A device for simulating rod-shaped fuel reactivity introduction accidents using laser heating

Abstract

The invention discloses a device for simulating a rod-shaped fuel reactivity introduction accident by using laser heating. The device comprises a furnace body with a window, two ytterbium-doped fiber lasers facing the furnace body, a positive cone prism and a lens arranged at the window position of the ytterbium-doped fiber laser on one side, a thermal imager, a digital image measuring device and a signal acquisition and control device arranged around the furnace body, and further comprises a helium tank, a helium inlet pipe and a helium control valve, an iodine generating device and an iodine vapor control valve, a sample stage arranged at the center of the furnace body, a sample stage bracket supporting the sample stage, and a gas outlet pipe connected to the sample stage and a gas collection device. The device preheats the experimental sample by using the thermal imager and the signal acquisition and control device, controls the iodine concentration inside the sample stage by using the iodine vapor control valve and the helium control valve, monitors the deformation of the experimental sample throughout the entire process by using the digital image measuring device, and forms a laser ring by using the ytterbium-doped fiber laser, the positive cone prism and the lens on the other side to simulate the rod-shaped fuel reactivity introduction accident.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear fuel and material performance testing, and in particular relates to a device for simulating rod-shaped fuel reactivity introduction accidents by utilizing laser heating. Background Art

[0002] Fuel elements exposed to high temperature, high pressure, and high irradiation operating environments for a long time will produce a variety of failure behaviors, among which the failure behavior caused by PCI (pellet-clad interaction) is one of the most representative failure behaviors of fuel elements. RIA (reactivity introduction accident) conditions are one of the most common conditions that lead to PCI failure of fuel elements. Under RIA conditions, due to the spatial self-screening effect, the temperature and nuclear power at the edge of the fuel element rise sharply, causing PCI failure of the fuel element. In severe cases, a large amount of radioactive material will enter the primary coolant, making it impossible for the primary system to discharge heat in time, leading to serious accidents. For the above reasons, conducting research on the PCI behavior of fuel under RIA conditions is of great significance to improving reactor safety. However, the PCI failure behavior of fuel elements in real reactors caused by RIA conditions is extremely complex, and the related irradiation environment and physical field conditions are very harsh.

[0003] Under RIA conditions, the temperature at the fuel edge can reach over 2000°C within tens of milliseconds, causing the fuel pellets to swell violently due to the heat. Therefore, how to achieve a significant fuel temperature increase in a very short period of time and monitor the entire process of PCI behavior caused by fuel deformation has become an urgent challenge.

[0004] To date, many domestic and foreign research institutions have conducted extensive research on the PCI behavior of fuel elements under RIA conditions.

[0005] For example, in the early 1990s, foreign countries conducted in-reactor power ramp tests (Power Ramp Tests). Ramp tests controlled the power of the experimental reactor to increase in a step-by-step manner, repeating the process until the fuel rods experienced PCI failure, in order to study the PCI failure behavior of the fuel under RIA conditions. Ramp tests have become an important basis for studying the PCI failure behavior of fuel under RIA conditions. However, ramp tests are complex and costly, and the experimental results cannot be extrapolated to other reactor types and operating conditions. At the same time, my country currently does not have the conditions to conduct ramp tests in experimental reactors, and the Halden reactor, which has long supported the international development of ramp tests, has also been shut down. Therefore, the in-reactor test method is not suitable for studying the PCI failure behavior of rod-shaped fuel under current RIA conditions.

[0006] For example, in recent years, both domestic and international research has used ex-pile PCI behavior experiments to simulate the PCI failure behavior of fuel elements under RIA conditions. Within the SCIP (Studsvik Cladding Integrity Project), the Swedish company Studsvik established a core shaft expansion test device. This experiment converts the axial displacement of the plunger into the radial deformation of the virtual core block, thereby simulating the cracking and outward expansion of the fuel core block during the transient process, thereby achieving the effect of simulating the PCI phenomenon. Ex-pile PCI behavior simulation experiments can significantly reduce experimental costs and complexity, but they do not consider the impact of temperature rise on fuel behavior. Therefore, the results obtained from ex-pile PCI simulation experiments are only an approximate description of the PCI failure behavior of rod-shaped fuel.

[0007] For example, the paper "Vidal T, Gallais L, et al."Simulation of reactivity initiated accident thermal transients on nuclear fuels with laser remote heating." Journal of Nuclear Materials 530(2020):151944. details an experimental method for simulating the RIA conditions of rod-shaped fuel elements using laser heating. This experiment uses pulsed laser signals to simulate the temperature rise of rod-shaped fuel under RIA conditions. This experiment can accurately control the temperature distribution of the rod-shaped fuel, and its heating rate is similar to the temperature rise rate of the fuel under RIA conditions in a real reactor. However, this experiment cannot achieve full-process monitoring of PCI behavior caused by fuel deformation. Summary of the Invention

[0008] To overcome the problems of the prior art described above, the present invention provides a device for simulating rod-shaped fuel reactivity introduction accidents using laser heating. The device utilizes a first ytterbium-doped fiber laser on one side to emit a laser beam to heat an experimental sample to normal operating conditions. A thermal imager is used to monitor the experimental sample temperature in real time. A signal acquisition and control device controls the emission power of the first ytterbium-doped fiber laser to maintain the experimental sample temperature within a set range during the preheating phase. An iodine vapor control valve and a helium control valve are used to control the iodine concentration within the sample stage. A digital image measurement device is used to monitor the deformation of the experimental sample throughout the entire process. A second ytterbium-doped fiber laser on the other side emits a laser beam, which passes through a positive pyramid prism and a lens to form a laser ring, thereby simulating rod-shaped fuel reactivity introduction accidents.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A device for simulating the reactivity of rod-shaped fuel by laser heating and introducing an accident includes a furnace body A, a first ytterbium-doped fiber laser F and a second ytterbium-doped fiber laser K arranged opposite the windows on both sides of the furnace body A, a positive cone prism L and a lens M placed at the window position of the second ytterbium-doped fiber laser K, a thermal imager G and a digital image measuring device J placed in the windows around the furnace body A, and a signal acquisition and control device H connected to the thermal imager G, the digital image measuring device J and the first ytterbium-doped fiber laser F; a helium tank D, a helium control valve E and a helium inlet pipe Q connected to the helium tank D, and an external iodine generation device. A furnace B is provided, wherein an iodine vapor inlet pipe P and an iodine vapor control valve C are connected to an iodine generator B and a helium inlet pipe Q. A sample stage N is placed in the center of the furnace A, and a sample stage support O supports the sample stage N. One end of the sample stage N is connected to a gas outlet pipe R, and the other end of the gas outlet pipe R is connected to a gas collection device I. The sample stage N includes: a grooved sapphire light window S for holding an experimental sample T, an annular air cavity U surrounding the experimental sample T, a sample stage fastener W, a sample support V for fixing the grooved sapphire light window S, and a sealing ring X for sealing the annular air cavity U. The experimental sample T is used to simulate a rod-shaped fuel.

[0011] When it is necessary to simulate the reactivity introduction accident of rod-shaped fuel, at the beginning of the experiment, the experimental sample T is placed in an iodine-containing irradiation environment for pretreatment, and then the sample stage bracket O is adjusted so that the centers of the sample stage N, the first ytterbium-doped fiber laser F and the second ytterbium-doped fiber laser K are located in the same straight line; the internal temperature of the furnace body A is set to realize the preheating of the experimental pipeline; the helium control valve E and the gas collection device I are opened to allow helium to enter the interior of the sample stage N through the helium inlet pipe Q at a preset temperature and flow rate; then the iodine generation device B and the iodine vapor control valve C are opened to allow iodine vapor to enter the helium inlet pipe Q through the iodine vapor inlet pipe P, and enter the interior of the sample stage N with the helium flow, thereby simulating the iodine environment in which the experimental sample T is located; then the thermal imager G, the first ytterbium-doped fiber laser F and the signal acquisition and control device H are turned on, and the first ytterbium-doped fiber laser F generates stable laser irradiation, allowing the laser beam to preheat the experimental sample T through the grooved sapphire optical window S, so that the temperature distribution of the experimental sample T is consistent with the temperature distribution under its normal operating conditions. The thermal imager G monitors the temperature of the experimental sample T and controls the emission power of the first ytterbium-doped fiber laser F in real time through the signal acquisition and control device H to ensure that the temperature of the experimental sample T remains within the set range in the later stage of the preheating phase. After the preheating of the experimental sample T is completed, the digital image measurement device J is turned on to monitor and record the behavior of the experimental sample T under the reactivity introduction accident. The second ytterbium-doped fiber laser K is turned on and generates pulsed laser irradiation. The second ytterbium-doped fiber laser K transmits through the positive cone prism L and the lens M to achieve annular pulsed laser signal heating at the edge of the experimental sample T, thereby simulating the reactivity introduction accident of the rod-shaped fuel.

[0012] The thickness of the experimental sample T is smaller than the thermal diffusion length of the experimental sample T.

[0013] The helium temperature at the inlet section of the helium tank D is higher than the iodine desublimation temperature, and the helium inlet pipe Q, the iodine vapor inlet pipe P and the gas outlet pipe R are covered with an insulation layer.

[0014] The temperature in the furnace body A cannot be too low to cause iodine vapor to condense, nor can it be too high to cause the sealing material to fail.

[0015] The grooved sapphire window S has no less than 4 grooves, and the groove depth is no more than 2 mm.

[0016] The present invention has the following advantages and beneficial effects:

[0017] 1. The present invention adopts laser heating method, which can achieve high temporal and spatial precision heating of experimental samples.

[0018] 2. The present invention has a high degree of integration and adopts a non-contact measurement method. It can use a computer to simultaneously collect multi-point signals from multiple physical fields, and the data monitoring and processing speed is relatively fast.

[0019] 3. The present invention uses digital image measurement technology to monitor the deformation of the experimental sample throughout the entire process, which can achieve high-resolution monitoring of the behavior of the experimental sample under reactive introduction accident conditions at a microscale, and the monitoring results can be visualized.

[0020] 4. The present invention uses an iodine vapor control valve and a helium control valve to control the iodine concentration in the experimental environment, which can effectively simulate iodine-induced stress corrosion cracking of the cladding under different irradiation environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention.

[0022] Figure 2 Schematic diagram of the sample stage structure of the present invention.

[0023] Figure 3 This is a schematic diagram of the sapphire light window structure with grooves of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] like Figure 1 and Figure 2As shown, the present invention provides a device for simulating the reactivity of rod-shaped fuel by laser heating and introducing an accident, comprising a furnace body A, a first ytterbium-doped fiber laser F and a second ytterbium-doped fiber laser K arranged opposite the windows on both sides of the furnace body A, a positive cone prism L and a lens M placed at the window position of the second ytterbium-doped fiber laser K, a thermal imager G and a digital image measuring device J placed in the windows around the furnace body A, a signal acquisition and control device H connected to the thermal imager G, the digital image measuring device J and the first ytterbium-doped fiber laser F, a helium tank D, a helium control valve E and a helium inlet pipe Q connected to the helium tank D, and an external iodine A generating device B, an iodine vapor inlet pipe P and an iodine vapor control valve C connecting the iodine generating device B and the helium inlet pipe Q, a sample stage N placed in the center of the furnace body A, a sample stage bracket O supporting the sample stage N, the lower end of the sample stage N connected to a gas outlet pipe R, and the other end of the gas outlet pipe R connected to a gas collection device I; the sample stage N includes: a grooved sapphire light window S for clamping the experimental sample T, an annular air cavity U around the experimental sample T, a sample stage fastener W, a sample bracket V for fixing the grooved sapphire light window S, and a sealing ring X for sealing the annular air cavity U; the experimental sample T is used to simulate rod-shaped fuel.

[0026] like Figure 3 As shown, the grooved sapphire light window S of the present invention has no less than 4 grooves to enable iodine vapor to enter the interior of the experimental sample T, thereby simulating the iodine-induced stress corrosion behavior of the shell of the experimental sample T; the depth of the grooves is no more than 2 mm to prevent the grooves from affecting the laser light path and causing the grooved sapphire light window S to break.

[0027] This embodiment obtains the behavior of the experimental sample under a reactivity introduction accident. Before the experiment begins, the experimental sample T is pretreated in an iodine-containing irradiation environment to simulate radiation damage to the experimental sample T in the reactor.

[0028] The general working principle of this embodiment is as follows: adjust the sample stage bracket O so that the centers of the sample stage N, the first ytterbium-doped fiber laser F and the second ytterbium-doped fiber laser K are located in the same straight line; set the internal temperature of the furnace body A to be higher than the desublimation temperature of iodine vapor, start the furnace body A to realize preheating of the experimental pipeline; then open the helium control valve E and the gas collection device I, so that helium enters the interior of the sample stage N through the helium inlet pipe Q at a temperature higher than the desublimation point of iodine vapor; after the high-purity helium enters the gas collection device I, open the iodine generation device B and the iodine vapor control valve C, so that iodine vapor enters the helium inlet pipe Q through the iodine vapor inlet pipe P, and enters the interior of the sample stage N with the helium flow, so as to realize the simulation of the iodine environment in which the experimental sample T is located; when the iodine concentration in the gas collection device I reaches the preset value, turn on the thermal imager G, the first ytterbium-doped fiber laser F and the signal acquisition and control device H, and the first ytterbium-doped fiber laser The device F generates stable, Gaussian-distributed laser irradiation, so that the laser beam passes through the grooved sapphire window S to preheat the experimental sample T, so that the temperature distribution of the experimental sample T is consistent with the temperature distribution of its normal operating conditions; the thermal imager G is turned on to monitor the temperature of the experimental sample T, and the emission power of the first ytterbium-doped fiber laser F is controlled in real time through the signal acquisition and control device H to ensure that the temperature of the experimental sample T is maintained within the set range in the later stage of the preheating stage; after the preheating of the experimental sample T is completed, the digital image measurement device is turned on to monitor and record the fuel behavior of the experimental sample T under the reactivity introduction accident condition; the second ytterbium-doped fiber laser K is turned on to generate pulsed laser irradiation, and by adjusting the positive cone prism L and the lens M, a ring-shaped pulsed laser signal heating is achieved at the edge of the experimental sample T, thereby simulating the reactivity introduction accident condition of the rod-shaped fuel.

[0029] As a preferred embodiment of the present invention, the furnace body A is a sealed furnace body.

[0030] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be considered that the specific embodiments of the present invention are limited to these. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions or substitutions without departing from the concept of the present invention, which should be regarded as belonging to the scope of patent protection determined by the submitted claims of the present invention.

Claims

1. A device for simulating the reactivity of rod-shaped fuel by laser heating, characterized by: The invention comprises a furnace body (A), a first ytterbium-doped fiber laser (F) and a second ytterbium-doped fiber laser (K) arranged at windows on both sides of the furnace body (A), a positive cone prism (L) and a lens (M) placed at the window position of the second ytterbium-doped fiber laser (K), a thermal imager (G) and a digital image measuring device (J) placed at the windows around the furnace body (A), and a signal acquisition and control device (H) connected to the thermal imager (G), the digital image measuring device (J) and the first ytterbium-doped fiber laser (F); and also includes a helium gas. a tank (D), a helium control valve (E) and a helium inlet pipe (Q) connected to the helium tank (D), an external iodine generator (B), an iodine vapor inlet pipe (P) and an iodine vapor control valve (C) connecting the iodine generator (B) and the helium inlet pipe (Q), a sample stage (N) placed at the center of the furnace body (A), a sample stage bracket (O) supporting the sample stage (N), one end of the sample stage (N) connected to the gas outlet pipe (R), and the other end of the gas outlet pipe (R) connected to the gas collection device (I); The sample stage (N) includes: a sapphire light window (S) with a groove for clamping an experimental sample (T), an annular air cavity (U) surrounding the experimental sample (T), a sample stage fastener (W), a sample holder (V) for fixing the sapphire light window (S) with the groove, and a sealing ring (X) for sealing the annular air cavity (U); the experimental sample (T) is used to simulate a rod-shaped fuel; When it is necessary to simulate the reactivity introduction accident of rod-shaped fuel, at the beginning of the experiment, the experimental sample (T) is placed in an iodine-containing irradiation environment for pretreatment, and then the sample stage bracket (O) is adjusted so that the centers of the sample stage (N), the first ytterbium-doped fiber laser (F) and the second ytterbium-doped fiber laser (K) are located in the same straight line; the internal temperature of the furnace body (A) is set to realize the preheating of the experimental pipeline; the helium control valve (E) and the gas collection device (I) are opened to allow helium to enter the interior of the sample stage (N) through the helium inlet pipe (Q) at a preset temperature and flow rate; then the iodine generation device (B) and the iodine vapor control valve (C) are opened to allow iodine vapor to enter the helium inlet pipe (Q) through the iodine vapor inlet pipe (P), and enter the interior of the sample stage (N) with the helium flow, thereby simulating the iodine environment in which the experimental sample (T) is located; then the thermal imager (G), the first ytterbium-doped fiber laser (F) and the signal acquisition and control device (H) are turned on, and the first ytterbium-doped fiber laser (F) and the signal acquisition and control device (H) are turned on. The optical device (F) generates stable laser irradiation, so that the laser beam passes through the grooved sapphire optical window (S) to preheat the experimental sample (T), so that the temperature distribution of the experimental sample (T) is consistent with the temperature distribution of its normal operating conditions. The thermal imager (G) monitors the temperature of the experimental sample (T) and controls the emission power of the first ytterbium-doped fiber laser (F) in real time through the signal acquisition and control device (H) to ensure that the temperature of the experimental sample (T) is maintained within the set range in the later stage of the preheating stage. After the preheating of the experimental sample (T) is completed, the digital image measurement device (J) is turned on to monitor and record the behavior of the experimental sample (T) under the reactivity introduction accident. The second ytterbium-doped fiber laser (K) is turned on and generates pulsed laser irradiation. Through the positive cone prism (L) and the lens (M), the edge position of the experimental sample (T) is heated by a ring-shaped pulsed laser signal, thereby simulating the reactivity introduction accident of the rod-shaped fuel.

2. The device for simulating the reactivity introduction accident of rod-shaped fuel using laser heating as claimed in claim 1, characterized in that: The thickness of the experimental sample (T) is smaller than the thermal diffusion length of the experimental sample (T).

3. The device for simulating the reactivity introduction accident of rod-shaped fuel using laser heating as claimed in claim 1, characterized in that: The helium temperature at the inlet section of the helium tank (D) is higher than the iodine desublimation temperature, and the helium inlet pipe (Q), the iodine vapor inlet pipe (P) and the gas outlet pipe (R) are covered with a thermal insulation layer.

4. The device for simulating the reactivity of rod-shaped fuel by laser heating as claimed in claim 1, characterized in that: The temperature in the furnace body (A) cannot be too low to cause iodine vapor to condense; nor can it be too high to cause the sealing material to fail.

5. The device for simulating the reactivity introduction accident of rod-shaped fuel using laser heating as claimed in claim 1, characterized in that: The grooved sapphire window (S) has no less than 4 grooves, and the groove depth is no more than 2 mm.

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