JPH0345543A - Inorganic soldifying material and solidification of radioactive waste disposal using same material - Google Patents

Abstract

PURPOSE:To obtain a hydraulic hardening agent blended with an inorganic compound capable of maintaining a high partition coefficient of Ca by using a solidifying material to increase exchange capacity of cation of adsorbent in cement paste having high pH and solidifying radioactive waste disposal. CONSTITUTION:An inorganic compound having properties wherein adsorption site (ion exchange group) of cation is increased in hydrolysis reaction in an atmosphere of high alkalinity (pH>10) and Ca adsorption capacity is increased rather in alkalinity is prepared. Then the inorganic compound is added to paste of hydraulic solidifying agent to give a solidifying agent. A silicon compound containing a skeleton comprising a siloxane bond and silanol group may be cited as the inorganic compound. Then radioactive waste disposal is solidified using the solidifying agent.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an assimilation material suitable for use in immobilizing radioactive waste in containers and backfilling disposal pits.

and a method for solidifying radioactive waste using the solidifying material.

[Conventional technology] Cement is used as a solidifying material to assimilate and solidify radioactive waste such as concentrated waste liquid, used ion exchange resin, and miscellaneous solids generated from nuclear power plants and nuclear fuel reprocessing facilities. Hydraulic inorganic solidifying materials such as water, glass (alkali silicate), etc. are known.

The solidifying material (filling material) used for the above purpose needs to have properties that can significantly delay the elution of radionuclides out of the assimilated body even under adverse conditions such as when the solidified body is submerged in water. For this purpose, the solidifying material (filling material) is required to have a property of adsorbing radionuclides, that is, to have a large distribution coefficient with respect to radionuclides.

Conventionally known cement-based assimilation materials 1 For example, hydraulic solidification materials such as Portland cement, blast furnace cement, silica cement, and alumina cement have a high pH of pore water in the solidified material after hardening, so All, C11 The distribution coefficients for transuranic elements such as uranium and transition metals such as Co are large, and the distribution coefficients for anions such as 131 are relatively large due to the characteristics of the charge distribution on the pore surface.On the other hand, for cations and alkali metals It does not have the property of adsorbing Cs.

Therefore, in order to increase the Cs distribution coefficient of the solidifying material, there is a method of mixing zeolite, which has a property of adsorbing cations, with cement 1-, as described in the Japan Atomic Energy Research Institute Newspaper JAERI-M5779.

[Problem M to be solved by the invention] However, in the conventional technology using the above-mentioned zeolite, the hydraulic solidifying material paste including cement is highly alkaline (pH>10), and its component cation Ca
The present inventors have found that there is a problem in that the Cs adsorption capacity (partition coefficient) of zeolite is significantly reduced because the fact that the solution is a highly concentrated solution of ``+'' is not taken into account.

The object of the present invention is also in the paste of a hydraulic solidifying material having alkaline liquid properties as described above.

It is an object of the present invention to provide a hydraulic solidifying material mixed with an inorganic compound that can maintain a high Cs distribution coefficient, and a method for solidifying radioactive waste using such a hydraulic solidifying material.

[Means for Solving the Problem] In order to achieve the above object, the present invention provides highly alkaline (pH >
In the atmosphere described in 10), Cs
15! The solidifying material is a mixture of an inorganic compound whose lti capacity increases with alkalinity into a hydraulic solidifying material paste, and this solidifying material is used to solidify radioactive waste.

Examples of inorganic compounds having the above properties include silicon compounds having a skeleton composed of siloxane bonds and silanol groups.

[Function] The inventors have developed a siloxane bond (SL-0-8i) as an inorganic compound that can maintain a high Cs distribution coefficient in a hydraulic solidifying material paste that is highly alkaline and has a high Ca ion concentration.
It has been experimentally found that a silicon compound having a skeleton consisting of and a silanol group (S i -OH) is suitable.

As an example of a hydraulic solidifying material, a calcium hydroxide saturated solution (pH
= 12.5) and in pure water (PH = 6), 137
Table 1 shows the results of measuring the Cs distribution coefficients of the various inorganic materials when a 1-racer amount (trace amount) of C was added and the following various inorganic materials were added thereto.

Comparison of Cs Distribution Coefficients for Surface Treatment Here, the inorganic material according to the present invention is a silicon compound having a skeleton composed of siloxane bonds and a silanol group.

As shown in Table 1, zeolite and fly ash exhibit high partition coefficients in pure water, but their Cs adsorption performance decreases significantly in a calcium hydroxide saturated solution that simulates the liquid property in cement paste. I understand that.

- Inorganic materials that distribute (that is, adsorb) Cs in their shells through ion exchange reactions generally exhibit such pH dependence.

In particular, inorganic materials that ion-exchange cations between the eyebrows of their crystal structures, such as zeolite and bentonite, which have a high adsorption coefficient in pure water, change their crystal structure when the pH increases, resulting in a significant decrease in their adsorption capacity.

On the other hand, the inorganic material according to the present invention, that is, the silicon compound having a siloxane skeleton and a silanol group, has the following properties. This compound was dissolved in pure water (pH=6
) has a structure like this, and has the property of adsorbing cations when the silanol group dissociates. in a highly alkaline atmosphere.

As shown in ○-H" 0, the siloxane bond (Si-0-8i) part partially undergoes a hydrolysis reaction and new silanol groups are generated. This means that the number of adsorption sites for cations increases. That is, the above-mentioned metal silicide has the characteristic that it can maintain a high cation distribution coefficient even in a highly alkaline solution.

The general structural formula of a silicon compound having a skeleton made of siloxane bonds and a silanol group, which is an inorganic material according to the present invention, is shown in Figure 1 under neutral conditions, and as shown in Figure 2 under alkaline conditions. As shown in the figure.

By mixing such an inorganic material with a hydraulic solidifying material such as Cement 1, a filler can be created that has both the anion adsorption ability inherent in cement and the cation adsorption ability of the added inorganic material. (solidified material). By using such a filler, it is possible to create a solidified body of radioactive waste in which the elution of various radionuclides is extremely small.

[Examples] Example 1 An example of the present invention will be described with reference to FIG. This embodiment is a suitable example for uniformly solidifying radioactive waste liquid in a container using a cement-based solidifying material.

Cement from the cement silo 1 is fed to the feeder 6, and inorganic powder according to the present invention as an adsorbent from the adsorbent tank 2 is fed to the feeder 7 in fixed amounts to the kneading tank 5.
supplied to Radioactive waste liquid is previously supplied to the kneading tank 5 from the waste liquid tank 3 via the valve 8 to the kneading tank 411y5, and when the cement is supplied, the stirring blade 1 is activated by the motor 10.
Rotate 1 to mix the cement. Depending on the case, kneading water is added from the kneading water tank 4 via the valve 9 to adjust the viscosity of the cement paste 1-. The kneading water tank 4 can be replaced with a water reducing agent tank, and β
Used when reducing paste viscosity using naphthalene sulfonate condensates, etc.

After the 1-minute crosstalk has been completed, the paste is poured into a solidification container 12, and after curing in a sealed container for about one month, a solidified product is completed.

The results of a water immersion test of the solidified body prepared by the above procedure are shown below. The cement used was ordinary Portland cement, to which activated silicic acid was mixed as the adsorbent. The amount of each input was 70 parts by weight of cement and 30 parts by weight of adsorbent. 7CsC as a simulated waste liquid
Q Pure water containing 100μCL was used. This simulated waste liquid does not contain any other inorganic salts. The waste liquid/(cement + adsorbent) weight ratio was 0.3. In order to compare with this example, a solidified body made using cement alone as a solidifying agent without an adsorbent, and a solidified body made using a solidifying agent mixed with cement using synthetic zeolite 1 as an adsorbent were also used. I tried it. ``'The conditions such as the amount of CsC11 added and the waste liquid/solid content ratio are the same as above.

"'Cs" after immersion in water from the above three types of solidified bodies
The leaching rate ratio is 1, and the leaching rate from solidified cement alone is 1.
The results are shown in Table 2. As can be seen from the results in Table 2, a comparison of Cs leaching rates, an assimilated material in which activated silicic acid is mixed with cement is used as the inorganic material according to the present invention. According to
The effect of reducing the amount below was obtained. This is because, as mentioned above, the active silicon added has a large Cs adsorption capacity even in the highly alkaline cement paste.

The amount of adsorbent added in this example is (solidified batten adsorbent)
10 to 50 parts by weight of the adsorbent is preferably 10 to 50 parts by weight, and optimally 20 to 30 parts by weight.

Furthermore, the same effect can be obtained by using organic silicon compounds such as silicones, alkali silicate polymers, hydrous titanium oxide, etc. in place of activated silicic acid.

Example 2 This example relates to a method for preparing a silicon compound that has a skeleton composed of siloxane bonds and silanol groups and has cation exchange ability even in a high pH region.

Silicon phosphate, preferably in an equimolar amount to the alkali silicate, is added as a polymerization initiator to an aqueous solution of water glass (alkali silicate) and stirred thoroughly. Mix this mixture at room temperature for 1 to 2
Let it cure for a week. During this time, the alkali silicate undergoes dehydration polymerization, forms a polymer with siloxane bonds, and hardens.

This hardened product is roughly pulverized to about 50 to 100 meshes and then washed with water to extract soluble salts such as phosphates. After washing with water.

By drying and pulverizing to about 25° mesh, an adsorbent for use in adding cement paste can be prepared.

As a result of measuring the 134C8 distribution coefficient of the silicon compound prepared by the above procedure, it was 2000 to 3000 in a neutral liquid.

It has been confirmed that it has high Cs adsorption performance independent of pH in the pH range of 3000 to 4000 in alkaline liquids and pH > 5, and has properties suitable as an adsorbent that can be mixed with hydraulic solidifying materials such as cement. Ta.

Example 3 Example 3 of the present invention will be described using FIG. 4.

This embodiment is a suitable example in which used radioactive ion exchange resin (referred to as waste resin) generated from a nuclear power plant is directly mixed with cement 1- and solidified in a container.

Waste resin discarded from a power plant is supplied to the resin dehydrator 13, and is dehydrated to a water content of around 50% by centrifugal dehydration. The l15I resin after dehydration is sent to the resin receiving tank 14 and fed in a fixed amount to the kneading tank 21 by the feeder 18. This waste resin adsorbs various radioactive nuclides in the form of ions or cladding. A fixed amount of cement is supplied to the kneading tank 21 from the cement silo 15 via the feeder 19, and a fixed amount of adsorbent is supplied from the adsorbent tank 16 via the feeder 29.

During this time, the forced stirring blades 22 are kept rotating. Stirring blade 22
The motor 23 that drives the is linked with a torque meter 241 and a tachometer 25, and these measurement signals 8 are sent to the control panel 26.
be monitored. While mainly monitoring the 1 to lux values,
If the torque value exceeds the set value, the valve 20 is opened to supply kneading water from the kneading water tank 17 to the kneading tank 21 to lower the paste viscosity and facilitate pouring into the container. Kneading tank 2
In step 1, the waste resin and cement, which are mixed for one minute and become a paste, are poured into a container 27. At this time, the vibrator 28
If defoaming is performed with , a good solidified material without macropores can be created.

The results of the water immersion test of the solidified body prepared by the above procedure are shown below. The cement used was Class 0 blast furnace cement 1~, and silicon compound powder prepared according to the procedure of Example 2 was mixed as an adsorbent. The cement/adsorbent weight ratio was 7/3. 13, which is a radioactive cation nuclide, was used as a simulated waste resin.
' Granular ion exchange resin (cation resin/anion resin =
2/1).

It was filled at a ratio of 50 kg/200Q assimilate. In order to compare with this example, the same experiment was also conducted on waste resin assimilate using an assimilation agent of cement alone without adsorbent, and waste resin assimilate using an assimilation agent of cement with synthetic zeolite added. did. All conditions such as the amount of radioactive nuclide added and the resin/(solidification material + adsorption material) ratio are the same. Above 3
Table 3 shows the leaching rates of 134 Cs and tzs I from different types of assimilates, based on the leaching rate of 1ff4C8 of waste resin solidified with cement alone.

Table 3: Comparison of leaching rates Since 12' is an anion and cement itself has adsorption capacity, the leaching rate is small for each solidified material. 13'C
Regarding s, the solidified material using the cement added with the adsorbent of Example 2 of the present invention is 1/10 compared to the assimilated material using the cement without additives, and the solidified material using the cement added with zeolite is The leaching rate was as low as 1/4 compared to the body, indicating that even if the form of the waste changed, the elution retardation effect due to Cs adsorption did not change.

The filler (solidifying material) according to the present invention has the ability to exchange cations regardless of the pH of the atmosphere, so it can be used not only for solidifying waste in solidifying containers, but also for radioactive waste that comes into direct contact with the natural environment. It is suitable for pit structure materials for disposal and backfilling materials in pits, and regardless of the nature of the nuclide (ion polarity), it is possible to reduce the migration speed to less than half that of conventional filling materials. .

[Effects of the Invention] According to the inorganic assimilation material of the present invention, the cation exchange capacity (adsorption capacity) of the adsorbent increases in cement paste with a high pH. Solidifying materials has the effect of significantly reducing the rate of leaching of soluble cation nuclides such as Cs to the outside.

[Brief explanation of drawings]

Figure 1 is a molecular structure diagram of the inorganic material mixed in the solidification material in the present invention in a neutral range, Figure 2 is a molecular structure diagram of the inorganic material in an alkaline range, and Figure 3 is an example of the present invention. FIG. 4 shows a flow diagram of another embodiment of the present invention. 5.21...Kneading pW 1.15...Cement silo 2.16...Adsorbent tank 4.17...Kneading water tank 12.27...Solidification container 3...Waste liquid tank 3...
・Resin dehydrator 0.23... Motor 5... Tachometer 8... Vibrator 14... Resin receiver tank 24... Torque meter 26... Control panel

Claims (1)

[Scope of Claims] 1. An inorganic compound having the property of adsorbing cations to negatively charged exchange groups, the inorganic compound having the property of increasing the number of cation exchange groups by hydrolysis in an alkaline atmosphere with pH > 10. An inorganic solidifying material made by mixing a compound into cement paste. 2. The inorganic solidifying material according to claim 1, wherein the inorganic compound is a silicon compound having a siloxane bond composed of silicon and oxygen and a silanol group composed of silicon, oxygen, and hydrogen. 3 The inorganic compound includes a siloxane bond composed of silicon and oxygen, an organic group bonded to the silicon atom, silicon,
The inorganic solidifying material according to claim 1, which is a silicon compound having a silanol group composed of oxygen and hydrogen. 4. The inorganic solidifying material according to claim 1, wherein the inorganic compound is a silicon compound obtained by dehydrating and polymerizing an alkali silicate and then extracting a soluble salt. 5. A method for solidifying radioactive waste using the inorganic solidifying material according to claim 1, 2, 3, or 4.