CN111341473A

CN111341473A - Spent fuel heat treatment device

Info

Publication number: CN111341473A
Application number: CN202010238991.2A
Authority: CN
Inventors: 王飞
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-03-30
Filing date: 2020-03-30
Publication date: 2020-06-26

Abstract

The invention relates to irradiated reprocessing equipment of solid fuel, in particular to a spent fuel heat treatment device which mainly comprises a storage hopper, a drum-type oxidation kettle, an intermediate hopper, a screen unit with a discharge hopper and a unit for cooling and unloading spent fuel powder which are connected in sequence.

Description

Spent fuel heat treatment device

Technical Field

The present invention relates to equipment for treating, handling or simplifying the handling of fuel or other materials in a reactor, such as in its pressure vessel, and more particularly to equipment for reprocessing irradiated solid fuels, and particularly to a spent fuel heat treatment apparatus.

Background

The spent fuel post-treatment is a key step for realizing the closed cycle of the nuclear fuel, can fully utilize uranium resources, safely and properly manage radioactive wastes, and has important significance for ensuring the sustainable development of nuclear energy. The structure of the nuclear fuel of the pressurized water reactor which is applied in large scale at present is a uranium dioxide ceramic pellet encapsulated in a corrosion-resistant cladding material (zirconium alloy). In the process of recovering uranium plutonium in spent fuel water method post-treatment, the cladding needs to be opened and dissolved in nitric acid solution, then the process enters a main chemical separation process, and the process of opening the cladding and contacting the fuel oxide ceramic pellet with nitric acid to dissolve the pellet in the nitric acid is called the head end of the water method post-treatment. The post-processing head end of the current stage of industrialization is realized by a head end system consisting of a shearing machine and a dissolver. There is a continuing desire in the art to incorporate high temperature oxidative volatilization technology into the head-end process to provide significant improvements over conventional post-treatment processes. The high-temperature oxidation volatilization technology is that between the shearing and the dissolution of a spent fuel element after the traditional spent fuel, UO2 ceramic pellets in the spent fuel element are oxidized into U3O8 or UO3 powder which is easy to be dissolved by nitric acid through the high-temperature oxidation volatilization technology, so that the separation of cladding and fuel pellets is realized, and simultaneously volatile and semi-volatile fission elements are completely or partially removed in the form of gas, although the technology is provided from the sixty-seven years of 20 th century, the device for high-temperature oxidation volatilization is only limited in the laboratory research level so far, and a machine which is really suitable for the industrial end is not designed, and moreover, even the device used in a laboratory has many problems, for example, the high-temperature oxidation volatilization cavity is only a heatable cavity, the high-temperature oxidation time of the spent fuel pellets cannot be fully oxidized, and the high-temperature oxidation time can not be accurately controlled, and the accurate weighing and metering are needed during feeding, the requirements of seamless connection with a post-treatment process system, economy (full oxidation can be realized and the feeding process can be greatly simplified) and the like cannot be met in the actual industrialization stage.

Disclosure of Invention

Based on the problems, the applicant research team designs a thermal treatment device for the spent fuel, which can realize the full oxidation of the spent fuel pellets in industrialization.

In order to achieve the purpose, the invention is realized by the following technical scheme:

a spent fuel heat treatment apparatus includes: the device comprises a storage hopper, a drum-type oxidation kettle, an intermediate hopper, a screen unit with a discharge hopper and a unit for cooling and unloading spent fuel powder which are connected in sequence, wherein the main body of the storage hopper is a tubular hopper, a vibrator and a vibration-proof frame are connected to the outside of the tubular hopper, the whole volume of the storage hopper can receive fragments of a whole spent fuel assembly from a device for shearing fuel elements, one end of the tubular hopper is connected to the drum-type oxidation kettle, the drum-type oxidation kettle comprises a welded steel flat drum-shaped roller unit made of corrosion-resistant steel, the roller unit is provided with a shell, the shell comprises a front wall and a rear wall, a loading conical pipe and a cylindrical pipe are welded along the central axis respectively on two sides of the shell of the roller unit, a spiral rod with spiral blades is arranged in the cylindrical pipe, inclined blades are arranged in the shell and close to the shell, and, the partition plate is equipped with a conical body extending into the cylindrical tube, the partition plate is connected with the rear wall, the blades and the conical body through radial ribs, a sector cavity formed between the radial ribs, the partition plate and the rear wall is communicated with the cylindrical tube, the roller unit is driven by a reversible rotary driver to rotate bidirectionally, the roller unit is externally surrounded by a heater, the heater is composed of a heat insulating material and a linear heater lined with stainless steel, the drum type oxidation kettle is connected with a screen unit through an intermediate hopper, and spent fuel powder screened by the screen unit enters a unit for cooling and unloading the spent fuel powder to be cooled.

Further, the volume of the roller unit is more than five times of the whole volume of the storage hopper.

Further, the pipe fittings at both ends of the storage hopper are both bellows assemblies to prevent the vibration generated by the vibrator from being transmitted to the equipment connected with the vibrator.

Further, the drum type oxidation kettle comprises a welded steel flat drum-shaped roller unit made of corrosion-resistant steel, a loading conical pipe and a cylindrical pipe are respectively arranged on a supporting roller arranged on the frame through a bearing fixedly connected with the roller unit, the roller unit rotates by using a chain transmission device, the chain transmission device comprises a driven chain wheel arranged on the loading conical pipe and a driving chain wheel arranged on the frame, the driven chain wheel and the driving chain wheel are interconnected by double rows of chains, the driving chain wheel is connected to a reversible rotation driver, and the driven chain wheel is driven to rotate by the driving chain wheel of the driver so as to control the rotation of the roller unit.

Furthermore, a group of redundant transmission devices is further arranged, the driven chain wheel is attached to the bearing of the cylindrical pipe, and the driving chain wheel drives the driven chain wheel to drive the bearing of the cylindrical pipe to rotate, so that the roller unit can also be driven to rotate.

Further, the drum unit is restrained on the support rollers by the upper rollers of the lever jigs, thereby preventing the possibility that the drum unit falls off from the support rollers.

Further, the discharge hopper of the screen unit with the discharge hopper is fixedly installed on the frame, the rotatable housing is installed on the roller with 3 degrees of inclination, an inner sieve hole pipe with holes is fixedly arranged in the rotatable housing, spent fuel powder is sufficiently sieved out by the sieve hole pipe during rotation to be separated from other structural materials, the discharge hopper and the housing are respectively provided with a fixing part 48 and a rotating part 49, a labyrinth seal is installed between the discharge hopper and the housing, and a nitrogen pressurizing fitting is arranged between the discharge hopper and the housing.

Further, the unit for cooling and discharging the spent fuel powder includes a steel flat cone container installed on a frame at an inclination angle of 40 ° with pipes for loading and unloading the spent fuel powder, respectively, cooling passages through which cooling water can pass are provided above and below the steel flat cone container, and a vibrator is installed at a lower portion of the steel flat cone container.

Compared with the prior art, the invention has the advantages that:

1) the invention is different from the laboratory device for the spent fuel heat treatment in the prior art, provides a spent fuel heat treatment device which can be used for industrial application through an integral innovative design, for example, a complicated feeder and a distributor are not used according to the conventional design, but through the precise design, the spent fuel part of one component of various spent fuel components used by the current domestic nuclear power station can be fully oxidized by high-temperature operation at each time, the problems of unreliable mechanical seal and durability possibly existing when the distributor is used at a feeding end are avoided, the problems are not fully known in the prior art, and a solution is not provided;

2) the arrangement of the deflection impeller is added to the oxidation cavity, the spent fuel can be fully oxidized when rotating in the cavity and can be smoothly shelled through the ingenious design of the angle of the blades, the material receiving process for oxidation can be realized when the spent fuel rotates in the forward direction, and the discharging process can be realized when the spent fuel rotates in the reverse direction;

3) the size of this application still ingenious design the device and the control of oxidation time, have guaranteed still to have compromise operating time and economic nature when can fully oxidize various types of spent fuel assembly pieces.

Drawings

Fig. 1 is a schematic view of the overall structure of the spent fuel heat treatment apparatus according to the present invention.

FIG. 2 is a schematic view of the storage hopper according to the present invention.

FIG. 3 is a schematic view of the structure of a drum type oxidation reactor of the present invention.

FIG. 4 is a schematic cross-sectional view of the drum oxidizer of FIG. 3.

FIG. 5 is a schematic view showing the overall structure of a drum type oxidation reactor with a frame fixing structure according to the present invention.

Fig. 6 is a schematic view of the construction of a screen unit with a discharge hopper according to the invention.

Fig. 7 is a schematic structural view of a unit for cooling and unloading spent fuel powder according to the present invention.

Detailed Description

The present invention is further described with reference to fig. 1-7, and while the description of one of the figures is provided, the structure of the present invention will be better understood with reference to the preceding and following figures, and one skilled in the art will readily appreciate that, because of the radiation hazards associated with nuclear fuels, the various vessels (including hoppers, pipes, oxidizers, drums, etc.) of the main body of the system are made of steel and the thickness of the outer shell is sufficiently nuclear safe to shield radiation.

As shown in fig. 1 and 2, the apparatus for thermal treatment of spent fuel comprises a storage hopper 1, a drum oxidation kettle 2, an intermediate hopper 3, a screen unit 4 with a discharge hopper 5 and a unit 6 for cooling and discharging spent fuel powder, which are connected in sequence, the storage hopper 1 has a tubular hopper 10, a vibrator 11 and a vibration-proof frame 12 are connected to the outside of the hopper 10, the entire volume of the storage hopper 1 can receive a whole spent fuel assembly fragment 13 from a device for shearing fuel elements, the volume of the device is 0.16-0.2 cubic meter, the storage hopper 1 and the device for shearing fuel elements are sealed and separated by a gate, the lower part of the device is provided with a gate 14, one end of the hopper 10 is provided with a loading pipe 7, the other end of the hopper is provided with a connecting pipe connected to the drum type oxidation kettle 2, and pipe fittings at two ends of the hopper 10 are all corrugated pipe assemblies 15 to prevent the vibration generated by the vibrator 11 from being transmitted to the device connected with the hopper.

As shown in fig. 3-5, the drum oxidation still 2 comprises a flat drum-shaped drum unit 16 made of corrosion-resistant steel and made of welded steel, the total volume of the drum unit 16 is 1 cubic meter, the drum unit 16 has a housing 17, the housing 17 comprises a front wall 18 and a rear wall 19, a loading conical tube 20 and a cylindrical tube 21 are welded along the central axis on both sides of the housing of the drum unit 16, a screw rod with helical blades 22 is arranged in the cylindrical tube 21, a helical propeller structure is formed for transporting oxidized spent fuel, an inclined blade 23 is arranged in the housing 17 in close proximity to the housing 17, the inclined blade 23 is arranged in the middle of the drum unit 16 by a longitudinal baffle 24, the drum 16 is divided into a front cavity 25 between the baffle 24 and the front wall 18 and a rear cavity 26 between the baffle 24 and the rear wall 19, the baffle 24 is provided with a cone 27, the cone 27 extends into the cylindrical tube 21, the baffle 24 is connected with the rear wall 19 by a radial rib 28, the blade 23 and the cone 27, the rear cavity 26 is divided into a plurality of fan-shaped cavities 29 by the radial rib 28, the blade 23 is connected with the cone-shaped driving unit 32, the cone-shaped driving unit 32 is connected with a chain wheel 32, the cylindrical blade 23 is connected with the rear wall 19, the rotating drum unit 32, the rotating drum unit is connected with a chain-carrying-roller-supporting roller-roller.

As shown in fig. 6, the screen unit 4 with the discharge hopper 5 for separating oxidized spent fuel powder and other structural materials of a spent fuel assembly including a cladding material, supplying the spent fuel powder to the unit 6 for cooling and discharging the spent fuel powder, supplying the other structural materials to the discharge hopper 5, the discharge duct 8 connected to the end of the discharge hopper 5 for discharging the other structural materials, the discharge hopper 5 fixedly installed on the frame 43, the rotatable housing 44 installed to be inclined at 3 ° on the roller 45, an inner mesh duct 46 having holes 47 fixedly provided in the housing 44, the spent fuel powder sufficiently screened out from the other structural materials during rotation by the mesh duct 46, the discharge hopper 5 and the housing 44 respectively provided with a fixing flange 48 and a rotating flange 49 between which a labyrinth seal 50 is installed, and with a nitrogen pressurizing fitting 51.

As shown in fig. 7, the unit 6 for cooling and unloading spent fuel powder for reducing the temperature of oxidized spent fuel powder before unloading it for dissolution includes a steel flat cone-shaped container 52 installed on a frame 54 with an inclination angle of 40 °, having

pipes

53 and 9 for loading and unloading spent fuel powder, respectively, cooling passages 55 having

nozzles

56 and 57 for inlet and outlet water, respectively, above and below the container 52, a vibrator 58 installed at a lower portion of the container 52, a shutter 59 installed on the pipe 9, and cooled spent fuel powder discharged through the pipe 9 after opening the shutter 59.

The operation of the device of the invention is briefly as follows:

after the fuel rods are sheared on the shear, fragments of fuel rods are poured through the loading tube 7 into the storage hopper 1 and accumulated in the hopper 10 until all fuel rods of one spent fuel assembly are cut. The gate 14 is opened to unload the hopper 10, the vibrator 11 is opened and the drum unit 16 is driven to rotate directly, while all the chips (the total volume of chips produced by the current domestic mainstream fuel assemblies is around 0.19 cubic meter) are poured into the lower part of the drum oxidation vessel 2 (drum unit 16) through the loading tapered tube 20, in the front chamber 25 and the rear chamber 26 between the inclined vanes 23. After the hopper 10 is completely emptied, the gate 14 is closed and the introduction of the fragments 13 of the next spent fuel assembly into the hopper 10 is continued.

The heater 42 performs oxidation of spent fuel while heating the temperature inside the drum unit 16 to at least 480 ℃, and introduces a reaction gas (air or a mixture of air and oxygen) thereto while maintaining the pressure inside the drum unit 16 at 100 to 200 Pa through a ventilation system.

With the rotation of the drum unit 16, by setting the angle α of the blade 23 relative to the housing 17 at an acute angle during rotation as specified above, the inclined blade 23 is able to lift the chips 13 from the bottom to the top of the drum unit 16 until the chips 13 fall from the blade 23 after the blade 23 has rotated with the drum unit 16 through a certain angle, the diameter of the drum unit 16 is designed to be at least 3.2 meters, so that the height of the chips 13 falling from the blade 23 is sufficiently large, by this setting, the chips 13 are sufficiently mixed to improve the efficiency of the oxidation of the chips, and for this effect the volume of the drum unit 16 should generally be set to be more than 5 times the volume of the storage hopper 1, and after the chips 13 have been sufficiently mixed and reached the set temperature, the pumping of the reaction gas is started, and the control system starts to calculate the two-stage oxidation process, the oxidation time is generally set to 10-12 hours, which is sufficient to ensure sufficient oxidation without wasting too much unnecessary oxidation time through practical verification.

Meanwhile, in order to monitor the oxidation degree, oxygen concentration sensors may be provided at the inlet and outlet of the drum unit 16, and the current and the latter oxygen concentrations are the same, indicating that the oxidation process is finished.

After the oxidation process is completed, the drum unit 16 is switched to reverse rotation, and the sieve unit 4 is driven to rotate to discharge the mixture of the oxidized spent fuel powder and other structural materials.

During the reverse rotation of the drum unit 16, the mixture of spent fuel powder and other structural material will move along the vane 23 towards the back chamber 26 due to the angle of inclination (180- α) of the vane 23 relative to the housing in the direction of movement (180- α) and the angle β between the vane 23 and the walls 18 and 19 (45), into the sector-shaped chamber 29 between the radial ribs 28, then from the cone 27 into the cylindrical tube 21, through the screw with the helical vanes 22 to transfer the mixture through the intermediate hopper 3 into the screen unit 4. after the drum unit 16 is completely emptied, the next spent fuel assembly fragment 13 is received from the storage hopper 1 to begin the next oxidation process.

The mixture enters the screen hole pipe 46 of the screen unit 4, the spent fuel powder is screened out by the holes of the screen hole pipe 46, in this system, the preferred diameter of the holes 47 is 5 mm (it is verified that the screening quality cannot be guaranteed by being too large and too small), and the screened-out spent fuel powder enters the unit 6 for cooling and unloading the spent fuel powder. Other structural material is discharged through the discharge hopper 5 into the discharge tube 8.

The spent fuel powder is cooled to 80C by the cooling water of the cooling passage 55 in the unit 6 for cooling and discharging the spent fuel powder, and then the shutter 59 and the vibrator 58 are opened to discharge the powder into the dissolver at the rear end, and the dissolving step is a conventional step known in the art and will not be described again.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. A spent fuel heat treatment device is characterized by comprising: the device comprises a storage hopper, a drum-type oxidation kettle, an intermediate hopper, a screen unit with a discharge hopper and a unit for cooling and unloading spent fuel powder which are connected in sequence, wherein the main body of the storage hopper is a tubular hopper, a vibrator and a vibration-proof frame are connected to the outside of the tubular hopper, the whole volume of the storage hopper can receive fragments of a whole spent fuel assembly from a device for shearing fuel elements, one end of the tubular hopper is connected to the drum-type oxidation kettle, the drum-type oxidation kettle comprises a welded steel flat drum-shaped roller unit made of corrosion-resistant steel, the roller unit is provided with a shell, the shell comprises a front wall and a rear wall, a loading conical pipe and a cylindrical pipe are welded along the central axis respectively on two sides of the shell of the roller unit, a spiral rod with spiral blades is arranged in the cylindrical pipe, inclined blades are arranged in the shell and close to the shell, and, the partition plate is equipped with a conical body extending into the cylindrical tube, the partition plate is connected with the rear wall, the blades and the conical body through radial ribs, a sector cavity formed between the radial ribs, the partition plate and the rear wall is communicated with the cylindrical tube, the roller unit is driven by a reversible rotary driver to rotate bidirectionally, the roller unit is externally surrounded by a heater, the heater is composed of a heat insulating material and a linear heater lined with stainless steel, the drum type oxidation kettle is connected with a screen unit through an intermediate hopper, and spent fuel powder screened by the screen unit enters a unit for cooling and unloading the spent fuel powder to be cooled.

2. The spent fuel heat treatment apparatus according to claim 1, wherein: the volume of the roller unit is more than five times of the whole volume of the storage hopper.

3. The spent fuel heat treatment apparatus according to claim 1 or 2, wherein: the pipe fittings at both ends of the storage hopper are both bellows assemblies to prevent the vibration generated by the vibrator from being transmitted to the equipment connected with the vibrator.

4. The spent fuel heat treatment apparatus according to claim 1, wherein: the drum type oxidation kettle comprises a welded steel flat drum-shaped roller unit made of corrosion-resistant steel, a loading conical pipe and a cylindrical pipe are respectively arranged on a supporting roller arranged on a frame through a bearing fixedly connected with the roller unit, the roller unit rotates by using a chain transmission device, the chain transmission device comprises a driven chain wheel arranged on the loading conical pipe and a driving chain wheel arranged on the frame, the driven chain wheel and the driving chain wheel are interconnected by double rows of chains, the driving chain wheel is connected to a reversible rotation driver, and the driven chain wheel is driven to rotate by the driving chain wheel of the driver so as to control the rotation of the roller unit.

5. The spent fuel heat treatment apparatus according to claim 4, wherein: and the driven chain wheel is attached to the bearing of the cylindrical pipe, and the driving chain wheel drives the driven chain wheel to drive the bearing of the cylindrical pipe to rotate so as to drive the roller unit to rotate.

6. The spent fuel heat treatment apparatus according to claim 5, wherein: the drum unit is restrained on the support rollers by the upper rollers of the lever jigs, thereby preventing the possibility of the drum unit falling off the support rollers.

7. The spent fuel heat treatment apparatus according to claim 1, wherein: the discharge hopper of the screen unit with the discharge hopper is fixedly arranged on the frame, the rotatable shell is obliquely arranged on the roller by 3 degrees, an inner sieve hole pipe with holes is fixedly arranged in the rotatable shell, spent fuel powder is sufficiently screened out by the sieve hole pipe in the rotating process to be separated from other structural materials, the discharge hopper and the shell are respectively provided with a fixed part 48 and a rotating part 49, a labyrinth sealing part is arranged between the discharge hopper and the shell, and a nitrogen pressurizing fitting is arranged between the discharge hopper and the shell.

8. The spent fuel heat treatment apparatus according to any one of claims 1 to 7, wherein: the unit for cooling and discharging the spent fuel powder includes a steel flat cone container installed on a frame at an inclination angle of 40 deg., having pipes for loading and unloading the spent fuel powder, respectively, cooling passages through which cooling water can pass are provided above and below the steel flat cone container, and a vibrator is installed at a lower portion of the steel flat cone container.