Abstract: Mixed crystals containing uranium and gadolinium for conversion into nuclear fuels by introducing NH.sub.3, CO.sub.2 and a uranyl salt solution containing dissolved gadolinium into a body of an aqueous solution of ammonium carbonate. As a result salts of gadolinium and uranium complexes precipitate and during precipitation there is a lowering of the pH from 9 down to 8.2. The precipitate is separated and converted to uranium and gadolinium oxides. Preparing the mixed crystals in this manner results in the gadolinium being finely and homogeneously distributed into the oxidic nuclear fuel.

Abstract: Process waste waters at a pH of about 7 contaminated with radioactive isotopes are decontaminated by (a) adjusting the pH to about 5.8, (b) adding CaO or Ca(OH).sub.2 to raise the pH to about 8.5, (c) agitating the mixture for at least 5 minutes to effect intimate contact and produce a suspension of solids containing radioactive contaminants, and (d) separating the suspension of solids from the water by centrifuging. Removal of radioactive uranium isotopes with an alpha emission is effected at a pH of about 10. The process provides a method for concentrating radioactive contaminants in water for subsequent ultimate storage and also purifies the contaminated water so it may be safe to discharge it into the sewer. The treatment may be carried out in a plurality of stages in series.