JPS6119958B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of treating radioactive waste liquid. More specifically, the present invention particularly relates to the treatment of medium and low level radioactive waste fluid containing radioactive ruthenium generated from spent nuclear fuel reprocessing plants. The radioactive ruthenium ^-106 Ru contained in the waste liquid forms many types of nitrosyl compounds with the coexisting nitric acid during the treatment process, and depending on one method, only some types of nitrosyl compounds are removed and other nitrosyl compounds remain. Therefore, removal efficiency cannot be improved, making it an extremely troublesome nuclide in terms of waste treatment. Evaporative concentration is a method for treating radioactive waste liquids that can be treated with relatively high removal efficiency even if they exist as a mixture of various chemical forms. Economical treatment is difficult with treatment methods, and ion exchange methods, coagulation precipitation methods, etc. are also used. The purpose of the present invention is to efficiently remove radioactive ruthenium, which has many different chemical forms, by using a column method using a mixture of metal powder and activated carbon as an adsorbent instead of the conventional coagulation-precipitation method or ion exchange method. It is in. The present invention consists of passing a waste liquid containing radioactive ruthenium ¹⁰⁶ Ru through a column packed with a mixture of metal powder and activated carbon. In carrying out the present invention, the pH is set to 3 to make ¹⁰⁶ Ru most easily adsorbed.
Efficiency can be increased by adjusting back and forth. The structure and effects of the present invention will be specifically explained below with reference to Examples. The waste liquid containing radioactive ruthenium used in this example and others is a liquid obtained by irradiating uranium oxide in a nuclear reactor, dissolving it in nitric acid, neutralizing it with caustic soda, and subjecting the uranium to uranium hydroxide by Hz over-separation. It contains only a small amount of chemically radioactive ruthenium that can be removed by the conventionally used iron hydroxide coprecipitation method. Example 1 Particle size 100 in a glass column with an inner diameter of 18 mm and a length of 83 mm.
It was filled with a mixture of 3 g of mesh activated carbon and 5 g of zinc powder, and a waste liquid containing ¹⁰⁶ Ru was passed through at 300 c.c./hour. Adjust the acidity of the waste liquid to PH = 2, 3, 4, and 5, respectively, and pass water through it.
The decontamination coefficient was determined by comparing the radioactivity concentration of ¹⁰⁶ Ru with the value before water flow (undiluted solution). The results are shown below.

[Table] Example 2 The acidity of the waste liquid containing ¹⁰⁶ Ru was adjusted to PH = 3,
Using the same column as used in Example 1, 100 meshes of copper powder and iron powder were used instead of zinc to determine the decontamination coefficient. In this experiment, the water flow rate was 500
I made it cc.

[Table] Comparative example 1 The acidity of waste liquid containing ¹⁰⁶ Ru was adjusted to PH = 3,
The decontamination coefficient was determined when activated carbon and zinc powder were used alone as fillers. In this experiment, the water flow rate was 200 c.c.

[Table] Comparative Example 2 Comparative experiments were conducted on some typical methods for removing ¹⁰⁶ Ru from radioactive waste liquid.

[Table] Sieve method As is clear from the results of Examples and Comparative Examples, ¹⁰⁶ Ru can be effectively removed using a column whose adsorbent is a mixture of activated carbon and zinc powder. Furthermore, by setting the pH of the solution containing ¹⁰⁶ Ru to 3 or less, ¹⁰⁶ Ru could be removed with an even higher decontamination coefficient. A similar tendency was observed when copper powder, iron powder, or a mixed powder thereof was used. Since only a low decontamination coefficient was obtained in experiments using activated carbon or zinc powder alone, the ¹⁰⁶ Ru compound contained in the waste liquid was used to cationize ruthenium, which is present as an anion, by the combination of zinc powder and activated carbon. This is thought to be due to the fact that it becomes easily adsorbed by activated carbon. Traditionally done
Comparative experiments were conducted on several ¹⁰⁶ Ru removal methods, but the decontamination coefficients for ¹⁰⁶ Ru were all low at 1.0 or less. As a removal method based on a principle relatively similar to the method of the present invention, there is a method in which ferrous ions are adsorbed on hydrous titanic acid, and ¹⁰⁶ Ru is reduced on a column to convert it into a chemical form that is easily adsorbed on hydrous titanic acid. The zinc powder + activated carbon according to the present invention has a higher decontamination coefficient, and unlike the ferrous titanate method, ferrous iron, which is a reducing agent, is not eluted and disappears, making it possible to increase the throughput.

Claims (1)

[Claims] 1. Radioactive ruthenium is removed by passing waste liquid containing radioactive ruthenium through a column packed with a mixture of activated carbon and metal powder selected from zinc, copper, iron, and mixtures thereof. Method of treatment of radioactive waste liquid. 2. The method according to claim 1, wherein the waste liquid is adjusted to a pH of about 3.