3-D analysis of the UH1.2 mock-up experiment using the Apollo3 IDT method and comparisons against Tripoli4 Monte-Carlo reference calculations

Within the framework of the V and V of the new Apollo3 French deterministic code, this paper focusses on its ability of analyzing integral mock-up experiments through straightforward 3-dimensional (3-D) IDT calculations. In the present case, the UH1.2 experiments involving voiding effects in standard PWR UOX lattices are investigated through 281 groups 3-D transport calculations using recent capabilities of IDT solver based on Sn short-characteristics method. We performed IDT calculations in the reference and void configurations and checked the results against reference continuous-energy Monte-Carlo (Tripoli4) simulations. In all cases the IDT solver (with dedicated self-shielding models) shows an excellent agreement with Monte-Carlo results regarding both reactivity and fission rate predictions. In particular it is shown that linear source description and refined spatial meshes (3 x 3 x 1) lead to the best agreement (less than 1% fission rate and void effect errors) with Tripoli4. The next step of this work will be devoted to the analysis of the 3-D TDT-MOC solver in the same configurations with ad-hoc axial reflector treatment. To remove the limitations in terms of CPU time and memory resources of this kind of calculations, ongoing developments devoted to hybrid shared/distributed parallelization (OpenMP/MPI) are also pointed out. (Author)