering, fine structure factorization) that are not always relevant, especially in case of voiding or for large metallic bulk treatment. Following a previous work based on the APOLLO2 subgroup method, this paper confirms more deeply the accuracy of the ECCO subgroup method in all kind of situations and establishes it as a reference self-shielding method for Light Water Reactor calculations with APOLLO3 ®. Using a 383-group energy mesh, it is shown that the Tone method can be substituted at the subgroup method at high energy (E > 3 keV) without loss of precision, allowing a significant reduction of the calculation time. It can be used alone for less demanding design studies, provided a uniform temperature distribution in fuel