Validation of the heat transfer enhancement models for spacer grids in the system code TRACE

The validation of thermal hydraulic system codes like TRACE is a demanding and highly needed task for the nuclear engineering community. In the present paper the validation of TRACE is focused on the heat transfer enhancement models for spacer grids. Several test sections are selected for that purpose whereas several coolants, different rod arrangements and dimensions, and various thermal hydraulic boundary conditions are considered. The systematic evaluation by means of post-test calculations shows that the present TRACE model is well able to represent the magnitude of the heat transfer enhancement directly at the spacer grid. Nevertheless, improvements of the model were necessary in order to catch the enhancement downstream of the spacer grid. With the present model, the exponential decay of the enhancement is over estimated. The comparison with experimental data suggests a faster establishment of the fully developed flow. Adjustments to the model are done in order to represent the data correctly in terms of magnitude and duration.