Indirect electrically heated rod with axial non-uniform power distribution

Abstract

The application discloses an indirect electric heating rod with axial non-uniform power distribution, which comprises a cladding, a ceramic sleeve and a heating section arranged in the cladding in sequence, wherein two ends of the heating section are provided with electrode sections, and the electrode sections are connected with positive and negative poles of a direct current power supply respectively. The application adopts a central heating and axial heating power step distribution structure, can simulate the axial non-uniform power distribution with higher middle part and lower two ends of a nuclear fuel rod, and more accurately reflects the heating characteristics of the actual nuclear fuel rod.

Description

Technical Field

[0001] This invention relates to a technology in the field of reactors, specifically an indirect electric heating rod with axial non-uniform power distribution. Background Technology

[0002] To study the heat transfer mechanism of reactor flow, thermal-hydraulic experiments typically use electrically heated rods to simulate the thermal characteristics of nuclear fuel rods, with temperature sensors mounted on their surfaces to monitor wall temperatures. The experimental results are of paramount value for nuclear reactor design, fluid dynamics model development, and safety analysis program verification. However, existing non-uniform electric heating technologies, due to their structural characteristics, cannot achieve a radial temperature distribution that is higher at the center and lower around the edges. Furthermore, the uniformity of the materials leads to variations in thermal expansion, which can easily cause temperature measurement points to shift. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies, such as inaccurate simulation of the thermal characteristics of nuclear fuel rods, susceptibility to temperature measurement point misalignment, and significant errors in temperature measurement results. It proposes an indirect electric heating rod with axially non-uniform power distribution. Employing a central heating structure with a stepped axial heating power distribution, it can simulate the axially non-uniform power distribution (higher in the center and lower at both ends) and the radial temperature distribution (higher in the center and lower around the perimeter) of a reactor nuclear fuel rod, thus more accurately reflecting the heating characteristics of actual nuclear fuel rods. Positioning pads and metal springs are used to fix the thermocouples, ensuring accurate positioning of the temperature measurement points and accurate temperature measurement results.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to an indirect electric heating rod with axial non-uniform power distribution, comprising: a shell and a ceramic sleeve and a heating section arranged therein in sequence, wherein: the heating section is provided with electrode sections at both ends, and the electrode sections are respectively connected to the positive and negative terminals of a DC power supply.

[0006] The heating section is formed by welding together several alloy round bars of different diameters and lengths. The diameter of each round bar decreases and then increases from the bottom. The two ends of the heating section are welded to the electrode section. Since the resistance per unit length of each round bar is different, the heat power per unit length after energization is also different, thereby achieving an axial non-uniform power distribution that is higher in the middle and lower at both ends.

[0007] The inner diameter of the ceramic sleeve matches the outer diameter of each section of the alloy round bar, and its inner wall surface is tightly attached to the outer wall surface of the alloy round bar. Positioning gaskets are set between the ceramic sleeves to fix the thermocouple.

[0008] A ceramic gasket is preferably provided between the positioning gasket and the heating section, and the positioning gasket is clamped by the upper and lower ceramic sleeves.

[0009] The thermocouple has one end fixed to the positioning gasket and the other end led out through the end of the heating section, and the thermocouple lead is installed in the groove on the outer wall surface of the ceramic sleeve.

[0010] The thermocouple preferably has four thermocouple probes, and each thermocouple probe is located on a different positioning gasket.

[0011] The positioning gasket and the matched thermocouple probe are provided with a metal spring plate, which presses the thermocouple probe against the inner wall surface of the cladding.

[0012] Technical effects

[0013] The heating section of the present application is indirectly heated at the radial center, and is formed by welding a plurality of alloy round rods with different diameters and lengths end to end. The diameters of the round rods decrease first and then increase successively from the bottom, so that the unit length resistance values of the round rods are different, and after being electrified, the axial non-uniform power distribution of higher in the middle and lower at both ends can be realized. By matching the outer wall surface of the alloy round rod with a different inner diameter ceramic sleeve, not only the insulation effect of avoiding leakage of the cladding is achieved, but also the heat generated by the heating core can be effectively conducted. Compared with the prior art, the present application can realize the axial non-uniform power distribution of higher in the middle and lower at both ends and the radial temperature distribution state of higher in the center and lower around, can accurately simulate the thermal characteristics of the nuclear fuel rod, and the thermal hydraulic test results obtained by using the electric heating rod are closer to the actual reactor conditions, while solving the problems of power deviation caused by leakage and temperature measurement inaccuracy caused by air gap in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is an axial sectional view of the heating rod of the present application.

[0015] Figure 2 It is a radial sectional view of the heating rod of the present application.

[0016] Figure 3 It is a structure diagram of the ceramic sleeve.

[0017] Figure 4 It is a schematic diagram of the fixing method of the thermocouple probe.

[0018] Figure 5 It is an axial temperature distribution diagram of the cladding outer wall surface simulated by COMSOL.

[0019] Figure 6 It is a radial temperature distribution diagram of the highest power section simulated by COMSOL.

[0020] In the figure: 1 electrode section, 2 heating section, 3 ceramic sleeve, 4 positioning gasket, 5 ceramic gasket, 6 cladding, 7 thermocouple, 8 ceramic end plug, 9 metal end plug, 10 metal spring plate. DETAILED DESCRIPTION

[0021] As Figure 1 shown, the embodiment relates to an indirect electric heating rod with axial non-uniform power distribution, comprising: a cladding 6, and ceramic sleeves 3 and heating segments 2 arranged in sequence in the cladding 6, wherein: the two ends of the heating segments 2 are provided with electrode segments 1, and the electrode segments are connected with positive and negative poles of a direct current power supply respectively.

[0022] The heating segments 2 are a plurality of alloy round rods with different diameters and lengths which are welded end to end, the diameters of the round rods decrease first and then increase in sequence from the bottom, and the two ends of the heating segments are welded with the electrode segments, since the unit length resistances of the round rods are different, the unit length heat power is also different after electrification, thereby realizing the axial non-uniform power distribution with higher middle and lower two ends.

[0023] The inner diameters of the ceramic sleeves 3 match the outer diameters of the alloy round rods, and the inner wall surfaces of the ceramic sleeves 3 tightly abut the outer wall surfaces of the alloy round rods, and positioning spacers 4 are arranged between the ceramic sleeves 3 for fixing thermocouples 7.

[0024] As Figure 2 shown, ceramic spacers 5 are preferably arranged between the positioning spacers 4 and the heating segments 2, and the positioning spacers are clamped by the upper and lower ceramic sleeves 3.

[0025] A plurality of thermocouples 7 parallel to the central axis of the cladding 6 are arranged between the cladding 6 and the ceramic sleeves 3, one end of the thermocouples 7 is preferably fixed to the positioning spacers 4, and the other end is led out through the end of the heating segments 2.

[0026] The thermocouples 7 are preferably four, and the probes of each thermocouple 7 are located on different positioning spacers 4.

[0027] As Figure 4 shown, metal springs 10 are arranged between the positioning spacers 4 and the matched thermocouple 7 probes, and the thermocouple probes are pressed against the inner wall surface of the cladding 6.

[0028] A plurality of grooves for arranging the lead wires of the thermocouples 7 are arranged on the outer wall surface of the ceramic sleeves 3, and the lead wires of the thermocouples 7 are installed in the grooves on the outer wall surface of the ceramic sleeves 3.

[0029] Ceramic end plugs 8 and metal end plugs 9 are arranged between the electrode segments 1 and the cladding 6, the metal end plugs are welded with the inner wall surfaces of the two ends of the cladding, and are used for packaging and fixing the insulation layer and the axial relative position of the cladding.

[0030] The cladding 6 is a seamless pipe structure with constant outer diameter and wall thickness.

[0031] The alloy round rod is at the radial center, and the temperature is high after power supply, and the temperature of the insulating layer and the cladding is sequentially reduced. The ceramic sleeve is installed between the cladding and the heating core, the ceramic gasket and the ceramic end plug are installed on the inner wall surface of the positioning gasket and the metal end plug, so that the heating core and the cladding are mutually insulated, and the actual heating power is accurately ensured.

[0032] The embodiment relates to a manufacturing method of the indirect electric heating rod. -6 Ω·m, and the diameter presents a trend of first decreasing and then increasing, and specific values are 4.5 mm, 4 mm, 3.5 mm, 3 mm, 4 mm and 4.5 mm, and corresponding lengths are 1000 mm, 1000 mm, 700 mm, 300 mm, 500 mm and 160 mm, and the diameters of two pure nickel electrode round rods are 4.5 mm, and lengths are 350 mm and 450 mm. The total length of the Cr20Ni80 round rod after splicing is 3.66 m, which is the same as the length of most pressurized water reactor nuclear fuel rods. Then, a plurality of boron nitride ceramic sleeves with the same outer diameter and the inner diameter matched with the outer diameters of the Cr20Ni80 round rods and the pure nickel electrodes are manufactured, and four grooves parallel to the axis are arranged on the outer surface. The boron nitride ceramic sleeves are respectively sleeved on the outer wall surfaces of the corresponding outer diameter round rods, the positioning gaskets and the ceramic gaskets are installed at the temperature measuring positions and are fixed by the upper and lower boron nitride ceramic sleeves. The assembled structure is arranged in the order of first decreasing and then increasing from the bottom to the top according to the diameters of the Cr20Ni80 round rods, and the pure nickel electrodes are arranged at two ends, and cold welding is sequentially performed and straightening is performed. The grooves of each ceramic tube and the positioning gasket are sequentially aligned in the axial direction, and four copper metal springs are spot-welded at the groove positions of the positioning gaskets. Four K-type armored non-grounded thermocouples with a temperature measuring range of more than 1000 DEG C and a diameter of 0.5 mm are adopted. Four thermocouple probes are respectively welded on the corresponding copper metal springs by laser cold welding, lead wires are arranged in the axial grooves on the outer wall surfaces of the boron nitride ceramic sleeves, and the lead wires are led out from one end of the electric heating rod. An Inconel 600 seamless pipe with an outer diameter of 9.5 mm and a wall thickness of 0.84 mm is processed by using a grinding tool cold rolling, and is sleeved on the outer wall surface of the insulating layer, metal end plugs are welded at two ends, and ceramic end plugs are insulated. The thermocouple is pressed on the inner wall surface of the Inconel 600 seamless pipe by the copper metal spring.

[0033] In order to further verify the effectiveness of the indirect electric heating rod with axial non-uniform power distribution in the aspect of nuclear fuel rod thermal characteristic simulation, COMSOL software is used for electric-thermal coupling simulation analysis. The specific method is that one end of the electric heating rod is grounded, and the other end is supplied with 127.3 A direct current, so that the linear power density of the alloy round rod with the smallest diameter is 2.5 kW / m, that is, the highest linear power density of the electric heating rod is 2.5 kW / m, and the outer wall surface of the cladding is provided with a heat transfer coefficient of 10 W / (m 2·K) the convective heat transfer boundary condition at 30℃, and the transient calculation is carried out. When the heating lasts until the highest power section temperature reaches 1000℃, the temperature distribution state is recorded: Figure 5 For the axial temperature distribution of the cladding outer wall surface, the middle part of the heating section is obviously higher than the two ends, and there are 6 temperature steps, which proves the accuracy of the heating rod structure of the application in simulating the axial temperature distribution of the nuclear fuel rod; Figure 6 For the highest power section radial temperature distribution, the temperature at the radial center position is the highest, which is 1011℃, and gradually decreases to 1000℃ outward along the radius, forming a radial temperature distribution state of higher center and lower periphery, which is consistent with the actual radial temperature distribution characteristics of the nuclear fuel rod.

[0034] The electric heating rod of the application has an outer diameter of 9.5mm, a heating length of 3660mm, and a total length of 4460mm, and the heating power is distributed in a 6-step ladder form with higher middle part and lower two ends. The heating rod is provided with four cladding inner wall surface temperature measuring points with different axial heights, and the maximum rod surface temperature can reach 1000℃, which meets the requirements of various thermal hydraulic tests such as flow boiling heat transfer test, re-submergence test, and critical heat flux density test.

[0035] Compared with the prior art, the heating core of the device is formed by welding alloy round rods with different lengths and diameters at the radial center position, and after being electrified, it simultaneously meets the axial non-uniform power distribution with higher middle part and lower two ends and the radial temperature distribution with higher center and lower periphery, more truly simulating the thermal characteristics of the fuel rod in the reactor; the specific power distribution state can be accurately controlled by adjusting the length and diameter of the alloy round rod; there is an insulating layer between the heating core and the cladding for electrical insulation, so that the outer wall surface is not electrified when electrified, ensuring the accuracy of the actual heating power; the thermocouple probe is pressed against the cladding inner wall surface by a metal spring, is not affected by air gap, and is accurately positioned and has high temperature measurement accuracy; the structure design allows monitoring of multiple temperature points on the cladding inner wall surface, while the temperature measuring points are accurately positioned; the cladding is a complete metal tube without welds, has good axial straightness, and has consistent surface characteristics.

[0036] The above specific embodiments can be adjusted in different ways by those skilled in the art without departing from the principles and purposes of the application, the protection scope of the application is subject to the claims and is not limited by the above specific embodiments, and each implementation scheme within the scope is subject to the constraints of the application.

Claims

1. An indirectly electrically heated rod of axial non-uniform power distribution, characterized in that, The utility model relates to a kind of heating element and temperature measuring device for high-temperature furnace, including: Cladding and ceramic sleeve and heating section arranged in sequence in it, wherein: two ends of heating section are equipped with electrode section, electrode section is connected with direct current power supply positive pole and negative pole respectively; The heating section is a plurality of alloy round rods with different diameters and lengths welded end to end, the diameter of each round rod decreases first and then increases from the bottom, and the two ends of the heating section are welded with the electrode section. Since the resistance per unit length of each round rod is different, the heat power per unit length is also different after power on, thereby realizing the axial non-uniform power distribution of higher middle and lower ends and the radial temperature distribution state of higher center and lower periphery. A plurality of thermocouples parallel to the central axis of the cladding are provided between the cladding and the ceramic sleeve, one end of the thermocouple is fixed to the positioning gasket, the other end is led out through the end of the heating section, and the thermocouple lead is installed in the groove on the outer wall surface of the ceramic sleeve. The inner diameter of the ceramic sleeve matches the outer diameter of each section of alloy round rod, and the inner wall surface of the ceramic sleeve closely matches the outer wall surface of the alloy round rod. Positioning gaskets are provided between the ceramic sleeves for fixing the thermocouples. The positioning gasket and the heating section are provided with a ceramic gasket, and the positioning gasket is clamped by the upper and lower ceramic sleeves. The four thermocouples are arranged on different positioning gaskets. Metallic springs are provided between the positioning gaskets and the matched thermocouple probes to press the thermocouple probes against the inner wall surface of the cladding. The electrode section and the cladding are provided with ceramic end plugs and metal end plugs, the metal end plugs are welded with the inner wall surface of the cladding at both ends, and are used to package and fix the insulation layer and the axial relative position of the cladding. The cladding is a seamless pipe structure with constant outer diameter and wall thickness.

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