École Nationale Supérieure de
Techniques Avancées

Abstract

Orphee is a research reactor producing cold neutrons for physicists’ use. It consists of eight fuel bundles surrounding a central reflector of beryllium, contained in a Zircaloy box, and surrounded by a pool of heavy water. Stemming from a former internship, a study in two dimensions with Sn transport is led using the APOLLO2 code, with thoroughly represented reactor geometry and using 172 energy groups. This study, validated by the TRIPOLI4 Monte Carlo code, makes it possible to build spatially homogenized and energetically condensed cross sections libraries that can be used in a simplified model. Studies in two dimensions using APOLLO2 and CRONOS2 led with this model gives mixed results due to the absence of equivalence coefficients. Then, a study with the CRONOS2 code in two dimensions shows that the diffusion approximation is too rough in the case of Orphée. The Sn method requires a lot of calculation time and memory. That’s why the SPn approximation is chosen, at the order 3, and combined with a 20 groups energy mesh. Cross sections libraries generated with APOLLO2 in two dimensions are then used to lead CRONOS2 calculations in three dimensions. The axial leakages are simulated introducing a formal absorption term called “Laplacien imposé”. The axial absorption and fission rates profiles obtained with various heights of control rods are presented and compared with the results of Monte Carlo calculations. All this paves the way for calculations in 3 dimensions with time evolution.