JPH0720292A - Method and facility for decontaminating metal waste - Google Patents

Abstract

PURPOSE:To provide a method and facility for decontaminating a metal waste constantly at a stabilized dissolution thickness regardless of the size thereof. CONSTITUTION:The temperature of decontaminating liquid and the dissolution time required for saturating the dissolving quantity of metal waste are determined and then the relationship between the ratio of dissolving area/quantity of decontaminating liquid and the thickness of dissolution is determined. A shape recognition device 2 then recognizes the shape of metal waste and calculates the surface area thereof. An operating means 3 substitutes the value into the relational equation and operates the quantity of decontamination liquid corresponding to a required thickness of dissolution. A liquid quantity control means 6 then controls the quantity of decontaminating liquid in a decontamination tank 4 based on the operation results and conducts the decontamination of the metal waste.

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 by dissolving the surface of the metal waste contaminated with radioactive substances to remove the radioactive substances adhering to the surface. Is.

[0002]

2. Description of the Related Art A metal waste such as a pipe made of stainless steel, which is generated at the time of periodic repair of a nuclear power plant, cannot be discarded because radioactive substances adhere to the surface of the metal waste. Is stored in a drum as it is. However, such a method requires an extremely large storage space, and therefore a solution is required.

Therefore, the present inventor has found that if the surface of a metal waste to which radioactive substances adhere is dissolved to a required depth, the inside can be handled as general waste,
A decontamination method for metallic waste, which uses a decontamination solution containing nitric acid as a main component for decontamination, was previously developed and a patent has been applied for. However, in the past, conditions such as decontamination temperature and decontamination time were set empirically, and decontamination was performed by immersing the metal waste in the decontamination liquid regardless of the size of the waste metal, and therefore the variation in the dissolution thickness was varied. However, there is a problem that the surface is unnecessarily dissolved and the dissolution thickness is insufficient, so that a sufficient decontamination effect cannot be achieved.

[0004]

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

[0005]

The method for decontaminating a metal waste of the present invention, which has been made to solve the above problems, is a method for decontaminating a metal waste by dissolving the surface of the metal waste with a decontamination solution. In, the relational expression of dissolution area / decontamination solution amount and dissolution thickness is obtained in advance based on the decontamination solution temperature and the dissolution time when the dissolution amount of the metal waste by the decontamination solution reaches saturation. It is characterized in that the shape of an object is recognized, its surface area is calculated, and this is substituted into the above-mentioned relational expression to perform decontamination with an amount of decontamination liquid corresponding to the required dissolution thickness. .

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

[0007]

According to the present invention, the shape recognition device provided on the entrance side of the decontamination chamber recognizes the shape of the metal waste and calculates the surface area. Then, based on a relational expression of dissolution area / decontamination solution amount and dissolution thickness under the decontamination solution temperature and dissolution time at which the dissolution amount of the metal waste by the decontamination solution reaches saturation, which is previously calculated Determines the amount of decontamination liquid corresponding to the required dissolution thickness, and the liquid amount control means controls the amount of decontamination liquid in the decontamination tank in accordance therewith. 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 of the metal waste will be removed more than necessary. It does not cause problems such as dissolution or lack of sufficient dissolution thickness to achieve a sufficient decontamination effect.

[0008]

The present invention will be described in more detail below with reference to the illustrated embodiments. In the present invention, first, the decontamination solution temperature and the dissolution time at which the amount of dissolved metal waste reaches saturation are determined. Conventionally, since decontamination was performed near room 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 decontamination solution temperature and dissolution time variously, the conditions under which the dissolution amount reached saturation in a relatively short time were understood.

Specifically, the decontamination solution used in this example is a mixed acid prepared 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 that of the conventional method, it reaches almost saturation in 20 minutes of dissolution time, and it becomes completely saturated in 1 hour of dissolution time. The reason why the dissolution amount decreases at 80 ° C. here is considered to be that the performance of the decontamination solution deteriorates due to evaporation. From this result, it can be seen that when the temperature of the decontamination solution is set to 70 ° C. and the dissolution time is set to 1 hour in consideration of safety, the dissolved amount of the metal waste reaches a complete saturation.

FIG. 2 is a graph showing the relationship between the dissolution area / amount of decontamination solution and the dissolution thickness and the relationship between the dissolution area / amount of decontamination solution and the metal ion concentration under the above conditions. This Figure 2
As shown in the graph, the dissolved metal ion concentration is 50 to 60 when the value of dissolved area / decontamination solution amount exceeds about 0.07 m ² / L.
It can be seen that the solution thickness of the metal waste (stainless steel) can be continuously changed by changing the value of the dissolution area / decontamination solution amount to be almost constant at the level of g / L. Therefore, if the dissolved area of the metal waste is measured in advance and the amount of the decontamination solution is adjusted, an arbitrary dissolved thickness can be obtained. In addition, it has been found that radioactive substances can be completely removed by dissolving 30 μm from the surface of metal waste, so the graph of Fig. 2 shows that the value of dissolved area / decontamination solution amount is 0.20 m. ^It can be confirmed that ² / L is enough.

FIG. 3 shows an apparatus for carrying out the present invention, in which the shape of the metal waste is automatically recognized by the shape recognizing device 2 for the metal waste 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. Further, the calculating means 3 substitutes the surface area of the metal waste calculated in this way into the relational expression between the dissolution area / the amount of the decontamination liquid and the dissolution thickness as shown in FIG. Calculate the amount of decontamination liquid required to dissolve the surface of to the required dissolution thickness.

On the other hand, in the decontamination tank 4 inside the decontamination chamber 1, 70 ° C.
Although the decontamination liquid kept in the above condition is filled, a circulation route of the decontamination liquid is formed between the decontamination liquid and the decontamination waste liquid treatment device 5 for the purpose of 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, by immersing the metal waste in the decontamination tank 4 and performing decontamination for 1 hour, for example, a certain thickness (for example, 30 μm) can be dissolved. After that, the metal waste is rinsed in the rinse tanks 7 and 8 by the crane 9 and taken out to the outside. The decontamination liquid containing the radioactive substance is regenerated by the decontamination waste liquid treatment device 5. The metal waste that has been decontaminated in this way is checked for radiation dose, and if it is confirmed to be 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 dissolution thickness regardless of the size of the metal waste. It is possible to prevent waste due to excessive dissolution and incomplete decontamination due to insufficient dissolution. Further, according to the decontamination apparatus for metal waste of the present invention, the above decontamination can be automatically performed. It should be noted that the examples relate to the decontamination liquid having a specific composition suitable for dissolving stainless steel, but it goes without saying that the type of metal waste and the composition of the decontamination liquid are not particularly limited to this. That is.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between dissolution time and 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 showing a decontamination device for metallic waste of an embodiment.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. A method for decontaminating a metal waste by dissolving the surface of the metal waste with a decontamination solution, which is based on the decontamination solution temperature and the dissolution time at which the amount of the metal waste dissolved by the decontamination solution reaches saturation. In addition, the relational expression between dissolved area / decontamination solution amount and dissolved thickness is obtained in advance, the shape of 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. 2. A device for recognizing the shape of a metal waste provided on the entrance side of a decontamination chamber, and calculating the surface area of the metal waste based on the recognition result and melting the surface area to a required dissolution thickness. An apparatus for decontaminating a metal waste, comprising: a calculation unit for calculating the amount of decontamination liquid and a liquid amount control unit for the decontamination tank controlled by the calculation unit.