cipally to obtain the fastest dissolution, but also because a precipitate of A1F3 is much easier to redissolve than a precipitate of ZrF4. Fortunately, the rate of approach to conditions that form a precipitate of ZrF4 decreases as fluoride is consumed, so that the formation of ZrF4 is unlikely. The composition of the final dissolver solution is sufficiently stable if processed immediately. Zirconium and aluminum may gradually precipitate over a period of several weeks, making it necessary to centrifuge out the solids prior to solvent extraction if the process is delayed (3, 6, 7, 7 7 ) . No further adjustment in salting strength is required prior to solvent extraction. The zirconium fuel element dissolved faster in this test than in the laboratory because of a larger surface-to-weight ratio. The elements were dissolved a t 70’ C. in 24 hours, including an 8- to 9-hour period during which the solution was penetrating the oxide layer. T h e rate of corrosion of the Type 304L stainless steel averaged 10 to 15 mils per year in the liquid phase and
