KR101523312B1 - A capture solution of radioactive iodine species containing platinum group metal elements and a capture method of radioactive iodine species thereof - Google Patents

Abstract

Provided is a capture solution of radioactive iodine species containing platinum group metal elements. A capture solution of radioactive iodine species according to the present invention is a capture solution of radioactive iodine species containing platinum group metal elements. Because the platinum group metal elements function as a catalyst for promoting recombination reaction of radiolyzed products and water molecules, the capture solution has a superior performance compared to an existing capture solution without a deterioration after long-term use. Also, it is used for a radioactive iodine collecting apparatus such as the filtering and exhausting system of a nuclear power plant and can improve the collection performance of volatile radioactive nuclide, especially, radioactive iodine.

Description

TECHNICAL FIELD The present invention relates to a radioactive iodine collecting solution containing a platinum group element and a method for collecting radioactive iodine using the radioactive iodine collecting solution.

The present invention relates to a radioactive iodine collection solution and a method for collecting radioactive iodine using the same.

Radioactive iodine is one of the fission products that are liable to leak into the atmosphere during reactor accident. Particularly, I-131 is a nuclide which should have special attention in case of accident because of high radiation level and high absorbability of human body.

Generally, radioactive iodine exists as cadmium iodide (CsI) in the spent nuclear fuel and is released to the outside of the fuel in the iodide form. In the event of a nuclear accident, radioactive iodine can be present in the air inside the containment building in the form of gas, aerosol, organic iodine, In the event of an accident, if the temperature inside the containment building rises and the internal pressure rises, the internal atmosphere containing water vapor is exhausted. At this time, the contaminated air passes through the filtration and exhaust system, while the radioactive material is filtered through the trapping solution or the metal filter of the filtration and exhaust system, and the purified air is discharged.

On the other hand, volatility, high molecular iodine to exist in a stable ionic in alkaline conditions and a reducing environment iodide ^ion-: in combination with (I Iodide ion) and stable tree iodide ion ^{_{(I 3 -: Tri-iodide}} ion ), The collection solution generally comprises an alkali substance, a reducing agent and a non-radioactive iodide compound. The alkaline substance may be a hydroxide, phosphoric acid or amine compound, and the reducing agent may be thiosulfate or hydrazine. Non-radioactive iodide compounds use salts of sodium and potassium. In addition, polymer surfactants may be used to promote dissolution of volatile materials.

As described above, an example of collecting volatile radioactive material from a radioactive contaminated gas is disclosed in Korean Patent Laid-Open No. 10-2012-0089558, which discloses a method of collecting, removing, and disposing radioactive species in an aqueous solution. In particular, there is provided a method of making a macroporous bead type isolation resin comprising: providing a macroporous bead type isolation resin; Applying the bead type isolation resin to a radioactive species contained in the aqueous solution so that the bead type isolation resin can capture the radioactive species; And disposing the radioactive species in a radioactive storage facility.

However, when the filter exhaust system is activated during a nuclear accident, many volatile radioactive materials including radioactive iodine are accumulated in the collection solution of the filtration and exhaust system, so that the radiation level is increased. In this highly radioactive environment, the water molecules present in the capture solution are radically decomposed to form unstable radicals. Among such unstable radiolytic products, OH radicals and hydrogen peroxide have a problem that iodide ions which are stably dissolved are converted into molecular iodine or organic iodine having high volatility and separated from the collection solution.

Accordingly, the inventors of the present invention developed a radioactive iodine collection solution capable of effectively suppressing the volatile increase of radioactive iodine by promoting the reaction of recombining radiolytic products with water molecules through a platinum group element while studying a radioactive iodine capture solution , Thereby completing the present invention.

It is an object of the present invention to provide a radioactive iodine capture solution and a method of capturing radioactive iodine using the same.

In order to achieve the above object,

The present invention provides a radioactive iodine collection solution characterized by containing a platinum group element.

In addition,

There is provided a radioactive iodine collecting apparatus from a radioactive contaminated gas containing the radioactive iodine collecting solution.

Further,

And passing the stream containing radioactive iodine through the apparatus according to the above.

The radioactive iodine collecting solution according to the present invention is a radioactive iodine collecting solution containing a platinum group element. Since the platinum group element acts as a catalyst for promoting the reaction of recombining the radiolytic product with water molecules, its performance is lowered even after prolonged use And it is superior to the existing collection solution performance. In addition, it can be used in a radioactive iodine collection device such as a nuclear filter and exhaust system to improve the collection performance of volatile radionuclides, particularly radioactive iodine.

1 is a schematic view of an air filtering and exhausting system within a nuclear power plant;
FIG. 2 is a graph of UV / VIS spectra measured after exposing the radioactive iodine collection solution prepared in Example 1 and Comparative Example 2 according to the present invention to a gamma irradiation environment. FIG.

The present invention

The present invention provides a radioactive iodine collection solution characterized by containing a platinum group element.

Hereinafter, the radioactive iodine collection solution according to the present invention will be described in detail.

The present invention is a technology for preparing for a serious accident occurring in a nuclear facility such as a nuclear power plant and a spent fuel intermediate storage facility. Critical accidents at nuclear facilities include the leakage of volatile radionuclides with high radioactivity from nuclear fuel. When it is necessary to discharge these radionuclides from the inside of the facility to the outside environment, the gas and aerosol type radioactive material contained in the contaminated air is collected using a device such as a filtration and exhaust system, and the purified atmosphere is discharged to the environment .

Currently, the capture solution containing iodide compounds, reducing agents, and the like, which provide iodide ions for use as radioactive iodine capture solutions, is known to have excellent ability to capture iodine species. However, if the radioactive material accumulates continuously in the collection solution, the water molecules are radiated by the radiation emitted from these materials, and the iodine chemical species stably dissolved by the radiolytic products such as OH radical and hydrogen peroxide can be volatilized again. In addition, since the concentration of the reducing agent contained in the trapping solution is reduced by the radiolysis product, the iodine trapping performance may be deteriorated.

In order to solve this problem, a platinum group element is added to the radioactive iodine collection solution. When the platinum group elements are dispersed in the collecting solution, the radiolytic products produced by the radiation are rapidly recombined from the platinum group element surface to water molecules. Therefore, it is possible to inhibit the generation reaction of molecular iodine generated by OH radicals, hydrogen peroxide, and the like, and to secure long-term stability of iodine species dissolution.

Thus, the radioactive iodine capture solution according to the present invention has superior properties compared with the conventional capture solution performance because the performance of the radioactive iodine capture solution according to the present invention is not degraded even after prolonged use, and is sustainable.

In the radioactive iodine collecting solution according to the present invention, the platinum group elements may be platinum group elements such as platinum (Pt), palladium (Pd) and rhodium (Rh). As an example, a platinum metal having excellent adsorption characteristics of hydrogen molecules can be used for the catalytic reaction of OH radical, H radical, recombination of dissolved hydrogen and hydrogen peroxide.

The content of the platinum group element may be 0.001 to 0.5% by weight based on the radioactive iodine collection solution. By way of example, the fine particles of the platinum group element are lost to some extent by porous surfaces and crevice deposits present in the radioactive iodine collection vessel. If the content of the platinum group element is less than 0.001% by weight based on the radioactive iodine collection solution, there is a problem in performance degradation below the effective content. If the content of the platinum group element exceeds 0.5% by weight, the catalytic performance is saturated, Which may interfere with the gas flow.

Further, the recombination of the radial decomposition products of water by the platinum group element proceeds through the catalytic reaction on the surface of the platinum group element. Therefore, the white metal element may have a high surface area per unit mass, and may have a wide effective surface area in the form of fine particles, a porous material, a thin film, a fiber, a net, and a liquid.

For example, the platinum group element may be formed by forming fine colloidal particles in a collection solution by using a platinum species dissolved in water to enlarge the surface area. As another example, a platinum group element And can be applied in the form of fine particles which can be easily dispersed in the iodine capture solution medium. In this case, the average diameter of fine particles which can be easily dispersed in an aqueous solution at room temperature is 1 μm or less which can exist as a colloid, but particles having a size of several tens of μm in diameter are well dispersed . In this case, the surface area of the platinum group element in the form of fine particles may be 0.1 square meter or more per gram of the unit, and may be 0.1 to 1,000 square meters per gram of the unit.

In addition, the average diameter of the platinum group elements in the form of fine particles may be 10.0 nm to 1.0 mm. If the average diameter of the platinum group element is less than 10.0 nm, it is difficult to handle such as passing through a general purifying filter. When the average diameter is more than 1.0 mm, the efficiency is lowered and stable dispersion is difficult there is a problem.

In the radioactive iodine collection solution according to the present invention, the collection solution may include a metal halide salt, an alkali compound, and a reducing agent.

At this time, the metal halide salt may be a salt containing a halogen ion such as chlorine ion (Cl ^- ), iodide ion (I ^- ) and bromine ion (Br ^- ). As an example, among halogen ions capable of stabilizing radioactive iodine, an iodide ion (I ^- ) is reacted with highly volatile molecular iodine by the reaction shown in the following Reaction Scheme 1 to form a stable soluble triiodide ion (i ₃ ^- : Tri-iodide ion) to reduce the volatility of iodine. Thus, a metal salt containing an iodide ion can be used.

<Reaction Scheme 1>

I ^- (aq) + I ₂ (dissolved gas) ^- I ₃ ^- (aq)

The metal salt containing the iodide ion may be iodide such as sodium (Na), potassium (K) and calcium (Ca), but is not limited thereto.

Further, the alkali compound decomposes molecular iodine (I ₂ ) through the reaction shown in the following reaction formula 2 to obtain stable stable iodide ion (I ^- ) and iodate ion (IO ₃ ^- : Iodate) Respectively, and the molecular iodine is an iodine species with high volatility and can be included in the polluted air. It may also occur when the iodide ion is reoxidized by the radiation emitted from the captured radioactive material in the collection solution.

<Reaction Scheme 2>

_{3I 2 (dissolved gas) + 6OH} - → 5I - (aq) + IO 3 - (aq) + 3H 2 O

At this time, the alkali compound may be a compound containing an alkali metal, a hydroxide ion, an ammonium ion and a calcium oxide. For example, the alkali compound may be alkali metals having a high ionization tendency such as lithium, potassium, and sodium, but the present invention is not limited thereto.

The reducing agent reduces the volatility by reducing molecular iodine (I ₂ ) to a stable soluble chemical species I ^- . The reducing agent is a thiosulfate ion (S ₂ O ₃ ^{2 -} ) or a tin ion (Sn ^{2 +} ), Hydrazine, zinc-mercury amalgam, and phosphoric acid-based reducing agents. For example, in the following Reaction Scheme 3, the thiosulfate ion as the reducing agent has shown a reaction of reducing molecular iodine to iodide ion, which is a stable dissolution substance.

<Reaction Scheme 3>

2S ₂ O ₃ ^{2 -} (aq) + I ₂ (gas) -> S ₄ O ₆ ^{2 -} (aq) + 2I ^- (aq)

At this time, the reducing agent may be a salt compound of sodium or potassium which generates thiosulfate ion, but is not limited thereto.

In addition,

There is provided a radioactive iodine collecting apparatus from a radioactive contaminated gas containing the radioactive iodine collecting solution.

The components of the radionuclide collection solution used in the containment building filtration and exhaust system, which is currently being installed in preparation for a major accident at a nuclear power plant, are composed of an alkali substance, a reducing agent, and an iodide compound. The solution can effectively capture radionuclides, but as the concentration of captured radionuclides increases, the water molecules in the capture solution are radiated by radiation emitted from these materials. Some of the chemical species, OH radicals, or hydrogen peroxide of the radiolytic products produced through the radial degradation of such water molecules have the problem of oxidizing stably dissolved iodine species to highly volatile species. At the same time, they react with one of the major components of the capture solution, which are mutually canceled, thereby deteriorating the capturing performance of the radionuclide.

Accordingly, the present invention provides a collecting device which can be used in a radioactive iodine collecting apparatus such as a nuclear power plant filter exhaust system to improve the collecting performance of a radioactive nuclide, in particular, radioactive iodine. The apparatus for collecting radioactive iodine according to the present invention is a device for collecting radioactive iodine from a radioactive contaminated gas using a radioactive iodine collection solution containing a platinum group element.

When the platinum group element is dispersed in the radioactive iodine collection solution, the radiolysis product produced by the radiation is rapidly recombined with water molecules. Therefore, it is possible to inhibit the generation reaction of molecular iodine generated by OH radicals, hydrogen peroxide, and the like, and to secure long-term stability of iodine species dissolution.

As a result, the radioactive iodine collecting apparatus according to the present invention has superior characteristics compared with the existing collecting apparatuses because the apparatus has a sustainable characteristic without deteriorating its performance even after prolonged use.

The radioactive iodine collecting apparatus according to the present invention may be configured as shown in Fig. 1 as an example. Specifically, the iodine collecting solution 1 is filled in the collecting solution part (not shown), and the injection tube 2 and the collecting solution replenishing tube 4 for the movement of the radioactive contaminated gas are positioned above the collecting solution part. In addition, a rupture valve 3 is located in the injection pipe 2, and a replenishment valve 5 is located in the collection solution replenishing pipe 4. At this time, the injection tube 2 is connected to the inside of the iodine collecting solution 1, and the nozzle 6 of the injection tube 2 is located in the radioactive iodine collecting solution 1. A drain pipe (7) is located at the lower part of the collection solution part and a right upper end, and a drain valve (8) is located at the drain pipe (7) located at the lower part of the collection solution part. A collection solution treatment reservoir (not shown) may be disposed below the drain pipe 7. Furthermore, a discharge pipe (6) is located at the upper right side of the collection solution part.

Further,

And passing the stream containing radioactive iodine through a collecting device according to the above.

The method for collecting radioactive iodine according to the present invention is a method for collecting radioactive iodine which is performed by passing a stream containing radioactive iodine through a radioactive iodine collection device using a radioactive iodine collection solution containing a platinum group element.

The radioactive iodine collection solution containing the platinum group element can inhibit generation of molecular iodine generated by OH radicals, hydrogen peroxide, and the like, so that the dissolution stability of the iodine species can be secured for a long time.

Specifically, the flow comprising the radioactive iodine occurs in the radioactive contaminated gas. As an example, it may be a radioactive iodine gas generated in a radioactive contaminated gas.

Hereinafter, the present invention will be described in detail with reference to the following examples and experimental examples.

It should be noted, however, that the following examples and experimental examples are illustrative of the present invention, but the scope of the invention is not limited by the examples and the experimental examples.

Example 1 Preparation of radioactive iodine collection solution 1

To the 5.0 mM NaI solution, platinum fine particles (particle diameter: 0.15 to 0.45 탆) were added at 0.1 wt% with respect to the total solution to prepare a radioactive iodine capturing solution.

Example 2 Preparation of radioactive iodine collection solution 2

To the 5.0 mM NaI solution, platinum fine particles (particle diameter: 0.15 to 0.45 탆) were added at 0.2 wt% with respect to the total solution to prepare a radioactive iodine collection solution.

&Lt; Example 3 > Preparation of radioactive iodine collection solution 3

A radioactive iodine collection solution was prepared by adding platinum fine particles (particle diameter: 0.15 to 0.45 mu m) to a 5.0 mM NaI solution at 0.3 wt% with respect to the total solution.

Example 4 Preparation of radioactive iodine collection solution 4

To the 5.0 mM NaI solution, platinum fine particles (particle diameter: 0.5 to 1.0 mu m) were added at 0.1 wt% with respect to the total solution to prepare a radioactive iodine collection solution.

Example 5 Production of radioactive iodine collection solution 5

To the 5.0 mM NaI solution, platinum fine particles (particle diameter: 0.5 to 1.0 mu m) were added at 0.2 wt% with respect to the total solution to prepare a radioactive iodine collection solution.

Example 6 Production of radioactive iodine collection solution 6

A radioactive iodine collection solution was prepared by adding platinum fine particles (particle diameter: 0.5 to 1.0 mu m) to a 5.0 mM NaI solution at 0.3 wt% with respect to the total solution.

&Lt; Comparative Example 1 &

5.0 mM NaI solution was prepared.

EXPERIMENTAL EXAMPLE 1 Phenomena Analysis for Suppressing Oxidation of Iodide Ion

In order to confirm the effect of the radioactive iodine capturing solution according to the present invention, the following experiment was performed using the radioactive iodine capturing solution prepared in Example 1 and Comparative Example 1.

The radioactive iodine collection solution prepared in Example 1 and Comparative Example 1 was exposed for 1 hour in a gamma irradiation environment of 10 kGy intensity. Gamma rays break down water molecules and generate both oxidizing and reducing chemistries simultaneously. Among them, oxidizing chemical species oxidize iodide ion to molecular iodine to increase the volatility of iodine. When molecular iodide coexists with an iodide ion, it forms a triiodide ion (I ₃ ^- ) as shown in the following reaction formula (4). The triiodide ion is easily detected at a wavelength of 288 or 351 nm with a UV / VIS spectrophotometer. Therefore, in this experiment, excessive iodide ion was used to induce the formation of triiodide ion (I ₃ ^- ) , And the amount of molecular iodine produced was evaluated. The results are shown in Fig.

<Reaction Scheme 4>

I ₂ (dissolved gas) + I ^- (aq) ^- I ₃ ^- (aq)

2, the no added platinum metal particles, radioactive compare the iodine absorption solution that Example 1 is iodide ion (I ^-) such as by oxidizing the radiation degradation products of OH radicals and hydrogen peroxide, a portion of iodine (I ₂ (2I ^- + 2OH ^- &gt; I ₂ + 2OH ^- ) and then to produce a stable triiodide ion (I ₃ ^- ). This reaction can be confirmed from two UV / VIS absorption peaks occurring at 288 and 351 nm. In an actual accident environment, the concentration of iodide ion is low, and it exists as a dissolved gas, iodine, rather than a triiodide ion, so that the volatility of iodine is increased.

On the other hand, the absorption spectrum of triiodide ion (I ₃ ^- ) at 288 and 351 nm was not observed in the case of Example 1, which is a radioactive iodine capturing solution containing platinum fine particles. This shows that the oxidation of the iodide ion (I ^- ) to iodine (I ₂ ) is extremely slight. Also, the oxidative decarboxylation product produced by the gamma ray is recombined with the reducing decomposition product by the catalytic reaction at the surface of the platinum fine particle and disappears rapidly.

Therefore, it was confirmed through the above experiments that the radioactive iodine collection solution containing the platinum fine particles according to the present invention can be an effective means for suppressing the increase in the volatility of iodine by the radial decomposition product of water.

1: iodine capture solution
2: Injection tube
3: Rupture valve
4: Collection solution replenishment tube
5: Replacement valve
6: Nozzle
7: Water pipe
8: Drain valve
9: discharge pipe

Claims (14)

A gaseous radioactive iodine collection solution containing an iodide compound containing an iodide ion, an alkali compound and a reducing agent,
Further comprising a platinum group element. &Lt; RTI ID = 0.0 &gt; 8. &lt; / RTI &gt;
The method according to claim 1,
Wherein the platinum group element is at least one selected from the group consisting of platinum (Pt), palladium (Pd), and rhodium (Rh).
The method according to claim 1,
Wherein the content of the platinum group element is 0.001 to 0.5 wt% with respect to the radioactive iodine collection solution.
delete delete The method according to claim 1,
Wherein the alkali compound is a compound containing at least one member selected from the group consisting of alkali metals, hydroxide ions, ammonium ions and calcium oxide.
The method according to claim 1,
Wherein the reducing agent is at least one selected from the group consisting of a salt containing a thiosulfate ion (S ₂ O ₃ ^2- ) or a tin ion (Sn ²⁺ ), a hydrazine, a zinc-mercury amalgam and a phosphoric acid-based reducing agent Gaseous radioactive iodine capture solution.
The method according to claim 1,
Wherein the platinum group element is one type selected from the group consisting of fine particles, porous materials, thin films, fibers, nets and liquids.
The method according to claim 1,
Wherein the platinum group element is in the form of a fine particle.
10. The method of claim 9,
Wherein the surface area of the platinum group element in the form of fine particles is 0.1 to 1,000 square meters per gram of radioactive iodine.
10. The method of claim 9,
Wherein the average diameter of the platinum group elements in the form of fine particles is 10.0 nm to 1.0 mm.
A collection solution part comprising the gaseous radioactive iodine collection solution of claim 1;
An inlet tube connected to the inside of the collection solution section for moving radioactive contaminated gas containing radioactive iodine;
A collection solution replenishment tube for replenishing the collection solution in the collection solution portion;
A drain pipe positioned below the collection solution unit and discharging the collection solution; And
And a discharge pipe located above the collection solution section for discharging the gas in which the radioactive iodine is captured, the radioactive iodine-containing gas containing radioactive iodine on the gaseous phase.
A method of collecting radioactive iodine comprising passing a stream comprising gaseous radioactive iodine through a collecting device according to claim 12.
14. The method of claim 13,
Characterized in that the stream comprising radioactive iodine on the gaseous phase is generated in the radioactive contaminated gas.

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