Method for the manufacture of PuO.sub.2 -containing crystals

In a method for the manufacture of PuO.sub.2 -containing crystals by oxidizing plutonium in a nitric acid solution to form Pu.sup.6+, precipitation of ammonium plutonyl carbonate containing crystals through reaction with ammonium and carbonate ions and subsequent separation and calcining of these crystals, the improvement comprising removing metal compound contaminents in the nitric acid solution which form difficult-to-dissolve metal hydroxide compounds by introducing the oxidized Pu.sup.6+ in solution in nitric acid into an aqueous solution of a salt selected from the group consisting of ammonium carbonate and ammonium acetate, dosing said aqueous solution with NH.sub.3 and acid ions selected from the group consisting of carbonate (CO.sub.3.sup.-2) ions and acetate (CH.sub.3 COO.sup.-) ions to produce a mol ratio of acid ions to the Pu.sup.6+ ions in said aqueous solution of at least 4:1, said acid ions forming complex compounds containing plutonium which remain dissolved in the aqueous solution, while the metal compound contaminants convert to difficult-to-dissolve metal hydroxide compounds and are precipitated, separating the precipitated metal hydroxide compounds from the aqueous solution, and thereafter adding NH.sub.3 and carbonate ions to effect precipitation of the ammonium plutonyl carbonate containing crystals.