Representative sampling analysis of radioactive airborne effluent for the stack system in a molten salt reactor

Highlights: • A stack system model in a molten salt reactor is built. • The gas velocity, cyclonic flow, gas concentration, and aerosol concentration have been obtained. • A sampling height above 11 m is recommended to satisfy the ISO Standard 2889-2010. During the operation of the molten salt reactor, the radioactive gas and radioactive aerosol particles will be generated, and should be discharged into the atmospheric environment through ventilation ducts and stacks after filtration and adsorption. In order to determine whether the radioactive airborne effluent emissions would meet the requirements of the National management limits (ISO 2889–2010), it is necessary to calculate and monitor the radioactive airborne effluents in the stack system. Therefore, a three-dimensional computational fluid dynamics (CFD) model is built to evaluate the flowing and mixing state for radioactive airborne effluent in the stack system of the molten salt reactor. The uniformities of velocity, cyclonic flow, tracer gas concentration, and aerosol particle concentration at different sampling heights in the stack are analyzed by CFD-Fluent. The results show that, the airflow and concentration of tracer gas easily tend to blend well at high flow speed, while there is a little random distribution effect for the aerosol particles due to their large densities, which needs a longer transport process to increase the uniformity. When the sampling height is above 11 m from the bottom of the stack, the variation coefficients of velocity, cyclonic flow, tracer gas concentration, and aerosol particle concentration are below 11.6%, 4.4%, 0.4% and 20% correspondingly, which all meet the well-mixed criteria and the requirement of representativeness sampling location in ISO 2889–2010. If the variation coefficient of aerosol particle concentration can be allowed to be less than 30%, then sampling height above 6 m will satisfy the ISO standard. The results of this study provide a good reference for the detection, sampling and analysis of radioactive gases and aerosol particles in the stack of the molten salt reactor.