KORSAR is a best estimate computer code [1].

The KORSAR code functionality includes:

- description of coolant water flows by a fully non-equilibrium two fluid model;
- consideration of noncondensable effects including dissolution of hydrogen, helium, nitrogen, and oxygen in water and their removal from water (degassing) and transport in both phases along the coolant flow path [9];
- modeling of soluble boron transport with consideration of boron precipitation if its concentration increases above the saturation point;
- description of specific effects, such as critical break flow, radiative heat transfer, water radiolysis, etc.;
- use of highly accurate computer programs for calculating thermal properties of water and water vapor in the subcritical region;
- description of reactor core neutron kinetics in a point approximation;
- specific models of equipment components: metal structures, centrifugal pumps, pressure vessels, tanks, etc.;
- numerical simulation of reactor core neutron kinetics by using a 3D diffusion model with consideration of thermo-mechanical effects in fuel rods. Few-group constants for the diffusion model are obtained using the SAPFIR-RC program package that is designed for transient neutronic calculations. The use of coupled SAPFIR-RC package and KORSAR allows for steady-state and dynamic calculations of reactor neutronics and thermal-hydraulics in a fully closed cycle;
- description of connections and input data for nodalization components, generation of disturbance inputs, programing of supporting calculations and control algorithms is carried out in the code input file using the own language, DLC (Data Language for Codes).