JP2003035797A - Method for relaxing stress corrosion cracking of reactor structural member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the adhesion property of elements of a platinum family to a reactor structural material and restrain the occurrence and development of stress corrosion cracking(SCC) of the reactor structural members in the injection of hydrogen. SOLUTION: The molar number of manganese in reactor water is set equal to or less than the sum of the molar numbers of precious metals such as platinum, rhodium and palladium or by injecting a manganese compound together with one or more precious metals mentioned above into the reactor water. The compound is injected during the time when the temperature of the reactor water lowers from 150 deg.C to 80 deg.C. The injected precious metals and manganese adhere to the surface of the reactor structural member. The action of manganese improves the adhesion efficiency of the precious metals and secures the adhesion to the region where it was difficult to adhere previously. The ECP is significantly lowered by supplying hydrogen to the reactor water in the operation of a reactor after the adhesion. Consequently, the effect for preventing SCC is improved better than ever.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mitigating stress corrosion cracking of a structural member of a nuclear reactor, and in particular, it is preferably applied to a nuclear reactor plant equipped with a boiling water reactor (hereinafter also referred to as BWR). TECHNICAL FIELD The present invention relates to a technology for mitigating stress corrosion cracking of structural members.

[0002]

2. Description of the Related Art Although the occurrence of stress corrosion cracking (hereinafter also referred to as SCC) in a material (stainless steel or nickel-base alloy) of a BWR nuclear reactor structural member is suppressed by the improvement of the material as compared with the past. Further, in order to suppress the generation and progress of SCC, hydrogen is being injected into reactor water of a nuclear reactor.

In the BWR, hydrogen is injected into reactor water by injecting hydrogen into the water supply system under pressure to dissolve hydrogen in the water supply and introducing the water supply containing hydrogen into the reactor. Here, the recombination reaction accompanying hydrogen injection will be described.

When hydrogen is added to reactor water, the added hydrogen is recombined with oxygen and hydrogen peroxide in the downcomer portion surrounding the reactor core. This recombination reaction
Reactive radical species such as OH generated by the action of irradiation with radiation act rapidly like a catalyst.

This recombination reaction reduces the concentrations of oxygen and hydrogen peroxide in the reactor water. As the concentrations of oxygen and hydrogen peroxide decrease, the corrosion potential (hereinafter also referred to as ECP) of the nuclear reactor structural member also decreases.

The dissolved oxygen concentration in the reactor water when hydrogen is not injected is about 200 ppb. The strong radiation energy in the reactor core decomposes the reactor water to produce oxygen and hydrogen peroxide. When the hydrogen peroxide generated at this time is sampled to measure the concentration, oxygen and water are produced by thermal decomposition in the sampling pipe and catalytic decomposition on the pipe surface.

Therefore, hydrogen peroxide is hardly detected in many nuclear reactors, and the measured dissolved oxygen concentration is the sum of the concentrations of oxygen originally present in reactor water and oxygen produced by decomposition of hydrogen peroxide. Has become.

The dissolved oxygen concentration in the reactor water decreases as the hydrogen injection amount increases. When the dissolved oxygen in the reactor water decreases to about 10 ppb, the SCC development speed decreases to about 1/10. If the ECP decreases to −230 mV vs SHE (standard hydrogen electrode potential reference), which is said to be the threshold for SCC generation, with the decrease in dissolved oxygen concentration, the generation of SCC is further suppressed.

However, if the amount of hydrogen injected into the reactor water is increased in order to greatly reduce the ECP, the radioactive nitrogen 16 dissolved in the reactor water is reduced and easily migrates to the main steam system, so that the main steam system dose is reduced. An increase in the rate occurs. When the hydrogen concentration in the feed water exceeds 0.4 ppm, the main steam system dose rate begins to rise, and when the hydrogen concentration becomes high, the dose rate becomes 4-5.
Doubles.

Therefore, in order to suppress the generation of SCC, the ECP is set to -23 without increasing the main steam system dose rate.
A technique of lowering it to 0 mV vs SHE or less is desired from the viewpoint of obtaining a larger effect with a small amount of hydrogen injection.

A first conventional technique for improving the hydrogen injection effect is described in PCT / JP97 / 03502. In this technique, an oxide or hydroxide of a platinum group precious metal element is added to reactor water to impart a catalytic function to the surface of the reactor structural member.

As a second conventional technique, Japanese Patent Laid-Open No. 7-
A method of reducing the corrosion of stainless steel components or related components in a water-cooled nuclear reactor, as described in JP 198893 and JP 7-209487 A, which is a solution or suspension of a metal compound. There is a technique of increasing the corrosion resistance of stainless steel by injecting water into reactor water and mixing or adhering these metals to the oxide film of stainless steel.

The compounds containing these metals have the property of decomposing under the heat generation condition of the nuclear reactor and releasing the ions or atoms of the contained metal. When these metals are mixed or adhered to the oxide film of stainless steel, the electrochemical potential of stainless steel becomes lower than the critical potential to protect against intergranular stress corrosion cracking, and hydrogen is added to the reactor water. Examples of these metals include white metal precious metals such as palladium, Zr, and Ti.

As a third conventional technique, Japanese Patent Application No. 11-
As described in No. 177512, a photocatalytic substance which is electromotively generated by irradiation of light or radiation existing in a nuclear reactor, a metal, a metal compound or a metal or metal compound which forms an optical substance under temperature and pressure conditions in a nuclear reactor. Pt, Rh, Ru on the surface
Alternatively, there is a nuclear reactor structural member having a substance to which one or more Pd are attached.

In this example, the case of adding hydrogen to the reactor water is also described. In the first prior art, just as the increase of the anode current due to the reaction of hydrogen on the noble metal lowers the ECP of the material, in this example, the anode current is increased by the photocatalytic effect to lower the ECP of the material. I am letting you. A noble metal is added to enhance this photocatalytic effect. In this case, examples of the photocatalytic substance include those exhibiting the property of an n-type semiconductor, and MnTiO ₃ is described as one of them.

In addition, as a fourth prior art, Japanese Patent Laid-Open No. 8-220293 discloses a solution containing at least one metal or metal compound at the time of starting or restarting a nuclear power plant or before or after the restart. A method for injecting into reactor water is described. However, in this example, there is no particular metal to be implanted. In the first place, this example is intended to suppress the adhesion of radioactive substances, and merely shows the prior art regarding the corrosion behavior.

[0017]

DISCLOSURE OF THE INVENTION In order to further reduce the corrosion potential of a structural member of a nuclear reactor plant, the present inventors conducted various experiments and studied the problem to be solved. The examination results will be described in detail below.

One of the structural materials widely used as a structural member for a nuclear reactor plant is stainless steel. The ECP of stainless steel that is in contact with reactor water in a nuclear reactor has an apparent current that flows in and out of a metal surface due to the balance between the total oxidation current density and the reduction current density generated by the reduction reaction of oxygen (or hydrogen peroxide). It is defined as the potential when the density becomes zero. The total oxidation current density is determined by the sum of the current density generated by the oxidation reaction of hydrogen and the current density generated by the corrosion elution of stainless steel. (See FIG. 10 (a))

On the surface of the stainless steel which is in contact with the reactor water, the oxidation reaction of hydrogen is not very active. Therefore, the ECP of the stainless steel depends on the current density generated by the reduction reaction of oxygen and the corrosion elution of the stainless steel. It depends on the generated current density.

Therefore, the hydrogen injection into the reactor water reduces the oxygen concentration in the reactor water by utilizing the recombination reaction of hydrogen and oxygen under irradiation of radiation. As a result, the reduction current density of oxygen decreases, and the ECP of stainless steel decreases.

However, on the surface of a platinum group noble metal element such as platinum, rhodium or palladium (hereinafter referred to as a noble metal element) attached to the surface of stainless steel, hydrogen is contained in the noble metal element due to its catalytic property to the reaction of hydrogen. The exchange current density of the redox reaction is higher than that of the surface of stainless steel by several orders of magnitude. Further, since the oxidation-reduction potential of the noble metal element is nobler than the oxygen generation potential, the oxidation elution reaction of the noble metal element itself does not occur.

Therefore, since the elution of the noble metal (platinum in this example) can be ignored, the ECP on the platinum surface is determined by the redox reaction of hydrogen and oxygen. At this time, the exchange current density of oxygen generated by the reduction reaction of oxygen is smaller than the exchange current density of hydrogen generated by the oxidation reaction of hydrogen, and the overvoltage is larger than hydrogen. (Fig. 10
(See (b))

Therefore, if hydrogen is excessive, the reduction current density of oxygen will be equal to or lower than the exchange current density of hydrogen, so that the potential of the platinum surface matches the redox potential of hydrogen. The potential at this time is -500 mV vs SHE in the BWR operation state.
It is a threshold value for SCC generation because it decreases to a level −
Potentials below 230 mV vs SHE are achieved.

The above phenomenon similarly occurs when rhodium or palladium adheres to the surface of stainless steel. The above is the principle of promoting the hydrogen injection effect due to the adhesion of the noble metal element.

In the field of electrochemistry, it has long been known that platinum has a good hydrogen reaction efficiency as a hydrogen electrode. Further, it is known that rhodium forms a film having high hardness in the field of plating and is resistant to wear. When platinum or rhodium having such physical properties is applied to the surface of the structural material, the sustainability of the catalytic effect is expected. Therefore, the present inventors have determined that these two noble metal elements are added to stainless steel 304.
It was considered to be attached to the surface of steel (SUS304).

Therefore, Na ₂ [Pt (OH) ₆ ] and Na ₃ [R, which are noble metal compounds, are used as the noble metal element reagent.
h (NO ₂ ) ₆ ] was used to carry out an adhesion test of platinum and rhodium on the surface of SUS304 at 120 ° C. for 5 hours. 150 ppb each of these two precious metal compounds
SUS304 was immersed in the contained aqueous solution to deposit platinum and rhodium on the surface of SUS304.

In the first case, SUS304 was dipped in a stationary aqueous solution, and in the second case, SUS304 was dipped in a fluid aqueous solution. In both the first and second cases, after depositing platinum and rhodium on the surface of SUS304, the corrosion potential at room temperature was investigated as a function of the molar ratio of hydrogen to oxygen.

In the first case, the ECP of SUS304 having platinum and rhodium deposited on the surface is the SU without deposition treatment as the molar ratio of hydrogen to oxygen increases.
It was lower than S304. Therefore, it was confirmed that platinum and rhodium were attached to the surface of SUS304. However, it was found that the potential drop was smaller than that of the ECP of the platinum plate, and there is room for improvement in the adhesion of platinum and rhodium to SUS304.

In the second case, the test piece SUS3
An experiment was conducted by pouring an aqueous solution containing the above two kinds of noble metal compounds around 04 at a rate of 0.1 cm / s. In this second case, the ECP behavior of SUS304 with platinum and rhodium deposited on the surface was similar to that of the platinum plate. This result indicates that the supply rates of platinum and rhodium to the surface of SUS304 strongly depend on the flow state of the aqueous solution. (See Figure 11)

In the nuclear reactor, there is a region where the flow velocity of the reactor water is low due to its structure. For example, there are a thermal sleeve portion of a pipe nozzle provided in a nuclear reactor, a narrow portion formed between the core support plate and the core shroud, and between the upper lattice plate and the core shroud.

In these regions where the flow of the reactor water is stagnant, the water quality is more likely to be a severe condition for the occurrence and progress of stress corrosion cracking, as compared with the region under flow conditions, and it is necessary to lower the corrosion potential. Therefore, in the first and second conventional techniques, in the region where the flow velocity of the reactor water is low, the amount of the noble metal deposited is small, and sufficient effect and durability may not be obtained.

An object of the present invention is to ensure that an element having a catalytic ability for lowering the corrosion potential of a reactor structural member is adhered not only in the flow region of the reactor water but also in the slow flow region, and The purpose is to mitigate stress corrosion cracking of structural members.

[0033]

The above-mentioned object is to mitigate stress corrosion cracking of a structural member of a reactor for injecting at least one or more precious metal compounds of platinum, rhodium or palladium into the reactor water. A method, wherein a compound of manganese is injected into the reactor water together with the precious metal compound, and the number of moles of manganese in the reactor water is equal to or less than the sum of the number of moles of the one or more precious metals injected into the reactor water. It is achieved by a method for mitigating stress corrosion cracking of a nuclear reactor structural member.

According to the experiments conducted by the present inventors, as will be described later, the addition of manganese promotes the adhesion of the noble metal having a high catalytic effect to the surface of the reactor structural member even in the region where the flow of reactor water is slow. Further, the hydrogen peroxide in the reactor water is decomposed by manganese, and the ECP is further reduced as compared with the conventional example. On the other hand, by controlling the number of moles of manganese to be not more than a predetermined value, the amount of the precious metal adhered can be increased while suppressing the burden on the reactor water purification system.
C can be relaxed.

Further, the injection of the one or more noble metal compounds and the manganese compound is carried out when the reactor water temperature falling during the shutdown operation of the nuclear reactor is within a range of 150 to 80 ° C. . As a result, it becomes possible to uniformly attach the precious metal without unevenness in the attachment. In addition, since the permissible value for the change in reactor water conductivity is widened during the stop operation, it is easier to raise the precious metal concentration than during operation.

Further, it is characterized in that hydrogen is supplied to the reactor water after injecting the noble metal compound and the manganese compound. As a result, hydrogen acts in the state where the above-mentioned noble metal is attached, so that the certainty of promoting ECP lowering increases. If hydrogen is first injected in the state where no metal is injected, the injected hydrogen is discharged from the reactor water and scattered, so that the ECP lowering effect hardly occurs.

Further, the effective hydrogen concentration obtained by multiplying the hydrogen concentration of the feed water supplied to the reactor by the quotient of the feed water flow rate and the core flow rate, and the effective oxygen concentration at the upper part of the reactor estimated from the reduction rate of the oxygen concentration of the main steam system. Therefore, the hydrogen / oxygen molar ratio in the reactor water is 3
It is characterized in that the hydrogen is supplied as described above. As a result, hydrogen can be made to be in an excess state over oxygen, so that the ECP lowering can be ensured, and by using the effective oxygen concentration in the upper part of the reactor, E
CP reduction can be realized.

Further, the reactor structural member is made of stainless steel or a nickel base alloy. S
By applying the above-mentioned mitigation method to those structural members in which CC is a concern, the soundness and reliability of the nuclear reactor are improved.

The inventors of the present invention conducted repeated experiments to increase the amount of platinum and rhodium deposited on the reactor structural members existing in the region where the flow velocity of the reactor water was low. The region in which the velocity of the reactor water is low is a region in which the reactor water is not forcibly flowing, but a convective flow is generated. In particular,
The thermal sleeve portion of the nozzle provided in the reactor pressure vessel, the narrow portion formed between the core support plate and the core shroud, and the like correspond to that region.

In this experiment, the corrosion potentials of SUS304 having an oxide film formed on its surface in high-temperature water of 280 ° C. were immersed in an aqueous solution of platinum and rhodium, and manganese was added to platinum and rhodium at 280 ° C. Was measured in high temperature water. Platinum and rhodium are Na ₂ [Pt
(OH) ₆ ] and Na ₃ [Rh (NO ₂ ) ₆ ] were used as a mixture. Manganese compound is manganese oxalate (M
nC ₂ O ₄ ) was used.

As a compound of platinum and rhodium
The following can be applied. Platinum compound is Na
_Two[Pt (OH)₆], [Pt (NH_Three)_Four] (N
O_Three)_Two , K_Two[Pt (C_TwoO_Four)_Two], K_Two[Pt
(NO_Two)_Four], [Pt (NH_Three)_Four] (OH)_Two,
[Pt (NH_Three)_Four] CO_Three, Or [Pt (N
H_Three)_Four] (CH_ThreeCOO)_TwoOne of
Rhodium compound is Na_Three[Rh (NO_Two)₆],
Rh (NO_Three)_3,Rh (CH_ThreeCOO)_Three, Rh_Two
(CH_ThreeCOO)_Four, [Rh (NH_Three)₅(H
_TwoO)] (NO_Three)_3,Or K _Three[Rh (C
_TwoO_Four)_Three] Can be adopted.

In the experiment, two Ti capsules lined with ethylene tetrafluoride were prepared.
₂ [Pt (OH) ₆ ] and Na ₃ [Rh (NO ₂ ).
₆ ] was immersed in an aqueous solution containing SUS304, and platinum and rhodium were attached to each test piece.

Each aqueous solution contains 100 ppb of the corresponding platinum compound as a platinum element and 100 ppb of the corresponding rhodium compound as a rhodium element. At this time, the flow of the aqueous solution was stationary, and the capsule was placed in an autoclave filled with water and the temperature was adjusted to 1
Maintaining the temperature at 50 ° C., each test piece was immersed in the corresponding aqueous solution for 48 hours.

[Pt.
(NH ₃ ) ₄ ] (NO ₃ ) ₂ and Rh (NO ₃ ) ₃
MnC ₂ O ₄ was added to the aqueous solution containing so that the amount of manganese was equal to the total number of moles of the noble metal element, and the test piece of SUS304 was immersed in this aqueous solution. Therefore, in this aqueous solution, the relevant platinum compound contained 100 ppb as the platinum element, the relevant rhodium compound contained 100 ppb as the rhodium element, and the relevant manganese compound contained 75 ppb.

This aqueous solution containing manganese is in a stationary state, and the temperature and the immersion time of the test piece are the same as those of the above-mentioned aqueous solution containing only the platinum compound and the rhodium compound. Compounds of platinum and rhodium are SUS3
No. 04 test piece adhered to the surface, part of the adhered surface was F
The metal element such as e is replaced with the noble metal element, and the noble metal adheres to the surface. At this time, nitrite ions and hydroxide ions in the compound are released into the aqueous solution.

FIG. 2 is a graph of 280 ° C. of each test piece in the above test.
The ECP of the platinum plate is shown as a result of measurement as a function of the hydrogen / oxygen molar ratio when the hydrogen concentration was changed while the oxygen concentration was kept constant at 200 ppb. Under this condition, even if the hydrogen / oxygen molar ratio increases, the corrosion potential of SUS304 that has not been subjected to the adhesion treatment is
Almost unchanged from hydrogen-free state.

SUS deposited with platinum and rhodium
The ECP of 304 shows a slightly higher value than the ECP of the platinum plate. Treated with platinum and rhodium to SUS304
ECP showed almost the same change as the ECP of the platinum plate, and the molar ratio of hydrogen to oxygen was about 3
With the above, ECP is lowered.

The reason why the ECP of SUS304, which has been subjected to the adhesion treatment with a mixed aqueous solution of platinum and rhodium, shows a slightly higher value than the ECP of the platinum plate is that the adhesion amount of platinum and rhodium to SUS304 is small. SUS
304 It is difficult to sufficiently cover the surface with platinum or rhodium in a system with a small flow.

On the other hand, when SUS304 is immersed in an aqueous solution of a platinum compound and a rhodium compound to which manganese is added, the hydrogen / oxygen molar ratio decreases to the same potential as that of the platinum plate at a molar ratio of about 3. The ECP was lower. This means that platinum and rhodium are SUS30.
4 shows that it is sufficiently adhered.

In particular, by adding manganese to the noble metal element and performing the treatment, a result having a larger effect than that of the treatment with the noble metal element alone was obtained. Therefore, even in a region where there is no flow of reactor water in the nuclear reactor, sufficient attachment of the noble metal element can be achieved by adding manganese.

This can be seen from the influence of the flow of the adhered amount shown in FIG. That is, when manganese is added to the treatment, the amount of Pt and Rh deposited in the stagnant water of FIG. 1A is 2%, as compared with the case where only Pt and Rh are treated.
About 0% increased.

Since the amount of Pt and Rh deposited is originally small, it is important to improve the deposited amount by 20%. A significant improvement in adhesion is observed even under flowing conditions. If the adhesion of the reactor water to the slow flow area can be promoted, naturally the adhesion of Pt and Rh at the place where the flow is present will be sufficient and the effect will be enhanced.

It is clear from FIG. 1 that the amount of the noble metal deposited on the portion where the flow is slow is small. Figure 1
(A) is in stagnant water, and (b) is the one in which noble metal is deposited on 304 stainless steel with an oxide film in a flow of 3 cm / s.

The concentrations of Pt and Rh are each 100 ppb.
And treated for 48 h. Comparing the adhesion conditions of only Pt and Rh in FIGS. 1 (a) and 1 (b), the sum of the adhesion amounts of Pt and Rh is 11 μg / cm ² under the flowing conditions, while it is about 0. 5 μg / cm ² and 1
It is about / 20 less.

Further, Ti is a titanyl salt (TiO3 ²⁻ ).
When added to Pt and Rh in the form of
As shown in FIG. 1, the adhesion amount of Pt and Rh is Pt and Rh.
It will decrease compared to the case of processing only. Therefore, when Mn is added for the purpose of increasing the amount of Pt or Rh deposited, the effects of the coexistence of Ti cancel each other out, so it is not appropriate to use Mn and Ti for the deposition of platinum group elements at the same time.

Therefore, as described in the third prior art, for the purpose of adhering the photocatalyst, MnTiO ₃
Even if the platinum group element and the platinum group element exist in the reactor water, the promotion of the adhesion of the platinum group element by Mn, which is the object of the present invention, is hindered by the coexisting Ti and the effect cannot be obtained.

In addition to promoting the attachment of platinum and rhodium by adding manganese, it is expected that hydrogen peroxide in the reactor water will be decomposed by the attachment of manganese in the nuclear reactor. This is an effect known as MnO ₂ hydrogen peroxide decomposition catalyst.

The oxidation number of manganese in MnC ₂ O ₄ injected into the reactor water and adhering to the surface of the structural member is divalent,
Part of the tetravalent MnO ₂ is further oxidized by contact with reactor water.
To generate. Hydrogen peroxide decomposes into water and oxygen on the surface of MnO ₂ by the reaction of the following chemical formula (1). When this is seen from hydrogen peroxide, it means that hydrogen peroxide itself is simultaneously undergoing oxidation and reduction. That is, the production of water is oxidation and the production of oxygen is reduction.

H ₂ O ₂ → H ₂ O + 1/2 O ₂ (1)

It is known that the ECP of SUS304 in an oxygen environment is lower than that of a hydrogen peroxide environment,
It is considered that the ECP on the Mn-attached surface is lower than that without Mn.

Thus, by injecting the precious metal element and manganese into the reactor water, the precious metal element on the surface of the structural member (made of stainless steel or nickel-base alloy) of the reactor plant existing in the region where the flow velocity of the reactor water is small. The adhered amount of is increased. Further, the amount of the precious metal element (at least one metal of platinum, rhodium, and palladium) attached to the structural members of the nuclear reactor plant existing in the region where the flow velocity of the reactor water is high naturally increases.

As a result, according to the method for mitigating stress corrosion cracking of a reactor structural member according to the present invention, the reactor water such as the thermal sleeve portion of the piping nozzle of the nuclear reactor, the narrow portion between the core support plate and the core shroud, etc. The amount of noble metal enough to lower the potential adheres to the stagnant area, so the ECP is -500 m.
It is reduced to about VvsSHE and the generation and progress of SCC can be effectively suppressed.

In the operation of the BWR after at least one of platinum, rhodium and palladium is attached to the surface of the structural member of the reactor plant by the addition of manganese, the hydrogen injection amount required to sufficiently reduce the ECP is At least, theoretically, the dissolved oxygen concentration in the reactor water and the stoichiometric ratio should be 2: 1 (molar ratio). Usually, the dissolved oxygen concentration in the BWR reactor pressure vessel when hydrogen is not injected is about 200 ppb. At this time, the hydrogen concentration at which the stoichiometric ratio is 2 is 15 ppb.

FIG. 3 shows the result of calculation of the required amount of hydrogen in consideration of the actual BWR response. B when hydrogen is injected
The water quality in the furnace of WR and the change of hydrogen / oxygen molar ratio are shown. When the effective oxygen concentration is expressed by the molar concentration, it is given by the chemical formula (2). It is an index of the oxidizing power in the furnace expressed by converting hydrogen peroxide into oxygen produced by decomposition. On the other hand, the effective hydrogen concentration is given by the following chemical formula (3),
It is the net amount of hydrogen added to the reactor water.

[0065]   (Effective oxygen concentration) = (oxygen concentration) + 1/2 (hydrogen peroxide concentration) ... (2)

[0066]   (Effective hydrogen concentration) = (Hydrogen concentration in feed water) x (Flow rate of feed water) / (Core flow rate)                                                       ……………… (3)

FIG. 3 shows the difference in recombination efficiency at each site of the nuclear reactor. Compared to the recirculation system and the reactor bottom located downstream of the downcomer where the recombination reaction occurs, the reactor top is
Efficiency of reducing effective oxygen concentration in reactor water is low. The upper part of the reactor mentioned here is above the downcomer and below the water supply sparger.

Therefore, for a large area in the reactor,
The amount of hydrogen required to protect from SCC may be considered based on the upper part of the reactor. Therefore, the EC shown in FIG.
From the relationship between P and the hydrogen / oxygen molar ratio, it can be seen that if the molar ratio is set to 3 or more, the ECP of the noble metal-adhered stainless steel is lowered, so consider the amount of hydrogen at which the molar ratio is 3 or more even in the upper part of the reactor.

At this time, from the curve shown as the molar ratio on the basis of the effective hydrogen concentration in FIG. 3, the hydrogen concentration in the feed water was 0.28.
It can be seen that it is sufficient if it is at least ppm. Since the calculated (feed water flow rate / core flow rate) in the reactor is 0.13, it is clear that the effective hydrogen concentration should be 38 or more. At this time, a sufficient hydrogen / oxygen molar ratio is achieved in the region located below the nuclear reactor, such as the recirculation system and the bottom of the reactor.

Generally, the water quality in the upper part of the reactor cannot be measured.
A normal reactor water quality sampling line is installed in the reactor cleaning system, the recirculation system, and the drain pipe at the bottom of the reactor, and these measure the water quality below the reactor. However, advanced BW
In R (ABWR) and overseas plants, a reactor cleaning system is installed in the upper part of the reactor, and in such a reactor, the water quality of the upper part of the reactor can be measured.

Therefore, as shown in FIG. 4, the water quality in the upper part of the reactor is judged from the oxygen concentration in the main steam. From the analysis of radiolysis at the upper part of the reactor, the oxygen concentration in the main steam and the effective oxygen concentration at the upper part of the reactor were 0.5 p
It can be seen that, up to about pm, when the hydrogen injection amount increases, the concentration decreases from the concentration when hydrogen is not injected at the same rate of change.

This is a region where boiling occurs in the furnace,
Oxygen in steam and oxygen in reactor water are in a pseudo equilibrium state,
This is because oxygen in the reactor water and hydrogen peroxide in the reactor water also maintain a pseudo equilibrium concentration by the action of radiation.

In addition, the effective oxygen concentration when hydrogen is not injected is 250 to 250 in many plants, based on the knowledge obtained so far.
The value is 300 ppb, and the value of the effective oxygen concentration in the upper part of the downcomer may be determined from the rate of change in the oxygen concentration of the main steam system with the effective oxygen value in this range as a reference. Of course, it can be combined with the calculation by radiolysis, but since the oxygen concentration in the main steam can be monitored using the sampling system of the main steam system, the injection amount should be changed considering the changes in the operating state of the reactor. Can be handled on the spot.

Since the hydrogen concentration in the upper part of the reactor is a region where recombination has not occurred, it is the sum of the hydrogen injected from the feed water and the hydrogen circulated from the core, and is slightly higher than the effective hydrogen concentration. Therefore, if the hydrogen / oxygen molar ratio is calculated on the basis of the effective hydrogen concentration, the required hydrogen amount becomes larger than the calculated value based on the actual hydrogen concentration, which gives a safer result.

On the other hand, the upper limit of the amount of hydrogen is given as follows.
It has been known from the BWR operation experience that the radiation dose rate of the main steam system starts to rise when the hydrogen concentration in the feed water rises to 0.4 ppm. This is because the ratio of feed water flow rate / core flow rate is
There are many data obtained in 13% of plants. At this time, the upper limit of the effective hydrogen concentration is 52 ppb. Therefore, the effective hydrogen concentration in the reactor water may be set in the range of 38 to 52 ppb.

Considering the case where the (water supply flow rate / core flow rate) ratio is about 15%, such as BWR and ABWR having a reactor output of 1.1 million kW class constructed in recent years, the upper limit of the effective hydrogen concentration is the same. If so, the upper limit of the hydrogen concentration of feed water is 0.35 ppm.

As shown in FIG. 5, in the operation of the nuclear reactor, the core flow rate is decreased at the beginning of the operation cycle and increased at the end of the cycle. This is to increase the amount of steam in the core, harden the neutron spectrum, accumulate plutonium, and increase the excess reactivity in order to efficiently burn the fuel. Therefore, the effective hydrogen concentration changes throughout the cycle.

Therefore, when the water quality is measured at the beginning of the cycle to determine the hydrogen supply amount, the hydrogen amount becomes insufficient when the core flow rate increases at the end of the cycle. Therefore, the feedwater hydrogen concentration was calculated from the effective hydrogen concentration at the time when the response of water quality to hydrogen injection was measured using the core flowrate at the time when the core flowrate was the maximum in the operation plan of each cycle (or The hydrogen injection operation is performed using the supplied hydrogen gas flow rate).

Alternatively, the ECP of the reactor plant structural member in contact with the reactor water is measured and the ECP is -230 mV.
The hydrogen injection amount may be determined so as to be less than vsSHE. Usually, the change in ECP of the structural member in the reactor plant with respect to the hydrogen injection amount is measured in advance, and the required hydrogen concentration in the reactor water is determined based on the measured value and the analysis result. Then, the injection amount of hydrogen may be controlled according to the feed water flow rate so that the determined hydrogen concentration is obtained.

[0080]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 6 shows the configuration of an embodiment of a BWR plant to which the method of the present invention is applied.

To describe the outline of the present embodiment, in FIG. 6, the precious metal compound injection device 31 is connected to the recirculation system pipe 4, and the hydrogen injection device 24 is connected to the water supply system pipe 2. The platinum compound, the rhodium compound, and the manganese compound, which is a feature of the present invention, are injected from the noble metal compound injection device 31 into the reactor water in the recirculation pipe 4 when the output decreases, such as during a reactor shutdown operation. Next, when the plant is started, hydrogen is injected from the hydrogen injection device 24 into the water supply system pipe 2,
It is introduced into the reactor pressure vessel 3.

As described above, the amount of platinum and rhodium deposited on the surface of the reactor structural member is increased by the action of manganese, and the catalytic action promotes the reaction between the injected hydrogen and the oxygen in the reactor water, and the reactor near the structural member Dissolved oxygen in water is reduced. Due to this reduction of dissolved oxygen, the corrosion potential of the structural member is lowered and stress corrosion cracking is significantly suppressed.

The present embodiment will be described in detail below. Figure 6
As shown in, the BWR plant includes a reactor pressure vessel 3 and a turbine 6. The reactor pressure vessel 3 is installed in the reactor containment vessel 35 and has a reactor core 13 inside.
Inside the reactor pressure vessel 3, core internals such as a core shroud 36 surrounding the core 13 and a shroud support (not shown) for supporting the core shroud 36 are installed,
A plurality of fuel assemblies (not shown) are loaded in the core 13.

The reactor water supplied into the reactor core 13 is heated by the nuclear fission of the fissile material in the fuel assembly into steam. This steam is guided from the reactor pressure vessel 3 to the turbine 6 by the main steam pipe 5. The turbine 6 is driven by steam to rotate an associated generator (not shown).

The steam discharged from the turbine 6 is transferred to the condenser 7
Is condensed in and supplied to the reactor pressure vessel 3 through the water supply pipe 2 as water supply. This water supply is provided in the water supply pipe 2, the condensate pump 8, the condensate demineralizer 9, the low-pressure water supply heater 1
0, the feed water pump 12, and the high-pressure feed water heater 11 are sequentially passed to form reactor water, which is supplied to the core 13. That is,
This reactor water descends the downcomer 14 located outside the core shroud 36 by driving the recirculation pump 4a,
Recycle system piping 4 to reach the lower plenum 15 to reach the core 1
Guided within 3.

The reactor water in the reactor pressure vessel 3 is pumped by the pump 17
It is guided into the reactor water purification system pipe 17 connected to the recirculation system pipe 4 by driving c. A regenerative heat exchanger 17a, a pump 17c, a non-regenerative heat exchanger 17b, and a demineralizer 18 are installed in the reactor water purification system pipe 17. Reactor water purification system piping 1
The reactor water in 7 passes through these devices, is purified by the demineralizer 18, and is returned to the reactor pressure vessel 3 via the water supply pipe 2.

A water quality measuring device 20b for measuring the water quality of the reactor water is installed in the sampling pipe 21 connected to the reactor water purification system pipe 17. A part of the reactor water in the lower plenum 14 is guided to the reactor water purification system pipe 17 by the drain pipe 16 connected to the bottom of the reactor pressure vessel 3, and the demineralizer 1
Purified by 8.

A corrosion potential (ECP) sensor 25 for measuring the corrosion potential of the reactor water is installed in the drain pipe 16. Also, a water quality measuring device 2 for measuring the water quality of the reactor water
0a is installed in the sampling pipe 22 connected to the drain pipe 16. Water quality of the reactor water (dissolved oxygen concentration, dissolved hydrogen concentration,
The pH, conductivity, etc.) are measured online by the water quality measuring devices 20a, 20b after decompressing and cooling the reactor water.

The ECP of the structural material in contact with the reactor water flowing in the drain pipe 16 is measured by the ECP sensor 25. Therefore, both the oxygen concentration and the hydrogen peroxide concentration of the reactor water can be measured. The water quality (dissolved oxygen concentration, dissolved hydrogen concentration, pH, conductivity, etc.) of the feed water in the feed water pipe 2 is collected by the sampling pipe 19, and after decompression and cooling,
It is measured online by the water quality measuring device 20c.

The sampling pipe 23 is also provided in the main steam pipe 5.
The water quality measuring device 20d is connected via. The water quality measuring device 20d condenses the steam extracted from the sampling pipe 23, decompresses and cools the condensed water, and then measures the water quality of the condensed water online. The main steam pipe 5 is provided with a dose rate monitor 26 for measuring the radiation dose rate of the main steam system.

The water quality measuring devices 20a to 20d are operated at a room temperature of about 50 ° C. by decompressing and cooling the target water.
Water quality is measured under conditions of 1 to about 5 atm. Dissolved oxygen concentration, dissolved hydrogen concentration, p by the water quality measuring devices 20a to 20d
Measurement results such as H and conductivity are displayed on a display device (not shown) and monitored. The pH of the reactor water is 5.3-8.
In the range of 6, the conductivity of the reactor water is kept below 10 μs / cm.

Then, the noble metal compound injection device 31 is connected to the recirculation system pipe 4, and the hydrogen injection device 24 is connected to the water supply pipe between the low-pressure water supply heater 10 and the water supply pump 12. An oxygen injection device 29 is connected between the condenser 7 and the steam extractor 27 of the offgas system pipe 28. In the off-gas system pipe 28, the steam extractor 27 and the recombiner 3 are connected.
0 is set.

The stress corrosion crack mitigation method according to the present invention in the BWR plant having the above structure will be described with reference to FIG. FIG. 8 schematically shows changes in the reactor water temperature and the noble metal element concentration in the reactor water during the reactor shutdown operation during one operation cycle period. The horizontal axis shows the operating time of the BWR plant, the vertical axis shows the reactor water temperature, and the noble metal element concentration in the reactor water.

Here, one operation cycle is a period from the startup of the nuclear reactor to the shutdown of the nuclear reactor to replace the fuel assembly, and the startup operation of the nuclear reactor and the rated output operation of the nuclear reactor ( (Rated operation) and reactor shutdown operation are included.
A part of the fuel assemblies loaded in the core 13 is taken out of the core 13 and replaced with a new fuel assembly after one operation cycle has passed.

In this embodiment, the manganese compound, the platinum compound, and the rhodium compound are used immediately before the reactor water temperature reaches 150 ° C. (for example, when the reactor water temperature decreases to 170 ° C.) during the reactor shutdown operation for reducing the reactor power. From the precious metal compound injection device 31, injection into the reactor water flowing in the recirculation pipe 4 is started.

Injection of these compounds was carried out at a reactor water temperature of 80.
It will be stopped when the temperature reaches ℃. Reactor water temperature 170 to 80
The period of C is the noble metal implantation period shown in FIG. During this period, the above-mentioned three kinds of compounds are injected, and the respective compounds are introduced into the lower plenum 15 of the reactor pressure vessel 3.

FIG. 7 shows the structure of the precious metal compound injection device 31. The noble metal compound injection device 31 has a tank 40 filled with a manganese compound solution, a tank 44 filled with a platinum compound solution, and a tank 48 filled with a rhodium compound solution. Each solution tank is equipped with a spare, and one can prepare a solution for the other while it is in use, and can switch to the other when the solution runs out to perform continuous injection.

Each solution tank has a separate pipe 4
The piping 52 connected to the recirculation system piping 4 is connected by 1, 45, 49. Pure water pressurized by a pump 55 is supplied to the pipe 52 from a pure water supply system 54 of the nuclear reactor. The pipe 41 is provided with a valve 42 and a pump 43, the pipe 45 is provided with a valve 46 and a pump 47, and the pipe 49 is provided with a valve 50 and a pump 51. The above three types (Pt, Rh, Mn) are provided. The start and stop of the supply of the compound are performed by opening and closing the valves 42, 46 and 50.

The injection amounts of the manganese compound, platinum compound and rhodium compound can be adjusted individually. That is, by using the measured values of the concentrations of manganese, platinum and rhodium in the reactor water measured by the inductively coupled plasma mass spectrometer (not shown), the setting of the controller 53 shown in FIG. The opening degrees of 42, 46 and 50 are individually controlled. Or
By changing the setting of the controller 53, each pump 43, 47, 51
The discharge amount of may be controlled individually.

Thus, each compound (Pt, Rh, M
n) It is very convenient to adjust the injection amount of the solution, because the deposition rate of each noble metal element on the surface of the structural member is different and the rate of change of the concentration of each noble metal element in the reactor water is different.

In this embodiment, M is used as the manganese compound.
nC_TwoO_Four, Platinum compound as Na _Two[Pt (O
H)₆], And Na as a rhodium compound_Three[Rh
(NO_Two) ₆Was used. These compounds are soluble in reactor water
The manganese, platinum and rhodium in the reactor water.
It exists in the form of ions and complex ions. Man in reactor water
Cancer concentration is 70 ppb, platinum concentration is 100 ppb, and
And rhodium concentration to 100 ppb
The amount of the compound injected into the reactor water controls the opening of the corresponding valve.
It is controlled by

During the above-mentioned precious metal injection period, reactor water temperature 1
In the period of 50 to 80 ° C., the respective concentrations of manganese, platinum and rhodium are controlled to the above respective set concentrations. The concentrations of manganese, platinum and rhodium are measured by the inductively coupled plasma mass spectrometer described above. Based on these measurements, the corresponding valves are adjusted to control their respective concentrations in the reactor water.

The platinum and rhodium compounds and the manganese compound supplied to the reactor water adhere to the surfaces of the structural members in the reactor water. At this time, the amount of platinum and rhodium deposited on the surface of the structural member increases due to the action of manganese. And
A film in which manganese, platinum, and rhodium are mixed is formed on the surface of the structural member.

Further, the amount of platinum and rhodium deposited on the surface of the structural member existing in the region where the flow velocity of the reactor water is low also increases. Especially, in the temperature range of the reactor water of 80 to 150 ° C,
The amount of platinum and rhodium deposited on the reactor structural members increases. Instead of MnC ₂ O ₄ , Mn (HC
O ₂ ) ₂ or Mn (NO ₃ ) ₂ may be used.

An inductively coupled plasma mass spectrometer is installed in the sampling pipes 21 and 22, and the concentration of each precious metal element in the reactor water is sampled by the sampling pipes 21 and 22 at regular intervals (or as needed). The reactor water can be confirmed by measuring it with an inductively coupled plasma mass spectrometer.

Instead of an inductively coupled plasma mass spectrometer,
A flameless atomic absorption spectrometer may be used. Further, the concentration of each noble metal element in the reactor water may be monitored by the reactor water conductivity meter (or pH meter) provided with a reactor water conductivity meter (or pH meter) in the sampling pipes 21 and 22. it can. That is, a change in the reactor water conductivity (or pH) due to a change in the concentration of noble metal in the reactor water when the reactor water is not collected is monitored by a reactor water conductivity meter (or pH meter).

The amounts of platinum, rhodium and manganese in the reactor water are determined by the amount of platinum on the surface of the structural member and the desalinator 1 of the reactor water purification system.
And the removal of platinum, rhodium, and manganese ions by 8. During the noble metal injection period, the injection of each compound of platinum, rhodium and manganese from the noble metal compound injection device 31 is performed so as to compensate each removal amount by the desalting device 18. After the lapse of the noble metal injection period, the concentration of platinum, rhodium and manganese in the reactor water decreases due to the removing action of the desalting device 18.

After the treatment of depositing platinum, rhodium and manganese on the reactor structural member by injecting each compound, the operation of the reactor is stopped. During the subsequent regular inspection period, the fuel assembly is replaced and the plant is regularly inspected. After the regular inspection is completed, a new operation cycle of the BWR plant is started.

As shown in FIG. 9, when the BWR plant is started, the operation of pulling out the control rod from the core is started. After the reactor water temperature reaches the rated temperature (about 280 ° C.) and the reactor pressure reaches the set pressure (70 atm), the reactor output is increased to 100% output. After the water supply pump 12 of the water supply system 2 is driven, a valve (not shown) of the hydrogen injection device 24 is opened and hydrogen (H ₂ ) is injected into the water supply pipe 2. This water containing hydrogen is used in the reactor pressure vessel 3
Be guided inside.

At this time, the hydrogen concentration in the reactor water in the reactor pressure vessel 3 is determined by examining the ECP response according to the hydrogen injection amount so that the ECP is sufficiently lowered. The effective hydrogen concentration is preferably 38 to 52 pp in the reactor water.
b. However, since the hydrogen concentration in the reactor water changes depending on the position in the reactor pressure vessel and the operating state of the reactor, the hydrogen concentration in the feed water is 0.28 ppm to 0.35 p.
The hydrogen injection amount is controlled so as to be in the range of pm. In this embodiment, the hydrogen concentration in the reactor water is controlled to 38 ppb.

If the ECP of the SCC protection target site can be directly measured or estimated by calculation,
The hydrogen injection amount from the hydrogen injection device 24 may be controlled so that the ECP at that portion becomes −230 mVvsSHE or less.

The injected hydrogen promotes the reaction with oxygen in the reactor water to produce water by the catalytic action of platinum and rhodium attached to the surface of the structural member of the reactor plant. Thus, hydrogen contributes to the reduction of dissolved oxygen in the reactor water near the structural members of the reactor plant.

Therefore, the ECP of the structural member in the reactor pressure vessel 3 is reduced, and the SCC of the structural member is significantly suppressed. Particularly, since platinum and rhodium are also attached to the surface of the reactor structural member in contact with the region where the flow velocity of the reactor water is very low, the ECP of the structural member in contact with the region of the reactor water where the flow velocity is low is Δ in FIG. As shown by the mark, it drops to -23
It becomes 0 mVvsSHE or less, and the SCC of the structural member in contact with the reactor water region is also significantly suppressed.

Moreover, since the catalytic action of platinum and rhodium is utilized, the amount of radioactive nitrogen 16 released into the vapor does not increase, although the effect of reducing ECP is large. for that reason,
The dose rate of the steam system such as the main steam pipe 5 and the turbine 6 does not increase.

As described above, according to the embodiment of the present invention, due to the action of manganese, the adhesion efficiency of noble metals such as platinum and rhodium to the structural members of the nuclear reactor is improved, and moreover, the low adhesion, which was difficult in the past, was achieved. Adhesion was also secured in the flow velocity region. Therefore, by supplying hydrogen to the reactor water during the operation of the reactor after the adhesion, the E
CP reduction can be promoted.

Therefore, S of the BWR nuclear reactor structural member is
A surface treatment method for a nuclear reactor structural member capable of effectively suppressing the occurrence and progress of CC, and an operation method for a nuclear power plant are provided, so that the effect of preventing stress corrosion cracking of the nuclear reactor structural member in a nuclear power plant is more enhanced than ever before. Will increase.

[0117]

According to the present invention, by adding manganese to the element having the catalytic ability for lowering the corrosion potential of the reactor structural member, not only the flow region of the reactor water but also the
It can be surely deposited even in a slow flow area, and the amount of precious metal deposited can be increased more than in the past by increasing the amount of manganese deposited while keeping the burden on the reactor water purification system by controlling the number of moles of manganese to below a certain level. The SCC can be alleviated.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the effect of promoting the adhesion of a noble metal by adding manganese and inhibiting the adhesion by Ti in the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the molar ratio of hydrogen to oxygen and the corrosion potential of a test piece at high temperature, showing the effect of manganese in the present invention.

FIG. 3 is a diagram in which a difference in recombination efficiency of each part of the BWR in the furnace is calculated by radiolysis and compared.

FIG. 4 is a diagram showing the result of radiolysis calculation of the hydrogen / oxygen molar ratio in the upper part of the reactor.

FIG. 5 is a diagram showing a relationship between a core flow rate, an effective hydrogen concentration, and a feedwater hydrogen concentration in a reactor operation cycle.

FIG. 6 is a configuration diagram showing an embodiment of a BWR plant to which the present invention is applied.

FIG. 7 is a configuration diagram showing an example of an injection device of each noble metal compound in the embodiment of the present invention.

FIG. 8 is an explanatory view showing the injection timing of each noble metal compound in the embodiment of the present invention.

FIG. 9 is an explanatory diagram showing a hydrogen injection timing in the embodiment of the present invention.

FIG. 10 shows the principle that the corrosion potential of SUS304 to which platinum is attached decreases, and FIG. 10 (a) shows the corrosion potential when platinum is not attached, and FIG. 10 (b) shows the corrosion potential when platinum is attached. Explanatory drawing.

FIG. 11 is a diagram showing a response of corrosion potential of SUS304 at room temperature when platinum and rhodium were attached to the surface of SUS304 under various conditions.

[Explanation of symbols]

1 Condensate system 2 Water supply piping 3 Reactor pressure vessel 4 Recirculation system 5 Main steam piping 13 core 14 Down Kama 15 Lower Reactor Plenum 16 drain piping 17 Furnace purification system piping 18 Desalinator for furnace purification system 19 Sampling piping 20a, 20b, 20c, 20d Water quality measuring device 21, 22, 23 Sampling pipe 24 Hydrogen injection device 25 Corrosion potential (ECP) sensor 26 Dose rate monitor 31 Metal injection device 35 Reactor containment vessel 36 Core Shroud 40, 44, 48 tanks 41, 45, 49, 52 Piping 42, 46, 50 valves 43, 47, 51, 55 pumps 53 controller 54 Pure water supply system 56 Sampling pipe 57 Inductively coupled plasma mass spectrometer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoto Uetake             2-12-1 Omika-cho, Hitachi-shi, Ibaraki Prefecture             Ceremony Company Hitachi, Ltd. (72) Inventor Kazuhiko Akamine             3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Stock Association             Hitachi, Ltd. Nuclear Business Division (72) Inventor Masato Nakamura             3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Stock Association             Hitachi, Ltd. Nuclear Business Division (72) Inventor Katsumi Ohsumi             3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Stock Association             Hitachi, Ltd. Nuclear Business Division

Claims (5)

[Claims] 1. A method for mitigating stress corrosion cracking of a reactor structural member, comprising injecting at least one or more noble metal compounds of platinum, rhodium, or palladium into the reactor water, said noble metal compound. At the same time, a manganese compound is injected into the reactor water so that the number of moles of manganese in the reactor water is equal to or less than the sum of the number of moles of the one or more noble metals injected into the reactor water. Method for mitigating stress corrosion cracking of nuclear reactor structural members. 2. The injection of the one or more noble metal compounds and the manganese compound is carried out when the reactor water temperature descending during the shutdown operation of the nuclear reactor is within a range of 150 to 80 ° C. The method for mitigating stress corrosion cracking of a reactor structural member according to claim 1. 3. The method for mitigating stress corrosion cracking of a reactor structural member according to claim 1, wherein hydrogen is supplied to the reactor water after injecting the noble metal compound and the manganese compound. 4. The effective hydrogen concentration obtained by multiplying the hydrogen concentration of the feed water supplied to the reactor by the quotient of the feed water flow rate and the core flow rate, and the effective oxygen concentration at the upper part of the reactor estimated from the rate of decrease in the oxygen concentration of the main steam system. Therefore, the hydrogen is supplied so that the hydrogen / oxygen molar ratio in the reactor water is 3 or more, and the method for mitigating stress corrosion cracking of a nuclear reactor structural member according to claim 3, wherein. 5. The reactor structural member is made of stainless steel or a nickel-based alloy.
A method for mitigating stress corrosion cracking of a reactor structural member according to.