JPS6025760B2 - Method of forming radioactive waste waste - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for disposing of radioactive waste.

More specifically, the waste containing highly radioactive fission products generated from the reprocessing of spent nuclear fuel is converted into a granular solidified material (vitrified solidified material, glass ceramic solidified material, or super calcine solidified material, etc.). This invention relates to an improvement in a method of forming a waste body by filling a container called a canister with metal as a matrix. Reprocessing of spent nuclear fuel (
For example, a nitric acid acidic solution containing fission products derived from the Purex method is added with a glass aid, etc., and heated and melted to solidify the radioactive material into a small spherical glass-like substance. The container (canister) contains a matrix of metals (metals or alloys such as lead, lead alloy, aluminum, aluminum alloy, copper, copper alloy, etc., which do not cause significant harm to the solidified radioactive waste and melt at a relatively low temperature). The idea is to fill it up, seal it, and bury it in a radioactive waste disposal site.

All of these operations must be performed remotely and behind closed doors, which poses various difficulties. Since the specific gravity of metal is much higher than the solidified granules that are embedded in it, first, a cylindrical cage is used to insert the solidified granules into the canister, so that the granules inside do not leak out. Moreover, the cage is placed in a cage with openings that are large enough not to obstruct the inflow and outflow of molten metal, and the cage is placed in a canister.
You can either put a calculated amount of molten metal into a canister and fix it so it doesn't float up before pouring the molten metal into it, or put a calculated amount of molten metal into a canister and sink the cage containing the solidified granules into it. The top of the container must be welded after the metal has solidified to prevent floating.

For these reasons, various methods have been devised, such as methods for fixing the cage containing the solidified granules so that they do not float up, methods for injecting metal, etc., so that they can be easily performed remotely while being shielded. All of the methods published to date involve first placing the cage in a container and fixing it, then filling it with solidified granules and injecting the metal.

This is to prevent the container from floating up, but for this purpose a very complex structure and procedure are used to inject metal and fix the lid of the container. For example, a cage with a metal injection tube passed through the center and fixed at the bottom is inserted into the container, solidified granules are introduced into the cage, and the upper part of the molten metal injection tube is fixed to fix the cage. The complicated procedure is to weld a diamond with a hole that extends outward, inject molten metal through the tube, cut off the protruding portion of the tube, and then weld a lid to cover the entire tube.

The inventors changed their thinking and developed a method of filling a cage with solidified granules outside the container, submerging the cage into a container containing a pre-calculated amount of molten metal, and fixing the cage until the metal solidifies. .

According to the present invention, radioactive waste is made into a granular solidified body, which is first packed in a metal cage, and then is placed in a corrosion-resistant metal container using a metal alloy (hereinafter referred to as metal) having a lower melting point than the solidified body as a matrix. In a method of forming a radioactive waste composite solidified body by filling and sealing it in a canister, the granular solidified body is filled into a cage, and after preheating, a pre-calculated amount of molten metal is added and the surface of the molten metal is purged or sealed with an inert gas. A method is provided, characterized in that the metal is submerged in a covered container and the lid is welded after the metal has solidified.

Although the method of the present invention requires equipment for submerging the cage filled with solidified granules in a molten metal (e.g., lead) bath and holding it there until the metal solidifies, no cutting operation is required and the welding operation is significantly simplified. Become.

Next, the present invention will be explained in detail with reference to the drawings. FIG. 1 shows the concept of a typical conventional method. According to this method, the left side {
As shown, first, a cylindrical cage 10 with a bottom fitted with a tube 11 is inserted into the container (canister), and the hover 30 is placed on top of the cage 10, and the solidified granules (glass small spheres) are placed in the canister. ) 40 into the cage. The canister 20 that has been filled is welded with a lid 21 with an opening in the center, as shown in the center (3), and is moved inside the heating element 50 (or the canister 50 may be moved upward), and the tube is closed. 1
Molten metal (lead) 60 is injected from 1, then the protrusion of the tube 11 is cut, and the second lid 22 is further welded as shown in the right glue. FIG. 2 shows the concept of the method of the invention.
In the present invention, a cage 10 having a smooth surf fin 12 may be used.

(The use of subasurfing is known per se.) This cage is conventionally filled with solidified granules (glass spherules) of radioactive waste from a hopper 30. After filling the cage 10', for example, as shown in (3), a lid 13 (preferably, the lid is mesh-like like the cage) with a suspension member 14 having a through hole 14' for receiving the hook 70 is welded or It is fixed using an engaging means as described below.

The cage to which the lid 13 is fixed is connected to the heating section by hooking the suspension member 14 with a hook 70 of a suspension device (not shown), which is operated by a traveling hoist, which is provided on the ceiling of the shielding room, as shown in ``3''. Move to. (At this time, the hopper may also be moved.) The heating section is composed of heaters 50 and 50' that are heated by suitable means (for example, electric resistance heating), and the upper heater is used to heat the solidified granules. The lower heater is used to keep the metal molten.

An inert gas introduction pipe 80 faces the lower heater.
In the prior art, the metal is introduced into the injection pipe 11 from the bottom of the ladle, so there is less dross being mixed in, but in the case of the present invention, the cage is sunk into the metal cage from the surface in advance, so there is less dross. It is especially desirable to provide this device in the case of the present invention, since ream incorporation is a problem. The cage transferred to the upper heating section is being heated while the metal is being melted in the lower heating section under an inert gas atmosphere introduced from the conduit 80.

The container (canister) used in the method of the present invention may be provided with a stopper 21 at a position corresponding to the bottom surf fin of the cage. After preheating, the cage is placed in a container containing enough metal to submerge the entire cage when the cage containing the solidified granules is melted under an inert atmosphere in the heater below. be lowered inside.
Solidified granules have a much lower specific gravity than metal, so they must be pushed in order to sink. This may be achieved by using a device that combines a gear and a threaded shaft, by a hanging odor with a weight, or by other means. If a single suspension device and multiple heating devices are used to produce a large number of canister fills, it is advantageous to use a finned cage and a stoppered canister.

If the cage is submerged in the molten metal at a position where the fins and the stopper are separated, and the suspension device is rotated so that the fins and the stopper are engaged, there is no need to leave the suspension device in place. After the metal has solidified, the lid 22 may be welded. In the case of this example, the cage was preheated to 35,000 ℃ after filling the cage with glass spheres having a diameter of 80 mm and a height of about 60% by volume.

Afterwards, add 3 liters of 5.5k9 lead in a canister in advance.
The cage was immersed in a solution heated to 50°C. For counterfeiting, hang the cage on the lower end of a male-threaded shaft.
It was immersed by moving it downwards by applying rotation to the shaft through an internally threaded fixture. After the immersion was completed, the cage was cooled (the cage was held down by the engagement of the screws while keeping it from floating). The outer lid was then welded and attached to the canister. The canister has a diameter of 90 mounds and a height of 15 Q. In an advantageous embodiment of the method according to the invention, the cage is provided with a stopper similar to that provided on the aforementioned canister, and the lid of the cage is provided with a recess at a position corresponding to the stopper, so that after filling the solidified granules, the lid is If you apply this to the cage and rotate it until the notch comes off the stopper, there is no need to weld the cage lid.

Although the present invention has been described in particular detail with respect to preferred embodiments thereof, it will be understood that various modifications may be made within the scope of the invention as set forth in the claims.

[Brief explanation of the drawing]

FIG. 1 shows the concept of the procedure in the prior art method. FIG. 2 is a diagram showing an example of the procedure in the method of the present invention. In these figures, 40... glass small sphere, 10... cage, 20... container (canister),
60... Molten metal. Boat plan N vertical

Claims (1)

[Claims] 1. Radioactive waste is made into a granular solidified material, which is first packed in a metal cage, and then a corrosion-resistant metal is placed in a matrix using a metal alloy (hereinafter referred to as metal) having a lower melting point than the solidified material. In the method of forming a solidified radioactive waste composite by filling and sealing a container (canister), the granular solidified material is filled into a cage, and after preheating, a pre-calculated amount of molten metal is added and the surface of the molten metal is purged with an inert gas. or a method characterized by submerging the metal in a covered container, solidifying the metal, and then welding the lid. 2. A method according to claim 1, characterized in that the cage has spacer fins and the lid has a member for engaging the suspension device. 3. A method according to claim 2, characterized in that the container has a stopper that engages the spacer fins of the cage. 4. A method according to any one of claims 1 to 3, characterized in that a container heater and a cage heater (preheater) are used. 5. The method according to any one of claims 3 to 4, characterized in that a suspension device capable of vertical, horizontal, and rotational movement is used. 6. A method according to claim 5, characterized in that the suspension device has a mechanism for sinking the cage into the molten metal against buoyant forces. 7. The method according to claim 6, wherein the cage has a stopper for the lid, the lid has a notch at a position corresponding to the stopper, and aligning the notch with the stopper, A method characterized in that the lid is fixed to the cage by applying the lid and then rotating the lid.