VVER-1000 pin cell benchmark for coupled neutronics/thermal-hydraulics calculations: preliminary results

There is a need for verification of coupled neutronics / thermal-hydraulics calculation schemes. For this, we propose to use the benchmark based on the pin cell of VVER-1000 reactor. This paper gives a detailed description of the benchmark as well as the results of calculations obtained by MCU/ATHLET and MCU/FLOWVISION coupled codes. We also proposed a new convergence criterion, and showed that some power levels lead to the iterative instability of coupled solution. To enhance the stability one could use stochastic method.