JP2004012162A - Method for suppressing corrosion of steam generator for nuclear reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent corrosion of heat conduction tube near the clevis section of steam generators for a nuclear reactor. <P>SOLUTION: At least one of calcium compound or magnesium compound is introduced in supply water for the steam generator for a nuclear reactor so that the ion concentration is set to 0.4 to 0.8 ppb. Amine with vapor-liquid partition ratio of 0.66 or less and degree of dissociation at 6.4 or less can be introduced in the supply water for the steam generator for a nuclear reactor. <P>COPYRIGHT: (C)2004,JPO

Description

【００２３】
ただし、Ｖ：クレビス部容積（リットル）、ρ：クレビス液密度（ｋｇ／リットル）、ｔ：時間（Ｈｒ）、Ｄ_ｖｊ：：気液分配率（ｊ化合物）（−）、ｄｍ_Ｉ／ｄｔ：クレビス部への侵入液量（ｋｇ／ｈｒ）、ｄｍ_ｏ／ｄｔ：クレビス部から排出する蒸気量（ｋｇ／ｈｒ）、Ｃ_ｉ：クレビス部の濃度（ｉ成分）（モル／ｋｇ）、Ｃ_ｂｉ：バルクの濃度（ｉ成分）（モル／ｋｇ）、α_ｊｉ：ｉ成分中，ｊ化合物のモル分率（−）である。
【００２４】
以上説明したシミュレーションの結果を図８に示す。この図８は、ミストキャリーオーバ率（蒸気によりミストキャリーされた液量／蒸発した液量）が１０^−５であり、高温におけるアミンの分解率が５０％と仮定した場合における、アミン濃度とクレビス部のｐＨとの関係を示すグラフである。図８に示した全てのアミンにおいて、中性点であるｐＨ＝５．５に達することが判った。
【００２５】
【発明の効果】
本発明によれば、給水中に、カルシウムイオンやマグネシウムイオンを含むバルク液、又はアミンを含むバルク液を導入するという非常に簡単な方法で、クレビス部に存在する濃縮水中のｐＨを中性の範囲に保持することができる。これによって、伝熱管を腐食から防止することができるため、蒸気発生器の寿命の延長のみならず、安全性の確保という観点からも非常に有利な効果を得ることができる。
【図面の簡単な説明】
【図１】原子炉用蒸気発生器の全体を示す断面図である。
【図２】図１におけるＡ部を示す拡大断面図である。
【図３】実施例１で用いた模擬試験装置の一部を示す断面図である。
【図４】実施例１で得られた、イオン注入後の経過時間とクレビス部のｐＨとの関係を示すグラフである。
【図５】実施例２で得られた、注入したエタノールアミンの濃度とクレビス部のｐＨとの関係を示すグラフである。
【図６】実施例２に用いたシミュレーションを実行するためのフローチャートである。
【図７】実施例２における模擬クレビス部のｉ成分濃度を説明する概念図である。
【図８】実施例２における、各種のアミンの濃度とクレビス部のｐＨとの関係を示すグラフである。
【符号の説明】
１　原子炉用蒸気発生器
３　管板
５　入口水室
７　出口水室
９　胴
１１　包囲管
１３　逆Ｕ字形伝熱管
１５　給水
１７　支持板
２１　給水リング
２３　汽水分離ベーン
２７　取付穴
２９　クレビス部
４１　試験装置
４３　模擬クレビス部
４５　模擬伝熱管
４７　模擬支持板
４９　模擬導入管[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for preventing a heat transfer tube near a clevis portion in a steam generator for a nuclear reactor from being corroded.
[0002]
[Prior art]
The steam generator for a nuclear reactor is an outside-tube evaporation type heat exchanger, in which water inside the steam generator flows upward, and a support plate and a heat transfer tube are disposed. A mounting hole is formed in the support plate, and a heat transfer tube is inserted and held in the mounting hole. Between these heat transfer tubes and the mounting holes, there are approximately 50,000 gaps called clevis portions having a size of about 0.2 mm or less.
In the clevis part, the concentration of ionic impurities in the water in the steam generator is concentrated to about 10 ³ to 10 ⁶ times, so that the impurity concentration of the concentrated water in the clevis part is in a very high state. Further, depending on the ion balance, the concentrated water in the clevis portion may be strongly alkaline or strongly acidic.
[0003]
As described above, when the impurity concentration in the system water is high, corrosion may occur in the heat transfer tube. Therefore, conventionally, the impurity concentration in the water in the steam generator is, for example, 0.1 to 1.0 μg. / L is managed at a low level.
However, in recent years, a condensate desalination device has been installed in a water supply system for the purpose of purifying water supply to a steam generator. The condensate desalination apparatus uses a cation exchange resin, and the environment in the clevis portion is weakly acidic due to sulfate ions (SO ₄ ²⁻ ) supplied from degradation products of the cation exchange resin. Could be. Therefore, there is a demand for a method of suppressing corrosion of the heat transfer tube due to the acidic environment near the clevis portion caused by SO ₄ .
[0004]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems and to provide a method for preventing corrosion of a heat transfer tube near a clevis portion of a steam generator for a nuclear reactor.
[0005]
[Means for Solving the Problems]
The method for inhibiting corrosion of a steam generator for a nuclear reactor according to the present invention is characterized in that the water in the steam generator for a nuclear reactor contains at least one of a calcium compound and a magnesium compound so that the ion concentration becomes 0.1 to 1.0 ppb. This is a method for suppressing corrosion of a steam generator for a nuclear reactor, which comprises introducing the following.
In the steam generator for a nuclear reactor, there is a gap (clevis portion) between an outer peripheral surface of the heat transfer tube and a mounting hole of a support plate for supporting the heat transfer tube. Having In the clevis part, the impurities in the reactor steam generator are concentrated, and depending on the balance, there is a possibility that the pH may be inclined to either acidic or alkaline. May occur. According to the present invention, by introducing at least one of a calcium compound and a magnesium compound into the steam generator, SO ₄ in the concentrated water in the clevis portion is neutralized, and the pH is maintained in a range near the neutral point. Therefore, there is no possibility of causing corrosion. Therefore, it is possible to obtain not only the effect of extending the life of the steam generator for a nuclear reactor, but also a very important effect in terms of safety, that is, significantly suppressing corrosion of the heat transfer tubes. Further, this method can be carried out by simply modifying the equipment, and is therefore an advantageous invention in terms of cost.
[0006]
In one embodiment of the method for suppressing corrosion of a steam generator for a nuclear reactor according to the present invention, the concentration of the calcium ion and the magnesium ion is 0.4 to 0.8 ppb. By setting the calcium ion and magnesium ion concentrations within this concentration range, the pH in the clevis portion can be more stably maintained near the neutral point. Examples of the calcium compound that can be used here include Ca (OH) _2, and examples of the magnesium compound include Mg (OH) ₂ .
[0007]
Another aspect of the method for suppressing corrosion of a steam generator for a nuclear reactor according to the present invention is that the pH of the water in the enrichment section in the steam generator is adjusted to 5 by introducing at least one of the calcium compound and the magnesium compound. -9.
Since the hydrogen ion concentration changes depending on the temperature, the neutral point of the system water also changes depending on the operating temperature. Usually, the temperature of the water in the reactor steam generator is about 280 ° C., and the neutral point at this temperature is pH = about 5.5.
[0008]
The method for suppressing corrosion of a steam generator for a nuclear reactor according to the present invention has a gas-liquid distribution ratio of 0.66 or less and a dissociation degree (pKb) of 6.4 in water in the steam generator for a nuclear reactor. This is a method comprising introducing the following amine.
Also in this case, the pH of the clevis part-concentrated water in the steam generator can be maintained in a neutral range within the same range as that by the introduction of the calcium compound and the magnesium compound described above. The gas-liquid distribution ratio and the dissociation degree are preferably 0.6 or less and 6 or less, respectively.
[0009]
Further, in another aspect of the method for suppressing corrosion of a steam generator for a nuclear reactor according to the present invention, as the amine, ethanolamine (etanol amine), aminoguanidine (CH ₆ N ₄ ), creatine (creatine: C ₄₎ H ₉ N ₃ O ₂ ), 2,3-diaminopropionic acid (C ₃ H ₈ N ₂ O ₂ ), diethylenetriamine (diethylenetriamine: C ₄ H ₁₃ N ₃ ), ixopterin _{: C 9 H 11 N 5 O} 4), Rinachin _{(linatine: C 10 H 17 N} 3 O 5), Metofomin _{(metformin: C 4 H 11 N} 5), Morokijin (moroxydine: C H ₁₃ N ₅ O) of it is possible to use at least one. And in still another aspect of the method for suppressing corrosion of a steam generator for a nuclear reactor according to the present invention, 10 to 100 ppm, preferably 20 to 50 ppm of ethanolamine can be used as the amine.
[0010]
Furthermore, in still another aspect of the method for suppressing corrosion of a steam generator for a nuclear reactor according to the present invention, the pH of the clevis part concentrated water in the steam generator is adjusted to 5 to 9 by introducing the amine. .
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for suppressing corrosion of a steam generator for a nuclear reactor according to an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a sectional view showing a steam generator 1 for a nuclear reactor. A tube plate 3 is provided at a lower side of the steam generator 1, and an inlet water chamber 5 and an outlet water chamber 7 for the reactor coolant are formed at a lower end of the tube sheet 3. Further, on the upper side of the steam generator 1, a body 9 is provided so as to surround the circumference thereof. Inside the body 9, an surrounding tube 11 and a plurality of inverted U-shaped heat transfer tubes 13 are provided. I have. The heat transfer tube 13 is formed to be thin and thin, and is configured such that a high-temperature reactor coolant flows through the heat transfer tube 13 to heat feed water 15 which is a body side fluid and generate steam. Have been. Both lower ends of the heat transfer tubes 13 are inserted into holes in the tube sheet 3. The heat transfer tube 13 is supported laterally by a plurality of support plates 17 spaced apart in the vertical direction.
[0012]
In the reactor steam generator 1 having this configuration, the high-temperature coolant supplied from the reactor flows into the heat transfer tube 13 through the inlet water chamber 5, flows through, and loses heat due to heat exchange. After the temperature becomes low and flows to the outlet water chamber 7, it returns to the reactor. On the other hand, the feedwater 15 flowing into the steam generator 1 from the feedwater ring 21 flows downward between the surrounding pipe 11 and the body 9, flows on the tube sheet 3, and then flows upward along the heat transfer pipe 13. Flows. At this time, the feed water 15 exchanges heat with the reactor coolant, and a part thereof becomes steam. As the heated feedwater 15 flows upward, the steam separated through the support plate 17 and the steam separated vane 23 flows out.
FIG. 2 is an enlarged cross-sectional view of the portion A in FIG. As shown in FIG. 2, a plurality of mounting holes 27 are formed in the support plate 17, and the heat transfer tubes 13 are inserted through the mounting holes 27 and supported. Between the inner peripheral surface 27a of the mounting hole 27 and the outer peripheral surface 13a of the heat transfer tube 13, a narrow gap (hereinafter, referred to as a clevis portion 29) of about 0.2 mm or less is partially generated.
[0013]
[First Embodiment]
In the first embodiment, at least one of a calcium compound and a magnesium compound is introduced so that the ion concentration in the water in the steam generator becomes 0.4 to 0.8 ppb.
The introduction into the water supply can be performed by mixing an aqueous solution of a calcium compound or a magnesium compound by, for example, a method of proportionally injecting each aqueous solution into the water supply system.
Thereby, the weakly acidic concentrated water near the clevis portion 29 is neutralized to a neutral range. In this neutral range, for example, the hydrogen ion concentration at about 280 ° C. is pH = 5 to 9, and preferably pH = 5.5 to 7. The calcium ion or magnesium ion reacts with sulfate ion (SO ₄ ²⁻ ) more easily than other alkali components to form a salt. Therefore, the neutralizing effect on the sulfuric acid acidic environment is high, and the sulfuric acid acidic environment is neutralized using this. Even if calcium ions or magnesium ions are excessively added, they precipitate as hydroxides, so that the concentrated water in the clevis portion 29, which is the site to be neutralized, does not have a strong alkali state.
According to the first embodiment, sulfuric acid having a pH of about 3.5 can be changed to a pH of 6 or more at about 280 ° C. (neutral pH = 5.5).
[0014]
[Second embodiment]
In the second embodiment, an acidic or alkaline concentrated water in the vicinity of the clevis portion 29 is neutralized to a neutral range by introducing an amine into the concentrated water. It is desirable that the amine is appropriately concentrated in the clevis portion 29, has an appropriate gas-liquid distribution ratio, and has a high degree of dissociation at a high temperature.
Examples of the amines, such as ethanolamine (Ethanol Amine), aminoguanidine _{(aminoguanidine: CH 6 N 4)} , creatine _{(creatine: C 4 H 9 N} 3 O 2), 2,3 -diaminopropionic acid (2,3 _{diaminopropionic acid: C 3 H 8 N} 2 O 2), diethylenetriamine _{(diethylenetriamine: C 4 H 13 N} 3), Ikuchioputerin _{(ichthyopterine: C 9 H 11 N} 5 O 4), Rinachin _{(linatine: C 10 H 17 N} 3 O _5), Metofomin _{(metformin: C 4 H 11 N} 5), Morokijin _{(moroxydine: C 6 H 13 N} 5 O) , etc. can be suitably used.
[0015]
In the neutral range, for example, when ethanolamine is used as the amine, the hydrogen ion concentration at 280 ° C. is pH = 5 to 9, and preferably pH = 5.5 to 7. When these amines are used, they need to be added at a higher concentration than the calcium earth ions or magnesium ions that are the alkaline earth metal ions described above. Less likely to generate.
[0016]
【Example】
Hereinafter, the present invention will be described specifically with reference to examples.
[Example 1]
FIG. 3 is a cross-sectional view illustrating the simulation clevis unit 43 in the test apparatus 41 used in the first embodiment.
A simulated support plate 47 is provided on the outer periphery of the simulated heat transfer tube 45, and a sample lead-out tube 49 is provided below the simulated support plate 47. The size of the gap (simulated clevis portion 43) L formed between the outer peripheral surface 45a of the simulated heat transfer tube 45 and the inner peripheral surface 51a of the mounting hole of the simulated support plate 47 was 0.2 mm. A heater for simulating a heat medium is installed inside the simulated heat transfer tube 45. A sample of the concentrated water in the simulated clevis section 43 can be collected from the outlet pipe 49.
An aqueous solution of Ca (OH) ₂ or Mg (OH) ₂ was added to the simulated concentrated water such that the concentration of calcium ions in the aqueous solution became 0.8 ppb or the concentration of magnesium ions became 0.4 ppb. When such a test apparatus 41 is placed in a container (not shown) filled with a diluted aqueous sulfuric acid solution for test prepared by diluting sulfuric acid, the aqueous solution is placed inside the simulated clevis portion 43 as shown by an arrow P in FIG. Flowed in. Next, when heating is started by the heater, steam is generated from the simulated clevis portion 43. In a steady state, the pH value of the aqueous sample solution was about 3.6. Thereafter, a small amount of the sample aqueous solution was appropriately taken out from the outlet pipe 49.
[0017]
FIG. 4 shows the result of measuring the pH in the simulated clevis 43 into which the aqueous solution of calcium or magnesium was injected. This is a graph showing the relationship between the elapsed time after injecting the aqueous solution containing calcium ions or magnesium ions and the pH in the simulated clevis portion 43. O is a graph when an aqueous solution containing 0.8 ppb calcium ions is injected, and Δ is a graph when an aqueous solution of 0.4 ppb magnesium ions is injected.
The heat transfer tube 13 of the steam generator (actual unit) 1 for a nuclear reactor is normally maintained at about 280 ° C., while the neutral point at 280 ° C. is pH = 5.5. Therefore, it was found from FIG. 4 that the concentrated water in the clevis portion 29 became neutral about 30 hours after the injection of the aqueous solution.
[0018]
[Example 2]
In Example 2, a predicted value of a change in pH of sulfuric acid when an aqueous solution containing ethanolamine was injected into feed water was simulated using a Clevis concentration calculation model. The results are shown in the graph of FIG.
According to this graph, it is found that the pH of the concentrated water (pH = 3.5) in the simulated clevis increases by gradually injecting ethanolamine at a high concentration. Since the neutral point at about 280 ° C. is pH = 5.5, if about 30 ppm of ethanolamine is injected, the concentrated water in the clevis section 29 of the reactor steam generator (real machine) may become neutral. understood.
[0019]
The contents of the simulation will be briefly described.
FIG. 6 is a flowchart showing a simulation for estimating the pH and composition of the concentrated water in the clevis unit.
First, initial conditions such as the clevis part volume V, the gas-liquid distribution ratio (j compound) D _vj , the amount of liquid entering the clevis part, and the amount of vapor discharged from the clevis part are set.
[0020]
Next, when the impurity concentration in the clevis portion is set to an appropriate value, chemical equilibrium calculation can be performed. Then, the molar fraction and the gas-liquid distribution of each component are calculated. After that, the impurity concentration in the clevis portion is calculated. This calculation can be performed from a value obtained by subtracting the steam amount and the mist emission amount from the inflow amount. If the simulation time is longer than the set time, the calculation is completed, and the calculation results of the pH and the composition of the concentrated water in the clevis are obtained.
[0021]
Here, the calculation contents of the impurity concentration in the clevis portion described above will be briefly described.
As shown in FIG. 7, the amount of the i component contained in the concentrated water liquid injected into the simulated clevis portion 43 is represented by A, and the amount of the i component contained in the steam discharged from the simulated clevis portion 43 (the vapor of the j compound) Assuming that B is the total content of the mist and the amount of the i component contained in the mist discharged from the simulated clevis portion 43 is C, the concentration D of the i component in the simulated clevis portion 43 is D = A−B−C It can be expressed as. This is shown in the following (Equation 1). The i component is, for example, sulfate ion (SO ₄ ²⁻ ), and the j compound is, for example, sulfuric acid (H ₂ SO ₄ ).
[0022]
(Equation 1)

[0023]
Here, V: clevis part volume (liter), ρ: clevis liquid density (kg / liter), t: time (Hr), D _vj :: gas-liquid partition ratio (j compound) (−), dm _I / dt: Amount of liquid entering the clevis part (kg / hr), dm _o / dt: amount of vapor discharged from the clevis part (kg / hr), C _i : concentration of clevis part (i component) (mol / kg), C _bi : Concentration of bulk (i-component) (mol / kg), α _ji : mole fraction (-) of j-compound in i-component.
[0024]
FIG. 8 shows the result of the simulation described above. FIG. 8 shows the amine concentration and the clevis assuming that the mist carryover ratio (the amount of liquid mist carried by steam / the amount of liquid evaporated) is 10 ⁻⁵ and the decomposition ratio of amine at high temperature is 50%. 4 is a graph showing the relationship between the pH and the pH of a part. It was found that all the amines shown in FIG. 8 reached a neutral point of pH = 5.5.
[0025]
【The invention's effect】
According to the present invention, in a very simple method of introducing a bulk liquid containing calcium ions or magnesium ions, or a bulk liquid containing an amine into the feed water, the pH of the concentrated water present in the clevis portion is neutralized. Can be kept in range. Thus, the heat transfer tube can be prevented from being corroded, so that a very advantageous effect can be obtained not only from extending the life of the steam generator but also from the viewpoint of ensuring safety.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an entire steam generator for a nuclear reactor.
FIG. 2 is an enlarged sectional view showing a portion A in FIG.
FIG. 3 is a cross-sectional view showing a part of a simulation test apparatus used in Example 1.
FIG. 4 is a graph showing the relationship between the elapsed time after ion implantation and the pH of a clevis part, obtained in Example 1.
FIG. 5 is a graph showing the relationship between the concentration of ethanolamine injected and the pH of the clevis part, obtained in Example 2.
FIG. 6 is a flowchart for executing a simulation used in the second embodiment.
FIG. 7 is a conceptual diagram illustrating an i-component concentration of a simulated clevis portion in Example 2.
FIG. 8 is a graph showing the relationship between the concentration of various amines and the pH of the clevis portion in Example 2.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Nuclear steam generator 3 Tube plate 5 Inlet water chamber 7 Outlet water chamber 9 Body 11 Surrounding pipe 13 Inverted U-shaped heat transfer tube 15 Water supply 17 Support plate 21 Water supply ring 23 Steam separation vane 27 Mounting hole 29 Clevis part 41 Test equipment 43 simulated clevis part 45 simulated heat transfer tube 47 simulated support plate 49 simulated introduction tube

Claims (7)

Corrosion of a steam generator for a nuclear reactor, which comprises introducing at least one of a calcium compound and a magnesium compound so that the ion concentration becomes 0.1 to 1.0 ppb in the water inside the reactor steam generator. Suppression method. The method for suppressing corrosion of a steam generator for a nuclear reactor according to claim 1, wherein the concentration of the ions is 0.4 to 0.8 ppb. The reactor according to claim 1 or 2, wherein the pH of the concentrated water in the clevis portion in the steam generator is adjusted to 5 to 9 by introducing at least one of the calcium compound and the magnesium compound. A method for controlling corrosion of steam generators. A steam generator for a nuclear reactor, comprising introducing an amine having a gas-liquid distribution ratio of 0.66 or less and a degree of dissociation (pKb) of 6.4 or less into the water in the reactor steam generator. Corrosion control method. The amine is ethanolamine, aminoguanidine (CH ₆ N ₄ ), creatine (creatine: C ₄ H ₉ N ₃ O ₂ ), 2,3-diaminopropionic acid (2,3-diaminopropionic acid). _{: C 3 H 8 N 2 O} 2), diethylenetriamine _{(diethylenetriamine: C 4 H 13 N} 3), Ikuchioputerin _{(ichthyopterine: C 9 H 11 N} 5 O 4), Rinachin _{(linatine: C 10 H 17 N} 3 O 5) , Metofomin _{(metformin: C 4 H 11 N} 5), Morokijin _{(moroxydine: C 6 H 13 N} 5 O) of claim 4, wherein at least either The method of corrosion inhibiting nuclear steam generator according The method for suppressing corrosion of a steam generator for a nuclear reactor according to claim 4 or 5, wherein 10 to 100 ppm of ethanolamine is used as the amine. The corrosion of the steam generator for a nuclear reactor according to any one of claims 4 to 6, wherein the pH of the concentrated water in the clevis portion in the steam generator is adjusted to 5 to 9 by introducing the amine. Suppression method.

Images