(A) study on the removal efficiency of multicomponent fission gas mixture using activated carbon beds

Abstract

The removal mechanisms of multicomponent fission product by activated charcoal bed was investigated. Mathematical models with linear driving force approximation for the adsorption of multicomponent fission products and the numerical method of a third order characteristic algorithms were used to analyze the dynamics characteristics of charcoal bed system. In this model, the competitive adsorption between adsorbable species was considered. The multicomponent gas phase adsorption isotherm is expressed by Langmuir type. The equilibrium concentration between adsorbent and adsorbates is calculated using this isotherm and compared it with other results, which agrees well to each other. As a result of this investigation, the removal efficiency of activated charcoal bed for radioactive multicomponent fission products is found to be influenced by the operation time and various operating conditions such as the mass transfer coefficient, the number of adsorbable component, bed length, relative humidity, particle density and bed voidage, and inlet concentration. Among these parameters, the mass transfer coefficient between adsorbates and adsorbent materials is the most important factors on the removal efficiency. That is, the removal efficiency increases with the increase of the value of the mass transfer coefficient. Also, as the number of adsorbable component is increased, the breakthrough time is decreased due to the increase of the value of competitive adsorption. In humid conditions, the decrease of the removal efficiency on the multicomponent fission gases was investigated. As the relative humidity is increased, the breakthrough time is decreased due to the reduction of equilibrium adsorption capacity and the decrease of the effective pore diffusivity.