Improvement of ATHLET modelling capability for asymmetric natural circulation phenomenon using uncertainty and sensitivity measures

In this paper, a post-test calculation is performed by best-estimate thermal-hydraulic code ATHLET to simulate PKL IIIB3.1 test. Due to the effect of isolated steam generator on the whole primary cooling system, the results show that the mass flow in the isolated loop is overpredicted significantly comparing to the experimental data. Many measures have been tried to improve the simulation results, but an effective method is still missing. Based on the post-test calculation results, an uncertainty and sensitivity analysis is carried out to find out the main reason causing this higher circulation mass flow. Lots of factors are considered in this study, e.g. the boundary conditions, thermal-hydraulic correlations, and model parameters. The most sensitive factors are selected and adopted to improve the simulation modelling. The results achieved so far indicate that with these measures, the ATHLET capability for the asymmetric natural circulation phenomenon is effectively improved.