RU2182378C2 - Method for producing sintered uranium oxide - Google Patents

Abstract

FIELD: sintering uranium oxide. SUBSTANCE: carbon-containing substance or mixture thereof capable of reducing uranium monoxideoxide in the course of thermal pre-treatment is added to uranium monoxide-oxide powder or to mixture of uranium monoxide-oxide and uranium oxides prior to compacting. Substance or mixture of substances introduced as pre-reducers function at the same time as plasticizer and lubricant for press tools in compacting source monoxide-oxide powder. Used as carbon-containing substance or substances are, for instance, glycerin, polyvinyl alcohol solution, polyethylene oxide, or mixture thereof. Thermal pre-treatment includes heating of powders compacted with plasticizer at dynamic vacuum below 20 mm Hg within temperature range of 250 to 260 C until oxygen-to-uranium ratio of at least 2.20 is attained. In the process uranium monoxide-oxide is primarily reduced by decomposition products. Sintering and additional reduction are effected in carbon-containing crucible due to reducing atmosphere formed with aid of crucible carbon. EFFECT: facilitated procedure, reduced consumption of gaseous agents. 4 cl, 3 ex

Description

 The invention relates to the technology of radioactive materials, and in particular to a method for producing a powder of uranium oxides.

A known method of producing uranium dioxide, including the preparation of a powder of uranium oxide to increase its activity, carrying out its contacting and low temperature sintering (see US patent 3087876, IPC G 21 C 3/00, 1963). In this method, in order to lower the temperature to 1200-1400 ^° C and to obtain the maximum density in the first stage, sintering is carried out in an oxidizing atmosphere, and then the atmosphere is replaced with a reducing one to obtain a composition of nuclear fuel close to uranium dioxide.

 The disadvantages of the method are the multi-stage and duration of the sintering process, the need to change the atmosphere from oxidizing to reducing, the inability to use certain types of materials, such as quartz, for the design of the furnace in the sintering zone, the most dangerous drawback of this process is the use of explosive hydrogen gas.

The closest in technical essence and the achieved result is a method of manufacturing oxidized sintered elements of nuclear fuel (see Germany 3142447, IPC G 21 C 3/62, 1983 - taken as a prototype), which includes heat treatment of pressed elements from UO ₂ powders at a temperature of 1000 -1400 ^o C in an oxidizing and then reducing gas atmosphere, and the oxygen of the oxidizing atmosphere is maintained in such an area that U ₄ O ₉ is formed in the pressed elements during heating to the treatment temperature.

 The disadvantages of this method are multi-stage and the need to use gas reagents.

 An object of the invention is to simplify the method, reducing the cost of gas reagents.

The problem is achieved in that in the proposed method for producing uranium oxide before compaction into a powder of uranium oxide and uranium oxide or a mixture of uranium oxide and uranium oxides, a substance and a mixture of substances containing carbon and reducing uranium oxide in the process of preliminary heat treatment are added, and a substance or mixture of substances introduced as a preliminary reducing agent is simultaneously a plasticizer and a lubricant of a pressing tool when compacting the starting powder of nitrous oxide si. As a carbon-containing substance or substances, for example, glycerin, a solution of polyvinyl alcohol, polyethylene oxide or mixtures thereof are used. Preliminary temperature preparation consists in heating powders compacted with a plasticizer with a dynamic vacuum of less than 20 mm Hg. Art. The lower temperature limit of 250 ^o C is selected from the start of decomposition of carbon-containing substances, the upper 650 ^o C is due to the complete termination of decomposition and removal of decomposed gaseous components, while the initial reduction of uranium oxide is carried out by decomposition products. The amount of carbon-containing substance introduced is determined on the basis of the requirements of the pressing conditions — pressure of 1.5-5 t / cm ² and the conditions for preliminary reduction of uranium oxide to the ratio of oxygen to uranium of at least 2.20. The total amount of carbon-containing substance is 4-20 wt.% The original powder.

The lower limit of the introduction of carbon-containing substances or mixtures thereof allows the compacting of the powder at a pressure of 5 t / cm ² . The upper limit of 20% is due to the lower limit of pressing pressure to 1.5 t / cm ² for powders with a specific surface area of 0.5 to 20 m ² / g.

 The task is also achieved by the fact that the sintering and re-reduction process is carried out in a carbon-graphite crucible.

The essence of the method lies in the fact that the carbon remaining after the decomposition of the carbon-containing substance by known reactions begins to interact at a temperature above 600 ^o С with the oxygen of the powder, restoring it, at a temperature of 800 ^o С, the carbon-containing crucible begins to dissociate. In contact with the walls of the carbon-graphite crucible, the residual quantities of oxygen at the process temperature interact by known reactions:
C + O ₂ = CO ₂
CO ₂ + C = 2CO
2CO + O ₂ = 2CO
2C + O ₂ = CO
Thus, a weak reducing atmosphere is created in the crucible volume with a dynamic rarefaction of less than 20 mm Hg. Art.

The essence of the method lies in the fact that the carbon introduced with the plasticizer in accordance with the invention, interacting during the preliminary heat treatment with a powder of uranium oxide and its mixture with uranium oxides, restores it to the composition of UO _{(2.25-2.40 )} . During heating to a temperature (1000-1400 ^o С) of sintering in a carbon-graphite crucible, an additional reduction of oxides takes place to the UO composition _{(2.20 -2.26)} , which is necessary to carry out the sintering process at low temperatures and to obtain oxides with the required uranium content. With an additional exposure in a carbon-graphite crucible, additional reduction of oxides to the composition of UO _{(2.05 -2.25) occurs} .

 The practical implementation of the method is illustrated by the following examples.

 Example 1

According to the proposed method, uranium oxide-oxide with a specific surface of 7 m ² / g is mixed with 13-16 wt. % organic plasticizer (69% solution of polyvinyl alcohol in water + 31% glycerol) and subjected to mouthpiece pressing to a density of 4.3-4.7 g / cm ³ at a compression pressure of 2-3 t / cm ² . The resulting rods are dried in vacuum at a temperature of 350-550 ^o C and sintered in a stepwise mode in a carbon-graphite crucible at a temperature of 1000-1200 ^o C with exposure for 1-2 hours.

Sintered uranium dioxide obtained by the proposed method is characterized by a bulk density of 10.3-10.8 g / cm ³ , a uranium content of 86.7-87.2% and a low carbon content of less than 0.001%.

 Example 2

Uranium oxide with a specific surface area of 2.5 m ² / g is granulated with 13 wt.% Plasticizer, dried in vacuum at 360 ^o C and sintered in a graphite crucible at a temperature of 1100-1200 ^o C with exposure for 2 hours. The resulting product has a density of 10.5 g / cm ³ and a uranium content of 86.9%.

 Example 3

Uranium oxide with a specific surface area of 10 m ² / g is granulated with uranium dioxide with a particle size of less than 10 microns with 9 wt.% Plasticizer (a mixture of 20% glycerol, 20% polyethylene oxide and 60% aqueous solution of polyvinyl alcohol). Subjected to processing as described in example 1. Sintered uranium dioxide has a density of 9.8-10.5 g / cm ³ , the uranium content of 86.9-87.6%.

 The data obtained show that as a result of the implementation of the method, an activated sintering process and the production of high density uranium dioxide with the required metal content directly from uranium oxide powder are provided.

Claims (4)

1. A method of producing sintered uranium oxide, including the preparation of powders of uranium oxide, their pressing and reducing sintering, characterized in that the powders are used as a powder of uranium oxide-oxide or a mixture of oxides, before pressing a carbon-containing substance or a mixture of substances reducing oxides is added to the powder uranium to a ratio of oxygen to uranium of not less than 2.20 in the temperature range 250-260 ^o C, and sintering and re-reduction is carried out in a carbon-containing crucible due to the reducing atmosphere formed with the participation of carbon crucible.  2. The method according to p. 1, characterized in that the introduction of a substance or substances containing carbon for recovery, and the introduction of a plasticizer to compress the powder are combined, and for the implementation of each of these functions use the same substance or the same mixture of substances .  3. The method according to p. 2, characterized in that as the carbon-containing plasticizer use polyvinyl alcohol, glycerin or polyethylene glycol, or a mixture thereof, containing 20-100 wt. % aqueous solution of polyvinyl alcohol, up to 80 wt. % glycerol or up to 80 wt. % polyethylene glycol in an amount of 4-20% of the mass of the original powder. 4. The method according to p. 1, characterized in that the recovery process is carried out with a dynamic vacuum of 0.1-20 mm RT. Art. , and the sintering and additional reduction process with dynamic rarefaction of 1 • 10 ^-3 -20 mm RT. Art.