Visualized experimental device and method for simulating melting and fragment migration of lead-bismuth reactor cladding

Abstract

The present invention discloses a visualization experimental device and method for simulating the melting of the cladding and the migration of fragments of a lead-bismuth pile. The visualization experimental device includes a visualization experimental chamber, a heating device, a simulated fuel rod, a temperature measuring device, a shooting device, a liquid storage tank and a heat exchanger; the simulated fuel rod is arranged inside the visualization experimental chamber, and each simulated fuel rod includes a plurality of simulated fuel pellets connected in series by a resistance wire and a simulated fuel rod cladding wrapped on the outside; each simulated fuel pellet includes a plurality of simulated fuel fragments; the coolant temperature is adjusted by a heating device and a heat exchanger; according to the principle of being close to the density ratio of the real material, the material of the simulated fuel fragments is organic glass, the material of the simulated fuel rod cladding is paraffin, and the coolant is triacetin. The present invention can carry out visualization simulation experiments of cladding melting and fragment migration of single rods and multiple rods, obtain visualization images and data for theoretical model verification, and provide important support for the safety analysis of lead-bismuth piles.

Description

Technical Field

[0001] The invention belongs to the field of advanced nuclear reactor accident analysis, and in particular relates to a visual experimental device and method for simulating lead-bismuth reactor cladding melting and debris migration. Background Art

[0002] As one of the fourth-generation advanced reactor types, the lead-bismuth fast reactor has the advantages of high power density, strong natural circulation capacity, stable coolant chemical properties, high boiling point, and no heat transfer deterioration, which can effectively improve the reactor's operating range and safety limits. During the operation of the reactor, fuel assembly blockage accidents and reactivity introduction accidents may cause safety problems such as local overheating and failure melting of fuel rods; broken fragments, fission products and cladding melts after the failure and melting of fuel rods enter the lead-bismuth coolant and solidify and aggregate into new blockages in the downstream low-temperature area, thereby forming secondary blockages, which seriously affect the normal transfer of heat in the assembly. For the study of fuel rod melting and fragment migration, experiments using real materials are difficult to carry out and are expensive. Therefore, it is an effective solution to carry out simulation experiments using alternative materials with properties similar to reactor materials.

[0003] Chinese invention patent CN108492897A discloses a visual experimental device for studying the melting characteristics of nuclear reactor fuel rods. The device uses substitute materials to simulate fuel rods to indirectly study the melting mechanism of core fuel rods. The main experimental piece is placed in a transparent quartz glass tube, and then deionized water is filled into the quartz glass container through a water injection device, and the simulated fuel rod is heated by an electric system. When the outer layer of the wrapping material is heated to melt, the temperature of the fuel rod is measured at different heights, and the experimental process is recorded by a high-speed camera. The invention aims to conduct simulation experiments on the high-temperature melting behavior of fuel rods under light water nuclear reactor accidents, but it cannot simulate the cladding melting and fragment migration behavior of lead-bismuth piles.

[0004] Lead-bismuth coolant has the characteristics of high density, high boiling point and opacity. In the event of a nuclear reactor accident, the lead-bismuth coolant will not boil and evaporate. Therefore, the melting of the cladding, the migration of the molten material and the solid fragments are all carried out immersed in the lead-bismuth coolant. This phenomenon is significantly different from the melting behavior of the fuel rods in the light water reactor. For the simulation experiment of the cladding melting and fragment migration of the lead-bismuth reactor, the selection of substitute materials is the main difficulty. In order to simulate the main accident phenomena and take into account the scalability of the experimental results, the selection of substitute materials should meet the following requirements: 1) have a similar density ratio to the real material; 2) the substitute material of the lead-bismuth coolant is a transparent liquid; 3) the melting point of the cladding substitute material is low. By selecting reasonable substitute materials and designing a set of low-temperature, highly operable and visual experimental equipment, it is the key to carry out the research on the cladding melting and fragment migration of the lead-bismuth reactor. Summary of the invention

[0005] The present invention proposes a visualization experimental device and method for simulating the melting of the lead-bismuth pile cladding and the migration of fragments, which provides the possibility for visually conducting research on the laws of cladding melting and fragment migration under low temperature conditions, and also provides comparative experimental data for the verification of theoretical models of numerical simulation.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a visualization experimental device and method for simulating the melting of lead-bismuth reactor cladding and the migration of fragments, comprising a visualization experimental chamber, a heating device, at least one simulated fuel rod, a temperature measuring device, a shooting device, a liquid storage tank and a heat exchanger;

[0007] The coolant can be contained in both the visualization experiment cavity and the liquid storage tank, and the heating device is used to adjust the temperature of the coolant in the liquid storage tank;

[0008] Each simulated fuel rod is arranged in a visual experimental cavity and can be immersed in a coolant. Each simulated fuel rod comprises a plurality of simulated fuel pellets connected in series by resistance wires and a simulated fuel rod cladding wrapped around the outside of the simulated fuel pellets. Each simulated fuel pellet comprises a plurality of simulated fuel fragments.

[0009] The temperature measuring device is arranged on the simulated fuel rod and is used to measure the temperature of the simulated fuel pellet and the simulated fuel rod cladding;

[0010] The photographing device is arranged opposite to the visualization experiment chamber, and the visualization experiment chamber is a visualization container, and the photographing device is used to record the melting of the simulated fuel rod cladding and the migration process of the simulated fuel fragments;

[0011] The liquid storage tank, the visualization experiment chamber and the heat exchanger are connected in sequence by pipelines to form a circulation loop, wherein the heat exchanger is used to discharge the heat of the coolant flowing out of the visualization experiment chamber, and the coolant temperature can be adjusted by the heat exchanger and the heating device.

[0012] Furthermore, it also includes an orifice plate, which is arranged in the visualization experiment cavity and below the simulated fuel rod. The coolant enters from the lower part of the visualization experiment cavity, is distributed through the orifice plate, and then returns to the liquid storage tank after heat exchange with the simulated fuel rod.

[0013] Furthermore, a plurality of simulated fuel fragments are bonded and combined into independent simulated fuel pellets by means of a paraffin adhesive, and the simulated fuel pellets are consistent in size with real fuel pellets of the reactor.

[0014] Furthermore, the temperature measuring device includes a plurality of pairs of thermocouples, and a plurality of groups of thermocouples are arranged at different height positions of the simulated fuel rods for measuring the temperature of the simulated fuel pellets and the simulated fuel rod cladding.

[0015] Furthermore, a regulating valve and a flow meter are also provided on the pipeline between the liquid storage tank and the visualization experiment chamber.

[0016] Furthermore, a driving pump is provided on the pipeline between the liquid storage tank and the visualization experiment chamber.

[0017] Furthermore, the heating device is an electric heating rod, and the electric heating rod is arranged in the liquid storage tank.

[0018] Furthermore, the material of the simulated fuel fragments is organic glass, the material of the simulated fuel rod cladding is paraffin, and the coolant is triacetin.

[0019] Furthermore, the density ratio of the substitute substances organic glass, paraffin, and triacetin is 1:0.75:0.96, which is very close to the density ratio of real mixed oxide nuclear fuel, stainless steel cladding, and lead-bismuth coolant of 1:0.72:0.97; the selected triacetin is a transparent liquid, and its boiling point is higher than the melting point of paraffin.

[0020] Among them, the method for making simulated fuel rods is as follows: according to the size of reactor fuel core blocks, simulated fuel fragments with fan-shaped columnar structures are made, and multiple simulated fuel fragments are bonded and combined into independent simulated fuel core blocks using paraffin adhesive; then, a resistance wire is passed through the central holes of multiple simulated fuel core blocks, and the upper and lower ends of the resistance wire are connected to the fixed bracket, and the cladding substitute material paraffin is applied to the outside of the simulated fuel core block to make a single simulated fuel rod; the prepared simulated fuel rod and the fixed bracket are placed in a visual experimental chamber 1 as a whole, and the joints between the fixed bracket and the experimental chamber are connected.

[0021] A visualization experimental method for simulating the melting of lead-bismuth reactor cladding and the migration of fragments comprises the following steps: injecting coolant into both the visualization experimental cavity and the liquid storage tank, immersing the simulated fuel rod in the coolant, then starting the driving pump for circulation, and heating the coolant in the liquid storage tank by a heating device; recording the temperature of the simulated fuel core block and the simulated fuel rod cladding by a temperature measuring device, and when the paraffin temperature is close to the melting point, turning on a shooting device to observe the melting of the simulated fuel rod cladding and the migration process of the simulated fuel fragments; wherein the heat of the coolant is discharged through a heat exchanger arranged on a circulation pipeline; adjusting the coolant flow rate by a regulating valve, and conducting experiments under different flow states; and conducting experiments under different heating rates by adjusting the voltage at both ends of a resistance wire.

[0022] Compared with the prior art, the present invention has at least the following advantages:

[0023] 1) This experimental device can carry out visual simulation experiments on cladding melting and fragment migration of single-rod and multi-rod simulated fuel rods at different heating rates, coolant temperatures and flow conditions, and obtain image data and temperature data.

[0024] 2) The density ratio of the substitute materials plexiglass, paraffin and triacetin is 1:0.75:0.96, which is very close to the density ratio of real mixed oxide nuclear fuel, stainless steel cladding and lead-bismuth coolant at high temperature of 1:0.72:0.97. It can accurately simulate the migration behavior of cladding melt and fuel fragments, and improve the scalability of experimental results.

[0025] 3) The simulated fuel pellets are made by bonding multiple simulated fuel fragments together, and the binder is the same material as the simulated fuel rod cladding, so that the simulated fuel fragments can migrate immediately after the simulated fuel rod cladding melts.

[0026] 4) The substitute material of lead-bismuth coolant, triacetin, is a transparent liquid, which can be used to record the process of simulating the melting of fuel rod cladding and the migration of simulated fuel fragments through a camera.

[0027] 5) The phase transition temperature of the paraffin wax selected as the simulated fuel rod cladding material is low, so the simulation experiment of cladding melting and fragment migration can be carried out under low temperature conditions, which improves the operability of the experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of a visual experimental device and method for simulating the melting of lead-bismuth pile cladding and fragment migration provided by an embodiment of the present invention.

[0029] Figure 2 Schematic diagram of a simulated fuel pellet in an embodiment of the present invention.

[0030] Figure 3 Schematic diagram of simulated fuel rods of a 3×3 rod bundle in an embodiment of the present invention.

[0031] 1—visualized experimental chamber; 2—simulated fuel rod; 3—simulated fuel pellet; 4—temperature measuring device; 5—orifice plate; 6—flow meter; 7—regulating valve; 8—driving pump; 9—heating device; 10—coolant; 11—liquid storage tank; 12—heat exchanger; 13—photographing device; 101—simulated fuel fragments; 102—paraffin adhesive; 201—simulated fuel rod cladding; 202—simulated fuel fragments; 203—resistance wire. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] See also Figure 1 The present invention provides a visualization experiment device and method for simulating the melting of lead-bismuth pile cladding and the migration of fragments, comprising a visualization experiment chamber 1, a heating device 9, at least one simulated fuel rod 2, a temperature measuring device 4, a shooting device 13, a liquid storage tank 11 and a heat exchanger 12. The visualization experiment chamber 1 and the liquid storage tank 11 can both contain the coolant 10, and the heating device 9 is used to adjust the temperature of the coolant 10 in the liquid storage tank 11; each simulated fuel rod 2 is arranged in the visualization experiment chamber 1 and can be immersed in the coolant 10, and each simulated fuel rod 2 includes a plurality of simulated fuel pellets 3 and a cladding connected in series by a resistance wire 203. A simulated fuel rod cladding 201 is wrapped around the outside of the simulated fuel pellet 3, and each simulated fuel pellet 3 includes a plurality of simulated fuel fragments 101; a temperature measuring device 4 is arranged on the simulated fuel rod 2, and is used to measure the temperature of the simulated fuel pellet 3 and the simulated fuel rod cladding 201; a photographing device 13 is arranged opposite to the visualization experiment cavity 1, and is used to record the melting of the simulated fuel rod cladding 201 and the migration process of the simulated fuel fragments 101; a liquid storage tank 11, a visualization experiment cavity 1 and a heat exchanger 12 are connected in sequence by pipelines to form a loop, wherein the heat exchanger 12 is used to discharge the heat of the coolant 10 flowing out of the visualization experiment cavity 1.

[0034] In some embodiments of the present invention, transparent liquid triacetin is selected as a substitute for the lead-bismuth coolant, and organic glass (ρ = 1200 kg / m 3 ) and paraffin (ρ=900kg / m 3 ) are used as substitutes for mixed oxide nuclear fuel and stainless steel cladding, respectively. Triacetin is transparent and can meet the needs of visualization experiments. It is chemically stable and has a higher boiling point than paraffin, which can ensure that there is still coolant around the simulated fuel rods when the paraffin melts. The substitutes for mixed oxide nuclear fuel and stainless steel are selected based on the principle that the density ratio of the substitute and the real material is close (1:0.72:0.97). In addition, the principles for selecting substitute materials also include (1) meeting the needs of visualization experiments and (2) facilitating experiments under low temperature conditions.

[0035] In some embodiments of the present invention, Figure 2 As shown, each simulated fuel pellet 3 is composed of three simulated fuel fragments 101 bonded together, and the interface is bonded with a paraffin adhesive 102 that is the same as the cladding substitute material, in order to present the phenomenon that the fuel fragments migrate immediately when the fuel cladding melts. In other embodiments, the number of simulated fuel fragments 101 in the simulated fuel pellet 3 can be set to other values ​​as needed.

[0036] In some embodiments of the present invention, Figure 1 As shown, three simulated fuel rods 2 are arranged in the visualized experimental chamber 1. It is understandable that in other embodiments, other numbers of simulated fuel rods 2 may be arranged as required. Multiple simulated fuel pellets are stacked in each simulated fuel rod, and each simulated fuel pellet is composed of three simulated fuel fragments bonded together.

[0037] In some embodiments of the present invention, the central hole of the simulated fuel pellet is a gap between a plurality of simulated fuel fragments of fan-shaped columnar structures, and the resistance wire passes through the central hole of the simulated fuel pellet to connect the plurality of simulated fuel pellets in series.

[0038] In some embodiments of the present invention, Figure 1 and 3 As shown, a resistance wire 203 is passed through the central hole of the simulated fuel pellet 3, multiple simulated fuel pellets 3 are connected in series, and then paraffin, a cladding substitute, is applied to the outside of the simulated fuel pellet 3 to make a simulated fuel rod 2; and multiple groups of temperature measuring devices 4 are arranged at different height positions of the simulated fuel rod 2 to measure the temperature of the simulated fuel pellet 3 and the simulated fuel rod cladding 201. In some embodiments of the present invention, the length of each simulated fuel rod is 0.5m. The temperature measuring device 4 is a thermocouple.

[0039] In some embodiments of the present invention, a perforated plate 5 is further provided in the visualization experiment chamber 1, and the perforated plate 5 is located below the simulated fuel rod 2. When conducting the experiment, due to the change in the flow area from the pipeline to the experimental chamber, the flow rate in the middle position of the chamber is larger and the flow rate at the edge position is smaller. After the flow rate is distributed by the perforated plate 5, the flow rate distribution can be ensured to be uniform.

[0040] In some embodiments of the present invention, a driving pump 8, a regulating valve 7 and a flow meter 6 are further provided on the pipeline between the liquid storage tank 11 and the visualization experiment chamber 1. Driven by the driving pump 8, the coolant 10 flows through the flow meter 6, the visualization experiment chamber 1, the heat exchanger 12, and then returns to the liquid storage tank 11.

[0041] Figure 1 In the experimental device shown, the coolant 10 in the liquid storage tank 11 enters from the lower part of the visual experimental chamber 1 and is distributed through the orifice plate 5; the temperature of the coolant 10 at the outlet of the heat exchanger 12 can be adjusted by adjusting the circulating water flow of the heat exchanger 12, and the temperature of the coolant 10 in the liquid storage tank 11 can be accurately adjusted by the heating device 9.

[0042] In some embodiments of the present invention, the heating device 9 is an electric heating rod, and the electric heating rod is arranged in the liquid storage tank 11. The shooting device 13 is a high-speed camera.

[0043] In some embodiments of the present invention, the preparation process of the simulated fuel rod 2 in the aforementioned device includes:

[0044] According to the size of the reactor fuel pellets, simulated fuel fragments 101 with fan-shaped columnar structures are manufactured, and multiple simulated fuel fragments 101 are bonded and assembled into independent simulated fuel pellets 3 using paraffin adhesive 102; then, a resistance wire 203 is passed through the central holes of multiple simulated fuel pellets 3, and the upper and lower ends of the resistance wire are connected to the fixed bracket, and the cladding substitute paraffin is applied to the outside of the simulated fuel pellets to manufacture simulated fuel rods 2. The manufactured simulated fuel rods 2 and the fixed bracket are placed in a visual experiment chamber 1 as a whole, and the joints between the fixed bracket and the visual experiment chamber 1 are connected.

[0045] The present invention also provides a method for conducting an experiment using the above device.

[0046] A visual experimental method for simulating the melting and debris migration of lead-bismuth reactor cladding, including:

[0047] Injecting coolant 10 into the visualization experiment chamber 1 and the liquid storage tank 11, so that the simulated fuel rod 2 is immersed in the coolant 10;

[0048] The driving pump 8 is started to circulate, and the coolant 10 in the liquid storage tank 11 is heated by the heating device 9;

[0049] The temperature of the simulated fuel pellets 3 and the simulated fuel rod cladding 201 is recorded by the temperature measuring device 4. When the temperature of the paraffin wax approaches the melting point, the photographing device 13 is turned on to record the melting of the simulated fuel rod cladding 201 and the migration process of the simulated fuel fragments 202.

[0050] Among them, the heat of the coolant 10 is discharged through the heat exchanger 12 arranged on the pipeline, and its temperature is adjusted by controlling the circulating water flow of the heat exchanger 12; the flow of the coolant 10 is adjusted by the regulating valve 7, and visualization experiments are carried out in static and flowing states; by adjusting the voltage at both ends of the resistance wire 203, experiments under different heating rates are carried out.

[0051] With the aid of the above-mentioned device and through the above-mentioned specific operating steps, a visual simulation experiment of lead-bismuth reactor cladding melting and fragment migration can be carried out under low temperature conditions, and images and quantitative data for theoretical model verification can be obtained, which is convenient for the study of core thermal hydraulics.

[0052] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A visual experimental device for simulating the melting of lead-bismuth pile cladding and the migration of fragments, characterized in that: It comprises a visual experiment chamber (1), a heating device (9), at least one simulated fuel rod (2), a temperature measuring device (4), a photographing device (13), a liquid storage tank (11) and a heat exchanger (12); The visualization experiment chamber (1) and the liquid storage tank (11) both contain a coolant (10), and the heating device (9) is used to adjust the temperature of the coolant (10) in the liquid storage tank (11); Each simulated fuel rod (2) is arranged in a visual experiment chamber (1) and immersed in a coolant (10); each simulated fuel rod (2) comprises a plurality of simulated fuel pellets (3) connected in series by a resistance wire (203) and a simulated fuel rod cladding (201) wrapped around the outside of the simulated fuel pellets (3); each simulated fuel pellet (3) comprises a plurality of simulated fuel fragments (101); the plurality of simulated fuel fragments (101) constituting the simulated fuel pellets (3) are bonded and fixed by a paraffin adhesive (102); the material of the simulated fuel fragments (101) is organic glass, the material of the simulated fuel rod cladding (201) is paraffin, and the coolant (10) is triacetin; The temperature measuring device (4) is arranged on the simulated fuel rod (2) and is used to measure the temperature of the simulated fuel pellet (3) and the simulated fuel rod cladding (201); The photographing device (13) is arranged opposite to the visualization experiment chamber (1) and is used to record the melting of the simulated fuel rod cladding (201) and the migration process of the simulated fuel fragments (101); The liquid storage tank (11), the visualization experiment chamber (1) and the heat exchanger (12) are connected in sequence by pipes to form a circulation loop, wherein the heat exchanger (12) is used to discharge the heat of the coolant (10) flowing out of the visualization experiment chamber (1).

2. A visualization experimental device for simulating lead-bismuth pile cladding melting and debris migration according to claim 1, characterized in that: It also includes a hole plate (5), which is arranged in the visualization experiment chamber (1) and is located below the simulated fuel rod (2).

3. A visualization experimental device for simulating lead-bismuth pile cladding melting and debris migration according to claim 1, characterized in that: The temperature measuring device (4) comprises a plurality of pairs of thermocouples arranged along the height direction of the simulated fuel rod (2).

4. A visualization experimental device for simulating lead-bismuth pile cladding melting and debris migration according to claim 1, characterized in that: A regulating valve (7) and a flow meter (6) are also provided on the pipeline between the liquid storage tank (11) and the visualization experiment chamber (1).

5. A visualization experimental device for simulating lead-bismuth pile cladding melting and debris migration according to claim 1, characterized in that: A driving pump (8) is also provided on the pipeline between the liquid storage tank (11) and the visualization experiment chamber (1).

6. A visualization experimental device for simulating lead-bismuth pile cladding melting and debris migration according to claim 1, characterized in that: The heating device (9) is an electric heating rod, and the electric heating rod is arranged in the liquid storage tank (11).

7. A visual experimental method for simulating the melting of lead-bismuth pile cladding and the migration of fragments, characterized in that: Using the device according to any one of claims 1 to 6, the method comprises: Injecting a coolant (10) into both the visualization experiment chamber (1) and the liquid storage tank (11), immersing the simulated fuel rod (2) in the coolant (10), starting a drive pump (8) for circulation, and heating the coolant (10) in the liquid storage tank (11) through a heating device (9); The temperature of the simulated fuel pellets (3) and the simulated fuel rod cladding (201) is recorded by a temperature measuring device (4); when the temperature of the paraffin wax approaches the melting point, the photographing device (13) is turned on to observe the melting of the simulated fuel rod cladding (201) and the migration process of the simulated fuel fragments (101); The heat of the coolant (10) is discharged through a heat exchanger (12) arranged on the pipeline; the flow rate of the coolant (10) is adjusted by a regulating valve (7) to carry out experiments under different flow conditions; and the voltage at both ends of the resistance wire (203) is adjusted to carry out experiments under different heating rates.

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