Radiological impact at the extraction stage of the thorium fuel cycle

Among the natural thorium resources, monazite and the residues of rare-earth extraction will very likely be exploited first in case of a significant use of thorium-based nuclear fuels. The different waste streams have been identified from the present industrial practices used in the production of nuclear grade thorium from monazite extracted from beach sands. The radionuclides of utmost importance in various waste streams are /sup 232/Th, /sup 228/Ra, and /sup 220/Rn from the thorium series and /sup 238/U, /sup 230/Th, /sup 226/Ra, and /sup 222/Rn from the uranium series. There are three important steps, where the major radioactivity is generated. It is found that the total amount of solid wastes generated for the production of 1 t of thorium metal is ~10 t, which is ~50 times less than in the case of 1 t of uranium production. Among them, long-lived wastes represent a small volume and could be disposed of in a deep geological repository, as for alpha-active reprocessing wastes. The raw materials at the mining site are lower by one to two orders of magnitude in the general case of high-grade thorium ore in comparison to the present commercially exploited uranium ore. The short- and long-term impact of these wastes on the environment and radiotoxicity has been calculated. It has been found that the short- and long-term impact for the public is about two orders of magnitude lower than for the equivalent front-end uranium cycles. On the contrary, inhalation and ingestion dose commitments for an adult are about five and two times higher, respectively, in the case of pure thorium as compared to the equivalent uranium case