Flow requirement of carbon dioxide through the AHWR-LEU Pressure tube-Calandria tube annulus has to be estimated from argon 41 radioactivity release, environmental and economic considerations. For a theoretical estimate of the flow requirement, a purpose built one-dimensional code for diffusion of argon 40 in carbon dioxide flow in AHWR annulus geometry has been developed. In this code, the species transport equation in fluid flow was discretised in the domain of the annulus geometry using Finite Element Method based on Galerkin Weighted Residual technique. The code was validated by comparing the numerical results with closed form solution of the governing equation for simple concentric tube annulus geometry. The theoretically validated code was used on the actual AHWR-LEU annulus design. The results suggest that for an acceptable reactivity release of 15Ci/day from the entire core would require 9.6ml/min carbon dioxide flow in each annulus.

Keywords: Diffusion, Argon 41, Radioactivity, Finite element, Galerkin method.