Modeling and Design Procedures for Decontamination of an Evaporation Tower with Sieve Trays in Radioactive Wastewater Treatment of Nuclear Power Plant

摘要

The working principle and operating characteristics of a decontamination tower with sieve trays, when used to wash radioactive droplets entrained by the vapor from a wastewater evaporation unit of nuclear power plants, were analyzed and the mixing and dilution mechanism for washing radioactive droplets presented. Based on results and proposed mechanism, a simple but useful engineering model was developed to describe the relationship of decontamination factor (DF) with the sieve tray number, entrainment rate in vapor, reflux ratio, and demister efficiency, as well as the mixing degree of the entrained droplets with the reflux distillate on the trays. Quantitative analysis indicates that this model can show how these factors affect the decontamination efficiency of the tower and thus can be used as an analytical tool for operation or design of the decontamination towers. Following the proposed model, a step-by-step design procedure is presented for calculating the required sieve tray number under the designated DF value. Finally, for the requirement and condition of boron recycle system, a decontamination tower was designed using the proposed model and procedure, and a pilot-scale test verified that the tower can achieve the design DF. Based on the pilot test, a plant-scale prototype tower has been designed and successfully put into use in the Hong Yanhe Nuclear Power Plant in China. The design practice indicates that this model, as a simple but useful tool, can also be applied to the operation analysis and the design of other sieve tray towers operating in similar cases.