Patent GB-860753-A (GB)
Title: Treatment of neutron-irradiated thorium
IPC: G21C19/46
Filed: 1945-11-15
Abstract: 860,753. Separation of uranium-233 and protactinium-233 from irradiated thorium. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Nov. 15, 1945 [Nov. 3, 1944], No. 30682/45. Class 39(4). [Also in Group XXXVI] Uranium-233 or protactinium-233 is extracted from a neutron-irradiated thorium compound by one of the following methods:- (a) The compound is dissolved in nitric acid in the presence of an oxidising agent to convert the uranium to the uranyl form, the pH is adjusted to about 3, uranium and thorium are precipitated as peroxides by adding excess hydrogen peroxide or alkali metal peroxide, and the precipitate is treated with aqueous alkali which dissolves the uranium peroxide but not the thorium peroxide. Uranium-233 is recovered from the alkali solution by adding acid to reprecipitate the peroxide. The uranium may be further purified from fission products by dissolving the precipitate in nitric acid at pH 1, reprecipitating with hydrogen peroxide, and repeating as necessary; alternatively uranyl nitrate may be crystallised out from the nitric acid solution and dissolved in ether. (b) The pH of the solution of irradiated thorium is adjusted to about 1 and the thorium precipitated as fluoride, iodate, oxalate, or phosphate, leaving uranium in solution; addition of alkali to the separated solution precipitates uranium. (c) Manganous chloride is added to the acid solution of irradiated thorium, followed by potassium permanganate to precipitate manganese dioxide which carries down protactinium-233; the precipitate is redissolved and zirconium phosphate precipitated in the solution to carry down the protactinium again, leaving manganese in solution; the precipitate is dissolved in dilute hydrogen fluoride, and alkali added to the cooled solution to precipitate zirconium and protactinium hydroxides; the manganese dioxide and zirconium phosphate precipitations are repeated as necessary. Finally the zirconium phosphate is converted to zirconium sulphate which is dissolved in fluoride solution and the protactinium-233 separated by electrolysis (see Group XXXVI). Another method of separating the zirconium and protactinium is precipitation alternately with manganese dioxide and with zirconium phosphate. Alternatively, lanthanum oxalate may be used to carry down the protactinium leaving zirconium in solution, or zirconium iodate may be formed and fractionally precipitated, the solution being finally fractionally crystallised to separate zirconium oxychloride. The protactinium obtained by method (c) may be allowed to decay to uranium-233 or may be separated from uranium-233 after partial decay; the separation method involves repeated precipitation from solution with zirconium phosphate followed by electrolysis (see Group XXXVI). Uranium-233 metal may be obtained from compounds thereof by reduction with sodium. The Specification as open to inspection under Sect. 91 discloses also a cyclic process in which thorium peroxide is irradiated with neutrons and then treated with sodium hydroxide or sodium peroxide solution to remove uranium-233, leaving the thorium peroxide ready for use again. This subjectmatter does not appear in the Specification as accepted.