Mathematical simulations for studying the effectiveness of HTO removal mechanism from spent fuel storage bay and estimating the environmental releases

Abstract

The diffusion of tritiated water (HTO) vapor from the spent fuel storage bay to the spent fuel storage building (SFSB) may lead to internal exposure to occupational workers. In order to reduce this internal exposure, air curtains are provided over the spent fuel storage bay to effectively remove HTO diffusing from spent fuel storage bay to SFSB. The radiation doses to the occupational workers are controlled well below the permissible level by monitoring the air concentration of HTO in the SFSB area. In the present study, it is brought out that few additional monitoring of air concentration of HTO above the spent fuel storage bay can give useful information about the effectiveness of air curtains in the removal of HTO and the estimation of environmental releases of HTO. A three-dimensional advection-diffusion-based model is developed to demonstrate the effectiveness of air curtains in the removal of HTO and for the estimation of environmental releases of HTO, utilizing these additional measurements. The study showed that air curtains are an effective mechanism to reduce the air concentration of HTO in SFSB and remove almost 50% of HTO activity using only around 24% of the ventilation air supplied to the SFSB. The environmental release rate of HTO estimated in this study was in good agreement with the measured release rate. The methodology developed here can also be utilized to carry out parametric studies to see the impact of changes in the parameters related with air curtains in the removal of HTO, thus for better designing of air curtains.

Keywords

• advection-diffusion
• air curtains
• modeling
• spent fuel storage bay
• tritiated water