PRELIMINARY RESULTS OF THE SEVENTH THREE-DIMENSIONAL AER DYNAMIC BENCHMARK PROBLEM CALCULATION. SOLUTION WITH DYN3D AND RELAP5-3D CODES. Marek Beník, Jan Hádek Nuclear Research Institute ež plc, 250 68 ež, Czech Republic E-mail:
[email protected] ABSTRACT The paper gives a brief survey of the 7th three-dimensional AER dynamic benchmark calculation results received with the codes DYN3D and RELAP5-3D at NRI ež. This benchmark was defined at the 20th AER Symposium in Hanassari (Finland). It is focused on investigation of transient behaviour in a VVER-440 nuclear power plant. Its initiating event is opening of the main isolation valve and re-connection of the loop with its main circulation pump in operation. The VVER-440 plant is at the end of the first fuel cycle and in hot full power conditions. Stationary and burnup calculations were performed with the code DYN3D. Transient calculation was made with the system code RELAP5-3D . The two-group homogenized cross sections library HELGD05 created by HELIOS code was used for the generation of reactor core neutronic parameters. The detailed six loops model of NPP th Dukovany was adopted for the 7 AER dynamic benchmark purposes. The RELAP5-3D full core neutronic model was coupled with 49 core thermal-hydraulic channels and 8 reflector channels connected with the three-dimensional model of the reactor vessel. The detailed nodalization of reactor downcomer, lower and upper plenum was used. Mixing in lower and upper plenum was simulated. The first part of paper contains a brief characteristic of RELAP5-3D system code and a short description of NPP input deck and reactor core model.