Steam generator corrosion product on-line sampling device and steam generator operating state evaluation method

Abstract

The application discloses a kind of steam generator corrosion product on-line sampling device, including sampling inlet pipeline, sampling circuit and bypass, sampling trench, the two ends of the sampling circuit and bypass are respectively communicated with the sampling inlet pipeline and sampling trench, a plurality of filters are sequentially arranged on the sampling circuit, sampling bypass is arranged between adjacent filters, another end of the sampling bypass is communicated to the sampling trench.The steam generator corrosion product on-line sampling device of the application can on-line sample the corrosion product of steam generator, and realizes the accurate calculation of CRP1000 unit steam generator dirt input;According to the deposit enrichment and the unit operating condition, the CRP1000 unit steam generator deposit thickness, thermal resistance and secondary side steam pressure prediction model during the service life are proposed, and the application effect of the treatment measures is predicted and evaluated, which can provide guidance for the safe and economic operation of CRP1000 unit steam generator in China.

Description

Technical Field

[0001] This invention relates to nuclear power, and more particularly to an online sampling device for corrosion products of steam generators in nuclear power plants and a method for assessing the operating status of steam generators. Background Technology

[0002] The steam generator is a crucial heat exchanger in the secondary loop. Poor water quality in the secondary loop can significantly impact the steam generator. Deposits on the heat transfer pipes affect the heat transfer characteristics of the steam generator, while deposits on the tube supports increase flow resistance and affect hydraulic characteristics. Simultaneously, impurities in the water can concentrate and deposit at locations with poor flow, such as gaps in the tube sheet and tube supports, creating a corrosive environment that affects the integrity of the steam generator (SG) heat transfer tubes. Therefore, it is necessary for power plants to monitor the content of corrosion products in the feedwater and SG wastewater to determine the migration of feedwater corrosion products to the SG and the water chemical environment within the SG. This also serves as one of the bases for assessing the necessity of mechanical or chemical cleaning of the SG.

[0003] Currently, the CPR1000 unit monitors the total iron content of the secondary main feedwater weekly during routine operations. Iron corrosion products are sampled simultaneously from the steam generator blowdown system and the main feedwater system, with sampling flow rates established temporarily during sampling. Sampling is conducted every six months using a 7-day cumulative flow rate method via online filtration. This method, however, requires temporary sampling flow rate establishment, necessitating a rebalancing process of deposition or release on the inner surface of the sampling pipeline, leading to insufficient sample representativeness. Furthermore, the sample sensitivity is insufficient, as the sample only represents the unit's state at a specific moment and does not establish a connection to the unit's long-term state, making accurate iron transport calculations impossible.

[0004] For AP1000 Generation III nuclear power units, the system design phase explicitly requires continuous monitoring of the quantity and trends of corrosion products in the secondary loop feedwater and steam generator effluent to assess the deposition of suspended solids in the steam generator. Currently, the majority of Generation II fuel cell units in my country lack online sampling devices and assessment methods for their steam generators. Summary of the Invention

[0005] In view of this, in order to overcome the shortcomings of the prior art, the purpose of this invention is to provide an online sampling device for corrosion products of steam generators.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An online sampling device for corrosion products of a steam generator includes a sampling inlet pipe, a sampling circuit and a bypass, and a sampling trench. The two ends of the sampling circuit and the bypass are respectively connected to the sampling inlet pipe and the sampling trench. Multiple filters are sequentially arranged on the sampling circuit, and a sampling bypass is arranged between adjacent filters. The other end of the sampling bypass is connected to the sampling trench.

[0008] According to some preferred embodiments of the invention, the pore sizes of the filter membranes in each of the filters may be the same or different.

[0009] According to some preferred embodiments of the invention, the pore size of the filter membrane in each of the filters is different, and the pore size of the filter membrane gradually decreases from the filter near the sampling inlet pipe end to the filter near the sampling trench end.

[0010] According to some preferred embodiments of the present invention, three filters are sequentially arranged on the sampling circuit, and the pore size of the filter membrane in each filter is different.

[0011] According to some preferred embodiments of the present invention, the pore sizes of the filter membranes in the filter are sequentially 0.4–3 μm, 0.1–0.4 μm, and 0.05–0.1 μm. In some embodiments, the online sampling device employs a three-stage filtration method with filter membrane pore sizes of 3 μm, 0.4 μm, and 0.1 μm, and analyzes the filtered sample solution. A bypass device analyzes the total iron content, and the results of the two sampling methods are cross-validated to ensure the accuracy of the sampling results. Furthermore, the three different filter membrane pore sizes of the device can be switched according to the unit conditions and different pH control agents. For example, two-stage filtration is used during the unit startup phase; three-stage filtration is used during the unit's full-power operation phase; and three-stage filtration is used when the unit uses a mixed control of NH3 and ETA.

[0012] According to some preferred embodiments of the present invention, a main valve is provided on the sampling inlet pipeline; a sampling valve is provided on the sampling circuit; and a bypass valve is provided on the bypass.

[0013] According to some preferred embodiments of the invention, a sampling bypass valve and / or a sampling flow meter are provided on the sampling bypass.

[0014] According to some preferred embodiments of the present invention, a sampling flow meter is provided on the sampling circuit; and a bypass rotor flow meter is provided on the bypass.

[0015] According to some preferred embodiments of the invention, the sampling circuit is provided with a sampling pump and a pressure gauge.

[0016] According to some preferred embodiments of the invention, the Reynolds number of the fluid in the sampling tube is greater than or equal to 8000. In some embodiments, the sampling device uses a 1 / 4-inch small diameter tube; the flow velocity inside the sampling tube is 1.8 m / s, the wall thickness is 0.89 mm; the sampling flow rate is 1772 mL / min, and the Reynolds number inside the sampling tube is 9220.

[0017] The present invention also provides a method for evaluating the operating status of a steam generator, comprising the following steps:

[0018] The steam generator feedwater and drainage water were simultaneously sampled online using the online sampling device described above, and the mass of corrosion products of the feedwater and drainage water during the sampling time was obtained.

[0019] The obtained corrosion product mass is combined with the unit operating status to calculate the amount of corrosion products accumulated in the steam generator under the current condition, and the cumulative calculation is performed.

[0020] Based on the current accumulation of corrosion products in the steam generator and the unit's operating status, the amount of corrosion products during the unit's life cycle is assessed.

[0021] The quality and concentration of corrosion products are combined with the current unit status as follows: if the sampling concentration is 6 ppb at 50% load, then the actual concentration at 100% load is 3 ppb.

[0022] In some embodiments, corrosion product prediction and assessment is performed by predicting the cumulative amount of corrosion products over the life cycle based on the current concentration level of corrosion products and the historical experience of the CPR1000 unit under the current pH control agent, including three scenarios: worst, appropriate, and best.

[0023] In some embodiments, based on the calculation results of corrosion products and combined with the operating status of the unit equipment, corresponding soft chemical cleaning and hardening cleaning methods are proposed, and the application effect after chemical cleaning is predicted.

[0024] According to some preferred embodiments of the present invention, the sampling time is 7 days during the stable operation phase of the unit and 1 day during the start-up phase of the unit to increase the sampling frequency and reduce the uncertainty of concentration data.

[0025] According to some preferred embodiments of the present invention, the cumulative calculation is performed according to the following formula:

[0026]

[0027] In the formula, m represents the amount of corrosion products accumulated in a single steam generator within a certain fuel cycle; m 给水 This refers to the cumulative amount of corrosion products that migrate from feedwater to the secondary side of a single steam generator within a given fuel cycle over one week; m排污 The cumulative amount of waste corrosion products from a single steam generator over one week within a given fuel cycle;

[0028] m 给水 =F 给水 ×C Fe给水

[0029] m 排污 =F 排污 ×C Fe排污

[0030] In the formula, F 给水 C represents the cumulative feedwater flow rate per week for a single steam generator. Fe给水 The iron content of the feedwater for the current week; C Fe排污 Iron content in wastewater discharged that week; F 排污 This represents the cumulative drainage flow rate of a single steam generator over one week.

[0031] According to some preferred embodiments of the present invention, the total iron content of the water supply and the total iron content of the wastewater are both calculated using the following formula:

[0032] The total iron content is:

[0033] C 总铁 (ppb) = Suspended iron content C Fe (ppb) + Iron content in filtrate C2(ppb)

[0034] Suspended iron content C Fe (ppb) is calculated using the following formula:

[0035]

[0036] In the formula, the iron concentration C1 (ppb) of the cellulose acetate filter membrane used for sampling is obtained by taking it out, dissolving it in concentrated acid and making it to a fixed volume, and then analyzing it. The iron concentration C0 (ppb) of the blank filter membrane is obtained by dissolving it in concentrated acid and making it to a fixed volume.

[0037] Compared with the prior art, the advantages of this invention due to the adoption of the above technical solutions are as follows: The online sampling device for corrosion products of steam generators of this invention can sample corrosion products of steam generators online and realize accurate calculation of the fouling input of CRP1000 unit steam generators; based on the sediment enrichment and unit operation status, a prediction model for sediment thickness, thermal resistance and secondary steam pressure of CRP1000 unit steam generators during their service life is proposed, and the application effect of treatment measures is predicted and evaluated, which can provide guidance for the safe and economical operation of CRP1000 unit steam generators in my country. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A schematic diagram of the structure of the online sampling device for corrosion products of a steam generator in a preferred embodiment of the present invention;

[0040] Figure 2 A sediment thickness prediction map provided for a preferred embodiment of the present invention;

[0041] Figure 3 A predicted thermal resistance diagram for sediment heat transfer provided in a preferred embodiment of the present invention;

[0042] Figure 4 This is a prediction diagram of the influence of sediments on secondary steam pressure provided in a preferred embodiment of the present invention. Detailed Implementation

[0043] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0044] Example 1: Online Sampling Device for Corrosion Products of Steam Generator

[0045] See Figure 1 The online sampling device for corrosion products of steam generator in this embodiment is a multi-stage filter membrane online sampling device suitable for steam generators of CRP1000 nuclear power units. Specifically, it includes a sampling inlet pipeline, a sampling circuit, a bypass, a sampling trench, three filters arranged sequentially on the sampling circuit, and a sampling bypass. The two ends of the sampling circuit and the bypass are respectively connected to the sampling inlet pipeline and the sampling trench. A sampling bypass is provided between adjacent filters, and the other end of the sampling bypass is connected to the sampling trench.

[0046] A main valve is installed on the sampling inlet pipeline. A sampling valve, pressure gauge, and sampling flow meter are installed on the sampling circuit. A bypass valve and bypass rotor flow meter are installed on the bypass. A sampling bypass valve and sampling flow meter are installed on the sampling bypass.

[0047] The pore size of the filter membranes in each filter is different, gradually decreasing from the filter near the sampling inlet pipe to the filter near the sampling trench. In this embodiment, the pore sizes of the filter membranes are 0.4–3 μm, 0.1–0.4 μm, and 0.05–0.1 μm, respectively. Preferably, the online sampling device uses a three-stage filtration method with filter membrane pore sizes of 3 μm, 0.4 μm, and 0.1 μm. The filtered sample solution is analyzed, and a bypass device analyzes the total iron. The results of the two sampling methods are cross-validated to ensure the accuracy of the sampling results. Furthermore, the three different filter membrane pore sizes of the device can be switched according to the unit conditions and different pH control agents. For example, two-stage filtration is used during the unit startup phase; three-stage filtration is used during the unit's full-power operation phase; and three-stage filtration is used when the unit uses a mixed control of NH3 and ETA.

[0048] Fe on the surface of carbon steel is corroded to form Fe. 2+ It will react with SO4 in the water 2- / Cl - / PO4 3- The particles combine to form FeSO4 / FeCl2 / Fe3(PO4)2, with a particle size of 0.1-0.5 μm, while the particle size of Fe2O3 and Fe3O4 is generally 0.5-5 μm. Colloidal sampling analysis only analyzes colloidal particles in the sample; therefore, the sampling device uses a three-stage filtration unit and filter elements with different pore sizes (0.1 μm, 0.4 μm, and 3 μm) to obtain colloidal particles from the sample for analysis of different parameters such as particle size, size distribution, and chemical elements. This allows for the analysis of scale morphology and characteristics, and the prediction of hard scale buildup.

[0049] The multi-stage continuous sampling device for steam generator feedwater and wastewater simultaneously operates online. It employs a three-stage filtration method with filter membrane pore sizes of 3µm, 0.4µm, and 0.1µm, primarily collecting colloids and suspended solids from secondary loop corrosion products. The filtered sample is then analyzed to determine the dissolved iron content. After reaching full power at the beginning of each cycle, a bypass device is used to analyze the total iron content, and the results of the filter membrane sampling method are cross-checked to ensure accuracy.

[0050] The sampling device uses a 1 / 4-inch small-diameter pipe. The design sampling flow rate is 1.8 m / s. When the wall thickness is 0.89 mm, the sampling flow rate is shown in Table 1, which is 1772 mL / min. The Reynolds number in the sampling pipe at this time is shown in Table 2, which is 9220, far exceeding 2000-3000. This ensures that the fluid in the sampling pipe is in a turbulent state. When the fluid in the pipeline is in a turbulent state, it increases the vertical disturbance in the pipeline, increases the flow velocity near the wall, reduces the accumulation of iron products, improves the representativeness of the sample, and allows the sample analysis to more objectively characterize the system state.

[0051] Table 1. Sampling tube flow rate (mL / min) required to achieve a sample flow rate of 1.8 m / s

[0052]

[0053]

[0054] Table 2. Reynolds number (dimensionless) for sample flow rates reaching 1.8 m / s

[0055]

[0056] Example 2: Evaluation Method for Steam Generators Based on Corrosion Products

[0057] This invention provides an online sampling method and device for corrosion products in nuclear power plant steam generators. By simultaneously sampling the main feedwater and wastewater through multi-stage filter membranes, and combining this with the unit's operating status, the method accurately calculates the amount of corrosion products migrating into the steam generator, predicts the amount of deposits on the steam generator tube bundles during its service life, recommends corresponding remediation methods, and evaluates the effectiveness of the remediation measures. The method includes the following steps:

[0058] S1. A multi-stage continuous sampling device for steam generator feedwater and sewage discharge, as shown in Example 1, is used for sampling and testing to ensure the authenticity of the samples.

[0059] S2, the mass of the corrosion products obtained in S1 (C of feedwater) Fe给水 C of drainage Fe排污 The cumulative amount of corrosion products in the steam generator under the current state of the computer group (m³) 给水 and m 排污 ), and perform cumulative calculations (m=∑m 给水 -∑m 排污 ).

[0060] S3. Based on the current accumulation of corrosion products in the steam generator in S2, predict and evaluate the amount of corrosion products on the steam generator tube bundle during the unit's life cycle.

[0061] S4. Based on the predicted corrosion product quantity in S3, propose corresponding remedial measures and predict the effects of the measures after application.

[0062] The CPR1000 unit operation status assessment method in this embodiment uses a continuous online sampling device with multi-stage filter membranes for feedwater and wastewater to cumulatively calculate the amount of corrosion products in the steam generator under multi-power operation conditions. It then predicts and evaluates the amount of corrosion products and their impact over the lifespan of the steam generator, and finally proposes corresponding remedial measures, predicting and evaluating the effectiveness of these measures. Specifically, it includes the following steps:

[0063] Step 1: Simultaneously online sample the steam generator feedwater and drainage using the online sampling device described in Example 1 above to obtain the mass of corrosion products in the feedwater and drainage during the sampling period. In this example, the sampling period is 7 days.

[0064] As mentioned above, the online sampling device is designed with three different filter membrane pore sizes. The appropriate pore size can be switched depending on the unit's condition and the pH control agent used. For example, two-stage filtration is used during unit startup, and three-stage filtration is used during full-power operation. Three-stage filtration is also used when the unit uses a mixed control of NH3 and ETA. This multi-stage filtration not only analyzes the quality of corrosion products but also collects and analyzes their particle size characteristics. X-ray fluorescence spectroscopy (XRF) is recommended for analyzing the filter membrane samples to determine the oxidation state of iron without dissolving the filter membrane. Alternatively, the filter membrane can be completely dissolved, and the solution analyzed by atomic absorption spectrometry. The results can be used to calculate the average equivalent concentration during the sampling period.

[0065] The cellulose acetate filter membrane used for sampling was removed, dissolved and diluted with concentrated acid, and analyzed to obtain the iron concentration C1 (ppb) of the filter membrane. A blank filter membrane was also dissolved and diluted to obtain the iron concentration C0 (ppb) of the blank filter membrane. The suspended iron concentration was then calculated using the following formula:

[0066]

[0067] The total iron concentration of the sample is:

[0068] C 总铁 (ppb) = Suspended iron content C Fe (ppb) + Iron content in filtrate C2(ppb)

[0069] The iron content (C2, ppb) in the filtrate was determined by collecting the filtered liquid and measuring it using atomic absorption spectroscopy.

[0070] Iron content in water supply C during the week Fe给水 Iron content in sewage discharged during the week (C) Fe排污 This is calculated based on the formula above.

[0071] Step 2: Based on the obtained corrosion product mass, calculate the amount of accumulated corrosion products in the steam generator under the current feedwater flow rate, and perform cumulative calculation.

[0072] The cumulative amount of feedwater migration to the secondary side of a single steam generator within a certain fuel cycle, amounting to m³ per cycle, represents corrosion products. 给水 The following formula is used to calculate:

[0073] m 给水 =F 给水 ×C Fe给水

[0074] F 给水 This represents the cumulative feedwater flow rate per week for a single steam generator.

[0075] The cumulative amount of corrosion products from a single steam generator discharged over one week in a given fuel cycle is m. 排污 The following formula is used to calculate:

[0076] m 排污 =F 排污 ×C Fe排污

[0077] F 排污 The cumulative blowdown flow rate for a single steam generator per week.

[0078] The amount of corrosion products m entering the steam generator within one cycle (e.g., 18 months) is calculated using the following formula:

[0079] m=∑m 给水 -∑m 排污

[0080] m represents the amount of corrosion products accumulated in a single steam generator within a certain fuel cycle (e.g., 18 months).

[0081] Step 3: Based on the current accumulation of corrosion products in the steam generator, calculate the future heat transfer resistance of the deposits and the actual steam pressure.

[0082] The thickness of the sediment depends, in turn, on the expected inflow rate of feedwater iron, the sediment composition, and porosity. The sediment thickness as a function of service time can predict the future thermal resistance and secondary steam pressure of the sediment, as shown in the model formula below. This allows for the determination of the steam generator's operating status.

[0083]

[0084] In the formula: k f The thermal conductivity of the sediment is W / (m·K); k mg The thermal conductivity of Fe3O4 is given in W / (m·K); k v ε is the saturated steam thermal conductivity, W / (m·K); f The porosity of the sediment was obtained through measurement.

[0085]

[0086] In the formula: R f Represents the future thermal resistance of the sediment; e f The thickness of the deposit, in meters, is calculated based on the amount of corrosion products accumulated in a single steam generator within a given fuel cycle, the density of the corrosion products, and the deposition area.

[0087] P = f·R f

[0088] In the formula: P is the steam pressure, bar; f is the correction factor for thermal resistance and steam pressure.

[0089] The inputs typically used to calculate the average deposit thickness in a natural circulation steam generator at a nuclear power plant are as follows:

[0090] In the 1970s and 1980s, the iron concentration in feedwater for steady-state operation of pressurized water reactor nuclear power units was typically 10 μg·kg⁻¹. -1 Even higher. In the 1990s and early 2000s, the industry worked together to reduce the accumulation of corrosion products within the SG (Self-Supporting Surface) system, aiming for concentrations below 3 μg / kg in feedwater. -1 This is quite typical, and in many cases it has reached below 1 ug·kg. -1 The iron concentration in feedwater under full-power conditions during future fuel cycles is estimated at 2 ppb, based on the steady-state iron concentration range exhibited by PWR units in my country and combined with domestic and international experience. In all cases, it is assumed that the average feedwater iron concentration during steady-state operation in past cycles was obtained from actual measurements; if no actual measurements were performed, it can be estimated at 3 ppb.

[0091] Corrosion products from the secondary loop of a nuclear power plant are transported to the secondary side of the steam generator along with feedwater. Inside the SG (Stationary Heat Transfer Unit), they remain suspended or gradually deposit, or can be removed through the blowdown system. The blowdown efficiency of these systems is typically low, and the vast majority of corrosion products accumulate continuously on the heat transfer tubes, support plates, and tube sheets. Although there can be significant differences between nuclear power plants, the deposit distribution within the SG is roughly as follows: tube bundles, including support plates, account for 75%, tube sheets for 10%, and blowdown for 15%. A large portion of the corrosion products transported to the SG originates from the restart process following a major overhaul. Considering this experience, the increased mass of this deposit needs to be assumed when predicting future deposit thickness and corresponding trends in thermal resistance. Based on industry experience, it is assumed that an additional 12% of corrosion products are transported to the SG during a single unit startup. Typically, the fouling composition of heat transfer tubes in a nuclear power plant SG is assumed to be 95% Fe3O4, 1% metallic copper, 1% nickel ferrite, and 3% other components. This composition is considered typical for copper-free pressurized water reactor nuclear power plants. Sediment porosity follows a typical evolution process, starting at about 30% in the early stages of commercial operation, decreasing to about 20% after 10 years of operation, and eventually dropping to about 4% after many years due to continuous maturation / densification.

[0092] Based on the above input, the thickness of deposits on the SG tube bundles during the 60-year service life of a CRP1000 nuclear power unit was calculated, and the predicted results are as follows: Figure 2As shown in the figure, the blue line represents the typical trend without any measures, indicating that the sediment thickness increases linearly with increasing operating time. After 60 years of operation, the secondary side sediment mass of this SG tube bundle reached 2466 kg, with an average thickness of approximately 95 μm.

[0093] Based on the current corrosion product concentration level and the usage of pH control agents, the cumulative amount of corrosion products on the steam generator tube bundle over its lifespan is predicted, including worst-case, appropriate, and best-case scenarios. The thickness of the deposits on the tube bundle depends, in order of importance, on the expected feedwater iron inflow rate, deposit composition, and porosity. Based on the operating experience of the CRP1000 unit, feedwater iron concentrations of 5 ppb, 2 ppb, and 0.7 ppb are selected as three levels, and prediction calculations are performed according to the formulas in steps 1 and 2. Figure 2 The figure shows the sediment mass at a concentration of 2 ppb. As shown, the sediment thickness increases linearly with increasing operating time. After 60 years of operation, the secondary side sediment mass of this SG tube bundle reached 2466 kg, with an average thickness of approximately 95 μm. The relationship between sediment thickness and service time determines the future thermal resistance of the sediment and the degree of reduction in steam-side pressure, such as... Figure 3 and Figure 4 As shown, the operating status of the steam generator can then be determined.

[0094] Step 4: Evaluation and prediction of the effectiveness of governance measures

[0095] When deposits accumulate to a certain level in a steam generator, chemical cleaning is necessary. Generally, chemical cleaning processes designed to remove all magnetic-based deposits from a steam generator (SG) are called hard chemical cleaning. Processes designed to remove only a portion of the magnetic-based deposits, or only the non-magnetic-based portions of the deposits, are called soft chemical cleaning. Soft chemical cleaning, also known as ASCA (Association for Coal Calibration) or diluted chemical cleaning, causes corrosion of carbon steel of 20-100 μm, far less than the 200 μm corrosion of hardening cleaning. Therefore, it can be applied multiple times. Hard chemical cleaning, on the other hand, is only applied once during its service life. B&W recommends that SG chemical cleaning be performed when the deposit weight on the SG tube bundle reaches 108-150 g / m. 2 .

[0096] The red trend line represents the effect of soft chemical cleaning (ASCA, Advanced Scale Conditioning Agent). Each application removes a portion of the accumulated deposits within the steam generator (SG). After multiple applications, the deposits on the surface of the steam generator heat transfer tubes are gradually and completely removed. Hard chemical cleaning (SGCC, Steam Generator Chemical Clean) can completely remove all deposits from the steam generator in one go, restoring the deposits within the SG to their initial commercial operation condition. The deposit condition after application is shown by the green trend line in the figure.

[0097] If the ASCA (Automatic Steering and Cleaning) strategy is adopted, approximately 317.5 kg of deposits will be removed from the SG (Self-Stabilizing Unit) each time. This is based on industry experience, including applications in units in Japan, South Korea, and the United States. In the short term, soft chemical cleaning significantly enhances heat transfer. With repeated applications, thermal resistance can be further reduced. If repeated applications continue, the thermal resistance will eventually return to the clean state of initial commercial operation (where thermal resistance change is 0).

[0098] The thermal resistance and steam pressure of accumulated deposits in the steam generator of a CRP1000 unit during its service life were predicted and calculated. With increasing operating time, without intervention or remediation, after 60 years of service, when the average thickness of accumulated deposits on the tube bundle reaches approximately 95 μm, the corresponding increase in thermal resistance is 3.08 × 10⁻⁶. -5 m 2 ·℃·W -1 (Corresponding to a 460 kPa reduction in steam pressure). After initial application of ASCA, the fouling thermal resistance decreased by approximately 4.54 × 10⁻⁶ kPa. -6 m 2 ·℃·W -1 (Corresponds to a 60 kPa increase in steam pressure). For example... Figure 3 and Figure 4 As shown, this effect may result from the outer scale layer more effectively promoting boiling, or from the solidified inner layer becoming thinner, or a combination of both. The application of ASCA can produce such results, as confirmed by laboratory tests and experience from numerous nuclear power plants over the past few years.

[0099] Following a typical full-tube hard chemical cleaning (SGCC) application, the initial best-estimated deposition thermal resistance returns to the clean state value at the start of commercial operation (thermal resistance change is 0). In subsequent cycles, the thermal resistance increases significantly. Over the following years of operation, due to the formation of a thin, heat-enhancing deposit layer, the thermal resistance decreases sharply and rapidly, then increases again at a rate similar to that before deposit removal. The magnitude of the initial increase and subsequent decrease is primarily based on actual nuclear power plant operating conditions. The short-term surge in thermal resistance after hard chemical cleaning is based on industry experience from many nuclear power plants. SGCC hard chemical cleaning should be implemented with caution in nuclear power plants. Although hard chemical cleaning is effective (restoring steam pressure to initial commercial operation levels), it causes severe corrosion to internal components of the steam generator, significantly delays unit overhauls, and is itself costly, thus having a significant impact on the economics of nuclear power plants.

[0100] The advantages of this invention are as follows: An online graded sampling device for the main feedwater and wastewater of the steam generator is designed, enabling real-time and accurate accumulation of the mass of corrosion products in the steam generator, and achieving precise calculation of the fouling input of the CRP1000 unit steam generator; based on sediment enrichment and unit operating conditions, a prediction model formula for sediment thickness, thermal resistance, and secondary steam pressure during the service life of the CRP1000 unit steam generator is proposed, and the application effect of treatment measures is predicted and evaluated. This invention can provide guidance for the safe and economical operation of CRP1000 unit steam generators in my country, filling the gap in supervision and management of CRP1000 and similar steam generators.

[0101] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for evaluating the operating status of a steam generator, characterized in that, Includes the following steps: The feedwater and drainage of the steam generator were simultaneously sampled online using an online sampling device to obtain the mass of corrosion products in the feedwater and drainage during the sampling time. Based on the obtained corrosion product mass, calculate the amount of accumulated corrosion products in the steam generator under the current condition; Based on the current accumulation of corrosion products in the steam generator, calculate the future heat transfer resistance of the deposits and the actual steam pressure of the steam generator; The online sampling device includes a sampling inlet pipe, a sampling circuit and a bypass, and a sampling trench. The two ends of the sampling circuit and the bypass are respectively connected to the sampling inlet pipe and the sampling trench. Multiple filters are sequentially arranged on the sampling circuit. A sampling bypass is arranged between adjacent filters. The other end of the sampling bypass is connected to the sampling trench. The sampling circuit is equipped with three filters in sequence, each with a different pore size of the filter membrane. The pore size of the filter membrane gradually decreases from the filter near the sampling inlet pipe end to the filter near the sampling trench end. The sampling bypass is equipped with a sampling bypass valve and a sampling flow meter. The amount of accumulated corrosion products is calculated according to the following formula: m=∑m 给水 -∑m 排污 In the formula, m represents the amount of corrosion products accumulated in a single steam generator within a certain fuel cycle; m 给水 This refers to the cumulative amount of corrosion products that migrate from feedwater to the secondary side of a single steam generator within a given fuel cycle over one week; m 排污 The cumulative amount of waste corrosion products from a single steam generator over one week within a given fuel cycle; m 给水 =F 给水 ×C Fe给水 m 排污 =F 排污 ×C Fe排污 In the formula, F 给水 C represents the cumulative feedwater flow rate per week for a single steam generator. Fe给水 The iron content in the water for the current week; C Fe排污 Iron content in wastewater discharged during the week; F 排污 The cumulative drainage flow rate of a single steam generator over one week; The total iron content of the water supply and the total iron content of the wastewater are calculated using the following formula: The total iron content is: C 总铁 (ppb) = Suspended iron content C Fe (ppb) + Iron content in filtrate C2(ppb) Suspended iron content C Fe (ppb) is calculated using the following formula: In the formula, the iron concentration C1 (ppb) of the cellulose acetate filter membrane used for sampling is obtained by taking it out, dissolving it in concentrated acid and making it to a fixed volume, and then analyzing it. The iron concentration C0 (ppb) of the blank filter membrane is obtained by dissolving it in concentrated acid and making it to a fixed volume.

2. The evaluation method according to claim 1, characterized in that, The filter membrane pore sizes in the filter are 0.4–3 μm, 0.1–0.4 μm, and 0.05–0.1 μm, respectively.

3. The evaluation method according to claim 1 or 2, characterized in that, A main valve is installed on the sampling inlet pipeline; a sampling valve is installed on the sampling circuit; and a bypass valve is installed on the bypass.

4. The evaluation method according to claim 1, characterized in that, A sampling flow meter is installed on the sampling circuit; a bypass flow meter is installed on the bypass circuit.

5. The evaluation method according to claim 1 or 4, characterized in that, The fluid Reynolds number in the sampling circuit and sampling bypass pipeline is greater than or equal to 8000.

6. The evaluation method according to claim 1, characterized in that, The sampling time is 7 days during the stable operation phase of the unit; and the cumulative sampling time for corrosion products during the start-up phase of the unit is 1 day.

7. The evaluation method according to claim 1, characterized in that, The future heat transfer resistance of the deposits in the steam generator and the actual steam pressure are calculated using the following formula: In the formula: k f The thermal conductivity of the sediment is W / (m·K); k mg The thermal conductivity of Fe3O4 is given in W / (m·K); k v ε is the saturated steam thermal conductivity, W / (m·K); f Porosity of sediments; In the formula: R f Represents the future thermal resistance of the sediment; e f The thickness of the sediment is in meters (m). P=f·R f In the formula: P is the actual steam pressure, in bar; f is the correction factor for thermal resistance and steam pressure.

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