Thermal-hydraulic analysis of steam generators: the ATHOS code

To address the needs of the Nuclear Power Industry for the evaluation of design and performance analysis of steam generators, a computer program capable of three-dimensional thermal-hydraulic analysis of different types of steam generators has been developed. This computer program, called ATHOS (Analysis of the Thermal Hydraulics of Steam Generators), is capable of simulating the geometry and internal structure, including tube bundle, tube support plates, baffles, etc. in considerable detail. The thermal hydraulics simulation is based on a description of the two-phase flow by means of a set of partial differential equations representing thermal equilibrium flow with slip between the two phases. An implicit numerical method is used to solve the set of finite difference equations derived from the governing partial difference equations using a set of constitutive models for slip, friction and heat transfer which will be described in detail in subsequent sections of this paper. The results of this solution include detailed distributions of the velocities of the two phases in R-O-Z coordinates, void fractions and enthalpies. In this paper the governing equations, the constitutive models, the assumptions, the solution procedure, typical calculation and result, and code verification studies are described