The purpose of this study is to develop a WIMS/CANDU code for a lattice calculation on the basis of WIMS-D5 code for the safety analysis of CANDU reactors. To assess WIMS-D5 applicability to a CANDU reactor, a lattice model was developed for CANDU-6 reactors at the Wolsong site. As for the benchmark of the code validation, a code-to-code comparison was performed between the WIMS-D5 code with both the 69- and 172-energy groups of ENDF/B-VI nuclear data library and the WIMS-AECL code with the 89-energy group. The comparison studies of the reactor physics parameters such as the void reactivity and the coolant/fuel/moderator temperature coefficients were conducted with a change of the internal isotopic composition due to the fuel burning-up using both WIMS-AECL and POWDERPUFS-V (PPV) codes. The results show that the present results from WIMS-D5 code and WIMS-AECL code agreed well with those of the PPV at the beginning of the fuel burn-up phase. As the burning-up progresses, the results of WIMS-D5 show a large deviation from those of PPV for the CANDU 6 reactors.