JPH10206594A - Method and device for disposing of radioactive waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the corrosion of a heating furnace and improve the recovery of radioactive substances by heating a radioactive waste containing volatile radioactive substances under a reduced pressure, condensing the radioactive substances after vaporizing and separating them and then recovering them in a liquid or solid state. SOLUTION: A waste 2 is loaded into a heating container 1, which is sealed up, a valve 8 is opened, a vacuum pump 10 is actuated and the pressure inside the heating container 1, a condensation pipe 4 and a recovery container 7 is reduced to a set degree of a vacuum with attention paid to a vacuum pressure gauge 9. Then, heaters 3 and 5 are heated up to prescribed temperatures respectively. In case of the recovery of only cesium from the waste 2 contaminated by radioactive cesium, for example, the temperature of the heaters 3 and 5 are set at about 900 deg.C and about 700 deg.C respectively of the set degree of a vacuum is about 10 Torr. Such decompression can reduce the vaporizing temperature of radioactive substances from the waste 2 and can also accelerate the vaporization of the radioactive substances which have permeated inside microprobes of the waste 2. Therefore, it is possible to reduce the corrosion of a heating furnace and improve a decontamination factor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating radioactive waste generated from nuclear facilities (power plants and reprocessing plants), and more particularly to a method for treating radioactive waste containing volatile radioactive substances. The present invention relates to a method and an apparatus for separating and collecting and solidifying a substance.

[0002]

2. Description of the Related Art Conventionally, solidification of low-level radioactive waste such as chemical waste liquid generated from a nuclear power plant has been proposed.
Generally, a cement-based solidifying material is used. on the other hand,
Regarding wastes with high radioactivity level generated from reprocessing plants, application of solidified materials more dense than cement such as glass is studied from the viewpoint of reducing leakage of radionuclides.

A method for stably solidifying radioactive waste containing a volatile radioactive substance typified by iodine is disclosed in Japanese Patent Application Laid-Open No. 8-75898.
A method of vitrifying at a temperature at which iodine does not volatilize using low-temperature molten glass made of phosphorus or the like is disclosed.

The applicant has also developed a method of separating and recovering radioactive iodine from radioactive waste containing radioactive iodine, and vitrifying only the recovered iodine at a temperature at which iodine does not evaporate.

[0005]

Among the above prior arts, the solidification method using a low-temperature molten glass made of vanadium, phosphorus or the like has no problem of iodine volatilization, but solidifies waste as it is without separating radioactive substances. There was a limit in volume reduction. In addition, since the solidified body is a non-homogeneous body, there is a problem that cracks may occur when the solidified body is cooled.

[0006] In the above prior art, radioactive iodine is separated and recovered from radioactive waste containing radioactive iodine.
In the method of glass solidification, volatilization of iodine at the time of solidification is prevented, and a solidified body having excellent volume reduction and uniformity of the solidified body can be produced. However, this prior art discloses a method of heating radioactive waste to vaporize radioactive iodine and then condensing to recover radioactive iodine.However, since the processing temperature is high, corrosion of a heating furnace, There is a problem that the recovery rate decreases due to thermal denaturation.

SUMMARY OF THE INVENTION The present invention has been made in view of the conventional problems. In a method of heating radioactive waste containing volatile radioactive material to vaporize and separate the radioactive material, the heating temperature is reduced. It is another object of the present invention to provide a method for treating radioactive waste in order to reduce the corrosion of a heating furnace and improve the recovery rate of radioactive materials.

Another object of the present invention is to provide a method for treating radioactive waste which achieves the first object and further reduces the cost and size of the treatment apparatus.

Further, the present invention provides a method for treating a radioactive waste which is suitable for heating a radioactive waste containing a volatile radioactive substance at a lower temperature to vaporize the radioactive substance and to separate and recover the radioactive waste in a high yield. It is intended to provide a device.

Another object of the present invention is to provide a radioactive waste treatment apparatus which achieves the above third object and is suitable for facilitating the recovery of separated radioactive materials.

Another object of the present invention is to provide a radioactive waste treatment apparatus which achieves the third and fourth objects and is suitable for facilitating the handling of recovered radioactive materials. .

[0012]

According to the first aspect of the present invention, a radioactive waste containing a volatile radioactive substance is heated under reduced pressure to vaporize the radioactive substance. The method is a method for treating radioactive waste in which the radioactive waste is separated from the radioactive waste and the vaporized radioactive substance is condensed and recovered as a liquid or a solid.

In the present invention, heating under reduced pressure has the following two effects.

[0014] The boiling point of the substance to be recovered can be lowered. For example, when evaporating and recovering radioactive iodine (existing in the form of silver iodide) from a silver-adsorbed adsorbent that has adsorbed radioactive iodine, the boiling point of silver iodide is 1506 ° C. under atmospheric pressure, whereas 1 Torr About 830 ° C under vacuum
Can be lowered.

When cesium halide is recovered by evaporation from waste contaminated with radioactive cesium (existing in the form of cesium halide), the boiling point of cesium halide is 1250 to 1300 ° C. under atmospheric pressure. On the other hand, the temperature can be lowered to about 750 ° C. in a state of a vacuum of 1 Torr.

In the case of zinc, the boiling point is 90 at atmospheric pressure.
While the temperature is 7 ° C., the temperature can be reduced to about 500 ° C. in a state of a vacuum of 1 Torr.

Therefore, it is possible to lower the processing temperature for obtaining the same evaporation efficiency as in the case of performing the heat treatment in the atmosphere.

In addition to the above effects, by heating under reduced pressure, it is possible to forcibly extract the radioactive material that has entered the gaps and micropores in the radioactive waste into the gas phase, so that the recovery rate of the radioactive material is reduced. Improve dramatically. Thereby, the decontamination coefficient of the radioactive substance is improved.

Further, in the present invention, a radioactive waste containing a volatile radioactive substance is heated under reduced pressure to vaporize the radioactive substance and separate it from the radioactive waste,
By condensing the vaporized radioactive material and removing the radioactive material vapor from the gas phase, the difference in vapor pressure of the radioactive material between the heating part and the condensation part can be created naturally, and the steam is automatically transferred from the heating part to the condensation part. Is obtained. Thus, the radioactive substance can be statically transferred from the waste to the condensing section without performing a mechanical blower operation.

According to a second aspect of the present invention, there is provided a radioactive waste containing a volatile radioactive substance, and the radioactive waste is alloyed, vitrified or combined with the radioactive substance to lower the melting point. A radioactive waste in which a substance (second substance) is heated under reduced pressure to vaporize the radioactive substance and the second substance at the same time, and to condense a mixture of the radioactive substance and the second substance to recover a liquid or a solid. It is a method of treating objects.

In the present invention, the second substance has an action of alloying, vitrifying or combining with the radioactive substance to be recovered to lower the melting point. When the object to be recovered is recovered as a liquid in the condensing section, the temperature of the condensing surface can be lowered by lowering the melting point by the action. This eliminates the need for a heating device for the condensing section and increases the temperature difference between the heating section and the condensing section, so that the vapor pressure difference between the heating surface and the condensing surface can be increased, and the recovery efficiency can be increased.

Finally, when the recovered radioactive substance is vitrified, the second substance in the present invention can be recovered as a glass melt in the condensing section by using a substance which is mixed with the radioactive substance and vitrified. A vitrified body can be formed by cooling and solidifying the melt. Therefore,
Separation and recovery of radioactive material and vitrification can be performed by the same apparatus.

According to a third aspect of the present invention, to achieve the third object, a loadable radioactive waste containing a volatile radioactive substance is provided, and a sealable unit having a heating unit for vaporizing the radioactive substance is provided. A container, a condensing unit connected to the heating unit and maintained at a lower temperature than the heating unit, and a collection container for separating the radioactive substance from the condensing unit in a liquid state and connected to the condensing unit in a separable manner. And a decompression means for depressurizing the inside of the container, the condensing section and the collection container.

According to the present invention, only volatile radioactive substances can be separated and recovered from waste with a static device having no moving parts.

According to a fourth aspect of the present invention, in order to achieve the fourth object, in the condensing section according to the third aspect,
A radioactive waste or a radioactive waste treatment apparatus which is maintained at a temperature equal to or higher than the melting point or fluidization temperature of a mixture of a radioactive substance or a substance which alloys, vitrifies or combines to lower the melting point and the radioactive substance, and I have.

According to the present invention, since the radioactive substance recovered in the condensing section is prevented from adhering in a solid state, the recovery rate can be increased.

According to a fifth aspect of the present invention, in order to achieve the fifth object, in the condensing section according to the fourth aspect,
It is an inclined tube or a trumpet tube, and is characterized by being a radioactive waste treatment device provided with a trap for collecting condensed liquid.

According to the present invention, it is possible to collect the condensed liquid radioactive material at one place, so that the handling of the collected material becomes easy.

The volatile radioactive substances referred to in the present invention include iodine, ruthenium, cesium, zinc, uranium, plutonium, iron, cobalt, nickel and compounds of these elements.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) An embodiment of the present invention will be described below. This embodiment relates to a method and an apparatus for separating and recovering radioactive iodine from a waste adsorbent after being used in an iodine filter.

FIG. 1 shows a configuration diagram of a recovery apparatus suitable for carrying out the present invention. This apparatus controls a heating vessel 1 for loading the waste 2 to be treated, a heater 3 for heating the loaded waste 2, a condensation pipe 4 directly connected to the heating vessel 1, and a temperature of a pipe wall of the condensation pipe 4. A flexible joint 6 for relieving the thermal stress of the heating vessel 1 and the condensation pipe 4, a recovery vessel 7 and a valve 8 directly connected to the condensation pipe 4, a vacuum pressure gauge 9, and a vacuum pump 10. .

The heating container 1 has a structure that can be opened and closed for loading and unloading the waste 2, and the airtightness can be maintained through an O-ring or a gasket at the joint. The collection container 7 also has a detachable structure, and can be kept airtight at the mating portion via an O-ring or a gasket. In order to collect the collected material in the collecting container 7, the collecting container 7 is arranged lower than the heating container 1, and the condenser tube 4 is inclined. The treatment operation is as follows. After the waste 2 (waste adsorbent) is loaded in the heating vessel 1 and sealed, the valve 8 is opened, the vacuum pump 10 is started, and the heating vessel 1 4. The pressure inside the collection container 7 is reduced to a set vacuum degree. Next, the heaters 3 and 5 are each heated to a predetermined temperature.

The test results of a simulated waste in which stable iodine was adsorbed on a silica gel adsorbent impregnated with silver are shown below.
In this case, the iodine in waste 2 was present in the form of silver iodide and was separated from the simulated waste in the form of silver iodide.
The set vacuum pressure was 1 Torr, the temperature of the heater 3 serving as the heating unit was set to 800 ° C., and the temperature of the heater 5 serving as the condensing unit was set to 560 ° C. higher than the melting point of silver iodide, 552 ° C. The mole fraction of silver iodide vapor under these conditions was equivalent to 1400 ° C. under atmospheric pressure conditions, and the heating section temperature could be greatly reduced by reducing the pressure. In the condenser tube 4, the vaporized silver iodide vapor is condensed. However, since the vapor was set at a temperature equal to or higher than the melting point, no solid precipitate was observed, and the vapor was recovered in the recovery container 7. The iodine concentration in the adsorbent after the treatment was measured, and the decontamination coefficient was determined by taking the ratio with the iodine concentration before the treatment. As a result, the decontamination coefficient was about 10 times lower than when heated at 1200 ° C. for 1 hour under atmospheric conditions. Doubled.

When only cesium is recovered from waste contaminated with radioactive cesium (cesium halide), when the set vacuum degree is 10 Torr, the temperature of the heater 3 as a heating unit is set to 900 ° C. A certain heater 5
Is set to 700 ° C., which is higher than the melting point of cesium halide.

According to the present embodiment, the effect of reducing the heating temperature when evaporating and recovering radioactive substances from the waste 2 can be obtained. Further, since the transition of the radioactive substance permeating into the micropores of the waste 2 (waste adsorbent) into the gas phase can be accelerated by reducing the pressure, the radioactive waste 2 (waste adsorbent) can be accelerated. ) Can be improved.

(Embodiment 2) Another embodiment of the present invention will be described with reference to FIG. The present embodiment relates to a processing apparatus in which a part of the heating vessel 11 is used as a condensing unit 13 for air cooling.

The upper portion of the heating vessel 11 is maintained by a heater 12 at a temperature at which the material to be recovered is vaporized. On the other hand, the lower part is provided with a condensing part 13 that is naturally air-cooled in a trumpet shape and a detachable collection container 14 that is directly connected to the condensing part 13. The heating vessel 11 has a basket 15 for supporting the waste 2 to be treated, and the waste 2 is loaded therein. Heating vessel 1
1, the condensing unit 13 and the collecting container 14 are structured to maintain airtightness, and the inside of the heating container 11, the condensing unit 13 and the collecting container 14 can be evacuated to a predetermined degree of vacuum by the vacuum pump 16. . When the waste loaded in the basket is heated under reduced pressure, a vapor of volatile radioactive material is generated from the waste and moves downward through the basket according to the difference between gravity and vapor pressure. The vapor of the radioactive substance is cooled and condensed on the inner wall of the condensing part 13 to be in a liquid state, and the liquid also moves downward according to the gravity, and finally the recovery container 1
4 and further cooled to a solid state. After the processing, the recovery container 14 is detached from the heating container 11 and the lid is welded and stored.

According to this embodiment, it is not necessary to adjust the temperature of the condensing section, a simple apparatus configuration can be realized, and the apparatus can be reduced in size and cost.

(Embodiment 3) Another embodiment of the present invention will be described with reference to FIG. The present embodiment relates to a processing apparatus in which a part of the heating vessel 11 is used as a condensing unit 13 for air cooling. In this example, the waste adsorbent after being used in the iodine filter,
The present invention relates to a method and an apparatus for separating and recovering radioactive iodine and further vitrifying the radioactive iodine.

In the processing apparatus shown in FIG. 3, the basket 15 of the processing apparatus described in the second embodiment is divided, and the waste 2 (waste adsorbent) to be processed is disposed on one side and the waste 2 (waste adsorbent) is disposed on the other side. A substance (glass-forming substance 17) that forms a glass by forming a solid solution with silver iodide separated and recovered from the glass is charged. Such materials include phosphorus oxide, a mixture of silver oxide and phosphorus oxide, silver metaphosphate, silver orthophosphate, silver pyrophosphate, polymerized silver phosphate, and the like. The glass-forming substance 17 is usually a powder, but is preferably in the form of pellets or granules formed by compression molding since the pressure is reduced after loading.

When the waste 2 (waste adsorbent) and the glass-forming substance 17 loaded in the basket are heated under reduced pressure,
Volatile silver iodide vapor is generated from the waste 2 (waste adsorbent) and moves downward through the basket according to the difference between gravity and vapor pressure. At the same time, the glass-forming substance 17
Is also turned into steam and moves downward through the basket. In the condensing section 13, the vapor of the silver iodide and the vapor of the glass-forming substance 17 are simultaneously condensed, so that both are dissolved to form a glass state. Therefore, the recovery form in the condenser 13 is a glass melt. The obtained glass melt moves downward according to gravity, finally enters the collection container 14, and is further cooled to a vitrified body. The collection container 14 is removed after the processing, and the lid is welded and stored.

In this embodiment, the following two effects can be obtained.

1) The melting point of silver iodide is 552 ° C.
Once in the glassy state, the fluidization temperature drops to about 300 ° C. Therefore, the coexistence of the glass forming substance 17 widens the temperature range that can be recovered in the liquid state,
The loss of the collected material in 3 can be reduced. In addition, the temperature difference between the heating unit and the condensing unit 13 can be set large, and the recovery rate in the condensing unit 13 increases.

2) Separation and recovery of radioactive substances from waste adsorbent and vitrification of radioactive substances can be performed by the same apparatus, so that the processing apparatus can be made compact, low-cost, and the processing steps can be simplified. .

As a modification of the present embodiment, a method is possible in which the glass-forming substance 17 is placed not in the basket 15 but in the collection container 14. In this case, the silver iodide liquid collected in the condensing section 13 flows down to the collection container 14, forms a solid solution with the glass-forming substance 17 inside the collection container 14, and vitrification proceeds. The collection container 14 is removed after the treatment, and the lid is welded and stored, or in order to obtain a more uniform vitrified body, the removed container is heated again to 300 ° C.
A process of inserting a stirring blade and stirring the inside is required.

In addition, as an example of alloying described in the claims, tin is used as a second material for zinc, iron is used as a second material for uranium, and uranium, plutonium, and Chlorine can be cited as the second substance with respect to iron, cobalt and nickel.

[0047]

According to the first aspect of the present invention, in a method of heating a radioactive waste containing a volatile radioactive substance to vaporize and separate the radioactive substance, the heating temperature can be reduced. Furnace corrosion can be reduced. In addition, it is possible to avoid a decrease in the recovery rate of radioactive materials due to thermal denaturation of waste, and to accelerate the vaporization of radioactive materials that have permeated into waste, thereby improving the decontamination coefficient of radioactive materials. it can.

According to the second aspect of the present invention, in addition to the effects obtained by the first aspect, it is possible to further reduce the cost of the processing apparatus, make it more compact, and greatly simplify the processing steps. it can.

According to the third aspect of the present invention, a radioactive waste containing a volatile radioactive substance is heated at a lower temperature to vaporize the radioactive substance, and is suitable for separation and recovery in a high yield. Processing device can be realized.

According to the invention of claim 4 of the present invention, in addition to the effects obtained by the invention of claim 3, it is possible to realize a processing apparatus in which the separated radioactive material can be recovered more easily.

According to the fifth aspect of the present invention, in addition to the effects obtained by the third and fourth aspects, it is possible to realize a processing apparatus which facilitates the handling of the recovered radioactive material.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a radioactive waste treatment apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a radioactive waste treatment apparatus according to another embodiment of the present invention.

FIG. 3 is a configuration diagram of a radioactive waste treatment apparatus according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating container, 2 ... Waste, 3 ... Heater, 4 ... Condenser tube, 5 ... Heater, 6 ... Flexible joint, 7 ...
Collection container, 8: Valve, 9: Vacuum pressure gauge, 10: Vacuum pump, 11: Heating container, 12: Heater, 13: Condenser, 14: Collection container, 15: Basket, 16: Vacuum pump, 17: Glass production material

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Tatsuo Izumida 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref.

Claims (5)

[Claims] 1. A radioactive waste containing a volatile radioactive substance is heated under reduced pressure to vaporize the radioactive substance and separate it from the radioactive waste, and condense the vaporized radioactive substance to form a liquid or A method for treating radioactive waste, comprising recovering the solid as a solid. 2. A radioactive waste containing a volatile radioactive substance, and a substance (second substance) which is alloyed, vitrified or combined with the radioactive substance and has a low melting point, is heated under reduced pressure to obtain the radioactive substance. And a method for treating a radioactive waste, comprising simultaneously vaporizing the second substance and condensing a mixture of the radioactive substance and the second substance to recover a liquid or a solid. 3. A sealable container loaded with a radioactive waste containing a volatile radioactive substance and having a heating section for vaporizing the radioactive substance, connected to the heating section and maintained at a lower temperature than the heating section. A condensing section, a collecting container connected to the condensing section in a separable manner and for collecting the radioactive substance from the condensing section in a liquid state, and for reducing the pressure in the container, the condensing section and the collecting container. And a decompression means. 4. The melting point or fluidization temperature of a mixture of a radioactive substance or a substance which is alloyed, vitrified or combined with the radioactive substance to lower the melting point and the radioactive substance, wherein the condensing section according to claim 3 is used. An apparatus for treating radioactive waste, wherein the apparatus is held as described above. 5. The radioactive waste treatment apparatus according to claim 4, wherein the condensing section is an inclined pipe or a trumpet pipe, and a trap for collecting condensed liquid is provided.