A method of manufacturing a ceramic fuel pellets for nuclear reactors

 

(57) Abstract:

Usage: in the technologies of production of sintered ceramic fuel pellets for a nuclear reactor containing the fissile material. The inventive method comprises pressing and sintering of pellets from the powder of uranium dioxide, and before pressing the powder UO2with a specific surface area of the particles is not less than 2.0 m2/g add ultrafine powder UO2with an average crystal size not exceeding the length of the vacancy diffusion uranium while the shutter was pressed tablets at sintering temperature, in an amount up to 30% in the mixture. The technical result is to reduce the sintering temperature with the conservation requirements on density and microstructure. table 1.

The invention relates to the technology for the production of sintered ceramic fuel pellets for a nuclear reactor containing the fissile material.

In the manufacture of fuel pellets for nuclear reactors used operations such as preparation of press powder of uranium dioxide, the pressing of tablets, sintering and grinding.

There is a way to obtain fuel pellets, in which the powder dio is the input of a low density CT, close to the lower limit of about 10.4 g/cm3as well as high temperature sintering of the obtained tablets.

The closest in technical essence is a method of obtaining fuel pellets, in which a powder of uranium dioxide get through poliwrath ammonium (HELL-process) [2] . The obtained powder with a size of 4 to 30 μm is pressed into tablets, is sintered and polished. The disadvantage of this method is the high temperature sintering tablets from 1650 to 1750oWith that in turn leads to high energy consumption and reduce resource furnaces.

The technical result, which directed this invention is to reduce the sintering temperature in the manufacture of fuel pellets with the conservation requirements on density and microstructure.

The essence of the proposed method lies in the fact that for pressing tablets use a mixture of a powder of uranium dioxide (Article), prepared according to one of the known technologies [3] with a specific surface area of the particles is not less than 2.02/g, and ultrafine (UD) powder UO2whose sizes are comparable with such physical quantities as the ranges of electrons or phonons, the length of the dislocation [4]. Chevannay tablets at sintering temperature, surrounding larger particles tablespoons of powder, will play the role of diffusion bridges between them. Their diffusion coupling will be provided not only spots of mutual contact, and ultrafine phase. The filling of voids in the particles of the Art powder particles UD powder will cause the contents in the mixture UD powder up to 30%.

To validate the proposed method made five batches of tablets with different content of ultrafine powder.

UD powder of uranium dioxide was obtained by precipitation polyuronide ammonium (POIX) at room temperature from a solution of uranyl nitrate to uranium concentration 80 g/l, the Deposition was carried out according to the method of "the last drop" - joint removal and ammonia water solution of uranyl nitrate in a buffer solution. The pH value of the system was maintained equal to 9.0. The deposition lasted for 3.5 hours, the agitation of the pulp 0.5 hour. The filter cake POIX washed and dried. Powder of uranium dioxide was obtained by recovery POIX at a temperature of 620oWith in a reducing environment.

To obtain a standard powder deposition POIX conducted in two stages: at pH 6.8 for 5 hours with dosedanjem at pH 8.0. The dried salt was progulivali when acteristic Article and UD powders are shown in table.

UD powder in number, %: 10, 20, 30, and 100 was added to the Article and was mixed for 3 hours in the mixer type "drunken barrel" (n=15 rpm). As a plasticizer were added 6% aqueous solution of polyvinyl alcohol in an amount of 10 wt.%. The mixture was once grained at a pressure of 1 mV/cm2, crushed, rubbed through a sieve with a mesh size of 1 mm and extruded into a tablet under a pressure of 1.9 mV/cm2. The diameter of the matrix of the mold was 9,34 mm. in order To remove moisture and polyvinyl alcohol compressed tablets were subjected to heat treatment in a stream of hydrogen at a temperature of 750oWith the duration of exposure, the maximum temperature was 1.5 hours Tablets were cooled in a stream of hydrogen to room temperature. Sintering of pellets was carried out in a reducing environment at temperaturesoFrom: 1700, 1600, 1500 and 1400. The rate of heating and cooling ranged from 250 to 300 deg/h

The composition of the mixtures, the parameters of the sintering and the main characteristics of the obtained tablets are presented in the table.

In all tested modes of sintering using only UD powder does not give a positive effect. Get tablets do not meet the density requirements.

When used the pax above 1600oC. the Increase in the content of UD powder in a mixture of 30% leads to the decrease of the density of the tablets. This content UD powder tablets that meet the requirements of the technical conditions are obtained when the sintering temperature 1400oC. Thus, studies show that using the proposed method allows to reduce the sintering temperature compared with the existing technology for the production of tablets by at least 300oWithout loss of quality.

The use of the proposed method will lead to the reduction of energy consumption by sintering of pellets by 15-20%. In addition to saving energy by reducing the operating temperature reduces the hardware requirements of sintering furnaces, increasing their reliability. There is, for example, the replacement of expensive heaters from alloys of molybdenum cheaper.

Sources of information

1. Development, production and operation of fuel cell power reactors. M.: Energoatomizdat, 1995, pp. 68-72.

2. Development, production and operation of fuel cell power reactors. M.: Energoatomizdat, 1995, pp. 66-67.

3. Development, production and e 4. ) I. D. , Petinov Century. And., Petrunin, C. F. and other Advances in physical Sciences, 1981, T. 133, pages 24-29.

A method of manufacturing a ceramic fuel pellets for nuclear reactors, including pressing and sintering of powder of uranium dioxide, characterized in that prior to pressing the powder UO2with a specific surface area of the particles is not less than 2.0 m2/g add ultrafine powder UO2with an average crystallite size not exceeding the length of the vacancy diffusion uranium while the shutter was pressed tablets at sintering temperature, in an amount up to 30% in the mixture.

 

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