Simulation of AER-7 benchmark problem with the coupled code DYN3D/ATHLET

The 7th dynamic benchmark is the most recent problem specified within the AER activities on verification of the coupled neutronic/thermal-hydraulic codes. This is the VVER-440 transient initiated by re-connection of the isolated reactor circulation loop filled with a low-temperature coolant. During the transient a core power excursion with a non-symmetric radial distribution is expected due to incomplete coolant mixing at the core inlet.

The externally coupled code system DYN3D/ATHLET developed in HZDR was used in the benchmark simulation. In the case of external coupling all neutronic and thermal-hydraulic parameters of the core are calculated by the 3D code of neutron kinetics DYN3D.

The computer model of the VVER-440 reactor used in the AER-7 calculations represents a modified version of the earlier developed input deck for the AER-6 benchmark simulation. The model includes 6 reactor loops with the main circulation pumps and steam generators. The secondary system is modelled up to the turbine valves. The 3D core model includes all 349 fuel assemblies (assembly-by-assembly approach).

The main results of the benchmark calculation are presented and discussed.