JPS61117494A - Method of treating radioactive waste - 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 [Field of Industrial Application] The present invention relates to a method for treating radioactive waste from nuclear power plants and the like.

[Conventional technology]

One method for treating radioactive waste fluid from nuclear power plants is to condense the waste fluid through evaporation, solidify it with asphalt, and seal it in drums.Currently, several hundred thousand drums have been produced. Although it has reached
Leakage and preservation of radioactive materials due to asphalt deterioration#
I have a problem. In addition, it is impossible to dump the waste into the ocean when it is solidified as asphalt, and 5th treatment using K, such as plastic solidification, is required.

[Problem that the invention seeks to solve]

The purpose of the present invention is to selectively recover a part of asphalt from the asphalt solidified product, reduce the volume of the asphalt solidified product, reduce the storage area of the reduced volume product, and further perform tertiary treatment such as plastic solidification. The purpose of the present invention is to provide a method for treating radioactive waste, which is a pre-process. In other words, according to the present invention, the area around the reduced volume of solidified asphalt is solidified with plastic, and it is again canned in drums to prevent the leakage of radioactive materials due to asphalt deterioration.Furthermore, depending on the performance of the plastic, it is possible to dump it into the ocean. The purpose is to provide a method for disposing of radioactive waste.

[Means for solving problems]

The present invention, as a means for achieving the above object, consists in mixing a solvent into a heat-treated mixture of radioactive waste and asphalt, and separating the mixture into asphalt and radioactive waste/residual liquid. That is, the present invention mixes and heats radioactive waste and asphalt, mixes a dissolving solvent into the heated mixture to produce a mixture, and then converts this mixture into asphalt and a residual liquid in which radioactive waste is concentrated. This is a method for treating radioactive waste, which is characterized by separating it.

The present inventor added a dissolving solvent that dissolves only a portion of the asphalt to an asphalt heat-treated mixture of radioactive waste, controlled the temperature and pressure, and carried out gravity sedimentation. M&*Ba0t or N
It was found that almost the entire amount of aW8Q4 and a part of the asphalt coagulated and selectively formed a precipitate. and,
The present invention was completed based on the discovery that radioactive waste can be reduced in volume by such a method. This volume reduction rate is based on the amount of bath M added to the asphalt solvent? When it is controlled, it can be controlled arbitrarily by K.

The present invention will be explained in detail below based on FIG. FIG. 1 shows a flow sheet for implementing the invention.

Radioactive waste is mixed with asphalt in heating zone 1,
A heat-treated mixture from which moisture has been almost completely removed is produced.

The typical main components and composition of the radioactive waste asphalt heat treatment mixture are asphalt about 6 to 40 (about 500pp)
m).

NhgBOa or lag B, Oy exists in the cooling water of nuclear reactors and is used in large amounts as a radiation absorber.

Next, the heat-treated mixture and the dissolving solvent are mixed in the mixing zone 2 to produce a mixture. The mixing zone 2 may be of a stirring shaft type or a known device such as a static mixer without any particular ingenuity.

Moreover, the heat-treated mixture 1 of the radioactive waste and asphalt
! It is preferable to add 1 part by weight of 2 to 8 parts of the dissolving solvent per i part.

If the amount added is less than 2 parts by weight, the separation performance will decrease due to an increase in viscosity. Moreover, when the amount added is 8i parts or more, the separation performance remains almost constant, resulting in a decrease in the thermal efficiency of the process and an increase in equipment cost.

The temperature reaction pressure is controlled for one period under almost the same conditions as the separation zone 3 in the next step.

In the present invention, the dissolving solvent is a paraffin compound, a monocyclic naphthenic compound, a monocyclic aromatic compound, or a mixture thereof, which must be liquid at room temperature for ease of handling, and because of its solubility in asphalt, and has a critical temperature of 350. ℃
The following substances are preferred. Typical dissolving solvents are shown in Table 1.The mixture is then introduced into the separation zone 3, where the asphalt substantially free of Mac B, 07 or Na1SO4 etc. is overflowed by power settling. The dissolved solvent is recovered in the solvent recovery zone 4.

On the other hand, part of the asphalt that does not dissolve in the dissolving solvent and Na1B
The substance consisting of aOt or Na1SO4 coagulates and settles and is recovered in the underflow, and the dissolved solvent is recovered in the solvent recovery zone 5.

Next, preferred conditions for the gravity sedimentation will be described below.

The operating temperature should be 150° C. or higher in order to minimize the viscosity and specific gravity of the mixture and increase the separation efficiency. However, since coking reactions due to polycondensation and thermal decomposition reactions occur at temperatures above about 550° C., the temperature of the treated product should be below this temperature.

Next, the pressure should be higher than the vapor pressure of the dissolving solvent in order to stably maintain the solvent in a homogeneous phase. Practically speaking, an enclosure of 1.0 to 5 times the vapor pressure is sufficient.

Hereinafter, the present invention will be explained in detail by giving examples of the present invention.

Example 1 6 parts by weight of n-hexano was added as a dissolving solvent to 1 part by weight of an asphalt heat-treated mixture of radioactive waste generated from a PWR nuclear power plant, and the mixture was charged into a vertical autoclave with an internal volume of 6 L. While stirring, increase the temperature to 20
After holding at 0°C and pressure of 4011y/, ff1G for 10 minutes, it was allowed to stand for about 30 minutes at the same temperature and pressure, and the supernatant liquid and residual liquid were collected from the sampling nozzle, and υn-hexane was removed by evaporation. .

The material balance results are shown in Table 2.

In this case, the volume reduction rate is It was made.

Table 2 (Example 1) Example 2 In Example 1, the separation performance was measured by changing the amount of dissolving solvent added.

As a result, when 2 parts or less of the dissolving solvent was added to 1 part by weight of the heat-treated mixture, the content of Na*E40y in the supernatant liquid increased to 4.0 parts by weight or more. .

Example 3 In Example 1, cyclohexane and Penze/ were used as the dissolving solvent. The results are shown in Table 5.4. The volume reduction rate was 40g CX and 56% by weight, respectively.

Table 3 (Example 3. Cyclohexane) Table 4 (Example 3. Benzene) Example 4 In Example 1, a radioactive waste heat treatment mixture generated from a BWR type nuclear power plant was treated. The results are shown in Table 5.

The volume reduction rate was 30X by weight.

Table 5 (Example 4) [Effects of the Invention] As detailed above, the present invention uses a dissolving solvent to asphalt heat-treated radioactive waste into asphalt and radioactive waste concentrated residual liquid. Since the asphalt is separated into two parts, it has the effect of reducing the volume of the solidified asphalt.
, As a result, the storage space for the solidified asphalt is reduced;
Furthermore, the plastic can be easily re-solidified, which has the effect of preventing leakage of radioactive substances due to deterioration of asphalt.

BRIEF DESCRIPTION OF THE FACE FIG. 1 is a flow sheet for carrying out the present invention.

Sub-agent: 1) Akira Sub-agent Ryo Ogihara -

Claims (1)

[Claims] Radioactive waste and asphalt are mixed and heated, a dissolving solvent is mixed into the heated mixture to produce a mixture, and then,
A method for treating radioactive waste, comprising separating the mixture into asphalt and a residual liquid in which radioactive waste is concentrated.