JPH0668553B2 - Continuous melting device for spent nuclear fuel - Google Patents

Description

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

<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 31 and 31 in the shape of a cylinder are shaped like a flat plate tank through a gas phase communication pipe 34 and upper and lower liquid communication pipes 35 and 36. A basket 33, which is connected to the slab 32 and has a large number of small holes formed therein, is inserted and set in each barrel 31. After filling the small pieces of spent nuclear fuel cut by the shearing device into the basket 33, the basket 33 is set in each barrel 31, the nitric acid solution is injected into the barrel 31 and the slab 32, and steam is sent to the jacket 37 of the barrel 31. The liquid temperature is raised to melt the cut pieces of spent nuclear fuel in the basket 33. At this time, the solution rises in the barrel 31 due to the heat convection generated by the temperature rise, enters the slab 32 through the upper liquid communication pipe 35, and returns to the lower portion of the barrel 31 again through the lower liquid communication pipe 36. Is formed. After the dissolution is completed, the dissolved solution in the barrel 31 is drained, a new nitric acid solution is injected for cleaning, and then the insoluble coating material and the like remaining in the basket 33 is taken out together with the basket 33 to the outside of the barrel 31 to be removed from the system. Discharge.

<Problems to be Solved by the Invention> As described above, in the conventional dissolution apparatus, the spent nuclear fuel cutting pieces are loaded into the basket, the basket is set in the barrel, the dissolution liquid is injected, the dissolution is performed, the dissolution liquid is extracted, and the basket is washed. Since the process of taking out was carried out by batch processing for each basket, it took a lot of time for processing and it was difficult to increase the processing capacity. Generally, in the reprocessing of spent nuclear fuel containing a large amount of fissile material, strict size and shape conditions are imposed on the criticality safety, so it is essential to improve the processing capacity.

An object of the present invention is to provide a device capable of continuously melting while reliably transferring the spent nuclear fuel cutting pieces in the melt regardless of the melt and its mist atmosphere, and ensuring the mechanical reliability. To provide.

Another object of the present invention is to provide a device suitable for ensuring a compact, efficient and critical safety by reducing the number of parts to be maintained as a whole.

Still another object of the present invention is to provide a device that facilitates continuous operation from loading of spent nuclear fuel cutting pieces to cleaning / discharging of insoluble fuel coating material and the like.

<Means for Solving the Problems> In order to achieve the above object, it can be said that the present invention applies the principle of the vibrating feeder to a continuous melting device for spent nuclear fuel. That is, the continuous dissolution apparatus for spent nuclear fuel according to the present invention is provided with a vertical partition wall in the annular dissolution tank in which the dissolution liquid flows, and a liquid supply port for the dissolution liquid is provided at the lower part on one side of the partition wall. , A liquid discharge port is formed on the other side.

Further, it corresponds to the partition wall and an outer trough in which multiple tracks for transporting spent nuclear fuel cutting pieces are formed in multiple stages in the circumferential direction on the inner peripheral surface of a cylindrical body plate having slits formed at positions corresponding to the partition wall. The outer trough track and the inner trough track alternate with the inner trough, which is formed by arranging the transport tracks for the spent nuclear fuel cutting pieces in multiple stages in the circumferential direction on the outer peripheral surface of the cylindrical body plate with slits formed at the positions. The two troughs are combined so as to be arranged in a circular shape and are immersed concentrically in an annular melting tank.

One end of each track of the outer trough and the inner trough is a closed part, and the other end is an open end that is not closed.When combining two troughs, a track end having a closed part and a track end having an open end are used. Are arranged alternately.

The outer trough and the inner trough are each equipped with a shaker to transfer the spent nuclear fuel cutting pieces alternately to two troughs along the track while continuously transferring from the upper fuel loading port to the lower discharge window. Dissolve.

If a liquid seal is placed between the annular dissolution tank and the outer trough and inner trough, at the same time as ensuring the airtightness of the entire device,
Prevents trough vibration from propagating to the tank side.

The critical safety of the present apparatus can be enhanced by disposing a container filled with water in the central space of the annular melting tank and attaching the thermal neutron absorber to the inner wall surface of the annular melting tank.

A discharge tank that communicates at a position corresponding to the discharge window is arranged outside the annular melting tank, and a discharge trough equipped with a spiral track is arranged inside the discharge tank. Along with this, the insoluble matter of the spent nuclear fuel cutting pieces can be moved upwards to be discharged from the top of the discharge tank, and if a cleaning spray is attached near the top of the discharge tank, the spent nuclear fuel cutting pieces can be loaded from the fuel coating material. Cleaning of insoluble materials such as
It is possible to make the discharge process continuous.

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

In FIG. 1, the inside of the dissolution tank 1 having an annular shape is partitioned by a vertical partition wall 3, and one of the partition walls 3 is provided with a solution supply port 12 for the solution at the lower part and the other is provided at the upper part. It forms the outlet 13. The outer trough 4 and the outer trough 5 forming a pair have a single cylindrical body plate 31, 32 with a slit 30 formed at a position corresponding to the partition wall 3, and a flat plate 8 perpendicular to one side edge of the slit 30.
A track 7 having one end joined to the flat plate 8 to form the closed portion 7b and the other end being an open end 7a is provided in multiple stages in the circumferential direction of the body plates 31 and 32. These multistage tracks are formed on the inner peripheral surface of the body plate 31 in the outer trough 4 and on the outer peripheral surface of the body plate 32 in the inner trough 5 (see FIG. 2). The combination of the outer trough 4 and the inner trough 5 is inserted into the melting tank 1 from above. When combining the two troughs, the tracks 7 of the outer trough 4 and the tracks 7 of the inner trough 5 are alternately arranged, and the closing portion 7b
And the track end having the open end 7a are arranged alternately. A frame-shaped loading port 9 is provided on the upper surface of the outer trough 4 so that the spent nuclear fuel pieces to be processed can be loaded on the truck 7 in the uppermost stage. The inside of the truck 7 is squeezed so as to surely fall, and at the open end 7a of the truck 7 at the lowermost step, the path is bent and the insoluble coating material or the like is discharged to the discharge window 10 provided in the outer trough 4. To guide you. If necessary, ventilation holes 11 are provided in the trough, and when a large amount of gas is generated due to a rapid reaction, dispersed exhaust is performed.

The outer trough 4 and the inner trough 5 are shakers 17, 1 described later.
8 is provided and the fuel is moved in the melting tank 1. This is the third
Explaining in the figure, the spent nuclear fuel piece 30 loaded from the loading port 9 starts moving from the closed portion 7b of the uppermost track 7 of the outer trough 4 vibrated by the shaker 17, and then opens at the open end 7a.
At the uppermost track 7 of the inner trough 5 which is vibrated by the vibration exciter 18, and then sequentially closed block 7b → open end 7a (fall) → closed block 7b and two troughs 4 and 5 are alternately moved. It moves downward and reaches the discharge window 10. Arrow 29 indicates the direction of fuel movement. As can be seen from the figure, the fuel on the truck progresses while maintaining a substantially constant interval, and during melting, the total vertical weight of the residual fuel on the truck is kept substantially constant, so that U and _Pu in the solution are kept constant. This will make the concentration stable and uniform.

In FIG. 2, the dissolution tank 1 is equipped with a steam jacket 25 for heating the dissolution liquid 22 at the bottom, and the inside of the tank is always kept at a negative pressure during operation via an exhaust port 14 connected to an exhaust device (not shown). A liquid seal 21 is provided between the melting tank 1 and the outer trough 4 and the inner trough 5. A cylindrical container 28 filled with water 27 is installed in the central space of the annular dissolution tank 1 and a thermal neutron absorber 26 is attached to the inner wall of the dissolution tank 1 to enhance the criticality safety. The container 28 of this example also serves as a member for attaching the vibrator 18 of the inner trough 5. Reference numeral 20 is a fixing member to which the vibrator 17 of the outer trough 4 is attached.

FIG. 2 shows a small-diameter discharge tank 2 which communicates with the liquid supply port 12 of the dissolution tank 1 through a ventilation pipe 16. The liquid level of the discharge tank 2 is the same as the liquid level of the dissolution liquid 22 in the dissolution tank 1 due to the liquid supply port 12, and the inside of the discharge tank 2 is due to the ventilation pipe 16
As always, it is kept at negative pressure. A discharge trough 6 vibrated by a shaker 19 is inserted into the discharge tank 2.
The discharge trough 6 is formed with a spiral track, the upper part thereof extends above the liquid surface, and the spray 23 is arranged around the spiral trough.

Explaining the operation of the discharge tank 2, the insoluble matter of the spent nuclear fuel cutting pieces such as insoluble coating material that has moved on the track 7 of the dissolution tank 1 is discharged from the discharge window 10 to the discharge trough 6 of the discharge tank 2. After falling onto the spiral track, the vibration of the vibration exciter 19 causes it to move upward along the spiral track and rise above the liquid surface, whereupon a new solution is sprayed by the spray 23 and the radioactive solution adhering to the coating material is washed, Discharge from the exhaust port 15 to the outside of the system. In this case, it is desirable to provide a detector 24 that can confirm whether or not the dissolution is completed,
If it is determined by the detector 24 that the dissolution is not completed, the shakers 17 and 18 are stopped on the dissolution tank 1 side, the fuel loading is also stopped, and the operation is switched to only supply and discharge of the solution,
On the side of the discharge tank 2, the shaker 19 of the discharge trough 6 is driven in reverse, the undissolved portion is returned to below the liquid surface and dissolved again, and after a certain period of time, normal operation is restored. The lowermost portion of the discharge trough 6 is set to a height capable of sufficiently retaining the volume so that the discharge trough 6 does not fall into the discharge tank 2 due to the deposition or extrusion of the coating material or the like.

<Effects of the Invention> According to the present invention, in order to vibrate two independent troughs in the dissolution tank to continuously transfer and dissolve the nuclear fuel, a mechanical drive unit is provided in the strongly corrosive solution and mist atmosphere. Since it does not have it, there is no problem of corrosion in the drive part, the nuclear fuel on the truck is constantly exposed to the solution flow and is continuously transferred, so the dissolution efficiency is good, and the variation in the reaction due to deposition is reduced, The total weight of the remaining fuel on the truck in the vertical direction is almost constant, and the U and P _u concentrations in the solution are made uniform and stable.

If the dissolution tank is annular, the two troughs are concentrically arranged, and a liquid seal is placed between the dissolution tank and the trough, the sealing of the entire device is ensured and the vibration of the trough is transmitted to the tank side. It is possible to reduce the number of parts as a whole without
Compact and easy to maintain. Moreover, it is easy to ensure criticality safety by installing a water container using the central space of the annular dissolution tank and lining the thermal neutron absorber.

Furthermore, a vertical partition wall is provided in the annular dissolution tank, and a solution supply port for the solution is formed in the lower part of one side of the partition wall, and a liquid discharge port is formed in the upper part of the other side. The flow of (nitric acid) from the supply port to the discharge port can be stably maintained in one direction, and the time until the dissolution liquid supplied to the dissolution tank is discharged can be maximized.
As a result, the contact time between the spent nuclear fuel cutting pieces and the solution can be lengthened, and the dissolution efficiency is improved.

In addition, a discharge tank is arranged outside the annular melting tank, and a discharge trough having a spiral track is arranged inside the discharge tank and is vibrated by a vibration exciter, so that the spent nuclear fuel cutting small pieces are cut along the spiral track. The insoluble matter is moved upwards so that it can be discharged from the top of the discharge tank, and by installing a cleaning spray near the top of the discharge tank, it is possible to remove insoluble fuel coating materials, etc. from the loading of spent nuclear fuel cutting pieces. The process of cleaning and discharging can be easily made continuous.

[Brief description of drawings]

FIG. 1 is a perspective view showing the basic structure of a continuous melting apparatus which is an embodiment of the present invention, FIG. 2 is a sectional view of the entire apparatus, and FIG. 3 is a development view showing the situation of fuel movement during operation, FIG. 4 is a diagram showing a conventional example of a melting apparatus. 1 ... Melting tank, 2 ... Discharge tank, 3 ... Partition wall, 4 ... Outer trough, 5 ... Inner trough, 6 ... Discharge trough, 7 ...
… Truck, 9 …… Fuel loading port, 10 …… Discharge window, 12 ……
Liquid supply port, 13 ... Liquid discharge port, 15 ... Discharge port, 17 ... Outer trough exciter, 18 ... Inner trough exciter, 19 ... Discharge trough exciter, 21 ... Liquid seal, 23 …… Spray,
24 ... Detector, 26 ... Thermal neutron absorber, 28 ... Water-filled container, 30 ... Slit, 31, 32 ... Body plate.

Claims (4)

[Claims] 1. A vertical partition wall is provided in an annular dissolution tank through which a dissolution liquid flows, and a dissolution liquid supply port is provided at a lower part on one side of the partition wall and a liquid discharge port is provided on an upper part of the other side. Outlets are formed respectively; an outer trough formed by forming a plurality of transportation tracks of spent nuclear fuel cutting pieces in a circumferential direction on an inner peripheral surface of a cylindrical body plate having slits at positions corresponding to the partition walls; An inner trough formed by forming a plurality of transportation trucks of spent nuclear fuel cutting pieces in multiple stages in the circumferential direction on the outer peripheral surface of a cylindrical body plate having a slit formed at a position corresponding to the partition wall; and a track of the outer trough. Two troughs are combined so as to be alternately arranged with the tracks of the inner trough and are concentrically immersed in the annular melting tank; one end of each track of the outer trough and the inner trough is not closed. , The other end is an open end that is not blocked. , When combining two troughs, the track end having the closed portion and the track end having the open end are alternately arranged; the outer trough and the inner trough are respectively provided with vibrators and used. A continuous melting device for spent nuclear fuel, characterized in that the small pieces of nuclear fuel are alternately transferred to two troughs along a truck while being continuously transferred from an upper fuel loading port to a lower discharge window to be melted. 2. The continuous melting apparatus for spent nuclear fuel according to claim 1, wherein a liquid seal is provided between the annular melting tank and the outer trough and inner trough. 3. A continuous nuclear fuel according to claim 1, wherein a container filled with water is arranged in a central space of the annular melting tank, and a thermal neutron absorbing material is attached to an inner wall surface of the annular melting tank. Dissolution equipment. 4. A discharge tank communicating with the discharge window portion at a position corresponding to the discharge window is provided outside the annular melting tank, and a discharge trough having a spiral track is provided in the discharge tank by a vibration exciter. An insoluble matter of the spent nuclear fuel cutting pieces is moved upward along the spiral track by vibrating so that the insoluble matter can be discharged from the top of the discharge tank, and a cleaning spray is attached near the top of the discharge tank. Item 1. A continuous melting device for spent nuclear fuel according to item 1.