ARIANT – A System Thermalhydraulics Code

ARIANT (AlgoRIthm for Analysis of Network Thermalhydraulics) is a generalized one-dimensional, non-equilibrium, two-fluid, two-phase system thermalhydraulics code developed by Canadian Nuclear Laboratories for the analysis of nuclear reactors and thermalhydraulics experimental facilities. The primary contribution of this work is the development and integration of a fully implicit, nonlinear solution framework with a flexible multiphysics architecture, enabling robust and thermodynamically consistent simulation of complex thermalhydraulic systems over a wide range of working fluids and reactor concepts. ARIANT supports conventional coolants such as light and heavy water as well as molten salts, liquid metals, and non-condensable gases, allowing application to both current and advanced reactor designs. The code incorporates detailed representations of flow-regime-dependent thermalhydraulics, heat transfer, and solid structures, together with modular system components and external coupling capabilities. The formulation and implementation are demonstrated through representative reactor safety and thermalhydraulic applications, including validation against RD-14M integral-effects experiments and international benchmark exercises. The results illustrate the applicability of ARIANT to both conventional and advanced reactor systems and support its use for research, design, and safety analysis of nuclear energy technologies.