JP3091349B2 - Metal waste decontamination method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for decontaminating a metal waste which dissolves the surface of the metal waste contaminated with a radioactive substance to remove the radioactive substance attached to the surface. It is.

[0002]

2. Description of the Related Art Metal waste such as stainless steel pipe generated during periodic repair of a nuclear power plant cannot be disposed of because radioactive substances are attached to its surface. Is stored in a drum as it is. However, such a method requires an extremely large storage space, and a solution is required.

Accordingly, the present inventor has found that if the surface of a metal waste to which a radioactive substance is attached is dissolved to a required depth, the inside can be handled as general waste.
A method for decontamination of metal waste, which is decontaminated using a decontamination solution containing nitric acid as a main component, has been previously developed and a patent application has been filed. However, in the past, conditions such as decontamination temperature and decontamination time were empirically set and decontamination was performed by immersion in a decontamination solution regardless of the size of the metal waste. However, there is a problem that the surface is dissolved more than necessary, and a sufficient decontamination effect cannot be achieved due to insufficient dissolved thickness.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, scientifically sets decontamination conditions, and always achieves a stable dissolved thickness regardless of the size of metal waste. The present invention has been made in order to provide a method and an apparatus for decontaminating metal waste that can be used.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and a method for decontaminating metal waste by dissolving the surface of the metal waste with a decontamination liquid is provided. In relation to the decontamination solution temperature and the dissolution time at which the amount of metal waste dissolved by the decontamination solution reaches saturation, the relational expression between the dissolution area / decontamination solution amount and the dissolution thickness is determined in advance, It is characterized in that decontamination is performed with an amount of decontamination solution corresponding to a required dissolved thickness obtained by recognizing a shape of an object, calculating a surface area thereof, and substituting the surface area into the above relational expression. .

A metal waste decontamination apparatus according to the present invention, which has been made to solve the above-mentioned problems, has a metal waste shape recognition apparatus provided at the entrance side of a decontamination chamber and a recognition result based on the recognition result. Calculating means for calculating the surface area of the metal waste and calculating the amount of decontamination liquid necessary to dissolve the surface area to a required dissolution thickness, and a liquid amount control means for the decontamination tank controlled by the calculation means It is characterized by having.

[0007]

According to the present invention, the shape of the metal waste is recognized by the shape recognition device provided on the entrance side of the decontamination chamber, and the surface area is calculated. The calculating means is based on a previously determined relational expression of the dissolution area / the amount of the decontamination solution and the dissolution thickness under the decontamination solution temperature and the dissolution time at which the amount of metal waste dissolved by the decontamination solution reaches saturation. Calculates the amount of decontamination liquid corresponding to the required dissolved thickness, and the liquid amount control means controls the amount of decontamination liquid in the decontamination tank accordingly. For this reason, if the metal waste is decontaminated in this decontamination tank under the above-mentioned decontamination solution temperature and dissolution time, the metal waste will always be dissolved to a certain thickness, and the surface will be unnecessarily exposed. It does not cause problems such as dissolution or insufficient decontamination effect due to insufficient dissolved thickness.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the illustrated embodiments. In the present invention, first, a decontamination solution temperature and a dissolution time at which the amount of dissolved metal waste reaches saturation are determined. Conventionally, decontamination was performed around normal temperature,
Although the amount of dissolution did not reach saturation by gradually increasing with the dissolution time, in the present invention, the composition of the decontamination solution,
By changing the temperature of the decontamination solution and the dissolution time in various ways, the conditions under which the dissolution amount reached saturation in a relatively short time were grasped.

Specifically, the decontamination solution used in this embodiment is a mixed acid obtained by mixing 2 parts by weight of hydrochloric acid and 3 parts by weight of hydrofluoric acid with 20 parts by weight of nitric acid. Stainless steel (SUS 304) was selected as the material. in this case,
As shown in FIG. 1, when the temperature of the decontamination solution is set to 70 ° C., which is higher than the conventional temperature, the solution almost reaches saturation in a dissolution time of 20 minutes. Here, the reason why the amount of dissolution decreases at 80 ° C. is considered to be that the performance of the decontamination liquid decreases due to evaporation. From this result, it can be seen that the dissolving amount of the metal waste reaches complete saturation when the decontaminating solution temperature is set to 70 ° C. and the dissolution time is set to 1 hour in view of safety.

FIG. 2 is a graph showing the relationship between the dissolution area / the amount of the decontamination solution and the dissolution thickness under the above conditions, and the relationship between the dissolution area / the amount of the decontamination solution and the metal ion concentration. This figure 2
As shown in the graph, when the value of the dissolving area / the amount of the decontamination solution exceeds about 0.07 m ² / L, the concentration of the dissolved metal ion becomes 50 to 60.
It can be seen that the melting thickness of the metal waste (stainless steel) can be continuously changed by changing the value of the dissolving area / the amount of the decontamination solution at a level of g / L. Therefore, if the dissolving area of the metal waste is measured in advance and the amount of the decontamination liquid is adjusted, an arbitrary dissolved thickness can be obtained. It is known that the radioactive substance can be completely removed by dissolving 30 μm from the surface of the metal waste, so that the value of “dissolved area / decontamination solution amount” is 0.20 m from the graph of FIG. ^It can be confirmed that ² / L should be used.

FIG. 3 shows an apparatus for carrying out the present invention. The shape of the metal waste is automatically recognized by the metal waste shape recognition device 2 provided at the entrance side of the decontamination chamber 1. Then, the calculation means 3 such as a microcomputer calculates the surface area of the metal waste. The arithmetic means 3 substitutes the surface area of the metal waste calculated in this way into the above-mentioned relational expression of the dissolution area / decontamination solution amount and the dissolution thickness as shown in FIG. Calculate the amount of decontamination solution necessary to dissolve the surface to the required dissolution thickness.

On the other hand, the decontamination tank 4 inside the decontamination chamber 1 has a temperature of 70 ° C.
Is filled with the decontamination liquid, and a decontamination liquid circulation path is formed between the decontamination liquid and the decontamination waste liquid treatment device 5 for regenerating the decontamination liquid. Therefore, the liquid amount control means 6 provided in this circulation path controls the decontamination liquid amount in the decontamination tank 4 based on the calculation result by the calculation means 3. Therefore, if the metal waste is immersed in the decontamination tank 4 and decontaminated for, for example, one hour, a certain thickness (for example, 30 μm) can be dissolved. After that, the metal waste is rinsed in the rinsing tanks 7 and 8 by the crane 9 and taken out. The decontamination liquid containing a radioactive substance is regenerated by the decontamination waste liquid treatment device 5. The metal waste after decontamination in this way is checked for radiation dose, and if it is confirmed that it is safe, it can be treated as general waste.

[0013]

As described above, according to the method for decontaminating metal waste of the present invention, decontamination can always be performed with a stable dissolved thickness regardless of the size of the metal waste. In addition, waste due to excessive dissolution and incomplete decontamination due to insufficient dissolution can be prevented. According to the metal waste decontamination apparatus of the present invention, the above decontamination can be performed automatically. In addition, although an Example is about the decontamination liquid of a specific composition suitable for melt | dissolving stainless steel, it cannot be overemphasized that the kind of metal waste and the composition of a decontamination liquid are not specifically limited to this. That is.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a dissolution time and a dissolution amount.

FIG. 2 is a graph showing the relationship between dissolution area / decontamination solution amount, dissolution thickness and metal ion concentration.

FIG. 3 is a block diagram illustrating an apparatus for decontaminating metal waste according to an embodiment.

[Explanation of symbols]

1 decontamination room, 2 shape recognition device, 3 calculation means, 6 liquid volume control means

Claims (2)

(57) [Claims] In a method for decontaminating metal waste by dissolving the surface of the metal waste with the decontamination solution, the temperature and the dissolution time of the decontamination solution at which the amount of the metal waste dissolved by the decontamination solution reaches saturation. First, a relational expression between the dissolving area / the amount of the decontamination solution and the dissolving thickness is obtained in advance, the shape of the metal waste is recognized, its surface area is calculated, and this is substituted into the above relational expression. A method for decontaminating metal waste, characterized in that decontamination is performed with an amount of decontamination liquid corresponding to the dissolved thickness of the metal. 2. An apparatus for recognizing a shape of a metal waste provided at an entrance side of a decontamination chamber, and calculating a surface area of the metal waste based on the recognition result and dissolving the surface area to a required melting thickness. A decontamination apparatus for metal waste, comprising: a calculating means for calculating a proper decontamination liquid amount; and a liquid amount control means for a decontamination tank controlled by the calculating means.