Some challenges to the thermal-hydraulic codes

The thermal-hydraulic codes were developed with the data and correlations obtained from separate effect tests. As such, there are some system-related phenomena which cannot be depicted properly by the codes. In this paper we discuss the difficulties encountered by code modeling for the following systems: feedback loop, multichannel system, multidimensional flow and multiloop circulation. The discussion shows that codes can only give probable answers; the difficulties encountered are due to maldistribution of heat and flow, primary-secondary interaction, feedback effect, instrumentation-control interaction and other unknown factors. ((orig.))