JPS5821600A - Method of solidifying and volume-decreasing radioactive metal waste - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Spent fuel cladding tube and upper and lower end members of a fuel assembly after shear melting. This invention relates to a volume reduction and stabilization treatment method for high-level radioactive metal waste such as spacers and springs (hereinafter referred to as hel etc.).

In recent years, nuclear energy has been attracting attention and being developed in response to energy shortages centered on petroleum. However, since nuclear energy emits energy during the energy production process, it is important to establish technology to safely store this radioactive waste. is an important problem that cannot be avoided. In particular, the hulls and the like are not made of highly radioactive materials, and their material (Zircaloy) poses a risk of spontaneous combustion, so special handling and storage techniques are strongly required.

Conventionally, the handling of health equipment containing radioactive materials was
Due to this difficulty, reprocessing facilities currently store waste by placing it in drums and submerging them in stainless steel-lined water tanks.

However, this method has a low density (ca. 1).

Since it is IF7, ), it is not compact, requires a huge amount of storage space, and has problems such as not being a stable combination against unexpected disturbances.

Therefore, more compact and stable storage formats are being investigated in various fields.For example, in the case of metal waste, it is possible to create a dense block by melting and solidifying it in a heating furnace. In the case of radioactive incineration ash generated by incinerating combustible waste, a method has been proposed in which it is melted and solidified using microwave melting means. Although these methods have achieved some success in terms of volume reduction,
The problem of disposing of secondary waste due to the radioactive gas during melting and the radioactivity of refractories in the furnace is becoming more and more difficult.

Recently, a method has been developed to overcome the above-mentioned difficulties by compressing radioactive waste with appropriate materials under high temperature and pressure for safe, hermetically sealed storage. There is a method in which fuel rods are pretreated through an inorganic ion exchange membrane and then solidified, and then compacted into a dense solid.The other method is to directly place the spent fuel rods themselves, which have been stored for a certain period of time, into an aluminum oxide container, seal it, and heat it at high temperatures. There is a method of compacting by applying high pressure, but the latter method is currently being researched preferentially.

The applicant also promptly responded to the trends of the times, and
・We have conducted various studies on methods to reduce the volume and solidify radioactive waste using P treatment, and have already proposed some of them. For example, Japanese Patent Application No. 53-146987 describes this, and according to the specification of the same issue, after metal waste is compressed into a block shape using a compression press, this block is filled into a container, and metal powder is poured into the container space. Alternatively, a method for preventing local deformation of a container by filling it with ceramic powder is disclosed.

However, although this method is effective in preventing damage to the container, the filling rate of the waste block inside the container is low, at most 50 to 60%.
Regardless of the degree of filling, metal powder or ceramic powder is filled to increase the filling rate, so more than 30% of the volume of the dense body after H-P treatment is occupied by non-radioactive materials, which is difficult from the perspective of volume reduction. It leaves a feeling of inadequacy.

By the way, various methods of volume reduction and solidification of radioactive waste using H-P are being studied, but the H-Plr used here is usually treated using an inert gas such as argon gas as a pressure medium. This method applies high temperature and three-dimensional hydrostatic pressure to the body at the same time to remove defects in sintered and diffusion bonded cast products.

However, such H-engine P is complicated to deal with the introduction of argon gas into the pressure vessel, the mechanism for discharging it from the vessel, safety due to compressible gas, installation under the High Pressure Gas Control Law, and maintenance. There are problems with long processing cycle times and low production efficiency, which depend on temperature and pressure rise times.
It is not necessarily suitable for widespread industrial use.

Recently, from this point of view, research has been carried out on the H-P treatment method itself, and the use of pressure media that does not rely on inert gases such as argon gas has been considered, and in some cases, BN powder, pyrophyllite, talc, r! A method has been proposed in which a powder or a fluid liquid such as zirconium monide, magnesium oxide, or molten salt is used as a pressure medium.

This method does not require a heating device in the compression device, allows the use of a simple compression device, has the advantages of significantly shortening the processing cycle time, and is not subject to the High Pressure Gas Control Law. It is extremely useful for practical purposes and deserves attention in the future.

The present invention is a method for isotropically highly compressing a heated object using a high-viscosity fluid or powdery solid pressure medium (hereinafter referred to as The first purpose of this project is to proceed with the volume reduction and solidification of the radioactive metal waste by utilizing the conventional H-work P and z'IJ-shi (abbreviated as semi-H-work P for convenience).

Another object of the present invention is to provide a method suitable for volume reduction and solidification of radioactive metal waste in proceeding with the above-mentioned semi-H-work P treatment.

The features of the present invention that achieve the above-mentioned objects can be understood by comparing the claims, but specific embodiments thereof will be described in detail below. First, the basics of the method of the present invention will be explained in detail. The process consists of pre-compression → filling into capsules → sealing → heating → semi-H process P treatment.

FIG. 1 shows each step of the method for volume reduction and solidification of radioactive waste according to the present invention. First, the metal waste (1) cut into appropriate dimensions is pre-compressed and put into a conventional press molding machine ( 2), press molding is performed once at a temperature around room temperature. The reason for performing press forming here is that if the apparent density is low when it is later loaded into a semi-HIP container, there is a risk of damage to the container when densification is performed using the semi-HIP method. be. Therefore, in order to prevent this damage, the material is compressed in advance to increase its density. Shigashi conventional normal H
In the case of H1P method, it is necessary to have a molded body having a density of 60% or more, but this is the case of gas pressure, and in the quasi-H1P method of the present invention, a lower density is sufficient.

Next, a plurality of blocks (3) of the metal waste, that is, hull molded bodies, are formed into disk shapes by the preliminary compression.
It is filled into a capsule container (4) made of metal material.

In this case, the materials used for the capsule include Ou,
A single At 2 tube, a double tube combined with stainless steel, or a plywood clad with these are used. This is to prevent as much as possible the tritium ('H) absorbed in the hull from coming out of the capsule during the subsequent heat treatment. Generally, the aforementioned Ou and At are considered to be materials that are difficult for tritium to pass through.

Stainless steel has a large permeation of tritium, but is effective against oxidation during heating in the post-process and corrosion during long-term storage of treated bodies after semi-H/P treatment.

When loading, it is reasonable to stack a plurality of the hull molded bodies as described above and load them into the capsule (4).

Next, the lid (6) with exhaust pipe (7) is welded to the capsule (4) filled with the molded body such as the hull, but during welding, the heat during welding completely activates the tritium absorbed by the hull etc. It is preferable to place the welding point as far away from the hull as possible to avoid this. In addition, considering the handling of the capsule, it is also a suitable means to weld a magnetic stainless steel plate to the lid to facilitate lifting and handling using a magnet.

In this way, the molded body such as the hull is loaded into the capsule (4),
After welding the lid (6), the capsule is sent to a sealing process, for which there are basically two methods.

The first method is to load the molded body such as the hull into a capsule, weld the lid (6) with the exhaust pipe (7), and then connect the exhaust pipe (7) to the vacuum device (8) as shown in the upper part of the figure. After heating and exhausting the inside of the capsule, press the exhaust pipe (7) and seal it.
This is a method to This method is effective in preventing damage to the capsule due to an increase in internal pressure during heating and in preventing ignition of Zircaloy, as well as in efficiently removing adsorbed gas adsorbed on the surface of the molded article, and also leads to improved quality of the treated article. Note that the exhausted gas is appropriately treated using known gas treatment techniques.

In the second method, as shown in the lower part of the figure, a capsule container loaded with a molded body such as a hull is placed in a state where air remains inside the capsule container.
This method is to weld the lid (6F) and seal it.

This method has the great advantage of producing no gaseous secondary waste and simplifying the operation process compared to the first heating vacuum degassing method. Since the metal particles are oxidized and nitrided by the air remaining in the container, diffusion through the interface of the metal pieces is suppressed, which weakens the bond. In this case, along with the molded body such as the hull mentioned above, Ti, Zr
If a small amount of deoxidizing or denitrifying getter metal powder (5) such as Cjr powder is added, these powder materials having a large specific surface area absorb oxygen and nitrogen, thereby reducing the oxidation and denitrification of the surface of metal waste. Nitriding can be suppressed, and as a result, bonding strength can be increased.

Note that the hull itself is Zircaloy and can act as a getter, but since its surface is oxidized during reprocessing, its ability is reduced to a small extent. Therefore, it is effective to separately insert the getter all over again. be.

The capsules are then sealed using the method described in part n above, and the capsules are then sent to a heating process such as an electric furnace (9).
is heated.

Heating is carried out to a temperature suitable for the subsequent semi-H-works P treatment, and usually varies depending on the type of pressure medium used during the semi-H-works P treatment, but it can be applied to BN powder, talc, pyrophyllite, 23 for zirconium oxide, magnesia oxide, etc.
An appropriate temperature is selected, which is below 0°C, above the melting point of the salt for molten salt, and below 1250'c for high temperature grease.

After the heat treatment is completed, the capsule is finally semi-H.
It is sent to the IP processing step and subjected to necessary compression processing.

In this semi-H engineering P process, a compression device consisting of a high-pressure cylinder QO1 and a reciprocating stem aυ is usually filled with a heat-resistant high viscosity fluid or a powder or pellet solid a2 to serve as the pressure medium. The heated sealed capsule (
A) is buried and compressed via the pressure medium by moving the stem 0υ.

Here, the conditions that the pressure medium should satisfy in the semi-HIP process of the present invention include the following points.

(1) It can be used repeatedly; in other words, the pressure medium is pressurized through the capsule, so there is no contamination of the pressure medium, but in the unlikely event that the capsule is damaged or the pressure medium is contaminated due to permeation of tritium. It is possible to do so.

Therefore, repeated use is required to avoid generation as secondary waste.

(2) It has heat insulation properties. It is preferable that the pressure medium has heat insulation properties so that the heat of the capsule does not transfer to the high pressure cylinder and reduce the strength of the cylinder.

(3) It is desirable to have lubricity and to have low frictional resistance with the cylinder, which moves in response to the entry of the stem into the cylinder.

(4) Low deformation resistance: In order to apply equal pressure to the capsule, low deformation resistance is required.

(5) It does not become a sintered body; if it becomes a sintered body, the isotropic compressibility will be hindered.

(6) No decomposition occurs due to heat, and (7) No damage to the inner wall of the cylinder.If these conditions are satisfied, BN(
boron nitride), graphite, pyrophyllite, talc.

Powder or pellets such as molybdenum disulfide may be used.If the processing temperature is low, high-temperature grease may be used in addition to molten salt.Although this is one of the preferred pressure media, the degree of deterioration due to repeated use is considerable. It is difficult. but,
High temperature grease is fluid.

It is extremely practical in terms of releasability and cost.

On the other hand, the shape of the high-pressure cylinder has a correlation with the shape of the capsule, and the shape shown in FIGS. 2 and 3 is usually adopted in order to equalize the pressure applied to the capsule.

That is, FIG. 2 shows a sealed metal capsule (in which the slope is cylindrical), and the high-pressure cylinder OO1 is provided with a bulging part (lOa) at the center of its inner wall, and the stem αυ moves from above and below. The upper and lower limits are controlled.

In addition, Fig. 3 shows that, conversely, the high-pressure cylinder OQ has a cylindrical inner wall surface, and the sealed capsule (A) buried inside has a medium-thick barrel-shaped outer shape.
The present invention is not limited to those shown in FIGS. 3 and 3, and a design modification of the device having the same effect can be easily implemented.

In any case, the pressure exerted on the sealed capsule due to the use of these pressure media becomes considerably large as it is incompressible unlike gas pressure, and although it is possible to handle up to 20,000 atmospheres, the pressure exerted on the sealed capsule is quite large. Considering the lifespan of 1000 to 10
It is carried out in the range of 000 atmospheres.

In this case, the retention time during semi-HIP treatment is
It may take an appropriate amount of time, but it is generally relatively short, and conventional H
While the IP treatment required 30 minutes or more, several minutes, or about 1 minute depending on the pressure medium, is sufficient.

Thus, through each of the above steps, the metal waste can be densified and compacted into a block with strong cohesive strength.

In addition, if a heat insulating layer is provided on the inner wall of the cylinder or the outer periphery of the capsule in the high-pressure cylinder QOI and the sealed capsule (A), the retention time of the sealed capsule in the compression device can be extended, so a pressure medium such as high-temperature grease can be used. It is suitable if

In addition, each of the above steps is a basic processing step, but the process may be modified at will, such as omitting the evacuation step.Furthermore, in order to prevent contamination of the press during pre-compression, heat treatment, etc. One method included in the present invention is to encapsulate and then pre-compress.

FIG. 4 shows an outline of such preliminary compression, and shows how Hull etc. (H) is filled into the capsule <4f, the lid α51 is closed, the exhaust is sealed, and the capsule is compressed by the preliminary compression press (■). ing.

In the figure, Q3 is a conveyor, (14) is a filler, α61 (
t9 is a welding tool, C1η is a sealing clamp, and 081 is a magnetic stainless steel plate.

(The gradient indicates a sealed capsule.

Furthermore, in the basic process described above, degassing and sealing and heating are performed separately, but there are advantages such as there is no risk of ignition and the ability to remove adsorbed gas. It is also advantageous to carry out air-tight sealing.

F. The density of the dense block body thus obtained is almost the true density or close to the true density. Therefore, the original radioactive waste was No. 1. The volume is greatly reduced by the second compression process, and the volume-reduced and solidified block can be easily stored inside a drum, canister, etc., or it can be stored stably as it is without being stored. .

Next, specific examples of the method of the present invention are listed.

(Example) External diameter 12 mm and thickness 0, which is substantially the same as a nuclear fuel cladding tube
．． A short piece of Zircaloy having a length of 8 mm and a length of 30 to 50 IOI was molded into a disk shape using a mechanical press at a pressure of 3.5 t4. Then, seven of these molded bodies were loaded into a capsule container made of mild steel with an inner diameter of 85 mm, and a lid having an exhaust pipe was welded to the capsule container. After that, connect the exhaust pipe to the vacuum device and
The inside of the container is heated to 0°C through the exhaust pipe.
The container was vacuum degassed to a level of 100 ml, and in that state, an exhaust pipe was connected and the container was sealed.

The thus formed sealed capsule container was placed in the compression device shown in FIG.
Semi-H engineering P processing was performed under YAxl turtle conditions. As a result, the sealed container was found to be a strong block with no voids, with a significant decrease in bulk compared to before the Semi-H Engineering P treatment, and when the cross section was examined, the density reached the theoretical density. According to the method of the present invention, radioactive metal waste can be compacted into blocks with true density and strong bonding, and therefore the initial volume of these wastes can be greatly reduced. As a result of being able to store waste, it becomes possible to use storage space more efficiently than conventional storage methods, and it is possible to store waste stably for a long period of time and rationally in a relatively small space. Moreover, since densification progresses through plastic deformation and diffusion bonding within an airtight container, there is no need to worry about the generation of secondary waste such as radioactive gas.

In addition, as mentioned above, the method of the present invention uses high viscosity fluid and granular solid as the pressure medium instead of inert gas pressure to carry out the H-P treatment, so it is not subject to the regulations of the High Pressure Control Act and is less prone to accidents. It has the advantage of being highly safe with little damage and easy to handle in terms of installation, maintenance, etc. Furthermore, it can be easily handled with ordinary press technology, so the equipment is simple and easy to operate. Compared to the H-process P used, the time required for pressurization is extremely short, significantly shortening the processing time. This shortens the cycle time, improving productivity and increasing the economic efficiency of the process, while reducing waste. Because it can be densified at a temperature of approximately % of the melting point of This is a useful method.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing the steps in the method of the present invention, FIGS. 2 and 3 are schematic diagrams showing each side of the compression device used for the semi-H process P processing of the method of the present invention, and FIG. 4 is a diagram showing the steps of the method of the present invention. FIG. 6 is a system diagram illustrating another embodiment of pre-compression in the method; (1)...Metal waste, (2)(a)...Press molding machine. (3)...Block, (4) (4)'...Capsule. (51.=key ter, (6) (6)' Q
51...Lid. (7)...Exhaust pipe, (8)...Vacuum device. (9)... Heating furnace, αQ... High pressure cylinder. (lOa)...Bulge, αυ...Stem. (One thing...Pressure medium, (H)...Hel etc. (A)...Sealed capsule.

Claims (1)

[Claims] The metal waste is compressed into blocks using a compression press to form a capsule containing one or more of the blocks, and the inside of the capsule is degassed. After heating the sealed capsule to a predetermined temperature, the capsule is embedded in a pressure medium of a flowable heat-resistant liquid or granular material, and then a compressive force is applied to the pressure medium. A method for volume reduction and solidification of radioactive metal waste, characterized in that the metal waste is compressed and densely integrated with the capsule by A method for volume reduction and solidification of radioactive metal waste according to claim 1, which is formed by: 3 Oxygen such as Ti, Zr, Nb, etc. in the metal capsule. 3. A method for volume reduction and solidification of radioactive metal waste according to claim 1 or 2, which comprises adding nitrogen and zwitterionic powder or granules. q Pressure medium is BN, graphite, pyrophyllite. The method for volume reduction and assimilation of radioactive metal waste according to claim 1, 2 or 3, wherein the powder is selected from talc and molybdenum disulfide. S Claim 1 in which the pressure medium is high temperature heat resistant grease
The method for volume reduction and solidification of radioactive metal waste according to claim 1, 2 or 3. Claim 1, wherein the pressure medium is a molten salt. The method for volume reduction and solidification of radioactive metal waste according to item 2 or 3. 7 Radioactive metal waste according to any one of claims 1 to 6, wherein a compression device consisting of a high-pressure cylinder and a stem is filled with a pressure medium, and a sealed capsule is buried in the pressure medium for compression treatment. A method for solidifying and reducing the volume of things. g. The method for volume reduction and solidification of radioactive metal waste according to claim 7, wherein the metal capsule is cylindrical and the high-pressure cylinder has a bulge in the center of its inner passage. 2. The method for volume reduction and solidification of radioactive metal waste according to claim 1, wherein the high-pressure cylinder is cylindrical and the metal capsule is formed into a medium-sized barrel-like body. 1α A method for volume reduction and solidification of radioactive metal waste according to any one of claims 1 to 9, wherein the internal space of a metal capsule filled with blocks of radioactive metal waste is filled with powder. 11. The method for volume reduction and solidification of radioactive metal waste according to claim 10, wherein the granular material is one or more selected from ceramic powder, metal powder, and incineration ash of combustible radioactive waste.