Method for promoting the discharge of harmful anions from gaps

Abstract

To promote discharge of a harmful anion infiltrated inside a gap.SOLUTION: A method for promoting discharge of harmful anions from a gap is a method for promoting discharge of harmful anions (Cl-), which are anions that have entered inside of a gap 20 communicating with a bulk space 10 and corrode a metallic material M that constitutes the gap 20 to the bulk space 10. The discharge promotion method includes a first step of dissolving a salt (Na2MoO4) containing a non-harmful anion (MoO42-) that has a migration speed lower than that of the harmful anions and does not promote corrosion of metallic materials, and a cation (Na+) that has a diffusion speed higher than that of the non-harmful anions is added to bulk water W filling the bulk space 10 and a second step of replacing bulk water W with water having a lower cation concentration than the inside of gap 20.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for promoting the discharge of harmful anions from gaps. [Background technology]

[0002] Plants such as nuclear power plants and thermal power plants are equipped with condensers that condense turbine exhaust gas, which has completed its expansion work in the steam turbine, with cooling water to produce condensed water, and send the condensed water to the steam generator (see, for example, Patent Document 1). Such condensers are equipped with a large number of condensation tubes through which seawater flows as cooling water.

[0003] Furthermore, in such plants, a large number of fastening parts such as bolts and nuts made of corrosion-resistant alloys such as stainless steel are provided. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-231809 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is a risk that seawater may flow into the plant due to damage to the condenser tubes, etc. In this case, harmful anions such as chloride ions contained in the seawater may penetrate into the gaps in the fastening parts, and as the temperature rises, the harmful anions may corrode the corrosion-resistant alloy.

[0006] During restoration work after seawater has infiltrated into a plant, harmful anions must be removed from gaps. A conventional method for this purpose is to fill the bulk space communicating with the gap with high-purity water, thereby using the concentration gradient of harmful anions inside and outside the gap as a driving force to remove the harmful anions from the gap. However, because the path connecting the inside and outside of the gap is narrow, there is a natural limit to how quickly the harmful anions can be removed. [Means for solving the problem]

[0007] A method for promoting the discharge of harmful anions from gaps to solve the above-mentioned problems is a method for promoting the discharge of harmful anions that have penetrated into gaps communicating with a bulk space and corrode the metallic materials that make up the gaps into the bulk space, and includes a first step of adding and dissolving a salt containing non-harmful anions that have a slower migration speed than the harmful anions and do not promote corrosion of the metallic materials, and cations that have a faster diffusion rate than the non-harmful anions, to bulk water filling the bulk space, and a second step of replacing the bulk water with water having a lower concentration of the cations than the interior of the gaps.

[0008] The movement of substances in a static solution occurs by two mechanisms: diffusion and migration. Diffusion is a mechanism by which substances move using the concentration gradient in a solution as a driving force. Migration is a mechanism by which charged substances move using the potential gradient in a solution as a driving force.

[0009] Therefore, ions, which are substances with electric charge, move (diffuse) in a solution using the concentration gradient as a driving force, and also move (migrate) using the potential gradient as a driving force. According to the above method, in the first step, a salt containing non-harmful anions and cations is added to bulk water filling the bulk space. As a result, the salt dissolves in the bulk water, and the concentrations of the non-harmful anions and cations in the bulk water become higher than the concentrations of the non-harmful anions and cations inside the gaps. Therefore, the non-harmful anions and cations move (diffuse) into the gaps, driven by the concentration gradient between the inside and outside of the gaps. Here, the larger the concentration gradient, the more the movement of the non-harmful anions and cations into the gaps is promoted.

[0010] Subsequently, in the second step, the bulk water is replaced with water having a lower concentration of the cations than the gap. As a result, the concentration of the cations in the gap becomes higher than the concentration of the cations in the bulk water. Here, the diffusion rate of the cations is higher than the diffusion rate of the non-harmful anions. Therefore, the cations in the gap move (diffuse) into the bulk water first, driven by the concentration gradient between the inside and outside of the gap. Furthermore, the harmful anions and non-harmful anions that have penetrated into the gap move (diffuse) into the bulk water, driven by the concentration gradient between the inside and outside of the gap. At this time, a potential gradient is generated as the cations move (diffuse) into the bulk water. The harmful anions and non-harmful anions that have penetrated into the gap move (migrate) into the bulk water, driven by the potential gradient, in order to maintain electrical neutrality.

[0011] Here, harmful anions have a higher migration speed than non-harmful anions, and therefore, harmful anions are more likely to migrate (migrate) into bulk water than non-harmful anions. On the other hand, non-harmful anions tend to remain inside the gaps. However, since non-harmful anions do not promote corrosion of the metallic materials that make up the gaps, the remaining non-harmful anions do not pose a problem.

[0012] Therefore, it is possible to promote the discharge of harmful anions that have entered the gaps. In the method for promoting the discharge of harmful anions from gaps, it is preferable that the first step and the second step are alternately and repeatedly performed.

[0013] According to this method, it is possible to accelerate the discharge of harmful anions that have infiltrated into the gaps, thereby further promoting the discharge of harmful anions that have infiltrated into the gaps.

[0014] In the method for promoting the discharge of harmful anions from gaps, the bulk water is preferably replaced with pure water in the second step. According to this method, the second step maximizes the concentration gradient between the inside and outside of the gaps, allowing the cations that have infiltrated into the gaps to migrate (diffuse) efficiently into the bulk water. This makes it easier for the cations to extract harmful anions into the bulk water. This further accelerates the removal of harmful anions that have infiltrated into the gaps.

[0015] In the method for promoting the discharge of harmful anions from gaps, it is preferable that the harmful anions are at least one of chloride ions and sulfate ions, the non-harmful anions are at least one of molybdate ions, tungstate ions, and phosphate ions, and the cations are at least one of sodium ions and potassium ions.

[0016] According to this method, it is possible to satisfy the relationship that the salt contains a non-harmful anion that has a slower migration speed than the harmful anion and does not promote corrosion of the metal-based material, and a cation that has a large diffusion coefficient, i.e., a high diffusion rate, and is also highly soluble.

[0017] In the above-mentioned method for promoting the discharge of harmful anions from gaps, it is preferable that the gaps constitute equipment in a nuclear power plant, the metallic material is stainless steel, and the non-harmful anions are molybdate ions.

[0018] Stainless steel containing molybdenum is widely used in nuclear power plant equipment. According to this method, molybdate ions containing molybdenum, which are used in nuclear power plant facilities, are used as non-harmful anions, so there is no risk of adverse effects on the facilities. [Effects of the Invention]

[0019] According to the present invention, it is possible to promote the discharge of harmful anions that have entered the gaps. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a graph showing the relationship between the migration time of various anions and the equivalent ion conductivity. [Figure 2] 2(a) to 2(c) are schematic diagrams sequentially showing the transition of the distribution of anions and cations in the bulk space and gaps in the first step of one embodiment. [Figure 3] 3(a) to 3(d) are schematic diagrams sequentially showing the transition of the distribution of anions and cations in the bulk space and gaps in the second step of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, one embodiment of a method for promoting the discharge of harmful anions from gaps will be described with reference to FIGS. The gap 20 of this embodiment is formed between a bolt and a nut that constitute equipment in a nuclear power plant, for example.

[0022] In this embodiment, the above-mentioned discharge promotion method is embodied as a method for promoting the discharge of chloride ions, which are anions that have penetrated into the gap 20 communicating with the bulk space 10 and corrode the stainless steel that constitutes the gap 20, into the bulk space 10.

[0023] The discharge promoting method includes a first step and a second step. In the first step, sodium molybdate is added to and dissolved in bulk water W that fills the bulk space 10. Sodium molybdate is a salt containing molybdate ions, which have a slower migration speed than chloride ions and do not promote corrosion of stainless steel, and sodium ions, which have a faster diffusion speed than molybdate ions.

[0024] In the second step, the bulk water W is replaced with water having a lower concentration of sodium ions than the inside of the gap 20. It is preferable that the first step and the second step are alternately and repeatedly performed.

[0025] In the second step, it is preferable to replace the bulk water W with pure water. The chloride ion in this embodiment corresponds to the harmful anion according to the present invention, the molybdate ion in this embodiment corresponds to the non-harmful anion according to the present invention, and the sodium ion in this embodiment corresponds to the cation according to the present invention.

[0026] Figure 1 shows the relationship between migration time and ionic equivalent conductance for various anions (WR Jones, P. Jandik, "Controlled changes of selectivity in the separation of ions by capillary electrophoresis", Journal of Chromatography, 546, (1991), pp. 445-458).

[0027] 1, the migration time of molybdate ions is longer than that of chloride ions, that is, the migration speed of molybdate ions is slower than that of chloride ions.

[0028] The anions representing the numbers 1 to 24 in FIG. 1 are as follows: 1: Thiosulfate ion, 2: Bromide ion, 3: Chloride ion, 4: Sulfate ion, 5: Nitrite ion, 6: Nitrate ion, 7: Oxalate ion, 8: Molybdate ion, 9: Azide ion, 10: Tungstate ion, 11: Chlorate ion, 12: Citrate ion, 13: Fluoride ion, 14: Formate ion, 15: Phosphate ion, 16: Chlorite ion, 17: Phthalate ion, 18: Carbonate ion, 19: Acetate ion, 20: Ethanesulfonate ion, 21: Propionate ion, 22: Propanesulfonate ion, 23: Butyrate ion, 24: Benzoate ion.

[0029] Table 1 shows the ion species i and charge number z i , equivalent ionic conductivity λ in infinitely dilute solution at 25 °C i ∞ (Source: Chemistry Handbook, Basics II, Revised 2nd Edition, Edited by the Chemical Society of Japan, Published in 1975), and the diffusion coefficient D i ∞ The relationship is shown below.

[0030] [Table 1]

[0031] Diffusion coefficient D i ∞ can be calculated from the Nernst-Einstein equation (Equation 1).

[0032]

number

[0033] In (Equation 1), the gas constant R is 8.31 (J / mol·K), the temperature T is 298 (K), and the Faraday constant F is 96,500 (C / mol). As shown in Table 1, the diffusion coefficient of sodium ions is 1.332 × 10 -5 (cm 2 / s), and the diffusion coefficient of the molybdate ion is 9.906×10 -6 (cm 2 / s), that is, the diffusion rate of sodium ions is greater than that of molybdate ions.

[0034] Next, the operation of this embodiment will be described. As shown in FIG. 2(a), chloride ions (Cl - ) and metal ions (M 2+ ) is present. Here, we will explain using divalent metal ions as an example.

[0035] First, sodium molybdate (Na2MoO4), which is a salt containing molybdate ions and sodium ions, is added to the bulk water W that fills the bulk space 10. As a result, as shown in FIG. 2(b), sodium molybdate is dissolved in the bulk water W, and the molybdate ions (MoO4 2- ) and sodium ions (Na + ) becomes higher than the concentrations of molybdate ions and sodium ions inside the gap 20.

[0036] 2(c), the molybdate ions and sodium ions move (diffuse) into the gap 20, driven by the concentration gradient between the inside and outside of the gap 20 (first step). Here, the larger the concentration gradient, the more the movement of the molybdate ions and sodium ions into the gap 20 is promoted.

[0037] 3(a), the bulk water W is replaced with water having a lower concentration of sodium ions than the inside of the gap 20. In this embodiment, the bulk water W is replaced with pure water. As a result, the concentration of sodium ions inside the gap 20 becomes higher than the concentration of sodium ions in the bulk water W. Here, as described above, the diffusion rate of sodium ions is higher than the diffusion rate of molybdate ions.

[0038] Therefore, as shown in FIG. 3(b), the sodium ions inside the gap 20 move (diffuse) into the bulk water W first, driven by the concentration gradient inside and outside the gap 20.

[0039] At this time, as shown in FIG. 3(c), chloride ions (Cl - ) and molybdate ions (MoO4 2- ) move (diffuse) into the bulk water W, driven by the concentration gradient inside and outside the gap 20. At this time, a potential gradient is generated as the sodium ions move into the bulk water W. The chloride ions and molybdate ions that have penetrated into the gap 20 move (migrate) into the bulk water W, driven by the potential gradient, in order to maintain electrical neutrality.

[0040] As described above, chloride ions have a higher migration speed than molybdate ions, and therefore chloride ions are more likely to migrate (migrate) into the bulk water W than molybdate ions.

[0041] On the other hand, molybdate ions tend to remain inside the gap 20. However, molybdate ions do not promote corrosion of the stainless steel that constitutes the gap 20. More specifically, molybdate ions have the effect of inhibiting corrosion of stainless steel. Therefore, the presence of residual molybdate ions does not pose a problem.

[0042] Next, as shown in FIG. 3(d), the bulk water W is replaced with pure water (this is the second step). The first step and the second step are alternately and repeatedly performed.

[0043] Next, the effects of this embodiment will be described. (1) The method for promoting the discharge of harmful anions from gaps includes the first step and the second step.

[0044] According to this method, the above-mentioned effect is achieved, and therefore, the discharge of chloride ions that have entered the gap 20 can be promoted. (2) The first step and the second step are alternately and repeatedly performed.

[0045] According to this method, it is possible to accelerate the discharge of chloride ions that have penetrated into the gap 20. This makes it possible to further promote the discharge of chloride ions that have penetrated into the gap 20.

[0046] (3) In the second step, the bulk water W is replaced with pure water. According to this method, the second step maximizes the concentration gradient inside and outside the gap 20, so that the sodium ions that have penetrated into the gap 20 can be efficiently diffused into the bulk water W. This makes it easier for the chloride ions to be drawn out into the bulk water W by the sodium ions. This further promotes the discharge of the chloride ions that have penetrated into the gap 20.

[0047] (4) The gap 20 constitutes a facility of a nuclear power plant, the metallic material is stainless steel, and the non-harmful anion is a molybdate ion. Stainless steel containing molybdenum is widely used in nuclear power plant equipment.

[0048] According to this method, molybdate ions containing molybdenum, which are used in nuclear power plant facilities, are used as non-harmful anions, so there is no risk of adverse effects on the facilities. <Modification> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0049] The gaps according to the present invention are not limited to those formed between bolts and nuts that constitute equipment in nuclear power plants. The present invention can also be applied to gaps that constitute equipment in thermal power plants, and can also be applied to gaps that constitute equipment other than power plants.

[0050] The metallic material that constitutes the gap according to the present invention is not limited to stainless steel, and the present invention can also be applied to gaps that are constituted by other metallic materials. The non-toxic anion according to the present invention is not limited to molybdate ion. Tungstate ion or phosphate ion can be used instead of or in addition to molybdate ion. These anions can provide the same effects as molybdate ion. Furthermore, the cation according to the present invention is not limited to sodium ion, and potassium ion can also be used. Potassium ion can provide the same effects as sodium ion.

[0051] The non-harmful anions constituting the salts of the present invention are sufficient as long as they have a slower migration speed than the harmful anions and do not promote corrosion of the metal-based material. The cations constituting the salts of the present invention are preferably those with a large diffusion coefficient, i.e., a high diffusion rate.

[0052] Harmful anions are not limited to chloride ions. The above embodiment is also effective against sulfate ions, which corrode metal materials. The water used for replacement in the second step is not limited to pure water, but may be water with a lower cation concentration than the inside of the gap after the first step.

[0053] It is preferable to alternately repeat the first and second steps in order to accelerate the discharge of harmful anions that have penetrated into the gap. However, the present invention requires that the first and second steps be performed at least once each. However, effect (1) of the above embodiment can be achieved by performing the first and second steps once each. [Explanation of symbols]

[0054] 10...Bulk space 20...Gap W: Bulk water

Claims

1. 1. A method for promoting the discharge of harmful anions into a bulk space, the harmful anions having infiltrated into a gap communicating with the bulk space and corroding a metallic material constituting the gap, comprising: a first step of adding and dissolving a salt containing a non-harmful anion having a migration speed slower than that of the harmful anion and not promoting corrosion of the metal-based material, and a cation having a diffusion speed faster than that of the non-harmful anion, into bulk water filling the bulk space; and a second step of replacing the bulk water with water having a lower concentration of the cations than the inside of the gap. A method for promoting the discharge of harmful anions from gaps.

2. The first step and the second step are alternately and repeatedly performed. The method for promoting the discharge of harmful anions from gaps according to claim 1.

3. In the second step, the bulk water is replaced with pure water. The method for promoting the discharge of harmful anions from gaps according to claim 1 or 2.

4. the harmful anion is at least one of a chloride ion and a sulfate ion; the non-harmful anion is at least one of a molybdate ion, a tungstate ion, and a phosphate ion; The cation is at least one of a sodium ion and a potassium ion. The method for promoting discharge of harmful anions from gaps according to any one of claims 1 to 3.

5. The gap constitutes a facility of a nuclear power plant, the metallic material is stainless steel, The non-toxic anion is a molybdate ion. The method for promoting the discharge of harmful anions from gaps according to claim 4.

Images