Uncertainty and sensitivity analyses of the Kozloduy pump trip test by coupled RELAP5/PARCS code

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. In the current paper a contribution to the assessment and validation of coupled code technique through the Kozloduy VVER100 pump trip test is performed. For this purpose, the coupled RELAP5/3.3-PARCS/2.6 code is used. The code results were assessed against experimental data and the comparison study shows good agreements between the calculations and the global kinetic and thermal-hydraulic aspects observed experimentally. It appears that at steady state level, the simulation errors are mainly due to the absence of ADF correction and to the model used for evaluating the Doppler feedback effect. During the transient, the discrepancies are mainly due to the combined effect of uncertain parameters related to the measurement of control rod course, and the estimation of the Doppler effect