KR102100873B1 - Decontamination method with reduced radioactive waste - Google Patents

Abstract

The present invention relates to a decontamination method with reduced radioactive waste. More specifically, the present invention relates to a decontamination method with reduced radioactive waste which comprises: a step of performing decontamination treatment by using a chemical decontamination agent including a step of using an oxidizing decontamination agent containing sulfuric acid (H_2SO_4) and a reducing decontamination agent (step 1); and a step of forming a precipitate which does not contain cobalt by adding salts of Ba or Sr cations and hydroxide ions or halogen anions to a waste solution generated in the step 1 at a concentration of 56 to 59% of a sulfuric acid molar concentration (M) (step 2).

Description

DECONTAMINATION METHOD WITH REDUCED RADIOACTIVE WASTE}

The present invention relates to a decontamination method in which radioactive waste is reduced, and when the decontamination waste solution generated after chemical decontamination is formed and treated as a sediment, the radioactive source of the sedimented sludge is reduced by separating a radiation source separately for ease of sediment treatment. It relates to a method for facilitating treatment and improving the continuity of the entire decontamination process.

In order to dismantle an old nuclear power plant, decontamination of the primary system is essential, and decontamination effects can be obtained by alternately applying oxidizing / reducing decontamination agents in decontamination of pressurized water reactors or pressurized heavy water reactors, which are major reactor types in Korea. At this time, the decomposition of the oxidizing agent or reducing agent remaining in the decontamination solution must be performed in order to proceed to the next step after each step of the process.

In the case of the inorganic acid-based chemical decontamination process developed to significantly reduce waste and increase water solubility in waste disposal sites as disclosed in Korean Patent Registration No. 10-1883895, BaSO OH ₂ is added after the oxidation / reduction step to form BaSO ₄ precipitation. This process is essential, and through this, the use of ion exchange resins can be minimized. However, in the case of general commercial nuclear power plants, the total decontamination solution volume for primary system decontamination is a large capacity of 130 m ³ (130 ton) or more, so securing continuity between steps through proper treatment of process water used for decontamination is an important technical element. You can say

In particular, the BaSO ₄ precipitation process not only removes sulfate ions (SO ₄ ^2- ), which are anions present in the decontamination waste solution, by precipitation, but also co-precipitates Fe ^{2 +} , Cr ^{3 +} , Ni ^{2 +,} and wastes. It has the advantage of significantly reducing, but co-precipitation of radioactive materials such as Co-60, Co-58, and Co-57 forms a high-radiation captain, which makes handling difficult and delays work.

Since the BaSO ₄ sediment contains 99.9% of the total radioactive material, it is difficult to access due to its high radioactivity, making it difficult to work with a filter press to filter the sediment, as well as a factor of delayed work. Can be. Among the radioactive materials in the precipitate, the radioactivity of Co-60, Co-58, and Co-57 accounts for about 90% of the total radioactivity. Therefore, the decontamination in the waste solution only Co-60, Co-58, Co-57 component is in the form of Co ^{2 +} ions there can handle formed was filtered and BaSO ₄ precipitate was then separated off operation access is easy and due to the filter press It is expected that it can be easily performed.

Accordingly, one aspect of the present invention is to provide a decontamination method capable of forming a radioactive waste, particularly a precipitate with reduced radioactive cobalt.

According to one aspect of the present invention, comprising a step of using an oxidizing agent containing sulfuric acid (H ₂ SO ₄ ) and a reducing agent using a reducing agent, decontamination treatment step using a chemical decontamination agent (step 1); The step of forming a precipitate containing no cobalt by introducing salts of Ba or Sr cations and hydroxide ions or halogen anions to the waste solution generated in step 1 at a concentration of 56 to 59% of the sulfuric acid molar concentration (M) (step A method of decontamination with reduced radioactive waste is provided, including 2).

When the decontamination process according to the present invention is applied, it is possible to dramatically improve the ease of sedimentation sludge treatment by reducing the radioactivity level in the sedimentation sludge generated during decontamination of the primary system for decommissioning an old nuclear power plant to 1/10 or less. In addition, if BaSO ₄ precipitation is applied only in the final stage after repeated oxidation and decomposition, the continuity of the process is improved by recycling sulfate ions in each cycle and the precipitation waste is reduced to less than 1/2, so the efficiency of decontamination during nuclear power plant decommissioning is reduced. And it has the effect of significantly improving the economic efficiency.

1 is a graph showing the differentiation behavior of the cobalt component upon BaSO ₄ precipitation.
2 is a graph showing the ionic fractions of chromium, iron, nickel and cobalt components according to the amount of barium added during BaSO ₄ precipitation.
Figure 3 is a graph showing the precipitate fraction of chromium, iron, nickel and cobalt components according to the amount of barium added during BaSO ₄ precipitation.
Figure 4 shows a process improvement flow diagram of the decontamination technique using potassium permanganate and hydrazine containing sulfuric acid as the main salt.
Figure 5 shows a graph comparing the waste generated by the existing process and the improvement process of the present invention.
6 shows a pH titration curve according to the addition of sulfuric acid when the reducing agent hydrazine is fixed at 50 mM.
7 is a graph showing the tendency of the decrease of Fe ^{2 +} and Ni ^{2 +} ions in solution and the increase of co-precipitation of Co ^{2 +} ions in solution while the amount of barium added increases from 0.020 M to 0.024 M.
Figure 8 shows the results of the dissolution test for the powder oxide of a component similar to the radioactive contaminated oxide film formed in the primary system of nuclear power in a reducing agent containing sulfuric acid, hydrazine and copper ions.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

According to the present invention, the continuity of the process during primary system decontamination for the decomposition of aged pressurized water reactors and pressurized heavy water reactors is enhanced, and the cobalt components of Co-60, Co-58, and Co-57 present in the decontamination waste liquid are separated from the precipitate. So, it is possible to separate with a small amount of cation exchange resin that is easy to handle, and other non-radioactive substances such as Fe ^{2 +} , Cr ^{3 +} , Ni ^{2 +} and a small amount of other components can be separated by BaSO ₄ precipitation Is provided.

In more detail, the decontamination method with reduced radioactive waste of the present invention includes a step of using an oxidizing agent that includes sulfuric acid (H ₂ SO ₄ ) and a step of using a reducing agent, and a step of decontamination using a chemical decontamination agent (step One); The step of forming a precipitate containing no cobalt by adding a salt of Ba or Sr cation and hydroxide or halogen anion to the waste solution generated in step 1 at a molar concentration of 56 to 59% of the molar concentration of sulfuric acid (M) ( Step 2).

The decontamination treatment step using the chemical decontamination agent of the present invention may include a combination of alternating repeating steps in the order of using the oxidizing agent and reducing agent salt or vice versa. For example, after using the oxidizing agent, the cycle of using the reducing agent salting agent is performed twice or three or more times, or after using the reducing agent salting agent, the cycle of using the oxidizing agent salting agent is performed twice or three times or more. All treatment steps are included.

In the decontamination step, the number of repetitions is not particularly limited within the range for obtaining the decontamination effect required, and may be usually 5 times, 4 times, 3 times, or 2 times.

In the step of desalting in step 1, when the cycle is repeated, the phylogenetic tree required for each decontamination is charged once and then purified. You can use it repeatedly or charge a separate system water for each decontamination.

In the case of using the system water once, in the case of decontamination treatment by alternately using the oxidizing agent reducing agent and reducing agent salt, it may further include the step of removing the residual oxidizing agent or reducing agent after each decontamination agent treatment. As an example, hydrazine (N ₂ H ₄ ) may be added to remove residual oxidant after each oxidant desalination step, and hydrogen peroxide (H ₂ 0 ₂ ) to remove residual reducing agent after each desalination step. Can be added.

When hydrazine (N ₂ H ₄ ) is added, a reaction as shown in Reaction Scheme 1 below is induced to decompose and remove residual oxidizing agent, for example, potassium permanganate.

 [Scheme 1]

_{4KMnO 4 + 5N 2 H 4 +} 6H 2 SO 4 → 4K + + 4Mn 2 + + 5N 2 + 16H 2 O + 6SO 4 2 -

The object of the decontamination step may be an object containing a radioactively contaminated metal or alloy, for example, may be generated inside the system of a nuclear power plant. At this time, the types of the nuclear power plant include light water deceleration reactor, boiling water reactor (BWR), pressurized water reactor (PWR), Russian pressurized water reactor (VVER), pressurized water reactor (PWR), heavy water reactor (HWR), pressurized heavy water reactor (PHWR) ), CANDU (Canada Deuterium Uranium), Gas Cooled Heavy Water Reactor, Graphite Reduction Furnace Magnox, Improved Gas Cooling Furnace (AGR), High Temperature Gas Cooling Furnace, Graphite Reduction Boiling Water Pressure Tube Reactor (RBMK), Pebble Bed Modular Reactor , The type of nuclear power plant is not limited thereto, but the nuclear power plant may include a pressurized light reactor or a pressurized heavy water reactor. In addition, the system may be a primary system, but the type of the system is not limited thereto.

The oxidizing agent salt may include an oxidizing agent and a metal ion, wherein the oxidizing agent may be one or more oxidizing agents selected from the group consisting of KMnO ₄ , NaMnO ₄ , H ₂ CrO ₄ and HMnO ₄ .

The metal ion may be one or more metal ions selected from the group consisting of Cu ^{2 +} , Fe ^{3 +} , Cr ^{3 +} , Ni ^{2 +} and Zn ^{2 +} , and among these, Cu ^{2 +} . By adding the metal ion, the potential of the object to which the oxidizing agent is applied, that is, the metal or alloy component, can be moved to the passivation region, thereby effectively preventing corrosion of the oxidative decontamination component.

Meanwhile, in the oxidizing agent anti-inflammatory agent according to the present invention, the concentration of the oxidizing agent may be 1Х10 ^-5 M to 1Х10 ^-2 M. When the concentration of the oxidizing agent is less than 1Х10 ^-5 M, the oxidizing capacity may not be sufficient, and when it exceeds 1Х10 ^-2 M, a lot of chemicals for decomposing it after deoxidation may be required.

In addition, in the oxidizing agent anti ^- inflammatory agent according to the present invention, the concentration of the sulfuric acid may be 1Х10 ^-3 M to 3Х10 ^-2 M. When the concentration of the sulfuric acid is less than 1Х10 ^-3 M, the oxidative decontamination effect is small, and when it exceeds 3Х10 ^-2 M, a large amount of neutralizing agent is required to neutralize it, and accelerated corrosion may occur.

In the oxidizing agent according to the present invention, when the metal ion is Cu ^{2 +} and Zn ^{2 +} , the concentration of the metal ion may be 2Х10 ^-5 M to 2Х10 ^-3 M, but need not be limited thereto, and those skilled in the art It can be changed within the range of exerting the effect of decontamination. If the concentration of the Cu ^{2 +} and Zn ^{2 +} ions is less than 2Х10 ^-5 M, the potential may not be effectively controlled to the passivation region, and if it exceeds 2Х10 ^-3 M, a metal component precipitate may be formed. .

Further, in the oxidizer salts in accordance with the present invention, the concentration of metal ions in the case where the metal ion is not a Cu ^{+ 2} and Zn ^{+ 2,} but can be selected at any 2Х10 ^-6 M to 2Х10 ^-5 M range, ordinary skill It can be changed within the range that can exert the decontamination effect. If the concentration of the metal ion is less than 2Х10 ^-6 M, the potential may not be effectively controlled to the passivation region, and if it exceeds 2Х10 ^-5 M, a precipitate of a metal component may be formed.

In the present invention, the oxidizing agent salt, a step of preparing a solution in which the oxidizing agent is dissolved in distilled water, adding sulfuric acid to the solution prepared in the step; And adding metal ions to the solution to which sulfuric acid has been added in the above step.

In the present invention, the reducing agent salt may be a reducing agent and a metal ion, the reducing agent may be one or more reducing agents selected from the group consisting of NaBH ₄ , H ₂ S, N ₂ H ₄ and LiAlH ₄ , , The metal ion is Ag ⁺ , Ag ^{2 +} , Mn ^{2 +} , Mn ^{3 +} , Co ²⁺ , Co ^{3 +} , Cr ^{2 +} , Cr ^{3 +} , Cu ⁺ , Cu ^{2 +} , Mn ^{2 +} , Mn ^{3 +} , Sn ^{2 +} , Sn ^{4 +} , Ti ^{2 +} and Ti ^{3 +} may be one or more metal ions selected from the group consisting of.

Furthermore, the reducing agent salt may be a reducing agent N ₂ H ₄ and LiAlH ₄ and the metal ion may be Cu ⁺ or Cu ^{2 +} , the reducing agent may be N ₂ H ₄ and the metal ion may be Cu ^{2 +} .

On the other hand, in the reducing agent salt according to the present invention, the concentration of the reducing agent may be 5Х10 ^-4 M to 0.5 M. If the concentration of the reducing agent is less than 5Х10 ^-4 M, the reducibility may not be sufficiently exhibited, and if it exceeds 0.5 M, a lot of chemicals for decomposing it after decontamination may be required.

In addition, in the reducing agent salt of the present invention, the concentration of the reducing metal ion may be 1Х10 ^-5 M to 0.1M. If the concentration of the reducing metal ion is less than 1Х10 ^-5 M, the decontamination effect may be reduced, and if it is more than 0.1 M, a metal component precipitate may be formed.

Furthermore, in the reducing agent salt of the present invention, the concentration of the sulfuric acid may be 1Х10 ^-4 to 0.5 M. If the concentration of the sulfuric acid is less than 1Х10 ^-4 M, the decontamination effect may be reduced, and if it is more than 0.5M, a large amount of neutralizing agent for neutralizing it may be required.

In the present invention, the reducing agent salt is prepared by dissolving a reducing agent in distilled water; Adding sulfuric acid to the solution prepared in the above step; And adding metal ions to the solution to which sulfuric acid has been added in the above step.

In performing the reducing agent desalination method of the present invention, the temperature and time range are not particularly limited, and may be selected from, for example, a temperature range of 70 ° C to 140 ° C.

Subsequently, salts of Ba or Sr cations and hydroxide ions or halogen anions are added to the waste solution generated in Step 1 at a concentration of 56 to 59% of the molar sulfuric acid concentration (M) to form a precipitate containing no cobalt. Perform the steps.

Precipitation in the present invention can be introduced into the waste solution as a precipitating agent without limitation, as long as it contains cations of sulfate ions (SO ₄ ^2- ) present in the waste solution and Ba or Sr capable of forming precipitation. That is, dissolved in the waste liquid can be used without limitation, if the salt which can provide the Ba or Sr cations, however, is too low salt solubility in the waste solution such as a precipitate of BaSO ₄ or SrSO ₄ to be formed it is not desirable It may not.

As an example, as an anion capable of forming a salt with a Ba or Sr cation, a hydroxide ion or a halogen anion may be selected. And halogen anions include fluoro anions, chloro anions, bromo anions, and iodine anions. In the case of the halogen anion, a process of separately removing the halogen anion from the waste liquid after precipitation may be required.

The precipitate of step 2 may be co-precipitated with radioactive materials and metal ions in the decontamination waste solution. However, in the present invention, a salt of a Ba or Sr cation used as the precipitating agent and a hydroxide ion or halogen anion is added at a concentration of 56 to 59% of the molar sulfuric acid concentration (M) to form a precipitate containing no cobalt. Perform the steps. The concentration of the salt of the Ba or Sr cation and the hydroxide or halogen anion is preferably introduced at a concentration of 56 to 59% based on the molar sulfuric acid concentration (M). For example, when sulfuric acid has a concentration of 39 mM, the concentration of the salt may be 22 to 23 mM.

That is, the metal ions generated in the decontamination process existing in the waste solution are co-precipitated in the process of BaSO ₄ or SrSO ₄ precipitation, and through such co-precipitation, the amount of metal ions to be removed through the ion exchange resin in the decontamination waste solution is significantly reduced. In addition, according to the present invention, since the radioactive substances Co-60, Co-58, and Co-57 are not included in the precipitate, the radioactive level in the precipitated sludge is reduced to 1/10 or less to treat the precipitated sludge. Ease of use can be dramatically improved.

In the present invention, mixing of the decontamination waste solution and the precipitating agent is performed by a mixing means capable of causing mixing, for example, a mixing means such as an in-line mixer, wherein the Reynolds number ranges from 10,000 to 50,000. You can use values.

In addition, the temperature in the mixer (mixer) to be used can be appropriately selected by a person skilled in the art within a range that can cause the effect of mixing, can be selected so that mixing can occur within the range of the Reynolds number, As an example, it may range from 25 ° C to 80 ° C.

Further, in the decontamination method with reduced radioactive waste of the present invention, the step of treating the waste solution formed in step 1 with an ion exchange resin (step 1-1) may be further included. More specifically, for example, the decontamination method of the present invention is not only capable of repeating steps 1, 2, 1 and 2, but also steps 1, 1-1, 1 and 2; Alternatively, steps 1, 2, 1, and 1-1 may be performed in the same order.

At this time, the cycle including the step 1 and step 1-1 may be performed repeatedly 2 to 3 times or more, for example, 2 to 5 times. In addition, the cycle including the steps 1 and 2 may also be performed repeatedly 2 to 3 times or more, for example, 2 to 5 times, and further, these cycles may be performed by mixing.

According to this process of the present invention, the radioactivity of all sludges can be reduced to 1/10 or less to easily treat difficult-to-treat precipitated sludge and dramatically improve the continuity of the entire decontamination process.

On the other hand, in the present invention, the reducing agent salt is preferably performed under the conditions of pH 2 to 4, more preferably, the pH is 2.5 to 3.5, but the closer to pH 3, the faster the reaction rate and the shorter the decontamination time. have. If the pH is less than 2, sulfuric acid and hydrazine consumption may increase rapidly, resulting in an increase in the amount of waste as well as an increase in the amount of dissolution of the base metal, and the concentration of hydrogen ions supplied to the oxide film exceeding pH 4 There is a problem that the dissolution rate is reduced by decreasing.

As a final step, the decontamination method of the present invention may further include a step of introducing a salt of Ba or Sr cation and hydroxide or halogen anion into the waste solution at a molar concentration equal to the molar concentration of sulfuric acid (M) (step 3). You can. When such a process is performed only at the final stage, the continuity of the process is improved by recycling sulfate ions, and the sedimentation waste is reduced to 1/2 or less, thereby significantly improving the efficiency and economic efficiency of decontamination when dismantling nuclear power plants.

Furthermore, the decontamination method of the present invention may further include the step of separating the precipitate after the precipitate is formed (step 4).

At this time, the sediment may have a solid or sludge form, and the separation of the solid sediment or sludge and the residual decontamination waste liquid may be performed using various separation means such as a filter paper, a separation membrane, and a filter. , It may be a polymer, ceramic, metal, or a composite thereof, and may be performed using a separation filter as an example, and may be performed using a candle filter among the separation filters.

The water content of the cake made by solid-liquid separation by a candle filter may be 40% or less, 30% or less, 20% or less, or 10% or less.

In addition, the made cake density may be 0.1 to 10 g / cm ³ , 1 to 5 g / cm ³ , 2 to 3 g / cm ³ , and as an example, 2.56 g / cm ³ , and the cake density is limited thereto. It is not.

As a method of disposing of the cake thus formed, various methods known as a method of treating radioactive waste can be disposed of, and a method of disposing a cement solidified body by directly injecting it into a radioactive waste drum container may be used. It is not limited.

According to the present invention, it is possible to dramatically improve the ease of treatment of the settling sludge by reducing the radioactive level in the settling sludge to 1/10 or less.

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are only examples to aid the understanding of the present invention, and the scope of the present invention is not limited thereto.

Example

1. Equilibrium calculation for primary waste precipitation

When decontamination, the primary waste that is dissolved in the oxide film of the object to be decontaminated is metal ions such as Fe ^{3 +} , Cr ³⁺ , Ni ^{2 +} and Co-60, Co-58, Co-57, which are radioactive substances present in the oxide film. And Mn-54, Fe-59, and Zn-65.

Metal ions, such as Fe ^{3 +} , Cr ^{3 +} , and Ni ^{2 +} , dissolved in the primary system corrosion-resistant oxide of a pressurized hard nuclear power plant and present in the waste solution are 50 ppm to 200 ppm, respectively, and contain them. In the case of the comparative example targeting the decontamination waste liquid to be treated, the oxidizing agent, the oxidizing agent decomposing agent, the reducing agent decontaminating agent, the reducing agent decontaminating agent, etc. were sequentially added according to the procedure of FIG. .

At this time, the components and concentrations of the decontamination agent and decontamination agent added are as follows.

Oxidizer: 6.33 mM KMnO ₄ + 3.25 mM H ₂ SO ₄

Oxidizing agent degrading agent: 7.91mM N ₂ H ₄ + 9.50mM H ₂ SO ₄

Reducing agent salt: 50.00mM N ₂ H ₄ + 26.39mM H ₂ SO ₄

Reducing agent decontaminating agent: 240.00mM H ₂ O ₂

However, in this case, in the case of the comparative example, BaSO ₄ was precipitated by adding 39.13 mM Ba (OH) ₂ precipitating agent, thereby inducing coprecipitation of all metal ions and anions in the decontamination waste solution. In the comparative example where the existing decontamination technology was applied, all primary wastes were BaSO ₄ Upon precipitation, it coprecipitated and was present in the precipitated sludge.

On the other hand, in the case of Examples, Ba (OH) ₂ precipitants were added at various concentrations, and FIGS. 1 to 3 are Fe ^{3 +} , Cr ^{3 +} present in the waste solution after reducing agent salt to evaluate the separation possibility of the main radioactive material, cobalt component. , Ni ^{2 +} and Co ^{2 + It} is the result of calculating the speciation of ions. The calculation was performed by a computer program using the reaction formulas and Log K values listed in Tables 1 and 2 below.

Reaction scheme and log K values of cobalt components in ions and precipitation Scheme Log K value H ₂ O + Co ^{2 +} = CoOH ⁺ + H ⁺ -9.697 2H ₂ O + Co ^{2 +} = Co (OH) ₂ (aq) + 2H ⁺ -18.794 ^{_{4H 2 O + Co 2 + =}} Co (OH) 4 2 - + 4H + -46.288 4H ₂ O + 4Co ^{2 +} = Co ₄ (OH) ₄ ^{4 +} + 4H ⁺ -30.488 ^{_{3H 2 O + Co 2 + =}} Co (OH) 3 - + 3H + -31.491 H ₂ O + 2Co ^{2 +} = Co ₂ OH ^{3 +} + H ⁺ -10.997 Co ^{2 +} + SO ₄ ^2- = CoSO ₄ (aq) 2.300 2H ₂ O + Co ^{2 +} = Co (OH) ₂ (s) + 2H ⁺ -13.94 Co ^{2 +} + SO ₄ ^2- = CoSO ₄ (s) -2.802

Reaction equation and Log K value related to pH in aqueous solutions containing sulfuric acid and hydrazine Scheme Log K value ^{_{H 2 O = OH - + H}} + -13.997 _{^{H + + SO 4 2- = HSO}} 4 - 1.990 _{^{K + + SO 4 2- = KSO}} 4 - 0.850 Mn ^{2 +} + SO ₄ ^2- = MnSO ₄ 2.250 Ba ^{2 +} + SO ₄ ^2- = BaSO ₄ 9.980 H ⁺ + N ₂ H ₄ = HN ₂ H ₄ ⁺ 8.100 2H ⁺ + N ₂ H ₄ = H ₂ -N ₂ H ₄ ^{2 +} 7.000

As a result, as an important result, it was confirmed that cobalt precipitates were not generated at all when the barium addition amount was about 0.02M or less, which is about 51% of the sulfuric acid concentration. At this time, only ionic and water-soluble substances such as Co ^{2 +} , CoSO ₄ (aq), Co (OH) ₂ (aq), and Co (OH) ₃ ^- were present in the solution, but when the amount of added barium increased by more than 0.02M, It was shown that the material disappeared rapidly and only the precipitate Co (OH) ₂ (s) was present.

On the other hand, ions such as Fe ^{3 +} , Cr ^{3 +} , and Ni ^{2 +} are mostly present as precipitates before the amount of barium addition is 0.02 M, as shown in FIGS. 2 and 3, and the Cr component is precipitated first, and Fe and Ni, etc. It precipitated in order. The present invention can separate Co ²⁺ components from Fe ^{3 +} , Cr ³⁺ , and Ni ²⁺ using these characteristics.

2. Process improvement and waste volume comparison

Figure 4 is a diagram showing the flow of the improvement process of the existing process and examples of the comparative example, Figure 5 shows a relative comparison of their waste amount.

In the process improved by the examples, cation waste is 8% or more compared to the comparative example. It can be seen that it decreases, and the equivalent of waste by anion decreases to 1/3 or less. According to the results of the present invention, it can be seen that, according to the present invention, it is a technology capable of improving the economic efficiency of the dismantling operation by reducing the waste treatment cost when dismantling the nuclear power plant as an additional benefit by process improvement.

3. To minimize waste generation Decontamination agent  Composition optimization

6 is a diagram showing the pH titration curve according to the addition of sulfuric acid when the reducing agent hydrazine is fixed at 50 mM in order to establish continuous process conditions without applying precipitation and solution purification in an intermediate step.

At this time, the chemical reaction formulas listed in Tables 1 and 2 and Log K values for these were utilized. As shown in this figure, it can be seen that as the concentrations of K ⁺ and Mn ^{2 +} ions in the decontamination solution increased, more and more sulfuric acid should be added to maintain pH = 3 suitable for decontamination conditions. At this time, the K ⁺ and Mn ^{2 +} ion concentrations are 2 and 3 times, respectively, and are calculated for 12.6 mM and 18.9 mM. It is possible to select the optimum decontamination agent composition that can minimize waste within the pH = 2 to 3 condition, which is the decontamination area.

Table 3 below shows the amount of sulfuric acid tour (mM) to maintain pH = 3 when N ₂ H ₄ = 50mM is maintained.

1 step reduction 2-step reduction 3-step reduction [H ₂ SO ₄ ] 39.13 47.45 58.74 [N ₂ H ₄ ] 50 50 50

4. Optimization of metal ion separation

If the co-precipitation fractions of Cr ^{3 +} , Fe ^{2 +} and Ni ^{2 +} ions are obtained when the barium addition amount given in Example 1 is 0.02M, they are 100%, 99.3%, and 93.4%, respectively. That is, in order to precipitate Fe ^{2 +} and Ni ^{2 +} ions as much as possible, the amount of barium added must be increased. On the other hand, as shown in FIG. 1, when the barium addition amount increases by 0.023 M or more, the co-precipitation amount of Co ^{2 +} ions increases rapidly.

7 is a graph showing the tendency of decreasing the Fe ^{2 +} and Ni ²⁺ ions in solution and increasing the co-precipitation of Co ^{2 +} ions in solution while the amount of barium addition increased from 0.02 M to 0.024 M. Based on this graph, the concentration of barium that can maximize the separation of metal ions is 0.0225M, based on the concentration of sulfuric acid 0.039M, and the optimization area of the actual metal ion is 0.022M <[Ba (OH) ₂ ] <0.023M.

5. Derivation of optimum decontamination conditions (pH conditions) in the reduction step

FIG. 8 shows an example of an experiment in which a dissolution test was performed with a powder oxide of a component similar to a radioactive contaminated oxide film formed in a primary nuclear power plant in a reducing agent containing sulfuric acid, hydrazine and copper ions.

That is, it is a graph showing the dissolving ability by time in the pH = 1 to 4 region. It was found from the dissolution experiments conducted in sulfuric acid, sulfuric acid, and hydrazine solutions that the acidity of the solution was dominant in the region of pH <2.0 and that of acidic dissolution was dominant in the region of pH> 2.0. This trend can be confirmed.

Therefore, in order to maximize the effect of reducing decontamination, it is preferable that decontamination is carried out near pH = 3. In particular, as the acidity of the solution approaches 3.0 at the beginning of the reaction, the reaction rate is faster, so that the decontamination time can be shortened. In the region of pH <1.5, the dissolution rate is large, but the consumption of sulfuric acid and hydrazine increases rapidly, so that the amount of waste increases as well as the dissolution of the base metal.

Although the embodiments of the present invention have been described in detail above, the scope of rights of the present invention is not limited to this, and various modifications and variations are possible without departing from the technical spirit of the present invention as set forth in the claims. It will be apparent to those of ordinary skill in the field.

Claims (12)

Decontamination treatment using a chemical decontamination agent, including the step of using an oxidizing agent containing sulfuric acid (H ₂ SO ₄ ) and a reducing agent using a reducing agent (step 1);
In the waste solution generated in step 1, salts of Ba or Sr cations and hydroxide ions or halogen anions are added at a concentration of more than 56.4% to less than 58.97% of the sulfuric acid molar concentration (M) to form a precipitate that does not contain cobalt. Step to do (step 2)
The method of decontamination containing radioactive waste is reduced.
The method of claim 1, wherein the halogen anion is selected from the group consisting of fluoro anion, chloro anion, bromo anion, and iodine anion.
The method according to claim 1, further comprising the step of treating the waste solution formed in step 1 with an ion exchange resin (step 1-1).
The decontamination method according to claim 3, wherein the cycle including the steps 1 and 1-1 is performed twice or more repeatedly.
The decontamination method according to claim 1, wherein the cycle including the steps 1 and 2 is repeatedly performed two or more times.
The decontamination method according to claim 1, wherein the decontamination is performed under conditions of pH 2 to 4.
The decontamination method according to claim 1, wherein the oxidizing agent salt comprises an oxidizing agent and a metal ion.
The method according to claim 7, wherein the oxidizing agent is at least one oxidizing agent selected from the group consisting of KMnO ₄ , NaMnO ₄ , H ₂ CrO ₄ and HMnO ₄ , wherein the radioactive waste is reduced.
The method of claim 1, wherein the reducing agent salt includes a reducing agent and a metal ion, and the radioactive waste is reduced.
The decontamination method according to claim 9, wherein the reducing agent is at least one reducing agent selected from the group consisting of NaBH ₄ , H ₂ S, N ₂ H ₄ and LiAlH ₄ .
The method of claim 1, wherein the decontamination method is a final step, in which a salt of Ba or Sr cation and a hydroxide ion or a halogen anion is added to the waste solution at a molar concentration equal to the molar concentration of sulfuric acid (M) (step 3). A method of decontamination, further comprising radioactive waste.
The decontamination method according to claim 1, wherein the decontamination method further comprises separating the precipitate (step 4).

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