JPS6266198A - Method of solidifying and processing radioactive waste solvent - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention relates to radioactive waste solvents used in solvent extraction methods in spent nuclear fuel reprocessing, particularly waste solvents containing phosphate esters such as tributyl phosphate. This article relates to a solidification treatment method.

<Prior Art> Solvent extraction is the most widely used method for reprocessing spent nuclear fuel from nuclear reactors to separate and remove fission products from uranium and plutonium. In this method, tributyl phosphate (hereinafter abbreviated as rTBPJ) diluted with a hydrocarbon such as dodecane is generally used as a solvent, but used TBP! Since this is radioactive waste, sufficient consideration must be given to the method of disposal.

As a treatment method for radioactive waste solvent containing TBP (hereinafter abbreviated as "rTBP-containing waste solvent"), methods of solidifying this waste solvent have been tried in the past.
Focusing on the fact that P has the property of plasticizing vinyl chloride resin (hereinafter abbreviated as rPVcJ), we solidified the TBP-containing waste solvent by mixing it with flaky PVC, such as the TBP-containing waste solvent. A method has been proposed to
No. 2040).

As a solidification treatment method filed by the same applicant as the present application, PVC plastisol containing a thermosetting plasticizer such as a polyfunctional acrylic or methacrylic monomer is mixed with a TBP-containing waste solvent, 1! There is a method of stirring and, if necessary, heat-treating to solidify (Patent Application No. 1986-3)
No. 0042).

<Problems to be Solved by the Invention> However, none of the above-mentioned conventional methods are necessarily satisfactory. That is, according to the solidification treatment method in which TBP is stirred and mixed with PVC in the form of strips, TBP merely absorbs and swells in the PVC, so although it no longer exhibits fluidity, it merely becomes a solidified material with a soft pudding-like viscosity. If this is stirred and heated at variable temperatures, the hardness of the solidified product will improve, but P
VC has poor thermal conductivity and requires long heating times.
Moreover, as the diameter of the solidified body increases, it becomes difficult for heat to be transmitted to the inside, and only a solidified body whose inside is significantly lower in hardness than the surface can be obtained.

This tendency becomes more serious as the amount of dodecane contained in the waste solvent increases.

On the other hand, according to the solidification treatment method of mixing with PVC plastisol, a solidified product with relatively good physical properties such as appearance, mechanical strength (hardness, compressive strength), and homogeneity can be obtained, but especially ioo f! .

When obtaining a large solidified material, there is room for improvement in the physical properties of the solidified material. Namely, PVC plastisol and TB
When the mixture with the P-containing waste solvent is solidified by heating at low temperatures, the appearance and homogeneity are good, but the mechanical strength is slightly low. The reason for this is that it is essential to use paraffin as a viscosity modifier when preparing PVC plastisol, and when this PVC plastisol is mixed with TBP-containing waste solvent, in addition to a certain amount of dodecane contained in the waste solvent, paraffin is used as a viscosity modifier. It is thought that the addition of paraffin increases the total amount of hydrocarbons (paraffin + dodecane) in the total amount of waste solvent to be solidified, and as a result, the mechanical strength of the solidified material decreases. In addition, when a mixture of PVC plastisol and waste M containing DBP is heated and solidified at high temperature for a long time to improve mechanical strength, shrinkage of PVC due to heat dissipation occurs at the outer periphery of the solidified material after heating is stopped. While the shrinkage phenomenon of the solidified body occurs, residual thermal stress occurs because the heat accumulated inside the solidified body is not radiated. There is a problem that cracks are likely to occur internally.

Therefore, this invention solves the drawbacks of the prior art as described above, and aims to solidify a radioactive waste solvent that can obtain a solidified product with excellent physical properties, including good mechanical strength and homogeneity even by low-temperature heat solidification treatment. This was done for the purpose of providing a processing method.

<Means for solving the problems> The radioactive waste solvent solidification treatment method according to the present invention is based on T'B
This method is characterized by adding PVC powder, an elastic polymer, and a moisture absorbent as a solidifying agent to a P-containing waste solvent, stirring and mixing the mixture, and then heating and solidifying the mixture.

Radioactive waste solvents to be subjected to the solidification treatment according to the present invention include phosphoric acid esters such as TBP containing radionuclides, as well as phosphoric acid esters and aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, Mixtures with mineral oil, water, etc. may be mentioned.

In this invention, the proportions of each component used as a solidifying agent are generally 2 to 10 parts by weight of the elastic polymer and 5 to 25 parts by weight of the moisture absorbent per part of the PVC powder.

The PVC used in this invention can be selected from vinyl chloride homopolymers, copolymers of vinyl chloride and monomers copolymerizable therewith, and mixtures thereof.

The elastic polymer imparts resistance to tearing forces to the solidified body,
In addition to preventing the occurrence of cracks due to shrinkage of the solidified material after heating is stopped, it also absorbs decane in the TBP-containing medium due to its own oil absorbing properties, thereby preventing the decrease in mechanical strength inside the solidified material. By reducing dodecane, which is a contributing factor, as much as possible, the mechanical strength of the solidified product is increased,
At the same time, bleeding of dodecane from the solidified body is prevented. Elastic polymers with such dodecane absorbability include:
Substances such as polynorbornene are known, and, for example, "Nosolex" (trade name: manufactured by dFChimie (France)) is available as a commercial product.

The hygroscopic agent absorbs and removes the moisture contained in the TBP-containing solvent, thereby preventing the foaming phenomenon inside the solidified body caused by the volatilization of moisture during the heat solidification process, and also absorbing the heat of hydration reaction generated due to moisture absorption. This increases the temperature at the center of the solidified body and improves the mechanical strength of the solidified body. Examples of moisture absorbing agents include calcium oxide and barium oxide.

Sodium oxide, calcium chloride, etc. can be preferably used.

In carrying out this invention, first, the above-mentioned PVC powder powder elastic polymer and moisture absorbent are mixed with a radioactive waste solvent, and the mixture is mixed into a planetary mixer, a kneader, a butterfly mixer, a Henschel mixer, a Disilver, a ribbon blender, and a Status. Stir and mix thoroughly using a conventional device such as a mixer or a stirring spatula.

The mixing ratio of the waste solvent and solidification agent is 100 parts by weight of the waste solvent to 100 parts by weight of the solidification agent (PVC powder).

Total elastic polymer and moisture absorbent ff1) 80-120
Parts by weight ranges are preferred.

This mixture is then heated from outside the container, typically at 8
By performing solidification treatment at a temperature of 0 to 100°C for about 7 hours, 1 q of solidified material with excellent physical properties can be obtained.

<Examples> The present invention will be described in detail below with reference to Examples and Comparative Examples. Note that both "%" and "part" are based on weight.

A non-radioactive simulated waste solvent consisting of 85% TBP, 10% n-dodecane, and 5% water was prepared as a waste solvent for X-direct knee solidification treatment, and this completely dissolved solvent was prepared. 50 pieces of garlic were put into a 100λ drum.

Next, the mixing ratio of solidification treatment agent to waste solvent is 46'/'5
The solidification treatment agent was added so that the weight ratio was 4 (weight ratio). The proportions of each component of the solidification treatment agent were as shown in the table below.

The PVC powder was Zeon 43BJ (Nippon Zeon ■), the elastic polymer was Nosolex, and the moisture absorbent was calcium oxide rCML#31j (Ohmi Kagaku ■).
(manufactured by) was used.

Next, the waste solvent and solidification agent in the drum were stirred and mixed at room temperature for about 1 hour using an in-drum mixer. Although the temperature of the mixed solution rose by about 10'C with stirring, the viscosity of the mixed solution was as low as about 250 cps.

Next, the mixed liquid in the drum was heated to about 800 ml using a low frequency induction heater.
The mixture was heat-treated at 0'C for about 7 hours to form a solidified product. After heating, the sample was left to cool naturally for about 16 hours with the heater hood covered.

Shore A hardness (J
Is K-7215) was measured to be 40 to 50, indicating relatively homogeneous physical properties.

Compressive strength of solidified sample in the center (JISK-720
8> was measured and it was 11.5kCI/CII! It was 2. Moreover, no cracks were observed on the surface or inside the solidified body.

Joukisei λ- The same procedure as Example 1 was carried out, except that the proportions of PVC powder, moisture absorbent and elastic polymer in the solidifying agent were as shown in the table below, and the mixture ratio of waste solvent/solidifying agent was 37/63. Solidification treatment was performed in the same manner. Note that the viscosity of the mixed liquid increased to about 800 cps after stirring and mixing for about 1 hour.

The Shore A hardness of the surface and interior of the obtained solidified body was uniform throughout and showed a hardness of 80 to 85.

The compressive strength of the solidified sample in the center is 24.0KMc!
l! It was 2. Further, although fine cracks were observed on the surface of the solidified body, no cracks were observed inside. .

Comparative Example 1 Solidification treatment was carried out in the same manner as in Example 1, except that only PVC powder was used as the solidification treatment agent without using a moisture absorbent or an elastic polymer.

The Shore A hardness of the surface of the 1q ton solidified product was 25 to 50, but the inside was almost O or less and had a pudding-like appearance. In addition, many large racks were observed on the surface and inside of the solidified body.

1 - Solidification treatment was carried out in the same manner as in Example 1, except that PVC powder and a moisture absorbent were used as the solidification treatment agent without using an elastic polymer.

The surface hardness of the obtained solidified material was 55 at the periphery of the drum and 10 at the center of the drum, and the internal hardness of the solidified material was 30 to 45 at the center and below O at the bottom, giving it a pudding-like appearance. It became a heterogeneous solidified body. In addition, large racks were observed on the surface of the solidified material.

Comparative Example 3゜PVCr Zeon 135JJ (manufactured by Nippon Zeon ■) 10
0 parts pvc r Zeon 121J (made by Nippon Zeon (II)
10 parts moisture absorbent (calcium oxide rc) IL #31J) 5
0 parts Elastic polymer "Nosolex" 13 parts Thermosetting plasticizer (acrylic acid ester) 70 parts Thinning agent 1"W-2
12-J J (manufactured by Katsuyama Kako ■) 5 parts Viscosity modifier (n-paraffin) 13 parts The above components were mixed in a planetary mixer and vacuum defoamed to prepare a PVC plastisol.

Next, the non-radioactive simulated waste solvent used in Example 1 and the above PVC
Plastisol and PVC plastisol were put into a 1001 drum so that the mixing ratio of waste solvent/PVC plastisol was 40/60 (weight ratio), and the mixture was stirred and mixed at room temperature for about 40 minutes using an in-drum mixer. Although the liquid temperature of the mixed liquid increased by about 15°C, the viscosity of the mixed liquid was as low as about 40 cps.

Next, the mixed liquid in the drum was heated to about 800 ml using a low frequency induction heater.
The mixture was heat-treated at 0° C. for about 7 hours to form a solidified product.

When the Shore A hardness of the surface and inside of the obtained solidified body was measured, the surface showed 5 to 301, the inside showed 10 to 15, but the lower part was soft as O to 3, and the solidified body was overall heterogeneous. It became. Furthermore, although there were no cracks on the surface of the solidified product, large racks were found inside.

Table note) *1 Smooth surface, no cracks *2 Fine cracks occur on the surface *3 The surface expands and a large rank occurs *4 See text *5 Compressive strength at the center of the solidified body (effect of the invention) As explained above In this invention, since the P■C powder powder elastomeric polymer and moisture absorbent are used as the solidifying agent, physical properties such as appearance, mechanical strength, and homogeneity do not change even after heating and solidifying at a relatively low temperature of about 80 parts. It is also possible to produce 1 q of good solidified material.

In particular, in this invention, since an elastic polymer having dodecane absorption properties is used, it is possible to impart resistance to the tearing force accompanying the thermal stress generated inside the solidified body after heating is stopped, and to prevent the occurrence of cracks. In addition, it reduces the mechanical strength reduction phenomenon inside the solidified body caused by dodecane contained in the waste solvent, improves the mechanical strength inside the solidified body, and prevents bleeding from the solidified body.
A homogeneous solidified body can be obtained throughout.

Claims (1)

[Claims] 1. Add vinyl chloride resin powder, an elastic polymer, and a moisture absorbent as a solidifying agent to a radioactive waste solvent containing a phosphoric acid ester, stir and mix, and then heat and solidify the mixture. A method for solidifying radioactive waste solvent, characterized by: 2. The solidification treatment agent according to claim 1, wherein the proportions of each component of the solidification treatment agent are 2 to 10 parts by weight of the elastic polymer and 5 to 25 parts by weight of the moisture absorbent to 100 parts by weight of the vinyl chloride resin powder. Processing method.