Development of tritium permeation model for Printed Circuit Heat Exchanger

The Very High Temperature Reactor (VHTR) has been noticed for its capability to provide process heat to various industrial processes due to its high operation temperature. However, this integration concept of VHTR and other industrial processes can potentially create a possibility of tritium exposure to other industrial processes and even to the final product of the process and to the users of the product. Thus, in terms of safety, it is crucial to understand the behavior of tritium in nuclear reactor systems, especially the permeation behavior of tritium in the heat exchanger as it is the main downstream route. VHTR employs Printed Circuit Heat Exchanger (PCHE) for its compactness and large surface area. And this PCHE possesses a very distinctive structure compared to other heat exchangers. Due to its distinctive structure, it is very difficult to estimate average wall thickness. In this study, permeation model which accounts the PCHE structure and temperature distribution across the PCHE wall is developed. The structure of the PCHE is reflected in the shape factors and the thermal distribution across the wall is reflected in the effective diffusivity. The developed PCHE permeation model is found to predict permeation rate within ±20% error bound whereas the existing model overpredicts permeation rate at maximum by 400% when temperature distribution exists and underpredicts permeation rate at maximum by 69% when no temperature distribution exists across the PCHE wall.