Incorporation of radionuclides from the electrometallurgical treatment of spent fuel into a ceramic waste form

Abstract

b + 6> @@&l ABSTRACT A %6 i An electrometallurgical process is being developed at Argonne National Laborato@o a treat spent metallic nuclear fuel. In this process, the spent nuclear fuel is electrorefined in a molten salt to separate uranium from the other constituents of the fuel. The geatment process generates a contaminated chloride salt that is incorporated into a ceramic waste form. The ceramic waste form, a composite of socialite and glass, contains the fission products (rare earths, alkalis, alkaline earth metals, and halides) and . . transuranic radionuclides that accumulated in the electrorefiner salt. These . radionuclides are incorporated into zeolite A, which can fully accommodate the salt in its crystal structure. The radionuclides are incorporated into the zeolite by hightemperature blending or by ion exchange. In the blending process the salt and zeolite are simply tumbled together at ti50°C (723 K), but in the ion exchange process, which yields a product more highly concentrated in fission products, the molten salt is passed through a bed of the zeolite. In either case, the salt-loaded zeolite A is mixed with glass frit and hot isostatically pressed to produce a monolithic leach resistant waste form. Zeolite is converted to sodalite during hot pressing. This paper presents experimental results on the fission product uptake of the zeolite as a function of time and salt composition. INTRODUCTIONIn the electrometallurgicrd treatment of spent nuclear fuel, metallic nuclear fhel is electrorefined in a mo~ten salt to separate uranium from the other constituents of the fuel. [1,2] The salt retains the rare earth, alkali, and alkaline earth fission products, as well as the transuranic radionuclides originally present in the spent fuel. Two options are currently under study for treating this salt. In one option, it is directly incorporated into zeolite and, eventually, a ceramic waste form. Fresh salt is then introduced into the electrorefiner to treat additional fuel. [3] In the second process, the radionuclides are removed from the salt by an ion-exchange process using zeolite columns. The radionuclides are concentrated in the zeolite, which also retains a portion of the salt. The effluent salt from the column is used to treat additional spent fuel, reducing the quantity of salt that must be disposed of, [4, 5, 6] In both processes, the salt and radionuclides are first incorporated into zeolite A, then combined with glass frit and consolidated by hot isostatic pressing. During consolidation, the salt-loaded zeolite is converted to sodalite, resulting in a monolithic composite of sodalite and glass. [7] In this paper we will discuss the incorporation of fission products into zeolite by ion exchange and some of the factors that play a role in incorporating the zeolite into a waste form. We are determining the effectiveness of the ion exchange process by examining the fission product uptake of the zeolite as a function of time and salt composition. From these tests we obtain kinetic and equilibrium dat...

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Projected Salt Waste Production from a Commercial Pyroprocessing Facility

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