JPS6331758B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to volume reduction and solidification treatment of radioactive solid waste containing tritium by hot isostatic pressing (hereinafter abbreviated as HIP).

Nowadays, fossil fuels such as petroleum are expected to run out sooner or later, and the use of nuclear power as an alternative energy source is being developed. Establishment of technology to safely store such radioactive waste is important in order to prevent environmental pollution. For example, used burnable poison, which suppresses and controls the burnup of new fuel in a power reactor and maintains a uniform burnup in the reactor, generates tritium when irradiated with neutrons inside the reactor. Alternatively, metal waste (hereinafter referred to as hull) such as spent fuel cladding tubes, upper and lower end members of fuel assemblies, spacers, and sprigs (hereinafter referred to as hulls) after shear melting generated from the pretreatment process of a reprocessing plant absorbs tritium. Not only does it constitute a high-level radioactive solid waste, but the material, namely Zircaloy, poses a risk of spontaneous combustion, which strongly requires special handling and storage techniques.

Conventionally, such radioactive solid waste has been stored in drums and submerged in stainless steel-lined water tanks due to the difficulty of handling.

However, with this method, Hull et al.
Since the density is as low as 1, a large amount of storage space is required, and there are other problems such as not being able to form a strong bond against unexpected disturbances.

Therefore, more compact and stable storage formats are being investigated in various fields. For example, in the case of metal waste, a method has been proposed in which it is melted and solidified in a heating furnace to form a dense block. Furthermore, in the case of radioactive incineration ash generated by incinerating combustible waste, a method has been proposed in which this is melted and solidified using microwave melting means.

All of these methods have achieved some success in terms of volume reduction, but they suffer from problems in the disposal of secondary waste, such as radioactive gas during melting and radioactive contamination of furnace refractories.

Recently, attention has been paid to the use of HIP to reduce the volume and solidify radioactive solid waste as a way to compensate for the above-mentioned difficulties.

HIP originally consists of inert gas such as argon gas, heat-resistant grease, heat-resistant incompressible fluid such as molten glass, etc.
Using heat-resistant powder such as BN powder, pyroferrite, talc, zirconium oxide, magnesium oxide, etc. as a pressure medium, three-dimensional hydrostatic pressure is applied to the object to be processed under high temperature to isotropically compress, sinter, and diffusion bond. This is a method for removing defects in cast products.

The applicant has also followed such technological trends and has
We have been conducting research on volume reduction and solidification methods for radioactive solid waste using HIP processing, and have already proposed some of them. For example, in order to prevent the capsule housing the hull etc. from being locally deformed and damaged during compression, the capsule space may be filled with metal powder or ceramic powder, or the hull etc. may be pre-compressed by mechanical pressing. We proposed that the material be placed in a highly ductile capsule and subjected to HIP treatment. In addition, in these methods, in order to prevent spontaneous combustion of Zircaloy, which constitutes the hull, etc., an oxygen getter such as Ti or Zr is added to the capsule, or the capsule is degassed before being sealed. Although consideration is given to
As a measure to contain the generated tritium gas, only the use of a material that is difficult to permeate tritium gas, such as Cu or Al, as an encapsulant material has been disclosed. However, Hull et al.
When HIPing, the temperature rises to approximately 60% of the melting point of the hull, etc., which significantly activates tritium, making it difficult to completely confine it within the capsule and securely immobilize it using conventional methods. Not only is this insufficient, but it is also impossible to completely prevent the leakage of radionuclides other than tritium, and there is a risk of secondary waste generation.

The present invention was completed after intensive research to solve the above-mentioned problems, and its purpose is to completely release radionuclides such as tritium so that it is suitable for long-term safe storage. The purpose of the present invention is to provide a block of radioactive solid waste that is immobilized and has a significantly reduced volume. Another purpose is to prevent radioactive substances such as tritium from leaking out of the system through the radioactive solid waste volume reduction treatment process used to form such blocks, and to prevent the generation of secondary waste. Yet another objective is to provide a device that can be effectively applied to achieve the above objectives. Other purposes will become clear from the description below.

The feature of the method of the present invention for achieving the above object is that a pre-compressed body formed by compressing radioactive solid waste with a compression press is stored in a metal capsule, degassed and sealed, and then subjected to HIP treatment. In this method, prior to degassing and sealing the metal capsule, the tritium gas released from the pre-compressed body is heated by the action of an oxidizing agent placed inside the metal capsule. If necessary, the water is oxidized and converted to water with the aid of an oxidation catalyst, and then the metal capsule is degassed and sealed with the water trapped inside. Further, an apparatus invented to suitably apply the method of the present invention includes a metal capsule formed of a composite metal plate having an inner surface made of copper or aluminum and an outer surface made of stainless steel, and the metal capsule. A heating means for heating the metal capsule, comprising a layer of an oxidizing agent or an oxidizing catalyst loaded on the inner surface so as to cover at least a conduit leading to the degassing tube, and a moisture adsorbent loaded in the degassing tube. and a cooling means for cooling the degassing pipe.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The basic steps of the method of the present invention are as follows.

(1) Mixing powder or pellets of an oxidizing agent or oxidizing catalyst into a radioactive solid waste such as a hull so that it is substantially uniformly dispersed.

(2) Preliminary compression of the above mixture using a compression press;
The pre-compressed body contains an oxidizing agent or an oxidizing catalyst substantially uniformly dispersed therein.

(3) Store the pre-compressed body in a metal capsule.

(4) Weld the lid with the degassing pipe upright.

(5) Raise the temperature of the metal capsule.

(6) Degas the inside of the metal capsule through the degassing pipe.

(7) Seal the degassing pipe.

(8) Subject the metal capsule to HIP treatment.

FIG. 1 is a system diagram showing each step of the method of the present invention. First, radioactive solid waste 1 such as a hull cut into an appropriate length is mixed with powder or pellets 2 of an oxidizing agent or an oxidation catalyst. The mixture is uniformly mixed and loaded into a press molding machine 3, and compressed at a temperature around room temperature to form a pre-compressed body 4. Oxidizing agents include metal oxides that easily release oxygen, such as copper oxide and silver oxide.
In addition to metal peroxides such as Na ₂ O ₂ and PbO ₂ , oxyacid salts and the like can also be used, but copper oxide and silver oxide are particularly suitable.

When oxygen in the air is used as the oxidizing agent, an oxidizing catalyst such as platinum or palladium is dispersed and mixed in order to promote the oxidizing reaction with the aid of an oxidizing catalyst. Thus, the oxidizing agent or oxidizing catalyst is contained in a substantially uniformly dispersed state during precompression. The main purpose of such pre-compression is to improve the apparent density when later charging into the HIP equipment, and if the apparent density is low, it may cause damage to the metal capsule during densification in the HIP process. There is a risk of causing Therefore, in order to prevent this damage, the molded product is compressed in advance to have a density of 60% or more of the true density.

In addition, HIP compresses using a mechanical press using an incompressible fluid such as heat-resistant grease or molten glass, or a fluid powder such as BN powder, talc, graphite, pyroferrite, or molybdenum disulfide as a pressure medium.
In the case of methods, lower densities are sufficient.

Next, a plurality of pre-compressed bodies 4 formed into a disk shape by the compression press are housed in a metal capsule 5 made of a metal material.

In this case, the material used for the capsule is
A composite board such as a double pipe made of Cu or Al alone or a combination of stainless steel or plywood made by cladding them is used. In the case of a composite board, Cu, Al, etc. are placed on the inside of the capsule, and stainless steel is placed on the outside. Use it like this.

By doing so, tritium ^3H absorbed in the hull, etc. is prevented as much as possible from leaking out of the capsule during subsequent heat treatment, and it is also effective in preventing oxidation during heating and corrosion resistance during long-term storage. be. This is because Cu and Al are generally considered to be materials that are difficult for tritium to pass through, and stainless steel allows tritium to pass through to a large extent, but is resistant to oxidation and corrosion.

Next, a lid 7 with a degassing pipe 6 erected is welded to the metal capsule 5 in which the pre-compressed body 4 is housed, but care is taken during welding to prevent the heat from welding from activating the tritium absorbed by the hull etc. It is preferable that the welding point be located as far away from the hull, etc. as possible. In addition, considering the handling of the metal capsule, it is also a suitable means to weld a magnetic stainless steel plate to the lid to facilitate handling such as lifting and transportation using a magnet.

In this way, the pre-compression body 4 is stored inside and the degassing pipe 6 is opened.
The metal capsule 5 with the lid 7 erected thereon welded thereon is then subjected to a temperature raising treatment. That is, when the metal capsule 5 is heated and heated by the heating means 8 such as electric heating, in the case of a pre-compressed body mixed with an oxidation catalyst,
Tritium gas activated by heating and released from the hull etc. reacts with oxygen in the air inside the capsule under the action of a catalyst and is converted to water. If the amount of tritium gas is large, air necessary for oxidation is supplied from the degassing pipe 6.

In addition, in the case of a pre-compressed body mixed with an oxidizing agent,
Similarly, tritium gas generated by heating reacts with the oxidizing agent and becomes tritium water. In this case, the degassing can be carried out by connecting the degassing tube 6 to the vacuum device 9 and degassing.

In either case, it is important to heat the inside of the metal capsule 5 to a degree that does not reach a temperature higher than the boiling point of water; at high temperatures, the tritium water generated becomes steam and is discharged from the degassing pipe, causing secondary pollution. There is a risk that it may cause

After converting the tritium gas in the metal capsule into water as described above, the vacuum device 9 connected to the deaeration pipe 6 is operated to deaerate the inside of the metal capsule 5, and then the deaeration pipe is pressed or forged 10. and seal. The metal capsule sealed and degassed in this way is free from the risk of damage to the metal capsule due to an increase in internal pressure during heating during subsequent HIP treatment, and is also effective in preventing ignition of Zircaloy.

The sealed metal capsule 5 containing the pre-compressed body 4 is then subjected to HIP treatment. As mentioned above, during HIP treatment, it is necessary to raise the temperature to approximately 60% of the melting point temperature of the solid waste, for example, in the case of a hull made of Zircaloy, it is necessary to raise the temperature to approximately 900°C. At this time, the tritium water inside the capsule turns into water vapor, and pressure is generated inside the capsule.
However, in reality, the amount of tritiated water is extremely small and does not generate enough pressure to destroy the capsule.

For example, the capsule size after HIP treatment is φ300.
The calculation for the case of mm x 600Hmm is as follows.

Hull weight = π/4×30 ² ×60×65×10 ^-3 = 275Kg Amount of tritium in hull = 300~1000μCi/g* =0.3~1 Ci/Kg *Note: The Community's R&D Programme on Radioactive Waste Management
By and Storage.

Amount of tritium in the capsule = 8.25-275Ci Volume of tritium gas = 0.37Nc.c./Ci Amount of tritium gas in the capsule = 31-102Nc.c. Amount of tritium water in the capsule = 31-102/22400×18 = 0.02-0.08g 900℃ Gas volume inside the capsule = (31-102) x 273 + 900/273 + 25 = 122-400 c.c. (1 atm) = 3.6-12 c.c. (30 atm) = 1-3 c.c. (130 atm) In other words, tritium in the capsule water is only 1
~ Only 2 drops, HIP at the same time when heated to 900℃
Because external pressures of up to 1,000 atm are applied for processing, there is no concern that the capsules will break.
Further, when the temperature of the treated body decreases after the HIP treatment, the water vapor within the capsule condenses again and becomes water, which remains within the capsule.

HIP treatment uses a conventionally known HIP device to heat the solid waste to a temperature that causes plastic deformation, while maintaining the high pressure using inert gas as a pressure medium for 30 minutes or more. It can be compacted and densified into a compact with a density close to that of the compact.

On the other hand, such HIP processing is complicated from the viewpoint of introducing inert gas into the HIP device, the mechanism for discharging from the HIP device, safety due to compressible gas, and handling of installation and maintenance under the regulations of the High Pressure Gas Control Law. Furthermore, there are problems such as a long processing cycle time and low production efficiency due to the time required to raise the temperature and pressure, and it cannot necessarily be said to be an optimal method.
Therefore, recently, pressure media that do not rely on inert gas, such as BN powder, graphite, pyroferite, etc.
Talc, molybdenum disulfide, zirconium oxide,
Using a powder or granular material such as magnesium oxide powder or an incompressible fluid such as molten glass or heat-resistant grease, the compressor is embedded within a compression device consisting of a high-pressure cylinder and a reciprocating stem via the medium. A method of compressing metal capsules (hereinafter referred to as quasi-HIP processing) has been adopted. Semi-HIP treatment can also be advantageously applied to the method of the present invention,
The process will be explained with reference to FIG. 1. The sealed metal capsule is sent to a heating process and heated in an electric furnace or the like 11.

Heating is carried out to a temperature suitable for the subsequent semi-HIP process, which usually varies depending on the type of pressure medium used during the semi-HIP process, and is 2300°C or lower for BN powder, talc, pyroferite, zirconium oxide, magnesium oxide, etc. For molten salt, an appropriate temperature is selected, which is above the melting point of the salt, and for heat-resistant grease, below 1250°C.

After the heat treatment, the sealed metal capsule 12 is
It is sent to the HIP process and subjected to the required compression process.

In the semi-HIP process, a pressure medium 15 is filled into a compression device consisting of a high-pressure cylinder 13 and a reciprocating stem 14, the heated sealed capsule 12 is buried in the pressure medium, and the stem 14 is moved. This results in compression via the pressure medium.

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

(1) Can be used repeatedly.

That is, since pressure is applied through the capsule, the pressure medium will not be contaminated in the first place, but if the capsule is damaged or tritium permeates, the pressure medium may be contaminated. Therefore, in that case, repeated use is required to prevent generation of secondary waste.

(2) Must have insulation properties.

The pressure medium preferably has heat insulating properties so that the heat of the capsule does not transfer to the high-pressure cylinder and reduce the strength of the cylinder.

(3) Must have lubricity.

It is desirable that the cylinder has low frictional resistance when moving 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) Do not become a sintered body.

If it becomes a sintered body, its isotropic compressibility will be hindered.

(6) No decomposition occurs due to heat.

(7) Do not damage the inner wall of the cylinder.

Powders or pellets of BN, graphite, pyropherite, talc, molybdenum disulfide, etc. can be considered as materials that satisfy the above conditions, depending on the temperature during the treatment. In addition to molten salt, heat-resistant grease is one of the preferred pressure media when the processing temperature is low, but it has some drawbacks in terms of deterioration due to repeated use. However, heat-resistant grease is extremely practical in terms of fluidity, mold releasability, and cost.

The pressure exerted on the sealed capsule by using these pressure media is different from gas pressure, and it can fully handle up to 20,000 atmospheres, but considering the life of the compression equipment,
It is carried out at a pressure of 10,000 atmospheres or less, usually in the range of 1,000 to 10,000 atmospheres.

In this case, the high pressure holding time during semi-HIP treatment is generally relatively short after pressurization, and can take several minutes depending on the pressure medium, whereas conventional HIP treatment requires 30 minutes or more. About 1 minute is sufficient.

Through each of the above steps, the radioactive solid waste is densified and reduced in volume while the tritium is converted into tritium water and confined inside without being discharged, and a block body with strong binding strength is created. It can be compacted.

Note that if a heat insulating layer is provided on the inner wall of the high-pressure cylinder 13 or on the outer periphery of the sealed metal capsule 12, the retention time of the sealed capsule in the compression device can be extended, so when a pressure medium such as heat-resistant grease is used. It is suitable for

Further, each of the above steps is a basic processing step of the method of the present invention, but various modifications can be made within the scope of the present invention.

That is, instead of uniformly dispersing and mixing the oxidizing agent or oxidizing catalyst in the metal capsule, as shown in FIG. A conduit 1 that communicates the layer 16 made of solids to at least the degassing pipe 6
The same effect can be obtained by covering and mounting 7.

Furthermore, when using the method shown in the basic process and the apparatus shown in Figure 2, if the conditions are incorrect when heating or degassing the metal capsule containing the pre-compressed body, trace amounts of tritium gas or tritium water vapor may be emitted. It cannot be said that there is no risk of Therefore,
Preferred embodiments of the present invention for completely eliminating these risks will be described below.

FIG. 3 is a schematic explanatory diagram of an apparatus used in a preferred embodiment of the method of the present invention, in which a moisture adsorbent 18 is placed inside the degassing tube 6 of the apparatus shown in FIG. is filled. The adsorbent 18 functions to trap moisture generated in the subsequent heating step, and for example, molecular sieves are preferably used.

In addition, the tip portion of the deaeration pipe 6 is left without being filled with adsorbent in case it becomes clogged due to forging pressure or the like.
Further, a cooling means such as a cooling coil 19 is provided around the degassing tube 6, and a heating means such as an electric heater 20 is provided around the metal capsule 5.

The pre-compressed body is stored in such a device and heated by electric heat for 20 minutes.
When heated by applying electricity, the tritium gas released from the pre-compressed body forms a layer 16 of an oxidizing agent or an oxidizing catalyst.
It is led into the water and converted to water, and at the same time, it is vaporized by high temperature and becomes water vapor. The water vapor is further conducted into the degassing tube 6, reaches the cooling zone, condenses, becomes water again, and is captured by the adsorbent 18. Thereafter, the inside of the metal capsule 5 is degassed by the vacuum device 9 connected to the deaeration pipe 6, and the metal capsule 5 is sealed as described above.

According to this device, even if the generated tritiated water is vaporized due to high temperature or reduced pressure, it becomes recondensed water or mist and is completely collected by the adsorbent, so that leakage to the outside can be prevented.

FIG. 4 is a schematic explanatory diagram showing an improved version of the device shown in FIG.
A carrier gas introduction pipe 22 is provided which opens towards the front. In such a device, from the carrier gas introduction pipe 22, the inner space 21 of the metal capsule, the layer 16 made of an oxidizing agent or an oxidizing catalyst, etc.
A carrier gas flow path leading to the degassing pipe 6 is formed through the degassing tube 6.

The pre-compressed body is housed in the above-mentioned device in which the layer 16 is an oxidizing agent, and a carrier gas made of an inert gas such as helium is introduced while heating to guide the generated tritium gas to the oxidizing agent layer 16. Convert to
The tritium water vapor vaporized due to the high heat is further guided to the cooling area of the degassing pipe 6 and condensed, and the adsorbent 18
Capture with.

Further, when the layer 16 is an oxidation catalyst, by introducing air from the carrier gas introduction pipe 22, a sufficient amount of air can be supplied to completely oxidize the tritium gas.

If such a device is used, tritium gas will not remain in the precompression body, but will contact and react with the oxidizing agent or oxidation catalyst one after another, and the generated water will also be efficiently captured by the adsorbent.

FIGS. 5 and 6 are schematic explanatory diagrams showing improved versions of FIGS. 3 and 4, respectively.

In FIG. 5, an inverted cup-shaped copper or aluminum inner capsule 23 having an outer diameter and height smaller than the inner diameter and height of the metal capsule 5, respectively, is housed concentrically inside the metal capsule 5. , a mantle-shaped portion is formed between the metal capsule 5 and the inner capsule 23, and
The lower end of the inner capsule is separated from the bottom surface, or if they are in close contact with each other, a through hole provided near the lower end forms a flow path between the internal space 21 of the capsule and the mantle. be done. The mantle is also loaded with a layer of an oxidizing agent or an oxidizing catalyst. According to this device, since copper or aluminum, which is difficult for tritium gas to permeate, is used for the inner capsule, the tritium gas released from the hull etc. by heating is absorbed over the entire length of the oxidizer or oxidation catalyst layer loaded in the mantle. The tritium gas inside the capsule is completely converted to tritium water without remaining, and this is adsorbed, so no tritium leaks out of the capsule.

Fig. 6 shows a device shown in Fig. 5 in which a carrier gas introduction pipe 22 is further inserted into the degassing pipe, and its operation is similar to that shown in Fig. 4, but the effect is the same as that of the device shown in Fig. 5. Needless to say, it is much better than the one using .

The effects of the present invention detailed above are as follows.

(1) Tritium (tritium gas or tritium water) will not leak out of the capsule during volume reduction treatment (HIP treatment or semi-HIP treatment) of hulls, etc.

(2) Since tritium water remains in the capsule after treatment, there is no leakage to the outside due to permeation through the capsule wall.

(3) Nuclides other than tritium are also captured by the oxidizer and adsorbent, and do not leak out of the capsule. That is, since powder or a sintered body of powder is used as the oxidizing agent and adsorbent, it acts as a filter, and dusty radionuclides are collected. Furthermore, the nuclide that has become fume-like due to heating is cooled in the cooling zone and becomes dust-like, which is collected by an adsorbent. In other words, no secondary waste is generated.

(4) In the method of collecting and processing tritium outside the capsule, in order to store the collected tritium, separate immobilization processing is required, such as absorption into titanium etc., conversion to tritium water, and hardening with cement.
A processing body will be generated separately from the waste processing body such as the hull. In the present invention, since tritium is sealed in the same capsule as the waste to be treated, the number of solidified bodies to be treated is minimized.

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

Example 1 A Zircaloy short tube with an outer diameter of 12 mm, a thickness of 0.8 mm, and a length of 30 to 50 mm, which is a waste product obtained by shearing spent nuclear fuel cladding tubes in a power reactor, was uniformly stripped of copper oxide powder. While mixing the cloth, it was loaded into a mechanical press and compressed at a pressure of 35 t/cm ² to preform into a disk shape with a diameter of about 80 mm and a thickness of about 50 mm. The apparent density of this precompacted body was 3.2 g/cm ² and the tritium content was about 800 μCi/g, or 0.6 Ci per disk. Six such pre-compressed bodies were then made of stainless steel with a copper plate clad on the inside.
It was housed in a steel capsule with an inner diameter of 85 mm and a height of 310 mm, and a lid with a degassing tube was welded to it. After that, connect the degassing tube to a vacuum device, and while raising the temperature of the capsule to about 80°C, vacuum deaerate the inside of the capsule to 10 ^-1 torr through the degassing tube, and in this state, forge weld the degassing tube to remove the capsule. Sealed. During vacuum suction,
There was virtually no detectable emission of tritium gas into the vacuum system.

The thus formed sealed capsule container is
The sample was placed in a HIP apparatus, and HIP treatment was performed using argon gas as a pressure medium under the conditions of 900°C x 1000Kg/cm ² x 1Hr (maintenance time after temperature and pressure rise). As a result, although the sealed capsule container had a significant decrease in bulk compared to before HIP treatment, the capsule did not break and was a strong block with no voids, and its density was 5.2 g/cm ² . It showed a value close to the theoretical density.

Example 2 Same as Example 1 except that the copper oxide powder was not removed and mixed.
A disc-shaped pre-compressed body was made in the same manner. Three such pre-compressed bodies were housed in a metal capsule of the type shown in Figure 5 with an inner diameter of 85 mm and a height of 155 mm.
Welded a lid with a 75 mm degassing tube. The mantle formed between the aluminum inner capsule 23 and the stainless steel outer capsule 15 on the peripheral wall and top wall of the metal capsule is filled with silver oxide particles, and the interior of the degassing tube is filled with silver oxide particles. Molecular sieves were filled leaving 45 mm at the tip. A cooling coil was installed around the deaeration tube while the deaeration tube was connected to a vacuum device, and an electric heating device was further provided around the metal capsule container. The electric heating device was energized to heat the capsule container to approximately 500°C, and at the same time, the cooling coil cooled the deaeration tube, the vacuum device was activated to evacuate the inside of the container to 10 ^-1 torr, and in that state. The degassing tube was forged and the capsule was sealed. . During the vacuum degassing operation, virtually no leakage of tritium gas or tritium water vapor from the container was detected.

The thus formed sealed capsule container is embedded in heat-resistant grease filled in a compression device consisting of a high-pressure cylinder and a reciprocating stem, and further,
After heating to a temperature of 1200° C., semi-HIP treatment was performed at 5000 kg/cm ² ×1 min using this heat-resistant grease as a pressure medium. As a result, the sealed capsule container had a significant decrease in bulk compared to before semi-HIP treatment, and was a solid block with no voids, and its density had reached the theoretical density. Furthermore, no leakage of radioactivity outside the container was detected.

Example 3 The pre-compressed body obtained in Example 2 was housed in a metal capsule container of the type shown in FIG. 4 using a sintered plate of platinum and palladium particles as the layer 16,
Electricity was applied to the electric heating device to heat the capsule container to 500° C., and at the same time, air was introduced into the capsule through the carrier gas introduction pipe 22 while cooling the degassing pipe portion with the cooling coil. During this period, no tritium or tritium water vapor was detected from the degassing tube. After that, the carrier gas introduction pipe 22 is forged welded,
A vacuum device was connected to the degassing tube, and the vacuum device was activated to evacuate the inside of the container to a vacuum of 10 ^-1 torr, sealing the capsule, and carrying out preparations in exactly the same manner as in Example 2 above.
Perform HIP processing. A stable and strong hull block with a density extremely close to the true density was molded.
No radioactivity leakage from this block was detected.

The density of the dense block body obtained according to the present invention described above is almost the true density or close to the true density. Therefore, the volume of the original radioactive solid waste can be significantly reduced through pre-compression and HIP treatment or semi-HIP treatment, and it can be easily stored inside a drum can as a volume-reduced and solidified block body, or It can be stored stably without being stored. As a result, it is possible to use storage space more efficiently than with conventional storage methods, and radioactive waste can be stored 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 airtightly sealed container, there is no need to worry about the generation of secondary waste such as radioactive gas.

As described above, the present invention is extremely useful and significant from the viewpoint of the safety of radioactive waste, which will be necessary in the future as the use of nuclear energy increases.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing the steps in the method of the present invention, and FIGS. 2 to 6 are schematic diagrams showing different embodiments of the metal capsule used in the method of the present invention. 1... Radioactive solid waste, 2... Oxidizing agent or oxidation catalyst, 3... Press molded body, 4... Pre-compressed body, 5... Metal capsule, 6... Degassing tube, 7...
Lid, 8... Heating means, 9... Vacuum device, 11...
Electric furnace, 12... sealed metal capsule, 13... high pressure cylinder, 14... stem, 15... pressure medium, 16... layer of sintered body, 17... guide hole, 18...
... Moisture adsorbent, 9 ... Cooling coil, 20 ... Electric heating, 21 ... Internal space, 22 ... Carrier gas introduction pipe, 23 ... Inner capsule.

Claims (1)

[Scope of Claims] 1. A pre-compressed body formed by compressing radioactive solid waste using a compression press is housed in a metal capsule, degassed and sealed, and then subjected to hot isostatic pressing treatment to form a dense unit. In the method, the metal capsule is subjected to a temperature raising treatment prior to being degassed and sealed, and the tritium gas released from the pre-compressed body is treated as an oxidation catalyst by the action of an oxidizing agent disposed inside the metal capsule. A method for volume reduction and solidification of radioactive solid waste, which comprises converting it into water through oxidation with the aid of a metal capsule, and then deaerating and sealing a metal capsule with water trapped inside. 2. The method for volume reduction and solidification of radioactive solid waste according to claim 1, wherein the metal capsule is made of copper, aluminum, or a composite material of these and stainless steel. 3. The method for volume reduction and solidification of radioactive solid waste according to claim 1 or 2, wherein the oxidation is carried out by the action of an oxidizing agent consisting of copper oxide or silver oxide. 4. Claim 1, wherein the oxidation is carried out using oxygen in the air as an oxidizing agent and by the action of an oxidation catalyst.
The method for volume reduction and solidification of radioactive solid waste according to item 1 or 2. 5. The method for volume reduction and solidification of radioactive solid waste according to claim 4, wherein the oxidation catalyst is platinum or palladium powder or pellets. 6. The oxidizing agent or oxidizing catalyst is uniformly dispersed and mixed in radioactive solid waste, and then compressed using a compression press to form a pre-compressed body, thereby pre-compressing the oxidizing agent or oxidizing catalyst housed in a metal capsule. A method for volume reduction and solidification of radioactive solid waste according to any one of the preceding claims, wherein the radioactive solid waste is disposed in a uniformly dispersed state throughout the body. 7 Tritium gas released from the pre-compression body is guided into a layer made of an oxidizing agent or an oxidizing catalyst in a metal capsule to be converted into water, and the water vapor produced by vaporization due to temperature rise is further guided to a cooling area where it is condensed. 6. The method for volume reduction and solidification of radioactive solid waste according to any one of claims 1 to 5, wherein the solid waste is captured by an adsorbent, and then the metal capsule is degassed and sealed. 8. The method for volume reduction and solidification of radioactive solid waste according to claim 7, wherein the adsorbent is molecular sieves. 9. Inject carrier gas into the pre-compressed body within the metal capsule to guide tritium gas to the oxidizer layer;
A method for volume reduction and solidification of radioactive solid waste according to claim 7 or 8, further comprising introducing water vapor into a cooling region. 10. The method for volume reduction and solidification of radioactive solid waste according to claim 9, wherein the carrier gas is an inert gas. 11. Reducing radioactive solid waste as set forth in claim 7 or 8 by introducing air into the pre-compression body within the metal capsule to guide tritium gas to the oxidation catalyst layer and further lead water vapor to the cooling zone. Consolidation method. 12 A hot isostatic press device and a metal capsule that can be loaded into the device and is formed from a composite metal plate with an inner surface made of copper or aluminum and an outer surface made of stainless steel; A deaeration pipe protruding from the top of the metal capsule, a layer made of an oxidizing agent or an oxidation catalyst added to the inner surface of the metal capsule so as to cover at least the conduit leading to the deaeration pipe, and a moisture adsorbent loaded in the deaeration pipe. 1. An apparatus for use in a method for volume reduction and solidification of radioactive solid waste, characterized in that it comprises a heating means for heating a metal capsule, and a cooling means for cooling a degassing tube. 13 An inverted cup-shaped copper or aluminum inner side having an outer diameter and height smaller than the inner diameter and height of the metal capsule, and installed inside the metal capsule concentrically and forming a flow path at the lower end. 13. The device of claim 12, comprising a capsule and a layer of oxidizing agent or oxidizing catalyst loaded into a mantle formed between the metal capsule and the inner capsule. 14 The above-mentioned patent is provided with a carrier gas introduction pipe that opens toward the internal space of a metal capsule, and forms a carrier gas flow path that sequentially passes from the carrier gas introduction pipe to the metal capsule internal space, an oxidizing agent or an oxidizing catalyst layer, and then a degassing pipe. An apparatus according to claim 12 or 13. 15. The device according to any one of claims 12 to 14, wherein the layer consisting of an oxidizing agent or an oxidizing catalyst is a sintered body of powder or granules of a metal or metal oxide. 16. The device according to any one of claims 12 to 15, wherein the moisture adsorbent is a molecular sieve. 17. The device according to any one of claims 12 to 16, wherein the oxidizing agent is copper oxide or silver oxide. 18. The device according to any one of claims 12 to 16, wherein the oxidation catalyst is platinum or palladium.