Modeling of NPP with WWER-1200 by the coupled system code ATHLET/BIPR-WWER using quasi 3D nodalization of reactor pressure vessel and steam generators

A detailed model of the primary and secondary loop of the new design of WWER-1200 NPP is being created for the coupled system code ATHLET/BIPR-WWER. On the basis of the previously gained experience, a very detailed 3D modeling of the reactor pressure vessel (RPV) and of the steam generators (SG) is being successfully applied. The nodalization schemes of these objects are chosen to be optimal ones concerning the fidelity to the real geometry and the needed CPU time. The thermal fluid objects are modeled in ATHLET as objects of type 'pipe' most of them connected with cross flows, that allow to describe the mixing phenomena in RPV and in steam generators near to reality. A pre-processor system supports automatically to prepare the complex and great number of nodalized volumes for the ATHLET input. A detailed modeling of the control and safety systems covers a wide spectrum of initiating events. Generic design data are used to model the 3D neutron-kinetics in BIPR, applying the modernized fuel assembly design for WWER-1200. As a demonstration of the simulation capabilities of the coupled system code ATHLET/BIPR-WWER for the new reactor design WWER-1200 a RIA transient is analysed. A rod ejection within 0.1 s is simulated at nominal reactor power. The results are visualized with a special 3D graphical system developed in RCI KI. This advanced tool allows through rotating the whole model or only selected parts of it to visualize the thermal-hydraulic values at any location. By applying the 'cut' function the internal volumes of the 3D objects can be selected and visualized too. The coupled system code ATHLET/BIPR-WWER is being applied successfully by performing calculations analysing transients for the new design of a NPP with WWER-1200 reactor (Authors)