JP4301992B2 - Decontamination waste liquid processing method and processing apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for treating a decontamination waste liquid after decontaminating radioactive substances adhering to piping, equipment, structural parts and the like with a chemical decontamination liquid in a nuclear facility or the like.

For example, in a nuclear facility, used equipment with radioactive materials attached is generated during maintenance. At the time of dismantling at the time of decommissioning of nuclear reactors, dismantling equipment with radioactive materials attached is generated. As such a decontamination technique for removing radioactive material from the device, the chemical decontamination methods have been developed at home and abroad using an inorganic acid decontamination liquid such as sulfuric acid (for example, see Patent Document 1.).

  In general, as a method of treating radioactive waste, a method of solidifying cement has been conventionally employed (see, for example, Patent Document 2 and Patent Document 3).

  For this reason, in the chemical decontamination method using an inorganic acid decontamination liquid such as sulfuric acid as described above, the used decontamination waste liquid is neutralized with caustic soda or the like to precipitate the eluted metal as a hydroxide, Decontamination waste liquid treatment that is heated, dried, pulverized and stabilized (cement solidified) has been studied. In such decontamination waste liquid treatment, the amount of cement solidified body that is the final treatment form is influenced by the amount of used sulfuric acid and the amount of metal elution, for example, in the case of sulfuric acid decontamination liquid. Since the filling amount of the cement solid body is small, there is a problem that the amount of cement solidified body, that is, the amount of secondary waste generated increases.

  In addition, the present inventors have conventionally developed a chemical decontamination method using an organic acid decontamination solution such as formic acid or oxalic acid.

  In the decontamination waste liquid treatment in the chemical decontamination method using an organic acid, the used organic acid is decomposed into carbon dioxide gas and water by adding hydrogen peroxide or the like (see, for example, Patent Document 4). For this reason, it has the advantage that there is little generation amount of a secondary waste compared with the case where the above-mentioned inorganic acid is used. However, in this decontamination waste liquid treatment, since the eluted metal is removed with an ion exchange resin, the used ion exchange resin must be stored as radioactive waste, and in terms of reducing secondary waste, It was not enough.

In addition, after the organic acid is decomposed as described above, it has been studied to adjust the alkali with caustic soda or the like to generate a metal hydroxide precipitate and solidify the cement (see, for example, Patent Document 5). Although this method has the advantage that the amount of secondary waste generated is small compared to the case of using an ion exchange resin, the metal hydroxide is a cement as in the case of the treatment of the above-mentioned inorganic acid decontamination waste liquid. There exists a subject that the filling amount to a solidified body is small.
JP 02-22597 (page 2-5, Fig. 1) JP 08-166492 A (page 2-13) JP 09-211194 A (page 4-8) JP 09-113690 A (page 4-9) JP 2002-333498 A (page 3-5, FIG. 1)

  As described above, in the conventional technology, since an ion exchange resin is used, this ion exchange resin becomes secondary waste, and the amount of secondary waste increases, or the amount of metal hydroxide filled in the cement solidified body Therefore, there is a problem that the amount of secondary waste generated increases.

The present invention has been made to solve the above-mentioned problems, and can convert metal ions dissolved in organic acid decontamination waste liquid into metal oxide powder. it is possible to reduce the goods generation amount, further aims to provide a processing method and processing apparatus for decontamination waste liquid that can reduce the generation amount of cement solidified bodies.

The treatment method of the decontamination waste liquid of the present invention is a treatment method of a decontamination waste liquid containing an organic acid and containing metal ions in which the metal is dissolved, and decomposes the organic acid in the decontamination waste liquid containing the metal ions. A decomposition step of decomposing it into carbon dioxide gas and water by the hydrogen peroxide solution as an agent, and heating and drying the decontamination waste liquid after the decomposition step to evaporate the water, thereby converting the metal ions into a metal oxide powder. And a solidifying step in which the metal oxide powder obtained by oxidizing the metal ions is solidified with cement.

Further, the treatment apparatus for decontamination waste liquid of the present invention is a treatment apparatus for decontamination waste liquid containing an organic acid and containing metal ions in which the metal is dissolved, and the organic acid in the decontamination waste liquid containing the metal ions A decomposition treatment section for decomposing the water into a carbon dioxide gas and water using a hydrogen peroxide solution as a decomposition agent, and heating and drying the decontamination waste liquid after the decomposition treatment by the decomposition treatment section to evaporate the water and It is characterized by comprising a drying processing section for forming a metal oxide powder and a solidification processing section for cement-solidifying the metal oxide powder obtained by oxidizing the metal ions .

According to the treatment method and the treatment apparatus for decontamination waste liquid of the present invention, metal ions dissolved in the organic acid decontamination waste liquid can be converted into metal oxide powder. The amount of material generated can be reduced , and further the amount of cement solidified body generated can be reduced .

  The details of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a decontamination waste liquid treatment apparatus according to an embodiment of the present invention. As shown in the figure, the decontamination waste liquid treatment apparatus includes a decomposition processing unit 1 that decomposes organic acids in the decontamination waste liquid into carbon dioxide gas and water, and heats the decontamination decontamination waste liquid to evaporate water. A drying processing unit 2 that dry-forms the metal contained in the decontamination waste liquid as a metal oxide and a solidification processing unit 3 that solidifies the dried and separated metal oxide into cement are provided. The decomposition processing unit 1 and the drying processing unit 2 are connected by a decomposition liquid transfer line 11, and the drying processing unit 2 and the solidification processing unit 3 are connected by a powder transfer line 15.

  The decomposition processing unit 1 contains a decontamination waste liquid, a decomposition tank 4 for decomposing the organic acid in the decontamination waste liquid, and a decontamination waste liquid supply line 5 for supplying the decontamination waste liquid to the decomposition tank 4 A decomposing agent supplying unit 6 for supplying hydrogen peroxide water as a decomposing agent into the decomposing tank 4 and a circulation line 8 provided with an overflow pump 7 for circulating decontamination waste liquid in the decomposing tank. It has. The overflow pump 7 is additionally provided with an ozone gas supply line 10 for supplying ozone gas from the ozone generator 9.

  The reason why the overflow pump 7 is used in the circulation line 8 as described above is that the overflow pump is suitable for transferring the gas-liquid mixed solution. When the organic acid in the decontamination waste liquid is formic acid alone, the ozone generator 9 and the ozone gas supply line 10 can be omitted.

  Further, the drying processing unit 2 includes a vertical centrifugal thin film dryer 12 and a condenser 13 for returning evaporated water to water. The condenser 13 is provided with a condensate transfer line 14, and water generated in the condenser 13 is transferred to the waste treatment system through the condensate transfer line 14 so as to be processed. It has become.

  Further, the solidification processing unit 3 includes a dry powder hopper 16, a cement hopper 17, an admixture hopper 18, a kneading water tank 19, and a kneading machine 20.

  In the decontamination waste liquid treatment apparatus having the above-described configuration, first, the decontamination waste liquid to be treated is supplied from the waste liquid supply line 5 to the decomposition tank 4, and the hydrogen peroxide solution is decomposed from the decomposition agent supply unit 6 as a decomposition agent. The organic acid in the decontamination waste liquid is decomposed into carbon dioxide gas and water. At this time, the decontamination waste liquid in the decomposition tank 4 is circulated by a circulation line 8 provided with an overflow pump 7, whereby hydrogen peroxide water as a decomposition agent is uniformly dispersed and decomposed efficiently. .

  Further, when ozone gas is used for the decomposition treatment, ozone gas is generated using the ozone generator 9, and ozone gas is supplied to the decomposition tank 4 through the overflow pump 7 through the ozone gas supply line 10. Even when ozone gas is supplied in this way, or when carbon dioxide gas is generated due to decomposition of the organic acid, the present embodiment uses the overflow pump 7, so the decontamination of the state of the gas-liquid mixed solution is performed. The waste liquid can be circulated stably.

  The decontamination waste liquid decomposed as described above is transferred to the vertical centrifugal thin film dryer 12 of the drying processing unit 2 through the decomposition liquid transfer line 11. The transferred decontamination waste liquid is heated and dried by the vertical centrifugal thin film dryer 12, the water is evaporated, and the dissolved metal becomes a metal oxide powder. The evaporated water is returned to water by the condenser 13 and then processed by the waste treatment system through the condensate transfer line 14.

  The metal oxide dried and powdered by the vertical centrifugal thin film dryer 12 as described above is transferred to the dry powder hopper 16 of the solidifying means 3 by the powder transfer line 15. The powder dried by the drying means 2 from the dry powder hopper 16, cement from the cement hopper 17, admixture from the admixture hopper 18, and kneading water from the kneading water tank 19 are respectively obtained. These are supplied to the kneading machine 20, and are kneaded in the kneading machine 20 for a predetermined time, discharged to the solidified drum can 21, and solidified.

  Next, the result of decomposing the organic acid in the decontamination waste liquid in which iron is actually dissolved in the decomposition processing unit 1 of the above-described decontamination waste liquid processing apparatus will be described with reference to FIG. In the graph shown in FIG. 2, the vertical axis represents the organic carbon concentration ratio (each concentration / initial concentration), and the horizontal axis represents the treatment time. Also, in the same graph, the results plotted for the formic acid alone solution are plotted with circular marks, and the results for the mixed solution of formic acid and oxalic acid are plotted with the square marks. ing.

  The initial concentration of formic acid alone is 2000 ppm. The initial concentration of the mixture of formic acid and oxalic acid is 2000 ppm formic acid and 100 ppm oxalic acid. As shown in the figure, in the case of formic acid alone solution, only hydrogen peroxide was used as a decomposition agent, and the organic carbon concentration dropped to 2 ppm or less (organic carbon concentration ratio 0.001 or less) in 2 hours.

  On the other hand, in the case of a mixture of formic acid and oxalic acid, the concentration of organic oxygen dropped to 20 ppm in 2 hours using only hydrogen peroxide, but no progress of the decomposition reaction was observed thereafter. As mentioned above, since formic acid decomposes only with hydrogen peroxide, residual organic carbon is considered to be a component of oxalic acid. When ozone gas was supplied to decompose this oxalic acid, the decomposition proceeded, and the organic carbon concentration decreased to 2 ppm or less in 3.5 hours.

  From the above results, when the organic acid contained in the decontamination waste liquid is formic acid alone, it is decomposed using hydrogen peroxide, and in the case of formic acid and oxalic acid (in the case of a mixed liquid), hydrogen peroxide and ozone are used. It is preferable to carry out a decomposition treatment using

Next, in the drying treatment unit 2 of the above decontamination waste liquid treatment apparatus, the decontamination waste liquid that actually decomposes the organic acid is heated, the moisture is evaporated, and the drying treatment is performed. The results of analysis by X-ray diffraction will be described. FIG. 3 shows that when the organic acid is formic acid alone, the decontamination waste liquid obtained by decomposing this formic acid into carbon dioxide gas and water as described above is treated with a heated steam temperature of 175 ° C. The results of line diffraction analysis are shown. The vertical axis represents the X-ray intensity, and the horizontal axis represents the diffraction angle. The X-ray intensity peak of the dried powder in this case is located at substantially the same diffraction angle as α-Fe ₂ O ₃ . Thus, the iron ions in the waste liquid after decomposing the formic acid was found to have been converted to iron oxide (α-Fe 2 _{O 3)} by heating and drying.

  On the other hand, FIG. 4 shows, for comparison, the result of X-ray diffraction analysis of a dried powdery product obtained by neutralizing a hydrochloric acid waste solution in which iron is dissolved with sodium hydroxide, and then heating and drying with a vertical centrifugal thin film dryer. Is shown. As shown in the figure, no clear X-ray intensity peak is observed in the X-ray diffraction analysis result. Therefore, it is presumed that the iron ions after neutralizing the inorganic acid are converted to amorphous iron hydroxide by heating and drying.

  Next, in the case where the organic acid is formic acid alone, the result of actually cement-solidifying the iron oxide powder generated from the decontamination waste liquid through the above-described decomposition treatment step and the drying treatment step in the solidification treatment unit 3 will be described. .

  A kneading machine 20 is kneaded from a kneading water tank 19 with a dry powder from a dry powder hopper 16, a blast furnace cement B from a cement hopper 17, and an inorganic admixture composed of sodium hexaphosphate and potassium carbonate from an admixture hopper 18. Water was supplied, kneaded by a kneader 20 for a predetermined time, and discharged to a solidified drum 21.

Table 1 shows the measurement results of the solidified body appearance and uniaxial compressive strength after the obtained solidified drum 21 (cement solidified body) was allowed to stand for one month.

  When cemented iron oxide produced from formic acid waste liquid, a uniaxial compressive strength greatly exceeding the target value of 1.5 MPa was obtained with a 200-liter drum can (hereinafter referred to as a 200-liter drum can) filling amount of 50 to 120 kg. Also, no void was observed.

  On the other hand, as a comparative example, when iron hydroxide produced from a hydrochloric acid waste solution was solidified, a large number of voids (voids) were observed at a filling amount of 100 kg, and thus it was evaluated as unqualified as a cement solidified body. In addition, no void was observed at a filling amount of 50 kg, and the uniaxial compressive strength greatly exceeded the target value of 1.5 MPa.

  From the above results, it is considered that the maximum amount of iron oxide cement solids produced from formic acid waste liquid is 120 kg / 200 L drum. On the other hand, the filling amount of cemented solid body of iron hydroxide produced from inorganic acid is considered to be 50kg / 200L drum can less than half of iron oxide.

  Next, the amount of secondary waste generated when the decontamination waste liquid was treated was calculated based on the cement solidification test results.

Assumptions, the surface area of the carbon steel of radioactive waste 100,000 m ^2, the amount of dissolved iron was 50 g / m ^2. The formic acid waste liquid decomposes formic acid and solidifies the dried iron oxide (Fe ₂ O ₃ ) powder produced by heating and drying. The hydrochloric acid waste liquid is neutralized with an aqueous solution of iron chloride (FeCl ₃ ), heated and dried to solidify the mixed powder of iron hydroxide (Fe (OH) ₃ ) and sodium chloride (NaCl).

  Figure 5 shows the results of a trial calculation of the amount of solidified cement (200L drum) generated under these conditions. The vertical axis of the figure indicates the ratio of 200L drum generation rate based on the generation amount of hydrochloric acid waste liquid. The amount of 200L drum generated when formic acid waste liquor was solidified was estimated to be about 1/7 of hydrochloric acid waste liquor.

  As shown in this result, the processing method and the processing apparatus of the decontamination waste liquid of the present invention can greatly reduce the amount of solidified cement and the disposal cost when the decontamination waste liquid is processed compared to the conventional method. It is.

As described above, according to the present embodiment, since the metal ions dissolved in the organic acid decontamination waste liquid can be converted into a metal oxide powder, the secondary waste is compared with the case of using an ion exchange resin. The amount generated can be reduced. Moreover, since the filling amount of the cement solid body is larger in the metal oxide than in the metal hydroxide, the cement solid body is compared with the conventional method of treating the eluted metal as a hydroxide and solidifying the cement. The amount of generation can be reduced.

  In addition, as an organic acid contained in the decontamination waste liquid, citric acid and the like can be used in addition to formic acid and oxalic acid. Examples of metals contained in the decontamination waste liquid include iron (Fe) dissolved from carbon steel, chromium (Cr) and nickel (Ni) dissolved from stainless steel, and Mn-54, Co— as radionuclides. 60 etc. are mentioned.

  Furthermore, as a method of decomposing an organic acid into carbon dioxide gas and water, in addition to a method using hydrogen peroxide and ozone, for example, a method of irradiating ultraviolet rays, a method of electrochemically oxidizing and decomposing at an anode, and the like are used. You can also.

The figure which shows the structure of the decontamination waste liquid processing method and processing apparatus which concern on one Embodiment of this invention. The figure which shows the mode of the change of the amount of organic carbon in a decomposition process. The figure which shows the X-ray-diffraction analysis result of the dry powder which decomposed | disassembled the organic acid waste liquid and was produced | generated by heating. The figure which shows the X-ray-diffraction analysis result of the dry powder produced by neutralizing the hydrochloric acid waste liquid and heating. The figure which shows the result of having calculated the amount of cement solid bodies generation | occurrence | production in this invention and the conventional method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Decomposition process part, 2 ... Drying process part, 3 ... Solidification process part, 4 ... Decomposition tank, 5 ... Waste liquid supply line, 6 ... Decomposition agent supply part, 7 ... Overflow pump, 8 ... Circulation line, 9 ... Ozone Generator 10 ... Ozone gas supply line 11 ... Decomposition liquid transfer line 12 ... Vertical centrifugal thin film dryer 13 ... Condenser 14 ... Condensate transfer line 15 ... Powder transfer line 16 ... Dry powder Hopper, 17 ... cement hopper, 18 ... admixture hopper, 19 ... kneading water tank, 20 ... kneading machine, 21 ... solidified drum

Claims (5)

A method for treating a decontamination waste liquid containing an organic acid and containing a metal ion in which a metal is dissolved,
A decomposition step of decomposing the organic acid in the decontamination waste liquid containing the metal ions into carbon dioxide gas and water with hydrogen peroxide water as a decomposition agent;
A drying step in which the decontamination waste liquid after the decomposition step is heated and dried to evaporate water and the metal ions are converted into a metal oxide powder;
A decontamination waste liquid treatment method comprising: a solidification step of solidifying cement powder of a metal oxide powder obtained by oxidizing the metal ions . The decomposition step includes
When the organic acid is formic acid alone, it is decomposed into carbon dioxide gas and water using hydrogen peroxide, and when the organic acid is formic acid and oxalic acid, it is decomposed into carbon dioxide gas and water using hydrogen peroxide and ozone. The processing method of the decontamination waste liquid of Claim 1 characterized by these. An apparatus for treating a decontamination waste liquid containing an organic acid and containing metal ions in which the metal is dissolved ,
A decomposition treatment unit that decomposes the organic acid in the decontamination waste liquid containing the metal ions into carbon dioxide gas and water with hydrogen peroxide water as a decomposition agent;
A drying treatment unit that heats and dehydrates the decontamination waste liquid after the decomposition treatment by the decomposition treatment unit , evaporates the water and turns the metal ions into a metal oxide powder, and
An apparatus for treating a decontamination waste liquid, comprising: a solidification processing unit configured to solidify a powder of the metal oxide obtained by oxidizing the metal ions . The decomposition processing unit
A decomposition tank for storing decontamination waste liquid;
And decomposing agent supplying section for supplying the decomposing agent to the decomposition bath,
4. The decontamination waste liquid treatment apparatus according to claim 3, further comprising a waste liquid circulation line provided with an overflow pump for circulating the decontamination waste liquid in the decomposition tank. The decomposition processing unit
The hydrogen peroxide is supplied to the decomposition tank from the decomposition agent supply unit, and ozone gas is supplied to the decomposition tank when the organic acid contains oxalic acid. Decontamination waste liquid treatment equipment.

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