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United States Patent Office Patented Nov 3,288,568 United States Patent Office Patented Nov. 29, 1966 1. 2 3,288,568 tion and extraction can be effected combinedly in one pro DIRECT DISSOLUTION OF WATER. INSOLUBLE cedure, and that stirring or agitation for dissolution and URANUM COMPOUNDS BY CONTACT WITH extraction is not necessarily continued, thus a simpler NEUTRAL, ORGANIC SOLVENTS PRETREATED apparatus suffices, are advantages of the method of the WITH NTRIC ACD invention. Ordinarily, when the water-insoluble nuclear Hiroshi Tomijima, Totsuka-ku, Yokohama, Kazushige fuel material is converted to a water-soluble compound or Tsukui, Tokyo, and Yoshimi Okoshi, Kawasaki-shi, a compound extractable with an extracting organic sol Japan, assignors to Tokyo Shibaura Electric Co., Ltd., vent, an excess amount of an acid is to be used, so that it Kawasaki-shi, Japan, a corporation of Japan causes a wasteful spending and needs apparatus and labor No Drawing. Filed Oct. 20, 1961, Ser. No. 146,447 10 Claims priority, application Japan, Nov. 18, 1960, for the recovery. According to the purifying method of 35/45,357 the invention, however, spending amount of the inorganic 9 Claims. (CI. 23-319) acid is limited to the theoretical amount, or an amount somewhat larger than that, for converting the material to This invention relates to the method for purifying nu 5 a compound extractable by the extracting solvent, thereby clear fuel materials. More particularly, it relates to a the amount of the inoganic acid required being smaller method for purifying nuclear fuel materials by contacting and the cost for recovering the acid being not needed. the same with a neutral organic solvent which has been Furthermore, purity of the nuclear fuel material is re treated with an inorganic acid. markably superior than that obtained according to the Among the purifying methods of nuclear fuel materials 20 conventional method, for example the one extracted by having heretofore been conducted, there are a method : an acidic organic phosphorus compound, e.g. di-2-ethyl in which an aqueous solution or solid of a water-soluble hexyl hydrogen phosphate. When extraction of a nuclear compound of these elements is extracted by an organic fuel material from a nuclear spent fuel having a higher solvent to yield the purified elements; a method in which radioactivity after being used for radiation in atomic pile a matrial containing these elements is mixed with an in is applied to the present method, a gentle solvent extrac organic acid, and the mixture is contacted with an organic tion is possible and cost of equipment is reduced. More solvent to extract these elements; and a method in which over, after decrement of the radio-activity to some extent, a solid containing nuclear fuel materials is contacted it is possible to allot the cooling time of the nuclear fuel with an acidic organic solvent, for example di-2-ethyl 30 to the time for extraction and extraction. In this case, hexyl hydrogen phosphate, without using inorganic acid physical form of the fuel is not important, and the meth in the prior step, thereby uranium being extracted from od can be directly applied to the metals, oxides, carbides, the solid. and their sintered products. An object of the invention is to provide a purifying Among the neutral organic solvent employed in the method of a water-insoluble compound of nuclear fuel 35 purifying method of the invention, there are neutral alkyl materials, such as various oxides, metals, carbides of phosphorus compound, such as trialkyl phosphate, dialkyl uranium, plutonium, and the like, and their molded arti alkylphosphonate, alkyl dialkylphosphinate, trialkylphos cles, which method does not involve a separate procedure phine oxide, ethers, esters, ketones, and the like. This of once converting the compound to a water-soluble com solvent may preferably be diluted to a required concen pound. Other objects will be apparent from the descrip 40 tration with a suitable water-insoluble organic diluent, tion which follows. such as kerosene, hexane, carbon tetrachloride, and the According to the present invention, thus, a method for like, according to the condition employed. This solvent purifying nuclear fuel materials is provided, in which a is shaken, prior to use for contact with the nuclear fuel water-insoluble nuclear fuel material is contacted with a material, with an inorganic acid, thereby involving the neutral organic solvent that includes an inorganic acid 45 inorganic acid in a complex compound form with the sol in a complex compound form with the solvent or in a vent or in a simple dissolved form. The content of the simple dissolved form through contact of the acid with inorganic acid in the solvent after the acid treatment is the solvent, thereby to separate from the impurities and adjusted according to the concentration of the neutral or to be extracted in the organic solvent. ganic solvent in the mixture of the same with the diluent, According to the purifying method of the present in 50 the concentration of the inorganic acid, and contacting vention, extracting ratio and degree of purification of the period of time. As to amount of the inorganic acid, nuclear fuel material to be extracted can be increased by powdered uranium oxide or yellow cake spends almost selection of a mixing ratio of a neutral organic solvent and theoretical amount of it, based upon the compound ex a diluent, content of an inorganic acid in the extracting 55 tracted into the extracting solvent, but pellets of uranium solvent volume of the extracting solvent used, extracting oxide or uranium carbide, or metallic uranium needs time, extracting temperature, size of the water-insoluble somewhat larger amount than the theoretical one. Nitric nuclear fuel material, and the kind of extracting neutral acid contents in the solvents, i.e. tributyl phosphate, di organic solvent. The facts that a specific step of convert butylbutylphosphonate, and methyl isobutyl ketone, in ing the water-insoluble nuclear fuel material to a water 60 cases of shaking the solvents with the same amount of soluble, or other, compound may be omitted, and dissolu nitric acid for five minutes, are shown in Table 1. 3,288,568 Table 1 Volume Concentra- Nitric acid Uranium percent of tion of nitric concentration concentration Neutral solvent Diluent neutral acid for in solvent in Solwent solvent in treatment after nitric after extracting of solvent, acid extraction, solvent Mil. treatment, Mil. Mi. Tributyl phosphate Kerosene--- 30 5 0.85 0.442 y phoSp - 30 9 1.00 0.4935 Do. 50 5 1.30 0.7650 50 7 1.55 0.8700 100 5 1.88 0.9500 100 7 2.41 2300 30 5 0.99 0. 5460 30 7 1, 10 0.5995 50 5 1.47 0.7500 50 7 i. 66 0.860 - - - - - 100 5 2, 16 1. 0300 100 7 2.77 1. 3800 100 0.1 0.04 100 3 0.65 0.23 100 4 1.07 0.356 100 5 1. 40 0.47 Upon contact of water-insoluble solid nuclear fuel 25 2. Almost 80% of the uranium value in the material is material with an organic solvent thus containing inor extracted within 30 min. ganic acid, the solvent dissolves and extracts the nuclear fuel material. The rightmost column of the Table 1 shows Table 2 saturated concentration of uranium in the solvent in case Uranium concentration of extracting uranium from powdered uranium dioxide of 30 Extracting time (hr.): in solvent, M/l. 0.5u average particle size, which has been reduced by hy 0.5 0.35 drogen at 900 C. Thus, uranium is dissolved up to about %, in case of alkyl phosphorus compound, and about /3, in case of methyl isobutyl ketone, of mol concentration of nitric acid in the extracting solvent used. This may be 35 because substitution of solvates mainly serves for ex tracting action. Application of the present extraction is The extracting velocity is influenced by temperature. also possible with uranic concentrate as with powdered Especially when uranium is extracted from sintered urani uranium dioxide. In this case, a larger part of the im um dioxide, the effect of temperature is remarkable, thus, purities in uranium concentrate remains undissolved in 40 the extracting time being shortened by warming the uranium extracting solvent. Also, uranium can be direct solvent up to about 50° C. This fact is shown in the ly extracted and purified from solid moldings (shaped next example. articles) of uranium, for example sintered uranium EXAMPLE 2 dioxide, sintered uranium carbide, graphite-uranium diox ide press moldings, and metallic uranium, by use of the A 3 gram portion of fragments of sintered uranium neutral organic solvent treated with an inorganic acid. dioxide, which has been sintered at 1700 C. and has The solvent extracting the nuclear fuel materials out is density of 95%, is immersed into 55 ml. of tributyl phos filtered to remove undissolved residue of impurities, and phate/kerosene which has been treated with the same then scrubbed and stripped to yield an aqueous solution amount of 10 Normal nitric acid, to dissolve and extract of purified nuclear fuel materials. 50 uranium completely. As shown in the Table 3, the ex In extraction of nuclear fuel material from a water tracting time required is exceedingly shortened by warm insoluble solid nuclear fuel material by use of a neutral ing the solvent up to 50° C. organic solvent treated with an inorganic acid, uranium concentration in organic solvent increases with increase Table 3 of contacting time. Longer period of time is necessary 55 Uranium Yield of for complete dissolution in cases of sintered uranium temperature Extracting concentra uranium dioxide and sintered uranium carbide, when compared Extracting( C.) time (hr.) tion in sol (percent) with the cases of powdered uranium dioxide, uranic con vent (Mil.) centrate sintered graphite-uranium dioxide, and metallic 22- - 168 0.283 99.7 uranium.
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