Calculation method for seawater design temperature of nuclear power plant in operation

Abstract

The invention discloses a method for calculating the seawater design temperature of an in-operation nuclear power plant, and belongs to the technical field of calculation of the seawater design temperature of the nuclear power plant. Comprising the following steps: collecting real-time monitoring seawater temperature data; setting a seawater temperature special observation station, and collecting data of the seawater temperature special observation station; eliminating distorted temperature data of a nuclear power plant circulating cooling water system and a nuclear island important service water system; the method comprises the following steps of: drawing a scatter diagram in a two-dimensional coordinate system by taking data of a special observation station for seawater temperature as an x value and taking real-time monitored seawater temperature data of a nuclear power plant as a y value, and preliminarily judging a correlation between two groups of data; and calculating a correlation coefficient r between the x value and the y value until the correlation is significant, and then calculating the design temperatures of the circulating cooling water system and the important service water system. According to the method, the influence coefficient of the vertical temperature stratification of the natural water body does not need to be calculated, and the influence of the warm discharged water backflow of the nuclear power plant on the final hot trap cooling water is included in the water taking actual measurement temperature data.

Description

Technical Field

[0001] The present invention relates to the technical field of calculating the seawater design temperature of nuclear power plants, and in particular to a method for calculating the seawater design temperature of operating nuclear power plants. Background Art

[0002] The ultimate heat sink forms of nuclear power plants mainly include the atmosphere and water bodies. For nuclear power plants adjacent to large rivers, large lakes or the ocean, directly using the surrounding water bodies as the cooling medium not only has high cooling efficiency but also simple operation. The value of the seawater design temperature is crucial for the design of the main equipment of the nuclear power plant, the operation mode of the unit, and nuclear safety assurance. In the past, the calculation of the seawater design temperature was mainly carried out in the engineering design stage, and most of the work focused on the temperature drainage return flow of the nuclear power plant and the vertical stratification of the water body temperature. The service life of nuclear power plants is relatively long, and there is a lack of systematic research on the long-term change trend of seawater temperature caused by climate change during the service life of nuclear power plants.

[0003] The siting characteristics of nuclear power plants make it difficult to obtain long-term water temperature observation data in the sea area of the plant site during the engineering design stage, and it is necessary to extend and analyze the plant site data based on the long-term data of nearby ocean observation stations. Usually, the nearby ocean stations are far from the plant site, and the distance can reach dozens or even hundreds of kilometers. For the nearshore sea area with complex water temperature distribution changes, there are problems such as weak correlation and inconsistent change rules between the water temperature of the nearby ocean station and the plant site. Therefore, the seawater design temperature calculated in the engineering design stage may have problems such as insufficient representativeness of the seawater temperature change trend and excessive adjustment of the operation mode of operating nuclear power plants.

[0004] Many domestic and foreign materials on the calculation method of the design temperature of nuclear power plants have clear requirements for the water temperature data used: the water temperature data should be the measured data in the engineering sea area. If there is a lack of measured series data in the engineering sea area, a hydrological observation point should be set up at the depth of the water intake of the engineering water area to establish a correlation with the station with long-term water temperature data in the vicinity. The length of the measured data should not be less than 1 year. For operating nuclear power plants, ignoring the temperature change of the water body in the water intake pump house, the "measured water temperature data of the nuclear power plant water intake" is an intuitive manifestation of the water temperature at the water intake of the engineering sea area and is the most direct data for calculating the seawater design temperature.

[0005] Previous calculation methods mainly targeted the nuclear power plant construction stage. At this stage, the nuclear power plant has not been built yet. When calculating the designed water temperature, it mainly relied on short-term seawater temperature observation data at the plant site and long-term seawater temperature observation data from nearby ocean stations. The calculation method mainly considered three factors: the water body stratification coefficient, the influence coefficient of warm water discharge reflux, and the statistical water temperature of the natural water body. Among them, the influence of warm water discharge reflux was mainly based on physical model or mathematical model tests, and the water body stratification coefficient was based on empirical coefficients. There were significant subjective influencing factors in the determination process of these two coefficients. In addition, the seawater designed temperature calculated during the engineering design stage may have problems such as insufficient representativeness of the seawater temperature change trend and excessive adjustment of the operating mode of the in-service nuclear power plant.

[0006] Therefore, a calculation method for the seawater designed temperature of in-service nuclear power plants is needed to avoid calculating the influence coefficient of the vertical temperature stratification of the natural water body and to additionally consider the temperature rise influence of warm water discharge. Summary of the Invention

[0007] The object of the present invention is to propose a calculation method for the seawater designed temperature of in-service nuclear power plants, including the following steps:

[0008] Collect real-time monitored seawater temperature data with an interval of 1 hour at the inlets of the nuclear power plant's circulating cooling water system and the important service water system of the nuclear island.

[0009] Set up dedicated seawater temperature observation stations at the nuclear power plant's water intake and in the sea area of the water intake channel, and collect data from the dedicated seawater temperature observation stations for measuring the seawater temperature in the hottest and coldest 3 months within 1 year in the nuclear power plant's water area.

[0010] Eliminate distorted temperature data of the nuclear power plant's circulating cooling water system and the important service water system of the nuclear island.

[0011] Take the data from the dedicated seawater temperature observation stations as the x value and the real-time monitored seawater temperature data of the nuclear power plant as the y value, draw a scatter plot in a two-dimensional coordinate system, and preliminarily judge the correlation between the two sets of data according to the distribution state of the scatter points.

[0012] Calculate the correlation coefficient r between the x value and the y value. If the correlation is significant, calculate the designed temperatures of the circulating cooling water system and the important service water system based on the real-time monitored seawater temperature data of the in-service nuclear power plant; if the correlation is not significant, re-collect the data from the dedicated seawater temperature observation stations for correlation analysis until the correlation is significant, and then calculate the designed temperatures of the circulating cooling water system and the important service water system.

[0013] Furthermore, the calculation formula for the correlation coefficient r is:

[0014]

[0015] Among them, n represents the number of data, x represents the average value of the data of the special seawater temperature observation station, y represents the average value of the real-time monitored seawater temperature data of the nuclear power plant, x i represents the i-th data of the special seawater temperature observation station, and y i represents the i-th data of the real-time monitored seawater temperature of the nuclear power plant.

[0016] Furthermore, the criterion for significant correlation is that the correlation coefficient r is greater than 0.9.

[0017] Furthermore, if the water intake method of the nuclear power plant is open channel water intake and the vertical stratification of the water body temperature in the sea area of the plant site is obvious, first calculate the vertical mixing temperature of the seawater at the plant site, and then use the vertical mixing temperature of the seawater at the plant site as the x value and the real-time monitored seawater temperature data of the nuclear power plant as the y value for correlation analysis.

[0018] Furthermore, the calculation formula for the vertical mixing temperature of the seawater at the plant site is as follows:

[0019]

[0020] Among them, T 垂向混合 represents the vertical mixing temperature of the seawater at the plant site, T 表层 represents the seawater surface temperature, °C; T 中层 represents the seawater middle layer temperature, °C; T 底层 represents the seawater bottom layer temperature, °C.

[0021] Furthermore, the formula for calculating the design temperature of the important component cooling water system based on the real-time monitored seawater temperature data of the operating nuclear power plant is as follows:

[0022] T 设计基准 = T 7历年最高 / 日平均 + ΔT climate

[0023] T 设计最高 = T max统计 + ΔT climate + ΔT fluctuation / max

[0024] T 设计最低 = T min统计

[0025] ΔT climate is obtained by converting the temperature rise value over a hundred-year change to within the service life of the nuclear power plant:

[0026]

[0027] Among them, T 设计基准 represents the design reference temperature of the important component cooling water system, °C; T 设计最高 represents the design maximum temperature of the important component cooling water system, °C; T 设计最低Represents the lowest temperature for the design of the essential service water system, °C; T 7历年最高 / 日平均 Represents the highest value of the average temperature of the 7th highest day of each year over the years, °C; T max统计 Represents the maximum value among the measured water intake temperatures hour by hour over the years, °C; T min统计 Represents the minimum value among the measured water intake temperatures hour by hour over the years, °C; ΔT climate Is the long-term change trend of water temperature under the background of climate change, °C; ΔT fluctuation / max Is the maximum value of the sea water temperature fluctuation in different years, °C; ΔT 100年温升 Represents the change value of sea water temperature during a 100-year period, °C; T 寿期 Represents the designed operating period of the nuclear power plant, years.

[0028] Furthermore, the formula for calculating the design temperature of the circulating cooling water system based on the real-time monitored sea water temperature data of operating nuclear power plants is as follows:

[0029] T 设计基准 = T 历年平均值 + ΔT climate

[0030] T 设计最高 = T 最热3月 / 10％日均 + ΔT climate + ΔT fluctuation / max

[0031] T 设计最低 = T min统计

[0032] Among them, T 历年平均值 Represents the average value of the measured water intake temperatures over the years, °C; T 最热3月 / 10％日均 Is the average temperature of the hottest three months of each year over the years arranged from largest to smallest, and the 10th percentile temperature value is taken, °C.

[0033] The beneficial effects of the present invention are as follows:

[0034] 1. For the essential service water system (SEC) and the circulating cooling water system (CRF) of the nuclear power plant of the present invention, the monitored water body temperature is fully mixed and uniform, and there is no need to calculate the influence coefficient of the vertical temperature stratification of the natural water body; the influence of the nuclear power plant's warm water discharge reflux on the cooling water of the ultimate heat sink is already included in the measured water intake temperature data, and there is no need to consider it additionally.

[0035] 2. The design temperatures of the SEC system and the CRF system of the operating nuclear power plant proposed by the present invention consider the long-term change trend of water temperature (ΔT climate ) under the background of climate change and the maximum value of the sea water temperature fluctuation in different years (ΔT fluctuation / max ). The calculated temperature obtained by its calculation method can better consider the temperature change situation during the service life of the nuclear power plant.

[0036] 3. The design temperatures of the SEC system and CRF system of an operating nuclear power plant proposed in the present invention are more representative of the water temperature at the plant site, and can better serve the safe operation and maintenance of the operating nuclear power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The figure is a schematic diagram of the overall flow of the method for calculating the design temperature of seawater in an operating nuclear power plant according to the present invention.

[0038] Figure 2 This is a correlation analysis chart of the observed temperature of the water intake channel of a coastal nuclear power plant in the south and the temperature monitored by the SEC system.

[0039] Figure 3 This is a long-term trend chart of sea surface temperature in the waters of a coastal nuclear power plant in the south. DETAILED DESCRIPTION

[0040] The present invention provides a method for calculating the design temperature of seawater in an operating nuclear power plant. The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0041] Figure 1 The figure is a schematic diagram of the overall flow of the method for calculating the design temperature of seawater in an operating nuclear power plant according to the present invention, which specifically includes the following steps:

[0042] 1. Collect the measured water temperature data since the operation of the nuclear power plant, including the real-time monitoring of seawater temperature data at the water inlet of the nuclear power plant's circulating cooling water system (CRF) and the nuclear power plant's important service water system (SEC), with a data interval of 1 hour.

[0043] 2. Collect data from a dedicated seawater temperature observation station at the plant site. Set up dedicated seawater temperature observation stations at the nuclear power plant water intake and open water intake channel to measure the seawater temperature data for the hottest and coldest three months of the year in the nuclear power plant waters. If water is taken from a culvert, the seawater temperature observation instrument needs to be set at the depth of the water intake. If water is taken from an open channel, at least the seawater temperatures of the surface, middle and bottom layers of the open water intake channel need to be observed.

[0044] 3. Preprocessing of seawater temperature data. The actual measured water intake temperature of nuclear power plants has the following problems: the temperature monitoring of the CRF and SEC systems is distorted due to maintenance shutdown or fault operation. The operation and standby status switching of different columns of equipment in the SEC system causes the monitoring temperature of the standby equipment to be distorted. Distorted temperature data needs to be eliminated.

[0045] 4. Data visualization (scatter plot): Using the data recorded by the dedicated seawater temperature observation stations as the x-values and the measured temperature data of the seawater intake at the nuclear power plant as the y-values, a scatter plot is drawn in a two-dimensional coordinate system. Based on the distribution of the scatter points, a preliminary judgment is made on the type of correlation between the two sets of data. If the scatter points determined by the measured temperature data of the seawater intake at the nuclear power plant and the dedicated seawater temperature observation data are densely distributed on the line y = x, it indicates that the two sets of data are linearly correlated.

[0046] 5. Correlation analysis: The correlation coefficient r between the "measured temperature of the seawater intake at the nuclear power plant" and the "data of the dedicated seawater temperature observation station at the plant site" is calculated to measure the degree of correlation between the two sets of data. The larger the r value, the stronger the correlation between the two sets of data. The calculation formula for the correlation coefficient r is:

[0047]

[0048] where n represents the number of data points, represents the average value of the data of the dedicated seawater temperature observation station, represents the average value of the real-time monitored seawater temperature data of the nuclear power plant, x i represents the i-th data point of the dedicated seawater temperature observation station, y i represents the i-th data point of the real-time monitored seawater temperature of the nuclear power plant.

[0049] 6. Through the analysis in the above steps, it can be seen that if the correlation coefficient r between the measured temperature of the seawater intake at the operating nuclear power plant and the data of the dedicated seawater temperature observation station at the plant site is greater than 0.9, it indicates that the two sets of data are significantly correlated, proving that the measured temperature data of the seawater intake at the nuclear power plant can be used to replace the data of the seawater temperature at the plant site to calculate the designed seawater temperature. Moreover, since the measured temperature of the seawater intake at the operating nuclear power plant is the temperature that has been fully mixed and already includes the influence factor of the return of the warm drainage, when calculating the designed temperature of the important service water system (SEC) of the nuclear power plant based on the measured temperature of the seawater intake at the operating nuclear power plant, the long-term change trend of the water temperature (ΔT climate ) and the maximum value of the sea temperature fluctuation in different years (ΔT fluctuation / max ) under the background of climate change are mainly considered. The calculation formulas are as follows:

[0050] T 设计基准 = T 7历年最高 / 日平均 + ΔT climate

[0051] T 设计最高 = T max统计 + ΔT climate + ΔT fluctuation / max

[0052] T 设计最低 = T min统计

[0053] where T 设计基准Indicates the design basis temperature of the essential service water system, °C; T 设计最高 Indicates the design maximum temperature of the essential service water system, °C; T 设计最低 Indicates the design minimum temperature of the essential service water system, °C; T 7历年最高 / 日平均 、T max统计 、T min统计 Obtained by statistically analyzing the measured hourly water intake temperature data of the nuclear power plant; T 7历年最高 / 日平均 Is the highest value of the 7th highest daily average temperature of each year, T max统计 Is the maximum value obtained by arranging the measured hourly water intake temperature data of each year from largest to smallest, T min统计 Is the minimum value of the measured hourly water intake temperature data of each year, ΔT climate Converted to the nuclear power plant's service life range according to the temperature rise value over a hundred-year change:

[0054]

[0055] Among them, ΔT 100年温升 Indicates the change value of seawater temperature during 100 years, °C; T 寿期 Indicates the design operation period of the nuclear power plant, years; ΔT fluctuation Is the difference between the observed or forecast value and the trend value in the long-term change prediction of seawater temperature. Considering leaving enough safety margin, take the maximum value in the analyzed years (ΔT fluctuation / max ) as the safety margin of the design maximum water temperature. During the analysis of correlation, if the water intake method of the nuclear power plant is open channel water intake and the vertical stratification of the water body temperature in the sea area of the plant site is obvious, there may be a phenomenon of weak correlation between the "measured water intake temperature data of the nuclear power plant" and the data of a certain layer of the "special seawater temperature observation station at the plant site". At this time, the "vertical mixing temperature of seawater at the plant site" needs to be calculated according to the following formula:

[0056]

[0057] Among them, T 表层 Indicates the surface seawater temperature, °C; T 中层 Indicates the middle layer seawater temperature, °C; T 底层 Indicates the bottom layer seawater temperature, °C.

[0058] Take T 垂向混合 As the x value and repeat the process from the fourth step to the sixth step to analyze the correlation between the "measured water intake temperature data of the nuclear power plant" and the "vertical mixing temperature of seawater at the plant site".

[0059] When calculating the design temperature of the circulating cooling water system (CRF) based on the measured water intake temperature of the operating nuclear power plant, the long-term change trend of water temperature (ΔT climate ) and the maximum value of seawater temperature fluctuation in different years (ΔT fluctuation / max ) are mainly considered. The calculation formula is as follows:

[0060] T 设计基准 = T 历年平均值 + ΔT climate

[0061] T 设计最高 = T 最热3月 / 10％日均 + ΔT climate + ΔT fluctuation / max

[0062] T 设计最低 = T min Statistics

[0063] T 历年平均值 represents the average value of the measured water intake temperature over the years, °C; T 最热3月 / 10％日均 is the average daily temperature of the hottest three months over the years arranged from largest to smallest, and the 10th percentile temperature value is taken.

[0064] This embodiment takes the data of a coastal nuclear power plant in the south as an example. Figure 2 is the correlation analysis diagram of the observed temperature in the water intake channel and the monitored temperature of the SEC system of a coastal nuclear power plant in the south. It can be seen that the correlation coefficient is 0.9961, indicating that the correlation between the two groups of data is significant. Figure 3 is the long-term change trend diagram of the sea surface temperature in the sea area of a coastal nuclear power plant in the south. SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 represent four core future test scenarios in the long-term predicted seawater temperature model, which are the low-emission scenario, the medium-emission scenario, the regional competition scenario, and the high-emission scenario in sequence. It can be seen that the temperature increase trend is obvious during the service life of the nuclear power plant.

[0065] For the important station service water system (SEC) and the circulating cooling water system (CRF) of the nuclear power plant of the present invention, the monitored water body temperature is fully mixed and uniform, and there is no need to calculate the influence coefficient of the vertical temperature stratification of the natural water body; moreover, the influence of the nuclear power plant's warm water discharge return on the cooling water of the final heat sink is already included in the measured water intake temperature data, and there is no need to consider it additionally, which can better serve the safe operation and maintenance of the operating nuclear power plant.

Claims

1. A calculation method for the design seawater temperature of an operating nuclear power plant, characterized in that, The steps are as follows: Collect the real-time monitored seawater temperature data with an interval of 1 hour at the water inlets of the circulating cooling water system and the important service water system in the nuclear island of the nuclear power plant; Set up special seawater temperature observation stations at the water intake of the nuclear power plant and in the sea area of the water intake open channel respectively, and collect the data of the special seawater temperature observation stations for measuring the seawater temperature in the hottest and coldest three months within one year in the waters of the nuclear power plant; Eliminate the distorted temperature data of the circulating cooling water system and the important service water system in the nuclear island; Take the data of the special seawater temperature observation station as the x value and the real-time monitored seawater temperature data of the nuclear power plant as the y value, draw a scatter plot in the two-dimensional coordinate system, and preliminarily judge the correlation between the two sets of data according to the distribution state of the scatter points; Calculate the correlation coefficient r between the x value and the y value. If the correlation is significant, calculate the design temperatures of the circulating cooling water system and the important service water system based on the real-time monitored seawater temperature data of the operating nuclear power plant; If the correlation is not significant, re-collect the data of the special seawater temperature observation station for correlation analysis until the correlation is significant, and then calculate the design temperatures of the circulating cooling water system and the important service water system.

2. The calculation method for the designed seawater temperature of an operating nuclear power plant according to claim 1, wherein The calculation formula for the correlation coefficient r is as follows: Among them, n represents the number of data, represents the average value of the data of the special observation station for seawater temperature, represents the average value of the real-time monitored seawater temperature data of the nuclear power plant, x i represents the i-th data of the special observation station for seawater temperature, y i represents the i-th data of the real-time monitored seawater temperature of the nuclear power plant.

3. The calculation method for the designed seawater temperature of an operating nuclear power plant according to claim 1 or 2, characterized in that, The criterion for significant correlation is that the correlation coefficient r is greater than 0.

9.

4. The calculation method for the designed seawater temperature of a nuclear power plant in operation according to claim 3, characterized in that If the water intake method of the nuclear power plant is open channel water intake and the vertical stratification of the water body temperature in the sea area of the plant site is obvious, first calculate the vertical mixing temperature of the seawater at the plant site, and then take the vertical mixing temperature of the seawater at the plant site as the x value and the real-time monitored seawater temperature data of the nuclear power plant as the y value for correlation analysis.

5. The calculation method for the designed seawater temperature of an operating nuclear power plant according to claim 4, characterized in that, The calculation formula for the vertical mixing temperature of the seawater at the plant site is as follows: Among them, T 垂向混合 represents the vertical mixing temperature of seawater at the plant site, T 表层 represents the surface seawater temperature, °C; T 中层 represents the middle-layer seawater temperature, °C; T 底层 represents the bottom-layer seawater temperature, °C.

6. The calculation method for the seawater design temperature of a nuclear power plant in operation according to claim 4 or 5, characterized in that, The formula for calculating the design temperature of the important service water system based on the real-time monitored seawater temperature data of the operating nuclear power plant is as follows: T 设计基准 = T 7历年最高 / 日平均 + ΔT climate T 设计最高 = T max统计 + ΔT climate + ΔT fluctuation / max T 设计最低 = T min统计 ΔT climate Converted from the temperature rise value over a century to the lifespan of the nuclear power plant, it is obtained that: Among them, T 设计基准 represents the design basis temperature of the essential service water system, °C; T 设计最高 represents the design maximum temperature of the essential service water system, °C; T 设计最低 represents the design minimum temperature of the essential service water system, °C; T 7历年最高 / 日平均 represents the highest value of the average temperature of the 7th highest day of each year, °C; T max统计 represents the maximum value of the measured water intake temperature hour by hour over the years, °C; T min统计 represents the minimum value of the measured water intake temperature hour by hour over the years, °C; ΔT climate is the long-term change trend of water temperature under the background of climate change, °C; ΔT fluctuation / max is the maximum value of the sea water temperature fluctuation in different years, °C; ΔT 100年温升 represents the change value of sea water temperature during 100 years, °C; T 寿期 represents the designed operation period of the nuclear power plant, years.

7. The calculation method for the designed seawater temperature of an operating nuclear power plant according to claim 6, characterized in that, The formula for calculating the design temperature of the circulating cooling water system based on the real-time monitored seawater temperature data of the operating nuclear power plant is as follows: T 设计基准 = T 历年平均值 + ΔT climate T 设计最高 = T 最热3月 / 10％日均 + ΔT climate + ΔT fluctuation / max T 设计最低 = T min统计 Among them, T 历年平均值 represents the average value of the measured water intake temperature over the years, in °C; T 最热3月 / 10％日均 is the average daily temperature of the hottest three months over the years arranged from largest to smallest, and the 10%th temperature value is taken.

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