JPH0395500A - Decontamination of equipment/member for fast breeder reactor - Google Patents

Abstract

PURPOSE:To intend decrement of worker's radioactive exposure by blowing high temperature argon gas and steam, to an equipment and the like on which a sodium and radioactivity stick, in order to remove the sodium and then by decontaminating them using an oxidizing alkaline decontaminating liquid and a reducing decontaminating liquid. CONSTITUTION:In a high temperature argon gas deterging process, the high temperature argon gas is blown to a valve and the like on which a sodium sticks and the sodium is coarsely removed. Then, in a steam deterging process, the steam is blown to, and the sticking sodium remaining on the equipment is converted into an hydroxide, and is removed. Subsequently, potassium permanganate is added to a sodium hyroxide solution recollected in a producing process of an oxidizing alkaline decontamination liquid, and an oxidizing alkaline decontaminating agent is produced. Decontamination work of the equipment from which the sodium is removed, is carried out by using the decontamination agent. Also, in a reducing decontamination process, a reducing decontamination work is carried out by using an oxalic acid. In this way, radioactivity sticking to the equipment and the like, can be removed by both the oxidizing alkaline decontamination process and the reducing decontamination process.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to fast reactor equipment that is contaminated with radioactivity generated during maintenance and inspection of fast reactor equipment that uses liquid sodium as a coolant. Concerning decontamination methods for equipment and parts.

(Prior art) Equipment decontamination in fast breeder reactors (hereinafter referred to as fast reactors) is conventionally carried out by cleaning contaminated equipment with inert gas or air, cleaning it with steam, and then immersing it in water to remove adhering sodium and radiation. Noh was removed.

This decontamination method is suitable for removing sodium adhering to equipment.

(Problems to be Solved by the Invention) However, this decontamination method was unable to completely remove the radioactivity attached to the mother shrine, resulting in the problem of increased radiation exposure of workers.

In addition, the waste liquid generated by steam cleaning and immersion in water was stored as is, resulting in an increase in secondary waste.

The present invention was made to solve this problem,
Sodium adhering to equipment and components is removed by high-temperature inert gas and steam cleaning, and radioactivity is completely removed using oxidizing and reducing decontamination to reduce radiation exposure of workers, and secondary disposal is also carried out. The object of the present invention is to provide a method for decontaminating fast reactor equipment and components that reduces the amount of waste generated.

[Structure of the Invention] (Means for Solving the Problems) The present invention roughly recovers the adhering sodium from equipment and components to which sodium and radioactivity have adhered in a high-temperature argon gas removal process, and then performs a steam cleaning process to remove the adhering sodium. The residual adhering sodium/lium is washed away, and then, as the first stage of decontamination, decontamination is carried out using an oxidizing alkaline decontamination solution consisting of a mixture of potassium permanganate and sodium hydroxide in the oxidizing alkaline decontamination process. After washing the adhesion decontamination solution with water, the second stage of decontamination is decontamination using a reducing (organic acid) decontamination solution such as oxalic acid or citric acid, followed by adhesion decontamination. It is characterized by washing the liquid with water.

In addition, the oxidizing alkali decontamination waste liquid and the reducing decontamination waste liquid generated in the oxidizing alkali decontamination process and the reducing alkali decontamination process are stabilized in the waste liquid treatment process, and are characterized by being concentrated, dried, and solidified.

(Function) When high-temperature argon gas is blown into equipment and parts contaminated with sodium and radioactivity, the sodium evaporates and is accompanied by argon gas, roughly removing sodium and lithium from the equipment.

Next, by blowing in steam, the residual sodium is converted into hydroxide and removed by washing with water. Radioactivity attached to equipment and parts is partially removed along with sodium through argon gas cleaning and steam cleaning, but radioactivity attached to base materials is not completely removed. Therefore, the water vapor after steam cleaning is condensed and recovered, an oxidizing agent is added to produce an oxidizing alkaline decontamination liquid, and this decontamination liquid is used for decontamination after steam cleaning. Next, decontamination is performed using a reducing decontamination solution. After decontamination, the decontamination waste liquid is mixed, stabilized, concentrated, dried, and solidified before being stored.

In this way, in the present invention, high-temperature argon gas and steam are blown into equipment and parts that are contaminated with sodium and radioactivity.
Since Na1 and Lium are removed and then decontamination is performed using an oxidizing alkaline decontamination solution and a reducing decontamination solution, radioactivity can be removed from equipment and parts, making it possible for workers to be exposed to radiation. Radiation exposure can be reduced. In addition, since the decontamination waste liquid is mixed stably, concentrated, dried, and solidified, secondary waste can be reduced.

(Example) Hereinafter, an example of the method for decontaminating fast reactor equipment and parts according to the present invention will be described in Section 1. This will be explained using figures. When argon gas at 300 to 500°C is blown into decontaminated equipment and parts such as valves or pumps that have sodium adhering to them during the high-temperature argon gas cleaning process, the sodium evaporates and roughly removes sodium from the equipment and parts. . The evaporated sodium is accompanied by argon gas, and when the argon gas is cooled in the argon gas purification step, the sodium is vapor trapped and recovered. The recovered sodium can be reused as a coolant for fast reactors. After the adhering sodium is roughly removed, water vapor is sprayed in a steam cleaning step, and the adhering sodium remaining on the equipment and parts is converted into hydroxide and removed. The water vapor contained in sodium hydroxide is condensed in a steam condensation step and recovered as a sodium hydroxide solution.

The high-temperature argon gas cleaning process and steam cleaning process can remove sodium attached to equipment and parts and the radioactivity contained in sodium, but cannot completely remove the radioactivity attached to the base materials of equipment and parts. Have difficulty. Therefore, a chemical decontamination agent is used to remove the radioactivity attached to the motherboard.

In the first stage of decontamination, potassium permanganate (K.Mn 04 ), an oxidizing agent, is added to the sodium hydroxide solution recovered in a certain process to produce an oxidizing alkaline decontamination solution. There is. This decontamination agent will be used to decontaminate equipment and parts from which sodium has been removed. After decontamination, the decontamination liquid adhering to equipment and parts is washed away with water during the washing process.

Next, as the second stage of decontamination, oxalic acid (
Perform reductive decontamination using a reducing decontamination solution (reducing decontamination solution). After reduction decontamination is completed, the decontamination agent adhering to equipment and parts is washed away with water in the washing process. After use, the rinsing liquid after decontamination in the second stage is used as the rinsing water in the first stage.

The oxidizing alkali decontamination process and the reducing decontamination process can remove radioactivity (60Co, 54Mn, etc.) attached to equipment and parts, making it possible to reuse decontaminated equipment and parts such as valves and pumps6. can do.

On the other hand, the oxidizing alkaline decontamination solution (mixture of potassium permanganate and sodium hydroxide) used in the first stage of decontamination
The reducing decontamination liquid (oxalic acid) and washing water used in the second stage are generated as decontamination wastewater, so they are mixed in the wastewater treatment process. When potassium permanganate and oxalic acid are mixed, the following redox reaction occurs and becomes stable.

M n o −+ 5/2H 2 C 2 0 44 → M n 2” + 5 C O 2↑+5H” This stabilized decontamination waste liquid is heated, concentrated, dried and solidified, and then stored.

Note that the reducing decontamination liquid used in the reducing decontamination step is not limited to oxalic acid, and similar effects can be obtained by using organic acids such as citric acid and formic acid.

Next, the results of decontamination carried out to confirm the effects of the above embodiment will be explained with reference to FIG. In FIG. 2, the vertical axis represents the amount of surface contamination in arbitrary units, and the horizontal axis represents the cleaning and decontamination steps of the decontamination method of the present invention. Further, the circles indicate the amount of surface contamination when decontaminated in each step, and the horizontal line a indicates the background level. As is clear from this Figure 2, by using the decontamination method according to the present invention, not only sodium adhering to equipment and parts, but also radioactivity can be reduced to the pack ground level, and the decontaminated equipment and parts can be reduced to the ground level. can be reused.

The embodiments of the present invention can be summarized as follows.

■ After steam cleaning, the steam is recovered as a sodium hydroxide solution in the steam condensation process, and the sodium hydroxide solution recovered in the process is mixed with potassium permanganate to produce an oxidizing alkaline decontamination solution. Use as an oxidizing alkaline decontamination solution in the process.

■ The used aqueous solution after the 2nd stage water washing should be used as the rinsing solution after the 1st stage decontamination.

■ Oxidizing alkaline decontamination wastewater and reducing decontamination wastewater generated after the ↓ stage decontamination and the second stage decontamination should be mixed and stabilized in the wastewater treatment process, and then concentrated and dried to solidify.

[Effect of the invention] According to the present invention, the following effects are achieved.

(1) Since sodium can be removed by high-temperature argon gas cleaning and steam cleaning, and radioactivity can be removed by oxidizing alkaline decontamination liquid and reducing decontamination liquid, radiation exposure of workers can be reduced.

(2) Since oxidizing alkaline decontamination liquid and reducing decontamination liquid are not corrosive, decontaminated equipment and parts can be reused.

(3) The decontamination waste liquid can be mixed, stabilized, condensed, dried, and solidified, so secondary waste can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block flow diagram showing a method for decontaminating fast reactor equipment and members according to the present invention, and FIG. 2 is a characteristic diagram showing the decontamination effect of the present invention. a...Background 9 Figure 1

Claims (1)

[Claims] Equipment and parts contaminated with sodium and radioactivity are subjected to a high-temperature argon gas removal process to roughly recover the adhering sodium, then a steam cleaning process to wash away the remaining adhering sodium, and then oxidizing alkali removal as the first stage of decontamination. Decontamination is performed using an oxidizing alkaline decontamination liquid in the contamination process, and after washing the adhering decontamination liquid with water, decontamination is performed using a reducing decontamination liquid in the reducing decontamination process as the second stage decontamination. A method for decontaminating fast reactor equipment and components, which comprises washing off the adhering decontamination liquid with water.