JP-2026075357-A - Hydraulic control unit in a nuclear power plant and method for predicting the static pressure of nitrogen gas in a hydraulic control unit in a nuclear power plant.

JP2026075357AJP 2026075357 AJP2026075357 AJP 2026075357AJP-2026075357-A

Abstract

【assignment】 The ability to predict the future statically determined pressure of nitrogen gas in the hydraulic control unit of a nuclear power plant with high accuracy and at an early stage. [Solution] To solve the above problems, the hydraulic pressure control unit for a nuclear power plant of the present invention is characterized by comprising: an accumulator temperature sensor and a nitrogen container temperature sensor installed on the outer surfaces of the accumulator and nitrogen container respectively to measure the outer surface temperature; a reference temperature measuring temperature sensor installed in the space where the connecting part connecting the accumulator and the nitrogen container is located to measure the room temperature (reference temperature); and a computer that predicts the future statically constant pressure of nitrogen gas based on the measured values from the accumulator temperature sensor, the nitrogen container temperature sensor and the reference temperature measuring temperature sensor. [Selection Diagram] Figure 1

Inventors

高橋志郎
田村明紀
新間大輔
坂井孝匡
金井司

Assignees

日立ＧＥベルノバニュークリアエナジー株式会社

Dates

Publication Date: 20260508
Application Date: 20241022

Claims (10)

A hydraulic pressure control unit for a nuclear power plant, comprising a metal accumulator and a metal nitrogen container for use in a nuclear power plant, and a connecting part that connects the accumulator and the nitrogen container and into which nitrogen gas is injected, wherein the pressure after injection of the nitrogen gas is monitored during inspection of the nuclear power plant, The hydraulic pressure control unit for a nuclear power plant is characterized by comprising: an accumulator temperature sensor and a nitrogen container temperature sensor installed on the respective metal outer surfaces of the accumulator and the nitrogen container to measure the outer surface temperature; a reference temperature measuring temperature sensor installed in the space where the connecting portion is located to measure the room temperature (reference temperature); and a computer that predicts the future statically constant pressure of nitrogen gas based on the measurements taken by the accumulator temperature sensor, the nitrogen container temperature sensor and the reference temperature measuring temperature sensor.
A hydraulic control unit for a nuclear power plant according to claim 1, A hydraulic pressure control unit for a nuclear power plant, characterized in that the central part of the accumulator is formed to be thinner than the other parts, the temperature sensor for the accumulator is installed in the thin-walled area of the central part of the accumulator, the upper part of the nitrogen container is formed to be a non-spherical portion, the temperature sensor for the nitrogen container is installed in the non-spherical area of the upper part of the nitrogen container, the accumulator and the nitrogen container are connected at the lower part by the connecting portion, and the temperature sensor for measuring the reference temperature is installed in the space below the connecting portion.
A hydraulic control unit for a nuclear power plant according to claim 2, A hydraulic control unit for a nuclear power plant, characterized in that the thin-walled region in the central part of the accumulator is the part where the nitrogen gas is sealed, and the non-spherical portion above the center of the nitrogen container is a cylindrical container portion.
A hydraulic control unit for a nuclear power plant according to any one of claims 1 to 3, A hydraulic pressure control unit for a nuclear power plant, characterized in that a pressure gauge is installed at the connecting portion to monitor the pressure of the nitrogen gas visually.
When inspecting a hydraulic control unit used in a nuclear power plant, which comprises a metal accumulator and a metal nitrogen container, and a connecting section that connects the accumulator and the nitrogen container and into which nitrogen gas is injected, and monitoring the pressure after the injection of nitrogen gas, A method for predicting the static determinate pressure of nitrogen gas in a hydraulic control unit of a nuclear power plant, characterized in that the outer surface temperature measured by an accumulator temperature sensor and a nitrogen container temperature sensor installed on the respective outer metal surfaces of the accumulator and the nitrogen container, and the reference temperature measured by a reference temperature measuring temperature sensor installed in the space where the connecting portion is located and which measures room temperature (reference temperature), are input into a computer, the computer predicts the average temperature of the nitrogen gas, and predicts the future static determinate pressure of the nitrogen gas from the current pressure and the average temperature of the nitrogen gas.
A method for predicting the statically determined pressure of nitrogen gas in a hydraulic control unit in a nuclear power plant according to claim 5, A method for predicting the statically determinate pressure of nitrogen gas in a hydraulic control unit of a nuclear power plant, characterized by determining the accuracy of the pressure prediction from predicted values of nitrogen gas pressure at multiple time points, and then predicting the future statically determinate pressure of nitrogen gas after determining that the pressure prediction is correct.
A method for predicting the statically determined pressure of nitrogen gas in a hydraulic control unit in a nuclear power plant according to claim 6, A method for predicting the statically determinate pressure of nitrogen gas in a hydraulic control unit of a nuclear power plant, characterized in that if the difference between the predicted future statically determinate pressure of nitrogen gas at a certain time and the final pressure of nitrogen gas obtained from an equation or approximation equation including an exponential function is within an acceptable limit, it is determined that the future statically determinate pressure of nitrogen gas can be predicted at that time.
A method for predicting the statically determined pressure of nitrogen gas in a hydraulic control unit in a nuclear power plant according to claim 6, A method for predicting the static pressure of nitrogen gas in a hydraulic control unit of a nuclear power plant, characterized in that if the future static pressure of nitrogen gas determined at a certain time is within the target pressure range, and the final nitrogen gas pressure determined from an exponential function-based or approximate formula predicted from multiple time points is within the target pressure range, then it is determined that the future static pressure of nitrogen gas can be predicted at the present time, and that the future static pressure of nitrogen gas is within the range of the target pressure.
A method for predicting the statically determined pressure of nitrogen gas in a hydraulic control unit in a nuclear power plant according to claim 6, A method for predicting the statically determined pressure of nitrogen gas in a hydraulic control unit of a nuclear power plant, characterized in that if the difference between the future statically determined pressure of nitrogen gas obtained at a certain time and the final pressure of nitrogen gas obtained from an exponential function or approximation formula is within an allowable value, but the nitrogen gas pressure deviates from the target pressure, it is determined that the future statically determined pressure of nitrogen gas will deviate from the target pressure.
A method for predicting the static pressure of nitrogen gas in a hydraulic control unit in a nuclear power plant according to any one of claims 5 to 9, The central part of the accumulator is formed to be thinner than the other parts, and the outer surface temperature of the accumulator is measured by the accumulator temperature sensor installed in the thin-walled region of the central part of the accumulator. The ends of the nitrogen container are formed in a spherical shape, and the temperature sensor for the nitrogen container, which is installed in the central region of the nitrogen container rather than in this spherical shape, measures the outer surface temperature of the nitrogen container. A method for predicting the static pressure of nitrogen gas in a hydraulic control unit of a nuclear power plant, characterized in that the accumulator and the nitrogen container are connected at their lower ends by the connecting portion, and the room temperature (reference temperature) is measured by the reference temperature measuring temperature sensor installed in the space below the connecting portion.

Description

This invention relates to a hydraulic control unit for a nuclear power plant and a method for predicting the statically determinate pressure of nitrogen gas in a hydraulic control unit for a nuclear power plant. For example, it is particularly suitable for predicting the statically determinate pressure after nitrogen gas filling during periodic inspections. Compared to Europe and the United States, Japanese nuclear power plants have longer periodic inspection intervals and lower capacity utilization rates (low operating rates of nuclear power plants). Therefore, Japanese power companies are aiming to reduce the number of periodic inspection days in order to improve the operating rates of nuclear power plants. Among the equipment and machinery required for periodic inspections at nuclear power plants, hydraulic control units, in particular, require a large volume of inspections, resulting in longer inspection periods. Therefore, there is a need to streamline periodic inspections of hydraulic control units. The hydraulic control units in a nuclear power plant are devices that store the high-pressure nitrogen gas necessary for the control rod drive mechanism, which uses nitrogen gas pressure to emergency-insert control rods into the reactor core. Normally, one hydraulic control unit is installed for every two control rods. Therefore, during each periodic inspection, it is necessary to refill all approximately 100 hydraulic control units with nitrogen gas to the specified pressure. Injecting high-pressure nitrogen gas causes the temperature of the structures constituting the hydraulic control unit to rise, and then it cools down to room temperature through natural convection of the surrounding air. Because the pressure of the nitrogen gas changes with this temperature change, it was necessary to visually monitor the nitrogen gas pressure until it stabilized. The hydraulic control unit has a large heat capacity, requiring more than 18 days for nitrogen gas pressure monitoring. Furthermore, the tolerance range for the nitrogen gas's statically stabilized pressure is narrow, within ±1% of the target value. As described above, the large number of structural components, the strict tolerance limits for the statically determinate pressure of nitrogen gas, and the long working days required for nitrogen gas pressure monitoring in the hydraulic control unit could potentially impact efforts to shorten the periodic inspection interval. Therefore, it is crucial to predict the statically stabilized pressure of nitrogen gas early on, whereas previously this was determined by visually reading the pressure gauge readings and monitoring the nitrogen gas pressure until it stabilized, a process that took considerable time. Furthermore, because deviations from the allowable pressure of the nitrogen gas statically stabilized pressure would necessitate rework, potentially significantly impacting the inspection time, it is essential to predict the statically stabilized pressure of nitrogen gas as quickly as possible. To address the above challenges, the development of technologies for predicting nitrogen gas pressure is necessary. On the other hand, several technologies have been developed for detecting gas leaks in tanks; for example, Patent Document 1 can be cited as one such example. This Patent Document 1 describes an apparatus and method for detecting gas leaks with high accuracy by installing multiple temperature sensors on the surface of a tank to measure temperature, correcting the gas pressure based on the measurement data from these temperature sensors, predicting the corrected gas pressure that minimizes the standard deviation value (variation in the corrected gas pressure) using the temperature sensors, and calculating the change in the corrected gas pressure over time using an approximate straight line. Japanese Patent Publication No. 2007-263584 This is a schematic diagram showing one embodiment of the hydraulic control unit for a nuclear power plant according to the present invention.This flowchart shows the processing steps for the nitrogen gas static pressure prediction method of a hydraulic control unit in a nuclear power plant according to the present invention.This figure shows the temperature distribution of the hydraulic control unit obtained by transient three-dimensional numerical thermal fluid analysis in the present invention.This is a characteristic diagram showing the pressure change after nitrogen injection in the hydraulic control unit of the nuclear power plant according to the present invention.This is a characteristic diagram showing the predicted change in static pressure of the hydraulic pressure control unit for a nuclear power plant according to the present invention. The following describes the present invention's hydraulic pressure control unit for a nuclear power plant and the method for predicting the statically determinate pressure of nitrogen gas in a hydraulic pressure control unit for a nu