[en] The primary coolant purification system of HANARO is required to maintain the chemical state of the reactor coolant and pool water within the specified limits. For this, reactor operators replace periodically the resin of ion exchanger and this is one of the operator activities which could bring large radiation dose. Therefore, we analysed the radiation level at the surface of resin cartridge from the previous replacement activities and found the required resin decay time to meet the limit specified for radiation protection. As results, three more resin cartridge were found to be required for the primary purification system to meet the radiation protection limit. This was effective in reducing the radiation dose to operators