Experimental device and method for studying the failure behavior of nuclear reactor fuel bundle accidents

Abstract

The application relates to an experimental device for studying the accident failure behavior of a nuclear reactor fuel rod bundle, comprising a high-temperature heating furnace, a fuel rod bundle and auxiliary equipment, the fuel rod bundle is composed of multiple fuel rods, the fuel rod bundle penetrates through the high-temperature heating furnace along the channel axis, the multiple fuel rods are arranged in a 5*5 matrix, including 20 heating rods, 1 non-heating rod and 4 corner rods, wherein the 1 non-heating rod is located at the center, and the 4 corner rods are located at the four corners of the matrix; electrodes are arranged at the two ends of the fuel rod bundle to heat the fuel rod bundle. The auxiliary equipment simulates the environment of the fuel rod bundle in the high-temperature heating furnace, so that the oxidation, expansion and failure states and data of the fuel rod bundle under different environments are obtained. Through the arrangement of the 25 fuel rods, the application can carry out fuel rod bundle experiments under the influence of factors such as flow channel blockage between the fuel rod bundles, rod extrusion, inter-rod thermal radiation and axial temperature difference under the influence of oxidation, expansion and failure mechanisms.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear grade fuel cladding element performance test experiment, in particular to an experimental device and method for studying the accident failure behavior of a nuclear reactor fuel rod bundle. BACKGROUND

[0002] In the development of nuclear grade fuel cladding performance test and mechanism model, the cladding under high temperature conditions in a severe accident, such as swelling and bursting, high temperature oxidation, and quenching failure model, is generally obtained through single rod mechanism experiment, which provides strong support for the development of accident acceptance criteria and severe accident failure criteria. However, the actual situation in the reactor under accident conditions is more complex. During the transient temperature rise of the fuel rod bundle composed of multiple fuel rods under a severe accident, the fuel rod bundle rapidly swells, bends and is pressed against each other, causing the arrangement of the rod bundle to be chaotic, the baffle to be deformed, and the flow channel to be blocked. The pressing between the rods and the blockage of the flow channel reduce the contact area of the cladding surface with the steam, and reduce the oxidation rate, causing uneven oxidation at different positions. In addition, the fuel rod bundle swells to different degrees under the action of high temperature and internal pressure, causing the cladding wall thickness to thin and eventually rupture, and the rupture of the cladding causes the oxidation of the inner surface, affecting the structural integrity of the cladding.

[0003] Therefore, the oxidation, swelling and failure empirical relationship obtained by single rod experiment cannot accurately reflect the influence of factors such as flow channel blockage, rod pressing, rod thermal radiation and axial temperature difference on the oxidation, swelling and failure mechanism. SUMMARY

[0004] Based on this, the present application provides an experimental device and method for studying the accident failure behavior of a nuclear reactor fuel rod bundle, which is used to develop the failure mechanism of the fuel rod bundle under severe accident conditions, and to adaptively correct the swelling model, oxidation model and failure model obtained by single rod experiment under the condition of the rod bundle. Specifically, it includes:

[0005] The high-temperature heating furnace includes an upper chamber, a middle cylinder and a lower chamber, which are connected in sequence;

[0006] The fuel rod bundle includes a plurality of fuel rods, and the fuel rod bundle penetrates the upper chamber, the middle cylinder and the lower chamber. The plurality of fuel rods are uniformly spaced in a 5x5 matrix, and the plurality of fuel rods include 20 heating rods, 1 non-heating rod and 4 corner rods. The 1 non-heating rod is located at the center, and the 4 corner rods are located at the 4 corners of the matrix. The two ends of the 25 fuel rods are provided with positioning grids to fix the relative positions of the plurality of fuel rods, and the two ends of the heating rods are respectively provided with heating electrodes;

[0007] The accessory device is connected with the high-temperature heating furnace and includes a water injection system, a gas system and a control system.

[0008] In one of the embodiments, the outer wall of the middle cylinder is provided with two interfaces for connecting with external swinging devices to swing the high-temperature heating furnace left and right.

[0009] In one of the embodiments, the heating rod includes a heating part and a cladding, the cladding encapsulates the heating part, and the heating part includes, from top to bottom, a first copper electrode, a first molybdenum electrode, a heating wire, a second molybdenum electrode and a second copper electrode connected in sequence; wherein the heating wire is stacked around a ceramic core block, and there is an air gap between the heating part and the cladding.

[0010] In one of the embodiments, the heating part is provided with two gas inlet channels, both of which are communicated with the air gap at one end and with the gas system at the other end; one of the gas inlet channels is arranged in the first copper electrode and the first molybdenum electrode, and the other gas inlet channel is arranged in the second copper electrode and the second molybdenum electrode.

[0011] In one of the embodiments, one non-heating rod is a first ring, eight heating rods around the non-heating rod are a second ring, and twelve heating rods around the eight heating rods are a third ring.

[0012] The eight heating rods of the second ring can inject a first inert gas through the gas inlet channel, the twelve heating rods of the third ring can inject a second inert gas through the gas inlet channel, and the first inert gas is different from the second inert gas.

[0013] In one of the embodiments, one of the corner rods is detachably connected with the positioning grid for fixing the fuel rod bundle.

[0014] In one of the embodiments, a plurality of thermocouples are further included, one of which is arranged in the interior of the non-heating rod and in the other three corner rods.

[0015] The remaining plurality of thermocouples are arranged on the outer wall of the cladding of the non-heating rod and part of the heating rods, and the height positions are different from each other; the thermocouples are in communication connection with the control and measurement system.

[0016] The application further provides a method for studying the accident failure behavior of a nuclear reactor fuel rod bundle, which uses the experimental device for studying the accident failure behavior of a nuclear reactor fuel rod bundle according to any one of the above embodiments and includes the following steps:

[0017] Check that the experimental device is in a safe and available state;

[0018] installing 5x5 array of fuel rod bundles into a high temperature furnace;

[0019] vacuuming the high temperature furnace;

[0020] performing a rocking operation on the high temperature furnace;

[0021] electrode heating the fuel rod bundles;

[0022] measuring data generated by the fuel rod bundles during the heating process by a control system;

[0023] turning off all power supplies.

[0024] In one embodiment, the step of electrode heating the fuel rod bundles further comprises,

[0025] pressurizing the fuel rod bundles by a gas system during the heating process;

[0026] injecting steam into the high temperature furnace by a water injection system during the constant temperature process;

[0027] increasing the electric power to reach a preset quenching temperature after the constant temperature process;

[0028] injecting cooling water into the high temperature furnace by the water injection system at the quenching temperature.

[0029] In one embodiment, the method of studying the behavior of nuclear reactor fuel rod bundles in an accident condition further comprises:

[0030] filling the fuel rod bundles and flow channels with gel and performing offline measurement after solidification.

[0031] The experimental device for studying the failure behavior of the nuclear reactor fuel rod bundle in the accident is characterized by comprising a high-temperature heating furnace, and an environment simulation of the fuel rod bundle in the high-temperature heating furnace is performed through an auxiliary device, so that the oxidation, expansion and failure states and data of the fuel rod bundle under different environments are obtained. Specifically, the high-temperature heating furnace comprises an upper chamber, a middle cylinder and a lower chamber, all of which are provided with coaxial channels and are detachably connected in sequence from top to bottom through flanges; the fuel rod bundle is composed of a plurality of fuel rods, the fuel rod bundle penetrates the high-temperature heating furnace along the channel axis, the plurality of fuel rods are arranged in a 5*5 matrix, including 20 heating rods, 1 non-heating rod and 4 corner rods, wherein the 1 non-heating rod is located at the center and the 4 corner rods are located at the 4 corners of the matrix; the 25 fuel rod bundles are provided with positioning grids at both ends to fix the relative positions of the plurality of fuel rods, and the fuel rod bundles are respectively provided with electrodes at both ends to heat the fuel rod bundles. The auxiliary device is connected with the high-temperature heating furnace and comprises a water injection system, a gas system and a control system, the water injection system is used for cooling the high-temperature heating furnace and / or submerging the cladding of the fuel rod bundle; the gas system is used for inputting and outputting gas into the high-temperature heating furnace to change the gas environment in the high-temperature heating furnace; the control and measurement system is in communication connection with the water injection system and the gas system to control the working states of the two systems and is used for monitoring the data in the high-temperature heating furnace. Through the arrangement of the 25 fuel rods, the influence of the flow channel blockage between the fuel rod bundles, the extrusion between the rods, the thermal radiation between the rods, the axial temperature difference and other factors on the oxidation, expansion and failure mechanism can be developed by the rod bundle experiment. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a schematic view of the connection of the high-temperature heating furnace and the auxiliary device.

[0033] Figure 2 It is a sectional view of the high-temperature heating furnace.

[0034] Figure 3 It is a sectional view of the fuel rod bundle.

[0035] Figure 4 It is a sectional view of the heating rod.

[0036] Figure 5 It is a temperature change curve of the second ring heating rod in the fuel rod bundle.

[0037] Figure 6 It is the main steam and coolant flow curve in the quenching stage.

[0038] Figure 7 It is a graph of the change of the oxidation layer of the fuel rod bundle with time.

[0039] Figure 8 It is a graph of the change of the hydrogen leakage amount of the fuel rod bundle with time.

[0040] Figure 9The macro-morphology of the cladding 211 at the axial height position of 400 mm.

[0041] Figure 10 The macro-morphology of the fuel rod bundle at each height position in the second fuel rod bundle.

[0042] Figure 11 The micro-morphology of the cladding oxidation and cracking of the fuel rod bundle.

[0043] Fig. 1 is a schematic diagram of a high-temperature furnace according to the present application. Fig. 2 is a schematic diagram of a high-temperature furnace according to the present application. DETAILED DESCRIPTION

[0044] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a number of different ways beyond the specific embodiments described and it is therefore contemplated to cover all such modifications as fall within the scope of the application. It is to be understood that other embodiments can be utilized and structural or logical changes can be made without departing from the scope of the present application. Therefore, the specific embodiments disclosed herein are not to be taken in a limiting sense and the scope of the present application is to be interpreted in accordance with the entire written specification and the claims.

[0045] In the description of the present application, it should be understood that, if there are terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0046] In addition, if there are these terms "first", "second", these terms are only for the purpose of description, and can not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined as "first", "second" can be explicitly or implicitly included at least one feature. In the description of the present application, if there are terms "a plurality of", the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise specifically limited.

[0047] In the present application, unless otherwise expressly specified and limited, if there are terms "installation", "connection", "connection", "fixation" and the like, these terms should be broadly understood. For example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise expressly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0048] In the present application, unless otherwise expressly specified and limited, if there are similar descriptions such as "first feature on" or "below" the second feature, the meaning can be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature "above", "above" and "above" the second feature can be the first feature directly above or obliquely above the second feature, or only indicates that the first feature is higher than the second feature in horizontal height. The first feature "below", "below" and "below" the second feature can be the first feature directly below or obliquely below the second feature, or only indicates that the first feature is lower than the second feature in horizontal height.

[0049] It should be noted that if an element is referred to as "fixed to" or "provided on" another element, it can be directly on another element or there can be a middle element. If an element is considered to be "connected" to another element, it can be directly connected to another element or there can be a middle element. If present, the terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used in the present application are only for the purpose of illustration, and do not represent the only implementation.

[0050] Referring to Figures 1 to 4 The present application provides an experimental device for studying the accident failure behavior of nuclear reactor fuel rod bundle 200 (hereinafter referred to as experimental device), the main container is high temperature heating furnace 100, the experimental material is fuel rod bundle 200, and in order to simulate various environments, the experimental device further includes some auxiliary equipment.

[0051] Specifically, the high-temperature heating furnace 100 includes an upper chamber 110, a middle cylinder 120, and a lower chamber 130, which are sequentially connected.

[0052] Referring to Figure 2 Preferably, the furnace body of the high-temperature heating furnace 100 is made of 304 stainless steel material, and the inner wall of the heating furnace is wrapped with a 42mm-thick heat preservation layer. The heat preservation layer of the high-temperature heating furnace 100 is arranged in the furnace body and is composed of an outer sleeve, a heat preservation layer, and an inner liner. The outer sleeve is composed of heat-resistant stainless steel plates and section steels and is welded. The heat insulation layer adopts a combined structure of molybdenum screens and zirconia heat preservation blocks. The middle cylinder 120 of the high-temperature heating furnace 100 is connected with the upper and lower chambers through water-cooled flanges, which are both made of stainless steel blind flanges. The water-cooled flanges become the upper and lower furnace doors of the middle cylinder 120, and both ends of the furnace doors are provided with furnace liner heat insulation doors and inlet and outlet water guide pipes. The upper and lower furnace doors adopt multi-layer molybdenum screen heat preservation, and the furnace body heat preservation layer and the upper and lower furnace door heat preservation layer adopt a boss cooperation. The outer part of the heat preservation layer in the middle cylinder 120 is water-cooled to prevent the temperature of the outer wall of the heating furnace body from being too high. The upper and lower furnace doors and the middle cylinder 120 adopt a manual hinge locking device, and the furnace door flange and the furnace body flange adopt a round strip type rubber ring for sealing and pressure bearing.

[0053] Specifically, the bottom of the lower chamber 130 is provided with a gas injection pipeline and a vacuum pump, inert gas, quenching water pipeline, which are used for vacuumizing and injecting superheated steam, inert gas, and quenching water during the experiment. The top of the upper chamber 110 is provided with a steam gas outlet for discharging the experimental mixed gas. The upper chamber 110 and the lower chamber 130 of the high-temperature heating furnace 100 are both provided with cooling water inlets and outlets for electrode cooling.

[0054] The fuel rod bundle 200 includes a plurality of fuel rods, and the fuel rod bundle 200 penetrates the upper chamber 110, the middle cylinder 120, and the lower chamber 130. The plurality of fuel rods are uniformly spaced in a 5×5 matrix and include 20 heating rods 210, 1 non-heating rod 220, and 4 corner rods 230. The 1 non-heating rod 220 is located at the center, and the 4 corner rods 230 are located at the 4 corners of the matrix. The two ends of the 25 fuel rod bundles 200 are provided with positioning grids to fix the relative positions of the plurality of fuel rods, and the two ends of the fuel rod bundle 200 are respectively provided with heating electrodes.

[0055] Specifically, the fuel rod bundle 200 constitutes a four-loop model, and the arrangement mode is as shown in Figure 3The non-heating rod 220 is located in the center of the rod bundle (the first ring), 8 heating rods 210 are arranged around the non-heating rod 220 (the second ring), 12 heating rods 210 are arranged in the outer ring (the third ring), and 4 zirconium alloy corner rods 230 are arranged in the four corners of the outermost periphery (the fourth ring). The non-heating rod 220 located in the center of the rod bundle can be used to investigate the experimental data between the comparative heating rod and the non-heating rod, and the 20 heating rods 210 located in the second ring and the third ring can be used to simulate the fuel elements in the edge channel, the corner channel and the middle channel. The four Zr alloy corner rods 230 with a diameter of 6 mm are inserted into the four corners of the outermost periphery, which can fill the large area irregular flow caused by the arrangement of the heating rods 210, so that the third ring heating rod 210 is in a more uniform temperature field.

[0056] The auxiliary equipment is connected with the high-temperature heating furnace 100, including a water injection system 310, a gas system and a control system. It can be understood that the auxiliary equipment belongs to the prior art, so the specific working principle is not introduced, and the connection method with the high-temperature heating furnace 100 and the cooperation with the high-temperature heating furnace 100 also belong to the prior art.

[0057] The water injection system 310 is used to cool the high-temperature heating furnace 100 and / or the cladding 211 of the flooded fuel rod bundle 200. Specifically, the water injection system 310 includes a cooling assembly and a water injection assembly. The cooling assembly is used to cool the electrode, the surface of the heating furnace body and the sealing flange of the furnace body. The cooling water flows from the total water inlet pipe of the cooling system to each cooling part through the distribution pipe, and then returns to the water cooler through the return pipe. The water injection assembly mainly consists of a stainless steel water tank, a pipeline centrifugal water pump, a mass flow meter and corresponding valves and instruments. In the water injection experiment after water loss, the speed of flooding the cladding 211 is controlled by the flow meter metering method.

[0058] The gas system includes a steam system 321, a vacuum system 322 and an inert gas system 323. The steam generated by the steam system 321 is adjusted by a valve to stably output the rated flow of steam, and then measured by a vortex flow meter and enters the high-temperature heating furnace 100 after passing through the preheating section. The vacuum system 322 is used to extract the air inside the furnace body of the high-temperature heating furnace 100, so that the vacuum degree inside the furnace body is less than 1 Pa. The inert gas system 323 includes a high-pressure gas cylinder, a pressure reducing valve and corresponding valves and instruments to realize the inert gas environment.

[0059] The control measurement system is in communication connection with the water injection system and the gas system to control the working states of the two systems and to monitor the data in the high-temperature heating furnace 100, such as the heating power, the temperature, the flow and pressure of the steam, the water injection flow and the vacuum degree of the heating furnace. Specifically, the measurement tools in the control measurement system include but are not limited to a pressure gauge, a mass spectrometer, various flow meters, a thermocouple 400, a thermometer, a length measuring scale, a sensor and the like, which can be determined according to different experimental requirements for the fuel rod bundle 200. Similarly, the control measurement system also belongs to the prior art.

[0060] The experimental device for studying the accident failure behavior of the nuclear reactor fuel rod bundle 200 includes the high-temperature heating furnace 100. The fuel rod bundle 200 in the high-temperature heating furnace 100 is subjected to environmental simulation by the auxiliary equipment, so as to obtain the oxidation, expansion and failure states and data of the fuel rod bundle 200 under different environments. Specifically, the high-temperature heating furnace 100 includes an upper chamber 110, a middle cylinder 120 and a lower chamber 130, all of which are provided with coaxial channels and are detachably connected in sequence from top to bottom through flanges. The fuel rod bundle 200 is composed of a plurality of fuel rods. The fuel rod bundle 200 penetrates the high-temperature heating furnace 100 along the channel axis. The plurality of fuel rods are arranged in a 5x5 matrix, including 20 heating rods 210, 1 non-heating rod 220 and 4 corner rods 230. The 1 non-heating rod 220 is located at the center, and the 4 corner rods 230 are located at the 4 corners of the matrix. The 5x5 fuel rod bundle 200 arrangement in the experimental system can consider the influence of four types of flow field channels, i.e., the edge channel, the corner channel, the middle channel and the center channel, on the flow and heat exchange of the fuel rod bundle 200. The positioning grids are arranged at both ends of the 25 fuel rods to fix the relative positions of the plurality of fuel rods. The positioning grids can better simulate the relatively large influence of the actual environment on the flow and heat exchange of the fuel rod bundle 200, the constraint force generated by the fuel rod bundle 200 and the influence on the oxidation, expansion, failure and other characteristics of the fuel rod bundle 200.

[0061] The working pressure range of the experimental device provided in the application is 0-12 MPa, the heating temperature range is room temperature to 2800℃, and the rated heating power of each heating rod 210 reaches 20 kW. The oxidation, expansion and damage experiments of the fuel rod bundle 200 under various conditions such as a vacuum environment, an inert gas environment, a steam environment and a water injection environment can be realized.

[0062] Referring to Figure 2 In one embodiment, the outer wall of the middle cylinder 120 is provided with two interfaces 121 for connecting with an external swinging device to swing the high-temperature heating furnace 100 left and right.

[0063] Specifically, the external swinging device can realize ±150° inclination of the high-temperature heating furnace 100, which is convenient for experimental loading and simulation of swinging experimental conditions.

[0064] Referring to Figure 4 In one embodiment, the heating rod 210 comprises a heating part and a cladding 211, the cladding 211 encapsulates the heating part, the heating part comprises, from top to bottom, a first copper electrode 212, a first molybdenum electrode 213, a heating wire 214, a second molybdenum electrode and a second copper electrode connected in sequence; the heating wire 214 is surrounded by stacked ceramic pellets 215, and there is an air gap 216 between the heating part and the ceramic pellets 215 and the cladding 211. The heating rod 210 is of a symmetrical structure, so Figure 3 Only the upper half is shown, and the second molybdenum electrode and the second copper electrode of the lower half are not shown.

[0065] Preferably, in one embodiment, the heating rod 210 uses internal electric heating. The heating rod 210 is heated by a clamp electrode, and a tantalum heating wire 214 is arranged in the center, and molybdenum electrodes are arranged at both ends for heating. This heating method can simulate the heat transfer of the actual pellets and the distribution of the axial power. The air gap 216 between the heating part and the cladding 211 is used to accommodate gas, which can adjust the pressure in the cladding 211. The fuel cladding 211 is sealed by an O-ring, which can move up and down at high temperature, without causing axial displacement or expansion of the rod bundle. The O-ring and the inner wall of the cladding 211 are pressed to seal the high-pressure gas in the cladding 211. Specifically, the cladding 211 is made of a zirconium tube. A red copper electrode is designed as the first copper electrode 212 above the first molybdenum electrode 213, and grooves are opened on the red copper electrode to install sealing rings, which can strengthen the sealing of the high-pressure gas in the zirconium tube, and provide an inert gas heating environment for the first molybdenum electrode 213 and the heating wire 214. There are a total of four O-rings in the electrode, which facilitates cooling by cooling water.

[0066] Referring to Figure 4In one embodiment, the heating section is provided with two gas inlets 217 (one of which is not shown), each of which is in communication with the gas gap 216 at one end and with the gas system at the other end. One of the gas inlets 217 is arranged in the first copper electrode 212 and the first molybdenum electrode 213, and the other gas inlet 217 is arranged in the second copper electrode and the second molybdenum electrode. The gas inlets 217 can facilitate the gas system to inject different gases into the second and third annular heating rods 210, respectively, as tracer gases. Specifically, in some embodiments, the eight heating rods 210 in the second annulus can be injected with a first inert gas through the gas inlets 217, and the twelve heating rods 210 in the third annulus can be injected with a second inert gas through the gas inlets 217. The first inert gas and the second inert gas are different. For example, the first inert gas can be a gas composed of 95% argon and 5% krypton, and the second inert gas can be helium. That is, 95% argon and 5% krypton can be injected into the heating rods 210 in the second annulus, and helium can be injected into the heating rods 210 in the third annulus as a tracer gas. Of course, the first inert gas and the second inert gas can also be other gases, which are not limited herein. Since the gases injected into the heating rods 210 in the second and third annuli are different, it can be determined whether the cladding 211 of the heating rods 210 in the second or third annulus has been damaged according to the composition of the detected excluded gas.

[0067] In one embodiment, one of the removable corner rods 231 is detachably connected to the positioning grid to measure the growth of the oxide layer during the experiment, and the remaining three fixed corner rods 232 are not detachable.

[0068] In one embodiment, a plurality of thermocouples 400 are further included, one of which is arranged in the interior of each of the non-heating rods 220 and the other three corner rods 230.

[0069] The remaining plurality of thermocouples 400 are arranged on the outer wall of the cladding 211 of the non-heating rods 220 and part of the heating rods 210, and the height positions are different from each other.

[0070] Specifically, in the above embodiment, in order to study the temperature distribution of the fuel rod bundle 200 and the differences in oxidation, expansion and failure characteristics in the radial and axial directions, the thermocouples 400 are arranged at different high-temperature positions of different fuel rod bundles 200 for measurement. Since the fuel rod bundle 200 contains 21 heating rods 210 and non-heating rods 220 and is arranged compactly, too many wall-mounted thermocouples 400 cannot be laid to avoid affecting the flow channel. Figure 3As shown, in the fuel rod bundle 200, the first ring non-heating rod 220 is internally arranged with a tungsten-rhenium thermocouple 400, specifically, the material of the thermocouple 400 is tungsten-rhenium, and the thermocouple 400 is arranged at different height positions of the wall surface of the cladding 211; three representative rods are selected from the second ring and the third ring, and the thermocouples 400 are arranged at different high-temperature positions for measuring the axial distribution of the cladding 211 temperature; three corner rods 230 are selected from the fourth ring, and the thermocouples 400 are arranged internally.

[0071] In one embodiment, the middle cylinder 120 is uniformly provided with four windows 122 along the circumference thereof, the window 122 is a quartz glass window 122, and an infrared temperature measuring instrument, a laser micrometer and a high-speed camera are arranged outside the window 122; the infrared temperature measuring instrument is used for measuring the temperature of the fuel rod bundle 200; the laser micrometer can measure the expansion process of the cladding 211 of the fuel rod bundle 200 under the action of internal pressure and high temperature in real time; and the high-speed camera is used for shooting the phenomena in the test process.

[0072] In addition, the infrared temperature measuring instrument can also be used to observe the growth condition of the oxidation layer on the detachable corner rod 231.

[0073] In order to monitor the generation rate of combustible gas in the experimental process and judge the oxidation starting time, a mass spectrometer is arranged at the steam gas outlet for gas monitoring. When the mass spectrometer detects hydrogen or carbon monoxide, or the measured value of the thermocouple 400 on the surface of the cladding 211 appears a clear step, it means that the oxidation reaction has occurred, and the corresponding temperature and time at this time are recorded as the starting condition of the rapid oxidation reaction of the cladding 211. The hydrogen and carbon monoxide generation rates of the cladding 211 as a whole are recorded by the mass spectrometer. In order to monitor the failure point position and failure sequence of the cladding 211 in the experimental process, the second ring heating rod 210 is filled with 95% argon + 5% krypton, and the third ring heating rod 210 is filled with helium. When the mass spectrometer detects that the exhaust gas contains krypton or helium, it can be judged that the cladding 211 in the second ring or the third ring has been damaged. In addition, there is an internal pressure detection table at the bottom of each of the 21 claddings 211, and when the pressure changes suddenly, the failure sequence of the cladding 211 can be further judged, and the failure point position distribution and the temperature when the cladding 211 is damaged are recorded.

[0074] The application also provides an experimental method for studying the accident failure behavior of a nuclear reactor fuel rod bundle 200, which uses the experimental device for studying the accident failure behavior of the nuclear reactor fuel rod bundle 200 in any of the above embodiments, and includes the following steps:

[0075] Check the experimental device is in a safe and available state. Specifically includes the pre-treatment of the experimental piece and the debugging of the experimental equipment. In the pre-treatment of the experimental piece, the end face of the cladding 211 experimental piece is polished, deburred and cleaned and dried. After completing the measurement and recording of the length, diameter and weight of each cladding 211, the installation of the 5x5 fuel rod bundle 200 and the positioning grid is carried out. The debugging of the experimental equipment needs to confirm that the main experimental systems including the heating furnace, the vacuum system 322, the water circulation system, the steam system 321 and the data acquisition system are in a safe and available state.

[0076] Install the 5x5 arranged fuel rod bundle 200 into the high temperature heating furnace 100.

[0077] Vacuumize the high temperature heating furnace 100, and after the vacuum degree in the furnace reaches the set value, the inert gas system 323 is started to fill gas into the heating furnace. After stabilizing for a period of time, vacuumize the furnace again, and repeat three times to remove the oxygen content in the interior of the furnace body. The oxygen content at this time is read through the oxygen sensor at the top of the furnace body, so as to ensure that only water vapor participates in the oxidation reaction when the formal experiment is carried out.

[0078] Carry out the swing operation of the high temperature heating furnace 100, and set different swing amplitudes and frequencies for simulating the ocean swing condition.

[0079] Carry out electrode heating on the fuel rod bundle 200;

[0080] Measure the data generated by the fuel rod bundle 200 in the heating process through the control system;

[0081] Turn off all power supplies.

[0082] In one embodiment, in the step of carrying out electrode heating on the fuel rod bundle 200, further comprising,

[0083] In the heating process of the fuel rod bundle 200, the internal pressure of the fuel rod bundle 200 is charged through the gas system, and the rod bundle is gradually increased in heating power in the steam and argon atmosphere, so that the temperature is increased from room temperature to a higher temperature (about 873K), and after stabilization, the heating power is gradually increased to increase the temperature to a high temperature interval (1273K~1673K). In this stage, the fuel cladding 211 will have phenomena such as internal pressure rise, hoop bulging, and rod extrusion, and finally burst pressure relief.

[0084] In the constant temperature process of the fuel rod bundle 200, water vapor is injected into the high temperature heating furnace 100 through the water injection system 310, so that the fuel rod bundle 200 enters the pre-oxidation stage, and the oxidation effect on the bright rod bundle under complex environment is studied.

[0085] After the constant temperature process of the fuel rod bundle 200, the electric power is increased, so that the highest temperature of the fuel rod bundle 200 reaches the preset quenching temperature;

[0086] The fuel rod bundle 200 is injected with cooling water by the water injection system 310 at the quenching temperature, and the highly oxidized fuel rod bundle 200 can be severely deformed or even fragmented under the severe thermal shock.

[0087] During the reaction of the fuel rod bundle 200, online measurement is needed, and the data to be measured mainly include the diameter of the cladding 211, the temperature of the cladding 211 and the steam, the internal pressure of the cladding 211 and the steam pressure, the steam flow, the expansion size of the cladding 211, the burst temperature and size, the oxidation depth, the fragmentation temperature and size, etc.

[0088] Specifically, in the online measurement experiment, the temperatures to be measured include the experimental section temperature, the heating furnace body internal temperature, the steam and cooling water temperature, and the cladding 211 temperature is measured by the armored tungsten-rhenium thermocouple 400 arranged on the outer surface of the cladding 211, and the thermocouple 400 is clamped on the outer wall of the cladding 211 by a zirconia oxide containing sprayed tantalum sheet; the pressures to be measured include the heating furnace internal pressure, the cladding 211 internal pressure, the steam generator and inert gas pressure, wherein the heating furnace internal pressure and the cladding 211 internal pressure are monitored and collected in real time by a pressure transmitter, and the steam generator and inert gas system 323 pressure is measured by a pressure gauge; the flow rates to be measured include the steam flow, the argon flow and the cooling water flow, wherein the steam and argon flow rates are measured by a turbine flowmeter, and the cooling water flow rate is measured by a mass flowmeter. In addition, the mass spectrometer can obtain the concentration of each component of the mixed gas in real time. When the mass spectrometer detects that the exhaust gas contains krypton or helium, it can be judged that the cladding 211 has burst, and the position, temperature and sequence of the cladding 211 burst point can be obtained by the internal pressure detection table. At the same time, the real-time oxidation process of the cladding 211 can be monitored by the concentration of combustible gases such as hydrogen and carbon monoxide.

[0089] In one embodiment, after all power supplies are turned off, the experimental method for studying the accident failure behavior of the nuclear reactor fuel rod bundle 200 further includes the steps of:

[0090] The gel is poured into the fuel rod bundle 200 and the flow channel, and after solidification, the experiment is carried out offline.

[0091] Specifically, after the gel solidifies, different sections are cut along the vertical axis to obtain the flow passage area and the blockage ratio of the flow passage at each height position when the cladding 211 is damaged, and to obtain the distribution law of the cladding 211 bulging and bursting position. Then, the cladding 211 bulging and rupture area, the cladding 211 fragmentation area, the positioning grid and the surrounding plate area are selected to make metallographic analysis samples, and the key information such as the microstructure deformation characteristics of the cladding 211 in each area, the morphology and thickness of the oxide layer and the like are observed under the SEM. The EDS is used to analyze the element composition distribution of the oxide layer related to the cladding 211 tube bulging deformation and bursting area, and the oxidation and failure law of the fuel rod under the rod bundle condition is obtained.

[0092] Figure 5 The temperature change curve of the cladding 211 of the heating rod 210 of the second ring of the fuel rod bundle at different axial height positions in the working condition development process (the heating, constant temperature, transient and quenching stages) is shown, Figure 5 In the figure, the vertical axis in English represents "temperature", and the horizontal axis represents "time". It is used to guide the experiment in real time and to correct the temperature of the cladding expansion and oxidation model in the offline measurement.

[0093] Figure 6 The main steam and coolant flow curves in the quenching stage are shown, in which the vertical axis in English represents "mass flow rate" with the unit of grams per second; the horizontal axis represents "time" with the unit of seconds. "Quench water" in the figure means "quenching water", and "uncorr, for delay" means "open loop, for delay".

[0094] Figure 7 The oxide layer thickness of the cladding 211 of the heating rod 210 of the second ring of the fuel rod bundle 200 at different axial height positions measured by the eddy current method and the microscopic detection method is shown, which is used to correct the oxidation model of the cladding 211. In which, "measured by eddy-current device" in English means "measured by eddy current device"; "metallographically determined" in English means "metallographically determined".

[0095] Figure 8The water vapor flow rate and hydrogen release rate (hydrogen is one of the main products of oxidation of cladding 211, and the main source of hydrogen explosion in the accident phase) in the transient and quenching stages are shown. The hydrogen release rate increases with the increase of temperature in the transient stage, but in the quenching stage, with the injection of water, the hydrogen release rate decreases rapidly, indicating that the cooling is effective, and the hydrogen release rate is used to correct the cladding oxidation model. Among them, "Onset of cooling" in English means "cooling begins"; the left vertical axis in English is the hydrogen release rate, and the right number axis in English means the water vapor flow rate, and the horizontal axis is time, units are: grams per second, grams per second, seconds.

[0096] Figure 9 The cladding 211 expansion, burst, and fragmentation at the 400mm axial height position are shown, and the temperature limit for correcting the burst and fragmentation model.

[0097] Figure 10 The flow channel flow area, flow channel blockage ratio, and cladding 211 position offset of fuel rod bundle 200 at different axial height positions are shown, which are used to correct the blockage rate in the cladding 211 expansion model. Among them, bottom means lower, top means upper, and "que" means the abbreviation of quench water.

[0098] Figure 11 The cladding 211 oxidation growth and cracking fragmentation characteristics at the 400mm axial height position are shown, wherein the English expression means the picture of a certain position of the cladding 211 under the condition of injecting cooling water. Of course, the characteristics of other heights are also obtained.

[0099] The technical features of the above-described embodiments can be combined in any manner. In order to make the description simple, not all possible combinations of technical features in the above-described embodiments are described, however, as long as the combination of technical features does not exist contradictory, it should be considered as the scope of the present application.

[0100] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent application scope. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. An experimental apparatus for the study of nuclear reactor fuel bundle accident failure behavior, characterized by, The application relates to a high-temperature heating furnace (100) and an auxiliary device thereof. The high-temperature heating furnace (100) comprises an upper chamber (110), a middle cylinder (120) and a lower chamber (130) which are sequentially connected. The fuel rod bundle (200) comprises a plurality of fuel rods, the fuel rod bundle (200) penetrates through the upper chamber (110), the middle cylinder (120) and the lower chamber (130), the plurality of fuel rods are uniformly spaced in a 5*5 matrix, the plurality of fuel rods comprise 20 heating rods (210), 1 non-heating rod (220) and 4 corner rods (230), wherein the 1 non-heating rod (220) is located at the center, and the 4 corner rods (230) are located at four corners of the matrix; both ends of the heating rod (210) are respectively provided with heating electrodes. The auxiliary device is connected with the high-temperature heating furnace (100) and comprises a water injection system (310), a gas system and a control and measurement system, the water injection system (310) is used for cooling the high-temperature heating furnace (100) and / or submerging the cladding (211) of the fuel rod bundle (200); the gas system is used for inputting or outputting gas into or out of the high-temperature heating furnace (100) to change the gas environment in the high-temperature heating furnace (100); the control and measurement system is in communication connection with the water injection system (310) and the gas system to control the working states of the two and is used for monitoring data in the high-temperature heating furnace (100).

2. The experimental apparatus for the study of nuclear reactor fuel bundle accident failure behavior according to claim 1, wherein, The outer wall of the middle cylinder (120) is provided with two interfaces (121) which are used for being connected with external swinging devices to swing the high-temperature heating furnace (100) left and right.

3. The experimental apparatus for the study of the behavior of the core reactor fuel bundle in the event of an accident according to claim 1 or 2, characterized in that, The heating rod (210) comprises a heating part and a cladding (211), the cladding (211) encapsulates the heating part, the heating part comprises, from top to bottom, a first copper electrode (212), a first molybdenum electrode (213), a heating wire (214), a second molybdenum electrode and a second copper electrode which are sequentially connected; a ceramic core block (215) is stacked around the heating wire, and an air gap (216) exists between the heating part and the cladding (211).

4. The experimental apparatus for the study of nuclear reactor fuel bundle accident failure behavior according to claim 3, wherein, The heating part is provided with two gas inlet channels (217), one end of each of the two gas inlet channels (217) is in communication with the air gap (216), and the other end is in communication with the gas system; one of the two gas inlet channels (217) is arranged in the first copper electrode (212) and the first molybdenum electrode (213), and the other gas inlet channel (217) is arranged in the second copper electrode and the second molybdenum electrode.

5. The experimental apparatus for studying the behavior of a nuclear reactor fuel bundle under accident conditions as defined in claim 4, wherein The non-heating rod is a first ring, 8 heating rods around the non-heating rod are a second ring, and 12 heating rods around the 8 heating rods are a third ring. The 8 heating rods of the second ring can inject a first inert gas through the gas inlet channel, the 12 heating rods of the third ring can inject a second inert gas through the gas inlet channel, and the first inert gas is different from the second inert gas.

6. The experimental apparatus for the study of nuclear reactor fuel bundle accident failure behavior according to claim 1, wherein, The angle bar (230) comprises one detachable angle bar (231) and three fixed angle bars (232), wherein the detachable angle bar (231) is detachably connected with the positioning grid for fixing the fuel rod bundle (200).

7. The experimental apparatus for the study of nuclear reactor fuel bundle accident failure behavior according to claim 6, wherein, A plurality of thermocouples (400) are further included, The non-heating rod (220) and the fixed angle bar (232) are each provided with one thermocouple (400); The remaining plurality of thermocouples (400) are arranged on the outer wall of the cladding (211) of the non-heating rod (220) and part of the heating rod (210), and the height positions are different from each other; the thermocouples (400) are in communication connection with the control measurement system.

8. A method for investigating the behavior of a nuclear reactor fuel bundle in an accident condition, using the experimental apparatus for investigating the behavior of a nuclear reactor fuel bundle in an accident condition according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: Checking that the experimental device is in a safe and available state; Installing the 5×5 arranged fuel rod bundle (200) into the high-temperature heating furnace (100); Vacuumizing the high-temperature heating furnace (100); Performing a swing operation on the high-temperature heating furnace (100); Electrode heating of the fuel rod bundle (200); Measuring the data generated by the fuel rod bundle (200) during the heating process through the control system; Turning off all power supplies.

9. The method for studying the accident failure behavior of the nuclear reactor fuel rod bundle according to claim 8, wherein, In the step of electrode heating of the fuel rod bundle (200), further comprising, During the temperature rising process of the fuel rod bundle (200), the internal pressure of the fuel rod bundle (200) is charged through a gas system; During the constant temperature process of the fuel rod bundle (200), water vapor is injected into the high-temperature heating furnace (100) through a water injection system (310); After the constant temperature process of the fuel rod bundle (200), the electric power is increased to make the maximum temperature of the fuel rod bundle (200) reach a preset quenching temperature; During the quenching temperature of the fuel rod bundle (200), cooling water is injected into the high-temperature heating furnace (100) through the water injection system (310).

10. The method of nuclear reactor fuel bundle accident failure behavior study of claim 9, wherein, After turning off all power supplies, the experimental method for studying the accident failure behavior of the nuclear reactor fuel rod bundle further comprises the following steps: Gel is poured into the fuel rod bundle (200) and flow channel, and after solidification, experimental offline measurement is carried out.

Images