New calculation method for PWR control rod assemblies with APOLLO3®

In this paper, we present recent advances on PWR core calculations schemes with the most advanced features of the new deterministic neutronic transport code APOLLO3®. We focus mostly on reactivity effects of control rod sub-assemblies representation. Two kinds of representation are being studied: a representation in which the control rod sub-assembly is surrounded by standard sub-assemblies, calculated using 2D TDT-MOC solver associated with the fine structure self-shielding method in 281 groups at the Lattice calculation level; and a semi-heterogeneous modeling (3 × 3 zones) of the control rod sub-assembly at the Core calculation level. Taking advantage of the possibility of subdividing a sub-assembly with the MINARET core solver which uses an unstructured conforming triangular spatial mesh (Discontinuous Galerkin Finite Elements), the core calculation represents much better the control rod shadowing effects within the control rod sub-assembly. Tests to demonstrate the ability of such a calculation scheme have been carried out on an UOX fueled PWR reactor. The accuracy of the new APOLLO3® scheme has been tested against TRIPOLI-4® and has been found extremely accurate without requiring any equivalency method. This calculation scheme lays down the foundations for a new upgrading approach for deterministic calculations to study PWR cores.