MUNGOS - FULLY INTERACTIVE MODEL FOR SUBCHANNEL ANALYSIS

A dynamic model for predicting thermal and hydraulic behaviour of fuel rod bundle, with full interaction between fuel rods and fluid flow subchannels is developed. Model consists of two submodels: SUBROD - asymetric model for fuel rod thermal response, and SUBMIX - model for subchannel fluid flow mixing. They are coupled on outside clad surface. SUBROD solves the heat balance equation in r−Ø geometry, including temperature history weighted factor, SUBMIX solves number of connected subchannels in a bundle, working with separate two-phase flow finite-difference equations in a fully ventilated subchannels. SUBMIX is four-equations-model with total continuity, vapor continuity, energy conservation and axial momentum. Verification is made comparing the results obtained by MUNGOS with refferenced R.T. Lahey's experiments, and with the computer codes COBRA, HAMBO and MATTEO. Influence of two phase friction multiplier selection model on sub-channels flow prediction is also analysed.