The thermalhydraulic analysis of CANDU-6 reactor channels with CANFLEX-NU fuel bundle

This report describes the thermalhydraulic characteristics of CANDU-6 reactors' fuel channels loaded with CANFLEX-NU (CANDU Flexible Fuelling -Natural Uranium) bundles. In this report, the distributions of channel flow rate, channel exit quality, Critical Channel Power(CCP) and Critical Power Ratio(CPR) for the CANFLEX-NU fuel's channel are evaluated by using NUCIRC-MOD2.001 code. The NUCIRC code incorporated with the pressure drop and Critical Heat Flux(CHF) models of CANFLEX fuel bundle. Especially, the effects of pressure tube creep and bearing pads height on the thermalhydraulic characteristics were also examined by performing the analysis for the uncrept, 3.3% and 5.1% peak crept tubes with the CANFLEX-NU bundles attached with 1.7mm height bearing pads. This high bearing pads are 0.3mm higher than the existing 1.4mm height bearing pads. The results of the minimum CPR data show that the operating thermal margins for the 1.4mm bearing-pad and the 1.7mm bearing-pad CANFLEX-NU bundles are increased about 3% and 8% respectively, as compared to the 37-element fuel bundle. The CCP decrease due to the pressure tube creep for CANFLEX-NU bundle is less than that for 37-element fuel bundle, and the CCP enhancement due to the increase of bearing pads height is estimated to be about 3%∼5%