Prediction of Void Fraction in a Subchannel and Bundle Geometry with FLICA4 and TRACE

Abstract

In order to encourage advancement in subchannel analyses of fluid flow in rod bundles, an international benchmark program, namely the OECD/NRC PWR Subchannel and Bundle Test (PSBT) benchmark, has been organized. The PSBT benchmark aims at assessing the capabilities of subchannel analysis codes, system codes, and computational fluid dynamics (CFD) codes for the prediction of detailed void distributions in subchannels, including departure from nucleate boiling, on the basis of experimental data measured at a full scale prototypical PWR rod bundle. Within the framework of the PSBT benchmark, analyses of the void distribution in a subchannel and bundle geometry have been performed at the Paul Scherrer Institut by means of the subchannel analysis code FLICA4, and the thermal-hydraulic system code TRACE. Steady-state scenarios are analyzed by using both FLICA4 and TRACE and transient analyses are performed with FLICA4. In particular, the TRACE calculations for bundle geometry have been carried out employing a three- dimensional vessel component to model cross flows between subchannels. The analysis aims at evaluating the applicability of a three-dimensional vessel component of TRACE for subchannel analyses, as well as validating the subchannel code FLICA4. The calculated void fractions are compared to the experimental data, and the accuracies of the predictions by both codes are appraised by means of a statistical analysis.