Computational thermal-hydraulic modeling for nuclear fusion and fission applications

Both nuclear fusion and fission devices have to face the issue of the cooling of some critical components, and in particular the cooling of the superconducting coils and of the core fuel assemblies, respectively. In order to investigate these issues during the design phase of new reactors, e.g. new tokamak experiments and the forthcoming Generation IV reactors, new dedicated models and reliable tools should be developed. In this work, two separate tools, for fusion and fission devices, respectively, are developed relying on the same quasi-3D thermal-hydraulic model, i.e. the 1D advection flow of the coolant in a diffusive (solid) bundle along the channel axis and the 2D coupling between the channels. The already available 4C code for the analysis of thermal-hydraulic transients in the superconducting coils of fusion devices is firstly validated against experimental data, then benchmarked against other tools and finally its predictive capability are checked performing the simulations before the experiment. The 4C code is thus proved to be able to simulate transients spanning from very short to week-long timescales with the very same model. The code is then applied to the analysis of operational transients in the ITER TF coils. Whenever the minimum temperature margin requirements are not satisfied, different possible mitigation strategies are investigated. Concerning the fission devices, a new multi-physics simulation tool (FRENETIC) is developed for the quasi-3D analysis of a lead-cooled fast reactor core with the closed hexagonal fuel element configuration, as currently proposed within the framework of the European project LEADER. The code couples a neutronic and a thermal-hydraulic analysis of the full reactor core, each performed in separate modules. A first validation of the thermal-hydraulic module of this code is presented both in the single assembly and, even if preliminarly, in the multi-assembly configuration. In the latter case, a benchmark against another qualified tool (RELAP5-3D©) is also carried out. Finally the coupled code is tested in some simple transients in order to assess at least qualitatively the effectiveness of the coupling and the representativity of the multi-physics results.