JP3232993B2 - Radioactive waste treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention provides a nuclear facility (e.g., nuclear power plants, nuclear fuel reprocessing plant) relates to how to process radioactive waste from, in particular the processing side of the radioactive waste containing radioactive iodine about the law.

[0002]

2. Description of the Related Art For solidification of waste having a low radioactivity level such as chemical waste liquid generated from a nuclear power plant, a cement-based solidification material is generally used. On the other hand, as for wastes with a high radioactivity level generated from reprocessing plants, denser solidification materials than cement such as glass have been studied from the viewpoint of improving the containment performance of radionuclides.

In vitrification, New Glass Vol. 9 No.
As described in 2 pp. 26-31, highly durable borosilicate glass or the like is melted at a temperature of several hundreds of degrees centigrade and mixed with waste to form a solid. The target waste is only liquid waste (high-level concentrated waste liquid), and a method has been developed in which a glass raw material is made into a fibrous form, impregnated with the waste liquid, and supplied to a melting furnace.

As for a method for stably solidifying radioactive waste containing radioactive iodine typified by iodine-129, as described in JP-A-62-124500, iodine is volatilized using a low-temperature molten glass. There is a method to vitrify at a temperature that does not. In this method, copper iodide, lead iodide or silver iodide powder is solidified by low-temperature melting glass, and iodine is melted at low temperature by copper iodide, lead iodide or silver iodide powder. Surrounded by glass.

[0005]

Since iodine-129 has a long half-life of about 16 million years, waste containing a high concentration of radioactive iodine is in the form of a vitrified solid like a high-level concentrated waste liquid. It is desirable to stabilize and isolate from the living area for a long time.

[0006] Among the above-mentioned prior arts, the stable solidification using borosilicate glass has a high solidification temperature. Therefore, when the solidification is applied to waste containing radioactive iodine in a high concentration, iodine volatilizes during solidification, and the immobilization rate is reduced. There is a problem with low.

Further, among the above prior arts, Japanese Patent Application Laid-Open No. Sho 62-1245
In the solidification using low-temperature molten glass described in Japanese Patent Publication No. 00, there is no problem of iodine volatilization, but the radioactive waste itself, that is, the powder of copper iodide, lead iodide or silver iodide does not change, so that the volume is reduced. There was a limit. In addition, since radioactive waste and glass do not melt uniformly, the solidified material becomes non-homogeneous,
Due to the difference in the thermal expansion coefficient between the radioactive waste and the glass, there is a problem that cracks are likely to occur when the solidified body is cooled.

[0008] A first object of the present invention is to stabilize radioactive waste containing radioactive iodine in a glass using a glass to prevent volatilization of the radioactive iodine at the time of solidification, improve the volume reduction property, and improve the waste volume. It is an object of the present invention to provide a method for producing a homogeneous solidified body in which the glass and the glass are uniformly melted and improving the iodine containment property and the crack resistance.

A second object of the present invention is to provide a method for stably and efficiently supplying a glass material to achieve the first object.

A third object of the present invention is to provide a method which achieves the first and second objects, further reduces the leakage rate of radioactive iodine from a vitrified body, and increases the performance of containing radioactive iodine. is there.

[0011] A fourth object of the present invention is to treat solid waste containing radioactive iodine by dry treatment without using water or additives to convert it into a stable vitrified solid without generating secondary waste. It is to provide a way to do it.

A fifth object of the present invention is to provide a method for treating liquid waste containing radioactive iodine, which reduces the amount of iodine-containing waste and converts it into a stable vitrified product. It is in.

A sixth object of the present invention is to treat a waste gas containing radioactive iodine by a method for absorbing and removing only radioactive iodine from a gas and converting the absorbing material directly into a stable vitrified material. To provide.

[0014]

[0015]

[0016]

The first object of the present invention to achieve the first object is that radioactive iodine is separated from radioactive waste containing radioactive iodine in the form of silver iodide, and then separated. Silver iodide and at least phosphorus,
A vitrified material consisting of three components of silver and oxygen, or at least four components of phosphorus, silver, oxygen and iodine is mixed and melted by heating, and the molten product is cooled and solidified to form a homogeneous vitrified body. is there.

In the present invention, the means for stabilizing radioactive iodine is achieved by the following two-stage process.

(1) Among the chemical forms of iodine, it is separated from waste in the form of silver iodide, which is the most stable (low water solubility) compound. When the form present in the waste is silver iodide, the form is used as it is, and when the form is other than silver iodide, the form is converted to silver iodide and separated and recovered.

(2) The silver iodide separated and recovered is converted into a glass which is a part of a constituent component, and cooled and solidified to obtain a homogeneous vitrified product.

By separating and recovering iodine from waste containing iodine, it is possible to reduce the management burden of the separated waste and to reduce the volume of waste containing radioactive iodine. Further, since the recovered iodine is stable silver iodide, it contributes to improving the safety of the final solid.

Next, in the process of vitrifying the recovered iodine, a vitrification material is required. The vitrification material for obtaining a stable vitrified body requires the following requirements.

(1) Glass-forming oxide (SiO_Two, Ge
O_Two, B_TwoO_Three, P_TwoO_Five, As_TwoO_ThreeEtc.). is there
Alternatively, an oxide (Mo) that reacts with other components to form a glass
O_Three, WO_Three , TeO_Two, SeO_TwoEtc.).

(2) In order to ensure the stability of the glass, the vitrification material itself has a low solubility.

(3) At the time of mixing and melting with the recovered silver iodide,
The vitrification material must have a low melting point to prevent iodine from re-evaporating. The temperature at the time of mixing and melting is desirably 600 ° C. or lower.

As a result of selecting a vitrified material by a basic experiment, the vitrified material satisfying the above requirements is at least three components of phosphorus, silver and oxygen, or at least phosphorus, silver and
We found that an inorganic substance containing four components, oxygen and iodine, was optimal. Specifically, silver phosphate or silver oxide (Ag
A mixture of ₂ O) and phosphorus oxide (P ₂ O ₅ ) applies as vitrifying material.

The vitrified material contains up to 70 silver iodide.
Since mol% can be dissolved, treatment with high volume reduction is possible. Further, the melting temperature is around 300 to 400 ° C., there is no iodine volatilization at the time of melting, and the immobilization rate of radioactive iodine can be increased to almost 100%. In the end, a homogeneous glass body mainly composed of four components of phosphorus, silver, oxygen, and iodine is obtained. However, since the glass is composed of a substance having a low solubility, the solubility of the glass itself is low, and thus the leaching of radioactive iodine is caused. The rate is also small. Further, by adding a stable isotope of iodine to the vitrification material in advance, the isotope can be diluted arbitrarily and the leaching rate of radioactive iodine can be reduced.

In the above vitrified material, Au, Cu, Pb as a substitute for silver, and Mo, W, or P as a substitute for phosphorus.
B, Si, and Al can be used, but the melting temperature and the iodine leaching rate are higher than in the case of the combination of silver and phosphorus, and the solidified body performance is reduced.

According to the present invention, a homogeneous vitrified body can be obtained, so that the iodine leaching rate from the solidified body can be controlled to be substantially constant, and furthermore, the occurrence of cracks due to thermal strain during cooling can be suppressed.

The feature of the second aspect of the present invention that achieves the second object is that, in addition to the features of the first aspect, silver metaphosphate, silver pyrophosphate, silver orthophosphate, and silver salt of polymerized phosphoric acid are used. One of them is to use as a vitrifying material.

According to the present invention, since the vitrified material can be made into one component, the storage tank and the supply line for the vitrified material can be unified, and the processing apparatus can be simplified. Further, since the molar ratio of silver and phosphorus, which are constituent elements of glass, can be kept constant, the quality of the produced vitrified product is stabilized. In addition, when phosphorus, which is one of the constituent elements, is supplied as an oxide, it is difficult to supply smoothly because of its hygroscopicity. However, if it is supplied as a compound with silver as in the present invention, the problem of hygroscopicity can be solved. .

The feature of the third aspect of the present invention that achieves the third object is that, in addition to the features of the first aspect, silver metaphosphate, silver pyrophosphate, silver orthophosphate, and silver salt of polymerized phosphoric acid are used. It is to use a mixture of one selected from the above and silver iodide as a vitrifying material. In addition to the second aspect,
By adding silver iodide, radioactive iodine can be isotope diluted. This makes it possible to reduce the leakage rate of radioactive iodine from the produced vitrified product in accordance with the dilution ratio, and to improve the safety after disposal of the vitrified product.

The feature of the fourth aspect of the present invention that achieves the fourth object is that, in addition to the features of the first, second, and third aspects, the radioactive waste containing radioactive iodine contains silver. A used iodine adsorbent contained therein, which is to be heated to vaporize and separate radioactive iodine in the form of silver iodide.

When radioactive iodine is separated and recovered from waste containing iodine, the use of heating makes it possible to eliminate the need for water and additives, and to obtain an effect of preventing the generation of secondary waste associated with the treatment.

According to a fifth aspect of the present invention which achieves the fifth object, in addition to the features of the first, second and third aspects of the present invention, the radioactive waste containing radioactive iodine is a liquid waste. A radioactive iodine is precipitated and separated in the form of silver iodide by adding a soluble silver compound thereto.

By adding silver to liquid waste containing iodine, radioactive iodine can be removed from the liquid with a high decontamination coefficient of 100 or more, and the management burden on liquid waste can be reduced. Further, the removed iodine can be converted into a stable vitrified material as it is, thereby improving the safety of subsequent disposal.

A feature of the sixth aspect of the present invention that achieves the sixth object is that the waste gas containing radioactive iodine is converted into at least three components of phosphorus, silver and oxygen, or at least phosphorus, silver and oxygen.
Silver, oxygen, after absorbing the blowing by radioiodine vitrified material in melt containing quaternary iodine is to a homogeneous vitrified by cooling and solidifying the melt.

In the present invention, the purification of the waste gas and the stable solidification of the removed radioactive iodine are performed in one step, so that the waste gas treatment system can be greatly simplified.

[0038]

[0039]

[0040]

[0041]

[0042]

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

(Embodiment 1) An embodiment of the present invention will be described below. This example is a result of preparing a vitrified body using silver iodide as a reagent as a radioactive iodine simulated body separated and recovered from waste. First, silver phosphate as a vitrification material was synthesized by the following method using the molar ratio of phosphorus to silver as a parameter. Silver phosphate (A) having a molar ratio of phosphorus to silver of 1: 1 is obtained by completely dissolving 1 mole of sodium hexametaphosphate and 6 moles of silver nitrate in water, mixing the two, filtering the precipitate, and filtering paper. The upper solid was collected and made. Silver phosphate (B) having a molar ratio of phosphorus to silver of 1: 2 is obtained by completely dissolving 1 mol of sodium pyrophosphate and 4 mol of silver nitrate in water, mixing the two, filtering the precipitate, and filtering the precipitate. The upper solid was collected and made. Silver phosphate (C) having a molar ratio of phosphorus to silver of 1: 3 is obtained by completely dissolving 1 mol of sodium (ortho) phosphate and 3 mol of silver nitrate in water, mixing the two, and filtering the precipitate. Then, the solid matter on the filter paper was collected and prepared.

Next, 50 mol% of silver iodide was added to each of the above three types of silver phosphate, mixed well in a mortar, and then placed in a crucible and melted by heating in an electric furnace. The melting temperature is
The lowest was about 300 ° C. for silver phosphate (A), about 350 ° C. for silver phosphate (B-50), and about 400 ° C. for silver phosphate (C). After the melt was sufficiently stirred with an alumina rod, it was poured into a stainless steel container and solidified by cooling.

In the same manner, silver iodide contained 60 mol% (B-60) and 70 mol% (B-7) of silver phosphate (B).
0) Added glass was also made. The composition of the glass produced in this example is shown by the triangular coordinates in FIG. In FIG. 1, the range in which a homogeneous glass body (including partially crystallized one) can be obtained is shaded.

The prepared glass body was processed into a test body having a surface area of 10 cm ² , and the iodine leaching rate was measured in hot water at 70 ° C. The glass body was immersed in warm water for one week, and after immersion, the iodine concentration in the water was analyzed and evaluated by ICP-MS. 5 above
FIG. 2 shows the measurement results of the iodine leaching rates of the various types of glass bodies. The iodine leaching rate was lowest for glass made of silver phosphate (B) with a phosphorus to silver molar ratio of 1: 2, followed by silver phosphate (A) and phosphorus with a phosphorus to silver molar ratio of 1: 1. The molar ratio of silver to silver was in the order of silver phosphate (C) of 1: 3. That is, it was found that iodine was most stabilized when the composition of the vitrified material had a molar ratio of phosphorus to silver of about 1: 2. Even when the amount of silver iodide added was increased to 70 mol%, no change was observed in the iodine leaching rate, indicating that silver iodide could be filled up to 70 mol%.

In this embodiment, as the phosphorus molar ratio of the vitrified material is increased, the specific gravity of the glass body is reduced, and the weight of the solidified body can be reduced. Further, since the silver content can be reduced, the material cost of the vitrified material can be reduced. Also, as the amount of silver iodide added increases, the number of vitrified materials generated per treated waste can be reduced, and the volume reduction ratio can be improved. Further, the vitrification material can be used as a mixture of silver oxide and phosphorus oxide corresponding to the molar ratio of phosphorus to silver of silver phosphate, but there is a disadvantage that the vitrification reaction takes longer than the case where silver phosphate is used.

(Embodiment 2) Another embodiment of the present invention will be described with reference to FIG. Example 1 This example shows a method suitable for vitrifying a solid waste containing radioactive iodine. Applicable wastes include alumina, zeolite,
There is used waste of an iodine adsorbent in which silver is impregnated on a carrier such as silica gel. These wastes contain radioactive iodine mainly in the form of silver iodide and silver iodate.

Next, a method for treating waste will be described. First, solid waste containing iodine is charged into the heating furnace 1 and heated to a predetermined temperature while flowing air. Here, iodine in the waste is vaporized as silver iodide. Silver iodate also changes to silver iodide by thermal decomposition and evaporates as silver iodide. This temperature is at least 550 ° C., the melting point of silver iodide, and the higher the temperature, the shorter the processing time. Next, the gas exiting the heating furnace is introduced into the cooling tower 2 to cool the vaporized silver iodide and deposit it on the wall surface. When the thickness of the precipitate on the wall surface of the cooling tower 2 is increased to some extent, the rotating blade 3 is operated to scrape the precipitate and turn it into powder. The silver iodide powder is weighed by a hopper 4 with a load cell at the bottom of the cooling tower, and a predetermined amount of silver iodide is weighed and then put into a melting furnace. At the same time, the vitrified material is supplied from the storage tank 6 to the hopper 7 with a load cell, and a predetermined amount of the vitrified material is measured and then charged into the melting furnace. Melting furnace is 300
The temperature is maintained at about 400 ° C., and the inside is stirred by a stirring blade. After stirring for 1 to 2 hours, the shutter 8 at the lower part of the melting furnace is opened, and the melt is poured into a solidification container 9 made of steel.
The solidification container 9 is cooled by natural air to obtain a vitrified body.

In this embodiment, the treatment in the heating furnace 1 is performed at 900.degree.
A vaporization rate of iodine of 99% or more was obtained by the treatment for 30 minutes. The form of the vaporized iodine was almost the form of silver iodide.

In the present embodiment, silver phosphate powder is optimal as the vitrifying material, but a mixture of silver oxide and phosphorus oxide is also possible. The use of silver phosphate powder has the advantage of requiring only one glass material storage tank, and the use of mixed oxides has the advantage that the molar ratio of phosphorus to silver can be set arbitrarily to control the properties of the glass. However, when phosphorus oxide is used alone, it is necessary to dehumidify the storage tank because it is deliquescent. In the case of isotope dilution, a considerable amount of silver iodide is added in advance to the vitrifying material with a reagent.

According to this embodiment, the concentration of iodine in the first solid waste can be reduced by more than two orders of magnitude, and the solid waste can be concentrated to a vitrified body. Therefore, the volume of the iodine-contaminated waste can be significantly reduced. Further, since the silver iodide and the vitrifying material are measured and controlled for each batch, a vitrified product having stable performance can be manufactured.

(Embodiment 3) Another embodiment of the present invention will be described with reference to FIG. Example 1 This example shows a method suitable for separating and recovering radioactive iodine from liquid waste containing radioactive iodine, followed by vitrification.

First, the waste liquid is received in the waste liquid receiving tank 10, a predetermined amount of silver salt such as silver nitrate is added, and the mixture is stirred. Here, radioactive iodine in the waste liquid precipitates as silver iodide. Next, the silver iodide precipitate is separated from the waste liquid by the filtration device 11. The separated silver iodide is weighed by a hopper 12 with a load cell, and then put into a melting furnace 13. In a melting furnace, a vitrified material and silver iodide are mixed and melted at 300 to 400 ° C., and then cooled and solidified to obtain a vitrified body. In this embodiment, radioactive iodine dispersed in a liquid can be converted not only into a precipitate but also into a stable vitrified body. Therefore, the burden of waste management can be reduced. The present embodiment is suitable for the treatment of cleaning (decontamination) waste liquid of solid waste contaminated with iodine. Further, the present invention is also applicable to the treatment of a cleaning liquid (scrubber waste liquid) for a radioactive waste gas containing radioactive iodine.

(Embodiment 4) Another embodiment of the present invention will be described with reference to FIG. Example 1 This example shows a method suitable for separating and recovering radioactive iodine from gaseous waste containing radioactive iodine, followed by vitrification.

The waste gas is introduced into the melting furnace 14 and is bubbled into the vitrified material that has been melted in advance. This causes iodine to be absorbed in the vitrified material. The iodine in the waste gas is in the form of molecular iodine (I ₂ ) and organic iodine (CH ₃ I). In order to efficiently absorb these in the vitrification material, the molar ratio of phosphorus to silver must be increased by excess silver. It is converted to silver iodide in the vitrification material and absorbed. Since the color of the vitrified material turns yellow with the absorption of iodine, the change is detected and discharged to the solidification container.

In this embodiment, a vitrified product can be directly obtained without providing a waste gas treatment device such as an iodine filter or an alkaline scrubber, and the waste gas treatment system can be greatly simplified.

(Embodiment 5) Another embodiment of the present invention will be described with reference to FIG. This embodiment is a modified example of Embodiments 2 and 4, and shows a method suitable for separating and recovering radioactive iodine from solid waste containing radioactive iodine, followed by vitrification.

First, solid waste containing iodine is charged into the heating furnace 15 and heated to a predetermined temperature while flowing air. Here, iodine in the waste is vaporized as silver iodide or molecular iodine. Silver iodate also changes to silver iodide by thermal decomposition and evaporates as silver iodide. Next, the gas that exited the heating furnace was previously melted with a vitrified material,
Into the melting furnace 16 maintained at the above temperature. Since the color of the vitrified material turns yellow with the absorption of iodine, the change is detected and the melt is discharged to the solidification container.

According to the present embodiment, since the cooling tower of the second embodiment can be dispensed with, the processing apparatus can be made compact.

[0061]

According to the first aspect of the present invention, since only radioactive iodine can be separated and concentrated from waste contaminated with radioactive iodine, the amount of solidified substances managed as iodine-containing waste can be significantly reduced. Can be. Further, the obtained vitrified body is homogeneous, hardly generates cracks due to thermal strain, and has low solubility, so that an effect of enhancing the performance of confining radioactive iodine can be obtained.

According to the second aspect of the invention, in addition to the effects obtained by the first aspect of the invention, the storage tank and the supply line for the vitrified material can be unified, and the processing apparatus can be simplified. Further, the effect of stabilizing the quality of the formed vitrified body can be obtained.

According to the third aspect of the present invention, in addition to the effects obtained by the first aspect of the present invention, it is possible to reduce the leakage rate of radioactive iodine from the produced vitrified product, and to reduce the radioactive iodine after disposal of the vitrified product. Safety can be improved.

According to the fourth aspect of the present invention, in addition to the effects obtained by the first, second or third aspect, water and additives are not required when radioactive iodine is separated and recovered from waste containing iodine. Thus, an effect that secondary waste accompanying the treatment is not generated can be obtained.

According to the fifth aspect of the present invention, in addition to the effects obtained by the first, second or third aspect of the present invention, the burden of managing liquid waste can be reduced.

According to the sixth aspect of the present invention, the purification of the waste gas and the stable solidification of the removed radioactive iodine can be performed in one step, so that the waste gas treatment system can be greatly simplified.

[0067]

[0068]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a composition example of a vitrified material used in the present invention.

FIG. 2 is an explanatory diagram showing iodine confinement performance of a vitrified product of the present invention.

FIG. 3 is a configuration diagram of a solid waste processing apparatus according to an embodiment of the present invention.

FIG. 4 is a configuration diagram of a solid waste processing apparatus according to another embodiment of the present invention.

FIG. 5 is a configuration diagram of a solid waste processing apparatus according to another embodiment of the present invention.

FIG. 6 is a configuration diagram of a solid waste processing apparatus according to another embodiment of the present invention.

[Explanation of symbols]

1, 15: heating furnace, 2: cooling tower, 9: solidification container, 5, 1
3, 14, 16 ... melting furnace.

Continuing on the front page (72) Inventor Shodo Matsuda 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Power & Electricity Development Division (72) Inventor Tetsuo Fukasawa 7-2 Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Hitachi, Ltd. Power and Electricity Development Division (72) Inventor Tatsuo Izumida 3-1-1, Sakaimachi, Hitachi, Ibaraki Pref.Hitachi, Ltd.Hitachi Plant (56) References JP-A-63-15200 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G21F 9/16 G21F 9/02 G21F 9/08 G21F 9/10 G21F 9/30

Claims (6)

(57) [Claims] (1) radioactive iodine is separated from radioactive waste containing radioactive iodine in the form of silver iodide, and then the separated silver iodide and at least three components of phosphorus, silver and oxygen;
Alternatively, a vitrified material composed of at least four components of phosphorus, silver, oxygen, and iodine is mixed and heated and melted, and the molten material is cooled and solidified to form a homogeneous vitrified product, which is a radioactive waste product. Processing method. 2. The method for treating radioactive waste according to claim 1, wherein said vitrification material is a substance selected from silver metaphosphate, silver pyrophosphate, silver orthophosphate, and silver salts of polymerized phosphoric acid. 3. The radioactive waste according to claim 1, wherein said vitrifying material is a mixture of silver iodide and a substance selected from silver metaphosphate, silver pyrophosphate, silver orthophosphate, and silver salt of polymerized phosphoric acid. How to handle things. 4. The radioactive waste containing radioactive iodine is a used iodine adsorbent containing silver, which is heated to vaporize and separate radioactive iodine in the form of silver iodide. Or the radioactive waste treatment method of 3. 5. The radioactive waste containing radioactive iodine is a liquid waste, to which a soluble silver compound is added to precipitate and separate radioactive iodine in the form of silver iodide. 3. A method for treating radioactive waste. 6. The waste gas containing radioactive iodine is at least three components of phosphorus, silver and oxygen, or at least phosphorus,
Silver, oxygen, after absorbing the blowing by radioiodine vitrified material in melt containing quaternary iodine, radioactive waste, characterized in that a homogeneous vitrified by cooling and solidifying the melt How to handle things.