(GRS-795) Further Development of the AC² Code ATHLET for Evolutionary Reactors an Research Reactors (Phase A)

In-house reseach project RS 1600

The project RS1600, funded by BMUV, on the Further Development of the AC² code ATHLET for Evolutionary Reactors and Research Reactors aimed to develop and upgrade models and methods for the thermal-hydraulic system code ATHLET to support the numerous national and international code users with a powerful and reliable tool for carrying out safety analyses according to the current state of science and technology for existing reactors, advanced future reactor designs, research reactors, and SMR.

The introduction of a central flow regime map module represents a significant milestone for the ATHLET development process. In addition to the consistent use of flow pattern information and associated closure equations in the models of interphase friction, mass and energy exchange, the calculation of additional variables such as the entrainment fraction, which was previously determined on a model-specific basis, was also standardized. The central module has been expanded to allow for the use of separate flow regime maps depending on the prevailing heat transfer conditions at the wall. This development enabled the introduction of specific flow patterns and transition criteria for conditions characterized by wall condensation, which differ from adiabatic flows or heating wall conditions. Additionally, a general interpolation routine was implemented to facilitate a smooth transition between two or more flow pattern maps. The new implementation could already be verified against several application cases with satisfactory results.