JPH09218297A - Method for treating radioactive waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve retain ability (distribution factor) of a radioactive waste solidified body to C-14. SOLUTION: A condensed waste liquid is dried, powdered and turned into pellets. The pellets are filled in a solidification container 4. A paste of solidifying material including a soluble substance which reacts with carbonic acid ions and produces an insoluble compound is formed. The paste of solidifying material is injected in the solidification container 4 filled with the pellets. The soluble substance reacting with carbonic acid ions and producing an insoluble compound reacts with C-14 in the pellets, whereby the C-14 becomes the insoluble compound. Accordingly, the retain ability (distribution factor) of a waste solidified body to the C-14 is improved nearly by one digit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solidifying material used for solidifying radioactive waste such as concentrated waste liquid and used ion-exchange resin, and a method for treating these radioactive wastes. The present invention relates to an optimum solidifying material for radioactive waste and a method for treating radioactive waste, which is most suitable for improving the retention ability of nuclides, especially C-14.

[0002]

2. Description of the Related Art Low-level radioactive waste generated from radioactive material handling facilities such as nuclear power plants is disclosed in JP-A-63-28.
As shown in Japanese Patent No. 9500, it is normally safely solidified with Portland cement or plastic.
Further, as the cement-based solidifying material, a material in which normal Portland cement is 30% or more and the rest is slag or fly ash, or cement glass containing sodium silicate as a main component is widely used. When radioactive waste is solidified using such a solidifying material, Co-6 in the waste is
Radionuclides such as 0, Sr-90, Cs-137 and C-14 are retained in the solidified body in a sufficiently stable state.

In order to further improve the ability of the solidified body to retain radionuclides, a radionuclide adsorbent such as zeolite may be added to a solidifying material such as cement, as disclosed in JP-A-3-105298. Has been done.

[0004]

Since such an adsorbent has a property of adsorbing cations, Co-60, Sr-
The holding performance of the solidified body for 90, Cs-137, etc. is dramatically improved. However, since C-14 is not a cation, the retention performance of the solidified body for C-14 is not improved even by the above-mentioned conventional technique.

C-1 contained in so-called low-level waste
Although the amount of 4 is small, it can be solidified sufficiently safely even with the conventional technology, but considering that the half-life of C-14 is as long as about 5700 years, it is necessary to further improve the C-14 retention performance of the solidified body. Is more desirable.

[0006] The object of the present invention is to solidify the radioactive waste C
It is an object of the present invention to provide a method for treating radioactive waste that can improve the retention performance for -14.

[0007]

Means for Solving the Problems The features of the present invention for achieving the above object are that when a radioactive waste is solidified in a container with a solidifying material, it reacts with carbonate ions together with the waste to form an insoluble precipitate. This is to make a substance co-exist in the container and to coagulate a solidifying material in the container, and to solidify it.

The present invention relates to C-1 contained in radioactive waste.
4 reacts with a substance that reacts with carbonate ions to form an insoluble precipitate, or by an isotope reaction between a carbonate ion containing C-14 and a carbonate ion of an insoluble carbonate compound,
An insoluble material containing -14 is produced. Therefore, the ability of the radioactive waste solidified body to retain C-14 is improved.

Hereinafter, a specific example of study of the present invention will be described. First, it is necessary to clarify the term of C-14 retention performance of the solidified body. It is well known that even if the solidified body is left in the air at room temperature, radioactive substances such as C-14 do not leak into the air. However, for example, when the solidified body is immersed in water assuming the case of land disposal, the radioactive substance may gradually leak into the water although the amount is small. A partition coefficient is an index for evaluating the retention performance of the radionuclide when immersed in the solidified water. That is, after stirring the solidified material in the form of fine powder in water to reach a steady state,
It is general that the partition coefficient is obtained from the equation (1), and the larger this value is, the higher the C-14 retention performance of the solidified body is.

Partition coefficient = C-14 concentration in solidified body / C-14 concentration in water (1) Also in a concrete study example of the present invention, C of solidified body is calculated by using the partition coefficient defined by the equation (1). -14 Retention performance shall be evaluated.

As a first step for increasing the partition coefficient of the solidified product with respect to C-14, the inventors first investigated various chemical forms of C-14 contained in radioactive waste. As a result, in many cases, most of the radioactive waste generated from nuclear power plants has C-14 as carbonate ion (CO ₃ ² ~).
It was found to be in the form of. Therefore, in order to increase the distribution coefficient for C-14, it was thought that the carbonate ion should be fixed in the solidified body, and the present invention described below was achieved.

That is, even if the solidified body comes into contact with water, C
In order to prevent -14 from being eluted in water, it was considered that the carbonate ion should be in the form of an insoluble compound. Examples of insoluble compounds of carbonate ions include alkaline earth metal compounds (CaCO ₃ etc.) and transition metal compounds (FeCO ₃ etc.). For example, after the radioactive waste is solidified using a solidifying material in which soluble CaCl ₂ is present, when this solidified body comes into contact with water, carbonate ions containing C-14 tend to be eluted into water, but at the same time, the soluble solid is dissolved in water. CaCl ₂ also tries to elute. Therefore, the chemical reaction represented by the formula (2) occurs in water, and carbonate ions are precipitated as calcium carbonate on the solidified body side.

CaCl ₂ + CO ₃ ² ~ → CaCO ₃ ↓ + 2Cl ~ (2) As a result, C-14 is substantially equivalent to being retained in the solidifying material, and the distribution coefficient defined by the equation (1) is Get higher The reaction represented by the formula (2) is not limited to CaCl ₂ , and a soluble alkaline earth metal compound (Ca (N
_{O 3) 2, SrCl 2,} MgSO 4, BaCl 2 , etc.) or a transition metal compound _{(FeCl 2, FeI 2, CoCl} 2, Mn (NO 3)
₂ ))).

As described above, when the radioactive waste is solidified by using the solidifying material in which the soluble alkaline earth metal compound or the transition metal compound is present, the partition coefficient of C-14 of the solidified body is greatly increased. However, in order to realize this, it is necessary to consider the following points. That is, for example, when cement is used as a solidifying material, even if a soluble alkaline earth metal compound such as CaCl ₂ or a transition metal compound (hereinafter, CaCl ₂ will be described as an example) is added to the cement. However, if kneading water is added to harden cement, CaCl ₂ will dissolve. Therefore, most of CaCl ₂ added at the stage of hardening the cement reacts with the cement and is consumed. As a result, the amount of soluble CaCl ₂ remaining in the solidified body becomes small, and the ability of the solidified body to precipitate carbonate ions when immersed in water is significantly reduced. As a result of various studies in order to solve such a problem, the soluble alkaline earth metal compound and the transition metal compound may be added to the solidifying material after they are in a granular state or after water repellent treatment. I understand.
That is, in the granular form having a small specific surface area, CaCl ₂ hardly reacts with the cement and is consumed during the hardening process of the cement. In addition, if CaCl ₂ is water repellent in advance, it dissolves C during the hardening process of cement.
aCl ₂ is greatly reduced. As a result, CaCl ₂ is present in the solid after the hardening reaction of the cement, and the partition coefficient of C-14 of the solidified body increases. Although CaCl ₂ is used as an example here, Ca (N
It is common to all of the above additives, such as O ₃ ) ₂ , SrCl ₂ , FeCl ₂ .

The above is a case where the solidifying material contains a substance that reacts with carbonate ions to form an insoluble compound.
However, the same effect can be obtained by pretreatment of waste. That is, in the liquid waste or the waste soaked in water, some or all of carbonate ions containing C-14 are present in water. If a soluble alkaline earth metal compound or transition metal compound is added in this state,
A reaction of the formula (2) or a similar reaction occurs, and the carbonate ion precipitates as an insoluble compound. When the waste is solidified after such a pretreatment, the carbonate ion is already insoluble. Therefore, even if the solidified body is immersed in water, the carbonate ion containing C-14 does not elute in water. , A high partition coefficient is obtained.

In addition to the above examples, the waste is solidified with a solidifying material containing an organic silane compound, or the liquid waste or the waste dipped in water is pretreated with the organic silane compound and then the waste is discarded. Even if the material is solidified, the solidified C-14
The distribution coefficient for is increased. In this case as well, it is considered that the organic silane reacted with carbonate ions to form an insoluble compound.

The above is for fixing carbonate ions in the solidified form in the form of an insoluble compound, but a method utilizing isotope exchange is also effective. For example, when an insoluble carbonate compound (CaCO ₃ or the like) is put in the solidifying material, a carbonate ion containing C-14 and a non-radioactive CaCO ₃ cause isotope exchange, and C-14 is contained in the insoluble carbonate compound. Move to. Therefore, C-14 is easily retained in the solidified body, and the distribution coefficient also increases. Examples of the insoluble carbonate compound include carbonates of alkaline earth metals and transition metals, and specifically,
MgCO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , F
eCO ₃ , CoCO ₃ , MnCO ₃ , NiCO _{3 and the} like are effective.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Example 1 In this Example, pellets of incinerated ash are solidified with a cement-based solidifying material. Cement-based solidifying materials (hydraulic inorganic solidifying materials) include Portland cement, slag cement, fly ash cement, alumina cement,
Although there is cement glass or the like, the same result can be obtained by using any solidifying material. Therefore, the case of using alumina cement will be described here.

As the simulated waste, after incineration of general industrial waste whose main component is combustible material such as paper, the incinerated ash 1
A sodium carbonate solution containing 1 mCi of C-14 in kg was uniformly dispersed. The incinerated ash was molded into pellets having a diameter of 1 cm and then filled in a container having an internal volume of 1 liter. afterwards,
A solidifying material paste containing alumina cement as a main component was prepared at a water / solidifying material ratio of 0.3 and poured into a container. As a result, the voids between the pellets could be almost completely filled with the solidifying material paste, and the simulated waste solidified body was completed after one month of curing. Then, 10 g of the powder prepared by crushing the solidified waste solid product was immersed in 100 ml of water, and (1)
The partition coefficient for C-14 was measured by the formula.

There are over 20 types of solidified products prepared, and different solidifying materials are used. An example of the solidifying material used is as follows: Alumina cement only Alumina cement 97 wt% + Ca with a particle size of 0.1 mm
(NO ₃ ) ₂ 3 wt% Alumina cement 97 wt% + Ca with a particle size of 0.5 mm
(NO ₃ ) ₂ 3 wt% Alumina cement 97 wt% + Ca (N
O _{3) 2} 3wt% alumina cement 90 wt% + particle diameter 2mm of Ca (N
O _{3) 2} 10wt% alumina cement 97 wt% + water repellent to the particle size _{0.1mm Ca (NO 3) 2 3wt} % Above all, was added as a C-14 adsorbent C
The effect of the particle size of a (NO ₃ ) ₂ (calcium nitrate) on the distribution coefficient, is the effect of the added amount of Ca (NO ₃ ) _{2 on} the distribution coefficient, and is the effect of Ca (NO ₃ ) ₂ on the distribution coefficient. The purpose of this study is to investigate the effects of water treatment on the distribution coefficient.

As an example of the experimental results, first, FIG. 1 shows the influence of the particle size and the addition amount of the adsorbent on the distribution coefficient. From this figure, it can be seen that the effect of the adsorbent (Ca (NO ₃ ) ₂ ) depends on the particle size and the addition amount. It can be seen that as the addition amount increases, the distribution coefficient also increases, and the C-14 retention performance of the solidified product is improved by one digit or more (the partition coefficient of the solidified product when using alumina cement containing no adsorbent as the solidifying material). Is 1 × 10 ⁴ m
1 / g). Further, regarding the particle size, it is understood that the performance as an adsorbent is exhibited when the particle size is 0.1 mm or more, preferably 1 mm or more. The cause is considered as follows. That is, even if Ca (NO ₃ ) ₂ in the form of fine powder has been added to the cement in advance, Ca (NO ₃ ) ₂ will dissolve if kneading water is added to harden the cement. Therefore, most of Ca (NO ₃ ) ₂ reacts with the cement and is consumed when the cement hardens, and the amount of soluble Ca (NO ₃ ) ₂ remaining in the solidified body becomes small and the performance as an adsorbent Is significantly reduced. However, if the adsorbent is in the form of granules with a large particle size, it hardly dissolves because the specific surface area is small,
Ca (NO ₃ ) ₂ is hardly consumed by reacting with the cement. Therefore, it is considered that the performance of the adsorbent depends on the particle size.

If the above estimation is correct, even if a fine powdery adsorbent is used, the adsorbent's performance should not be impaired if measures are taken to prevent the adsorbent from dissolving during the cement hardening reaction. is there. Therefore, Ca (NO ₃ ) _{2 in the} form of fine powder is used.
Decided to make it water repellent. Specifically, the particle size is 0.1 mm
Ca (NO ₃ ) ₂ in Example ₂ was immersed in an emulsion-state styrene-butadiene polymer and then dried to remove water. This Ca (NO ₃ ) ₂ 3 wt% and alumina cement 97
As a result of measuring the partition coefficient again by using the solidifying material composed of wt%, the value was 2 × 10 ⁵ ml / g, which was about 20 times higher than that in the case where the adsorbent was not added.

Next, the effect of the adsorbent when the incinerated ash pellets are solidified with cement glass will be described. The cement glass was an inorganic solidifying material containing sodium silicate, sodium fluorosilicate and cement as main components, and the pH of the kneading paste was about 8. FIG. 2 shows the distribution coefficient of the solidified body when 5% iron sulfate was added to cement glass as an adsorbent. Also in this case, a remarkable effect was observed in the region where the particle size of the adsorbent was 0.1 mm or more. Further, when the iron sulphate treated with water repellency as described above was used, a high partition coefficient of 3 × 10 ⁵ ml / g was obtained even if the particle size was 0.1 mm or less.

As described above, if a granular adsorbent, specifically, an adsorbent having a particle size of 0.1 mm or more, preferably 1 mm or more is added to the cement-based solidifying material, the C-14 retention of the solidified body is maintained. Performance is significantly improved. Further, even if the particle size is small, the C-14 retention performance of the solidified body is remarkably improved if the water-repellent adsorbent is used.

In the above experimental results, the effect of using calcium nitrate and iron sulfate as the adsorbent was shown, but as explained in the section (action), the adsorbent is soluble and reacts with carbonate ions. Any compound which causes precipitation can be used. Specifically, an alkaline earth metal compound (CaC
l ₂ , Ca (NO ₃ ) ₂ , SrCl ₂ , MgSO ₄ , BaCl ₂
Etc.) and transition metal compounds (FeCl ₂ , FeI ₂ , CoC)
l ₂ , Mn (NO ₃ ) _2, etc.).

It was also found that organosilane is effective as another substance. FIG. 3 shows the molecular structure of the organic silane used as the adsorbent, which originally has water repellency. Therefore, a solidifying material composed of 98 wt% of slag cement and 2 wt% of organic silane was prepared, and the incinerated ash pellets were solidified. After that, when the distribution coefficient of C-14 was measured, it was 8 × 10 with 100 wt% of slag cement.
^While it was ⁴ ml / g, it was improved to 3 × 10 ⁵ ml / g by adding the organic silane. C of this organosilane
Although the -14 adsorption mechanism is not always clear, it is presumed that a carbonate ion precipitate was formed as in calcium nitrate and iron sulfate. The adsorbents described above do not have to be used alone, and a plurality of adsorbents can be mixed and used.

As a summary of the findings of this example, as the C-14 adsorbent mixed in advance with the solidifying material, a compound that is soluble and that reacts with carbonate ions to cause precipitation is effective. Granular compound (particle size 1mm or more)
Alternatively, it is desirable to add it to the solidifying material in a state of being treated to be water repellent.

Example 2 In this example, concentrated waste liquid generated from a boiling water nuclear power plant (BWR plant) is dried and molded into pellets, which is then solidified. FIG. 4 shows a flow of the processing system of this embodiment.

The concentrated waste liquid containing sodium sulfate as a main component generated from the BWR plant is powdered by a drier and further made into an almond-shaped pellet having a length of about 3 cm by a granulator and stored in the pellet storage tank 1. There is. After the pellets are taken out by the pellet take-out device 2, the belt conveyor 3
Is transferred to and filled in the solidification container 4. In this way, the solidification container 4 is filled with 220 kg of pellets. On the other hand, 150 kg of the cement-based solidifying material from the solidifying material hopper 5 and 45 kg of water from the kneading water tank 6 are sent to the kneading machine 7 and the solidifying material paste is prepared by the stirrer 8. This solidifying material paste is poured into the solidifying container 4 filled with pellets, and the pellets, which are waste, are solidified. In this example, eight types shown in Table 1 were used as the cement-based solidifying material. Cement glass is the same as in Example 1,
A solidifying material composed mainly of sodium silicate, sodium fluorosilicate and cement was used.

[0030]

[Table 1]

After curing the obtained 8 kinds of solidified bodies for 3 months, samples were taken by core boring,
The partition coefficient for C-14 was measured. Table 1 also shows the results. First, in the case of using an alkaline earth metal salt as the adsorbent (,, in Table 1), although the distribution coefficient is increased as compared with the comparative example, the increase is as small as about 3 times at maximum. As a result of investigating the cause, the following was found. First, in this embodiment (action)
As described in Section 1, we expect the carbonate ion to precipitate by the following reaction.

MCl ₂ + CO ₃ ² ~ → MCO ₃ ↓ + 2Cl ~ (3) Here, M represents an alkaline earth metal. However, if the waste contains sodium sulfate as in this embodiment,
The reaction of the formula (4) also occurs at the same time, and a part of the alkaline earth metal added carefully reacts with the sulfate ion and is consumed.

MCl ₂ + SO ₄ ² to MSO ₄ ↓ + 2Cl to (4) As a result, it is considered that the reaction of the formula (3) did not sufficiently occur and the increase of the partition coefficient was small.

On the other hand, when the transition metal salt was used as the adsorbent (in Table 1), the partition coefficient increased by one digit or more as compared with the comparative example, and high adsorption performance was obtained. It is considered that this is because the transition metal salt does not promote the reaction of consuming the transition metal as shown in the formula (4).

Table 1 shows the results when iron carbonate (insoluble carbonic acid compound) having an average particle size of 50 μm was added. In this way, the insoluble carbonic acid compound was added to the solidifying material. Also proves to be effective. The reason for this is
It is considered that the carbonate ions were fixed by isotope exchange as described in the section (action). In this case, the rate of isotope exchange depends on the crystallinity and the specific surface area of the carbonic acid compound, so it is necessary to select these at the design stage according to the purpose. In addition to the transition metal carbonate, an insoluble alkaline earth metal carbonate is also effective as the carbonate compound.

Although not shown in Table 1, the sodium sulfate pellets were solidified with cement glass containing 4 wt% of an organic silane compound and the partition coefficient was measured. As a result, the value was 5.3 × 10 ² ml / g. Therefore, the same effect as that obtained by adding FeCO ₃ was obtained.

In summary, the findings of this example are as follows. As the C-14 adsorbent to be mixed in the solidifying material in advance, a compound which is soluble and causes precipitation by reacting with carbonate ions or an insoluble carbonate compound is effective. Is. However, when these compounds are consumed by reacting with a specific substance contained in the waste, the performance as an adsorbent may be deteriorated, so caution is required. Specifically, a soluble transition metal compound, a carbonate of a transition metal or an alkaline earth metal, or an organic silane compound is particularly effective for waste containing sodium sulfate.

Further, based on the findings of Examples 1 and 2 above, as the adsorbent, hydroxides of alkaline earth metals and transition metals such as Ca (OH) ₂ , Ba (OH) ₂ , Fe (OH) are used. )
₂ , ₂ , Fe (OH) _{3 and the} like should be effective, but it was found that the distribution coefficient of C-14 hardly increased even if these were added to the solidifying material as an adsorbent. The reason for this is considered as follows. The first reason is that the solubility of hydroxides of these alkaline earth metals and transition metals is two orders of magnitude lower than that of CaCl _2, etc., so that precipitation reactions corresponding to equations (3) and (4) Because it rarely happens.
The second reason is that since the cementitious solidifying material already contains Ca (OH) _{2 in the} solidifying material itself, there is almost no effect even if an additional hydroxide adsorbent is added. Conceivable. Such a phenomenon is not peculiar to this embodiment and is applicable to other embodiments. For reference, the solubility of a typical adsorbent of the present invention in water is shown in Table 2 in comparison with hydroxide.

[0039]

[Table 2]

Example 3 In Example 1 and Example 2, the C-14 adsorbent was put in the solidifying material, but it is possible to replace a part of the waste pellets with the adsorbent. That is, a conventional cement glass or the like is used as the solidifying material, and when the solidifying container is filled with the waste pellets, the adsorbent pelletized with calcium chloride or the like is also put therein. Even in this case, when the carbonate ion containing C-14 is dissolved in water, an adsorbent such as calcium chloride is also dissolved out and reacts with this dissolved adsorbent to form a precipitate, which is high. The partition coefficient is obtained.

In this example, 20 parts by weight of the waste pellets used in Example 2 was uniformly mixed with 1 part by weight of pelletized calcium chloride having substantially the same shape, which was then placed in a solidification container. Filled and solidified with cement glass. The partition coefficient of the obtained solidified product was 7.5 × 10 ¹ ml / g without the adsorbent, whereas it was 2.5 × 10 ² ml in the present example containing the adsorbent pellet. / G, an improvement of an order of magnitude. Although calcium chloride was used as the adsorbent in this example, it is a matter of course that all the adsorbents described above can be used. Further, it goes without saying that such a method can be applied to a so-called non-uniform solidified body that solidifies a metal waste material or the like.

Example 4 In this example, a used ion exchange resin (hereinafter abbreviated as waste resin) generated from a pressurized water nuclear power plant (PWR plant) is solidified. FIG. 5 shows the flow of the processing system.

First, 120 kg of the cement-based solidifying material in the solidifying material hopper 5 and 50 kg of water in the kneading water tank 6 are transferred to the solidifying container 4. A stirrer 8 is previously inserted in the solidification container 4, and a solidifying material paste is prepared using this. On the other hand, the waste resin stored in the waste resin tank 9 is sent to the dehydrator 11 in a slurry state by the transfer pump 10, and the waste resin having a water content of about 50% is obtained by centrifugal dehydration. Next, after 120 kg of this waste resin is transferred to the solidification container 4 containing the solidification material paste, the stirrer 8 is operated again to uniformly knead the solidification material paste and the waste resin. After the completion of the kneading, the stirrer 8 is withdrawn from the solidification container 4 and the solidified body preparation work is completed. Then, the solidified container was covered and aged at room temperature for 1 month, and the partition coefficient of C-14 of the solidified body was measured.

The specifications of the five types of solidifying materials used in this example are shown in Table 3 together with the obtained distribution coefficient values. here,
In the case shown by in Table 3, in order to make the adsorbent water repellent, silicon oil dissolved in an organic solvent was sprayed on strontium chloride having an average particle size of 0.1 mm, and then dried to remove the solvent. . In addition, the main component of the organic silane shown in Table 3 is vinyltrietoquinsilane (CH ₂ · CH
Si (OC ₂ H ₄ OCH ₃ ) ₃ ), in which case the organosilane dissolved in the solvent was sprayed directly onto the cement to prepare the solidifying material. The carbon fiber is added to improve the strength and the like of the solidified body.

[0045]

[Table 3]

From the results regarding the distribution coefficient shown in Table 3,
It can be seen that SrCl ₂ having a particle size of 1 mm has almost no effect as an adsorbent in this example. The reason for this is that it is relatively difficult to uniformly mix waste resin and cement, so the time required for kneading becomes as long as about 1 hour, and SrCl
_It is considered that ₂ was melted (kneading time was short at 5 minutes in Examples 1 and 2). On the other hand, all of the adsorbents obtained from (1) and (2) showed remarkable effects, and it was found that the present invention is effective not only for pelletized waste, but also for so-called homogeneous solidified bodies.

Further, using SrCl ₂ which has been subjected to water repellent treatment,
Small-scale (100 ml) relationship between adsorbent addition and partition coefficient
It was measured with the waste resin solidified product. The result is shown in FIG.
The effect of the adsorbent appears from the addition amount of about 1 wt%,
When it exceeded 20 wt%, a saturation tendency was observed. Quantitative values differ depending on the type of solidifying material and adsorbent used, but the appearance of such a saturation tendency is the same in Example 1 and Example 2.

As shown in the comparative example in Table 3, when the cement-based solidifying material is used, a relatively high partition coefficient can be obtained even without the adsorbent. The reason for this is considered to be that a large amount of calcium is contained in the cement and this reacts with carbonate ions containing C-14 to form a precipitate. However, the solubility of calcium in cement is as low as about 1 g per liter of water. On the other hand, SrC
Since the l ₂ solubility is large by two digits or more, it is considered that it exhibits high performance as an adsorbent. Therefore, it is desirable that the soluble adsorbent used in the present invention of Examples 1 to 3 has a solubility of 1 g or more per 1 liter of water.

Example 5 This example relates to a solidified plastic body having an excellent C-14 holding performance. BACKGROUND ART It is widely practiced that a liquid radioactive waste is powdered by a dryer and then uniformly kneaded with a plastic such as unsaturated polyester to form a solidified body.

In this example, 0.1 wt% of sodium carbonate containing C-14, 9 wt% of sodium sulfate and 0.9 wt of iron oxide.
A simulated concentrated waste liquid having a concentration of 10% was used. First, the concentrated waste liquid is made into a powder having an average particle size of about 50 μm by a centrifugal thin film dryer, and then 5 parts by weight of iron sulfate having a particle size of about 100 μm as an adsorbent is used with respect to 100 parts by weight of waste powder using a powder mixer. Add. Then, 20 kg of this powder and 30 kg of unsaturated polyester to which a polymerization initiator has been added are uniformly mixed with a kneader to prepare a plastic solidified body. The partition coefficient of C-14 of the obtained solidified product was measured and found to be 1.4 × 10 ⁰ ml / g without the adsorbent, but increased to 7.8 × 10 ² ml / g by adding the adsorbent. did.

In this embodiment, since the plastic and the adsorbent hardly react with each other when the solidified body is prepared, there is no problem even if the adsorbent is added not in the form of granules but in the form of powder. The adsorbent may be added to the waste powder as in this embodiment, but may be added to the plastic in advance. Next, such an embodiment will be described.

Here, too, sodium carbonate containing C-14 was added.
1wt%, sodium sulfate 9wt%, iron oxide 0.9wt%
Using a simulated concentrated waste liquid having a concentration of 10%, the concentrated waste liquid is first made into powder with an average particle size of about 50 μm by a centrifugal thin film dryer. On the other hand, 20% by weight of cobalt carbonate is used as the solidifying material.
An unsaturated polyester containing was prepared. Then, 20 kg of the waste powder and 30 kg of the solidifying material were uniformly kneaded, and 100 g of a polymerization initiator was added to proceed a polymerization and curing reaction of the plastic to prepare a solidified plastic body. The partition coefficient of C-14 of the obtained solidified product was measured and found to be 1.4 × 10 ⁰ ml / g without an adsorbent.
The amount of adsorbent was increased to 5.1 × 10 ² ml / g.

As described above, the adsorbent can be added to the solidifying material for the solidification of the plastic, or can be mixed in the waste powder. Further, since the adsorbent is less likely to dissolve and react with plastic, the adsorbent can be added in the form of powder rather than granules. In this example, iron sulfate and cobalt carbonate were used as adsorbents. However, as described in (Action), a substance that is soluble and reacts with carbonate ions to form an insoluble precipitate (such as the alkaline earth metal compounds, transition metal compounds, and organic silanes described above), or insoluble Of course, carbonates (carbonic acid salts of alkaline earth metals and transition metals described above) are effective as adsorbents.

Example 6 In this example, the solidified product C- was prepared by pretreating the waste.
14 is to improve the holding performance. FIG. 7 shows an overall flow of a treatment system for a waste liquid containing sodium sulfate as a main component generated from a BWR plant.

The radioactive liquid waste containing sodium sulfate as a main component, which is generated by the regenerating operation of the condensate demineralizer of the BWR plant, is temporarily stored in the liquid waste receiving tank 12. After adjusting the pH of this waste liquid to a range of 7 to 9, adjust the waste liquid concentration to 2
It is sent to the concentrator 13 in order to increase it to about 0 wt%. The conventional concentrator merely concentrates the waste liquid here, but the concentrator 13 used in the present embodiment is provided with the pipe 14 for adding the adsorbent, and the waste liquid in the concentrator 13 has the adsorbent. Powdered iron sulfate (Fe) stored in the hopper 15
A predetermined amount of SO ₄ · 7H ₂ O) is supplied. Here, regarding the addition amount of iron sulfate as an adsorbent, the solid content concentration of the waste liquid is 10
It was decided to change the amount of the adsorbent in the range of 0 to 5 parts by weight with respect to 0 part by weight, and to examine the effect of the amount of the adsorbent added on the C-14 retention performance of the solidified body. 90 ° C in the concentrator 13
Since the adsorbent dissolved in the waste liquid is involved, the following reaction proceeds efficiently.

FeSO ₄ + CO ₃ ² ~ → FeCO ₃ ↓ + SO ₄ ² ~ (5) As a result, the waste liquid is concentrated in the concentrator 13 and at the same time,
The carbonate ion containing C-14 was changed to insoluble iron carbonate. The above reaction is not limited to iron sulfate, and any soluble transition metal salt as described above may be used. Soluble alkaline earth metal salts can also be used as the adsorbent, but in this case, the adsorbent reacts with sodium sulfate, which is a waste liquid component, as shown in equation (6), and part of the adsorbent is consumed. Therefore, the efficiency becomes lower than that when a transition metal salt is used.

Na ₂ SO ₄ + CaCl ₂ → CaSO ₄ ↓ + 2NaCl (6) The concentrated waste liquid in which the carbonate ion containing C-14 is made insoluble as described above is once transferred to the concentrated waste liquid receiving tank 16 and then dried. The powder is pulverized in 17 and further formed into almond-shaped pellets in the granulator 18. This pellet 220
kg is filled in a drum having an internal volume of 200 liters, that is, the solidification container 4. On the other hand, from the solidifying material hopper 5, cement glass 15 containing sodium silicate and silicon phosphate as main components is provided.
0 kg and 45 kg of water from the kneading water tank 6 are sent to the kneading machine 7 and the stirrer 8 prepares a solidifying material paste. The solidifying material paste is poured into the solidifying container 4 filled with pellets, and the concentrated waste liquid pellets, which are wastes, are solidified. The obtained solidified body was cured for 3 months, and then a sample was collected by core boring to obtain C-1.
The partition coefficient for 4 was measured.

The obtained results are shown in FIG. Here, the vertical axis represents the C-14 distribution coefficient, and the horizontal axis represents the addition amount of the adsorbent (converted to FeSO ₄ ) with respect to the solid content concentration of the waste liquid. From this figure, the distribution coefficient increases with the amount of adsorbent added, and the amount added is 1 wt%.
Although a saturation tendency is shown above, the partition coefficient at this time is improved by almost two orders of magnitude as compared with the case where no adsorbent was added. The reason why the effect of the adsorbent tends to be saturated when the addition amount is 1 wt% or more is that the waste liquid contains only a small amount of carbonate ion and the addition amount is 1 w
It is considered that the precipitation reaction of the formula (5) proceeded completely at t%.

Further, the addition amount of the adsorbent at which the increase in the distribution coefficient saturates was also examined for those other than FeSO ₄ described above.
The results are shown in Table 4.

[0060]

[Table 4]

As described above, the reason why the optimum value of the adsorbent is larger in CaCl ₂ or SrSO ₄ than in FeSO ₄ or CoCl _{2 is} that the adsorbent represented by the formula (6) is used for the alkaline earth metal as described above. This is because the consumption reactions proceed in parallel. Therefore, considering the safety margin, the upper limit of the amount of adsorbent added is about twice the value at which the distribution coefficient saturates (for example, in the present embodiment, 2 wt% for FeSO ₄ , SrSO ₄
In this case, 4 wt%) is desirable. Of course, adding more adsorbents does not affect the effect, but increasing the amount added increases the amount of waste and adversely affects volume reduction. Also, as the lower limit of the amount of adsorbent added, the stoichiometric ratio of equation (5) is 1
The value should be However, in the waste liquid, C-14
It should be taken into consideration that, in addition to the carbonate ions containing, there are also a large amount of non-radioactive carbonate ions in which carbon dioxide in the air is dissolved. For example, if carbonate ions are present in an amount of about 200 ppm in the waste liquid containing sodium sulfate having a solid content concentration of 20 wt%, carbonate ions are present in an amount of 1000 ppm with respect to the solid content. If all of these are attempted to be precipitated as in equation (5), the stoichiometric amount of adsorbent added will be about 0.25 wt% of the solid content of the waste, which is the lower limit of adsorbent addition. give. To summarize the above, in order to make carbonate ions contained in liquid or slurry radioactive waste into an insoluble precipitate, the amount of adsorbent added must be such that carbonate ions are stoichiometrically insoluble. It is desirable that the amount is sufficient and more than twice the amount at which the increase in the distribution coefficient of the solidified substance is saturated. In implementation, the amount of carbonate ions may be measured in advance in the waste liquid receiving tank 12 or the like, and the amount of adsorbent may be determined based on the above-mentioned idea.

The above is an example in which the adsorbent is added in the concentrator 13 to pretreat the waste. However, an apparatus dedicated to pretreatment is provided in the pre-stage of the concentrator or in the post-stage of the concentrator, and the waste liquid is received. It is of course possible to add the adsorbent using the tank 12 or the concentrated waste liquid receiving tank 16. Further, in this example, an example of pelletizing the radioactive waste was shown, but the homogenized solidification in which the concentrated waste liquid and the solidifying material are directly kneaded and solidified by the cement-based solidifying material, or the powdered waste in a peristaltic manner. It is also applicable to the case of solidifying, and in this case, the system after the concentrated waste liquid receiving tank 16 may be changed according to the solidifying method.

Example 7 In this example, waste resin is pretreated and then solidified with cement. FIG. 9 shows the flow of the processing system.

First, the waste resin stored in the waste resin tank 9 is slurried using the transfer pump 10 to form the dehydrator 1.
The waste resin having a water content of about 50% is obtained by centrifugal dehydration. After 120 kg of this waste resin is transferred to the solidification container 4, 50 kg of water in the kneading water tank 6 is also supplied to the solidification container 4. Then, 2 kg of liquid adsorbent is supplied from the adsorbent tank 19 while operating the stirrer 8 to uniformly mix the kneading water and the waste resin. The adsorbent used in this example is an organic silane compound in an emulsion state having a water content of about 50%, and its main component is γ-mercaptopropyltrimethoxysilane (HSC ₃ H ₆ Si (OCH ₃ ) ₃ ). After the stirring is continued for about 1 hour after the addition of the adsorbent, 120 kg of the solidifying material (class C blast furnace cement) in the solidifying material hopper 5 is additionally supplied to the solidifying container 4 to prepare a final solidified body. Then, the stirrer 8 was pulled out from the solidification container 4, the solidification container was covered, and the mixture was aged for 1 month at room temperature, and the distribution coefficient of the solidified product to C-14 was measured. As a result, the distribution coefficient is 5.5 ×
It was as high as 10 ⁴ ml / g, which was almost the same as the result when the adsorbent was added to the solidified material shown in Example 4. In this example, organic silane was used as the adsorbent, but soluble alkaline earth metal salts and transition metal salts were not very effective. The reason for this is that if a soluble alkaline earth metal salt or transition metal salt is mixed with the ion exchange resin for a long time, the alkaline earth metal ion or transition metal ion that is the active ingredient of the adsorbent will be adsorbed on the resin. It turns out that this is because of the loss.

[0065]

According to the present invention, since C-14 contained in radioactive waste can be converted into an insoluble substance, the C-14 retention performance of the waste solidified product is increased by about one digit, and the solidified product is higher than before. Increases the safety of.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the effect of a calcium nitrate adsorbent used in an example of the present invention.

FIG. 2 is a diagram for explaining the effect of another adsorbent used in the examples of the present invention.

FIG. 3 is a diagram illustrating a molecular structure of an adsorbent used in another example of the present invention.

FIG. 4 is a diagram illustrating a treatment system for solidifying waste pellets used in another embodiment of the present invention.

FIG. 5 is a diagram illustrating a treatment system for uniformly solidifying waste resin used in another embodiment of the present invention with cement.

FIG. 6 is a diagram illustrating the effect of the strontium chloride adsorbent used in another example of the present invention.

FIG. 7 is a diagram illustrating a treatment system for pretreating concentrated waste liquid used in another embodiment of the present invention to solidify pellets.

FIG. 8 is a diagram illustrating the effect of the iron sulfate adsorbent used in another example of the present invention.

FIG. 9 is a diagram illustrating a treatment system in which a waste resin used in another example of the present invention is pretreated and homogeneously solidified with cement.

[Explanation of symbols]

4 ... Solidifying container, 5 ... Solidifying material hopper, 7 ... Kneader, 9 ...
Waste resin tank, 12 ... Waste liquid receiving tank, 13 ... Concentrator,
15 ... Adsorbent hopper.

Front Page Continuation (72) Inventor Tsuyoshi Kikuchi 1168 Moriyama-cho, Hitachi City, Ibaraki Pref., Energy Research Laboratory, Hiritsu Manufacturing Co., Ltd. Hitachi, Ltd. (72) Inventor Shin Tamada 3-1-1, Sachimachi, Hitachi, Ibaraki Hitachi Ltd. Hitachi, Ltd. (72) Inventor, Yoshimasa Kiuchi, 3-2, Saiwaicho, Hitachi, Ibaraki No. Stock Company Hitachi Engineering Service

Claims (10)

[Claims] 1. When a radioactive waste is solidified in a container with a solidifying material, any one of a substance that reacts with carbonate ions to form an insoluble precipitate and an insoluble carbonate compound together with the waste. A method for treating radioactive waste, characterized in that the solidified material is injected into the container and solidified after the coexisting state in the container. 2. The substance which reacts with the carbonate ion to form an insoluble precipitate, and includes at least one of a soluble alkaline earth metal compound, a soluble transition metal compound, and an organic silane compound. Radioactive waste treatment method. 3. A radioactive waste is premixed with at least one of a substance that reacts with carbonate ions to form an insoluble precipitate or an insoluble carbonate compound, and then solidified in a container with a solidifying material. A method for treating radioactive waste, comprising: 4. The substance which reacts with the carbonate ion to form an insoluble precipitate contains at least one of a soluble alkaline earth metal compound, a soluble transition metal compound and an organic silane compound. Radioactive waste treatment method. 5. The method for treating radioactive waste according to claim 3, wherein the insoluble carbonate compound is a carbonate compound of an alkaline earth metal or a transition metal. 6. The soluble alkaline earth metal compound or the soluble transition metal compound is an alkaline earth metal compound or transition metal compound having a solubility in water of 1 gram or more per liter of water. 4. The method for treating radioactive waste. 7. The soluble alkaline earth metal compound or the soluble transition metal compound has a solubility in water higher than that of the alkaline earth metal compound or the transition metal hydroxide, or an alkaline earth metal compound or a transition metal compound. 5. The method for treating radioactive waste according to claim 4, wherein. 8. The radioactive waste is a liquid or slurry state radioactive waste, and the reaction between the liquid or slurry state radioactive waste and a substance which reacts with carbonate ions to form an insoluble precipitate, The method for treating radioactive waste according to claim 3, which is carried out in a concentrator. 9. The radioactive waste is a liquid or slurry state radioactive waste, and the reaction between the liquid or slurry state radioactive waste and a substance which reacts with carbonate ions to form an insoluble precipitate. The method for treating radioactive waste according to claim 3, which is carried out in a solidification container. 10. When solidifying a radioactive waste, the radioactive waste in a liquid or slurry state is reacted with an organosilane compound which reacts with carbonate ions to produce an insoluble precipitate, and then the liquid or the A method for treating radioactive waste, which comprises solidifying the radioactive waste in a slurry state.