Pelletized fuel manufacturing method for fuel elements

FIELD: nuclear power engineering.

SUBSTANCE: pelletized fuel is produced for fuel elements of nuclear reactor fuel assemblies from uranium dioxide. Pellets are gradually sintered in tunnel furnace by zones isolated with heat barriers at definite heating and cooling temperatures. In the process pellets of desired density, microstructure, volume fraction of open pores, and tendency of sintered pellets to additional sintering are produced.

EFFECT: enhanced yield.

1 cl, 2 dwg

 

The invention relates to the nuclear industry and can find application in the manufacturing pelletized fuel from uranium dioxide (UO2for fuel elements of nuclear reactors.

A known method of making pelletized fuel for fuel cells, including:

- a mixture of uranium dioxide powder UO2, uranium oxide U3O8and stearate of zinc [Zn(C17H35Soo)2];

- pressing tablets from a mixture of uranium dioxide powder UO2, uranium oxide U3O8and zinc stearate;

- sintering of pellets in the furnace of the tunnel type, having three temperature zones of heating, sintering the pellets in a reducing environment and cooling with promotion of boats with tablets in three areas;

wet grinding surface tablets and drying (see “Development, production and operation of fuel cell power reactors”. Edited Fgurative, M.: Energoatomizdat, 1995, Book 1, p.93-95, 98-99, 101-102). A given mode of sintering tablets is provided by the promotion of boats with tablets in the furnace of the tunnel type, operating in the continuous mode and having three temperature zones: heating pellets, sintering and cooling (see ibid., p.99).

However, with the rapid sintering have a significant negative jawline is. Sintering of pellets begins long before the maximum temperature of 1750°C. When this first happens sintering and compaction of surface layers of the tablet. This contributes not only inevitable temperature gradient in the tablet on its thickness, but also the presence of a density gradient tablets due to surface sealing layer formed by the pressing of the tablet. Compacted sintered surface layer tablets complicates the gaseous products formed by the decomposition of binders, and at the expense of other processes occurring at higher temperatures. This leads to cracking and destruction of the tablets and, as a consequence, the decrease of the yield (see ibid., p.99).

The closest to the technical conditions and the achieved effect is a method of making pelletized fuel for fuel elements of a nuclear reactor, including:

- a mixture of uranium dioxide powder UO2, stearate of zinc [Zn(C17H35COO)2] and uranium oxide U3O8;

- pressing tablets from a mixture of powders dioxide UO2, uranium oxide U3O8and zinc stearate;

- sintering of pellets in the furnace of the tunnel type heating sections, sintering in a reducing environment and cooling with promotion of boats with tablets the mi through the furnace section;

wet grinding surface tablets;

- drying of the tablets;

- processing of defective tablets;

- wiring with operations on the operation of powder and tablets (see Russian Federation Patent RU 2158030, IPC 7 G 21 3/62, 21/10 dated 18.11.1998, publ. 20.10.2000 “Method of making pelletized fuel for fuel cells and a device for its implementation”).

A method of making pelletized fuel for fuel elements of a nuclear reactor according to the patent 2158030 most characteristic of the inventive method, however, it has the same disadvantages as the method-analogue.

A given mode of sintering tablets is provided by the promotion of boats with tablets in the furnace of the tunnel type, operating in the continuous mode and having three temperature zones: heating and removal of the binder, sintering the pellets in a reducing environment and cooling (see Patent 2158030, s). As already mentioned, at the fast sintering have significant negative effects, leading to cracking and destruction of the tablets, which reduces the yield of the tablets.

An object of the invention is to increase the yield tablets of the desired density, microstructure, the volume fraction of open pores and depechemode sintered tablets.

This technical problem is solved in that in the method of manufacturing the same is matirovannogo fuel for fuel elements of a nuclear reactor, including:

- a mixture of uranium dioxide powder UO2, uranium oxide U3O8and stearate of zinc [Zn(C17H35Soo)2];

- pressing tablets from a mixture of powders dioxide UO2, oxide U3O8and zinc stearate;

- sintering of pellets in the furnace of the tunnel type heating sections, sintering in a reducing environment and cooling with promotion of boats with tablets through the furnace section;

wet grinding surface tablets;

- drying of the tablets;

- processing of defective tablets;

- wiring with operations on the operation of powder and tablets.

according to the invention, the sintering of pellets in the furnace of the tunnel type heating sections, sintering in the reducing environment of hydrogen and cooling with promotion of boats with compressed raw tablets through the sections of the furnace is carried out by gradual preparation of tablets for subsequent heat treatment, for which section of the heating to remove the binder component is formed from three separate thermal barriers zones with temperature tablets

in the first zone 220-240°C

in the second zone 280-300°and

in the third zone 480-500°C

additional section comprises preheating tablets with final removal of the binder components of the two isolated thermal barriers is he with temperature tablets

in the fourth zone 980-1000°C

in the fifth zone 1100-1200°C

section sintering tablets form of three isolated high-temperature thermal barriers zones with temperature sintering tablets

in the sixth zone 1750-1770°C

in the seventh zone 1780-1800°C

in the eighth district 1750-1770°and

in the ninth district-a section of the cooling of the sintered pellets carried out with a temperature lapse rate 145-340°C/hour.

The proposed method allows to have a high yield tablets of the desired density, microstructure, the volume fraction of open pores and depechemode sintered tablets.

The drawings show a method of making pelletized fuel for fuel cells, where

- figure 1 is a furnace sintering tablets tunnel type

- figure 2 - scheme of the method.

A method of making pelletized fuel for fuel cells includes the steps:

- 1 - mixture of uranium dioxide powder UO2, stearate of zinc [Zn(C17H35Soo)2], uranium oxide U3O8;

- 2 - tablet pressing 3 from a mixture of powders dioxide UO2, oxide U3O8and zinc stearate;

- sintering tablets 3 furnace 4 tunnel type heating sections 5, sintering 6 in the reducing environment of hydrogen and cooling 7 promotion 8 boats with tablets the mi through the furnace section;

- 9 - wet grinding surface tablets 3;

- 10 - drying 3 tablets;

- 11 - processing of defective tablets 3;

- the vehicle 12 transaction powder and tablets with 3 operations on the operation.

In the sintering furnace 4 tablets 3 section 5 heating made of three zones: the first 13, second 14 and third 15 remove the binder components - thermal decomposition of zinc stearate and two zones: 16 fourth and fifth 17 preheating tablets 3 and section 6 of the sintering tablets 3 is made of three zones: the sixth 18, 19 seventh and eighth 20.

Loading boats with 8 pills 3 through node 21, and the discharge through the node 22.

Gaseous decomposition products are burned together with hydrogen in the tubes of the combustion chamber 23, 24, 25.

Each zone sintering furnace 4 are isolated from other zones of thermal barriers, called screens 26.

Moving boats 8 to furnace 4 carried by the vehicle 27.

A method of making pelletized fuel for fuel cells is as follows.

Powder of uranium dioxide UO2enriched with uranium 235 from 2-5% mix Paladino in unit 1 with a dry binder stearate zinc [Zn(C17H35Soo)2] and uranium oxide U3O8obtained by thermal oxidation of marriage tablets 3 unit 11 recycling scrap tablets. From socioloskoj dioxide UO 2, oxide U3O8and dry binder stearate zinc in unit 2 is pressed tablet 3, which in a molybdenum boat 8 is directed to the sintering and load through the loading unit 21 into the furnace 4 sintering. In section 5, with the first three zones 13, 14, 15, carry out heating of the raw and prepare tablets 3 tablets 3 for further heat treatment. Section 5 is the removal of the binder components. Each of the 13, 14, 15 zones are isolated from each other by thermal barriers-screens 26.

The temperature in the first zone (13) is supported 220-240°With, in the second zone (14) - 280-300°and in the third (15) - 480-500°C.

Volatile impurities are destroyed in the flame tube of the combustion chamber 23 of hydrogen.

In the fourth (16) and fifth (17) areas further heating of the tablets at 980-1000°in the fourth zone (16) and 1100-1200°in the fifth (17) zones. Volatile impurities are burnt in the flame tube of the combustion chamber 24. In the sixth zone (18) conduct sintering of pellets when 1750-1770°With, in the seventh zone (19) - 1780-1800°and the eighth (20) zone when 1750-1770°With the oxidation of hydrogen in the pipe 25 afterburning. In the ninth district section 7 cools tablets with falling temperature 145-340°/h and through node 22 tablets are unloaded from the furnace.

In unit 9 tablets are ground and dried in the unit 10. All move with the unit on the unit carried by the vehicle 12, and Tran is assisted boats 8 tablets of the furnace is carried out by the vehicle 27.

The method has been tested and received a positive result and the goal of the project is reached.

All parameters are optimal and any deviation in a direction more or less will not solve the technical problem.

A method of making pelletized fuel for fuel elements of a nuclear reactor, including:

- a mixture of uranium dioxide powder UO2, uranium oxide U3O8and stearate of zinc [Zn(C17H35COO)2];

- pressing tablets from a mixture of uranium dioxide powder UO2, uranium oxide U3About8and zinc stearate;

- sintering of pellets in the furnace of the tunnel type heating sections, sintering in the reducing environment of hydrogen and cooling with promotion of boats with tablets through the furnace section;

wet grinding surface tablets;

- drying of the tablets;

- processing of defective tablets;

- wiring with operations on the operation of powder and tablets, characterized in that the sintering of pellets in the furnace of the tunnel type heating sections, sintering in the reducing environment of hydrogen and cooling with promotion of boats with compressed raw tablets through the sections of the furnace is carried out by gradual preparation of tablets for subsequent heat treatment, for which s is the s heating to remove the binder component is formed from three separate thermal barriers zones with the temperature of the tablets in the first zone 220-240° Since, in the second zone 280-700°in the third zone 480-500°C

additional section comprises preheating tablets with final removal of the binder components of the two isolated thermal barriers zones with the temperature of the tablets in the fourth zone 980-1000°With, in the fifth zone 1100-1200°C

section sintering tablets form of three high-temperature, insulated thermal barriers zones with sintering temperature of the tablets in the sixth zone 1750-1770°With, in the seventh district 1780-1800°With, in the eighth district 1750-1770°C

and in the ninth district cooling sintered pellets carried out with a temperature lapse rate 145-340°S/h



 

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