Demonstration of a Method to Suppress Radon Emanation from Uranium-bearing Wastes

摘要

The authors have previously done a theoretical study of radon emanation and quantitatively demonstrated that a small pore of even nanometer size with moisture in its microscopic grain structure can give as high a radon emanation coefficient as around 0.18. Therefore, it was concluded necessary to remove pores of any size in the grain in order to suppress radon emanation. Melting of uranium-bearing wastes is one of the best technologies for this purpose. In order to verify this theoretical finding, a series of experiments was carried out using three test samples; unprocessed, cemented and vitrified calcium superphosphate. Calcium superphosphate was chosen because it resembles a uranium-bearing waste like sludge in terms of both radioactive nuclide adhesion on the grain surface of the waste matrix (surface contamination) and the grain geometric shape. As expected from the theory, radon emanation from the vitrified sample was extremely low compared to the unprocessed sample. On the other hand, radon emanation from the cemented sample remained very high, The present study opens doors to suppression of radiation exposure from radon and to safe disposal which does not depend on integrity of the final waste form and the site cover soil.