METHOD FOR PRODUCING PELLETIZED FUEL FROM URANIUM-MOLYBDENUM POWDERS

Abstract

The invention relates to the nuclear industry and can be used for producing fuel pellets from uranium-molybdenum metal powders enriched to 7% uranium 235 for nuclear reactor fuel elements. The pellets are sintered in an inert atmosphere of argon at a temperature ranging from 1100° C. to 1155° C., and the initial powder is a uranium-molybdenum powder having a fraction size of 160 .Math.m and a molybdenum con¬tent of 9.0 to 10.5 wt%. The powder is pre-heated at a temperature of 500° C. for 10-20 hours (in an atmosphere of argon) and is subsequently cold pressed into pellets in a die under a force of up to 950 MPa. In an alternative emb¬odiment for producing uranium-molybdenum pellets with a binder (plasticizer), the step of sintering is preceded by heating the pellets in an atmosphere of argon at 300° C. to 450° C. for 2-4 hours to remove the binder. The invention makes it possible to increase the uranium intensity of the fuel, reduce the amount of heat buildup in a reactor core, and lower the amount of energy released in the event of abnormalities in the operation of a nuclear reactor, thus providing increased reactor safety and resilience to accidents.

Claims

1. A method for producing pelletized fuel from uranium-molybdenum powders for fuel elements of a nuclear reactor, comprising preparation of powder, pressing into pellets in a die, sintering them in a gaseous atmosphere, grinding, drying, rejection of the pellets, characterized in that the pellets are sintered in an inert atmosphere, and uranium-molybdenum powder with uranium 235 enrichment to 7% and molybdenum content of 9.0 to 10.5 wt% is used as an initial powder.

2. The method according to claim 1, characterized in that the uranium-molybdenum powder fraction size does not exceed 160 .Math.m.

3. The method according to claim 1, characterized in that prior to pressing into the pellets in the die, the uranium-molybdenum powder is heated in argon at 500° C. for 10-20 hours.

4. The method according to claim 1, characterized in that a force of up to 950 MPa is applied to press the pellets in the die.

5. The method according to claim 1, characterized in that the pellets are sintered in an atmosphere of argon at a temperature from 1100° C. to 1155° C. for 4-12 hours.

6. A method for producing pelletized fuel from uranium-molybdenum powders for nuclear reactor fuel elements, comprising preparation of powder, stage-by-stage mixing with a binder, pressing into pellets in a die, thermal removal of the binder, sintering the pellets in a gaseous atmosphere, grinding, drying, rejection of the pellets, characterized in that the pellets are sintered in an inert atmosphere, and uranium-molybdenum powder with uranium 235 enrichment to 7% and with molybdenum content of 9.0 to 10.5 wt% is used as an initial powder.

7. The method according to claim 6, characterized in that the uranium-molybdenum powder fraction size does not exceed 160 .Math.m.

8. The method according to claim 6, characterized in that a force of up to 950 MPa is applied to press into the pellets in the die.

9. The method according to claim 6, characterized in that the thermal removal of the binder is done by heating the pellets in an atmosphere of argon at from 300° C. to 450° C. for 2-4 hours.

10. The method according to claim 6, characterized in that the pellets are sintered in an atmosphere of argon at from 1100° C. - 1155° C. for 4-12 hours.

Description

[0028] FIG. 1 shows uranium-molybdenum pellets after sintering and machining.

[0029] Thus, the proposed method, compared with the known ones, helps obtain fuel pellets from uranium-molybdenum powders with uranium 235 enrichment to 7% and molybdenum content from 9.0 to 10.5 wt% for nuclear reactor fuel elements with improved performance.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Provided below are examples of embodiment of the proposed uranium-molybdenum pellet production method.

[0024] Example 1 (according to the first embodiment). A uranium-molybdenum powder with molybdenum content in the alloy of 9.0 wt% obtained by centrifugal atomization from an ingot of the same alloy, with uranium 235 enrichment to 7%, is used as an initial powder. Centrifugal atomization of an uranium-molybdenum ingot with molybdenum content in the alloy of 9.0 wt% helps obtain a uniform molybdenum content in the initial powder. The powder is screened through a 160 .Math.m sieve. The screened uranium-molybdenum powder with a molybdenum content of 9.0 wt% is heated at 500° C. for 20 hours in a top-loader vacuum furnace SShVE (in argon). The resulting powder is pressed in a cylindrical die at a molding pressure of 750 MPa without adding a binder (plasticizer). The pellets are sintered in argon (with water content not exceeding 80 ppm) at (1125.sup.+10/-5)° C at an isothermal exposure time of 4 hours in an SShVE furnace (or XERION XVAC-2200) . Heating to isothermal exposure is carried out in a stream of argon 1 1/min at a heating rate not exceeding 5° C./min, followed by cooling in static argon at a cooling rate of (15-20)° C/min. After that, pellets are ground, dried, and rejected for compliance with technical requirements.

[0025] Example 2 (according to the first embodiment). A uranium-molybdenum powder with molybdenum content in the alloy of 10.5 wt% obtained by centrifugal atomization from an ingot of the same alloy, with uranium 235 enrichment to 7%, is used as an initial powder. Centrifugal atomization of an uranium-molybdenum ingot with molybdenum content in the alloy of 10.5 wt% helps obtain a uniform molybdenum content in the initial powder. The powder is screened through a 160 .Math.m sieve. The screened uranium-molybdenum powder with a molybdenum content of 10.25 wt% is heated at 500° C. for 10 hours in a top-loader vacuum furnace SShVE (in argon). The resulting powder is pressed in a cylindrical die at a molding pressure of 950 MPa without adding a binder (plasticizer). The pellets are sintered in argon (with water content not exceeding 80 ppm)at (1125.sup.+10/-5)° C at an isothermal exposure time of 12 hours in an SShVE furnace (or XERION XVAC-2200). Heating to isothermal exposure is carried out in a stream of argon 1 1/min at a heating rate not exceeding 5° C./min, followed by cooling in static argon at a cooling rate of (15-20)° C/min. After that, pellets are ground, dried, and rejected for compliance with technical requirements.

[0026] Example 3 (according to the second embodiment). A uranium-molybdenum powder with molybdenum content in the alloy of 9.0 wt% obtained by centrifugal atomization from an ingot of the same alloy, with uranium 235 enrichment to 7% and screened through a 160 .Math.m sieve, is used as an initial powder. Centrifugal atomization of an uranium-molybdenum ingot with molybdenum content in the alloy of 9.0 wt% helps obtain a uniform molybdenum content in the initial powder. 8% aqueous solution of polyvinyl alcohol with 1% glycerol (3% by weight of the uranium-molybdenum alloy) is used as a plasticizer (binder). Mixing includes three stages. At the first stage, the entire amount of the binder and uranium-molybdenum alloy powder in an amount up to 10 wt% are mixed to get a homogeneous mixture. At the second stage, the resulting mixture is mixed with up to 40 wt% uranium-molybdenum alloy powder to get a homogeneous mixture. At the third stage, the remaining amount of uranium-molybdenum alloy powder is added into the mixture obtained at the second stage and mixed to get a homogeneous mixture. The powder is mixed in a Turbula mixer for 20-30 minutes. The prepared powder is pressed in a cylindrical die at a molding pressure of 850 MPa. Before sintering, the pellets are heated in argon at 300° C. to 450° C. for 4 hours to remove the binder. The pellets are sintered in argon (with water content not exceeding 80 ppm) at (1125.sup.+10/-5)° C at an isothermal exposure time of about 4 hours in a top-loader furnace SShVE. Heating to isothermal exposure is carried out in a stream of argon 1 l/min at a heating rate not exceeding 5° C./min, followed by cooling in static argon at a cooling rate of (15-20)° C/min. After that, pellets are ground, dried, and rejected for compliance with technical requirements.

[0027] Example 4 (according to the second embodiment). A uranium-molybdenum powder with molybdenum content in the alloy of 10.5 wt% obtained by centrifugal atomization from an ingot of the same alloy, with uranium 235 enrichment to 7% and screened through a 160 .Math.m sieve, is used as an initial powder. Centrifugal atomization of an uranium-molybdenum ingot with molybdenum content in the alloy of 10.5 wt% helps obtain a uniform molybdenum content in the initial powder. 8% aqueous solution of polyvinyl alcohol with 1% glycerol (3% by weight of the uranium-molybdenum alloy) is used as a plasticizer (binder). Mixing includes three stages. At the first stage, the entire amount of the binder and uranium-molybdenum alloy powder in an amount up to 10 wt% are mixed to get a homogeneous mixture. At the second stage, the resulting mixture is mixed with up to 40 wt% uranium-molybdenum alloy powder to get a homogeneous mixture. At the third stage, the remaining amount of uranium-molybdenum alloy powder is added into the mixture obtained at the second stage and mixed to get a homogeneous mixture. The powder is mixed in a Turbula mixer for 20-30 minutes. The prepared powder is pressed in a cylindrical die at a molding pressure of 950 MPa. Before sintering, the pellets are heated in argon at 300° C. to 450° C. for 2 hours to remove the binder. The pellets are sintered in argon (with water content not exceeding 80 ppm) at (125.sup.+10/-5)° C at an isothermal exposure time of about 12 hours in a top-loader furnace SShVE. Heating to isothermal exposure is carried out in a stream of argon 1 1/min at a heating rate not exceeding 5° C./min, followed by cooling in static argon at a cooling rate of (15-20) °C/min. After that, pellets are ground, dried, and rejected for compliance with technical requirements.