Abstract: The paper mainly introduces a new natural cycle evaporator with central downcomer, which is used to process the low and medial level radioactive wastewater in the reactor operation. The designed evaporator is integrated with the process of evaporated concentration, cleaning demister, and entrainment eliminator. All the assemblies are set in a single pressure vessel. Through the integrated collocation, the cleaning water form demister is reasonably treated, the equipment required less space, the whole evaporated system is simplified and can be handled easily. Through the multi-effect purification, the quantity of entrained mist and volatile product in the produced steam significantly reduced. The proposed evaporator can improve the purification and the decontamination factor of radioactive wastewater, which is accorded with the radioactive waste minimization principle.