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Special Features of ATHLET

Flexibility: Highly flexible network and thermo-fluid dynamics allowing for the simulation of a large variety of thermal hydraulic systems and multi-dimensional processes (clip 1). 

Steady state capability: A true steady state for the complete network - including heat conduction and neutron kinetics - is automatically established starting from the given mass flow distribution and initial and boundary conditions.

Dynamic mixture level tracking: In a user defined vertical stack of control volumes, a two phase mixture level is calculated and dynamically traced across control volume boundaries, considering rising bubbles with entrained droplets, falling droplets, as well as evaporation and condensation at the mixture level surface (clips 2 and 3).

Critical discharge model: Tables of critical two-phase mass fluxes are calculated and stored for individual discharge geometries during the ATHLET run. 

Control and balance-of-plant: A high level simulation language (GCSM) allows to simulate control, reactor protection and other balance-of-plant (BOP) systems via input. Control circuits or even simplified fluid systems can be conveniently modeled this way. In addition, GCSM has a general interface for user provided external BOP models.

Integrated mass and momentum balance(IMMB): This simplified treatment of the mixture momentum equation (one dynamic pressure for a whole loop) is a fast running option especially valuable for long term transients.

Plant analyzer: ATHLET can be run interactively in the frame of an engineering plant analyzer ATLAS (Fig. 1).

3D Neutron kinetics: There are couplings of ATHLET with the 3D neutron kinetics programs QUABOX/CUBBOX, DYN3D, BIPR8, and KIKO3D. The thermalhydraulics of the core is represented by parallel channel technique (Fig. 2 and Fig. 3).

For the analysis of reactor accidents with core degradation, ATHLET-CD is being developed. This code is based on the ATHLET thermo-fluiddynamics and includes modules for the simulation of core degradation, melting and relocation, of fission product and aerosol release and transport, and of debris bed behavior.