JPH0648316B2 - Treatment method of radioactive waste liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention heat-treats various radioactive liquid wastes generated from a reprocessing plant, a nuclear power plant, etc., and decomposes and vaporizes sodium compounds contained therein. The present invention relates to a method for treating radioactive waste liquid, which can achieve a large volume reduction of the final disposal body by removing it.

[Prior art] Sodium nitrate from nuclear reactors and various nuclear facilities,
A large amount of radioactive waste liquid containing sodium compounds such as sodium sulfate and sodium hydroxide is generated.

For example, a reprocessing plant produces high-level waste liquid and medium- and low-level waste liquid. The high-level waste liquid mainly consists of a large amount of sodium nitrate and a small amount of fission products, and in general, a treatment method is adopted in which a large amount of glass forming material is added and melted and solidified to form a vitrified body. The medium-to-low level waste liquid mainly consists of sodium nitrate and a trace amount of fission products, and is treated by mixing and heating with asphalt or plastic to form an asphalt solidified product or a plastic solidified product.

Furthermore, sodium hydroxide is contained in the radioactive waste liquid obtained by cleaning sodium and corrosion products attached to the spent fuel generated from the fast reactor. After this type of waste liquid is evaporated and dried, a glass forming material is added and the mixture is melted and solidified into a vitrified body.

[Problems to be Solved by the Invention] There is a limit to the amount of sodium that can be contained in glass in order to produce a vitrified body having good properties. In order to make a high-level waste liquid into a good vitrified body, a large amount of glass forming material must be added, and the amount of waste generated becomes very large. In addition, when treating middle- and low-level waste liquid, if sodium nitrate, sodium sulfate, etc. are mixed and heated with asphalt, plastics, etc., there is a risk of fire, explosion, etc.

In any case, a large amount of various forming materials was required due to the sodium compound present in the waste liquid, and there was a big drawback that the volume of the final disposal body remarkably increased.

Further, if the high-level waste liquid is vitrified, it is difficult to separate and collect useful elements contained in the waste liquid.

The object of the present invention is to eliminate the drawbacks of the prior art as described above, decompose and vaporize and remove the sodium compound in the waste liquid by a reliable and simple process of continuously heating the radioactive waste liquid, and remove the volume of the final disposal body. It is an object of the present invention to provide a method for treating radioactive waste that can significantly reduce the treatment cost and the disposal cost.

[Means for Solving Problems] In the present invention capable of achieving the above-mentioned object, the radioactive waste liquid containing a sodium compound is heated and evaporated to a dry body, and the sodium contained therein is further heated. It is a method for treating radioactive waste liquid, which is configured to decompose and vaporize a compound to separate and remove it to obtain a radioactive solid residue.

INDUSTRIAL APPLICABILITY The present invention can be applied not only to the treatment of high-level waste liquid, but also to the treatment of waste liquid containing various sodium compounds such as the treatment of medium-low level waste liquid.

[Operation] When radioactive waste liquid is heated, its liquid component evaporates and becomes a dried body. Then, by continuing heating further, various sodium compounds contained therein are decomposed and vaporized, separated and removed, and a radioactive solid residue remains. This will significantly reduce the amount of radioactive waste to be treated.

For example, in the case of high-level liquid waste, the radioactive solid residue is mainly composed of fission products, actinides, corrosion products, etc., and is mainly in an oxide state, so that it does not need to be vitrified. Therefore, the useful element can be easily recovered, and as it is, it can be temporarily stored for recovering the useful element in the future.

In addition, it is possible to work safely when solidifying asphalt or plastic in the case of medium- and low-level waste liquid.

[Embodiment] FIG. 1 is an explanatory view showing the simplest apparatus configuration for carrying out the method of the present invention. Resonance type microwave heater body 1
A crucible 14 for accommodating the radioactive waste liquid 12 is attached to the lower part of 0 by means of a flange 16. Radioactive waste liquid 12
Should be filled in advance before attaching the crucible 14, or
Alternatively, it is supplied continuously or batchwise from the upper injection pipe 18.

The microwave used for heating is supplied from the microwave waveguide attachment port 20 and resonates with the resonance type microwave heater to intensively heat the radioactive waste liquid 12. As a result, the liquid component evaporates and becomes a dried body. If microwave heating is further continued, the sodium compounds contained in the waste liquid will decompose and
It is vaporized and sent to the off-gas processing system through the exhaust port 22. In this way, the radioactive fixed residue 24 that is not decomposed and vaporized by microwave heating remains at the bottom of the crucible 14.

The radioactive solid residue 24 is a substance mainly composed of a high-boiling point component, and its volume is greatly reduced because the sodium compound is removed.

For example, the amount of sodium oxide in the solid content contained in the high-level waste liquid is about 40%. Therefore, if the sodium content is removed as described above, the amount of radioactive solid waste resulting from the high level waste liquid is reduced to about 60%. Further, conventionally, when the high-level waste liquid is vitrified, the high-level waste liquid has a solid content of about 25% (including sodium oxide) and the glass forming material is about 75%. The reason why there are many glass forming materials here is to make sodium into stable glass. Therefore, if sodium can be removed from the high-level waste liquid as in the present invention, the radioactive solid residue is mainly in the form of oxide, and it is not necessary to vitrify the sodium in order to solidify it stably. A large volume reduction (about 1/7) can be expected.

As described above, the radioactive solid residue obtained by the method of the present invention can be disposed of as it is or after being subjected to stabilization treatment such as removal treatment of heat generated, or conventionally, to recover useful elements. Also suitable for primary storage.

According to the result of the heating experiment using the highly radioactive simulated waste liquid, when the simulated waste liquid 1 containing the solid content of 76.54 g / was heated with the microwave of 2 kW for 1 hour, about 21 g of the heating residue could be obtained. . This indicates that the sodium compound and various simulated radioactive substances having a low boiling point were removed, which shows that the method of the present invention is effective.

Low-boiling radioactive nuclides (eg, cesium) that vaporize by heating are collected in an off-gas treatment system and separately treated.

FIG. 2 is an explanatory view showing another processing apparatus suitable for carrying out the method of the present invention. The radioactive waste liquid 30 containing sodium nitrate is stored in a storage tank 32 and supplied to a screw feeder type microwave denitration device 34 via an injection pipe 36. The supplied radioactive waste liquid 30 is heated by the microwaves entering from the microwave waveguide 38 and becomes a denitration body. That is, by heating, sodium nitrate decomposes at 380 ° C. and releases oxygen to become sodium nitrite, and when heating is continued, it becomes sodium peroxide at 750 ° C. or higher and then sodium oxide. The object to be heated is transferred while being stirred and mixed by the screw 40. The exhaust gas generated by decomposition is discharged from the exhaust port 42 and sent to the off-gas processing system.

The object to be heated containing sodium peroxide or sodium oxide is extracted from the denitration body extraction port 44 and sent to the sodium oxide decomposition device 46. The sodium oxide decomposing device 46 is composed of a resonance type microwave heater and is provided with a flange 5
The crucible 50 is attached to the lower part by the structure 2. The microwave energy used for decomposition is supplied from the microwave waveguide attachment port 54 to heat the object to be heated containing sodium oxide, sodium peroxide and sodium. For example, sodium oxide is decomposed into sodium peroxide at 400 ° C. or higher, and sodium vaporizes at a boiling point of 877.5 ° C. and a heat of vaporization of 1100 cal / g. The radioactive solid residue 58 remains in the crucible 50. The vaporized substance is discharged through the exhaust port 60 and processed by an external off-gas processing system.

Although the preferred embodiments of the present invention have been described above in detail, it goes without saying that the present invention is not limited to such a configuration. The heating method is not particularly limited. However, if heating is performed using microwaves as in this embodiment,
Since the sodium compound is heated from the inside, a layer of the sodium compound is formed on the inner surface of the crucible, which serves as a heat retaining function, can easily decompose and vaporize, and does not cause a problem of heat resistance of the crucible. There are advantages.

The solidified substances contained in the medium- and low-level waste liquids contain more salt than radioactive substances. For this reason, in the prior art, a solidified body was prepared by mixing with asphalt having a salt content of 4 to 5 times. However, since the salt can be removed by the process of the present invention, the amount of the asphalt solidified product is significantly reduced.

The present invention is sufficiently applicable not only to the treatment of waste liquid containing sodium nitrate, but also to the treatment of waste liquid containing sodium sulfate, sodium hydroxide or the like.

Further, in order to allow the radioactive substance contained in the waste liquid to remain as a radioactive solid as much as possible, it is also effective to add a substance such as iron hydroxide or iron oxide capable of binding and adsorbing a radionuclide to the treatment.

EFFECTS OF THE INVENTION The present invention is a treatment method for decomposing and removing a sodium compound by heating to obtain a radioactive solid residue as described above,
There is an excellent effect that the solid waste generation amount can be greatly reduced only by a reliable and simple process of heating.

For example, when a high level waste liquid is treated by the method of the present invention,
The residue from which sodium has been removed mainly becomes an oxide and does not have to be vitrified, so that the amount of waste generated is further reduced, and the useful element contained can be easily recovered from the residue.

In addition, even when various forming materials are added and solidified, the amount of the forming materials mixed can be reduced because the sodium content is removed by the present invention, and the volume of the final waste can be greatly reduced as a whole.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a heat treatment apparatus for carrying out the method of the present invention, and FIG. 2 is an explanatory view showing another processing apparatus for carrying out the method of the present invention. 10 ... Resonance type microwave heater main body, 12 ... Radioactive waste liquid, 14 ... Crucible, 16 ... Flange, 18 ... Injection tube, 20 ... Microwave waveguide mounting port, 22 ...
Exhaust port, 24 ... Radioactive solid residue.

Claims (1)

[Claims] 1. A radioactive waste liquid containing a sodium compound is heated and evaporated to form a dried body, and further heating is continued to decompose and vaporize the contained sodium compound to separate and remove to obtain a radioactive solid residue. Radioactive waste liquid treatment method.