JP4861252B2 - Chemical decontamination method before reactor demolition - Google Patents

Description

  The present invention relates to a chemical decontamination method before reactor demolition, and more particularly to a chemical decontamination method before demolition at the time of decommissioning of a reactor.

Commercial light-water reactor nuclear power plants that have reached the operating life are expected to be decontaminated and removed after system decontamination after a spent fuel is removed and after a safe storage period (5 to 10 years). .
System decontamination is intended for decontamination of reactor pressure vessels and primary coolant systems that have a high radiation dose equivalent rate in order to reduce the exposure of workers dismantling and removal. For large-scale decontamination that collectively decontaminates the reactor pressure vessel and the primary coolant system, it is considered to apply chemical decontamination that combines organic acid and ozone to the oxide film that is the source of contamination (for example, patents) Reference 1).

On the other hand, commercial light water reactor nuclear power plants that started operation in the 1970s may have a water-based anticorrosive agent added to the pressure-suppressed pool water. It is necessary to detoxify the water-based rust inhibitor added to the pressure suppression pool water when the reactor is dismantled, especially when the reactor is decommissioned. Water-based rust inhibitors include organic rust inhibitors and inorganic rust inhibitors, organic rust inhibitors are organic carboxylates or azole organic compounds, and inorganic rust inhibitors are chromates (for example, K ₂ CrO ₄ ). It has been known. As a method for treating an organic rust inhibitor, a method of decomposing and demineralizing an organic substance with ozone is known.
In addition, as a method for treating an inorganic rust preventive, there are known methods for detoxifying hexavalent chromium by reducing to hexavalent chromium with hydrogen peroxide under acidic conditions with formic acid (for example, Patent Document 1, Patent Document). 2).
JP 2004-233156 A JP 2005-326361 A

However, the pressure suppression pool water has a volume of 1000 m ³ or more. For example, when an aqueous rust inhibitor is rendered harmless over 3 days using a treatment apparatus having a volume of 10 m ³ , the treatment period for the entire volume is 300 days or more, and a huge number of days are required.
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a chemical decontamination method before reactor demolition that can shorten the treatment period of the water-based anticorrosive agent in the pressure-suppressed pool water.

  In order to achieve the above object, a chemical decontamination method prior to reactor dismantling according to an embodiment of the present invention includes a reductive decontamination solution and an oxidative decontamination supplied from a chemical decontamination facility in a reactor pressure vessel. System decontamination process that performs chemical decontamination using liquid, and waste liquid that contains water-based anticorrosive agent in the pressure suppression pool in the reactor pressure vessel that has been chemically decontaminated (pressure suppression that contains water-based anticorrosive agent) A water-based anticorrosive-containing waste liquid supply step for supplying (pool water), and an anticorrosive treatment step for decomposing the water-based anticorrosive in the waste liquid supplied into the reactor pressure vessel.

  ADVANTAGE OF THE INVENTION According to this invention, the chemical decontamination method before the nuclear reactor demolition which can shorten the processing period of the water-system antirust agent in pressure suppression pool water can be provided.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated based on drawing. The present invention is not limited to these embodiments.

  FIG. 1 is a flowchart showing the procedure of a chemical decontamination method before reactor demolition according to the first embodiment of the present invention. FIG. 2 is a diagram schematically illustrating an example of a configuration of main parts including a reactor pressure vessel, a reactor recirculation system, and chemical decontamination equipment used in the chemical decontamination method before reactor demolition according to this embodiment. is there. Here, the reactor pressure vessel and the reactor recirculation system (configured with the reactor recirculation system piping, the reactor recirculation system pump, etc.) are supplied with the reducing decontamination liquid supplied from the chemical decontamination equipment. And chemical decontamination (process) using an oxidative decontamination solution, that is, a system decontamination target. FIG. 3 is a diagram schematically showing a main configuration of an example of the chemical decontamination equipment used in this embodiment. First, the reactor pressure vessel, the reactor recirculation system, and the chemical decontamination equipment used in the chemical decontamination method will be described with reference to FIGS. 2 and 3, and then the chemical decontamination method will be described.

  As described above, the reactor pressure vessel 1 and the reactor recirculation system 2 are subject to system decontamination. The nuclear reactor recirculation system 2 includes a nuclear reactor recirculation system pipe 3, a nuclear reactor recirculation system pump 4, a nuclear reactor recirculation system inlet / outlet valve 5, and the like. The reactor recirculation system pump 4 is, for example, a saddle type single-stage mixed flow centrifugal pump, the pump shaft is sealed with a two-stage mechanical seal, and the shaft seal is cooled by flowing cooling water using a pump provided on the pump shaft. .

  In order to obtain the flow of the decontamination liquid in the reactor pressure vessel 1, the reactor recirculation system piping 3 of the reactor recirculation system 2 is circulated by the reactor recirculation system pump 4, and the bottom of the reactor pressure vessel 1 In addition, the flow rate of the decontamination solution near the bottom of the jet pump 6 can be ensured. That is, by operating the reactor recirculation pump 4, the decontamination liquid in the reactor pressure vessel 1 passes from the reactor recirculation system piping 3 through the jet pump riser pipe 7 and the jet pump 6 to the reactor pressure vessel 1. It is blown out at the bottom inside. The inside of the shroud 8 is further raised, the annulus portion 9 is lowered again, and the reactor recirculation system 2 is entered. As a result, a necessary flow can be obtained in the reactor pressure vessel 1 and the decontamination efficiency can be increased.

  The shroud 8 holds the upper lattice plate 10 and the core support plate 11 and wraps the entire fuel assembly (not shown) to form a core. The core support plate 11 holds the fuel assembly via the control rod guide tube of the control rod drive mechanism (CRD) 12 and the fuel support fitting. The jet pump 6 is disposed between the shroud 8 and the nuclear pressure vessel 1 and forcibly circulates the coolant. Reference numeral 13 denotes a water supply sparger, reference numeral 14 denotes a core spray pipe (sparger), reference numeral 15 denotes an ozonizer, and reference numeral 16 denotes an air diffuser.

  A temporary decontamination loop (system) 21 for performing chemical decontamination (system decontamination and treatment of a water-based anticorrosive agent described later) includes a temporary circulation line 22, a temporary circulation pump 23, a chemical decontamination equipment 25, and a spraying 24. It is prepared for. The temporary decontamination loop (system) 21 extracts the decontamination liquid from the lower part of the reactor pressure vessel 1 through the temporary circulation line 22 by the temporary circulation pump 23 and sends it to the chemical decontamination equipment 25.

  As shown in FIG. 3, the chemical decontamination equipment 25 includes an ozonizer 15, an organic acid (for example, organic acid mainly containing formic acid) injection device 31, a hydrogen peroxide injection device 32, a heater 33 for heating, an ultraviolet irradiation device 34, and a cation exchange. The apparatus includes a resin tower 35, and a device that smoothly performs chemical decontamination such as a mixed bed resin tower 36 in which a cation exchange resin and an anion exchange resin are mixed and packed. The chemical decontamination equipment 25 can also include other drug injection devices (not shown). When the ozonizer 15 supplies ozone (gas) to the temporary circulation line 22, a mixer 37 for mixing ozone gas may be provided. It is preferable to add ozone (gas) by the ozonizer 15 directly to the reactor pressure vessel 1 because the ozone concentration in the solution (decontamination solution) can be kept high.

  In the cation exchange resin tower 35, the cation exchange resin packed in the cation exchange resin tower 35 collects radionuclides such as cobalt ions (Co-60, Co-58) as cation components. The mixed bed resin tower 36 removes salt from the liquid to be treated after the decontamination and finally purifies it. Note that the decontamination liquid flowing in the temporary circulation line 22 can be passed through a predetermined circulation line by adjusting a switching valve (not shown), and a predetermined process is performed.

  Next, the chemical decontamination method before reactor dismantling according to this embodiment will be described. First, as shown in FIG. 2, chemical decontamination of the pre-disassembly system (system decontamination) with the primary cooling system including the reactor pressure vessel 1 and the reactor recirculation system 2 of the boiling water nuclear power plant as the decontamination target. (FIG. 1, step 1 (hereinafter referred to as “S1”)).

  This system decontamination consists of the following steps. First, the reactor pressure vessel 1 and the reactor recirculation system 2 are subjected to reductive decontamination using a reductive decontamination solution with an organic acid whose main component is formic acid. For reductive decontamination, an appropriate amount of a reducing agent such as an organic acid (an organic acid mainly containing formic acid) is added from the organic acid injection device 31 of the chemical decontamination equipment via the temporary circulation line 22 to obtain a decontamination liquid. The liquid is supplied into the reactor pressure vessel 1 through the spraying 24. Here, the reactor recirculation system pump 4 is operated to circulate the decontamination liquid through the reactor pressure vessel 1 and the reactor recirculation system 2 to increase the decontamination efficiency. The decontamination liquid is extracted from the lower part of the reactor pressure vessel 1 through the temporary circulation line 22 by the temporary circulation pump 23 and sent to the chemical decontamination equipment 25.

  By this decontamination, an oxidation film (oxide) containing a radionuclide adhering to the inside of the reactor pressure vessel 1 or the inner wall surface of the recirculation pipe 3 of the reactor recirculation system 2, for example, oxidation of iron The film and the radionuclide incorporated therein, such as Co-60 and Co-58, are dissolved in the liquid.

  Here, as the organic acid constituting the reductive decontamination solution, for example, oxalic acid having a concentration of about 1/10 of formic acid can be added in addition to formic acid. By adding oxalic acid, the iron oxide can be easily dissolved. Formic acid and oxalic acid may be mixed and injected into the temporary circulation line 22 from the organic acid injection device 31 as an organic acid. Formic acid and oxalic acid are respectively supplied from the formic acid injection device (not shown) 31 to the temporary circulation line 22. Or formic acid and oxalic acid may be injected from respective drug injection devices.

  In addition, each compounding ratio in an organic acid and the addition amount (concentration) in the decontamination liquid are determined suitably. Cobalt ions such as radionuclides and iron ions eluted from the oxide film of iron eluted in the water in the reactor pressure vessel 1 (hereinafter also referred to as “reactor water”) are chemically passed through the temporary circulation line 22. It passes through the cation exchange resin tower 35 of the decontamination equipment 25 and is separated and removed.

Next, after the elution of the iron oxide film and the radionuclide incorporated therein into the liquid is completed, the organic acid mainly composed of formic acid remaining in the solution is decomposed using hydrogen peroxide. An appropriate amount of hydrogen peroxide is added through the temporary circulation line 22 using the hydrogen peroxide injection device 32 of the chemical decontamination equipment 25 and supplied into the reactor pressure vessel 1. The organic acid (mainly formic acid) remaining in the reactor water is decomposed into carbon dioxide (carbon dioxide) and water by hydrogen peroxide. Further, the reactor recirculation pump 4 necessary for the flow in the reactor pressure vessel 1 is operated for the purpose of increasing the decomposition efficiency. Note that the organic acid can be decomposed using ozone instead of hydrogen peroxide.
When hydrogen peroxide or ozone remains in the reactor water, ultraviolet rays are irradiated from the ultraviolet irradiation device 34 of the chemical decontamination equipment 25 through the temporary circulation line 22, and the hydrogen peroxide is converted into oxygen and water. Decomposes and ozone can be decomposed into oxygen.

  Thereafter, oxidative decontamination using an oxidative decontamination solution is performed. This oxidative decontamination is performed in particular to dissolve an oxide film having a high chromium content in an inner layer such as the inner wall surface of the reactor pressure vessel 1 or the recirculation piping 3 of the reactor recirculation system 2. As the oxidizing agent constituting the oxidative decontamination solution, ozone (water), permanganic acid, permanganate (potassium permanganate) or the like can be used. However, post-treatment performed with a metal such as manganese is ozone (water). In this case, ozone (water) is preferable. Note that ozone is a self-decomposing gas and has a short life, so it is necessary to always inject the gas into water. Ozone gas is generated by the ozonizer 15 and injected into the reactor pressure vessel 1 through the air diffuser 16. The injection point is sucked into the jet pump 6 on the upper part of the annulus portion 9 by the flow in the reactor by the reactor recirculation pump 4. The installation position in the height direction is preferably close to the jet pump. Oxidation decontamination ends when the dissolution of chromium oxide (oxide film) ends. Further, the reactor recirculation pump 4 necessary for the flow in the reactor pressure vessel 1 is operated for the purpose of increasing the decontamination efficiency.

Metal ions (for example, chromium ions) remaining in the reactor water (decontamination liquid) after the oxidative decontamination is completed are transferred to the cation exchange resin tower 35 of the chemical decontamination equipment 25 via the temporary circulation line 22. Separation and removal through. Further, when ozone remains, when this reactor water (decontamination liquid) is passed through the cation exchange resin tower 35, ultraviolet rays are irradiated from the ultraviolet irradiation device 34 of the chemical decontamination equipment 25, It can decompose ozone into oxygen. The decontamination liquid treated in this way, that is, the liquid to be treated can be discharged as demineralized water to an existing liquid waste treatment system.
Thus, system decontamination of the reactor pressure vessel 1 and the recirculation system 2, that is, system decontamination of the primary cooling system is completed.

Next, a method of detoxifying (decomposing) the pressure-suppressed pool water in the reactor pressure vessel 1 after system decontamination of the primary cooling system will be described.
First, a predetermined amount of pressure suppression pool water is supplied into the reactor pressure vessel 1 (FIG. 1, S2). FIG. 4 is a schematic view schematically showing a main part of an emergency core cooling system (ECCS) system. In addition, except the structure which supplies pressure suppression pool water in the reactor pressure vessel 1, such as a heat exchanger and a condensate storage tank, abbreviate | omits. For example, as shown in FIG. 4, the pressure suppression pool water existing at the bottom in the reactor containment vessel 41 is sprayed by the spray pump 44 via the emergency core cooling pipe 43 by opening and closing the intake port 42 of the pressure suppression pool water. Is supplied into the reactor pressure vessel 1 through the core spray pipe (sparger) 13 via the supply valve 45 and the check valve 46. The amount of pressure suppression pool water supplied into the reactor pressure vessel 1 is appropriately determined.

  Further, ozone (gas) is supplied as an oxidizing agent into the reactor pressure vessel 1 to perform oxidative decomposition (FIG. 1, S3). After supplying a predetermined amount of pressure suppression pool water into the reactor pressure vessel 1, the reactor recirculation system pump 4 is operated to cause flow in the reactor pressure vessel 1 and generate ozone gas from the ozonizer 15. The ozone gas is sucked into the jet pump 6 through the air diffuser 16 and moves along the flow in the furnace. As the ozonizer 15, the ozonizer 15 of the chemical decontamination equipment 25 used for the system decontamination of the primary cooling system can be used.

Here, when the anticorrosive in the pressure suppression pool water is an organic anticorrosive, the organic anticorrosive is decomposed by ozone as described below. For example, benzotriazole (C ₆ H ₅ N ₃ ), which is a component of organic anticorrosives, is cleaved by the reaction shown in the following formula (1) to produce organic acids (for example, carboxylic acids), ammonium ions, etc. To do.
C ₆ H ₅ N ₃ + O ₃ + 11H ₂ O → 6HCOO ⁻ + 9H ⁺ + 3NH ₄ ⁺
+ O ₂ + 6e ⁻ (1)
Furthermore, carboxylic acid is decomposed into carbon dioxide and water by the reaction of the following formula (2), and ammonium ions are oxidized to nitrate ions through ammonia by the reactions of the following formulas (3) to (5).
_{HCOOH + O 3 → CO 2 +} O 2 + H 2 O (2)
NH ₄ ⁺ OH ⁻ → NH ₃ + H ₂ O (3)
NH ₃ + O ₃ → NO ₂ ⁻ + H ⁺ + H ₂ O (4)
NO ₂ ⁻ + O ₃ → NO ₃ ⁻ + O ₂ (5)

In order to confirm the reactions of the above formulas (1) to (5), a decomposition test of an organic anticorrosive with ozone was performed. The organic anticorrosive composition of the stock solution is benzotriazole _{(C 6 H 5 N 3)} 0.2wt%, 1- hydroxybenzotriazole _{(monohydrate) (C 6 H 5 N 3} O · H 2 O) 14wt% , 3-methyl-5-pyrazolone _{(C 4 H 6 N 2 O} ) 0.3wt%, is sodium hydroxide (NaOH) 4.3 wt%, adjusted it to 1500 ppm. The result of the decomposition test of the organic anticorrosive is shown in FIG. The test conditions are a supply ozone concentration (supply ozone amount / liquid amount) of 1000 g · h ⁻¹ · m ⁻³ and a temperature of 50 ° C. In FIG. 5, the pH is represented by a triangle (Δ), and the total organic carbon (TOC) concentration is represented by a circle (◯). The total organic carbon (TOC) concentration in the aqueous solution decreased gradually and decreased from 140 ppm to 8.4 ppm in 2 hours. On the other hand, the pH in the aqueous solution once decreased from 6.5 to 3.3 and then increased to 6.7. The decrease in pH in the aqueous solution is considered to be because the organic anticorrosive was cleaved by the oxidizing power of ozone to generate an organic acid as shown in the above formula (1). Further, the decrease in the total organic carbon concentration is considered to be due to the decomposition of the organic acid into carbon dioxide and water by the oxidizing power of ozone as shown in the formula (2). Nitrate ions were detected in the aqueous solution. The production of nitrate ions is considered to be because ammonium ions were oxidized to nitrate ions via ammonia as shown in formulas (3) to (5).

  The decomposition waste liquid oxidized in this way can be passed through the cation exchange resin tower 35 of the chemical decontamination equipment 25 via the temporary circulation line 22 to remove the cation component. Further, when ozone remains in the decomposition waste liquid, the ozone is decomposed into oxygen by passing through the ultraviolet irradiation device 34 of the chemical decontamination equipment 25 before passing through the cation exchange resin tower 35. it can.

Next, an appropriate amount of formic acid is injected into the reactor pressure vessel 1 through the temporary circulation line 22 from the formic acid injection device 31 of the chemical decontamination equipment 25, and the pH of the reactor water is adjusted to 3 or less (FIG. 1, S4). ). By the addition of this formic acid, the inorganic anticorrosive (chromate (chromate)) in the aqueous anticorrosive is converted from chromic acid to dichromic acid by the reaction shown in the following formula (6).
2K ₂ CrO ₄ + 4HCOOH → H ₂ Cr ₂ O ₇ + 4HCOOK + H ₂ O (6)
Here, the redox system and standard redox potential (E ⁰ ) of chromic acid and dichromic acid are shown in the following formula (7) and the following formula (8), respectively.
CrO ₄ ²⁻ + 4H ₂ O + 3e ⁻ = Cr (OH) ₃ + 5OH ⁻
E ⁰ = −0.13 V (at 25 ° C.) (7)
Cr ₂ O ₇ ²⁻ + 14H ⁺ + 6e ⁻ = 2Cr ³⁺ + 7H ₂ O
E ⁰ = + 1.33 V (at 25 ° C.) (8)
Since chromic acid has a low redox potential, hexavalent chromium is difficult to be reduced to trivalent chromium. On the other hand, since dichromic acid has a large redox potential, hexavalent chromium is easily reduced to trivalent chromium by the addition of a reducing agent in the next step. In addition, said reaction is accelerated | stimulated by adding pH to 3 or less by addition of formic acid. Further, the reactor recirculation pump 4 necessary for the flow in the reactor pressure vessel 1 is operated for the purpose of increasing the reaction efficiency.

Next, hydrogen peroxide (H ₂ O ₂ ) is supplied into the reactor pressure vessel 1 through the temporary circulation line 22 from the hydrogen peroxide injection device 32 of the chemical decontamination equipment 25 (FIG. 1, S5). Hexavalent chromium in the reactor water (treatment liquid) in the reactor pressure vessel 1 is reduced to trivalent chromium by hydrogen peroxide. The redox system of hydrogen peroxide and the standard redox potential are shown in the following formula (9).
O ₂ + 2H ⁺ + 2e ⁻ = H ₂ O ₂ E ⁰ = −0.68 V (at 25 ° C.) (9)
Since the oxidation-reduction potential of hydrogen peroxide is smaller than that of dichromic acid, hexavalent chromium is reduced to trivalent chromium by the reaction shown in the following formula (10).
H ₂ Cr ₂ O ₇ + 6HCOOH + H ₂ O ₂ → 2Cr (HCOO) ₃ + 2O ₂
+ 5H ₂ O (10)
Note that the reactor recirculation pump 4 necessary for the flow in the reactor pressure vessel 1 is operated for the purpose of increasing the reaction efficiency.

  In order to confirm the reactions of the above formulas (6) to (10), 7000 ppm of formic acid was added to an aqueous solution in which 100 ppm of potassium chromate was dissolved. Next, hydrogen peroxide was added with the temperature (40 to 80 ° C.) as a parameter to reduce hexavalent chromium to trivalent chromium. The reduction test result of hexavalent chromium is shown in FIG. The amount of hydrogen peroxide added is three times the chemical equivalent (stoichiometric value) required for the reduction of hexavalent chromium. The hexavalent chromium concentration was measured with a visible / ultraviolet spectrophotometer (manufactured by Shimadzu Corporation, model number: UV-2450). At a temperature of 50 ° C. or less, the hexavalent chromium concentration reached a target concentration of 0.5 ppm or less. However, the target concentration was not reached when the temperature was 80 ° C. This is presumably because formic acid decomposition reaction with hydrogen peroxide occurred preferentially under the condition of a temperature of 80 ° C. From the above results, it was found that 50 ° C. or less is effective for reducing hexavalent chromium to trivalent chromium with hydrogen peroxide under acidic formic acid.

Next, the processing liquid in the reactor pressure vessel 1 is passed through the temporary irradiation line 22 to the ultraviolet irradiation tower 34 of the chemical decontamination equipment 25 (FIG. 1, S6). When the treatment liquid is irradiated with ultraviolet rays, the hydrogen peroxide remaining in the treatment liquid is decomposed into water and oxygen by the reaction shown in the following formula (11).
_{H 2 O 2 = H 2 O} + 1 / 2O 2 (11)
Note that the ultraviolet irradiation conditions and the like are appropriately determined according to the concentration of the remaining hydrogen peroxide.

Next, the treatment liquid after decomposing hydrogen peroxide is passed through the cation exchange resin tower 35 of the chemical decontamination equipment 25 (FIG. 1, S7). Sodium contained in the organic anticorrosive component remaining in the treatment liquid, and chromium and potassium contained in the chromate of the inorganic anticorrosive (chromate (for example, K ₂ CrO ₄ )) are represented by the following formula (12): It is adsorbed on the cation exchange resin by the reaction of formula 14) and removed from the treatment liquid.
3R-H + HCOONa → 3R-Na + 3HCOOH (12)
_{3R-H + Cr (HCOO)} 3 → R 3 -Cr + 3HCOOH (13)
RH + HCOOK → RK + HCOOH (14)

Next, an appropriate amount of hydrogen peroxide solution is supplied into the reactor pressure vessel 1 from the hydrogen peroxide injector 34 of the chemical decontamination equipment 25 via the temporary circulation line 22 (FIG. 1, S8). Formic acid remaining in the treatment liquid is decomposed into carbon dioxide and water by the oxidizing power of hydrogen peroxide. The redox system and standard redox potential of formic acid and hydrogen peroxide are shown in the following formula (15) and the following formula (16), respectively.
CO ₂ + 2H ⁺ + 2e ⁻ = HCOOH E ⁰ = −0.12 V (at 25 ° C.) (15)
H ₂ O ₂ + 2H ⁺ + 2e ⁻ = H ₂ O E ⁰ = 1.77 V (at 25 ° C.) (16)
Hydrogen peroxide has two redox systems and acts as an oxidizing agent for formic acid. Therefore, formic acid is decomposed into carbon dioxide and water by the oxidizing power of hydrogen peroxide by the reaction shown in the following formula (17).
HCOOH + H ₂ O ₂ = CO ₂ + 2H ₂ O (17)
Note that the reactor recirculation pump 4 necessary for the flow in the reactor pressure vessel 1 is operated for the purpose of increasing the reaction efficiency.

In order to confirm the reactions of the above formulas (11) to (17), a decomposition test of formic acid with hydrogen peroxide was performed. The test results are shown in FIG. The vertical axis in FIG. 7 represents the total organic carbon (TOC) concentration ratio (arbitrary time / initial). The reaction temperature condition is 80 ° C., the initial concentration of formic acid is 2000 ppm, and the amount of hydrogen peroxide added is 2 to 3 times the chemical equivalent (stoichiometric value) required for the decomposition of formic acid in each temperature condition. is there. In FIG. 7, the one without the catalyst is added with an asterisk (*), the iron is dissolved and added at 90 mg · dm ⁻³ with a circle (◯), and SUS304 is added with a surface area of 500 cm ² · dm ⁻³ . Things are represented by triangles (Δ). Under the condition where the temperature was 80 ° C., the Fe-free formic acid aqueous solution showed almost no decrease in the total organic carbon (TOC) concentration. On the other hand, the formic acid aqueous solution in which Fe was dissolved as Fe ions as a catalyst and the formic acid aqueous solution in contact with SUS304 were decomposed to a total organic carbon (TOC) concentration of 5 ppm or less.

From the above results, it was found that the formic acid decomposition reaction with hydrogen peroxide was promoted by iron ions and / or stainless steel (dissolved in the solution) as catalysts. The amount of iron added is preferably 90 mg · dm ⁻³ , and the stainless steel (SUS304) preferably has a surface area of 500 cm ² · dm ⁻³ or more.
In addition, said iron ion and stainless steel can use the stainless steel which is the iron ion eluted from a nuclear reactor structural material, or a nuclear reactor structural material as a catalyst.

  Next, the treatment liquid in the reactor pressure vessel 1 is passed through the ultraviolet irradiation tower 34 of the chemical decontamination equipment 25 through the temporary circulation line 22 and irradiated with ultraviolet rays (FIG. 1, S9). By irradiating the treatment liquid with ultraviolet light, the hydrogen peroxide remaining in the treatment liquid is decomposed into water and oxygen by the reaction shown in the above formula (11). Ultraviolet irradiation conditions are appropriately determined according to the concentration of the remaining hydrogen peroxide.

  Next, the treatment liquid after decomposing hydrogen peroxide is passed through the mixed bed resin tower 36 in which the cation exchange resin and the anion exchange resin of the chemical decontamination apparatus 25 are mixed (FIG. 1, S10). The cation component and the anion component slightly remaining in the treatment liquid are collected in the mixed bed resin tower 36 and separated. As a result, the treatment liquid treated in this way can be discharged as demineralized water to an existing liquid waste treatment system (FIG. 1, S11).

  As described above, the chemical decontamination equipment 25 for treating the water-based anticorrosive agent in the pressure suppression pool water can use the same chemical decontamination equipment as the chemical decontamination equipment 25 used for system decontamination of the primary cooling system. In addition, when the chemicals used for the above system decontamination, such as formic acid and ozone, are the same as the chemicals for decomposing the water-based anticorrosive in the pressure-suppressed pool water, the chemical injection in the chemical decontamination equipment 25 is performed. The same device can be used for the (addition) device, such as the formic acid injection device 31, and the cost of the water-based anticorrosive treatment is greatly reduced.

According to the present embodiment, the system acid decontamination is performed by chemical decontamination using an organic acid as a reducing agent (reducing decontamination liquid) and ozone water as an oxidizing agent (oxidative decontamination liquid), After that, it is possible to mineralize and / or detoxify the water-based anticorrosive agent in the pressure suppression pool water by supplying the pressure suppression pool water to the reactor pressure vessel, so compared with the case of processing with a dedicated processing device , The treatment period of pressure suppression pool water is greatly shortened.
In addition, after the above decontamination system decontamination, the reactor pressure vessel and the reactor recirculation system are used to mineralize and / or detoxify the water-based anticorrosive agent in the pressure suppression pool water. And radioactive material is further removed from the primary cooling system, such as the reactor recirculation system. This significantly reduces the exposure of workers during the subsequent dismantling and removal of the reactor.
Furthermore, the same chemical decontamination equipment as that used for system decontamination, especially the same chemical injection equipment, should be used for mineralization and / or detoxification of water-based anticorrosives in pressure-suppressed pool water. Can do. As a result, the chemical decontamination equipment can be diverted to treat the aqueous anticorrosive agent, so that the equipment cost for the aqueous anticorrosive agent treatment is greatly reduced.

It is a flowchart which shows the procedure of the chemical decontamination method before the nuclear reactor demolition which concerns on the 1st Embodiment of this invention. It is a figure which shows typically an example of a principal part structure containing the reactor pressure vessel, the reactor recirculation system, and chemical decontamination equipment which are used for the chemical decontamination method before the nuclear reactor demolition which concerns on this embodiment. It is a figure which shows typically the principal part structure of an example of the chemical decontamination equipment used for this embodiment. It is the schematic which shows typically the principal part of an emergency core cooling system (ECCS) system | strain. It is a figure (graph) which shows the result of decomposition | disassembly of an organic anticorrosive. It is a figure (graph) which shows the reduction test result of hexavalent chromium. It is a figure (graph) which shows the result of decomposition | disassembly of formic acid with hydrogen peroxide.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 Reactor recirculation system, 3 ... Reactor recirculation system piping, 4 ... Reactor recirculation system pump, 5 ... Reactor recirculation system inlet / outlet valve, 6 ... Jet pump, 7 ... Jet Pump riser pipe, 8 ... shroud, 9 ... annulus, 10 ... upper lattice plate, 11 ... core support plate, 12 ... control rod drive mechanism (CRD), 13 ... water absorption sparger, 14 ... core spray piping (sparger), 15 DESCRIPTION OF SYMBOLS ... Ozonizer, 16 ... Diffuser, 21 ... Temporary decontamination loop (system), 22 ... Temporary circulation line, 23 ... Temporary circulation pump, 24 ... Spraying, 25 ... Chemical decontamination equipment, 31 ... Organic acid injection apparatus, 32 DESCRIPTION OF SYMBOLS ... Hydrogen peroxide injection | pouring apparatus, 33 ... Heating heater, 34 ... Ultraviolet irradiation apparatus, 35 ... Cation exchange resin tower, 36 ... Mixed bed resin tower, 37 ... Mixer, 41 ... Reactor containment vessel, 42 ... (Pressure suppression Pooh Intake of water), 43 ... emergency core cooling pipe, 44 ... spray pump, 45 ... supply valve, 46 ... check valve.

Claims (12)

A system decontamination process for performing chemical decontamination using a reducing decontamination solution and an oxidative decontamination solution supplied from a chemical decontamination facility in the reactor pressure vessel;
In the reactor pressure vessel that has been subjected to chemical decontamination, an aqueous anticorrosive-containing waste liquid supply step for supplying a waste liquid containing an aqueous anticorrosive in the pressure suppression pool, and
A chemical decontamination method before dismantling the reactor, comprising: an anticorrosive treatment step for decomposing the aqueous anticorrosive agent in the waste liquid supplied into the reactor pressure vessel.   The said anticorrosive treatment process decomposes | disassembles an aqueous | water-based anticorrosive with the reducing agent and / or oxidizing agent supplied from the chemical decontamination equipment used for the said system | strain decontamination process, The atom of Claim 1 characterized by the above-mentioned. Chemical decontamination method before furnace dismantling.   The aqueous anticorrosive in the anticorrosive treatment step is an organic anticorrosive containing one or more of an azole organic compound or an organic carboxylate, and the anticorrosive treatment step is an oxidizing agent for the chemical decontamination equipment. The chemical decontamination method before reactor demolition according to claim 2, wherein an oxidizing agent is supplied from a supply device into the reactor pressure vessel to decompose organic substances of the organic anticorrosive.   The chemical decontamination method before reactor demolition according to claim 3, wherein the oxidizing agent is ozone.   The water-based anticorrosive agent in the anticorrosive agent treatment step is an inorganic anticorrosive agent containing chromate, and the anticorrosive agent treatment step introduces an organic acid from the organic acid supply device of the chemical decontamination equipment into the reactor pressure vessel. And then reducing the hexavalent chromium in the chromate to trivalent chromium under the acidic conditions of the organic acid by supplying the reducing agent from the reducing agent supply device of the chemical decontamination equipment. The chemical decontamination method before reactor demolition according to claim 2.   6. The chemical decontamination method before reactor demolition according to claim 5, wherein the organic acid is formic acid and the reducing agent is hydrogen peroxide.   The reactor demolition according to claim 6, wherein the anticorrosive treatment step reduces hexavalent chromium to trivalent chromium with the hydrogen peroxide at a temperature of 50 ° C. or less under the acidic condition of the formic acid. Previous chemical decontamination method. Hydrogen peroxide remaining in the waste liquid after reducing hexavalent chromium to trivalent chromium in the anticorrosive treatment process is passed through the chemical decontamination equipment, and ultraviolet rays are emitted by the ultraviolet irradiation device of the chemical decontamination equipment. 8. The chemical decontamination method before reactor demolition according to claim 6 or 7 , further comprising a first hydrogen peroxide decomposition step of irradiating and decomposing into oxygen and water.   A cation component removing step of removing the cation component in the waste solution by passing the waste solution after decomposing hydrogen peroxide in the first hydrogen peroxide decomposition step through the cation exchange resin tower of the chemical decontamination equipment. The chemical decontamination method before reactor demolition according to claim 8, further comprising:   Formic acid remaining in the waste liquid after removing the cation component in the cation component removal step, hydrogen peroxide is supplied from the hydrogen peroxide supply device of the chemical decontamination equipment, and stainless steel and / or iron ions are used as a catalyst. The chemical decontamination method before reactor demolition according to claim 9, further comprising a formic acid decomposition step of decomposing into carbon dioxide and water.   Hydrogen peroxide remaining in the waste liquid after decomposing formic acid in the formic acid decomposition step is passed through the chemical decontamination equipment, and irradiated with ultraviolet rays by the ultraviolet irradiation device of the chemical decontamination equipment to form carbon dioxide. The chemical decontamination method before reactor demolition according to claim 10, further comprising a second hydrogen peroxide decomposition step that decomposes into water.   Desalting treatment in which the waste liquid after decomposing hydrogen peroxide in the second hydrogen peroxide decomposing step is passed through a mixed bed tower of a cation exchange resin and an anion exchange resin of the chemical decontamination equipment for desalting treatment. The chemical decontamination method before reactor demolition according to claim 11, further comprising a step.

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