JPH10227895A - Solidification processing method of radioactive waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve holding performance for radioactive iodine of radioactive waste solid body by adding an oxidizing agent of a specific concentration in the case of solidifying processing radioactive waste with a cement group solidifier agent. SOLUTION: In solidifying processing, condensed waste liquid is supplied form a waste liquid tank 1 through a constant amount supply device 4 to a kneader 5 and a cement group solidifying agent is supplied from a solidifying agent tank 2 through a quantifying supply device 6 to the kneader 5. The oxidizing agent is supplied so as to be 0.01mol for 100g of waste solid weight from a oxidizing agent tank 3 through a constant amount supply device 7 to the kneader 5. For oxidizing agent, peroxodisulfate, silver oxide, permanganate or dichromate are used. After sufficiently mixing with the kneader 5, the cement paste of the condensed waste liquid is injected in a solidifying vessel 9 with an electromagnetic valve 8 and is statically cured for ca. a month. By this, holding capability of radioactive iodine of solid by cement group solidifying agent can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for solidifying radioactive waste.

[0002]

2. Description of the Related Art Radioactive waste generated from facilities handling radioactive materials such as nuclear power plants is described in, for example, "R & D on Radioactive Waste Treatment and Disposal" (Industrial Technology Publishing, pp. 57).
-65, 1983, Ryo Amanuma and Sadahiro Sakata) show that a cement-based solidifying agent can stably solidify.

[0003] On the other hand, in order to hold radioactive nuclides in a solidified state in a solid state for a long period of time, solid radioactive nuclides to be disposed of on land are evaluated for their retention performance. That is, assuming the case where the solidified body is disposed of on land, the amount of radionuclide leakage from the solidified body to the groundwater when groundwater infiltrates the repository is evaluated by the distribution coefficient which is an index of the retention performance. The partition coefficient is determined by Equation 1 after the solidified waste in the form of fine powder is stirred in water to be in a steady state, and the larger the value is, the higher the radionuclide retention performance of the solidified body is. It is common to judge.

[0004]

## EQU00001 ## Partition coefficient (mL / g) = concentration of radionuclide in solidified body (Bq / g) / concentration of radionuclide in water (Bq / mL) ... (Equation 1) Each radionuclide of solidified waste The partition coefficient varies depending on the type of radioactive waste to be solidified. For example, the partition coefficient of a solidified cement containing no waste is described in “S. Hoglund, L. Eliasson, B. Allard, K. Ander.
sson, B. Torstenfelt; Sorption of Some Fissi
on Products and Actinides in ConcreteSystems, Mate
rials Research Society Symposium Proceeding Vol.
50, pp. 683-690, 1985 ". For example, the distribution coefficient of the solidified waste pellets of the used ion exchange resin is referred to as the" partition coefficient of the solidified intermediate storage pellets "((Corporation ) Abstracts of the Atomic Energy Society of Japan, 1996 Annual Meeting, p. 639, Masaaki Kaneko, Naomi Toyohara, Tatsuaki Sato, Masahiko Inakuma). From these reports,
It turns out that the partition coefficient of radioactive iodine is lower than that of other radionuclides.

On the other hand, means for improving the distribution coefficient of radioactive iodine is described in "Immobilization of radioactive iodine by cement" (Abstracts of the Atomic Energy Society of Japan, 1995 Autumn Meeting, p.681, Masaaki Kaneko, As reported by Naomi Toyohara and Mikio Wada), a method of adjusting the calcium / aluminum ratio in cement to about 2 has been reported.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the holding performance of radioactive waste solidified body using a cement-based solidifying material for radioactive iodine.

[0007]

The above object can be achieved by adding an oxidizing agent at the time of producing a solidified radioactive waste.

[0008] In order to improve the retention performance of radioactive iodine by the solidified radioactive waste using a cement-based solidifying material, that is, to improve the distribution coefficient, the present inventors first settled the iodine contained in the radioactive waste. The chemical form was investigated.
As a result, in most cases, most of the radioactive waste, especially from nuclear power plants, is mostly iodine ions (I ~).
). However, some iodine was found to exist as iodate ions (IO ₃ ~). Then, the inventors obtained the distribution coefficients of iodine ions and iodate ions as follows. That is, radioactive iodine is prepared with iodine ions and iodide ions, each of which is solidified using ordinary Portland cement, which is the most common cement-based solidifying material. Was core-bored, and the sample was immersed in water to obtain the distribution coefficient of radioactive iodine. as a result,
The partition coefficient of iodine ion was 50 (mL / g), while the partition coefficient of iodine ion was 2800 (mL / g).
g) and more than 50 times higher.

[0009] Therefore, the present inventors thought that if the iodine ions contained in the radioactive waste could be converted into iodide ions, the retention performance of the radioactive iodine by the cement could be improved. Also, it was considered effective to add an oxidizing agent at the time of producing the solidified waste as a means for that.

A specific oxidizing agent is described in “Marcel Pourbaix, A
tlas of Electrochemical Equilibria, Pergamon Pres
s, p618, 1966 ", oxidation of 1.085 (V) or more, which is the difference between the standard electrode potentials of iodide ions and iodate ions in an aqueous alkaline solution having a pH of about 12, such as cement. From the viewpoint of reducing the influence on the other physical properties of the solidified waste such as physical strength, etc., these oxidizing agents are preferably used in the form of solid peroxodisulfate, silver oxide, permanganate. Salts and dichromates are more preferred.

Further, the method of adding the oxidizing agent includes a method of adding to the cement-based solidifying material, a method of adding to the kneading water, a method of adding to the radioactive waste, a method of adding to the admixing material to the solidifying material, and a method of kneading with the solidifying material. It is considered that any method of adding water when mixing is effective.

Further, these methods can be applied not only to solidifying materials for directly solidifying radioactive waste, but also to cement-based backfill materials used in land disposal facilities.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) In this embodiment, a concentrated waste liquid generated from a BWR plant is solidified, and FIG. 1 shows a flow of a treatment system.

The concentrated waste liquid generated from the BWR plant has been stored in the waste liquid tank 1. Further, the cement-based solidifying material was stored in the solidifying material tank 2 and the oxidizing agent was stored in the oxidizing agent tank 3.

At the time of the solidification treatment, 167 kg of the concentrated waste liquid was supplied to the kneading device 5 through the quantitative supply device 4. The cement-based solidification material is supplied to the kneading device 5 through the
kg supplied. Further, in this example, in order to examine the effect of adding various oxidizing agents, the oxidizing agent was changed to a waste solidified body weight of 100 g.
And supplied to the kneading device 5 through the fixed amount supplying device 7 so as to be 0.01 mol. At this time, as the type of the oxidizing agent, a case where no oxidizing agent was added and a case where peroxodisulfate, silver oxide, permanganate and dichromate were added as the oxidizing agent were implemented.

Then, after sufficiently kneading in the kneading device 5, the cement paste of the concentrated waste liquid was injected into the solidification container 9 by the electromagnetic valve 8. After curing for about one month, the core of each solid was core-bored, and the sample was immersed in water to obtain the distribution coefficient of radioactive iodine.

Table 1 shows a comparison of the distribution coefficients of radioactive iodine when each oxidizing agent is added. as a result,
When no oxidizing agent was added, the partition coefficient was 50 (mL /
g), it was found that the distribution coefficient could be improved to 20 times or more in any case by adding the oxidizing agent.

[0018]

[Table 1]

In this embodiment, the concentrated waste liquid is taken as the radioactive waste. However, the present method is effective when all the radioactive wastes including radioactive iodine are maintained with the cement-based solidifying material. .

(Embodiment 2) In this embodiment, a concentrated waste liquid pellet generated from a BWR plant of a nuclear power plant is solidified, and FIG. 2 shows a flow of a treatment system.

The concentrated waste liquid generated from the BWR plant is
The powder was formed into a powder by a drier, and further formed into almond-shaped pellets having a length of about 3 cm by a granulator. Further, the solidification material tank 11 stores the cement-based solidification material, and the mixing water tank 12 stores the mixing water. In this example, peroxodisulfate was added as an oxidizing agent to the kneading water in advance with the addition amount as a parameter.

During the solidification process, the pellets are taken out of the take-out device 13.
After that, it was transferred to the pellet hopper 15 by the suction device 14. Thereafter, 200 kg was supplied to the kneader 17 through the fixed amount transfer device 16. 151 kg of the cement-based solidified material was supplied to the kneading device 17 through the quantitative supply device 18. In addition, 83 L of the kneading water was supplied to the kneading device 17 through the quantitative supply device 19. Then, the kneading device 17
After sufficiently kneading, the cement paste of the pellets was poured into the solidification container 21 by the electromagnetic valve 20. About 1
After curing for one month, the core of each solid was core-bored and the sample was immersed in water to obtain the distribution coefficient of radioactive iodine.

FIG. 2 shows a comparison of the distribution coefficient of radioactive iodine when the amount of peroxodisulfate is used as a parameter. As a result, the amount of the oxidizing agent added becomes
It was found that when 0.01 mol or more was added to 0 g, the distribution coefficient was significantly improved. It was found that the same tendency was exhibited when other oxidizing agents, that is, silver oxide, permanganate, and dichromate were added.

In the present embodiment, the concentrated waste liquid pellets are taken as the radioactive waste. However, the present method is effective for securing the holding performance of all radioactive wastes including radioactive iodine by the cement-based solidifying material. is there.

[0025]

According to the present invention, there is an effect that the radioactive iodine retention performance of the solidified radioactive waste solidified by the cement-based solidifying material can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a system for solidifying a concentrated waste liquid used in an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a system for solidifying radioactive waste used in an embodiment of the present invention.

FIG. 3 is an explanatory diagram of the influence of the amount of an oxidizing agent used in an example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Waste liquid tank, 2 ... Solidification material tank, 3 ... Oxidizing agent tank, 5 ... Kneading apparatus, 8 ... Electromagnetic valve, 9 ... Solidification container.

Claims (4)

[Claims] 1. A method for solidifying radioactive waste, comprising the step of solidifying a radioactive waste containing radioactive iodine with an oxidizing agent when solidifying the radioactive waste with a cement-based solidifying material. 2. The method according to claim 1, wherein the oxidizing agent has a standard electrode potential difference of 1.085.
2. The method for solidifying radioactive waste according to claim 1, wherein the method further comprises (V) oxidizing power. 3. The method for solidifying radioactive waste according to claim 2, wherein said oxidizing agent is peroxodisulfate, silver oxide, permanganate or dichromate. 4. The method for solidifying radioactive waste according to claim 3, wherein the oxidizing agent is added in an amount of 0.01 mol or more based on 100 g of the solidified radioactive waste.