KR20110051499A - Method for chemical decontamination of surface of radioactive metal waste using acid/acid salt mixture - Google Patents

Abstract

PURPOSE: A chemical salt method of a radioactive pollution metal waste surface using slat solution which an acid and an acid salt are mixed is provided to eliminate a concern about damage of a base material, convenient to treat, and reduce all kinds of risk. CONSTITUTION: An ultrasonic wave generating device smoothly enables fluid of salt and secesses an oxide film of the salt manufacturing object in a salt. An electronic heater is operated as two. The ultrasonic wave generating device is operated after injecting the salt to the salt tub. By using the electric heater, the temperature is adjusted and maintained. By circulating the active carbon tower, radioactive pollution material in the salt is removed.

Description

Method for chemical decontamination of surface of radioactive metal waste using acid / acid salt mixture}

The present invention relates to a method for chemical decontamination of radioactive contaminated metal waste surfaces using a salt solution in which acid and acid salts are mixed.

In general, in nuclear power plants, radioactive pollution is generated by the operation of equipment. Pollution in a nuclear power plant occurs when performing parts replacement of various equipment such as a power plant, and the work of removing unwanted radioactive substances on the contaminated area is called decontamination.

The radioactive material is generated in the primary system of a nuclear power plant. The radionuclides produced by nuclear fission products and neutron irradiation, and the radionuclides generated by neutron irradiation are mainly radioactive species generated by neutron irradiation. It is a decontamination target. The radioactive material generated in this state flows in the primary system of the power plant or adheres to the inner wall of the pipe or part, and leaks to the outside by air exposure during leakage or periodic maintenance, thereby polluting the surrounding environment.

In particular, most of the facilities or tools used in nuclear power facilities are contaminated with radioactivity. Radioactive decontamination is essential when repairing, reusing, replacing, or disposing of such equipment or equipment.

Decontamination processes of metal wastes whose surfaces are contaminated by radioactive materials generally include various kinds of physical decontamination, chemical decontamination, electrolytic decontamination, etc. However, chemical decontamination processes using an acid solution are typically used.

The chemical decontamination process uses an sulfuric acid, nitric acid, or a mixed solution thereof as the decontamination liquid to submerge the decontamination liquid in the decontamination liquid, which is effective for radioactive metal wastes of complex shapes such as curved pipes and valves.

As a conventional technique of the chemical decontamination process, Japanese Patent Laid-Open No. 5-273389 discloses a decontamination method for decontaminating stainless radioactive waste by contact with a mixture of nitric acid, hydrochloric acid and hydrofluoric acid.

In addition, Korean Patent Registration No. 505470 discloses a concentrated chemical decontamination method using oxalic acid or nitric acid and oxalic acid.

However, when decontaminating a metal contaminated with a radioactive material using a conventional mixed solution consisting only of acid (acid), there is a problem that the metal surface is roughly shaved and the surface shape is uneven, which makes it difficult to recycle the metal. .

Therefore, the present inventors can easily handle the decontamination solution, exhibit decontamination efficiency equal to or higher than that of the decontamination with the existing acid solution, and smooth the metal surface and make the metal surface uniform, so that the metal can be easily recycled. During the study, when the acid-sodium salt mixed solution was used as the decontamination solution, the decontamination efficiency was equal to or greater than that of the conventional decontamination solution consisting only of acid, and the metal surface was smoothed and the decontamination solution was easy to handle. It confirmed and completed this invention.

It is an object of the present invention to provide a method for decontaminating radioactive contaminated metal waste surfaces by using a solution of an acid and a sodium salt of acid as a decontamination solution.

In order to achieve the above object, the present invention provides a method for decontaminating radioactive contaminated metal waste surfaces using a salt solution in which sodium nitrate is mixed with hydrofluoric acid or a salt solution in which sodium fluoride is mixed with nitric acid.

According to the present invention, when decontaminating the radioactive contaminated metal waste surface by using a salt solution in which sodium nitrate is mixed with hydrofluoric acid or sodium fluoride in nitric acid, when compared with the conventional salt solution mixed with nitric acid and hydrofluoric acid It shows the same level of decontamination efficiency, eliminates the risks caused by the handling of toxic chemicals by the operator, and is easy to handle, and there is no risk of damage to the base metal such as smooth metal surface and uniform surface shape. It can be easily used for decontamination of components made of expensive materials, and the amount of waste generated is small, so that the burden of radioactive waste treatment due to the generation of radioactive waste during decontamination of nuclear power plants can be drastically reduced.

Hereinafter, the present invention will be described in detail.

The present invention focuses on the decontamination and decontamination process for chemical decontamination for components of a domestic PWR-type power plant, and puts the components to be decontaminated directly into the decontamination tank to circulate the decontamination agent into the decontamination tank. Use the method.

Chemical decontamination method of the radioactive contamination metal waste surface according to the present invention can be made in a chemical decontamination apparatus generally used in nuclear power plants, as one embodiment of the chemical decontamination apparatus, as disclosed in Korean Patent Registration No. 605558, Ultrasonic generator is installed inside, the decontamination tank for storing the decontamination agent; An electric heater for controlling the temperature of the decontamination agent; filter; A cation resin tower filled with a strong acid type cation exchange resin having a sulfonic acid as a functional group; An interphase resin tower in which an anion exchange resin having a quaternary amine as a functional group is mixed with a cation exchange resin; And activated carbon towers filled with activated carbon (see FIG. 1 ), but are not limited thereto.

The ultrasonic wave generator 12 serves to facilitate the flow of the decontamination agent and to easily detach the oxide film of the decontamination object into the decontamination agent.

The electric heater 13 is composed of two sets of operation, one electric heater is to increase the temperature of the decontamination agent to a temperature 2 ℃ lower than the set temperature, the temperature difference between the set temperature and the decontamination agent is 2 ℃ or less When the temperature of the decontamination agent is raised by another electric heater.

The filter 14 has two upper and lower parts, and the filter 14 is replaced when the differential pressure of the pressure gauge installed at the front and rear of the filter is 0.15 mPa or more.

The activated carbon filled in the activated carbon tower 18 is activated carbon having a specific gravity of 0.40 to 0.45 g / cm 3, a particle diameter of 8 to 32 mesh, and an ignition residue of 0.5% or less.

In the present invention, the decontamination agent is preferably a decontamination solution in which sodium nitrate (NaNO ₃ ) is mixed with hydrofluoric acid (HF) or a decontamination solution in which sodium fluoride (NaF) is mixed with nitric acid (HNO ₃ ), more preferably. It is preferable to use the solution which mixed 0.05-1.0 M hydrofluoric acid and 0.1-2.0 M sodium nitrate, or the solution which mixed 0.1-2.0 M nitric acid and 0.05-1.0 M sodium fluoride. If it is out of the above range, there is a problem that decontamination efficiency is lowered or the surface is changed.

In the present invention, a method of decontamination of radioactive contaminated metal wastes surface in the incore chemical decontamination apparatus of FIG. 1 is as follows.

First, open the eighteenth valve 48 and remove the decontamination solution in which hydrofluoric acid (HF) and sodium nitrate (NaNO ₃ ) are mixed or the decontamination solution in which nitric acid (HNO ₃ ) and sodium fluoride (NaF) are mixed. After the injection using the chemical injection pump 11, the eighteenth valve 48 is closed.

Next, after opening the first valve 31, the second valve 32, the eleventh valve 41, the thirteenth valve 43, and the fifteenth valve 45, the circulation pump 20 and the ultrasonic generator ( 12) is activated.

Next, the opening degree of the first valve 31 is adjusted to adjust the flow rate to 30 l / min, and the electric heater 13 waits until the temperature reaches the set value, and if necessary, opens the sixteenth valve 46. Exhaust.

Thereafter, the decontamination solution is circulated at a temperature of 90 ° C. for about 2 to 3 hours to elute radioactive contaminants on the metal specimen into the decontamination solution.

Next, the decontamination solution can be reused by closing the eleventh valve 41 and opening the nineteenth valve 49 to cause the decontamination solution to circulate through the activated carbon tower 18 to remove radioactive contaminants in the decontamination solution.

The chemical decontamination method of the surface of radioactive contaminated metal wastes according to the present invention uses a decontamination solution containing sodium nitrate in hydrofluoric acid or a decontamination solution in which sodium fluoride is mixed with nitric acid. It has the advantage of easy handling and eliminating various dangers caused by the handling of toxic chemicals.

In particular, since there is no risk of damage to the base metal such as smooth metal surface and uniform surface shape, it is easy to recycle the metal, which can be useful for decontamination of components made of expensive materials. There is an effect that can significantly reduce the burden of radioactive waste disposal due to waste generation.

Hereinafter, the present invention will be described in more detail by the following examples. However, the following examples merely illustrate the present invention, and the contents of the present invention are not limited by the following examples.

< Example  1> According to the decontamination solution Base material  Decontamination Efficiency of Chemical and Oxidized Specimens

In order to determine the effect of the decontamination solution according to the present invention on the decontamination of the base material and oxidized specimens, the experiment was carried out as follows.

STS 304 and Inconel 600 were used as the base material and the oxidized specimen, and HF 0.5M / HNO ₃ 1.0M mixed solution, HF 0.5M / NaNO ₃ 1.0M mixed solution, or NaF 0.5M / HNO ₃ 1.0M mixed solution for decontamination. Solution was used. A constant temperature agitation tank was used to promote uniform reaction of the decontamination solution with the base material and the oxidized specimen. 100 mL each of the prepared HF 0.5M / HNO ₃ 1.0M mixed solution, HF 0.5M / NaNO ₃ 1.0M mixed solution or NaF 0.5M / HNO ₃ 1.0M mixed solution was aliquoted into a plastic bottle. After confirming that the mixture was reacted, and after confirming that there is no change of the solution, the weighed base material and the oxidized specimens were put into each bottle. Next, put the decontamination solution and the base material and or the oxidized specimen in a constant temperature stirring tank, the temperature range is set to 90 ℃, the stirring speed is set to 120 rpm, every 30 minutes, 1 hour, 2 hours The specimen and the decontamination solution were separated and the weight of the specimen changed after the reaction was measured.

The measurement results are shown in Table 1, Table 2, Figs. 2 and 3 .

Table 1 and Figure 2 shows the weight loss of the STS 304 according to the decontamination solution, Table 2 and Figure 3 shows the weight loss of the Inconel 600 according to the decontamination solution.

STS  Weight loss of 304 Time (h)
Weight loss (g) HNO ₃ HF NaF / HNO ₃ HF / NaNO ₃ HF / HNO ₃ 0.5 - - 0.3171 0.0913 0.2629 One 0.0 0.0403 0.5643 0.2124 0.4935 2 0.0004 0.0689 0.8098 0.3491 0.7722

Inconel  600 weight loss Time (h)
Weight loss (g) NaF / HNO ₃ HF / NaNO ₃ HF / HNO ₃ 0.5 0.557 0.3143 0.6634 One 1.2248 0.4305 1.573 2 2.6259 0.7074 3.6765

As shown in Table 1 and Figure 2 , first put the STS 304 in the decontamination solution consisting of HF / HNO ₃ solution and conducted a decontamination experiment for 2 hours, it can be seen that the weight of the STS 304 was reduced by about 0.77 g, In the case of using the decontamination solution consisting of NaF / HNO _{3 It} was found that after 2 hours the weight of STS 304 is reduced by about 0.8 g, rather than HF / HNO ₃ showed better efficiency. In addition, when using the decontamination solution consisting of HF / NaNO ₃ , the weight of the STS 304 was reduced by about 0.35 g after 2 hours, the decontamination efficiency was not better than the two mixed solutions described above, The comparison showed similar efficiency.

In addition, as a result of the decontamination experiment using a single acid of hydrofluoric acid (HF) or nitric acid (HNO ₃ ), almost no weight loss of STS 304 was lost, and when using a decontamination solution consisting of hydrofluoric acid (HF), the surface of STS 304 was rather reduced. This turned black.

As a result of the decontamination experiment of Inconel 600 and mixed decontamination solution in the same manner as STS 304, as shown in Table 2 and Figure 3 , when using the HF / HNO ₃ decontamination mixed solution, the weight loss of Inconel 600 is about 3.7 g, the weight of about 2.6 g when using NaF / HNO ₃ decontamination mixed solution, 0.7 g when using the HF / NaNO ₃ decontamination mixed solution can be seen that the weight was reduced.

Therefore, NaF / HNO ₃ or HF / NaNO ₃ mixed decontamination solution according to the present invention was found to be equivalent to the decontamination efficiency compared to the conventional HF / HNO ₃ solution.

< Example  2> according to the decontamination solution Base material  Measurement of surface and oxidized specimens

After the decontamination experiment according to the decontamination solution for the STS 304 and Inconel 600 by the method of Example 1 was photographed the surface of the metal.

The photographing results are shown in FIGS . 4 and 5 .

4 shows the surface of STS 304 with decontamination solution, and FIG. 5 shows the surface of Inconel 600 with decontamination solution.

As shown in FIG . 4 , when the metal is STS 304, the surface difference does not appear to be large when HF / HNO ₃ decontamination mixed solution, NaF / HNO ₃ decontamination mixed solution, or HF / NaNO ₃ decontamination mixed solution is used. . However, as shown in FIG . 5 , when the metal is Inconel 600, when the HF / HNO ₃ decontamination mixed solution is used, the gap of the metal surface may be cracked. In contrast, the NaF / HNO ₃ decontamination mixed solution or HF The surface remained constant when using the / NaNO ₃ decontamination mixture solution.

Therefore, the NaF / HNO ₃ or HF / NaNO ₃ mixed decontamination solution according to the present invention can be easily recycled because the metal surface is smoothly cut and the surface shape is uniform.

1 is an overall configuration diagram of a chemical decontamination apparatus of a conventional embodiment.

2 is a graph showing the weight loss amount of STS 304 according to the decontamination liquid.

3 is a graph showing the weight loss of Inconel 600 according to the decontamination liquid.

4 is a surface photograph of STS 304 according to the decontamination solution.

5 is a surface photograph of Inconel 600 according to the decontamination solution.

<Description of the symbols for the main parts of the drawings>

10: decontamination tank 11: chemical injection pump

12: ultrasonic generator 13: electric heater

14 filter 15 exhaust port

16: cation resin tower 17: anion resin tower

18: activated carbon tower 19: flow meter

20: circulation pump 21: drain

22: sampling hole 23: the basket

24: basket 31: the first valve

32: second valve 33: third valve

34: fourth valve 35: fifth valve

36: sixth valve 37: seventh valve

38: eighth valve 39: ninth valve

40: tenth valve 41: eleventh valve

42: twelfth valve 43: thirteenth valve

44: 14th valve 45: 15th valve

46: 16th Valve 47: 17th Valve

48: 18th valve 49: 19th valve

Claims (9)

Putting radioactive contaminated metal waste into the decontamination tank in the chemical decontamination apparatus, injecting the decontamination solution mixed with hydrofluoric acid and sodium nitrate or the decontamination solution mixed with nitric acid and sodium fluoride as the decontamination solution, and then circulating the decontamination solution Chemical decontamination method of radioactive contamination metal waste surface comprising a. Putting radioactive contaminated metal waste into a salt tank in a chemical decontamination apparatus, injecting a salt solution mixed with 0.05 to 1.0 M hydrofluoric acid and 0.1 to 2.0 M sodium nitrate as the salt to the salt bath, and then circulating the salt solution Chemical decontamination method of radioactive contamination metal waste surface comprising a. Putting radioactive contaminated metal waste in a salt tank in a chemical decontamination apparatus, injecting a salt solution mixed with 0.1 to 2.0 M nitric acid and 0.05 to 1.0 M sodium fluoride as the salt, and circulating the salt solution Chemical decontamination method of radioactive contamination metal waste surface comprising a. Radioactive contaminated metal waste is placed in a decontamination tank in a chemical decontamination apparatus, and a decontamination solution containing 0.05 to 1.0 M hydrofluoric acid and 0.1 to 2.0 M sodium nitrate is injected into the decontamination tank, and then, at a temperature of 80 to 100 ° C. Circulating the decontamination solution for 2 to 3 hours to elute the radioactive contaminants on the metal specimen into the decontamination solution. The radioactive contaminated metal waste is placed in a decontamination tank in a chemical decontamination apparatus, and a decontamination solution containing 0.1 to 2.0 M nitric acid and 0.05 to 1.0 M sodium fluoride is injected into the decontamination tank, and then, at a temperature of 80 to 100 ° C. Circulating the decontamination solution for 2 to 3 hours to elute the radioactive contaminants on the metal specimen into the decontamination solution. The method according to any one of claims 1 to 5, wherein the decontamination solution is easy to handle and eliminates the dangers caused by the handling of toxic chemicals by the worker. 6. The method of claim 1, wherein the decontamination liquid smoothes the metal surface. 7. The method for chemical decontamination of radioactive contaminated metal waste surfaces according to any one of claims 1 to 5, wherein the decontamination method makes it easy to recycle the metal by making the shape of the metal surface uniform. The chemical decontamination method according to any one of claims 1 to 5, wherein the decontamination method has a small amount of waste generation.

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