Conception and development of an adaptive energy mesher for multigroup library generation of the transport codes
The deterministic transport codes solve the stationary Boltzmann equation in a discretized energy formalism called multigroup. The trans- formation of continuous data in a multigroup form is obtained by avera- ging the highly variable cross sections of the resonant isotopes with the solution of the self-shielding models and the remaining ones with the co- arse energy spectrum of the reactor type. So far the error of such an ap- proach could only be evaluated retrospectively. To remedy this, we stu- died in this thesis a set of methods to control a priori the accuracy and the cost of the multigroup transport computation. The energy mesh optimisation is achieved using a two step process : the creation of a reference mesh and its optimized condensation. In the ﬁrst stage, by reﬁning locally and globally the energy mesh, we seek, on a ﬁne energy mesh with subgroup self-shielding, a solution equivalent to a reference solver (Monte Carlo or pointwise deterministic solver). In the second step, once ﬁxed the number of groups, depending on the accep- table computational cost, and chosen the most appropriate self-shielding models to the reactor type, we look for the best bounds of the reference mesh minimizing reaction rate errors by the particle swarm optimization algorithm. This new approach allowed to deﬁne new meshes for fast reactors as accurate as the currently used ones, but with fewer groups.