JPH0356900A - Separation of radioactive nuclide - Google Patents

Abstract

PURPOSE:To allow the adequate management meeting respective cases by separating a specific radioactive nuclide from other radioactive nuclides and separately forming the waste bodies corresponding to the length of a half-life. CONSTITUTION:A diffusion dialysis cell 1 is divided by diffusion dialysis membrane 2 to two chambers so that a liquid 3 to be treated contg. the radioactive nuclides flows in upward current in the left chamber and a recovered liquid 4 flows in downward current in the right chamber. For example, stable Ni<2+> having a sufficiently high concn. is added as a stable isotope 5 to the inlet of the diffusion dialysis cell 1 of the recovery side liquid 4 when the <63>Ni<2+> contained in the liquid to be treated is going to be separated from the other nuclides (R), such a <60>Co<2+>, <90>Sr<2+> and <137>Cs<+>. Both of the liquid 3 to be treated and the recovered liquid 4 are preferably made acidic in such a manner that the stable isotope 5 to be added exists sufficiently as an ion when the cations are separated from each other as in this case. For example, the addition of a small amt. of sulfuric acid to the liquids on both sides suffices.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for separating two or more types of radionuclides of different elements into their respective nuclides, and in particular, a method for separating radionuclides in radioactive waste liquid generated at nuclear facilities. Concerning how to separate.

[Conventional technology]

Radioactive waste fluids generated by nuclear power plants are generally low-level radioactive and contain various types of radionuclides. The conventional processing technology for this is shown in Figure 3.
First, if necessary, suspended solids, that is, solid particles, in the radioactive waste liquid are separated by filtration. The separated particles are taken out together with the filter element of the filtration device or as a liquid with a high particle concentration by backflow, and solidified in a drum can or with cement, etc.
It becomes a waste body. Removal of the solid particles can be omitted if it does not interfere with the subsequent S-condensation operation for reducing the volume of the waste.

Next, from the viewpoint of reducing the amount of waste generated, a reduction operation is performed to obtain a concentrated waste liquid whose volume is reduced. This concentration operation is generally carried out by evaporating water by heating and evaporating. Concentrated waste liquid is solidified in a drum with cement, polymer, etc. and becomes waste. In the case of asphalt solidification, which is one of the solidification methods, water evaporation, that is, concentration operation, and solidification are performed simultaneously with just one operation.

The main part of these low-level radioactive waste liquids is, for example, PWR.
In the case of nuclear power plants, it is boric acid, BWR
In the case of nuclear power plants, it is mirabilite, which has a very low concentration of radionuclides and their isotopes.

It is expected that a permissible concentration limit will be established for each radionuclide (synonymous with the type of radioactive substance) contained in waste, and even radionuclides will no longer be able to be transported outside the plant site if their concentration exceeds that concentration. However, in the conventional method, the generated waste liquid is concentrated without changing the abundance ratio of radionuclides, so there is a high possibility that it will not be able to be transported outside the plant site.

Also, from the perspective of waste management, if radionuclides with various half-lives are mixed, each waste must be managed until the radionuclides with long half-lives have sufficiently decayed.

By the way, the Enforcement Order of the Act on "Regulations for Nuclear Source Materials, Nuclear Fuel Materials and Nuclear Reactors" [Cabinet Order No. 324 of November 21, 1950, revised Cabinet Order No. 41 of March 17, 1988] states that The radioactive substances and their concentrations that shall not be exceeded after the time of carrying out are determined as shown in the following table1.
, [Problems to be Solved by the Invention] In the conventional radioactive waste liquid treatment method, only the volume of the waste is reduced by concentration, so that the radionuclides originally contained in the radioactive waste liquid are concentrated as they are.

Therefore, if even one of the nuclides exceeds the permissible limit concentration, it will no longer be possible to transport them from the plant site.

Furthermore, it is necessary to strictly manage all waste materials until long-half-life nuclides are attenuated.

In order to solve these problems, the present invention aims to provide a method for separating radionuclides that can selectively separate long half-life nuclides.

[Means to solve the problem]

In the present invention, a liquid to be treated and a recovery side liquid containing various radionuclides are caused to flow in countercurrents through a diffusion dialysis membrane, and stable isotopes of a specific radionuclide to be separated in the liquid to be treated are separated from the liquid to be treated. A method for separating radionuclides, which is characterized in that the radionuclides are added to the recovery liquid in the same existing form as the radionuclides in the liquid, and the 11 radionuclides in the liquid to be treated are separated from other radionuclides. be.

[　f乍は]　〕

If there is a difference in the concentration of an element in a certain existing form, the element moves from the higher concentration to the lower concentration through the diffusion dialysis membrane. This movement occurs for each type of element and its existing form, and the difference between isotopes can be ignored for one element and its existing form.

Therefore, if the element concentration on the recovery side is low, the elements contained in the liquid to be treated (including radionuclides, of course) will move to the recovery side via the dialysis membrane.

If the concentration of an element in the recovery liquid is higher than that of the same existing type in the liquid to be treated, conversely, the element will migrate from the liquid to be treated to the liquid to be treated.

Therefore, the stable isotope of the nuclide to be separated into the recovery liquid can be contained at a sufficiently higher concentration (
For example, if the nuclide is added in the same form as the liquid to be treated, so that the concentration is 10 times that of the liquid to be treated, the nuclide that attempts to separate will be recovered from the liquid to be treated. On the contrary, the stable isotope moves from the recovery side to the liquid to be treated.

On the other hand, other nuclides move from the liquid to be treated side to the recovery side due to the difference in concentration. As a result, only the elements containing the nuclide to be separated remain in the liquid to be treated.

In other words, they can be separated.

〔Example〕

[Example 1] An embodiment will be described based on FIG.

The diffusion dialysis tank 1 is divided into two chambers by a diffusion dialysis membrane 2. The liquid to be treated 3 containing radionuclides flows in the left ventricle in a two-way flow, and the recovery liquid 4 flows in the right ventricle in a downward flow. It's flowing.

For example, 6J12+ contained in the liquid to be treated is 60[:
o 2 +! When trying to separate from other nuclides such as lOSr2+, 137c, + (these are collectively abbreviated as R), stable Ni2+ is added to one population of the diffusion dialysis tank of the recovery side liquid 4 at a high concentration for 1 minute. There is 4 added as a stable isotope 5. When separating cations as in this case, both the liquid to be treated 3 and the recovery side A, 4 are made acidic so that the stable isotope 5 to be added is present in a sufficient amount. This is desirable. For example, a small amount of i"1τ1t acid may be added to the liquids on both sides. If the concentrations of sulfuric acid in both liquids are the same, there will be no movement of sulfuric acid through the diffusion dialysis membrane 2. For example, if 1χ, the liquid to be treated When various nuclides exist as ions in a 2N sulfuric acid aqueous solution, the recovery side liquid is also a 2N (1j:j acid aqueous solution), so that sulfuric acid does not migrate through the dialysis membrane. Diffusion A cation exchange model that selectively dialyzes cations is used as dialysis v2.

This supported NiS[) is a stable addition form of N12゛.
An aqueous solution of 4 is preferable, but NiCh, Ni(N[]
．． )2 etc., if Ni exists as Nl2+, {
11f may be sufficient.

The structure of a diffusion dialysis tank is schematically shown in Figure 1 as having one diffusion dialysis membrane, but in reality it is necessary to increase the area of the diffusion dialysis membrane to increase the throughput. As shown, it has a structure with multiple diffusion dialysis membranes. That is, the expansion H
It is common that the liquid to be treated 3 and the liquid on the recovery side flow through the dialysis membrane 2 in countercurrent flow.

The amount of stable isotope added to the recovery side liquid varies depending on the operating conditions and the type of nuclear power to be separated, but in general, the stable isotope is added so that the concentration is about 10 times that of the liquid to be treated. It is sufficient to add the body.

〔Effect of the invention〕

According to the present invention, the following effects can be obtained by separating specific radionuclides from other radionuclides.

(1) It is now possible to create separate waste bodies according to the length of the f-life period, and the pipe J for each waste body is now possible! 11
! Periods can be divided and appropriate management can be carried out according to each period.

(2) By removing nuclides exceeding the permissible limit concentration, the waste produced therefrom can be transported outside the plant.

(3) If there is an optimal assimilation method for each type of nuclide, for example, if there is an optimal assimilation method for each type of nuclear extraction, that method can be used. Alternatively, waste can be sorted by type and intensity of radiation source. This makes it possible to optimally manage each waste, resulting in superior safety, economy, and other aspects.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an apparatus for carrying out an embodiment of the present invention, Fig. 2 is a practical schematic diagram of diffusion dialysis yuzu used in the present invention, and Fig. 3 is a system diagram showing a conventional radionuclide processing system. It is.

Claims (1)

[Claims] The liquid to be treated and the recovery side liquid containing various radionuclides are flowed in countercurrents through a diffusion dialysis membrane, and the stable isotope of the specific radionuclide to be separated in the liquid to be treated is isolated from the radioactivity in the liquid to be treated. 1. A method for separating radionuclides, which comprises adding radionuclides to a recovery liquid in the same form as the nuclides, and separating specific radionuclides in the liquid to be treated from other radionuclides.