JP3044221B1 - Rotary cylindrical continuous melting tank - Google Patents

Abstract

[PROBLEMS] To ensure stable operation and improve reliability. It reduces sticking and accumulation of powdered fuel and prevents dripping while ensuring continuous nitric acid supply. SOLUTION: A rotary drum 10 having a spiral space, a shroud 12 containing the same, and a driving device 14 are provided, and a fuel scissor input section 20 and a solution discharge section 22 are provided at one end side.
The other end side has a nitric acid supply nozzle 24 and a metal piece discharging unit 2
6. A solution communication passage is provided between each stage of the rotating drum. The fuel fragments are sent to the next stage by the intermittent rotation of the rotating drum, and come into contact with the solution at each stage and dissolve. The fuel fragment input section is provided offset from the rotation center axis, and the fuel fragment is dropped directly into the solution of the first stage. Nitric acid supply nozzle to supply liquid buffer 5
Nitric acid supply path 50 for supplying nitric acid to the rotating drum via
Is shifted to the rotation center side with respect to the solution communication passage 36, a level gradient is provided in the nitric acid supply path, and the supply liquid buffer is adjusted to the position on the lower surface of the nitric acid supply path.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary cylindrical continuous melting tank for dissolving fuel shear fragments with nitric acid as a pretreatment in a reprocessing step of spent fuel taken out of a nuclear reactor. .

[0002]

2. Description of the Related Art In the process of reprocessing spent fuel,
As a pretreatment, the fuel pins are mechanically cut into appropriate lengths, sent to a dissolving tank, and dissolved with nitric acid. Regarding the dissolution of the fuel shear fragments, in recent years, a rotary cylindrical continuous melting tank has been developed from the viewpoint of improving the efficiency of dissolution while ensuring criticality safety.

FIG. 7 shows an example of a conventional rotary cylindrical continuous melting tank.
Shown in A is an overall view with a part cut away, and B is a schematic view of a main part thereof. This rotary cylindrical continuous melting tank is a horizontal cylindrical rotary drum 10 having a spiral internal space.
And a shroud 12 having an upper and lower split structure including the rotary drum 10 and a driving device 14 for swinging and rotating the rotary drum 10, and these are mounted on a gantry 16. A fuel scissor input section 20 is provided at an upper portion on one end side (opposite to the drive section) of the shroud 12, and a solution discharge portion 2 is provided at a lower portion thereof.
2 and a nitric acid supply nozzle 24 at the other end (drive unit side),
A metal piece discharging portion 26 is provided at a lower portion on the other end side. Further, a heating panel 28 is provided outside the shroud 12 for keeping the whole body warm and heating, so that the temperature can be controlled so that an appropriate melting temperature can be maintained in the rotating drum.

[0004] The rotary drum 10 comprises a drum auger 30 which is processed into a spiral shape, and a cylindrical drum shell 32 which covers the outside thereof. The drum shell 32 is fixed to the outer periphery of the drum auger 30 by shrink fitting or welding, and the center shaft 34 is supported by a bearing, and is integrally rotated by the driving device 14. As described above, the rotating drum 10 has a plurality of stages formed by the internal space being rotated a plurality of times in a spiral shape, and the plurality of dissolved liquid communication passages 36 are provided in the drum auger 30 separating the stages. Are arranged on the circumference.

[0005] The fuel shearing fragments introduced into the rotary drum 10 from the fuel shearing fragment introduction section 20 through the fuel shearing fragment introduction port 42 come into countercurrent contact with the solution (nitric acid) supplied from the nitric acid supply nozzle 24. Dissolution processing is performed while rocking. Due to the rotation of the cylindrical drum 10 at regular intervals, the fuel shear fragments of a certain stage are sequentially sent to the next stage, where they also oscillate in countercurrent contact with the solution and are subjected to a melting process. Finally, the metal pieces (such as the blank cladding pipe pieces after the fuel dissolution and the cut pieces of the spacer wires) are discharged from the metal piece discharge portion 26 located immediately below the final stage, and the dissolved liquid overflows from the first stage. The solution is discharged from the solution discharge part 22 through the hole 38.

[0006]

In such a conventional rotary cylindrical type continuous melting tank, the fuel shearing piece charging section 20 is provided with a fuel shearing section 20 as shown in FIG.
As shown in the figure, the rotary drum 10 is disposed immediately above the central axis 34. Then, the fuel shears 40 supplied from the fuel shears input section 20 pass through the fuel shears input port 42 of the first stage of the rotary drum 10, and the taper section 44 of the rotary drum 10 (the fuel shears inputting section). It slides on the end of the spiral space of one stage) and is fed into the solution 46 at the bottom of the rotating drum 10. Therefore, this structure has the following problem. The powdered fuel injected into the rotary drum 10 from the fuel shearing piece input section 20 reacts with the mist inside the rotary drum and is fixed to the tapered section 44. The fixing point is indicated by reference numeral a. Therefore, the supplied fuel fragments 40 are less likely to slip, and the undissolved fuel remains in the tapered portion 44, and directly goes out of the rotating drum during rotation. As shown in FIG. 7A, the end wall surface (the surface indicated by reference numeral 30a) of the drum auger in the first stage has a helical shape. The solution is deposited near a screen 48 that covers the overflow hole 38 of the solution (the location where the solution is deposited is indicated by the symbol b), and the overflow of the solution 46 is prevented.

In a conventional rotary cylindrical continuous dissolution tank, as shown in FIG. 9, the level of a nitric acid supply passage 50 provided in the rotary drum 10 is the same as that of a solution communication passage 36 between the stages. Level. Further, the level of the supply liquid buffer 52 is lower than that of the nitric acid supply path 50. Further, the nitric acid supply passage 50 is formed horizontally. However, with this structure, the following problems occur at the time of melting behavior such as swinging of the rotating drum 10 for accelerating dissolution and rotation for feeding fuel shear fragments. The nitric acid and undissolved solids flow back through the nitric acid supply path 50. The nitric acid and undissolved solids accumulate in the feed buffer 52 (the accumulating portion is indicated by the symbol c) and spills out of the rotating drum.

[0008] In addition, fuel shear fragments and metal chips are caught between the rotating drum and the shroud during rotation, accumulation of shear powder near the solution discharge portion, and washing liquid flows to the metal chip discharge portion during cleaning. There were also problems such as.

An object of the present invention is to eliminate mechanical troubles such as blockage and biting during operation due to solid components (metal pieces, wires, metal powder, fuel powder, etc.) and to ensure stable operation.
An object of the present invention is to provide a rotary cylindrical continuous melting tank devised so that reliability can be improved. It is another object of the present invention to provide a rotary cylindrical continuous melting tank having a fuel shearing section inputting portion capable of reducing sticking and accumulation of powdered fuel in a rotary drum. Still another object of the present invention is to provide a rotary cylindrical continuous melting tank having a liquid supply structure such that dripping and accumulation of shearing powder and the like do not occur while ensuring a reliable supply of nitric acid during the dissolution treatment. It is.

[0010]

SUMMARY OF THE INVENTION A rotary cylindrical continuous melting tank according to the present invention comprises a horizontal cylindrical rotary drum having a spiral internal space, a shroud including the rotary drum, and a rotary drum. A drive device for rocking and rotating the shroud.The shroud has a fuel scissor introduction portion at an upper portion on one end side, a solution discharge portion at a lower portion, a nitric acid supply nozzle at the other end, and a other end. It has a metal piece discharge part at the lower part on the side. The rotating drum forms a plurality of stages by rotating the internal space of the rotating drum a plurality of times, and a plurality of solution communication passages are arranged on the circumference between the stages. The fuel shearing fragments charged into the rotary drum from the fuel shearing portion input portion are sequentially sent to the next stage by intermittent rotation of the rotary drum, and the fuel shearing fragments are dissolved in a solution (nitric acid) supplied from a nitric acid supply nozzle. ) While being oscillated while countercurrently contacting with each other to perform the dissolution treatment, the metal pieces are discharged from the metal piece discharge section, and the solution is discharged from the solution discharge section.

[0011] In the present invention, the fuel shearing portion input portion is provided offset from the center axis of the rotary drum, and the end wall surface for regulating the helical space in the rotary drum below the fuel shearing portion input portion is made vertical. Thus, the fuel fragments are dropped directly into the first stage solution (without contacting any wall surface). Further, in the present invention, the position of the nitric acid supply path for supplying nitric acid from the nitric acid supply nozzle to the rotating drum via the supply liquid buffer is shifted to the rotation center side from the position of the solution communication passage between the stages, and the nitric acid supply is performed. A level gradient is provided in the passage to prevent reverse flow of the dissolved liquid or undissolved solid, and the lower surface of the supply buffer is adjusted to the position of the lower surface of the nitric acid supply passage. Here, a part of the supply liquid buffer can be constituted by a circumferential groove cut so as to partially connect a plurality of nitric acid supply paths at an end face of the rotary drum on the nitric acid supply nozzle side.

Further, the metal piece discharging portion is formed by a combination of a cylindrical portion hanging down from the shroud and a funnel-shaped portion connected to a lower end of the cylindrical portion, and the cylindrical portion and the funnel-shaped portion form a metal piece discharging space. Is preferably enlarged. Further, it is preferable that the dissolving liquid discharge part is expanded in a funnel shape and is located immediately below the fuel shearing piece charging part. Preferably, the distance between the rotating drum and the shroud around the fuel shearing piece input section and the metal piece discharging section is enlarged to be equal to or larger than the size of the fuel shearing piece or the metal piece.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a rotary cylindrical continuous melting tank according to the present invention will be described below. The basic configuration of this device is
It may be substantially the same as that shown in FIG. Therefore,
The description thereof will be omitted because it is redundant. Here, the rotating drum has eight stages (i.e., the first to eighth stages) formed by spirally rotating its internal space eight times, and a large number of drum augers (the first to eighth stages) partition between the stages. (For example, 18) solution communication passages are arranged on the circumference.

As shown schematically in FIG. 1, the continuous melting tank of this embodiment also has a
Through the rotary drum 10
Dissolved solution (nitric acid) supplied from nitric acid supply nozzle 24
The dissolution treatment is carried out while contacting countercurrent with. At this time, the rotating drum 10 swings to promote melting. After a certain period of time, by rotating the rotary drum 10 once, the fuel shear fragments of a certain stage are sequentially sent to the next stage, where they are also subjected to a dissolution treatment while being brought into countercurrent contact with the solution. Finally, the metal pieces (empty cladding pieces after fuel dissolution or cut pieces of spacer wires) are placed in the final stage (eighth stage).
The solution is discharged from the metal piece discharge portion 26 through the metal piece discharge port 54 of the first stage, and the solution is discharged from the solution discharge portion 22 of the first stage.

FIG. 2 shows the structure of the fuel shearing section charging section. In the present invention, the fuel shearing piece charging section 20 is provided offset from the central axis of the rotating drum 10 (provided at a shifted position as shown in FIG. 2B). Then, the conventional taper portion in the rotary drum below the fuel fragment input section and the spiral shape on the non-drive side that regulates the spiral space are eliminated, and the drum auger end wall surface 30b is set in a vertical state (when the fuel shear fragment is input). , The fuel shears 40 are the first stage solution 4
In 6, it is configured to drop directly without almost touching any wall surface. As a result, there is almost no area where the fuel shearing fragments come into contact with the inner surface of the rotating drum, so that it is possible to prevent the fuel shearing powder from adhering and sticking to a wall surface or the like. The fuel shearing fragments fall directly into the solution of the first stage, and it is possible to prevent undissolved fuel and the like remaining in the tapered portion from driving out of the rotary drum when the rotary drum is driven as in the related art. In addition, the fuel shear fragments are used to form the overflow holes 38 of the solution.
The fuel is supplied without directly contacting the screen 48 covering the fuel cell, so that the accumulation of the fuel powder near the screen 48 can be prevented.

Further, in this embodiment, as shown in an enlarged view of FIG. 2B, in order to ensure that the fuel fragments are injected into the rotary drum, the tip of the fuel shears input section 20 is moved in the axial direction of the rotary drum. In addition to being inclined, a drainer 20a is added to the tip.

FIGS. 3 and 4 show the structure of the nitric acid supply unit to the rotary drum. The position of the nitric acid supply path 50 that supplies nitric acid from the nitric acid supply nozzle 24 to the rotary drum 10 via the supply liquid buffer 56 is shifted to the rotation center side from the position of the solution communication passage 36 between the stages, and 50 is provided with a level gradient (0.6 °) to prevent backflow of the dissolved liquid and undissolved solid, and the lower surface of the supply buffer 56 is aligned with the lower surface of the nitric acid supply passage 50. Here, a part of the supply liquid buffer 56 is formed by a plurality of nitric acid supply paths
It is constituted by a circumferential groove 58 cut by the depth D so that 0 is partially connected. Due to the formation of the circumferential groove 58,
The 18 nitric acid supply paths 50 arranged on the circumference are connected. Here, the reason why the part is referred to as "partly" is that the circumferential groove 58 is processed only to a certain depth (D) from the end face of the drum. The bottom surface of the supply liquid buffer 56 is lifted, and the capacity is reduced by forming a circumferential groove 58 to the extent that the capacity is reduced, so that a buffer capacity larger than that of the conventional technology can be finally secured.

By moving the level of the nitric acid supply passage 50 to the center side of the rotary drum with respect to the dissolving liquid communication passage 36 formed in the drum auger, the supply liquid level between the stages rises (indicated by L). During the operation of the rotary drum 10 such as rocking and rotation, backflow of undissolved solids such as sheared powder and the supply liquid can be prevented. By providing a level gradient (0.6 °) in the nitric acid supply path 50, backflow of undissolved solids and the supply liquid can be prevented. By adjusting the lower surface of the supply buffer 56 to the position of the lower surface of the nitric acid supply passage 50, it is possible to prevent the supply liquid and undissolved solids from accumulating in the supply buffer 56 and spilling out of the rotary drum. A part of the nitric acid supply path 50 is connected on the circumference to form the supply liquid buffer 56 by the circumferential groove 58, so that the supply liquid and the undissolved solids rotate from the supply liquid buffer 56 when the rotary drum 10 swings. It can be prevented from spilling out of the drum. Further, by providing a slight gradient in the piping of the nitric acid supply nozzle 24, it is possible to prevent liquid dripping outside the rotating drum,
Even if liquid dripping occurs, the liquid dripping direction is changed to supply liquid buffer 5.
6 can be led.

In the prior art shown in FIG. 7B,
Although the shroud 12 is designed to include the rotary drum 10 at intervals of 6 mm, the rotation of the rotary drum 10 around the fuel shearing piece input section 20 and the metal piece discharge section 26,
A phenomenon occurred in which shear fragments and the like bited during rotation. Although the conventional idea was to "prevent biting fragments and the like from entering by preventing a bite from being inserted by narrowing the interval", this cannot sufficiently cope with deformed metal pieces and wire pieces. Therefore, in the present embodiment, from the viewpoint of “if it is easy to discharge even if it enters the gap”, as shown in FIG. 1, the gap g around the fuel shear piece input section 20 and the metal piece discharge section 26 is formed. It is four times larger (26 mm) than the conventional one. As a result, the problem of bites such as shear fragments between the rotating drum 10 and the shroud 12 can be solved.

FIG. 5 shows an improved example in the vicinity of the solution discharge section. In the prior art (see FIG. 7B), since the solution discharging portion 22 has a horizontal portion in the lower shroud, fine shear powder in the solution discharged from the end of the rotating drum accumulates. Further, during the cleaning operation in the drum (during reverse rotation), a phenomenon occurs in which a part of the cleaning liquid flows out to the metal piece discharging unit side. However, in the present embodiment, as shown in FIG. 5, the portion where the solution flows down is provided with an inclination, the shape of the solution discharge portion 22 is expanded upward in a funnel shape, and the portion immediately below the fuel shear fragment inlet 42 is opened. Installed in As a result, the disadvantages of the prior art during normal operation and during cleaning can be eliminated. The dissolving solution is smoothly discharged from the dissolving solution discharge portion 22, and neither the shear powder is deposited on the lower shroud nor flows out to the metal piece discharge portion side.

Further, as shown in FIG.
Is formed by a combination of a cylindrical portion 26a hanging down from the shroud 12 and a funnel-shaped portion 26b continuous with the lower end of the cylindrical portion 26a, and the cylindrical portion 26a and the funnel-shaped portion 26b increase the discharge space of the metal piece. doing. As a result, the area where the metal pieces fall and come into contact with each other is enlarged, so that the accumulation of shear fragments and shearing powder can be prevented, and the rocking of the pieces during rocking can be prevented.

The entire apparatus is installed in a cell and assembled so that maintenance can be performed by remote control.
At this time, the drive side (metal piece discharge side) to release thermal expansion
And the opposite side is designed to be slidable. Note that a neutron absorber of B ₄ C is incorporated in the center of the rotating drum for criticality management.

[0023]

Since the present invention is a rotary cylindrical continuous melting tank improved as described above, solid components (metal fragments, wires, metal powder, fuel, etc.) can be obtained under severe conditions of dissolving nuclear fuel material with nitric acid. Mechanical problems such as blockage and biting during operation due to powder, etc., to ensure stable operation,
Reliability can be improved. In particular, by improving the structure in the vicinity of the fuel shearing piece charging section, the sticking and accumulation of the powder fuel in the rotating drum can be reduced. In addition, by improving the supply structure of nitric acid, it is possible to ensure that the nitric acid is supplied when the rotary drum is driven, and to prevent the accumulation of dripping or shearing powder.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a main part of an embodiment of a rotary cylindrical continuous melting tank according to the present invention.

FIG. 2 is an explanatory view of the fuel shearing piece charging section.

FIG. 3 is an explanatory view of the nitric acid supply unit.

FIG. 4 is a detailed explanatory diagram of a nitric acid supply unit.

FIG. 5 is an explanatory view of the solution discharging section.

FIG. 6 is an explanatory view of the metal piece discharging section.

FIG. 7 is a schematic configuration diagram of a conventional rotary cylindrical continuous melting tank.

FIG. 8 is an explanatory view of the fuel shearing piece charging section.

FIG. 9 is an explanatory diagram of the nitric acid supply unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Rotary drum 12 Shroud 14 Drive device 20 Fuel shearing piece charging part 22 Dissolving liquid discharging part 24 Nitric acid supply nozzle 26 Metal piece discharging part 36 Dissolving liquid communication passage 38 Overflow hole 50 Nitric acid supplying path 56 Supply liquid buffer

Continuation of front page (72) Inventor Masayuki Nodaka 2-3-1 Shinhama, Arai-machi, Takasago-shi, Hyogo Prefecture Inside Kobe Steel, Ltd. Takasago Works (56) References JP-A-64-65497 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) G21C 19/46

Claims (5)

(57) [Claims] A rotary drum having a horizontal cylindrical shape having a spiral internal space, a shroud enclosing the rotary drum, and a driving device for swinging and rotating the rotary drum;
The shroud has a fuel scissor input portion at an upper portion on one end side, a solution discharge portion at a lower portion, a nitric acid supply nozzle at the other end, and a metal piece discharge portion at a lower portion on the other end side, The rotating drum forms a plurality of stages by rotating its internal space a plurality of times in a spiral shape, and a plurality of solution communication passages are arranged on the circumference between each stage, and the fuel The fuel shear fragments supplied from the shear fragment input section into the rotary drum are sequentially sent to the next stage by the intermittent rotation of the rotary drum, and the fuel shear fragments are supplied to the melt solution supplied from the nitric acid supply nozzle at each stage. In a rotating cylindrical continuous melting tank in which the metal piece is discharged from the metal piece discharge section and the solution is discharged from the solution discharge section while being swirled while being in countercurrent contact with Offset from the center axis of The end wall that regulates the helical space in the rotary drum below the fuel shearing piece input section is set in a vertical state so that the fuel shearing pieces fall directly into the solution of the first stage. The position of the nitric acid supply path for supplying nitric acid to the rotating drum via the supply liquid buffer is shifted to the rotation center side from the position of the dissolving liquid communication path between the stages, and a level gradient is provided in the nitric acid supplying path to dissolve the nitric acid. A rotary cylindrical continuous dissolution tank wherein the backflow of undissolved solids is prevented and the lower surface of the supply liquid buffer is aligned with the lower surface of the nitric acid supply path. 2. The liquid supply buffer according to claim 1, wherein a part of the supply liquid buffer is a circumferential groove formed by partially cutting a plurality of nitric acid supply paths at an end surface of the rotary drum on the nitric acid supply nozzle side. Rotary cylindrical continuous melting tank. 3. A metal piece discharge space is formed by a combination of a cylindrical portion hanging down from a shroud and a funnel-shaped portion continuous with a lower end of the cylindrical portion, and the cylindrical portion and the funnel-shaped portion form a metal piece discharge space. 3. The rotary cylindrical continuous melting tank according to claim 1, wherein 4. The rotary cylindrical continuous melting tank according to claim 1, wherein the solution discharging portion is expanded in a funnel shape and is located immediately below the fuel shearing portion input portion. 5. The rotation according to claim 1, wherein the distance between the rotary drum and the shroud around the fuel shearing piece input section and the metal piece discharging section is enlarged to be equal to or larger than the size of the fuel shearing piece or the metal piece. Cylindrical continuous melting tank.