Method for achieving non-uniform temperature distribution in a fuel element base

Abstract

The present application belongs to the technical field of nuclear reactor fuel element thermal hydraulic, and particularly relates to a method for realizing non-uniform temperature distribution of a fuel element base body. The method comprises: arranging thermocouples for temperature measurement at different positions on the side surface of the base body and the surfaces of the electric heating element and the metal gas cooling pipe, and monitoring the temperature distribution of the fuel element base body structure in real time. The method provided by the present application considers the influence of the coolant flow in the real nuclear reactor fuel element on the temperature distribution of the base body, divides the different channels in the fuel element base body into heating channels and cooling channels by function division, integrates the electric heating element in the heating channels to simulate the heat release of the nuclear reactor fuel element, integrates the metal gas cooling pipe in the cooling channels to simulate the cooling effect of the nuclear reactor coolant, and thus realizes more realistic simulation of the temperature field distribution of the nuclear reactor.

Description

Technical Field

[0001] This invention belongs to the field of thermal-hydraulic technology of nuclear reactor fuel elements, specifically relating to a method for achieving non-uniform temperature distribution in the fuel element substrate. Background Technology

[0002] During nuclear reactor operation, due to factors such as heat release from fuel elements and coolant flow within the reactor core, the fuel element matrix structure exhibits a significant non-uniform temperature distribution. This distribution directly affects the mechanical properties, service life, and operational safety of the nuclear reactor. Therefore, realistically simulating the non-uniform temperature distribution of the fuel element matrix in an experimental environment is essential for conducting research on the thermal-hydraulic characteristics of nuclear reactor fuel elements and validating numerical calculation models. Current fuel element matrix temperature distribution testing techniques typically focus on the heating state of electrically heated elements, neglecting the influence of coolant on the matrix temperature distribution. These techniques can only achieve simple gradient temperature distributions and cannot reproduce the actual non-uniformity of the fuel element temperature distribution within a nuclear reactor. Furthermore, they cannot flexibly and effectively control the fuel element matrix temperature field according to different operating conditions, resulting in insufficient realism and reliability of the experimental simulation results. Therefore, a new method for realizing the non-uniform temperature distribution of the fuel element matrix is ​​needed to realistically reproduce the actual reactor temperature environment and enable precise and effective control, thereby meeting the requirements for high-fidelity, high-precision, and multi-condition thermal-hydraulic testing of fuel elements. Summary of the Invention

[0003] The purpose of this invention is to provide a method for realizing non-uniform temperature distribution in fuel element matrix, which can overcome the problems of low accuracy of fuel element matrix temperature field simulation, small range of operating conditions that can be covered, and insufficient authenticity and reliability of results in the prior art.

[0004] The technical solution of the present invention is as follows: A method for achieving non-uniform temperature distribution in a fuel element substrate, comprising the following steps: Step 1: The electric heating element is a rod-shaped structure. Each electric heating element is independently connected to an adjustable power supply via an external wire. The heat release rate of the electric heating element is controlled by adjusting the output power of the power supply, thereby regulating the temperature of the substrate. Step 2: Each metal air-cooled pipe is equipped with a vertical gas inlet pipe and a horizontal gas outlet pipe. The gas inlet pipe is connected to a temperature-controlled gas source to introduce cooling gas into the cooling channel, and the horizontal gas outlet pipe is used to discharge the cooling gas after heat absorption. Step 3: Install thermocouples for temperature measurement at different positions on the side of the substrate and on the surface of the electric heating element and the metal gas cooling pipe to monitor the temperature distribution of the fuel element substrate structure in real time. Step 4: By adjusting the power of the electric heating elements in different heating channels and the temperature and flow rate of the cooling gas in the metal air-cooled pipes in different cooling channels, a temperature gradient is formed inside the substrate, ultimately achieving the preset non-uniform temperature distribution field. Step 5: The fuel element substrate is composed of multiple basic structures. A cylindrical mounting cavity is opened in the center of the basic structure, and an electric heating element is inserted into it and sealed and fixed. Step 6: Arrange three sets of cylindrical mounting cavities evenly around the electric heating element mounting cavity, and insert metal air-cooling pipes into them; Step 7: Based on the power simulation requirements of the reactor core fuel elements, combine multiple basic structures, input different heating power to each electric heating element through an independent adjustable power supply via an external wire, and at the same time connect an external temperature-controlled gas source system through a gas inlet pipe to adjust the temperature and flow rate of the cooling gas in the metal cooling pipe. After stabilization, a temperature field distribution with different temperature gradients is formed inside the matrix. Step 8: Temperature measurement of the fuel element substrate unit; Step 9: Measure the temperature of the electric heating element; Step 10: Measure the temperature of the metal air-cooled pipe.

[0005] In step 1, the electric heating element is made of carbide or nitride non-metallic materials or tungsten or tungsten alloy metallic materials. The size of the electric heating element is slightly smaller than the heating channel of the substrate, and a temperature measurement space is reserved on the surface of the electric heating element.

[0006] In step 2, the metal air cooling pipe is made of stainless steel or Inconel alloy. The size of the metal air cooling pipe matches the cooling channels of the substrate. The cooling gas is an inert gas, and the gas flow rate is adjusted by a flow meter.

[0007] In step 5, high-temperature resistant metals or ceramic materials are selected as the fuel element substrate.

[0008] In step 8, the fuel element substrate unit structure uses C-type and N-type thermocouples for temperature measurement. A total of 9 thermocouples are arranged in the fuel element substrate unit structure: 3 thermocouples are arranged on the surface of the electric heating element, evenly distributed along the axial and circumferential directions; 2 thermocouples are arranged on the surface of each metal cooling pipe, circumferentially opposite to the measurement point of the electric heating element.

[0009] In step 9, the thermocouple is vertically inserted into the gap between the electric heating element and the substrate. The thermocouple is then bound to the surface of the electric heating element using a high-temperature wire. At the same time, high-temperature insulation cotton is placed between the thermocouple end and the electric heating element, pressing the thermocouple end against the surface of the electric heating element.

[0010] In step 10, for the metal air-cooled pipe, a groove is cut into the surface of the pipe, the thermocouple is vertically inserted into the groove, and the thermocouple is bound to the surface of the metal air-cooled pipe using a high-temperature wire. High-temperature insulation cotton is placed between the end of the thermocouple and the metal air-cooled pipe, and the end of the thermocouple is pressed against the surface of the metal air-cooled pipe.

[0011] The beneficial effects of this invention are as follows: The method provided by this invention considers the influence of coolant flow on the substrate temperature distribution in a real nuclear reactor fuel element. It divides the different channels inside the fuel element substrate into heating channels and cooling channels, integrating electric heating elements in the heating channels to simulate the heat release of the nuclear reactor fuel element, and integrating metal gas-cooled pipes in the cooling channels to simulate the cooling effect of the nuclear reactor coolant, thereby achieving a more realistic simulation of the nuclear reactor temperature field distribution. Simultaneously, by adjusting the heating power of the electric heating elements and the temperature and flow rate of the cooling gas in the metal gas-cooled pipes, the temperature field distribution of the fuel element substrate under different operating conditions can be flexibly controlled to meet the requirements of high simulation fidelity, high precision, and high flexibility in fuel element thermal-hydraulic testing. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the circumferential cross-section of the fuel element matrix structure; Figure 2 This is a schematic diagram of the axial cross-section of the fuel element matrix structure.

[0013] In the diagram, 1 is the fuel element substrate, 2 is the electric heating element, 3 is the external wiring, 4 is the metal gas cooling pipe, 5 is the gas inlet pipe, 6 is the metal expansion joint, and 7 is the thermocouple. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0015] This invention provides a method for achieving non-uniform temperature distribution in a fuel element substrate. The fuel element substrate used is a porous block structure with multiple through-holes vertically oriented inside. These holes are divided into heating holes and cooling holes, which are spaced apart. The center-to-center distance between adjacent holes can be flexibly adjusted according to the substrate size and experimental requirements. The substrate material can be a metal or ceramic material consistent with the substrate of an actual nuclear reactor element, ensuring that the thermophysical properties match those of the actual operating element.

[0016] A method for achieving non-uniform temperature distribution in a fuel element substrate includes the following steps: Step 1: The electric heating element is a rod-shaped structure, made of non-metallic materials such as carbides and nitrides, or metallic materials such as tungsten and tungsten alloys. It exhibits rapid heat conduction in high-temperature environments while providing more stable heating performance and superior radiation resistance. Considering the lower mechanical strength of non-metallic electric heating elements and their susceptibility to breakage under stress, the size of the electric heating element is slightly smaller than the heating channels in the substrate, with a temperature measurement space reserved on the surface of the electric heating element. Each electric heating element is independently connected to an adjustable power supply via an external wire. The heat release rate of the electric heating element is controlled by adjusting the output power of the power supply, thereby regulating the substrate temperature.

[0017] Step 2: The metal air-cooling pipes are made of high-temperature resistant and thermally conductive metal materials such as stainless steel and Inconel alloy. The dimensions of the metal air-cooling pipes match the cooling channels of the substrate and are tightly fitted within the cooling channels. Each metal air-cooling pipe is equipped with a vertical gas inlet pipe and a horizontal gas outlet pipe. The gas inlet pipe is connected to a temperature-controlled gas source to introduce cooling gas into the cooling channels, while the horizontal gas outlet pipe is used to discharge the cooled gas after heat absorption. Inert gases such as argon and nitrogen are used for cooling to avoid chemical reactions with the metal pipes at high temperatures. The gas flow rate is adjusted using a flow meter.

[0018] Step 3: Temperature measurement thermocouples are installed at different positions on the side of the substrate and on the surface of the electric heating element and the metal gas cooling pipe. This allows for real-time monitoring of the temperature distribution of the fuel element substrate structure, confirming the stable maintenance of the non-uniform temperature field, and meeting the requirements of thermal-hydraulic tests of nuclear reactor fuel elements.

[0019] Step 4: The overall temperature distribution of the fuel element substrate is determined by the synergistic effect of the heating and cooling channels. The electric heating elements within the heating channels transfer heat to the substrate through thermal conduction, raising the temperature of the corresponding areas of the substrate. The metal gas-cooled pipes within the cooling channels remove heat from the substrate through thermal conduction and convective heat transfer of the cooling gas, lowering the temperature of the corresponding areas of the substrate. By flexibly adjusting the power of the electric heating elements in different heating channels and the temperature and flow rate of the cooling gas in the metal gas-cooled pipes in different cooling channels, a complex temperature gradient can be formed within the substrate, ultimately achieving the preset non-uniform temperature distribution field.

[0020] Step 5: As Figure 1 As shown, a high-temperature resistant metal or ceramic material (such as alumina ceramic, boron nitride ceramic, etc.) is selected for the fuel element substrate. The fuel element substrate is composed of multiple basic structures, each with a side length of 12mm. A cylindrical mounting cavity with a diameter of 20mm and a depth of 600mm is opened at the center of the basic structure, and an electric heating element with a length of 650mm is inserted into it and sealed and fixed. The electric heating element is made of non-metallic materials such as carbides and nitrides, or metallic materials such as tungsten and tungsten alloys, and is connected to an independent adjustable power supply via an external wire.

[0021] Step 6: As Figure 1 As shown, three sets of cylindrical mounting cavities, each 10mm in diameter and 600mm deep, are evenly arranged around the mounting cavity of the electric heating element, and a 650mm long metal air-cooling pipe is inserted into each cavity. The metal air-cooling pipe can be made of stainless steel, Inconel alloy, or other metal materials. The metal air-cooling pipe is connected to an external temperature-controlled gas source system via a gas inlet pipe to ensure no gas leakage.

[0022] Step 7: As Figure 2 As shown, multiple basic structures are combined according to the power simulation requirements of the reactor core fuel elements. Different heating powers are input to each electric heating element through an independently adjustable power supply connected by external wires. At the same time, an external temperature-controlled gas source system is connected through a gas inlet pipe to regulate the temperature and flow rate of the cooling gas in the metal cooling pipes. After stabilization, a temperature field distribution with different temperature gradients is formed inside the matrix.

[0023] Step 8: Temperature measurement is performed using C-type and N-type thermocouples in the fuel element substrate structure. Considering the small gap between the electric heating element and the metal cooling pipe and the cylindrical mounting cavity, a total of 9 thermocouples are arranged in the fuel element substrate structure: 3 thermocouples are arranged on the surface of the electric heating element, evenly distributed along the axial and circumferential directions; 2 thermocouples are arranged on the surface of each metal cooling pipe, circumferentially opposite the measurement point of the electric heating element.

[0024] Step 9: For the electric heating element, since the size of the electric heating element is slightly smaller than the heating channel of the substrate, there is a space for temperature measurement on the surface of the electric heating element. Therefore, the thermocouple is vertically inserted into the gap between the electric heating element and the substrate. The thermocouple is bound to the surface of the electric heating element using a high-temperature wire. At the same time, high-temperature insulation cotton is placed between the end of the thermocouple and the electric heating element, pressing the end of the thermocouple against the surface of the electric heating element.

[0025] Step 10: For metal air-cooled pipes, grooves are cut into the pipe surface, the thermocouple is vertically inserted into the groove, and the thermocouple is bound to the surface of the metal air-cooled pipe using high-temperature wire. High-temperature insulation cotton is placed between the end of the thermocouple and the metal air-cooled pipe, and the end of the thermocouple is pressed against the surface of the metal air-cooled pipe.

Claims

1. A method for achieving non-uniform temperature distribution in a fuel element substrate, characterized in that, Includes the following steps: Step 1: The electric heating element is a rod-shaped structure. Each electric heating element is independently connected to an adjustable power supply via an external wire. The heat release rate of the electric heating element is controlled by adjusting the output power of the power supply, thereby regulating the temperature of the substrate. Step 2: Each metal air-cooled pipe is equipped with a vertical gas inlet pipe and a horizontal gas outlet pipe. The gas inlet pipe is connected to a temperature-controlled gas source to introduce cooling gas into the cooling channel, and the horizontal gas outlet pipe is used to discharge the cooling gas after heat absorption. Step 3: Install thermocouples for temperature measurement at different positions on the side of the substrate and on the surface of the electric heating element and the metal gas cooling pipe to monitor the temperature distribution of the fuel element substrate structure in real time. Step 4: By adjusting the power of the electric heating elements in different heating channels and the temperature and flow rate of the cooling gas in the metal air-cooled pipes in different cooling channels, a temperature gradient is formed inside the substrate, ultimately achieving the preset non-uniform temperature distribution field. Step 5: The fuel element substrate is composed of multiple basic structures. A cylindrical mounting cavity is opened in the center of the basic structure, and an electric heating element is inserted into it and sealed and fixed. Step 6: Arrange three sets of cylindrical mounting cavities evenly around the electric heating element mounting cavity, and insert metal air-cooling pipes into them; Step 7: Based on the power simulation requirements of the reactor core fuel elements, combine multiple basic structures, input different heating power to each electric heating element through an independent adjustable power supply via an external wire, and at the same time connect an external temperature-controlled gas source system through a gas inlet pipe to adjust the temperature and flow rate of the cooling gas in the metal cooling pipe. After stabilization, a temperature field distribution with different temperature gradients is formed inside the matrix. Step 8: Temperature measurement of the fuel element substrate unit; Step 9: Measure the temperature of the electric heating element; Step 10: Measure the temperature of the metal air-cooled pipe.

2. The method for achieving non-uniform temperature distribution in a fuel element substrate as described in claim 1, characterized in that: In step 1, the electric heating element is made of carbide or nitride non-metallic materials or tungsten or tungsten alloy metallic materials. The size of the electric heating element is slightly smaller than the heating channel of the substrate, and a temperature measurement space is reserved on the surface of the electric heating element.

3. The method for achieving non-uniform temperature distribution in a fuel element substrate as described in claim 1, characterized in that: In step 2, the metal air cooling pipe is made of stainless steel or Inconel alloy. The size of the metal air cooling pipe matches the cooling channels of the substrate. The cooling gas is an inert gas, and the gas flow rate is adjusted by a flow meter.

4. The method for achieving non-uniform temperature distribution in a fuel element substrate as described in claim 1, characterized in that: In step 5, high-temperature resistant metals or ceramic materials are selected as the fuel element substrate.

5. The method for achieving non-uniform temperature distribution in a fuel element substrate as described in claim 1, characterized in that: In step 8, the fuel element substrate unit structure uses C-type and N-type thermocouples for temperature measurement. A total of 9 thermocouples are arranged in the fuel element substrate unit structure: 3 thermocouples are arranged on the surface of the electric heating element, evenly distributed along the axial and circumferential directions; 2 thermocouples are arranged on the surface of each metal cooling pipe, circumferentially opposite to the measurement point of the electric heating element.

6. The method for achieving non-uniform temperature distribution in a fuel element substrate as described in claim 1, characterized in that: In step 9, the thermocouple is vertically inserted into the gap between the electric heating element and the substrate. The thermocouple is then bound to the surface of the electric heating element using a high-temperature wire. At the same time, high-temperature insulation cotton is placed between the thermocouple end and the electric heating element, pressing the thermocouple end against the surface of the electric heating element.

7. The method for achieving non-uniform temperature distribution in a fuel element substrate as described in claim 1, characterized in that: In step 10, for the metal air-cooled pipe, a groove is cut into the surface of the pipe, the thermocouple is vertically inserted into the groove, and the thermocouple is bound to the surface of the metal air-cooled pipe using a high-temperature wire. High-temperature insulation cotton is placed between the end of the thermocouple and the metal air-cooled pipe, and the end of the thermocouple is pressed against the surface of the metal air-cooled pipe.

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