WO2001057879A1

WO2001057879A1 - Method for mitigating stress corrosion cracking of structural member of atomic reactor plant

Info

Publication number: WO2001057879A1
Application number: PCT/JP2000/000563
Authority: WO
Inventors: Yoichi Wada; Masahiko Tachibana; Naohito Uetake
Original assignee: Hitachi, Ltd.
Priority date: 2000-02-02
Filing date: 2000-02-02
Publication date: 2001-08-09
Also published as: JP3941503B2; TW498348B

Abstract

A method for mitigating stress corrosion cracking of a structural member of an atomic reactor plant which comprises injecting a platinum compound, a rhodium compound and a palladium compound into the reactor water in a pressure vessel of an atomic reactor, in a manner such that palladium is present in the reactor water in a less mole number than those of platinum and rhodium. The injection of the above compounds is preferably carried out during the lowering of the temperature of the reactor water from 150°C to 80°C upon the shutdown of a BWR plant. The platinum, rhodium and palladium in the form of ions in the reactor water are deposited on the surface of a structural member of an atomic reactor plant, thereby to significantly reduce the ECP of the structural member.

Description

Specification

Method of mitigating stress corrosion cracking of reactor blunt structural members

The present invention relates to a method for alleviating stress corrosion cracking of a structural member of a nuclear reactor plant, and more particularly to a nuclear reactor plant suitable for application to a nuclear reactor plant having a boiling water reactor (hereinafter, referred to as BWR). It relates to a method for mitigating stress corrosion cracking of structural members. Background art

The occurrence of stress corrosion cracking (hereinafter referred to as SCC) in BWR reactor structural materials (stainless steel and nickel-based alloys, etc.) has been suppressed more than before due to improvements in materials. In addition, hydrogen injection is being performed to suppress the generation and progress of SCC.

Hydrogen injection is performed in BWR by injecting hydrogen into the water supply system under pressure by injecting hydrogen into the water supply system, and guiding the water containing hydrogen to the reactor. Here, the recombination reaction accompanying hydrogen implantation will be described. When hydrogen is added to the reactor water in the reactor, the hydrogen recombines with oxygen and hydrogen peroxide in the downforce surrounding the core in the reactor. This recombination reaction proceeds rapidly when reactive radical species such as OH generated by the action of radiation act like a catalyst. Due to this recombination reaction, the concentrations of oxygen and hydrogen peroxide in the reactor water decrease. As the concentration of oxygen and hydrogen peroxide decreases, the corrosion potential (E CP) of reactor structural materials also decreases.

As the amount of hydrogen injected increases, the concentration of dissolved oxygen in the reactor water decreases. Underwater When the dissolved oxygen of the SCC decreases to about 10 ppb, the progress rate of SCC decreases to about 110. If the ECP drops below -230 mVvs SHE (standard hydrogen electrode potential reference) with a decrease in dissolved oxygen concentration, the occurrence of SCC is further suppressed. However, if the amount of hydrogen injected into the reactor water is increased to greatly reduce the ECP, the radioactive nitrogen 16 dissolved in the reactor water is reduced and easily transferred to the main steam system. An increase occurs. When the hydrogen concentration in the feedwater exceeds 0.4 ppm, the dose rate of the main steam system starts to increase, and when the hydrogen concentration increases, the dose rate reaches 4 to 5 times. Therefore, in order to suppress the generation of SCC, a technology for lowering the ECP to less than 13 OmVvsS HE without increasing the main steam dose rate is desired from the viewpoint of increasing the hydrogen injection effect.

The first prior art relating to the improvement of the hydrogen implantation effect is described in Japanese Patent No. 2818943 and Japanese Patent Application Laid-Open No. 10-319181. In this technology, hydrogen is added to the reactor water, and a platinum group noble metal element for accelerating the reduction of the oxidizing agent by the hydrogen is added to the reactor water to form a catalyst layer on the surface of the structural material.

A second prior art for improving the hydrogen implantation effect is described in PCTZJ97 / 0352. In this technology, an oxide or hydroxide of a platinum group noble metal is added to reactor water to impart a catalytic function to the surface of a structural material. Disclosure of the invention

An object of the present invention is to provide a method for alleviating stress corrosion cracking of a reactor blunt structural member capable of reducing the corrosion potential of a reactor plant structural member existing in a region where the flow rate of reactor water is low.

The feature of the present invention that achieves the above object is a noble metal element of platinum and rhodium. Injecting a compound of at least one of the noble metal elements and a compound of palladium into the reactor water of the reactor, wherein the number of moles of palladium in the reactor water is such that The noble metal element compound and the palladium compound are to be injected into the reactor water so as to be smaller than the number of moles. By injecting such a compound of the noble metal element and palladium into the reactor water, the noble metal element (platinum and rhodium) on the surface of the structural member of the reactor plant existing in the region where the flow rate of the reactor water is low is reduced. At least one metal) is deposited and palladium is also deposited. As a result, the ECP of the structural member is reduced, and the occurrence and progress of SCC in the reactor plant structural member existing in the region where the flow rate of the reactor water is low are suppressed. The region where the flow velocity of the reactor water is low is the region where the reactor water is not forcibly flowing and a convective flow is generated. Specifically, the thermal sleeve portion of the nozzle provided in the reactor pressure vessel, and a narrow portion formed between the core support plate and the core shell correspond to the region. BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 is an explanatory diagram showing the principle of the reduction of the corrosion potential of SUS 304 with platinum, and Fig. 1 (a) is an explanatory diagram showing the corrosion potential of SUS 304 without platinum. Fig. 1 (b) is an explanatory diagram showing the corrosion potential of SUS 304 with platinum, and Fig. 2 shows the corrosion potential of SUS 304 at room temperature when platinum and rhodium are deposited on the surface of SUS 304 under various conditions. Figure 3 shows the relationship between the deposition rate of palladium and temperature, and Figure 4 shows the relationship between the molar ratio of hydrogen to oxygen and the corrosion potential of the specimen at room temperature. FIG. 5 is a BWR to which a method of alleviating stress corrosion cracking of a reactor plant structural member according to a first embodiment of the present invention is applied. FIG. 6 is a detailed configuration diagram of the noble metal compound injection apparatus shown in FIG. 5, FIG. 7 is an explanatory view showing injection timings of platinum, rhodium, and palladium compounds in the first embodiment. FIG. 8 is an explanatory view showing a hydrogen injection time in the first embodiment, and FIG. 9 is a diagram showing platinum, rhodium and palladium in the method for mitigating stress corrosion cracking of a reactor plant structural member according to the second embodiment of the present invention. Explanatory diagram showing the injection timing of each compound in the dome.Fig. 10 is a configuration diagram of a BWR plant to which the method of alleviating stress corrosion cracking of a reactor blunt structural member according to a third embodiment of the present invention is applied. Fig. 11 is a system diagram of the primary cooling system of the BWR to which the reactor operating method of the third embodiment is applied, and Fig. 12 is a description showing the injection timing of hydrogen and Al-Li solution in the third embodiment. FIG. BEST MODE FOR CARRYING OUT THE INVENTION

The inventors conducted various studies in order to further reduce the corrosion potential of a reactor blunt structural member. The results of the study will be described in detail below. As shown in Fig. 1 (a), the ECP of stainless steel that is in contact with reactor water, which is one of the structural materials used as structural members for a reactor plant, shows the total oxidation current density and oxygen (or excess). It is defined as the potential at which the density of the current flowing into and out of the metal surface becomes zero, apparently in proportion to the reduction current density generated by the reduction reaction of (hydrogen oxide). 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 corrosion elution of stainless steel.

On the surface of stainless steel in contact with reactor water, the oxidation reaction of hydrogen is not very active, so the ECP of stainless steel is almost equal to the current density generated by the oxygen reduction reaction and the current generated by corrosion elution of stainless steel. Determined by density. Therefore, hydrogen injection into the reactor water is The oxygen concentration in the reactor water is reduced by utilizing the recombination reaction of oxygen. As a result, the ECP of stainless steel is reduced due to the reduced oxygen reduction current density.

On the surface of stainless steel in contact with reactor water, the oxidation reaction of hydrogen is not very active, so the ECP of stainless steel is almost equal to the current density generated by the oxygen reduction reaction and the current generated by corrosion elution of stainless steel. Determined by density. Therefore, 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. As a result, the ECP of stainless steel decreases due to the reduction in the reduction current density of oxygen.

However, on the surface of platinum group noble metal elements (hereinafter referred to as noble metal elements) such as platinum, rhodium, and palladium attached to the surface of stainless steel, the catalytic activity of the noble metal element on the reaction of hydrogen causes The exchange current density of the redox reaction is orders of magnitude higher than that of stainless steel surfaces. Also, since the oxidation-reduction potential of the noble metal element is more noble than the oxygen generation potential, no oxidation elution reaction of the noble metal group element itself occurs. Therefore, as shown in Fig. 1 (b), elution of the noble metal (platinum in this example) is negligible, and its 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 lower than the exchange current density of hydrogen generated by the oxidation reaction of hydrogen, and the overvoltage is higher than that of hydrogen. Therefore, if the amount of hydrogen is excessive, the reduction current density of oxygen becomes lower than the exchange current density of hydrogen, and the potential of the platinum surface matches the oxidation-reduction potential of hydrogen. Since the potential at this time drops to about -500 mV vs SHE in the BWR operation state, a potential equal to or lower than the threshold value of SCC generation of 230 mV vs SHE is achieved. The above phenomenon is caused by This also occurs when rhodium or palladium adheres to the surface. The above is the principle of promoting the hydrogen injection effect by the attachment of the noble metal element.

Platinum has long been known as a hydrogen electrode in the field of electrochemistry for its high hydrogen reaction efficiency. Rhodium is known to form a film with high hardness in the field of plating and is resistant to abrasion. Therefore, when applied to the surface of structural materials, it is expected that the catalytic effect will be persistent. Therefore, the inventors initially considered attaching these two noble metal elements to the surface of stainless 304 steel (SUS304).

Therefore, using the noble metal element reagents Na ₂ [N (0H) ₆ ] and Na ₃ [R h (N0 ₂ ) ₆ ], which are noble metal compounds, we performed an adhesion test of platinum and rhodium on the surface of SUS304. The test was performed at 120 ° C for 5 hours. SUS304 was immersed in an aqueous solution containing 150 ppb of each of these two noble metal compounds, and platinum and rhodium were adhered to the surface of SUS304. In the first case, the SUS304 was immersed in the aqueous solution in a stationary state. In the second case, the SUS304 was immersed in the aqueous solution in a flowing state. After deposition of 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.

As shown in Fig. 2, in the first case, the ECP of SUS304 with platinum and rhodium adhered to the surface is lower than that of SUS304 without adhesion treatment, as the molar ratio of hydrogen to oxygen increases. . Therefore, it was confirmed that platinum and rhodium were attached to the surface of SUS304. However, the decrease in potential was small compared to the ECP of the platinum plate, indicating that there is room for improvement in the adhesion of platinum and rhodium to SUS304.

In the second case, the above two types of precious metal were placed around the test piece SUS304. The experiment was performed by flowing an aqueous solution containing a metal compound at a speed of 0.1 cmZ s. In this second case, the behavior of ECP of SUS304 with platinum and rhodium attached to the surface was similar to that of the platinum plate. This result is due to the fact that the supply rates of platinum and rhodium to the surface of SUS304 are increased by the flow of the aqueous solution, and the decomposition products of the noble metal compounds are present near the metal surface during the initial deposition of the noble metal, and the subsequent noble metal This suggests that there is an inactive state on the surface of SUS304 that inhibits the decomposition and adhesion of elements. Therefore, platinum and rhodium sufficiently adhere to the reactor structural members located in the region where the reactor water is sufficiently flowing.

However, in the reactor, there are regions where the flow rate of the reactor water is low due to its structure. For example, there is a thermal sleeve portion of a piping nozzle provided in a nuclear reactor, a narrow portion formed between a core support plate and a core shroud, and between an upper lattice plate and a core shroud. In these regions where the flow velocity of the reactor water is low, the probability of occurrence of SCC is higher than in other regions where the flow velocity of the reactor water is high.

Therefore, the inventors examined a solution to increase the amount of platinum and rhodium attached to the reactor structural material existing in the region where the flow rate of the reactor water is low. First, the adhesion characteristics of palladium tested on palladium nitrate to SUS304 were confirmed by tests. Figure 3 shows the experimental results. Palladium has a large deposition rate from a relatively low temperature. 1 5 0 ^e C around at deposition rate is maximized, the deposition rate is lowered and a high temperature.

This is considered to be related to the stability of the surface film of SUS304. The metal surface becomes most unstable around 150, and the elution of the metal is maximized, and the adhesion reaction of palladium to the metal surface increases with increasing temperature. At 0, the deposition rate of palladium is maximum. Become. When the temperature further rises, the rate of elution of the deposited palladium increases, and the rate of deposition of palladium relatively decreases. Therefore, palladium adheres most effectively when used around 80 to 150 ° C. From the temperature dependence test described above, it was found that palladium had the property of easily adhering to the metal surface and easily detaching from the metal surface.

Next, the inventors conducted a test in which SUS304 was immersed in an aqueous solution to which a nitric acid compound of each of palladium, platinum and rhodium was added, to confirm the adhesion of palladium, platinum and rhodium to SUS304. Platinum and rhodium were obtained by combining Na ₂ [P t (01 ^) ₆ ] and 1 ^ & ₃ [1 ^ 11 (1 ^ 0 ₂ ) ₆ ] with [P t (NH ₃ ) _4] (N_〇 ₃₎ ₂ and the two kinds of the combination of R h (N0 ₃₎ _3, Examples of the palladium using P d (N0 ₃₎ _2. The exam first, '

N a ₂ aqueous solution containing [P t (OH) _6], and _{N a 3 [R h (N0} 2) 6] and,

_{[P t (NH 3) J} (N 0 3) 2 and R h (N0 _{₃₎ 3} of an aqueous solution containing the SUS304 of test pieces were dipped respectively, were deposited platinum and rhodium in each specimen. Each aqueous solution contains 150 ppb of the corresponding platinum compound and 150 ppb of the corresponding rhodium compound. Each aqueous solution was stationary and the temperature was kept at 150 ° C, and each specimen was immersed in the corresponding aqueous solution for 48 hours. No significant difference was observed in the adhesion characteristics of platinum and rhodium to the SUS304 test piece in both aqueous solutions. After confirming this was added _{_{[Pt (ΝΗ 3) 4]}} (· 0 3) 2及Beauty R h (N_〇 ₃₎ ₃ P d (N_〇 ₃₎ an aqueous solution containing _2, to the aqueous solution A test piece of SUS304 was immersed. This aqueous solution contains 100 ppb of the corresponding platinum compound, 150 ppb of the corresponding rhodium compound, and 50 ppb of the corresponding palladium compound. The aqueous solution containing P d (N0 ₃₎ ₂ is a stationary state, the temperature and dipping time of the specimen is the same as that in the aqueous solution containing the above-described platinum compound and the rhodium compound. Platinum, Logi And palladium compounds decompose in aqueous solution to release their respective precious metal ions. Ionized platinum, rhodium and palladium adhere to the surface of the SUS304 specimen. Platinum and rhodium compounds were selected from nitrate-soluble compounds in water so that the effects of nitrate ions do not occur when palladium is added in the form of nitrates.

FIG. 4 shows the results of measuring the ECP at room temperature of each test piece on which platinum, rhodium, etc. were adhered in the above test, together with the ECP of the platinum plate. The ECP of SUS304 with platinum and rhodium is considerably higher than the ECP of a platinum plate. Platinum and attachment to SUS304 rhodium was done by dipping the above _{[P t (NH 3) J} (N 0 3) 2 and _{R h (N 0 3) SUS304} 3 to an aqueous solution containing. The ECP of SUS304 to which platinum, rhodium and palladium are attached shows almost the same change as the ECP of the platinum plate, and falls to the level of platinum ECP when the molar ratio of hydrogen to oxygen is about 3 or more.

The reason why the ECP of SUS304 treated with platinum and rhodium shows a higher value than the ECP of the platinum plate is that the amount of platinum and rhodium deposited on SUS304 is small. That is, rhodium by itself is less likely to adhere to SUS304 than platinum. Also, even if it adheres, it is difficult for the metal to be reduced to a state. On the other hand, when SUS304 is immersed in an aqueous solution containing a rhodium compound and a platinum compound, the amount of adhered platinum decreases. Rhodium deposits do not change, but are reduced to metal. This is because it is used to reduce rhodium with coexisting platinum. For the above reasons, it is difficult to cover SUS304 with sufficient platinum and rhodium in a low flow system.

For aqueous solutions containing palladium compounds, mouth compounds and platinum compounds When SUS304 is immersed, palladium replaces platinum and contributes to the reduction of rhodium. Therefore, the adhesion of platinum to SUS304 is restored. The rhodium changes from Rh ^{3 +} to metal Rh by reduction on the metal surface. Palladium adheres to the surface of SUS 304 more easily than platinum and rhodium. For this reason, the P d palladium metal ions are first reduced by adhering to the metal surface on the surface of the SUS304, then ⁺ platinum ion and R h ³ is attached to the surface of the SUS304 is replaced with palladium. By substitution, metallic palladium reduces platinum and rhodium ions to the metallic state, and becomes itself an ion again and is released from the surface of SUS 304 into water. Some of palladium, without being replaced with platinum ion and R h ^{3 +,} is attached to the surface of SUS304. The palladium ions released from the metal are combined with the decomposition products generated and accumulated near the metal surface due to the decomposition of platinum and rhodium compounds, and are carried away in water. This decomposition product is carried away by the stream where the flow is fast. As a result of the above phenomena, the amount of platinum and rhodium adhering to the surface of SUS304 increases, the amount of rhodium reduced to metal increases, and a small amount of palladium also adheres, so that palladium compounds, rhodium compounds and platinum compounds When the test piece of SUS 304 is immersed in an aqueous solution containing, the ECP of the test piece drops significantly. Rhodium that has not been reduced to metal is presumed to be loosely physically adsorbed on the metal surface, and is easily peeled off from the metal surface. When reduced to metallic rhodium, it increases surface stability and contributes to lowering ECP over time.

Even when a SUS304 test piece is immersed in an aqueous solution containing a platinum compound and a palladium compound, platinum adheres to the test piece by the action of palladium compared to when a SUS304 test piece is immersed in an aqueous solution containing a platinum compound. The amount increases. In addition, water containing rhodium compounds and palladium compounds Even when the SUS304 test piece is immersed in the solution, the amount of rhodium adhering to the test piece increases due to the action of palladium compared to when the SUS304 test piece is immersed in an aqueous solution containing a rhodium compound. .

From the above experimental results, when an aqueous solution containing at least one of a platinum compound and a rhodium compound is used, it is essential to add a palladium compound in order to improve the adhesion efficiency of the corresponding noble metal element.

Based on the above study results, the inventors injected a compound of at least one of the noble metal elements of platinum and rhodium and a compound of palladium into the reactor water of the reactor, We noticed that the precious metal element compound and the palladium compound should be injected into the reactor water such that the molar number of palladium in the water is smaller than the molar number of the noble metal element in the reactor water. By injecting such precious metal elements and palladium into the reactor water, the precious metal elements (platinum and rhodium) on the surface of the structural members (stainless steel) of the reactor plant that exist in the region where the flow rate of the reactor water is low are At least one of these metals) and palladium will increase for these reasons. Naturally, the amount of noble metal elements (at least one of platinum and rhodium) and palladium adhering to the structural members of the reactor plant that exist in the region where the flow rate of the reactor water is high will increase.

At least one of platinum and rhodium and palladium are deposited on the surface of the reactor plant components and the hydrogen injection required to reduce the temperature to -500 mV vs SHE during BWR operation The amount should be at least 2: 1 (molar ratio) in stoichiometric ratio with the dissolved oxygen concentration in the reactor water. Normally, the concentration of dissolved oxygen in a BWR reactor pressure vessel when hydrogen is not injected is 20 O ppb. Therefore, the hydrogen concentration at which the stoichiometric ratio is 2 is 15 ppb. On the other hand, the hydrogen concentration in the feedwater rose to 0.4 ppm When the radiation dose rate of the main steam system starts to rise, the case where the feedwater flow rate and the core flow rate ratio are about 15%, such as a BWR with a reactor power of 110 MW and an advanced BWR (ABWR), is used. Considering that, the hydrogen concentration in the reactor water is 60 ppb. Therefore, the hydrogen concentration in the reactor water should be in the range of 15 to 60 ppb. This is 0.1 to 0.4 ppm of hydrogen concentration in feed water. This set value of hydrogen concentration can be covered by BWRs with different reactor power.

Alternatively, the hydrogen injection amount may be controlled such that the ECP is equal to or less than −23 OmVvsS HE while measuring the ECP of the reactor blunt structural member in contact with the reactor water. Normally, the change in ECP of the reactor plant structural components 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 values and the analysis results. The amount of hydrogen injected is controlled according to the feedwater flow rate so that the determined hydrogen concentration is reached.

Next, the effect of the reactor water pH on the ECP will be examined. The reduction reactions of oxygen and hydrogen peroxide that have been considered up to now are specifically described in the following (1), and

It is shown by equation (2). The reactions in equations (1) and (2) are represented by the

(H +) involved

0 ₂ + 4 H ⁺ + 4 e-→ 2H ₂ 0

H ₂ 〇 ₂ + 2 H ⁺ + 2 e-→ 2 H ₂ 0… (2) and depends on the reactor water pH. The reaction from the left side to the right side is suppressed because the proton concentration decreases as the reactor water pH increases. The hydrogen oxidation reaction is expressed by equation (3). However, hydrogen is reversible on precious metals,

H ₂ → 2 H ⁺ + 2 e-(3)

The reaction of equation (4) occurs similarly. These reactions become equilibrium systems, pH is

2 H ⁺ + 2 e-→ H, ... (4) As the concentration increases, the concentration of the proton decreases, and the reaction of equation (4) is suppressed.

The reaction of equation (3) proceeds predominantly. For this reason, if the surface of a reactor plant structural member to which noble metals are attached is placed in an environment where hydrogen is injected during hydrogen injection operation, the reduction current density of oxygen is further reduced and the oxidation current density of hydrogen is further increased. Therefore, according to the relationship shown in Fig. 1, the amount of hydrogen required to lower the corrosion potential of the structural members of the nuclear reactor plant may be less neutral and sometimes less. The concentration of dissolved oxygen in the reactor water without hydrogen injection is about 20 Opb. At this time, the stoichiometrically required amount of hydrogen is 15 ppb. Since the reactor water hydrogen concentration without hydrogen injection was measured at about 1 Oppb, if the reduction current density of oxygen and hydrogen peroxide on the surface with noble metal attached was suppressed to about 2Z3 by pH control, The potential drops to about 500 mVvsS HE only with hydrogen that is already present. Since the principle pro ton concentrations of high temperature water may be reduced to below 1 XI 0- ⁶ molZ rate Torr may Re be controlled to about p H 8. Similarly, the same effect can be obtained by adding an element acting only on the reduction reaction of oxygen and hydrogen peroxide to reduce the reduction reaction.

Based on this result, the inventors, in a new operation cycle after injecting the selected compound of the noble metal element and the palladium compound into the reactor water, convert the hydrogen and the alkaline material into the reactor water. Has the idea that it can be supplied to The hydrogen injection effect and the effect of weak alkaline water synergize to further reduce the ECP of the reactor plant structural members.

(First embodiment)

A method for alleviating stress corrosion cracking of a reactor plant structural member according to a preferred embodiment of the present invention will be described with reference to the drawings. Fig. 5 shows the method of this embodiment. Indicates the BWR plant to which is applied.

The BWR plant includes a reactor pressure vessel 3 and a turbine 6. The reactor pressure vessel 3 is installed in a reactor containment vessel 35, and has a reactor core 13 inside. In the reactor pressure vessel 3, core internal structures 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 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 to become steam. This steam is guided from the reactor pressure vessel 3 to the turbine 6 by the main steam pipe 5. The turbine 6 drives and rotates a connected generator (not shown). The steam discharged from the turbine 6 is condensed in the condenser 7 and supplied as water to the reactor pressure vessel 3 from the water supply pipe 2. This water supply sequentially passes through a condensate pump 8, a condensate desalinator 9, a low-pressure feed water heater 10, a feed water pump 12, and a high-pressure feed water heater 11 provided in the water supply pipe 2. The water supply becomes reactor water and is supplied to reactor core 13. The reactor water is driven by the recirculation pump 1 to move down the downforce 14 located outside the core shroud 36, reaches the lower plenum 14 via the recirculation pipe 4, and is guided into the core 13. .

The reactor water in the reactor pressure vessel 3 is guided into the reactor water purification system pipe 17 connected to the recirculation system pipe 4 by driving the pump 17 c. The regenerative heat exchanger 17a, pump 17c, non-regenerative heat exchanger 17b and desalinator 18ka are installed in the reactor water purification system piping 17. The reactor water in the reactor water purification system pipe 17 passes through these devices, is purified in particular by the desalter 18, and is returned to the reactor pressure vessel 3 via the water supply pipe 2. A water quality measuring device 20a for measuring the water quality of the reactor water is installed in the sampling piping 21 connected to the reactor water purification system piping 1Ί. Is placed. Part of the reactor water in the lower plenum 14 is led to the reactor water purification system piping 17 by the drain piping 16 connected to the bottom of the reactor pressure vessel 3, and is purified by the desalter 18 . Corrosion potential (ECP) sensor for measuring the corrosion potential of reactor water 2 5 Force Installed on drain pipe 16. A water quality measuring device 20 b for measuring the water quality of the reactor water is installed on a sampling pipe 22 connected to a drain pipe 16.

The water quality (dissolved oxygen concentration, dissolved hydrogen concentration, PH, conductivity, etc.) of the reactor water sampled from the sampling pipes 21 and 22 was measured using a water quality measurement device 20a after depressurizing and cooling the reactor water. And measured online by 2 Ob. 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.) collected from the water supply pipe 2 by the sampling pipe 19 is measured by the water quality measurement device 20c after depressurizing and cooling the water supply. Measured online. The main steam pipe 5 is also connected to a water quality measuring device 20 d via a sampling pipe 23. The water quality measuring device 20d condenses the steam extracted from the sampling pipe 23, decompresses and cools the condensed water, and 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 measure the water quality from room temperature to about 50 ° (:, and 1 to about 5 atm by reducing and cooling the target water. The measurement results such as the dissolved oxygen concentration, dissolved hydrogen concentration, PH, and conductivity by the water quality measurement device 20a to 20d are displayed and monitored on a display device (not shown). Is in the range of 5.3 to 8.6, and the conductivity of the reactor water is It is kept below 10 it s / cm.

The noble metal compound injector 31 is connected to the recirculation pipe 4. A hydrogen injection device 24 is connected to the water supply pipe between the low pressure water heater 10 and the water pump 12.

The off-gas piping 28 is connected to the condenser 7. The steam extractor 27 and the recombiner 30 are installed on the off-gas piping 28. The oxygen injection device 29 is connected to the offgas piping 28 between the condenser 7 and the steam extractor 27. The method of alleviating the stress corrosion cracking of the present embodiment in the BWR plant having the above-mentioned structure is described with reference to FIG. In Fig. 7, the horizontal axis shows the operation time of the BWR plant, and the vertical axis shows the temperature of the reactor water and the concentration of noble metal elements in the reactor water. FIG. 7 schematically shows changes in the temperature of the reactor water and the concentration of noble metal elements in the reactor water during the shutdown operation of the reactor during one operation cycle. Here, one operation cycle is a period from the start of the reactor to the shutdown of the reactor for replacement of the fuel assembly. The start operation of the reactor, the rated output operation of the reactor (rated operation), Includes reactor shutdown operation. A portion of the fuel assemblies loaded in the core 13 are taken out of the core 13 and replaced with a new fuel assembly after one operation cycle.

In this embodiment, the palladium compound, the platinum compound, and the rhodium compound are used immediately before the reactor water temperature reaches 150 (for example, when the reactor water temperature drops to 170) during the reactor shutdown operation for reducing the reactor power. The injection from the noble metal compound injection device 31 into the reactor water flowing in the recirculation pipe 4 starts. The injection of these compounds is stopped when the reactor water temperature reaches 8 O :. The period when the reactor water temperature is between 170 and 80 is the precious metal injection period (Fig. 7). During this period, the three compounds mentioned above are injected. Each compound has an atom It is led into the lower plenum 15 of the furnace pressure vessel 3. The start and stop of the supply of those compounds from the noble metal compound injection device 31 are performed by opening and closing valves 42, 46, 50 provided in the noble metal compound injection device 31.

The noble metal compound injection device 31 has a tank 40 filled with a solution of a palladium compound, a tank 44 filled with a solution of a platinum compound, and a tank 48 filled with a solution of a rhodium compound. Each tank is connected to a pipe 52 connected to the recirculation pipe 4 by separate pipes 41, 45, and 49. A valve 42 and a pump 43 are provided on a pipe 41, a valve 46 and a pump 47 are provided on a pipe 45, and a valve 50 and a pump 51 are provided on a pipe 49. The injection amount of palladium compound, platinum compound and mouth compound can be adjusted individually. In other words, using the measured values of the concentrations of palladium, platinum and rhodium in the reactor water measured by the controller 53 inductively coupled plasma mass spectrometer 38 (or inductively coupled plasma mass spectrometer 37), each valve 42 , 46, 50 are controlled individually. Such adjustment of the injection amount of each compound solution is very convenient because the deposition rate of each noble metal element on the surface of the structural member is different and the change rate of the concentration of each noble metal element in the reactor water is different. .

In this embodiment, P d (N0 ₃₎ as a palladium compound _2, as a platinum compound _{_{[P t (NH 3) 4}} ] (N0 3) 2, and R h (N_〇 ₃₎ ₃ used as the rhodium compound Was done. These compounds are dissolved in the reactor water, and palladium, platinum and rhodium are present in the reactor water as ions. Adjust the valve opening corresponding to the amount of each compound injected into the reactor water so that the palladium concentration in the reactor water is 50 ppb, the platinum concentration is 100 ppb, and the rhodium concentration is 100 ppb. Is controlled by During the precious metal injection period described above, During the period of the reactor water temperature of 150 to 80, the concentrations of palladium and platinum and the concentration of orifice are controlled to the above-mentioned set concentrations. The concentrations of palladium, platinum and rhodium are measured by inductively coupled plasma mass spectrometers 37 and 38 described below. Based on these measurements, the corresponding valve is adjusted to control the respective concentration in the reactor water. Palladium, platinum and rhodium ions in the reactor water adhere to the surface of the BWR plant structural members that come into contact with the reactor water. On the surface of the structural member, a film in which these metals are mixed is formed by adhesion of palladium, platinum and rhodium. The addition of the palladium compound increases the amount of platinum and rhodium deposited on the surface of the structural member. Furthermore, the amount of platinum and rhodium adhering to the surface of the structural member existing in the region where the flow rate of the reactor water is low increases. In the reactor water temperature range of 80 to 150 ° C, the amount of platinum and rhodium adhering to reactor plant structural members increases.

Instead of P d (N0 ₃ ) ₂ , [P d (NH ₃ ) J (N0 ₃ ) ₂ , or

_{_{P d (N0 2) 2 (}} NH 3) 2 may be used. _{[P d (NH 3) J} (N0 3) to Ri replacement of _{_{2 [P t (NH 3)}} 4] (OH) 2 may be used. R h (N_〇 ₃₎ ₃ instead _{_{[R h (NH 3) 5}} (H 2 〇)] (N0 ₃₎ ₃ The use Ite also Yoi. For each compound of the three types of noble metal elements shown above, a compound was selected that produced ammonium ion and nitrate ion when each compound was decomposed. These two ions have a small effect on the corrosion of structural components of the reactor plant. Also, the pH of the reactor water is less likely to change significantly due to the buffering effect of ammonia. Inductively coupled plasma mass spectrometers 37 and 38 are installed in sampling pipes 21 and 22. The concentration of each noble metal element in the reactor water shall be measured periodically (or as necessary) by using the inductively coupled plasma mass spectrometer 37 and 38 on the reactor water collected by the sampling pipes 21 and 22. To Therefore, it can be confirmed. A flameless atomic absorption spectrometer may be used instead of the inductively coupled plasma mass spectrometer. Furthermore, the concentration of each precious metal element in the reactor water is monitored by installing a reactor water conductivity meter (or pH meter) on the sampling pipes 21 and 22 and using this reactor water conductivity meter (or PH meter). You can also do it. That is, the change in the reactor water conductivity (or pH) due to the change in precious metal concentration in the reactor water when the reactor water is not sampled is monitored by the reactor water conductivity meter (or pH meter).

The amounts of platinum, rhodium and palladium in the reactor water are reduced by the attachment to the surface of structural members and the removal of platinum, rhodium and palladium ions by the desalter 18 of the reactor water purification system. The injection of each of the platinum, rhodium and palladium compounds from the noble metal compound injector 31 during the noble metal injection period is performed so as to compensate for the respective removal amounts by the desalter 18. After the noble metal injection period, the concentration of platinum, rhodium and palladium in the reactor water decreases due to the removal action by the desalter 18.

After the treatment of depositing platinum, rhodium and palladium on the reactor plant structural members by the injection of each compound is completed, the operation of the BWR plant is stopped. During the subsequent periodic inspection period, replacement of the fuel assemblies and periodic inspection of the plant will be carried out. After the periodic inspection, when the BWR plant starts up, as shown in Fig. 7, the operation of pulling out the control rods from the reactor 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 power is increased to 100% output.

After the water supply pump 12 is driven, the valve (not shown) of the hydrogen injection device 24 is opened and injected into the water supply pipe 2. The feedwater containing hydrogen is guided into the reactor pressure vessel 3. At this time, the reactor water in the reactor pressure vessel 3 The hydrogen concentration in the medium is determined by setting the ECP to a sufficiently low value and examining the ECP response according to the amount of hydrogen injected. Its hydrogen concentration is preferably 20 to 60 ppb in reactor water. However, since the hydrogen concentration in the reactor water changes depending on the position in the reactor pressure vessel and the operating conditions of the reactor, the hydrogen concentration in the feedwater is 0.1 ρρπ! The hydrogen injection amount is controlled to be in the range of ~ 0.4 ppm. In this embodiment, the hydrogen concentration in the reactor water is controlled to 25 ppb as shown in FIG. If the ECP force at the SCC protection target site can be measured directly or can be estimated by calculation, the ECP force at that site should be less than −23 OmV vs SHE and the hydrogen injection device 24 should be used. The hydrogen injection amount may be controlled.

The reaction between the injected hydrogen and the oxygen contained in the reactor water is promoted by the catalytic action of platinum, rhodium and palladium attached to the surface of the reactor plant structural member, and water is generated. Thus, hydrogen contributes to the reduction of dissolved oxygen in the reactor water near the reactor plant structural members. For this reason, the ECP of the reactor brand structural member in the reactor pressure vessel 3 is reduced, and the SCC of the structural member is significantly suppressed. In particular, since platinum, rhodium, and palladium also adhere to the surface of the reactor plant structural members that are in contact with the reactor water region where the flow rate of the reactor water is extremely low, the ECP of the structural members that are in contact with the reactor water region is low. As shown by the symbol in Fig. 4, it decreases and falls below 23 OmV vs SHE. SCC of the structural member in contact with the reactor water area is also significantly suppressed. Utilizing the catalytic action of platinum, rhodium and palladium, the amount of hydrogen required for reaction with dissolved oxygen is significantly reduced. Therefore, although the effect of reducing the dissolved oxygen amount is large, the amount of generated nitrogen 16 is significantly reduced. Since the surface dose rate of the steam system such as the main steam pipe 5 and the turbine 6 does not increase, these maintenance inspections are facilitated and the time required for the maintenance inspections is shortened. In this embodiment, the palladium concentration in the reactor water is lower than the platinum concentration and the rhodium concentration because the platinum concentration and the rhodium concentration in the reactor water are equal. That is, the number of moles of palladium is smaller than the number of moles of platinum and rhodium. This increases the amount of platinum and rhodium deposited. When the number of moles of palladium is larger than the number of moles of platinum and rhodium, the attachment of platinum and rhodium to the structural member is hindered, and the amount of the attachment decreases. This is because the amount of palladium that is easily deposited increases. Palladium adheres easily, but on the other hand, it is more easily ionized than platinum and rhodium, and is easily dissolved in reactor water from the surface of the structural member to which it adheres. Platinum and rhodium have been attached to the surface of structural materials for a long time. For this reason, the increase in the amount of platinum and rhodium deposited reduces the concentration of dissolved oxygen in the reactor water near the surface of the structural member over a long period of time, thereby reducing the ECP of the structural member of the reactor plant.

(Second embodiment)

A method of mitigating stress corrosion cracking of a reactor plant structural member according to another embodiment of the present invention will be described with reference to FIG. The configuration of the BWR plant used in this embodiment is the same as the configuration of the BWR plant to which the first embodiment described with reference to FIG. 5 is applied. This embodiment, until the reactor water temperature at the time of reactor shutdown operation drops to 8 0 ° C from 1 7 0, a palladium compound (P d (Nyu_〇 ₃₎ 2), platinum compounds ([ P t (NH ₃₎ J (N_〇 ₃₎ ₂₎ and Logistics © beam compound _{(R h (N 0 3)} 3) is injected into the reactor water. However, in this embodiment, palladium easily adheres to structural members even in a temperature range of 150-200, so that as shown in FIG. 9, the palladium compound is earlier than the platinum compound and the rhodium compound. Inject at high temperature. In this example, the palladium concentration in the reactor water was 105 ppb, and the concentrations of platinum and rhodium were Is controlled to be 125 ppb. Also in this embodiment, the mole number of palladium in the reactor water is smaller than the mole numbers of platinum and rhodium. In this embodiment, palladium is first deposited on the reactor plant structural member, and then platinum and rhodium are deposited on the structural member.

This embodiment can provide the same effect as the first embodiment. In this embodiment, since palladium is first attached to the structural member, palladium can be injected at a high concentration within a range that does not affect the conductivity and pH of the reactor water. In addition, platinum and rhodium can be injected at a higher concentration as long as palladium does not coexist. For this reason, the amount of platinum and rhodium adhering to the structural members of the reactor plant can be increased as compared with the first embodiment.

(Third embodiment)

A method of alleviating stress corrosion cracking of a reactor plant structural member according to another embodiment of the present invention will be described below. The configuration of a BWR plant to which this embodiment is applied has a configuration in which an alkali injection device 32 is added to the configuration of FIG. 5, as shown in FIG. The alkali injection device 32 is connected to the water supply pipe 2 on the downstream side of the low-pressure water heater 10.

In this embodiment, as in the first embodiment, a platinum compound, a rhodium compound and a palladium compound are injected, and platinum, rhodium and palladium are attached to the surface of the reactor plant structural member. In this embodiment, the method of alleviating stress corrosion cracking is to open the valve of the alkali injection device 32 and inject the alkali solution into the feed water in the next operation cycle after the work of depositing platinum, rhodium and palladium has been completed. As shown in Fig. 11, the injection of the alkaline solution is performed during the period from the start of control rod withdrawal when the BWR plant starts up to the shutdown of the reactor. By supplying the feedwater containing the reactor water into the reactor pressure vessel 3, the pH of the reactor water is weakened throughout the operation cycle. It is maintained at about 8 which is Lucari. The pH of the reactor water is measured using a water quality measuring device 20a or 20b. Based on the measured pH value, the opening of the valve of the alkali injection device 32 is adjusted to control the pH of the reactor water. An Na〇H solution is used as the alkaline solution. However, Li アルカリ H solution, aqueous ammonia, or a solution containing sodium hydrogen carbonate and sodium carbonate may be used as the alkaline solution.

In the present embodiment, the effects produced in the first embodiment can be obtained. In this embodiment, since the reactor water is controlled to be weakly alkaline, the pH at the crack tip of the reactor plant structural member can be shifted to the alkaline side. For this reason, the propagation of cracks in the structural member can be effectively suppressed. Since the amount of hydrogen injected can be reduced by weak control of the reactor water, the hydrogen concentration in the reactor water can be reduced to about 17 ppb. For this reason, the amount of generated nitrogen 16 is smaller than in the first embodiment. In the operation cycle, the room temperature pH of the reactor water is desirably controlled within the range of 7 to 8.5. It is also desirable to control the hydrogen concentration of the reactor water in the operation cycle within the range of 15 to 6 O ppb. By controlling the room temperature pH and the hydrogen concentration within the above ranges, the effect of hydrogen injection and the effect of weak water force are synergistically achieved, and the ECP of the structural member can be reduced to −500 with a smaller amount of hydrogen injection. m V vs SHE.

The pH adjustment of the reactor water of the present embodiment is performed by using a part of the H-type cation resin filled in the condensate desalter 9 or the desalter 18 without using the power injection device 32. It is also possible to change to an alkaline type cationic resin such as Na type. By using the Na-type cationic resin, Na ions flowing out of the Na-type cationic resin are injected into the reactor water, so that the pH of the reactor water can be controlled to a weak alkali. As the alkali type cationic resin, K type, Li type or NH type may be used in addition to Na type. Alkali-type cation tree The use of the fat eliminates the need for the alkali injection device 32, and simplifies the configuration of the BWR plant.

In the first, second and third embodiments, the platinum compound and the rhodium compound are injected so that the moles of platinum and rhodium in the reactor water are the same. However, the platinum compound and the rhodium compound may be injected such that one mole number of platinum and rhodium in the reactor water is smaller than the other mole number. In this case, the palladium compound is injected so that the number of moles of palladium in the reactor water is even smaller than the smaller number of moles of platinum and the orifice. For example, in the configuration of FIG. 5, the platinum compound, the rhodium compound, and the palladium compound are noble gold so that the platinum concentration in the reactor water is 50 ppb, the rhodium concentration is 100 ppb, and the palladium concentration is 10 ppb. It is injected into the reactor water from the metal injection device 31. Palladium functions to promote the deposition of platinum and rhodium on the surfaces of reactor plant components because the moles of palladium are even smaller than the smaller moles of platinum, platinum and rhodium. . This function is exhibited at a palladium concentration of less than 50 ppb under the conditions of a platinum concentration of 50 ppb and a rhodium concentration of 10 O ppb. When the number of moles of palladium is greater than the number of moles of platinum, which is a small number of moles, palladium functions to suppress the adhesion of platinum and rhodium.

Conversely, when the number of moles of rhodium in the reactor water is smaller than the number of moles of platinum, the palladium compound is injected into the reactor water so that the number of moles of palladium in the reactor water becomes smaller than the number of moles of rhodium. . This is for exhibiting the function of accelerating the adhesion of platinum and rhodium by palladium.

Palladium compound with either platinum compound or rhodium compound Injection into the reactor water is also conceivable. In this case, the palladium compound is injected into the reactor water such that the number of moles of palladium is smaller than the number of moles of platinum (or rhodium). This promotes the adhesion of platinum (or rhodium). Injecting two types of compounds, a platinum compound and a palladium compound (or an orifice compound and a palladium compound), also has an effect obtained when three types of compounds of a platinum compound, a rhodium compound and a palladium compound are injected.

In each of the embodiments described above, the noble metal compound injection device 31 was connected to the recirculation system piping 4, but the noble metal compound injection device 31 was connected to the reactor water purification system piping 17 (preferably downstream from the pump 17c). Or on the downstream side of the condensate desalter 9. Further, a noble metal compound injection device 31 may be connected to a residual heat removal system pipe (not shown) to which reactor water is supplied when the reactor is stopped. The residual heat removal piping connects the recirculation piping 4 to the reactor pressure vessel 3.

Platinum and rhodium are deposited on the surface of reactor plant structural members when the reactor water temperature is in the range of 80 to 150. If the reactor water temperature satisfies the conditions, palladium, platinum, and rhodium compounds should be injected during reactor shutdown (for example, during periodic inspections) or when the reactor starts up, not during reactor shutdown operation. May go. In each of the above-described embodiments, the above-mentioned compounds are injected while the reactor water temperature is lowered from 150 to 80. However, the above compounds may be injected at a certain reactor water temperature (for example, 150 t :) within the temperature range. Industrial applicability

The present invention is applicable not only to BWR plants but also to pressurized water reactor plants. Applicable.

Claims

The scope of the claims

1. a step of injecting a compound of at least one noble metal element selected from the noble metal elements of platinum and rhodium, and a compound of palladium into reactor water of a reactor, wherein palladium in the reactor water is included. Wherein the noble metal compound and the palladium compound are injected into the reactor water such that the number of moles of the noble metal element in the reactor water is smaller than the number of moles of the noble metal element in the reactor water. How to ease.

2. The selected noble metal element compounds to be injected into the reactor water are a platinum compound and a rhodium compound, and the mole number of palladium in the reactor water is a smaller mole of the platinum and rhodium moles in the reactor water. 2. The method for mitigating stress corrosion cracking of a reactor plant structural member according to claim 1, wherein the palladium compound is injected so as to be smaller than the number.

3. The platinum compound and rhodium compound are injected into the reactor water at 80 to 150 t :. A method for mitigating stress corrosion cracking of a structural member of a nuclear reactor plant according to claim 2.

4. The method of claim 1, wherein the palladium compound is injected before the selected noble metal element compound is injected.

5. The method of claim 1, wherein the selected noble metal element compound and palladium compound are compounds that generate nitrate ions.

6. The method for mitigating stress corrosion cracking of a reactor plant structural member according to claim 5, wherein the selected noble metal element compound and palladium compound are compounds that generate ion nitrate and ammonia ions.

7. New after injection of the selected noble metal element compound and palladium compound 2. The method for mitigating stress corrosion cracking of a reactor plant structural member according to claim 1, wherein hydrogen is supplied to the reactor water during the operation period of the reactor in a new operation cycle.

8. In the operation cycle, the hydrogen concentration of the feedwater supplied to the reactor is controlled within a range of 0.1 to 0.4 ppm, and the stress corrosion cracking of the structural members of the reactor plant according to claim 7 is reduced. Method.

9.Hydrogen is added to the reactor water so that the corrosion potential of the reactor plant structural members in contact with the reactor water is not more than 230 mV vs SHE or less. How to mitigate cracks.

10. A step of injecting at least one compound of a noble metal element selected from platinum and rhodium noble metal elements and a compound of palladium into reactor water of a reactor, wherein the atom in contact with the reactor water is included. A method for alleviating stress corrosion cracking of a reactor plant structural member, wherein the selected noble metal element is attached to the surface in place of at least a part of palladium attached to the surface of the reactor plant structural member.

11. A step of injecting at least one compound of a noble metal element selected from platinum and rhodium noble metal elements, and a compound of palladium into reactor water of a reactor, The noble metal compound and the palladium compound are injected into the reactor water such that the number of moles is smaller than the number of moles of the noble metal element in the reactor water, and the selected noble metal element compound and the new palladium compound after the injection are mixed. Stress corrosion of a reactor plant structural member characterized by supplying hydrogen to the reactor water during the operation period of the reactor in a simple operation cycle, and supplying the reactor water to the reactor water during the operation period. How to mitigate cracks.

12. In the above operation cycle, the room temperature pH of the reactor water is in the range of 7 to 8.5. The method for mitigating stress corrosion cracking of a reactor blunt structural member according to claim 11, wherein the hydrogen concentration in the reactor water is controlled within a range of 15 to 6 O ppb.

13. The method of alleviating stress corrosion cracking of a structural member of a nuclear reactor plant according to claim 11, wherein the supply of the alkaline substance is performed by using an ion exchange resin filled in a desalter for purifying reactor water.

14. The method for alleviating stress corrosion cracking of a reactor blunt structural member according to claim 13, wherein the ion exchange resin is an Al-based cation resin.