Reactor cell calculations with the codes HELIOS, MCNP and TransRay and comparison of the results

The DYN3D code allowing to calculate the whole reactor core of light water reactors and its transient behaviour has been developed at the Forschungszentrum Rossendorf (FZR). It treats the three-dimensional (3d) neutron kinetics with a two-group diffusion approximation using the nodal method for assemblies with quadratic and hexagonal geometry. As input data DYN3D needs two-group cross sections for the neutrons, which are averaged over each node. These cross sections are generated using the 2d-code-system HELIOS. The necessity to calculate these two-group cross sections three-dimensionally was evaluated with the Monte-Carlo code MCNP and the 2d- and 3d-cell-code TransRay, which has been specially developed for that purpose at FZR. TransRay uses the same solution method as employed by HELIOS. The following reactor cells were investigated: A partially inserted control rod and void (or moderator with a lower density respectively) around a fuel rod as a model for a steam bubble in the moderator region. In general it could be concluded, that a three-dimensional data generation of averaged two-group cross sections is rather necessary for reactor cells with steam bubbles than for reactor cells with absorbers.