Method for evaluating quality of anti-combustion oil of main steam isolation valve of nuclear power plant

Abstract

The application relates to the technical field of nuclear power plant oil control, in particular to a quality evaluation method for main steam isolation valve fire-resistant oil of a nuclear power plant. The quality evaluation method provided by the application comprises the following steps: taking used fire-resistant oil samples with different acid values from a plurality of main steam isolation valves; adding unused fire-resistant oil with different proportions to the used fire-resistant oil samples to obtain a plurality of mixed oil samples; aging the mixed oil samples and monitoring the acid values of the mixed oil samples until at least 30 days of aging and the acid values of each mixed oil sample after aging exceed 9 mgKOH / g, and then stopping the aging; and evaluating the quality of the used fire-resistant oil samples according to the growth trend of the acid values of the mixed oil samples with aging time. The application can analyze the change of the main steam isolation valve fire-resistant oil according to the growth trend of the acid values of the mixed oil samples, provide data support for whether the fire-resistant oil can continue to be used, and thus better facilitate the safe operation of equipment.

Description

Technical Field

[0001] This application belongs to the field of nuclear power plant oil control technology, and in particular relates to a quality assessment method for fire-resistant oil in the main steam isolation valve of a nuclear power plant. Background Technology

[0002] A pressurized water reactor (PWR) nuclear power plant mainly consists of a nuclear steam supply system (primary loop), a turbine generator system (secondary loop), and other auxiliary systems. The main steam isolation valve is a nuclear safety-grade valve used in the secondary loop main steam system (VVP) of a PWR nuclear power plant. It is primarily located on the roofs of nuclear safety-related buildings and electrical buildings, outside the containment structure, and is one of the major critical pieces of equipment in the nuclear power plant. The main function of the main steam isolation valve is to provide containment isolation for the main steam piping, preventing containment overpressure caused by a rupture in the main steam piping, and limiting the cooling of the main system due to a rupture in the steam piping or main feedwater piping. Simultaneously, it prevents the diffusion of radioactive media from the primary loop into the secondary loop in the event of a rupture in the steam generator heat transfer tubes.

[0003] The main steam isolation valve uses fire-resistant oil, which has advantages such as flame retardancy, good anti-wear properties, and stable physical properties. Due to the importance of the main steam isolation valve, the quality of the fire-resistant oil used in it needs to be properly monitored. Currently, there is no clear monitoring standard for the quality of the main steam isolation valve oil; monitoring is only carried out with reference to the operating oil standard of the turbine speed control system. However, due to the differences between the two, the reference effect is limited. In order to ensure the long-term safe operation of the equipment, it is necessary to reasonably regulate and control the oil quality of the main steam isolation valve during operation, and a quality assessment method for the fire-resistant oil of the main steam isolation valve that conforms to the actual production conditions on site is required. Summary of the Invention

[0004] The purpose of this application is to provide a quality assessment method for fire-resistant oil in the main steam isolation valve of a nuclear power plant, aiming to solve the technical problem of how to better assess the quality of fire-resistant oil in the main steam isolation valve of a nuclear power plant in order to provide early warning and improve the safety of equipment operation.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] This application provides a method for quality assessment of fire-resistant oil for main steam isolation valves in nuclear power plants, including:

[0007] Take used fire-resistant oil samples with different acid values ​​from multiple main steam isolation valves;

[0008] Different proportions of unused fire-resistant oil were added to the used fire-resistant oil sample to obtain multiple mixed oil samples;

[0009] The mixed oil samples were aged and the acid value of the mixed oil samples was monitored until aging lasted for at least 30 days and the acid value of each mixed oil sample after aging exceeded 9 mg KOH / g.

[0010] The quality of the used fire-resistant oil was evaluated based on the relationship between the acid value of the mixed oil sample and the aging time.

[0011] The quality assessment method for fire-resistant oil in the main steam isolation valve of a nuclear power plant provided in this application involves aging multiple mixed oil samples obtained by mixing used fire-resistant oil samples with unused fire-resistant oil in the main steam isolation valve, monitoring the acid value during the aging process, and assessing the quality of the used fire-resistant oil based on the growth trend of the acid value of the mixed oil samples with aging time. This process can analyze the changes in the fire-resistant oil quality of the main steam isolation valve based on the growth trend of the acid value of the mixed oil samples, providing data support for whether the fire-resistant oil should continue to be used. This allows for early warning, clarifies oil replacement standards, improves work efficiency, reduces cost waste, and better facilitates the safe operation of the equipment. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a graph showing the change in acid value of a fire-resistant oil sample with an acid value of 1.19 mg KOH / g after use, mixed with different proportions of unused fire-resistant oil, as a function of aging time.

[0014] Figure 2 This is a graph showing the change in acid value of a fire-resistant oil sample with an acid value of 0.32 mg KOH / g after use, mixed with different proportions of unused fire-resistant oil, as a function of aging time.

[0015] Figure 3 This is a graph showing the change in acid value of a fire-resistant oil sample with an acid value of 8.01 mg KOH / g after use, mixed with different proportions of unused fire-resistant oil, as a function of aging time.

[0016] Figure 4 This is a graph showing the change in acid value of a fire-resistant oil sample with an acid value of 6.89 mg KOH / g after use, mixed with different proportions of unused fire-resistant oil, as a function of aging time. Detailed Implementation

[0017] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0018] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0019] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items.

[0020] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0021] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0022] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0023] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0024] Since the operation of the pressurized water reactor nuclear power units in the nuclear power base, there has been no clear monitoring standard for the quality of the fire-resistant oil used in the main steam isolation valve. The monitoring is only carried out with reference to the operating oil standard of the turbine speed control system. However, because the two conditions are different, it is difficult to provide good guidance for the use of fire-resistant oil in the main steam isolation valve.

[0025] Because the main steam isolation valve operates at high temperatures and lacks its own oil purification system, the fire-resistant oil in the main steam isolation valve is highly susceptible to aging. During the operation of a nuclear power plant unit, flocculent matter appeared in the fire-resistant oil of the main steam isolation valve, making it difficult to meet quality requirements. Upon disassembly, corrosion was found on the surfaces of components such as the copper sleeve and large piston, causing blockage of the high-pressure filter at the pump outlet. Once the high-pressure filter loses its filtering function, the deteriorated fire-resistant oil will directly enter the entire oil system, affecting the reliability of every component and threatening the safe operation of the unit. Since it is difficult to sample and analyze the fire-resistant oil in the main steam isolation valve during routine unit operation, if the oil quality is found to be substandard during a major overhaul, an oil change is necessary. Oil changes during overhauls often involve managing project timelines and incur significant manpower, time, and oil costs. Therefore, reasonable monitoring of the fire-resistant oil quality in the main steam isolation valve is crucial for the safe operation of the equipment.

[0026] Based on this, this application provides a quality assessment method for fire-resistant oil in the main steam isolation valve of a nuclear power plant, providing key support for unit decision-making in nuclear power plants. By conducting early warning analysis of the fire-resistant oil quality in the main steam isolation valve, the oil replacement standards can be clarified, improving work efficiency and reducing costs during overhauls. The specific technical solution is as follows.

[0027] This application provides a method for quality assessment of fire-resistant oil for main steam isolation valves in nuclear power plants. Specifically, the quality assessment method of this application includes:

[0028] S01: Take used fire-resistant oil samples with different acid values ​​from multiple main steam isolation valves;

[0029] S02: Add different proportions of unused fire-resistant oil to the used fire-resistant oil sample to obtain multiple mixed oil samples;

[0030] S03: The mixed oil samples are aged and the acid value of the mixed oil samples is monitored until aging is completed for at least 30 days and the acid value of each mixed oil sample exceeds 9 mg KOH / g after aging.

[0031] S04: The quality of fire-resistant oil after use is evaluated based on the relationship between the acid value of the mixed oil sample and the aging time.

[0032] It should be noted that the various terms mentioned in the quality assessment method of this application are explained as follows.

[0033] "Fire-resistant oil" is a synthetic oil with low volatility, good anti-wear properties, and physical stability. It is generally composed of phosphate ester liquids, and its flame retardancy is one of its most prominent characteristics. It is typically used in electro-hydraulic control systems of power plants. This application's embodiment focuses on the quality assessment of fire-resistant oil used in the main steam isolation valves of nuclear power plants.

[0034] "Used fire-resistant oil samples" refer to fire-resistant oil samples taken from the main steam isolation valve after the nuclear power plant unit has been in operation, i.e., used fire-resistant oil that has already been in operation. This application's embodiments analyze oil samples from multiple main steam isolation valves. These oil samples have different acid values ​​and can be oil samples from the same unit or different units. It is necessary to find used fire-resistant oil samples with different acid values ​​to facilitate the subsequent preparation of multiple mixed oil samples for analysis.

[0035] "Unused fire-resistant oil" refers to fire-resistant oil samples that have not been installed in the main steam isolation valve, i.e., new fire-resistant oil that is not in operation. It can be synthetic fire-resistant oil ready for use or fire-resistant oil that has just been purchased and is ready for use.

[0036] "Mixed oil sample" refers to a mixed oil sample obtained by mixing the aforementioned used fire-resistant oil sample with a certain proportion of unused fire-resistant oil, and subsequently analyzing the change trend of its acid value with aging time. Among them, when subsequent aging treatment is carried out, adding 0% unused fire-resistant oil (i.e., no new fire-resistant oil is added) and adding 100% unused fire-resistant oil (i.e., replacing all used fire-resistant oil samples with new fire-resistant oil) can be regarded as special cases of mixed oil samples for aging treatment and acid value analysis.

[0037] "Acid value" indicates the number of milligrams of potassium hydroxide (KOH) required to neutralize 1 gram of a chemical substance. It is a measurement standard for the number of free carboxylic acid groups in a compound or mixture, and is commonly used to measure the acidic components in materials such as greases, lubricants, and plastics. The sample in this application is a fire-resistant oil, and its acid value test method refers to the national standard GB / T264 "Determination of Acid Value of Petroleum Products".

[0038] The quality assessment method of this application embodiment first obtains multiple used fire-resistant oil samples with different acid values, then adds different proportions of unused fire-resistant oil to obtain multiple mixed oil samples. These mixed oil samples are aged until at least 30 days, and the acid value of each mixed oil sample exceeds 9 mg KOH / g, after which aging is stopped. The relationship between the acid value of the mixed oil samples and the growth trend of aging time is analyzed, so as to evaluate the quality of the used fire-resistant oil. By analyzing the growth trend of the acid value of the mixed oil samples, the changes in the fire-resistant oil quality of the main steam isolation valve can be analyzed, providing data support for whether the fire-resistant oil should continue to be used. This allows for early warning, clarifies oil change standards, improves work efficiency, reduces cost waste, and better facilitates the safe operation of equipment.

[0039] During subsequent overhauls of nuclear power plants, the applicant utilized the aforementioned quality assessment method to sample and test the oil in the main steam isolation valve. The analysis results showed that the quality of the fire-resistant oil in the VVP main steam isolation valve could be well controlled, ensuring that the oil was less prone to flocculent formation during daily operation and slowing down the degree of oil deterioration.

[0040] Step S01: Preparation of fire-resistant oil samples after use.

[0041] Multiple used fire-resistant oil samples can be fire-resistant oil samples from the main steam isolation valves of the same unit or different units. It is necessary to ensure that each used fire-resistant oil sample has a different acid value to facilitate the preparation of samples for subsequent aging tests. For example, a nuclear power plant has multiple pressurized water reactor nuclear power units, each with 3 main steam isolation valves. Used fire-resistant oil samples with different acid values ​​can be found from these different main steam isolation valves.

[0042] In some embodiments, the properties of the main steam isolation valve oil generally change after one fuel cycle. To explore the acid value growth pattern of the main steam isolation valve fire-resistant oil, an aging test can be conducted on the main steam isolation valve fire-resistant oil after one fuel cycle of use by developing a detailed experimental plan. This will determine the service life of the oil and ensure that the oil quality does not continue to deteriorate in the next fuel cycle. This will enable the equipment to operate safely for a longer period of time and better standardize oil quality testing and quality control during operation.

[0043] One fuel cycle refers to the period from the completion of refueling and restarting of a nuclear power plant unit to the next shutdown for refueling. A certain nuclear power plant unit currently undergoes refueling approximately every 18 months, followed by shutdown for maintenance during the refueling window; therefore, one fuel cycle is approximately 18 months. Taking one fuel cycle as an example, through analysis and statistical analysis of the oil quality test data of the VVP main steam isolation valve fire-resistant oil during each major overhaul, it was found that the oil properties of the VVP main steam isolation valve fire-resistant oil changed after one fuel cycle. Furthermore, the acid value growth trend after mixing fire-resistant oil with different proportions of new oil and different acid values ​​was examined to determine the changes in fire-resistant oil quality during operation.

[0044] Step S02: Prepare the mixed oil sample.

[0045] Based on the acid value of the fire-resistant oil sample after the main steam isolation valve was used, the unused fire-resistant oil (i.e., new oil) and the used fire-resistant oil sample were mixed in a preset ratio to obtain multiple mixed oil samples containing different proportions of new oil.

[0046] In some embodiments, the used fire-resistant oil sample and the unused fire-resistant oil can be phosphate ester fire-resistant oils of the same material. Specifically, they can be phosphate ester fire-resistant oils of the same brand, for example, AKZO Fyrquel EHC.

[0047] In some embodiments, the step of adding different proportions of unused fire-resistant oil to a used fire-resistant oil sample includes: (1) if the acid value of the used fire-resistant oil sample is <1.5 mg KOH / g, then adding different proportions of unused fire-resistant oil to the used fire-resistant oil sample at a ratio of 0 to 15% of the total volume; (2) if the acid value of the used fire-resistant oil sample is ≥1.5 mg KOH / g, then adding different proportions of unused fire-resistant oil to the used fire-resistant oil sample at a ratio of 25 to 100% of the total volume.

[0048] Based on a total volume of used and unused fire-resistant oil samples of 100%, if the acid value of the used fire-resistant oil sample is <1.5 mg KOH / g, the mixing ratio of unused fire-resistant oil is 0-15%. If the acid value of the used fire-resistant oil sample is ≥1.5 mg KOH / g, the mixing ratio of unused fire-resistant oil is 25-100%. For each used fire-resistant oil sample with a different acid value, different proportions of unused fire-resistant oil can be added within the above range to obtain multiple mixed oil samples. Of course, the more mixed oil samples prepared, the better. Specifically, 3-5 mixed oil samples can be prepared according to actual needs. The main purpose is to verify, through experiments, the rate of acid value increase after aging of the mixed oil samples after mixing new and old oils in different proportions, thereby verifying the rate of oil aging.

[0049] Specifically, if the acid value of the used fire-resistant oil sample is <1.5 mg KOH / g, then add it to the used fire-resistant oil sample at a percentage of 0%, 5%, 10%, and 15% of the total volume of unused fire-resistant oil; if the acid value of the used fire-resistant oil sample is ≥1.5 mg KOH / g, then add it to the used fire-resistant oil sample at a percentage of 25%, 50%, 75%, and 100% of the total volume of unused fire-resistant oil.

[0050] Step S03: Aging treatment.

[0051] The acid value generally increases during the aging process. The standard for stopping aging is: aging for at least 30 days, and the acid value of each mixed oil sample exceeding 9 mg KOH / g. If, after 30 days, the acid value of some mixed oil samples is less than 9 mg KOH / g, aging continues until the acid value of all samples exceeds 9 mg KOH / g.

[0052] In some embodiments, the aging treatment temperature is 118–122°C. The aging treatment can be carried out in a laboratory oven, which facilitates setting the temperature conditions required for aging.

[0053] In some embodiments, the aging treatment is carried out under conditions containing a composite catalyst of copper and iron. The volume-to-weight ratio of the mixed oil sample to copper is 100 mL: 0.4–0.6 g; the volume-to-weight ratio of the mixed oil sample to iron is 100 mL: 2.4–2.6 g.

[0054] In some embodiments, aging the mixed oil samples and monitoring their acid values ​​includes: during the aging process, (1) if the acid value of the mixed oil sample is ≤0.2 mgKOH / g, the acid value of the mixed oil sample is measured every 4 to 5 days; (2) if 0.2 mgKOH / g < acid value of the mixed oil sample ≤0.5 mgKOH / g, the acid value of the mixed oil sample is measured every 1 to 2 days; (3) if 0.5 mgKOH / g < acid value of the mixed oil sample ≤1.5 mgKOH / g, the acid value of the mixed oil sample is measured daily; (4) if 1.5 mgKOH / g < acid value of the mixed oil sample ≤9 mgKOH / g, the acid value of the mixed oil sample is measured every 4 to 5 days; (5) if the acid value of the mixed oil sample is >9 mgKOH / g, the acid value of the mixed oil sample is measured every 6 to 7 days. The analysis is performed according to the above-mentioned frequency based on the acid value of each sample.

[0055] Generally, if the acid value of the mixed oil sample is ≤0.2 mgKOH / g, it will exceed 0.2 mgKOH / g in about 9-10 days; if 0.2 mgKOH / g < acid value of the mixed oil sample ≤0.5 mgKOH / g, it will exceed 0.5 mgKOH / g in about 2-3 days; if 0.5 mgKOH / g < acid value of the mixed oil sample ≤1.5 mgKOH / g, it will exceed 1.5 mgKOH / g in about 5-6 days; if 1.5 mgKOH / g < acid value of the mixed oil sample ≤9 mgKOH / g, it will exceed 9 mgKOH / g in about 18-20 days. Finally, on the 30th day after aging, the acid value of all samples can be tested once to determine the conditions for stopping acid value measurement: the samples have been aged for 30 days and the acid value of all oil samples exceeds 9 mgKOH / g.

[0056] Step S04: Quality assessment.

[0057] In some embodiments, evaluating the quality of used fire-resistant oil samples includes: (1) if the acid value of the used fire-resistant oil sample is less than 1.5 mg KOH / g, the used fire-resistant oil sample can continue to be used; (2) if the acid value of the used fire-resistant oil sample is equal to or greater than 1.5 mg KOH / g, at least 15% of unused fire-resistant oil by volume can be added to the used fire-resistant oil sample before continued use, or the used fire-resistant oil sample can be discontinued. For example, if the acid value of the used fire-resistant oil sample is in the range of 1.5 to 8 mg KOH / g, 15% to 90% of unused fire-resistant oil by volume can be added to the used fire-resistant oil sample before continued use; if the acid value of the used fire-resistant oil sample exceeds 8 mg KOH / g, the used fire-resistant oil sample can be discontinued.

[0058] Through quality assessment and analysis, when the acid value of the used fire-resistant oil sample is below 1.5 mg KOH / g, its acid value growth trend after aging is basically consistent with that of the mixed oil sample containing unused fire-resistant oil. Therefore, the used fire-resistant oil sample with such an acid value can continue to be used and generally will not deteriorate rapidly immediately. When the acid value of the used fire-resistant oil sample is between 1.5 and 8 mg KOH / g, the acid value growth trend of mixed oil samples with different proportions of unused fire-resistant oil is examined to determine the oil quality changes after adding unused fire-resistant oil during operation (accounting for 15% to 90% of the total volume), providing data support for adding fire-resistant oil when the level is low during routine operation. When the acid value of the used fire-resistant oil sample is greater than 8 mg KOH / g, the acid value growth trend of mixed oil samples with different proportions of unused fire-resistant oil is examined to provide data support for oil changes in extreme cases. For example, if the acid value reaches above 8 mg KOH / g, it can be considered to discontinue the use of the used fire-resistant oil sample and use 100% new oil.

[0059] In some embodiments, the quality assessment method further includes detecting the kinematic viscosity and particulate contamination of the used fire-resistant oil sample.

[0060] To develop more reasonable and feasible oil quality control standards, this study, based on the characteristics of the VVP main steam isolation valve equipment and the properties of fire-resistant oil, and combined with years of field experience at nuclear power plants, summarized the relevant factors contributing to oil degradation in the VVP main steam isolation valve. Oil performance verification tests were conducted in the laboratory. The main reasons for the reduced performance of the fire-resistant oil in the main steam isolation valve were analyzed as follows: excessively high operating oil temperature leading to oil aging; localized high temperatures in the oil system; and high water content in the oil causing hydrolysis and resulting in a high acid value. Besides acid value, kinematic viscosity and particulate contamination are also important indicators of oil quality deterioration. Therefore, abnormal indicators of the fire-resistant oil in the main steam isolation valve can be further focused on acid value, kinematic viscosity, and particulate contamination.

[0061] Among them, based on the quality assessment method of this application embodiment and combined with years of field experience in nuclear power bases, the following indicators are specified for the fire-resistant oil of the main steam isolation valve: (1) Acid value: ≤1.5mgKOH / g; the test method can refer to the national standard GB / T264 "Determination of Acid Value of Petroleum Products". (2) Kinematic viscosity (40℃): 28.8~35.2mm 2 / s(IOS VG32) / 41.4~50.6mm 2 / s(IOS VG46); the test method can refer to the national standard GB / T265 "Petroleum Products Engler Viscosity Determination Method". (3) Particle contamination degree (AS4059F): ≤8 / 8; the test method can refer to the power industry standard DL / T432-2007 "Method for Measurement of Particle Contamination Degree in Power Oil".

[0062] Based on years of practical experience with fire-resistant oil for main steam isolation valves, and combined with system manuals, maintenance outlines, and laboratory mixing test results, the applicant selected acid value, and further adopted kinematic viscosity and particulate contamination degree as the three indicators for quality control and monitoring of VVP main steam isolation valve operating oil. This led to the development of VVP main steam isolation valve operating oil quality control and oil change diagnostic standards. These standards are used to evaluate the quality assessment method for fire-resistant oil in nuclear power plant main steam isolation valves as described in this application.

[0063] The implementation of the standard for main steam isolation valves in nuclear power plants can reduce the frequent problem of oil exceeding the quality standards when referring to the operating and maintenance guidelines for phosphate ester fire-resistant oil used in power plants. This aligns with field practice and saves manpower and oil costs while ensuring equipment safety. Combined with the quality assessment method in the embodiments of this application, it can significantly improve the early warning capability of nuclear safety equipment faults, providing a solid foundation for ensuring the safety and reliability of equipment.

[0064] Through field practice, the quality assessment method of this application embodiment can promptly detect equipment anomalies and take early intervention measures, effectively improving the safety of nuclear power plant units. Therefore, the oil quality monitoring and assessment of the fire-resistant oil of the main steam isolation valve can serve as a diagnostic standard for oil replacement in nuclear power plant main steam isolation valves, and has broad promotion and application value in the nuclear power industry.

[0065] The following description is based on specific embodiments.

[0066] Example 1

[0067] A quality assessment method for fire-resistant oil in the main steam isolation valve of a nuclear power plant, comprising the following specific steps:

[0068] Step 1: After one fuel cycle of a pressurized water reactor nuclear power plant unit, use fire-resistant oil samples with different acid values ​​are obtained from multiple main steam isolation valves;

[0069] Step 2: Based on the acid value of the used fire-resistant oil samples after the main steam isolation valve is used, mix the unused fire-resistant oil (i.e., new oil) with the used fire-resistant oil samples according to a preset ratio to obtain multiple mixed oil samples. The preset ratios are as follows: if the acid value of the used fire-resistant oil sample is <1.5mgKOH / g, the total volume percentage of the unused fire-resistant oil mixed in is 0%, 5%, 10%, and 15%, respectively; if the acid value of the used fire-resistant oil sample is ≥1.5mgKOH / g, the total volume percentage of the unused fire-resistant oil mixed in is 90%, 75%, 50%, and 25%, respectively. The used and unused fire-resistant oil samples are from the same brand (AKZOFyrquel EHC).

[0070] Step 3: Aging treatment was carried out on the above-mentioned multiple mixed oil samples (120℃ high temperature, aging with copper and iron catalysts, wherein 1g of copper and 5g of iron were added for every 200mL of mixed oil sample), and the initial acid value of each mixed oil sample was measured with reference to the method of national standard GB / T264. Based on the acid value of each mixed oil sample, the acid value was monitored at the following analysis frequency during the aging process.

[0071] 1) Acid value ≤ 0.2 mg KOH / g, acid value measured at 5-day intervals;

[0072] 2) If the acid value is between 0.2 mg KOH / g and 0.5 mg KOH / g, measure the acid value at 2-day intervals.

[0073] 3) 0.5 mg KOH / g < acid value ≤ 1.5 mg KOH / g, measure the acid value daily;

[0074] 4) If the acid value is between 1.5 mg KOH / g and 9 mg KOH / g, measure the acid value every 5 days.

[0075] 5) If the acid value is >9 mg KOH / g, measure the acid value every 7 days;

[0076] On the 30th day after aging, the acid value of all samples was tested once, and the conditions for stopping aging were determined: the samples were aged for at least 30 days and the acid value of all oil samples exceeded 9 mg KOH / g.

[0077] Step 4: Analyze each sample and record its acid value, obtaining a trend chart of acid value growth over aging time for each sample; based on the acid value trend chart and experimental results, the following conclusions can be drawn:

[0078] a) After using one fuel cycle, the acid value of the fire-resistant oil after the main steam isolation valve is determined. When the acid value of the fire-resistant oil after use is less than 1.5 mg KOH / g, the growth trend of its acid value after aging is basically consistent with the growth trend of the mixed oil sample after mixing with some new oil. The oil can continue to be used to ensure that it will not deteriorate sharply in the next fuel cycle.

[0079] b) Examine the acid value growth trend after mixing different proportions of unused new oil with used fire-fighting oil with an acid value of 1.5–8 mg KOH / g, in order to determine the changes in oil quality after replenishing fire-fighting oil during operation. For example, replenishing with new oil accounting for 15%–90% of the total volume will provide data support for replenishing fire-fighting oil when the level is low during routine operation.

[0080] c) Examine the acid value growth trend after mixing different proportions of unused new oil with used fire-resistant oil with an acid value exceeding 8 mg KOH / g. For example, if the acid value reaches 8 mg KOH / g or higher, it may be considered to discontinue the use of the used fire-resistant oil sample to provide data support for oil change in extreme cases.

[0081] See Figures 1-4 This is a graph showing the trend of acid value change over aging time for a mixture of four used fire-resistant oil samples with unused fire-resistant oil, obtained according to the above quality assessment method. Specifically: the first used fire-resistant oil sample is designated L2VVP001VV (acid value 1.19 mg KOH / g), the second is designated L2VVP002VV (acid value 0.32 mg KOH / g), the third is designated L2VVP003VV (acid value 8.01 mg KOH / g), and the fourth is designated D2VVP002VV (acid value 6.89 mg KOH / g). The horizontal axis represents aging time (unit: days, specifically 10 days, 20 days, 30 days, 40 days, 50 days, etc.), and the vertical axis represents acid value (unit: mgKOH / g, specifically 1 mgKOH / g, 2 mgKOH / g, 3 mgKOH / g, 4 mgKOH / g, 5 mgKOH / g, 6 mgKOH / g, etc.). "0% Mixed Oil" means no new oil was added; "5% Mixed Oil" means new oil accounted for 5% of the total volume; "10% Mixed Oil" means new oil accounted for 10% of the total volume; "15% Mixed Oil" means new oil accounted for 15% of the total volume; "25% Mixed Oil" means new oil accounted for 25% of the total volume; "50% Mixed Oil" means new oil accounted for 50% of the total volume; "75% Mixed Oil" means new oil accounted for 75% of the total volume; "90% Mixed Oil" means new oil accounted for 90% of the total volume; and "100% Mixed Oil" means the fire-resistant oil sample was completely replaced with new oil after use. Therefore, the acid value growth trend of the first and second fire-resistant oil samples after aging is basically consistent with the growth trend of the mixed oil samples containing some new oil, and continued use can be considered. The fourth fire-resistant oil sample can be considered for continued use after adding 75% or even 90% new oil to the total volume. The third fire-resistant oil sample can be considered for discontinuation.

[0082] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for quality assessment of fire-resistant oil for main steam isolation valves in nuclear power plants, characterized in that, include: Take used fire-resistant oil samples with different acid values ​​from multiple main steam isolation valves; Different proportions of unused fire-resistant oil were added to the used fire-resistant oil sample to obtain multiple mixed oil samples; The mixed oil samples were aged and the acid value of the mixed oil samples was monitored until aging lasted for at least 30 days and the acid value of each mixed oil sample after aging exceeded 9 mg KOH / g. The quality of the used fire-resistant oil sample was evaluated based on the increasing trend of the acid value of the mixed oil sample with aging time. The steps of adding different proportions of unused fire-resistant oil to the used fire-resistant oil sample include: If the acid value of the used fire-resistant oil sample is <1.5mgKOH / g, then add different proportions of the unused fire-resistant oil to the used fire-resistant oil sample according to the percentage of the unused fire-resistant oil in the total volume of 0~15%. If the acid value of the used fire-resistant oil sample is ≥1.5mgKOH / g, then add different proportions of the unused fire-resistant oil to the used fire-resistant oil sample according to the percentage of the unused fire-resistant oil in the total volume being 25~100%. The quality assessment of the used fire-resistant oil samples includes: If the acid value of the used fire-resistant oil sample is less than 1.5 mg KOH / g, then the used fire-resistant oil sample can continue to be used. If the acid value of the used fire-resistant oil sample is equal to or greater than 1.5 mg KOH / g, then add at least 15% of the unused fire-resistant oil by volume to the used fire-resistant oil sample and continue using it, or discontinue using the used fire-resistant oil sample.

2. The quality assessment method as described in claim 1, characterized in that, If the acid value of the used fire-resistant oil sample is <1.5mgKOH / g, then add the unused fire-resistant oil to the used fire-resistant oil sample at a percentage of 0%, 5%, 10%, and 15% of the total volume, respectively. If the acid value of the used fire-resistant oil sample is ≥1.5 mg KOH / g, then the unused fire-resistant oil is added to the used fire-resistant oil sample at a percentage of 25%, 50%, 75%, and 100% of the total volume, respectively.

3. The quality assessment method as described in claim 1, characterized in that, The aging treatment temperature is 118~122℃.

4. The quality assessment method as described in claim 1, characterized in that, The aging process was carried out under conditions containing a composite catalyst of copper and iron.

5. The quality assessment method as described in claim 4, characterized in that, The volume ratio of the mixed oil sample to the weight of the copper is 100 mL: 0.4~0.6 g; and / or, the volume ratio of the mixed oil sample to the weight of the iron is 100 mL: 2.4~2.6 g.

6. The quality assessment method as described in claim 1, characterized in that, The process of aging the mixed oil sample and monitoring its acid value includes: During the aging process, if the acid value of the mixed oil sample is ≤0.2mgKOH / g, the acid value of the mixed oil sample is measured every 4-5 days; if 0.2mgKOH / g < acid value of the mixed oil sample ≤0.5mgKOH / g, the acid value of the mixed oil sample is measured every 1-2 days; if 0.5mgKOH / g < acid value of the mixed oil sample ≤1.5mgKOH / g, the acid value of the mixed oil sample is measured daily; if 1.5mgKOH / g < acid value of the mixed oil sample ≤9mgKOH / g, the acid value of the mixed oil sample is measured every 4-5 days; if the acid value of the mixed oil sample >9mgKOH / g, the acid value of the mixed oil sample is measured every 6-7 days.

7. The quality assessment method according to any one of claims 1-6, characterized in that, Also includes: The kinematic viscosity and particulate contamination level of the used fire-resistant oil samples were tested.

8. The quality assessment method according to any one of claims 1-6, characterized in that, The used fire-resistant oil sample and the unused fire-resistant oil are both phosphate ester fire-resistant oils of the same material.

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