JP2021124360A - Nuclear reactor water-level measurement system and nuclear reactor water-level measurement method - Google Patents

Abstract

To provide a nuclear reactor water-level measurement art that can measure an in-pile water level consistently during from a normal operation to a severe accident.SOLUTION: A nuclear reactor water-level measurement system 1 comprises: a prediction model preparation unit 13 that analyzes a relationship between an in-pile water level analyzed by an accident analysis unit 11 and a water-level measurement value analyzed by a water-level measurement value analysis unit 12, and prepares a prediction model to be used in predicting an in-pile water level from a plurality of water-level measurement values; a data accumulation unit 10 that accumulates a water-level measurement value actually measured in a nuclear reactor 19 by a plurality of kinds of water-level gauges 5 to 7; an in-pile water level prediction unit 14 that predicts an actual in-pile water level in the nuclear reactor 19 on the basis of respective water-level measurement values accumulated in the data accumulation unit 10 and the prediction model prepared by the prediction model preparation unit 13; and an in-pile information output unit 15 that outputs in-pile information on the in-pile water level predicted by the in-pile water level prediction unit 14.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to a reactor water level measurement system and a reactor water level measurement method.

When a severe accident occurs in a nuclear reactor plant, it is necessary to understand the internal situation of the reactor in order to decide the countermeasures. In particular, in order to grasp the cooling or damage state of the fuel, information on the internal conditions such as the water level inside the reactor pressure vessel (RPV) is extremely important. As a method for measuring the water level in a reactor, in a general boiling water reactor (BWR), a condensing tank and a reference water column detection pipe connected to the steam phase part of the RPV and a fluctuating water column detection pipe connected to the liquid phase part of the RPV. A differential pressure type water level gauge that detects the differential pressure due to the above is used. However, in the accident at the nuclear power plant following the Great East Japan Earthquake, the water level in the reactor containment vessel (PCV) could not be measured because the water in the reference water column detection pipe and the fluctuating water column detection pipe became hot and evaporated. rice field. Since this accident, a plurality of water level gauges with different principles have been proposed in order to accurately measure the water level in the reactor even in the event of a severe accident.

JP-A-2007-205912 Japanese Unexamined Patent Publication No. 2008-170223

While water level gauges assuming severe accidents have been proposed, the conventional differential pressure type is also effective for measuring the water level in the furnace during normal operation, and it is considered to be highly reliable from many years of experience. .. In the event of a severe accident, it is extremely important to measure the water level in the furnace, but there is a problem that there is no water level gauge that can consistently respond from normal operation to the time of a severe accident.

An embodiment of the present invention has been made in consideration of such circumstances, and provides a reactor water level measurement technique capable of consistently measuring the water level in a reactor from normal operation to a severe accident. The purpose.

The reactor water level measurement system according to the embodiment of the present invention includes an accident analysis unit that analyzes a severe accident in a reactor and analyzes the water level in the reactor corresponding to the progress of the severe accident, and analyzes the severe accident. Based on this, the water level measurement value analysis unit that analyzes the water level measurement values measured according to the progress status by a plurality of types of water level meters having different measurement principles, and the in-core water level analyzed by the accident analysis unit. A prediction model creation unit that analyzes the relationship between the water level measurement values analyzed by the water level measurement value analysis unit and creates a prediction model used for predicting the in-furnace water level from a plurality of the water level measurement values, and a plurality of prediction model creation units. It is created by the data accumulation unit that accumulates the water level measurement values actually measured in the reactor by the water level gauge of the type, the water level measurement values accumulated in the data accumulation unit, and the prediction model creation unit. A furnace that outputs in-core information regarding the in-core water level predicted by the in-core water level prediction unit and the in-core water level prediction unit that predicts the in-core water level of the actual reactor based on the prediction model. It is equipped with an internal information output unit.

An embodiment of the present invention provides a reactor water level measurement technique capable of consistently measuring the water level in a reactor from normal operation to a severe accident.

The block diagram which shows the reactor water level measurement system of this embodiment. Sectional drawing which shows the nuclear reactor. Explanatory drawing which shows the measurement principle of a thermocouple type water level gauge. The graph which shows the example of the output signal of the thermocouple type water level gauge. The graph which shows the measurement principle of a radiation type water level gauge. Explanatory drawing which shows the in-core situation data set. Explanatory drawing which shows the measured value data set. A graph showing the water level in the furnace at the time of a severe accident. A graph showing the pressure inside the furnace at the time of a severe accident. A graph showing the temperature inside the furnace at the time of a severe accident. A graph showing the measured values of multiple types of water level gauges. A graph showing the actual reactor water level and the predicted reactor water level. The flowchart which shows the reactor water level measurement method.

Hereinafter, embodiments of the reactor water level measurement system and the reactor water level measurement method will be described in detail with reference to the drawings.

Reference numeral 1 in FIG. 1 is the reactor water level measurement system of the present embodiment. This reactor water level measurement system 1 is used in a reactor plant to consistently measure the water level in the reactor from the time of normal operation to the time of a severe accident.

The reactor water level measurement system 1 includes a water level measurement unit 2, an in-reactor measurement unit 3, and a water level prediction computer 4.

The water level measuring unit 2 includes a plurality of types (three types) of water level gauges 5 to 7 having different measurement principles. The water level measuring unit 2 of the present embodiment includes a differential pressure type water level gauge 5 as a type 1 water level gauge, a thermocouple type water level gauge 6 as a type 2 water level gauge, and a radiation type water level gauge as a type 3 water level gauge. 7 and.

It is sufficient that at least two of these water level gauges 5 to 7 are provided. In this way, it is possible to provide a plurality of types of water level gauges 5 to 7 having different durability against severe accidents. It is preferable that at least one water level gauge 7 operates without losing its function from the time of normal operation to the time of a severe accident. In addition to these water level gauges 5 to 7, a water level gauge having another measurement principle may be provided.

The in-core measurement unit 3 includes an in-core thermometer 8 and an in-core pressure gauge 9. Further, the in-core measurement unit 3 may be provided with other measuring devices for grasping the situation in the furnace. The in-core thermometer 8 measures the temperature of the atmosphere inside the pressure vessel 22 (FIG. 2) (gas phase temperature) and the temperature of the furnace water 24 (liquid phase temperature). The in-core pressure gauge 9 measures the air pressure inside the pressure vessel 22.

The water level prediction computer 4 includes a data collection unit 10, an accident analysis unit 11, a water level measurement value analysis unit 12, a prediction model creation unit 13, an in-core water level prediction unit 14, an in-core information output unit 15, an information input unit 16, and a storage unit. A 17 and a main control unit 18 are provided.

The data collection unit 10 collects the water level measurement values (indicated values) actually measured in the reactor by a plurality of types of water level gauges 5 to 7. Each of the water level gauges 5 to 7 independently measures the water level in the furnace and transmits the measured water level value to the data collection unit 10.

The data collection unit 10 of the present embodiment collects the in-core temperature measurement values actually measured in the reactor by the in-core thermometer 8. Further, the data collection unit 10 collects the in-core pressure measurement values actually measured in the reactor by the in-core pressure gauge 9.

The data collection unit 10 collects the time when the water level measurement value is measured in each of the water level meters 5 to 7 in association with each water level measurement value. In this way, the water level in the furnace can be predicted based on the measured water level according to the situation of the severe accident that progresses in chronological order. The time of accumulation may be the elapsed time from the occurrence of a severe accident.

The accident analysis unit 11 analyzes the severe accident of the nuclear reactor in advance and analyzes the water level (true value) in the reactor corresponding to the progress of the severe accident.

The accident analysis unit 11 of the present embodiment simulates a severe accident, and changes with time corresponding to the progress of each parameter indicating at least one of the furnace temperature, the furnace pressure, the molten state of the fuel, and the water level in the furnace. Is analyzed, and an in-core condition data set (Fig. 6) is created in which the elapsed time from the occurrence of the severe accident and the parameters are associated with each other. In this way, it is possible to grasp the in-core condition corresponding to the elapsed time of the severe accident and obtain the in-core water level. The simulation performed by the accident analysis unit 11 includes not only a severe accident but also a simulation in the furnace during normal operation.

The water level measurement value analysis unit 12 analyzes the water level measurement values measured by the respective water level gauges 5 to 7 according to the progress of the severe accident based on the analysis of the severe accident using the accident analysis unit 11.

The water level measurement value analysis unit 12 of the present embodiment analyzes the water level measurement values measured by a plurality of types of water level gauges 5 to 7 based on the in-core condition data set (FIG. 6) created by the accident analysis unit 11. Then, a measured value data set (FIG. 7) in which the elapsed time and the measured water level are associated with each other is created. In this way, the water level in the furnace can be obtained based on the water level measurement value corresponding to the elapsed time of the severe accident.

The prediction model creation unit 13 analyzes the relationship between the in-furnace water level analyzed by the accident analysis unit 11 and the water level measurement value analyzed by the water level measurement value analysis unit 12. Furthermore, a prediction model used to predict the water level in the furnace from a plurality of water level measurements is created.

The prediction model is used to predict the water level in the furnace from multiple water level measurements by performing multiple regression analysis. In this way, the water level in the furnace can be predicted from a plurality of measured water level values by arithmetic processing based on the prediction model. The prediction model is a function for predicting the water level in the furnace, that is, a function for obtaining the water level in the furnace (true value) from the measured water level (indicated value) measured by a plurality of types of water level gauges 5 to 7. Includes configuration.

The prediction model creation unit 13 of the present embodiment uses the in-core water level as an objective variable and the measured water level as an explanatory variable based on the in-core data set (FIG. 6) and the measured value data set (FIG. 7). A prediction model used to predict the in-core water level from multiple water level measurements is created by performing regression analysis. In this way, it is possible to create a prediction model corresponding to the elapsed time.

Further, the prediction model creation unit 13 may create a prediction model used for predicting the water level in the furnace by adding a value other than the measured water level value as an explanatory variable. The value other than the measured water level value includes at least one of the value of the pressure inside the furnace and the value of the temperature inside the furnace. In this way, values other than the measured water level are used for predicting the water level in the furnace, so that the prediction accuracy can be improved.

In addition, the prediction model creation unit 13 analyzes the relationship between the water level measured by the water level gauge after damage due to a severe accident and the water level in the furnace, and creates a prediction model. In this way, the water level in the furnace can be predicted based on the information including the fact that the water level gauges 5 and 6 are damaged.

The in-core water level prediction unit 14 predicts the actual in-reactor water level of the reactor based on the respective water level measurement values accumulated in the data accumulation unit 10 and the prediction model created by the prediction model creation unit 13.

The in-core information output unit 15 outputs in-core information regarding the in-core water level predicted by the in-core water level prediction unit 14.

The water level prediction computer 4 of the present embodiment includes a display device such as a display that outputs the analysis result. That is, the in-core information output unit 15 controls the image displayed on the display. The display may be separate from the computer body or may be integrated. Further, the in-core information output unit 15 may control the image displayed on the display of another computer connected via the network.

In this embodiment, a display is illustrated as a display device, but other embodiments may be used. For example, information may be displayed using a projector. Further, a printer that prints information on a paper medium may be used instead of the display. That is, a projector or a printer may be included as an object to be controlled by the in-core information output unit 15.

The information input unit 16 inputs predetermined information according to the operation of the user who uses the water level prediction computer 4. The information input unit 16 includes an input device such as a mouse or a keyboard. That is, predetermined information is input to the information input unit 16 according to the operation of these input devices.

The storage unit 17 stores predetermined information. The storage unit 17 is composed of a memory or an HDD. The storage unit 17 may store a database, which is a collection of information organized so that it can be searched or stored. For example, the storage unit 17 may store the prediction model created by the prediction model creation unit 13.

The main control unit 18 comprehensively controls the water level prediction computer 4. The main control unit 18 may control the water level measuring unit 2.

The water level prediction computer 4 of the present embodiment has hardware resources such as a CPU, ROM, RAM, and HDD, and when the CPU executes various programs, information processing by software is realized by using the hardware resources. .. Further, the reactor water level measurement method of the present embodiment is realized by causing a computer to execute various programs.

At least the accident analysis unit 11, the water level measurement value analysis unit 12, the prediction model creation unit 13, and the in-core water level prediction unit 14 are realized by executing a program stored in the memory or HDD by the CPU.

As shown in FIG. 2, the nuclear reactor 19 provided in the nuclear power plant stores a core 21 composed of a plurality of fuel assemblies 20, a pressure vessel 22 for storing the core 21, and the pressure vessel 22. It is provided with a reactor containment vessel 23.

The pressure vessel 22 is a container for the core 21, and is a stainless steel structure that allows water as a coolant to flow between the pressure vessel and the outside while withstanding the high temperature and high pressure inside. Further, the reactor containment vessel 23 for accommodating the pressure vessel 22 also has a function of blocking the radioactive material and radiation generated in the core 21 from the outside so as not to leak. The water level in the furnace indicates the water level of the furnace water 24 inside the pressure vessel 22. That is, the value of the height from the bottom of the pressure vessel 22 to the water surface is shown.

Further, inside the pressure vessel 22, a steam separator 25 for separating steam from the furnace water 24 heated in the core 21 and a steam dryer 26 for drying the separated steam are provided. In addition, many other in-core structures are provided. Further, at the bottom of the pressure vessel 22, a recirculation pump 27 or the like for circulating the furnace water 24 inside the pressure vessel 22 is provided.

The reactor 19 of the present embodiment exemplifies ABWR (advanced boiling water reactor) of a boiling water reactor in which a reactor containment vessel 23 and a suppression chamber are integrally provided, but in other embodiments. There may be. For example, the present embodiment may be applied to a boiling water reactor (BWR) in which the reactor containment vessel 23 and the suppression chamber (torus chamber) are separately provided, or to a pressurized water reactor (PWR). The present embodiment may be applied.

The reactor 19 of the present embodiment includes a differential pressure type water level gauge 5 as a type 1 water level gauge, a thermocouple type water level gauge 6 as a type 2 water level gauge, and a radiation type water level gauge as a type 3 water level gauge. 7 and are provided.

The differential pressure type water level gauge 5 measures the water level inside the pressure vessel 22 by the pressure difference between the upper part and the lower part of the pressure vessel 22 of the reactor 19.

The differential pressure type water level gauge 5 includes a condensing tank 28, a reference water column detection pipe 29, a first fluctuating water column detection pipe 30, a second fluctuating water column detection pipe 31, a broadband differential pressure detection unit 32, and a fuel area differential pressure detection unit 33. ..

The condensing tank 28 is provided inside the reactor containment vessel 23 and outside the pressure vessel 22. The condensing tank 28 is connected to the upper part of the pressure vessel 22. Water collects in the condensing tank 28.

The reference water column detection pipe 29 is provided outside the pressure vessel 22. The reference water column detection pipe 29 extends diagonally downward from the condensing tank 28 and extends to the outside of the reactor containment vessel 23. The reference water column detection pipe 29 is branched in two directions. Each tip of the reference water column detection pipe 29 is connected to the broadband differential pressure detection unit 32 and the fuel area differential pressure detection unit 33.

The first fluctuating water column detection pipe 30 is provided outside the pressure vessel 22. The first variable water column detection pipe 30 is connected to the central portion in the vertical direction of the pressure vessel 22, extends diagonally downward, and further extends to the outside of the reactor containment vessel 23. The tip of the first fluctuating water column detection pipe 30 is connected to the broadband differential pressure detection unit 32.

The second variable water column detection pipe 31 is provided outside the pressure vessel 22. The second variable water column detection pipe 31 is connected to the bottom of the pressure vessel 22, extends diagonally downward, and further extends to the outside of the reactor containment vessel 23. The tip of the second fluctuating water column detection pipe 31 is connected to the fuel area differential pressure detection unit 33.

Water collects inside the reference water column detection pipe 29, the first variable water column detection pipe 30, and the second variable water column detection pipe 31. By detecting the pressure of the water inside this as a differential pressure, the water level in the furnace can be measured. For example, when the water level in the furnace drops, the differential pressure between the reference water column detection pipe 29 and the fluctuating water column detection pipes 30 and 31 increases, and when the water level in the furnace rises, the reference water column detection pipe 29 and the fluctuating water column detection pipe 30 , 31 and the differential pressure are reduced.

The wideband differential pressure detection unit 32 detects a change in the internal pressure of the reference water column detection pipe 29 and the internal pressure of the first fluctuating water column detection pipe 30 as the differential pressure. The broadband differential pressure detection unit 32 can be used for monitoring changes in the water level during normal operation and transient changes.

Further, the fuel area differential pressure detection unit 33 detects a change in the internal pressure of the reference water column detection pipe 29 and the internal pressure of the second fluctuating water column detection pipe 31 as the differential pressure. The fuel area differential pressure detection unit 33 can be used for confirming core flooding in the event of a severe accident.

The differential pressure type water level gauge 5 converts the differential pressure detected by the broadband differential pressure detection unit 32 and the fuel area differential pressure detection unit 33 into the in-core water level. The water level measurement value indicating the water level in the furnace is accumulated in the data collection unit 10. A value indicating the differential pressure before being converted as the water level in the furnace may be accumulated in the data collection unit 10 as a water level measurement value.

As shown in FIG. 2, the thermocouple type water level gauge 6 (differential thermocouple water level gauge) is a furnace inside the pressure vessel 22 by means of thermocouple elements 36 and 37 (FIG. 3) provided inside the pressure vessel 22. Measure the internal water level (gas-liquid boundary).

The thermocouple type water level gauge 6 has a plurality of sensor rods 34 provided between the fuel assemblies 20 of the core 21. These sensor rods 34 are tubular parts extending from the inside to the outside of the pressure vessel 22. Since the sensor rod 34 is provided inside the pressure vessel 22, the sensor rod 34 is in contact with the furnace water 24, and the water level in the furnace can be directly measured.

As shown in FIG. 3, inside one sensor rod 34, one heater 35 extending in the longitudinal direction thereof is provided. Further, the thermocouple element 36 for the hot contact and the thermocouple element 37 for the cold contact are provided in close proximity to each other.

Further, a heat insulating portion 38 is provided which surrounds the thermocouple element 36 for the hot contact together with the heater 35. A heat insulating portion 38 is not provided around the thermocouple element 37 for the cold contact. A set of sensor units 39 is composed of a heat insulating portion 38, a thermocouple element 36 for hot contacts, and a thermocouple element 37 for cold contacts.

A specific measurement principle will be described. The heater 35 heats both the thermocouple element 36 for hot contacts and the thermocouple element 37 for cold contacts. Since the thermal conductivity is different between the air and the water, the mode in which the heat 40 of the heater 35 is released to the outside differs depending on whether the sensor unit 39 is in the air or in the water.

For example, as shown in FIG. 3A, when the sensor unit 39 is underwater, the amount of heat released from the thermocouple element 36 for hot contacts and the release of the thermocouple element 37 for cold contacts 37. The difference in calorific value becomes large. Further, as shown in FIG. 3B, when the sensor unit 39 is in the air, the amount of heat released from the thermocouple element 36 for the hot contact and the heat radiation amount of the thermocouple element 37 for the cold contact The difference in heat dissipation is small. In this way, whether the sensor unit 39 is in the air or in the water is determined by the difference between the heat dissipation amount of the thermocouple element 36 for the hot contact and the heat dissipation amount of the thermocouple element 37 for the cold contact. Can be detected.

FIG. 4 shows a graph Q1 when the sensor unit 39 is in water and a graph Q2 when the sensor unit 39 is in the air. As described above, the output voltage of the output signal of the thermocouple type water level gauge 6 differs depending on whether the sensor unit 39 is in the air or in the water. For example, by setting the threshold value H in advance and determining whether or not the output voltage exceeds this threshold value H, it is possible to detect whether the sensor unit 39 is in the air or in the water.

The water level in the furnace can be measured by detecting whether each sensor unit 39 is in the air or in the water. The water level measurement value indicating the water level in the furnace is accumulated in the data collection unit 10. A value indicating the output voltage of the output signal of each sensor unit 39 may be integrated in the data accumulation unit 10 as a water level measurement value.

A plurality of sensor units 39 are arranged on the sensor rod 34 along the longitudinal direction thereof. For example, one sensor rod 34 is provided with nine sensor units 39 arranged in the vertical direction. With these sensor units 39, it is possible to measure at which height position the water surface of the furnace water 24 exists between the core 21 and the bottom of the pressure vessel 22. It suffices if it is possible to measure at least the height position of the reactor water 24 from the effective fuel top (TAF) to the effective fuel bottom (BAF) in the core 21.

As shown in FIG. 2, the radiation type water level gauge 7 measures the water level in the furnace inside the pressure vessel 22 by gamma rays 41 (radiation rays) emitted from the pressure vessel 22 to the outside. The radiation type water level gauge 7 is provided inside the reactor containment vessel 23 (biological shielding portion) and outside the pressure vessel 22.

The radiation type water level gauge 7 includes a plurality of dose detection units 42 arranged in the vertical direction along the pressure vessel 22. These dose detection units 42 are arranged from the center to the bottom of the pressure vessel 22. Each dose detection unit 42 is provided, for example, every 1 m in the height direction. Each dose detection unit 42 detects, for example, gamma rays 41 emitted from the core 21 (fuel). Then, the radiation type water level gauge 7 can measure the water level in the furnace by detecting the attenuation of the gamma ray 41 due to the water shielding effect.

The intensity of the gamma ray 41 is measured by each dose detection unit 42, and the height at which the difference (Δγ) of the gamma ray intensity of each dose detection unit 42 is maximized is determined as the water level in the furnace.

FIG. 5A is a graph showing the relationship between the radiation type water level gauge 7, the core 21 and the pressure vessel 22. FIG. 5B is a graph showing the gamma ray intensity at each height position measured by the radiation type water level gauge 7. FIG. 5C is a graph showing the difference in gamma ray intensity (Δγ).

For example, it is assumed that the in-core water level (WL) exists between the effective fuel top (TAF) and the effective fuel bottom (BAF) in the core 21 (FIG. 5 (A)). Here, the gamma ray intensity is attenuated in the portion where the furnace water 24 is present. On the other hand, the gamma ray intensity of the exposed portion of the fuel is not attenuated (FIG. 5 (B)).

In each dose detection unit 42, a portion where the difference (Δγ) with the adjacent dose detection unit 42 above or below is maximum is determined. This difference (Δγ) becomes maximum when the dose detection unit 42 immersed in the furnace water 24 and the dose detection unit 42 not immersed in the furnace water 24 are compared (FIG. 5 (C)).

It can be measured that the portion where this difference (Δγ) is maximized is the in-core water level (WL). The water level measurement value indicating the water level in the furnace is accumulated in the data collection unit 10. The gamma ray intensity value detected by each dose detection unit 42 or the value of the gamma ray intensity difference (Δγ) may be accumulated in the data accumulation unit 10 as a water level measurement value.

In the radiation type water level gauge 7 of the present embodiment, the water surface (gas-liquid boundary) of the furnace water 24 exists at any height position between the core 21 and the bottom of the pressure vessel 22 based on the intensity of the gamma ray 41. Can be measured. Further, the radiation type water level gauge 7 can measure the water level in the furnace from the outside of the pressure vessel 22 without contact. Therefore, even if the fuel is exposed or melted during a severe accident, the measurement of the water level in the furnace (gas-liquid boundary) can be continued.

Further, when the fuel melts and falls to the bottom of the pressure vessel 22, the emission mode of gamma rays also changes. For example, when the water level in the furnace drops and the core 21 is exposed from the furnace water 24, the intensity of the gamma rays 41 increases. Further, when the fuel is melted and melted down into the furnace water 24 at the bottom of the pressure vessel 22, the fuel is immersed in the furnace water 24 again, so that the gamma rays 41 are attenuated. And the strength comes to decrease. That is, the radiation type water level gauge 7 can grasp the cooling state and the melting state of the fuel at the time of a severe accident. It is also possible to grasp the distribution of fuel at the time of a severe accident.

As shown in FIG. 2, the differential pressure type water level gauge 5 loses its measuring function because the water inside the reference water column detection pipe 29 evaporates in the event of a severe accident. The thermocouple type water level gauge 6 can maintain the measurement of the water level in the furnace before the fuel is melted in a severe accident, but after the fuel is melted, the sensor rod 34 also melts, so that the measurement function Will be lost. On the other hand, since the radiation type water level gauge 7 is provided outside the pressure vessel 22 and can measure the water level in the furnace without contacting the pressure vessel 22 and the core 21, it has a measurement function even in the event of a severe accident. Will not be lost.

The analysis results obtained by simulating the severe accident of the reactor 19 by the accident analysis unit 11 will be described with reference to the graphs of FIGS. 8 to 12.

The accident analysis unit 11 performs a simulation when a severe accident such as a fuel melting accident occurs in a furnace type (for example, a boiling water type light water reactor) in which water level gauges 5 to 7 are installed, and determines the water level in the furnace at the time of the severe accident. Analyze changes in reactor temperature, reactor pressure, etc.

FIG. 8 is graphs G1 and G2 showing the water level in the furnace at the time of a severe accident evaluated by the accident analysis unit 11. The horizontal axis shows the elapsed time (unit is seconds), and the vertical axis shows the water level in the furnace (unit is meters). The collapse water level and the two-layer water level are used as the values of the water level in the furnace of this embodiment. Graph G1 shows the collapse water level, and graph G2 shows the two-layer water level. Since the definitions of the collapse water level and the two-layer water level are different, the graphs G1 and G2 do not always match.

When a severe accident occurs, the cooling of the fuel is delayed, so the water level in the furnace begins to drop sharply from the start (origin) of the severe accident. Fuel is exposed from the furnace water 24 due to the decrease in the water level in the furnace. Then, the graph G2 of the two-layer water level changes significantly at the time point F when the fuel melts and falls into the furnace water 24.

FIG. 9 is a graph G3 showing the pressure inside the furnace at the time of a severe accident evaluated by the accident analysis unit 11. The horizontal axis shows the elapsed time (unit is seconds), and the vertical axis shows the pressure inside the furnace (unit is megapascal).

The pressure inside the furnace rises at the start (origin) of a severe accident and decreases as the accident progresses. Then, at the time point F when the fuel melts and falls into the furnace water 24, the graph G3 of the pressure inside the furnace rises sharply.

FIG. 10 is graphs G4 and G5 showing the temperature inside the furnace at the time of a severe accident. The horizontal axis shows the elapsed time (unit is seconds), and the vertical axis shows the temperature inside the furnace (unit is ° C). Graph G4 shows the gas phase temperature, and graph G5 shows the liquid phase temperature.

The graph G4 of the gas phase temperature gradually rises from the start point (origin) of the severe accident as the accident progresses. The graph G5 of the liquidus temperature gradually decreases with the evaporation of the furnace water 24 from the start point (origin) of the severe accident. Then, at the time point F when the fuel melts and falls into the furnace water 24, the gas phase temperature graph G4 temporarily decreases, and the liquid phase temperature graph G5 temporarily increases.

As shown in FIG. 1, in the accident analysis unit 11, the reactor water level, the reactor temperature, the reactor pressure, and the fuel are corresponding to various accident scenarios assumed for the target reactor 19 in advance. Analyze the inside of the furnace such as the molten state and save the result. Further, the information in the furnace is transmitted to the water level measurement value analysis unit 12. Here, the accident analysis unit 11 creates an in-core situation data set and saves this in-core situation data set.

As shown in FIG. 6, in the furnace condition data set, information indicating the furnace water level, the furnace temperature, the furnace pressure, and the molten state of the fuel is registered in association with the elapsed time (progress status) of the severe accident. Will be done. In addition, other information in the furnace may be registered.

As shown in FIG. 1, in the water level measurement value analysis unit 12, the water level gauges 5 to 7 of all types installed in the target reactor 19 are based on the in-reactor information analyzed by the accident analysis unit 11. Analyze the measured water level (indicated value).

FIG. 11 is graphs G6 to G8 showing the water level measurement values of a plurality of types of water level gauges 5 to 7 analyzed by the water level measurement value analysis unit 12. The horizontal axis shows the elapsed time (unit is seconds), and the vertical axis shows the water level measurement value (unit is meters). Graph G6 shows the water level measurement value of the differential pressure type water level gauge 5, graph G7 shows the water level measurement value of the thermocouple type water level gauge 6, and graph G8 shows the water level measurement value of the radiation type water level gauge 7.

Since the differential pressure type water level gauge 5 and the thermocouple type water level gauge 6 are damaged (failed) at the time point B, their respective water level measurement values indicate zero. In the present embodiment, information indicating that the differential pressure type water level gauge 5 and the thermocouple type water level gauge 6 are damaged is also used for predicting the water level in the furnace. In other words, even if the water level measurement value shows zero, that value is used for multiple regression analysis.

The water level measurements of each type of water level gauges 5-7 have their own unique characteristics. For example, the measured water level of the differential pressure type water level gauge 5 shows a value close to the collapse water level (FIG. 8), and the thermocouple type water level gauge 6 shows a value close to the two-phase water level (FIG. 8).

Further, since the differential pressure type water level gauge 5 and the thermocouple type water level gauge 6 are installed inside the pressure vessel 22, the operation is stopped when the fuel melts. On the other hand, the radiation type water level gauge 7 does not directly measure the water level in the furnace. In this radiation type water level gauge 7, the radiation intensity is reduced due to the difference in water density in the height direction of the pressure vessel 22, and the water level in the furnace is estimated from the distribution of radiation emitted from the fuel.

In the case of the radiation type water level gauge 7, the water level can be measured with a certain accuracy in the vicinity of the core 21, but the water level in the reactor is measured in the portion above the upper end of the core 21 and the portion below the lower end of the core 21. The accuracy is low. However, since the radiation type water level gauge 7 is installed outside the pressure vessel 22, it operates without losing its function even when the fuel melts. It can be seen that the graph G8 of the radiation type water level gauge 7 changes even at the time F when the fuel melts and falls into the furnace water 24, and the water level measurement value can be obtained according to the situation in the furnace.

The water level measurement value analysis unit 12 creates a measurement value data set in which the in-core water level output from the accident analysis unit 11 and the water level measurement value analyzed by the water level measurement value analysis unit 12 correspond to each other, and the prediction model creation unit 13 Send to.

As shown in FIG. 7, the measured value data set includes the water level measured value of the differential pressure type water level gauge 5 (type 1 water level gauge) and the thermocouple type water level in association with the elapsed time (progress status) of the severe accident. Information indicating the water level measurement value of the total 6 (type 2 water level gauge) and the water level measurement value of the radiation type water level gauge 7 (type 3 water level gauge) is registered.

As shown in FIG. 1, the prediction model creation unit 13 performs multiple regression analysis using the in-core water level as an objective variable and the water level measurement value as an explanatory variable from the measurement value data set created by the water level measurement value analysis unit 12. By doing so, a regression equation that predicts the water level in the furnace from the measured water level is created. A water level prediction model using this regression equation is transmitted to the in-core water level prediction unit 14.

The in-core water level prediction unit 14 receives the water level measurement values accumulated in the data collection unit 10 and the prediction model based on the multiple regression analysis created by the prediction model creation unit 13. By applying this prediction model to the measured water level, the predicted value of the water level in the reactor 19 is derived.

FIG. 12 is a graph P showing the predicted value of the furnace water level obtained by the furnace water level prediction unit 14, and a graph G2 showing the true value of the furnace water level. The true value exemplifies the two-layer water level.

Graph P of the predicted value of the in-core water level includes the effects of the differential pressure type water level gauge 5 and the thermocouple type water level gauge 6 which are effective in normal times and the radiation type water level gauge 7 which is effective in a severe accident to predict the in-core water level. Therefore, it is possible to measure the water level in the reactor from normal times to severe accidents without losing its function.

As shown in FIG. 1, the in-core information output unit 15 obtains in-core information including the predicted value of the in-core water level evaluated by the in-core water level predicting unit 14 and the measured value of the water level measured by the water level measuring unit 2. Controls the display on a display or the like. This display is installed in the central control room of a nuclear power plant and is monitored by operators consistently from normal operation to severe accidents.

Next, the reactor water level measurement method will be described with reference to the flowchart of FIG. The block diagram shown in FIG. 1 will be referred to as appropriate.

As shown in FIG. 13, first, the user of the water level prediction computer 4 performs the pre-processing. In this pre-processing, a prediction model is created. In step S11, various data related to the reactor 19 are input to the accident analysis unit 11.

In the next step S12, the accident analysis unit 11 simulates a severe accident in the reactor 19.

In the next step S13, the accident analysis unit 11 analyzes the severe accident of the reactor 19 and analyzes the water level in the reactor corresponding to the progress of the severe accident.

In the next step S14, the water level measurement value analysis unit 12 determines the progress of the severe accident with a plurality of types of water level gauges 5 to 7 having different measurement principles based on the analysis of the severe accident performed by the accident analysis unit 11. Analyze the water level measurements measured accordingly.

In the next step S15, the prediction model creation unit 13 analyzes the relationship between the in-core water level analyzed by the accident analysis unit and the water level measurement value analyzed by the water level measurement value analysis unit 12, and the in-core water level is obtained from the water level measurement value. Create a prediction model used to predict.

At this point, the pre-processing using the water level prediction computer 4 is completed. Next, the in-core water level prediction process of the actual reactor 19 is started using the water level prediction computer 4.

In the next step S16, the data accumulation unit 10 accumulates the water level measurement values actually measured in the reactor 19 by a plurality of types of water level gauges 5 to 7. The data accumulation unit 10 may accumulate the in-core temperature measurement values actually measured in the reactor by the in-core thermometer 8.

In the next step S17, the in-core water level prediction unit 14 actually uses the in-core water level of the reactor 19 based on the respective water level measurement values accumulated in the data collection unit and the prediction model created by the prediction model creation unit. Predict.

In the next step S18, the in-core information output unit 15 outputs in-core information regarding the in-core water level predicted by the in-core water level prediction unit 14. Then, the in-core water level prediction process is completed.

By repeating the process of predicting the water level in the furnace from steps S16 to S18, the water level in the furnace can be measured consistently from the time of normal operation to the time of a severe accident, and the operator can grasp the water level in the furnace. can.

Although the flowchart of the present embodiment illustrates a mode in which each step is executed in series, the context of each step is not necessarily fixed, and even if the context of some steps is exchanged. good. Also, some steps may be executed in parallel with other steps.

The water level prediction computer 4 of the present embodiment includes a control device in which a dedicated chip, a controller such as an FPGA (Field Programmable Gate Array), a GPU (Graphics Processing Unit), or a CPU (Central Processing Unit) is highly integrated, and a ROM. Storage devices such as (Read Only Memory) or RAM (Random Access Memory), external storage devices such as HDD (Hard Disk Drive) or SSD (Solid State Drive), display devices such as displays, and mice or keyboards. It includes an input device and a communication interface. The water level prediction computer 4 can be realized by a hardware configuration using a normal computer.

The program executed by the water level prediction computer 4 of the present embodiment is provided by incorporating it into a ROM or the like in advance. Alternatively, the program may be a computer-readable, non-transient storage medium such as a CD-ROM, CD-R, memory card, DVD, or flexible disk (FD) that is a file in an installable or executable format. It may be stored and provided in.

Further, the program executed by the water level prediction computer 4 may be stored on a computer connected to a network such as the Internet, downloaded via the network, and provided. Further, the water level prediction computer 4 can also be configured by connecting separate modules that independently exhibit the functions of the components to each other by a network or a dedicated line and combining them.

In this embodiment, one water level gauge 5 to 7 having different measurement principles is provided, but other embodiments may be used. For example, two or more water level gauges having the same type of measurement principle may be provided. For example, two or more radiation type water level gauges 7 may be provided.

In the present embodiment, the in-core condition data set (FIG. 6) and the measured value data set (FIG. 7) are created as separate data sets, but other embodiments may be used. For example, the furnace condition data set and the measured value data set may be created as one data set.

According to the embodiment described above, the relationship between the in-core water level analyzed by the accident analysis unit and the water level measurement value analyzed by the water level measurement value analysis unit is analyzed, and the in-core water level is predicted from a plurality of water level measurement values. By providing a prediction model creation unit that creates a prediction model used for this purpose, it is possible to consistently measure the water level in the furnace from the time of normal operation to the time of a severe accident.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Reactor water level measurement system, 2 ... Water level measurement unit, 3 ... In-reactor measurement unit, 4 ... Water level prediction computer, 5 ... Differential pressure type water level gauge, 6 ... Thermoelectric pair type water level gauge, 7 ... Radiation type water level gauge, 8 ... In-reactor thermometer, 9 ... In-reactor pressure gauge, 10 ... Data collection unit, 11 ... Accident analysis unit, 12 ... Water level measurement value analysis unit, 13 ... Prediction model creation unit, 14 ... In-reactor water level prediction unit, 15 ... In-reactor information output unit, 16 ... information input unit, 17 ... storage unit, 18 ... main control unit, 19 ... reactor, 20 ... fuel assembly, 21 ... core, 22 ... pressure vessel, 23 ... reactor storage vessel, 24 ... Reactor water, 25 ... Air-water separator, 26 ... Steam dryer, 27 ... Recirculation pump, 28 ... Condensing tank, 29 ... Reference water column detection pipe, 30 ... First fluctuation water column detection pipe, 31 ... Second fluctuation Water column detection pipe, 32 ... Wideband differential pressure detection unit, 33 ... Fuel area differential pressure detection unit, 34 ... Sensor rod, 35 ... Heater, 36 ... Thermoelectric pair element for hot contact, 37 ... Thermoelectric pair element for cold contact, 38 ... Insulation unit, 39 ... Sensor unit, 40 ... Heat, 41 ... Gamma ray, 42 ... Dose detection unit.

Claims (10)

An accident analysis unit that analyzes the severe accident of a nuclear reactor and analyzes the water level in the reactor corresponding to the progress of the severe accident.
Based on the analysis of the severe accident, the water level measurement value analysis unit that analyzes the water level measurement values measured according to the progress status by a plurality of types of water level meters having different measurement principles, and
Used to analyze the relationship between the in-core water level analyzed by the accident analysis unit and the water level measurement value analyzed by the water level measurement value analysis unit, and to predict the in-core water level from a plurality of the water level measurement values. Predictive model creation unit that creates a predictive model
A data collection unit that collects the water level measurements actually measured in the reactor by the water level gauges of a plurality of types, and
With the in-core water level prediction unit that predicts the in-core water level of the actual reactor based on the respective water level measurement values accumulated in the data accumulation unit and the prediction model created by the prediction model creation unit. ,
An in-core information output unit that outputs in-core information regarding the in-core water level predicted by the in-core water level prediction unit, and an in-core information output unit.
To prepare
Reactor water level measurement system. The prediction model is used to predict the water level in the furnace from a plurality of the water level measurements by performing multiple regression analysis.
The reactor water level measurement system according to claim 1. Multiple types of water level gauges
A differential pressure type water level gauge that measures the water level inside the pressure vessel by the pressure difference between the upper part and the lower part of the pressure vessel of the reactor.
A thermocouple type water level gauge that measures the water level inside the pressure vessel with a thermocouple element provided in the pressure vessel.
A radiation type water level gauge that measures the water level inside the pressure vessel by radiation emitted from the pressure vessel to the outside,
Including at least two of
The reactor water level measuring system according to claim 1 or 2. The data collecting unit collects the time when the water level measurement value is measured in association with each of the water level measurement values.
The reactor water level measurement system according to any one of claims 1 to 3. The accident analysis unit
Simulate the severe accident
Analysis of the time change corresponding to the progress of each parameter indicating the temperature in the furnace, the pressure in the furnace, at least one of the molten states of the fuel and the water level in the furnace was analyzed.
Create an in-core status data set in which the elapsed time from the occurrence of the severe accident and the parameters are associated with each other.
The reactor water level measurement system according to any one of claims 1 to 4. The water level measurement value analysis unit
Based on the in-core condition data set created by the accident analysis unit, the water level measurement values measured by the water level gauges of a plurality of types are analyzed.
Create a measured value data set in which the elapsed time is associated with the water level measured value.
The reactor water level measurement system according to claim 5. The prediction model creation unit
Based on the in-fire condition data set and the measured value data set
By performing multiple regression analysis with the water level in the furnace as the objective variable and the measured water level as the explanatory variable, the prediction model used for predicting the water level in the furnace from a plurality of the measured water levels is created.
The reactor water level measurement system according to claim 6. The prediction model creation unit creates the prediction model used for predicting the water level in the furnace by adding a value other than the water level measurement value as the explanatory variable.
The reactor water level measurement system according to claim 7. The prediction model creation unit analyzes the relationship between the water level measurement value measured by the water level gauge and the water level in the furnace after being damaged in the severe accident, and creates the prediction model.
The reactor water level measurement system according to any one of claims 1 to 8. The step that the accident analysis department analyzes the severe accident of the nuclear reactor and analyzes the water level in the reactor corresponding to the progress of the severe accident,
Based on the analysis of the severe accident, the water level measurement value analysis unit analyzes the water level measurement value measured according to the progress with a plurality of types of water level meters having different measurement principles.
The prediction model creation unit analyzes the relationship between the in-core water level analyzed by the accident analysis unit and the water level measurement value analyzed by the water level measurement value analysis unit, and predicts the in-core water level from the water level measurement value. And the steps to create a predictive model used to do
A step in which the data collection unit collects the water level measurement values actually measured in the reactor by the water level gauges of a plurality of types, and
The in-core water level prediction unit predicts the actual in-core water level of the reactor based on the respective water level measurement values accumulated in the data accumulation unit and the prediction model created by the prediction model creation unit. Steps to do and
A step in which the in-core information output unit outputs in-core information regarding the in-core water level predicted by the in-core water level prediction unit, and
including,
Reactor water level measurement method.

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