JPH09281297A - Method for making organic matter accompanying radioactive metallic waste into inorganic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the org. matter accompanying radioacive metallic waste into inorg. with a simple method at a low cost and further to reduce the radioactive pollution of a treating equipment. SOLUTION: A radioactive metallic waste contg. a zircalloy is sealed into a capsule 4 in a vacuum vessel 1, the inside of the capsule 4 is made oxygen- deficient, the capsule 4 is introduced into the vacuum vessel 1, and the vessel 1 is closed. The vessel is evacuated by a evacuating device 8 and filler with an inert gas atmosphere from a gas feeder 7, the capsule 4 is heated, and the org. matter in the capsule 4 is decomposed and made into inorganic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mineralizing an organic substance that accompanies radioactive metal waste.

[0002]

2. Description of the Related Art Radioactive metal wastes from reprocessing plants include radioactive metal wastes such as zircaloyhal and the accompanying organic materials such as poly sheet, which are hydrogenated by radiolysis during storage or disposal. It is necessary to remove or detoxify the exposure to radionuclides that generate gas and increase the amount of radionuclides that migrate to the environment due to organic substances during hydrogen explosion and disposal.
Conventionally, as a method of treating radioactive metal waste, for example, in Japanese Patent Laid-Open No. 55-65817, a radioactive metal waste is thermally decomposed in a thermal decomposition furnace to form a decomposition residue, which is burned in a combustor to generate combustion exhaust gas. By incineration,
A method of reducing the volume is disclosed. Also, JP-A-63-2
Japanese Patent No. 8278 discloses a method of digesting radioactive solid waste with a mixed solution of sulfuric acid and nitric acid, which is acid digested in order to sufficiently contact the radioactive solid waste with a mixed solution of sulfuric acid and nitric acid. The inside of the tank is agitated. As the agitation method, the inside of the acid digestion tank is divided into two areas, and the gas generated by the reaction between sulfuric acid and nitric acid and the object to be treated is used as the agitation driving gas. The acid digestion solution is circulated and stirred.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
According to the method described in Japanese Patent No. 817, a large amount of combustion exhaust gas is generated, and it is very expensive to treat this exhaust gas, and fine can react with oxygen in the air and ignite when Zircaloyhal is heated. Therefore, there is a need for means to prevent this. In addition, JP-A-63-282
The method described in Japanese Patent No. 78 has a problem of treating secondary waste such as sludge generated by the digestion reaction. Further, after the treatment, it is necessary to sufficiently wash and remove the mixed liquid of sulfuric acid and nitric acid adhering to the zircaloy-hal, and measures for this need to be taken.

The present invention has been made in order to solve the conventional problems as described above, and provides a radioactive metal waste which can be processed at a low cost by a simple method and has less radioactive contamination of the processing equipment. The present invention provides a method of mineralizing accompanying organic matter.

[0005]

According to a first aspect of the present invention, the radioactive metal waste containing zircaloy is sealed in the capsule, the inside of the capsule is made oxygen-deficient, and the organic matter in the capsule is heated by heating the capsule. It is designed to be decomposed and mineralized.

According to the first aspect of the present invention, the radioactive metal waste sealed in the capsule is made harmless by heating so that the organic matter is made inorganic and the generated radioactive nuclides such as oxygen, nitrogen and carbon are stored in the capsule. Be trapped. Zircaloy itself becomes a getter, and most of hydrogen can be trapped in zirconium.

According to a second aspect of the present invention, the capsule is placed in a vacuum container, and the heating is performed in the vacuum container in a vacuum state or an inert gas atmosphere.

According to the second aspect of the present invention, the capsules are prevented from being oxidized during heating, and even if the capsules are damaged, the contents are prevented from coming into contact with oxygen to prevent the ignition of Halfine. It

According to the third aspect of the invention, the getter function is enhanced by adding a zirconium getter to the radioactive metal waste in the capsule.

According to the third aspect of the invention, the getter function for hydrogen, oxygen, nitrogen, etc. generated by thermal decomposition can be enhanced.

According to a fourth aspect of the present invention, before encapsulating the radioactive metal waste in capsules, the organic substances are roughly removed by floating sorting in advance.

According to the fourth aspect of the present invention, even if the amount of organic substances accompanying the hull or the like is large, it is possible to reduce the organic substances accompanying in the capsule by the floating sorting, and thus, the decomposition and mineralization of the organic substances by heating can be more reliably performed. Can be

According to a fifth aspect of the present invention, radioactive waste containing zircaloy is stored in a capsule and compressed, and the capsule compact is heated in a vacuum or an inert gas atmosphere, whereby the capsule compact in the capsule compact is heated. It is designed to decompose and mineralize organic substances.

In the invention of claim 5, the heating furnace may be a small one in order to heat the capsule after compressing the capsule containing waste to make it compact, and this heating is optional apart from the compression step. Can be done during the period.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a vacuum container 1 has an opening 20 formed in one side wall, and an opening / closing lid 2 for opening / closing the opening 20 is attached to the opening / closing lid 2. The opening / closing lid 2 can be operated remotely. It is configured to be opened and closed by an opening / closing means 21 composed of a cylinder, and in a closed state, it is sealed by a packing 22 so that the inside of the container becomes a closed space. A gas introduction pipe 51 and an exhaust pipe 52 are connected to the other side wall of the vacuum container 1, the other end of the gas introduction pipe 51 is connected to the inert gas supply device 7, and the other end of the exhaust pipe 52 is connected to the other end. It is connected to the vacuum exhaust device 8. Further, a thermometer 6 for measuring the temperature inside the container is attached to the upper wall of the vacuum container 1. Further, a large number of rollers 3 are lined up on the bottom wall of the vacuum container 1 so that a heavy object can be easily moved thereon, and the capsule 4 can be loaded and unloaded through the transfer means 30 outside the opening 20. It is easy to do. Further, an off-gas processing device (not shown) is connected to the vacuum container 1, and a filter is provided in the off-gas processing device so that the radioactive nuclide leaked into the off-gas is collected by the filter.

The inert gas supply device 7 is provided with a heating means (not shown) so that the heated inert gas is supplied into the vacuum container 1 through the gas introduction pipe 51.
Further, the heating of the inside of the vacuum container 1 may be performed by an electric heater or induction heating means provided, or the heated inert gas and heating by an electric heater may be used together. Since heating with this inert gas is less likely to cause an electric system failure than when an electric heater is used, it can be expected to reduce the frequency of maintenance. However, since the inert gas contaminated with radioactivity cannot be discharged as it is, it is necessary to remove the contamination through a filter or the like.

Next, the processing method of the present invention will be described with reference to the flowchart of FIG. First, in the outside of the vacuum container 1, the capsule 4 is filled with radioactive metal waste, which is an object to be processed (step S1). At this time, a zirconium getter material may be inserted into the capsule 4 to enhance the getter function. Further, before or after the zircaloy is filled in the capsule, the zircaloy is dried to remove the water adhering to the hull. After degassing the inside of the capsule 4 filled with the hull under vacuum, the lid is covered and sealed by welding (step S2). As a result, the inside of the capsule 4 is made oxygen-deficient to prevent the hull and the like in the capsule 4 from being oxidized during heating, and also to prevent the ignition of hull fine.

Next, after the opening / closing lid 2 of the vacuum container 1 is opened and the capsule 4 is loaded into the vacuum container 1, the opening / closing lid 2 is closed to make the inside of the vacuum container 1 an inert gas atmosphere or a vacuum state and oxygen. A deficiency state is set (step S3). That is, the gas in the vacuum container 1 is discharged through the exhaust pipe 52 by the vacuum exhaust device 8 to make the inside of the vacuum container 1 in a vacuum state, or thereafter, the inert gas is supplied through the gas introduction pipe 51 by the inert gas supply device 7. By introducing into the vacuum container 1, the inside is made into an inert gas atmosphere. This prevents the stainless steel or copper capsules 4 from oxidizing during heating, and prevents the contents from coming into contact with oxygen even if the capsules 4 are damaged, preventing the ignition of Halfine. To be done.

Then, the capsule 4 is heated to decompose and mineralize the organic substance inside (step S4). The heating at this time may be carried out by heating the inert gas to be introduced so that the inside of the container becomes an inert gas atmosphere, or the vacuum container 1 is provided with another heating means. In advance, it may be heated by the heating means. The heating temperature is lower than the melting points of the contents such as zircaloy hull and hardware and the capsule.

Next, the capsule 4 is cooled by stopping the heating and leaving it to be cooled to a certain temperature, and then the capsule 4 is taken out from the vacuum container 1 (step S5).
Each element decomposed by the above-mentioned heating is confined in the capsule and is dissolved in zircaloyhal as a solid solution or is trapped as a compound. Next, the capsule 4 is compressed by a known compression device to reduce its volume (step S6).

In the above operation, among various gases generated by thermal decomposition, most of hydrogen, which has a risk of gas explosion, is occluded and fixed in Zircaloy which occupies most of metal waste. Oxygen and nitrogen also easily form a solid solution with Zircaloy or form a compound with Zircaloy, and Zircaloy itself serves as a getter, and many of these elements can be confined in Zircaloy hull. Residues that were not trapped in Zircaloy are also mineralized and trapped in capsules. As a result, the organic substances in the capsule 4 are made inorganic and harmless.

In addition to the above method, radioactive waste containing zircaloy is stored in a capsule 4 and compressed in advance, and the compressed capsule body is heated in a vacuum or an inert gas atmosphere to compress the capsule. The organic substances in the body may be decomposed and made inorganic. As the capsule 4, stainless steel or copper having excellent ductility is used, but minute cracks may occur during compression. In the case where such cracks occur, an offgas treatment device is provided in a heating furnace or the like, and even if a small amount of radionuclide leaks out of the capsule, it is collected by a filter of the offgas treatment device. Also, after inserting an appropriate number of capsules compacted by compression into a new capsule, deaeration and encapsulation, heating using a heating device as shown in FIG. 1, decomposition, and mineralization Good.

As described above, if the capsule containing the waste is compressed and compacted and then heat-treated, the heating furnace may be of a small size, and this heating may be separated from the compression step. It can be done at the right time.

Zircaloy is an extremely active element and has a strong binding property with each element constituting an organic substance. The bondability with each element is as follows.

Relationship between Zircaloy and Hydrogen Zircaloy is 100 to 200 pp during use in a nuclear reactor.
m of hydrogen is absorbed, and these hydrogens hardly form a solid solution in Zircaloy at room temperature, form a hydride, and are dispersed and precipitated in Zircaloy.

Therefore, most of the hydrogen generated by the decomposition of organic substances by heating at high temperature is dispersed and precipitated in zircaloy as a hydride at room temperature. Although some of the hydrogen released by high temperature heating escapes to the outside of the capsule container, the hydrogen accumulated in the capsule container is trapped in the zircaloy as a hydride again during cooling.

Relationship between Zircaloy and Oxygen The bond between zircaloy and oxygen is strong, and according to the binary phase diagram of zirconium and oxygen, oxygen is about 6.5 at room temperature.
% Dissolved in zirconium. Therefore, the oxygen generated by the decomposition of the organic matter is consumed for forming the oxide film or is solid-dissolved in Zircaloy. In addition to this, it is partially confined in the form of carbon monoxide or carbon dioxide.

Relationship between Zircaloy and Carbon The bond between zircaloy and carbon is strong, and according to the binary phase diagram of zirconium and carbon, it is solid-dissolved in zirconium up to about 7.5% at room temperature. It is considered that the carbon generated by the decomposition of organic matter is trapped in the capsule in the form of carbon monoxide or carbon dioxide as it is, but it partially forms carbide with zirconium and is trapped by Zircaloy. it is conceivable that.

Relationship between Zircaloy and Nitrogen Zircaloy has a strong bonding property with nitrogen, and it dissolves in zirconium up to about 4.2% at room temperature. Therefore, it is considered that most of the nitrogen generated by the decomposition of the organic substance exists as a solid solution in zircaloy or forms a nitride.

[0030]

According to the first aspect of the present invention, the radioactive metal waste sealed in the capsule is made harmless by heating so that the organic matter is made inorganic and the generated radioactive nuclides such as hydrogen, oxygen, nitrogen and carbon are generated. Is trapped in a capsule. Then, Zircaloy itself becomes a getter, and it can be expected that many of these elements are confined in Zircaloy.

According to the second aspect of the invention, since the capsules are treated in a non-oxidizing atmosphere, oxidation of the capsules during heating is prevented, and even if the capsules are damaged, the contents contact oxygen. Doing so will prevent Halfine from catching fire.

According to the third aspect of the invention, the getter function for hydrogen, oxygen, nitrogen, carbon, etc. generated by thermal decomposition can be enhanced.

According to the invention of claim 4, even if a large amount of organic matter is associated with the hull and the like, it is possible to reduce the organic matter associated with the capsule by the floating sorting, thereby more reliably decomposing and mineralizing the organic matter by heating. Can be

In the invention of claim 5, the heating furnace may be of a small size in order to heat the capsule after the capsule containing the waste is compressed and compacted, and the heating may be separated from the compression step. Can be done during the period.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view showing an example of an apparatus for carrying out the present invention.

FIG. 2 is a flow chart showing the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Opening / closing lid 3 Roller 4 Capsule 7 Gas supply device 8 Vacuum exhaust device 51 Gas introduction pipe 52 Exhaust pipe

Claims (5)

[Claims] 1. A radioactive radioactive waste characterized in that a radioactive metal waste containing zircaloy is sealed in the capsule, the inside of the capsule is made oxygen-deficient, and the organic matter in the capsule is decomposed and made inorganic by heating the capsule. A method for mineralizing organic substances accompanying metal waste. 2. The radioactive metal waste according to claim 1, wherein the capsule is placed in a vacuum container, and the heating is carried out in a vacuum state or in an inert gas atmosphere. Method of mineralizing organic matter. 3. The method for mineralizing an organic substance accompanying a radioactive metal waste according to claim 1, wherein a getter function is enhanced by adding a zirconium getter to the radioactive metal waste in the capsule. . 4. The radioactive metal waste according to any one of claims 1 to 3, wherein organic substances are roughly removed in advance by floating sorting before encapsulating the radioactive metal waste in a capsule. A method for mineralizing an organic substance. 5. A radioactive waste containing zircaloy is stored in a capsule and compressed, and the compressed capsule is heated in a vacuum or an inert gas atmosphere to decompose the organic matter in the compressed capsule to obtain an inorganic substance. A method for mineralizing an organic substance associated with a radioactive metal waste, which comprises: