[en] This report describes the thermalhydraulic characteristics of CANDU-6 reactors fuel channels loaded with 37-element fuel bundles and CANFLEX (CANDU Flexible Fueling) fuel bundles after the refurbishment of Wolsong Unit 1. The channel flow rate, critical channel power(CCP) and critical power ratio(CPR) distribution for two-kinds nuclear bundles are evaluated by the NUCIRC-MOD2.001, which is incorporated with the pressure drop and critical heat flux(CHF) models of CANFLEX fuel bundle. In order to examine the thermalhydraulic characteristics with respect to the EFPY (Effective Full Power Year) after the refurbishment of Wolsong Unit 1, the creep data and friction factors are generated for each EFPY, and the input data for two-kind fuel bundles are compared. It is shown that, for the same EFPY, the CCP of CANFLEX fuel bundle has a higher value, compared to 37-element fuel bundles. And, the CCP values are decreased with EFPY for two-kind fuel bundles. However, for CANFLEX fuel bundle, the decrease of CCP with EFPY is smaller compared to 37-element fuel bundles. By this characteristic, the CPR of CANFLEX fuel bundles has a higher value than 37-element fuel bundle. For 37-element fuel bundles, the minimum CPR is lower than 1.3, while CANFLEX fuel bundle has a higher value than 1.4