JPH0675112B2 - Continuous melting device for spent nuclear fuel - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus for dissolving a nuclear fuel in a nitric acid solution in a spent nuclear fuel reprocessing step, and particularly to an apparatus for continuously and efficiently dissolving the nuclear fuel. .

<Prior Art> A conventional example of a spent nuclear fuel melting apparatus will be described with reference to FIG. This is called a 2-barrel-1 slab type dissolution tank, and the two barrels 50, 50 having a cylindrical shape have a flat plate tank shape through a gas phase communication pipe 53 and upper and lower liquid communication pipes 54, 55. Contacted with Slab 51. Inside each barrel 50 is a basket filled with small pieces of nuclear fuel cut by a shearing device.
52 is set, and a large number of small holes are formed in the basket 52 to ensure the exchangability of the liquid. When the nitric acid solution is injected into the barrel 50 and the slab 51 and steam is sent to the jacket 56 to raise the liquid temperature to dissolve the nuclear fuel pieces in the basket 52, the solution rises in the barrel 50 due to the heat convection caused by the temperature rise. , Through the upper liquid communication pipe 54 into the slab 51, and through the lower liquid communication pipe 55 to the lower part of the barrel 50 again to form a circulating flow. After the dissolution is completed, the dissolution liquid in the barrel 50 is drained, a new nitric acid solution is injected to perform cleaning, and then the insoluble coating material and the like remaining in the basket 52 is barreled together with the basket 52.
50 It is designed to be taken out and discharged to the outside of the system.

<Problems to be Solved by the Invention> As described above, in the conventional melting apparatus, batch processing is performed for each basket, and moreover, loading of small pieces of nuclear fuel into the basket, setting in the barrel of the basket, solution injection, melting,
Since the process proceeds in the order of extracting the solution, washing, and taking out the basket, a lot of time was required for the treatment. Further, it has been difficult to increase the processing capacity due to equipment restrictions.

Generally, in the reprocessing of a nuclear fuel containing a large amount of fissile material, it is necessary to improve the processing capacity because severe size and shape conditions are imposed for criticality safety. Therefore, the present invention relates to an apparatus for dissolving spent nuclear fuel, particularly nuclear fuel containing a large amount of fissile material, and has a critical safety and does not have a mechanical driving part in the solution and its mist atmosphere. Secure reliability,
From the loading of nuclear fuel to the cleaning and discharge of insoluble fuel coating materials, etc., while maintaining reliable transfer, it is carried out continuously, reducing the number of parts as a whole, reducing the maintenance target part,
To provide a compact and efficient continuous melting device,
It was made for that purpose.

<Means for Solving the Problems> In order to achieve the above object, in the spent nuclear fuel continuous melting apparatus of the present invention, a hollow spiral shape in which the diameter of the rear spiral portion is continuously reduced A container, a means for rotating the container from the outside, a means for loading a cut piece of spent nuclear fuel into the front spiral portion of the container, and a solution for dissolving the cut piece of spent nuclear fuel at the other end of the container. Section, a means for supplying the washing container subsequent to the rear reduced diameter portion of the container, and a spiral container side provided with an inner edge of the rear reduced diameter portion to overflow the solution on the washing container side. Liquid supply weir to be stored on the side,
A cutting piece of the spent nuclear fuel, which has a liquid overflow weir provided at an inner edge of an end of the front spiral portion of the container and which is lower than the liquid supply weir and overflows the dissolution liquid on the side of the spiral container to a dissolution liquid discharge container. Is adapted to be dissolved by a solution to form an insoluble coating material while the bottom of the container is sequentially and continuously moved by the rotation of the container.

Provided at one end of the spiral container is a solution discharge container in which a plurality of chambers for receiving the solution overflowing from the solution overflow weir are radially formed, and at the other end of the spiral container, an insoluble liquid overflowing from the solution supply weir A washing container having a plurality of chambers for receiving the coating material formed radially is provided, and a disk-shaped container for discharging the insoluble coating material is provided. The dissolution liquid discharged from the chambers is externally provided in the dissolution liquid discharge container. When a solution discharge pipe for discharging is inserted and a discharge tray for discharging the insoluble coating material scraped out by the chamber is inserted into the cleaning container,
On the one hand, fuel loading and liquid discharge are performed, and on the other hand, insoluble coating materials and the like are continuously washed, discharged and liquid supply is performed.

In order to secure the criticality safety, it is advisable to dispose a steel plate to which a fixed neutron absorbing material is attached between the spiral parts of the spiral container and between the containers.

<Operation> The dissolved liquid in the spiral container flows due to the difference in height between the liquid supply weir and the liquid overflow weir, and is replaced by the rotation of the container in the reduced diameter portion of the rear spiral part as the liquid rises and stirred. Enhance the effect. Further, the nuclear fuel in the spiral container is moved by being pushed by the bottom surface of the container as the container rotates.

<Example> Below, it demonstrates based on the Example of this invention.

The schematic configuration of this continuous melting apparatus will be described with reference to FIG. 1. The melting apparatus main body 1 made of a corrosion-resistant material is a solid-liquid separating section 2b for taking out insoluble fuel coating material and the like from the melting solution from the nuclear fuel receiving section 2a. Continuous spiral hollow container (hereinafter referred to as a helical slab) 2, a disk-shaped solution discharge container 3 adjacent to the nuclear fuel receiving section 2a, and a disk-shaped cleaning container adjacent to the solid-liquid separation section 2b 4 between the helical slab 2 and the solution discharge container 3, between the slabs of the helical slab 2,
Further, between the helical slab 2 and the cleaning container 4, as shown by the dotted line in the figure, a steel plate 5 provided with a fixed neutron absorber is arranged to ensure criticality safety. As shown in the figure, the shape of the helical slab 2 is such that most of the helical slab 2 has a substantially equal outer diameter, but the helical slab 2 near the solid-liquid separation portion 2b has a continuously reduced diameter. The left side of the illustrated melting device body 1 is a nuclear fuel receiving side on which a shooter 6, a liquid seal 16, a vibration driving device 7, an exhaust pipe 8 and the like for loading cut pieces of spent nuclear fuel (hereinafter referred to as nuclear fuel) are arranged. Yes, the right side of the dissolution apparatus main body 1 is a liquid supply pipe 9, a monitor 10, a discharge tray 29, and a discharge vibration for transferring insoluble coating material and the like (hereinafter, referred to as coating material) remaining after melting the nuclear fuel. It is a cleaning / discharging side of the coating material and the like in which the drive device 11, the coating material discharge port 12 and the like are arranged. Bearing having rollers 21 for rotatably supporting both ends of the melting apparatus main body 1
20, motor 14 that holds the equal diameter part of helical slab 2
Driving support roller 13, meshing drive gears 15, 15 provided around the end of the support roller 13 and the solution discharge container 3.
The melting device main body 1 can be rotated by the rotating means of the melting device main body 1. The vibration drive device 7 is attached to a tilting base 18 which can be tilted by the movements of an arcuate rack 19a and a gear 19b around a rotary shaft 17 of a two-armed column attached to a fixed base 22. Will be described later. In FIG. 1, the soaking and heat retaining cover 42 indicated by the alternate long and short dash line is a heat retaining cover that uses steam as a heat source, and the melting device main body 1
This is for keeping the temperature of the dissolution liquid in the container constant by covering it with.

FIG. 2 shows the details of the nuclear fuel receiving section 2a. It is connected to the shooter 6 via a liquid seal 16, and the loading vibration driving device 7
The loading tray 23, which is attached to and is capable of vibrating, transfers the nuclear fuel 38 that has fallen via the shooter 6 onto the nuclear fuel receiving portion 2a of the helical callab 2 along the loading tray 23 to be vibrated and puts it in the container. The pressure inside the tray and the inside of the helical slab are kept equal by the ventilation hole 23a formed in a part, and the tip portion bent downward is constantly immersed in the dissolution liquid during the dissolution operation, so that the nuclear fuel or the cladding is covered. The fine powder of the material is suppressed as much as possible from flowing into the dissolution liquid discharge container 3 and is connected to the exhaust pipe 8 via the vibration isolator 25 to absorb vibration and tilt the loading tray 23. Making it easy. A seal 26 is provided between the rotating melting device main body 1 and the fixed portion, and is fixed by a seal fixing pedestal 26a and a seal pressing metal fitting 26b.

The nuclear fuel receiving section 2a is also provided with a dissolution liquid discharge pipe 24 that receives the dissolution liquid raised by the rotation of the dissolution liquid discharge container 3 and sends it to the outside of the system. The solution discharge pipe 24 preferably has a mounting structure capable of being taken out from the container together with the loading tray 23 at the time of inspection or the like. In the illustrated example, after the loading shooter 6 is pulled up and pulled out from the liquid seal 16, the tilting rod 27 is pulled down and the tilting rack 18 and the loading tray 23 are driven by the circular rack 19a and the gear 19b. Then, the seal fixing base 26a is removed from the container and the fixing base 22 is moved, so that the loading tray 23 and the solution discharge pipe 24 can be extracted from the container.

A liquid overflow weir 34 and a liquid outflow prevention weir 35 having heights that can maintain criticality safety are provided on the inner edge of the dissolution liquid discharge container 3, and the dissolution liquid surface 33 in the discharge container 3 is set lower than the liquid surface on the helical slab 2 side. Then, the solution 33 on the side of the helical slab 2 that has passed through the solution overflow weir 34 flows into the solution discharge container 3. As shown in FIG. 4, a partition plate 28 is provided inside the dissolution liquid discharge container 3 to form a chamber that is radially divided into 12 parts with respect to the dissolution liquid discharge pipe 24 arranged in the central space. There is. Although these chambers are empty in the upper part, when they come to the lower part by the rotation in the direction of the arrow 39, the dissolved liquid overflowing the liquid overflow weir 34 flows in to store a certain amount, and the chamber is laterally extended further as the rotation continues. When it is reversed, the stored dissolution liquid is discharged from the free edge of the partition plate 28 to the dissolution liquid discharge pipe 24, and thus the dissolution liquid is discharged to the outside of the system.

The nuclear fuel 38 (or the covering material) in the helical slab 2 is pushed by the inner wall surface of the lower part of the helical slab 2 and melts while moving sequentially, and almost completely dissolves when the nuclear fuel 38 reaches the solid-liquid separation part 2b. However, it is only an insoluble coating material. FIG. 5 (a) is an explanatory view showing a state where the nuclear fuel 38 (or the covering material) has not yet reached the solid-liquid separation section 2b, and FIG. 5 (b) is an explanatory diagram showing a state where it has reached the solid-liquid separation section 2b. is there. Fifth
It can be seen from the diagram (b) that the covering material 38 (or nuclear fuel) is separated by scooping from the solution and falls.

Next, the coating material discharge part will be described with reference to FIG. 3. The coating material 38 (or nuclear fuel) separated by scooping from the solution as described above falls into the cleaning container 4 via the cleaning inlet 30. Then, preliminary cleaning is performed in the cleaning container 4. At the inner edge of the cleaning container 4, the liquid overflow weir 34 in FIG.
A liquid supply weir 36 set higher than the above and a liquid outflow prevention weir 37 having the same height as the liquid outflow prevention weir 35 in FIG. 2 are formed. As shown in FIG. 6, the cleaning container 4 includes a partition plate 32.
The chamber is divided into eight, and the coating material 38 that drops (direction arrow 40) through the cleaning inlet 30 in FIG. 3 is successively introduced into the chamber and is transferred upward by rotation.
While returning the washing liquid to the washing container 4 during the ascent, the covering material 38
Is guided to the discharge tray 29 through the discharge receiving port 31 and continuously vibrated. The discharge tray 29 is provided with a cleaning liquid reservoir 29a in which the coating material can be sufficiently dipped in order to perform the final cleaning of the coating material with the injection liquid from the liquid supply pipe 9. The coating material that has undergone the final cleaning will be taken out of the system through the coating material discharge port 12 after being inspected by the monitor 10 as to whether or not it has been completely dissolved. When it is detected that the undissolved nuclear fuel has been discharged, the discharge vibration driving device 11 is driven in reverse to transfer the undissolved nuclear fuel back to the cleaning container 4. This reverse transfer is performed in a short time, but during this period, the rotation of the apparatus main body 1 is stopped, and the rest of the operation is in a steady operation.

Finally, the flow of the liquid system will be described in summary. The new dissolving liquid supplied from the liquid supply pipe 9 is first sent to the cleaning liquid reservoir 29a of the discharge tray 29 and used as the cleaning liquid, and then the overflow liquid is used as the liquid guide plate 29b. It is used as a pre-cleaning liquid by dropping it to the cleaning container 4 along with, and the overflow liquid that has passed through the liquid supply weir 36 is sent to the dissolution section and used as a dissolution liquid. In this case, since the liquid overflow weir 34 is lower than the liquid supply weir 36 as described above, the dissolution liquid flows toward the dissolution liquid discharge container 3 as a whole, and the dissolution liquid discharge container 3 has a volume almost equal to that of the supplied liquid. 3 and is transferred to the next process from the solution discharge pipe 24 as described above. On the other hand, since the diameter of the helical slab 2 portion near the solid-liquid separation section 2a is continuously reduced, as described above, the rotation of the helical slab 2 causes the washing container 4 to rotate. The dissolution liquid in the helical slab 2 that has moved toward the upper part generates an ascending flow as the diameter of the spiral portion decreases, and forms a circulation flow for liquid exchange with the cleaning liquid toward the dissolution liquid discharge container 3. .

<Effects of the Invention> With the present invention having the above-described configuration, the nuclear fuel loaded in the hollow spiral container is continuously and continuously formed at the bottom of the spiral container only by rotating the spiral container from the outside. Since there is no mechanical drive for moving the nuclear fuel in the strongly corrosive solution and mist atmosphere, there is no problem of corrosion damage of the drive because it can be moved to. In addition, since the container that holds the solution and the container that holds the fuel are shared and integrated, the liquid contact with the fuel is good, the dissolution efficiency is improved, and the fuel is not caught or dropped between the containers. Since the diameter of the rear spiral portion is continuously reduced, it is possible to enhance the liquid stirring effect in each liquid storage portion and increase the liquid flow velocity in the surface layer portion.

Further, at one end of the spiral container is provided a dissolution liquid discharge container in which a plurality of chambers for receiving the dissolution liquid overflowing from the liquid overflow weir are radially formed, and at the other end of the spiral container, an insoluble substance overflowing from the liquid supply weir is provided. A washing container in which a plurality of chambers for receiving the coating material are formed radially, and a disc-shaped container for discharging the insoluble coating material is provided, and the dissolution liquid discharged from the chamber is externally provided in the dissolution liquid discharge container. When a discharge tray for discharging the insoluble coating material scraped out by the chamber is inserted into the cleaning container, a continuous transfer from the loading of the nuclear fuel to the insoluble discharge is performed. Since the liquid can be circulated and discharged only by rotating the spiral container, the overall structure is simple, the number of parts is small, and the maintenance is easy.

The criticality safety can be easily ensured by disposing the steel plate to which the fixed neutron absorbing material is attached between the spiral parts of the spiral container and between the spiral containers.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a continuous dissolution apparatus which is an embodiment of the present invention, FIG. 2 is a sectional view of a nuclear fuel loading section, FIG. 3 is a sectional view of an insoluble coating material discharge section, and FIG. 5 (a), 5 (b) and 6 are explanatory views showing the movement of the nuclear fuel (coating material) in the helical slab and the cleaning section, and FIG. 7 is a view showing the main body of the melting apparatus. FIG. 8 is an explanatory diagram showing the flow of the liquid system, and FIG. 8 is an explanatory diagram showing an example of a conventional dissolution apparatus. DESCRIPTION OF SYMBOLS 1 ... Melting apparatus main body, 2 ... Spiral container (helical slab), 2a ... Nuclear fuel receiving part, 2b ... Solid separation part, 3 ... Melt solution discharge container, 4 ... Washing container, 5 ... Steel plate to which fixed neutron absorbing material is attached , 6 ... Shooter, 7 ... Loading vibration drive device, 8 ... Exhaust pipe, 9 ... Liquid supply pipe, 10 ... Monitor, 11 ... Discharge vibration drive device, 13 ... Support roller, 14 ... Motor,
15 ... Drive gear, 20 ... Bearing, 21 ... Roller, 22 ... Fixed base, 23 ... Loading tray, 24 ... Dissolution liquid discharge pipe, 28 ... Partition plate, 29 ... Discharge tray, 29a ... Cleaning liquid reservoir, 29b ... Liquid guide plate, 30 ... Cleaning inlet, 31 ... Discharge inlet, 32 ... Partition plate, 34
... Liquid overflow weir, 36 ... Liquid supply weir, 35, 37 ... Liquid outflow prevention weir, 38
… Nuclear fuel (cladding material)

Claims (1)

[Claims] 1. A hollow spiral container in which the diameter of a rear spiral portion is continuously reduced, and a means for rotating the container from the outside.
Means for loading a cut piece of spent nuclear fuel into the front spiral portion of the container; means for supplying a solution for dissolving the cut piece of the spent nuclear fuel to a washing container following the rear reduced diameter portion of the container; A liquid supply weir provided at the inner edge of the rear reduced diameter portion of the container and overflowing the solution on the side of the cleaning container to collect the solution on the side of the spiral container, and the liquid provided at the inner edge of the front spiral portion of the container. And a liquid overflow weir that is lower than the supply weir and causes the solution on the side of the spiral container to overflow into the solution discharge container, and the cut pieces of the spent nuclear fuel continuously and continuously at the bottom of the container by the rotation of the container. A continuous dissolution apparatus for spent nuclear fuel, characterized by being dissolved by a dissolution liquid to form an insoluble coating material while moving to the.