Application of the SUSA and CIAU methods to the calculation of a NPP start-up experiment using a coupled code system

The modeling of complex transients in Nuclear Power Plants (NPP) remains a challenging topic for Best Estimate three-dimensional coupled code computational tools. This technique is, nowadays, extensively used since it allows decreasing conservatism in the calculation models and performs more realistic simulating and more precise consideration of multidimensional effects under complex transients in NPPs. Therefore, large international activities are in progress aiming to assess the capabilities of coupled codes and the new frontiers for the nuclear technology that could be opened by this technique. In the current paper a contribution to the assessment and validation of coupled code technique through the Kolzoduy VVER100 pump trip test is performed. For this purpose, the coupled REALP5/3.3-PARCS/2.6 code is used. The code results were assessed against experimental data and the overall data comparison shows good agreements between the calculations and the global kinetic and thermal-hydraulic aspects observed experimentally. Further investigations through the use of two “antagonist” GRS and the CIAU methods, in order to evaluate and quantify the origin of the observed discrepancies. It was revealed on one hand that relative error quantification discrepancies exist between the two approaches, and on the other hand deviations between code predictions and measurements are mainly due to the used models for evaluating and modeling of the Doppler feedback effect.