| Fourth generation very high temperature reactors (VHTRs) present characteristics that tend to be harder than conventional geometries to analyze using conventional methods available in traditional deterministic neutronics computer codes. Worthy of interest in the scope of this document are the random character of fuel elements in a uniform matrix, and the spherical geometry of these same fuel elements.;A new option has also been incorporated, allowing the program to randomly generate pin positions until the density specified by the user has been reached, offering an alternative to methods traditionally used to treat problems presenting characteristics of double-heterogeneity, and eventually permitting comparisons of results with these models.;Finally, preliminary validation runs have been carried out, comparing results obtained using the new module on a simple spherical geometry with a benchmark established using Monte-Carlo code Serpent and previously implemented double heterogeneity treatment in DRAGON. The new NXT: capabilities have been tested with an increasing angular and spatial discretization, leading to results approaching those generated by the Monte-Carlo method, for a difference inferior to 0.5 mk.;The goal of this project was to integrate the capacity to analyze such properties in module NXT: of the transport lattice code DRAGON. A geometrical analysis of spherical volumes have allowed us to develop analytical volumes calculation, as well as tracking and intersection distances with spherical geometry elements. Routines enabling this exact geometrical analysis of multi-layered, randomly disposed spherical particles have been successfully incorporated and tested in this module. A thorough analysis of combinations of spherical and Cartesian meshes has also been performed, to ensure the validity of the lengths and volumes calculated by the new routines. |
