Single-rod CHF test device and method

Abstract

The invention discloses a single-rod CHF test device and method, and belongs to the field of thermal hydraulic tests. The single-rod CHF test device comprises a heating rod, a thermal insulation pipe and a fixed grillwork, the heating rod coaxially penetrates through the thermal insulation pipe and is radially limited by the fixed grillwork, a cooling medium is filled between the thermal insulation pipe and the heating rod, the diameter d of the heating rod and the inner diameter D of the thermal insulation pipe meet Dh = De = (D2-d2) / d, Dh is the thermal diameter corresponding to a simulated fuel rod, and De is the thermal diameter corresponding to the simulated fuel rod. De is the hydraulic diameter corresponding to the simulated fuel rod. According to the device, the thermal hydraulic characteristics of the full-length rod bundle fuel can be accurately simulated through the single heating rod, the cost of a CHF test is effectively reduced, and the test efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the field of thermal-hydraulic experiments, and particularly relates to a single-rod CHF test device and method. Background Art

[0002] Critical Heat Flux (CHF) is an important limiting thermal-hydraulic parameter related to reactor safety. The design criteria of a pressurized water reactor require that departure from nucleate boiling should not occur in the reactor core under normal operation or medium-frequency accident conditions. To quantitatively evaluate the margin of the reactor from the occurrence of departure from nucleate boiling, it is first necessary to determine the CHF value. However, due to the complex mechanism of the CHF phenomenon, it is difficult to obtain it solely through simulation calculations. Currently, the CHF correlation for pressurized water reactor nuclear power plants still needs to be obtained through full-length fuel rod bundle CHF tests. The full-length fuel rod bundle CHF test is costly and risky. Especially in a low-flow natural circulation core, the CHF test also faces the risks of low coolant flow rate and insufficient core cooling capacity. Therefore, providing a simpler, safer, and lower-cost pre-experiment or alternative test has positive significance for optimizing the CHF test process. Summary of the Invention

[0003] The purpose of the present invention is to provide a single-rod CHF test device to equivalently simulate the thermal-hydraulic behavior of a full-length fuel rod bundle in a CHF test with a single heating rod. The present invention also provides a single-rod CHF test method.

[0004] According to an embodiment of one aspect of the present invention, there is provided a single-rod CHF test device, which includes a heating rod, and also includes a heat preservation tube and a fixed grid. Wherein, the heating rod is disposed coaxially within the heat preservation tube, and a cooling medium is filled between the inner wall of the heat preservation tube and the heating rod. The diameter d of the heating rod is the same as the diameter of the fuel rod to be simulated. The inner diameter D of the heat preservation tube satisfies: D h = D e =(D 2 - d 2 ) / d. Where D h is the thermal diameter of the fuel rod to be simulated, and D e is the hydraulic diameter of the fuel rod to be simulated. The fixed grid is fixedly disposed on the inner wall of the heat preservation tube and abuts against the surface of the heating rod to provide radial limitation to the heating rod.

[0005] This device can accurately simulate the thermal-hydraulic characteristics of a full-length fuel rod in a fuel assembly under actual conditions with a single heating rod, so as to be applied to a low-cost and accurate simulation test before conducting a full-length fuel rod bundle CHF test.

[0006] Furthermore, in some embodiments, the fixed grid is configured as a ceramic grid.

[0007] Further, in some embodiments, the fixed grid is configured as a rod, and an enlarged end contact is provided at one end of the fixed grid that abuts against the heating rod.

[0008] Further, in some embodiments, the fixed grids are uniformly arranged circumferentially along the insulation pipe.

[0009] Further, in some embodiments, the pressure between the fixed grid and the heating rod is 1 N - 50 N.

[0010] According to an embodiment of another aspect of the present invention, a single-rod CHF test method is provided, and the method includes the following steps:

[0011] Step a): Provide the geometric parameters of the simulated fuel rod and the simulated working conditions;

[0012] Step b): According to step a), provide a single-rod CHF test device corresponding to the simulated fuel rod, and the single-rod CHF test device uses the single-rod CHF test device provided in any of the foregoing embodiments;

[0013] Step c): Use the single-rod CHF test device to perform a single-rod CHF test on the simulated fuel rod.

[0014] Further, in some embodiments, in step a), the geometric parameters include the dimensions of the simulated fuel rod, and the simulated working conditions include the heating power, flow field environment, thermal diameter, and hydraulic diameter of the simulated fuel rod.

[0015] Further, in some embodiments, step c) includes the following steps:

[0016] Step c1): Calibrate the single-rod CHF test device;

[0017] Step c2): Verify the consistency between the model characteristics and the test design scheme of the single-rod CHF test device;

[0018] Step c3): Calibrate the flow sensor, temperature sensor, and pressure sensor used;

[0019] Step c4): Conduct a preliminary experiment to determine the deviation range of the test data and the stability of the test working conditions;

[0020] Step c5): Conduct a sealing test to verify the thermal balance data;

[0021] Step c6): Conduct a repeatability verification of the preliminary experiment;

[0022] Step c7): Conduct a formal CHF test.

[0023] Further, in some embodiments, in step c2), the model features include the heating rod structure, the test flow channel structure, the installation state of the heating rod, the coolant temperature, the coolant pressure, the coolant flow rate, the voltage and current of the single-rod CHF test device.

[0024] Further, in some embodiments, in step c5), when the thermal equilibrium data is above 92%, it is determined that the verification result meets the test requirements.

[0025] Further, in some embodiments, in step c6), when the deviations of the outlet pressure, the inlet coolant temperature, the mass flow rate, and the test power in multiple preliminary experiments do not exceed ±5%, it is determined that the verification result meets the repeatability requirements. Description of the Drawings

[0026] Figure 1 It is a schematic cross-sectional structure diagram of the CHF single-rod test device in one embodiment;

[0027] Figure 2 It is a schematic structure diagram of the ceramic grid in one embodiment;

[0028] Figure 3 It is a schematic flow chart of step c) in one embodiment;

[0029] Figure 4 It is a schematic diagram of the flow channel range corresponding to the fuel rod to be simulated in one embodiment.

[0030] Meanings of the reference numerals: 1 - heating rod; 2 - heat preservation pipe; 3 - coolant flow channel; 4 - ceramic grid; 5 - end contact; 6 - equivalent flow channel.

[0031] The purpose of the above drawings is to illustrate the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, rather than to limit the present invention. For the sake of simplicity, the above drawings only schematically show the structures related to the technical features of the present invention and do not draw the complete structure and all details strictly according to the actual proportion. Detailed Embodiments

[0032] The present invention will be further described in detail below through specific embodiments in conjunction with the drawings.

[0033] The mention of "embodiments" in this article means that the specific features, structures, or characteristics described in conjunction with the embodiments can be included in at least one embodiment of the present invention. The phrase appearing in various positions in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments in this article can be combined with other embodiments without structural conflicts.

[0034] In the description of this article, unless otherwise clearly specified and defined, technical terms such as "installation", "connection", and "linkage" should be understood in a broad sense. For example, it can be a movable connection, a fixed connection, or integrated. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of this application can be understood according to specific circumstances.

[0035] In the description of this article, terms indicating orientation or positional relationships such as "upper", "lower", "left", "right", "lateral", "longitudinal", "height", "length", "width", etc. are intended to accurately describe the embodiments and simplify the description, rather than limiting that the parts or structures involved must have a specific orientation, be installed or operated in a specific orientation, and should not be construed as a limitation to the embodiments in this article.

[0036] In the description of this article, terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order, or primary and secondary relationships of the described technical features. In the description of this article, the meaning of "a plurality" is at least two.

[0037] The thermal-hydraulic design criteria for a pressurized water reactor require that during normal operation and medium-frequency accident conditions (i.e., Class I and Class II conditions), departure from nuclear boiling (DNB) should not occur in the reactor core. In order to quantitatively evaluate the margin of the reactor from DNB under specific operating conditions, it is necessary to first determine its critical heat flux (CHF). However, CHF is determined by the combined effects of hydrodynamics and thermodynamic phenomena, and its mechanism and influencing factors are very complex. Currently, the research on the CHF phenomenon at the theoretical level is not sufficient. Under the existing technical conditions, it is not possible to accurately simulate and calculate CHF completely through theoretical simulation. Therefore, current CHF research still highly relies on experiments.

[0038] At present, the CHF correlation used in the licensing application of pressurized water reactor nuclear power plants needs to be obtained through full-length fuel rod bundle CHF experiments. However, the CHF experiment of fuel assemblies is costly and risky. Especially in a low-flow natural circulation core, the CHF experiment also faces additional risks such as low coolant flow rate and insufficient core cooling capacity. If the test conditions are set unreasonably, it may cause damage to the test equipment or even more serious safety accidents. These factors also lead to a further extension of the CHF verification test cycle and a further increase in costs, which is not conducive to improving the design and R & D efficiency of pressurized water reactor nuclear power plants.

[0039] To solve the above problems, an embodiment of one aspect of the present invention provides a single-rod CHF test device for conducting preliminary or alternative test verification work for full-length fuel rod bundle CHF experiments.

[0040] The cross-sectional structure of the device is as shown in Figure 1 , and it only includes a heating rod 1. The heating rod 1 is arranged inside the heat preservation pipe 2 and coaxially with the heat preservation pipe 2. A coolant flow channel 3 is formed between the heating rod 1 and the heat preservation pipe 2, and the coolant flow channel 3 is filled with a cooling medium. A plurality of ceramic grids 4 serving as fixed grids are fixedly arranged on the inner wall of the heat preservation pipe 2. The ceramic grids 4 abut against the surface of the heating rod 1 to provide radial limit for the heating rod, so as to prevent the heating rod 1 from deforming due to thermal stress or coolant impact during the test.

[0041] Among them, in order to accurately simulate the thermohydraulic properties of the full-length fuel rod bundle under actual conditions with a single heating rod, the diameter d of the heating rod 1 is the same as the diameter of the fuel rod to be simulated, while the inner diameter D of the heat preservation pipe needs to satisfy D h = D e =(D 2 -d 2 ) / d, where D h is the thermal diameter of the fuel rod to be simulated, and D e is the hydraulic diameter of the fuel rod to be simulated.

[0042] Specifically, in combination with Figure 4 , in the fuel rod bundle adopted in the reactor core, multiple fuel rods jointly participate in forming the coolant flow channel. The equivalent flow channel 6 of the coolant flow channel formed by a single fuel rod is as shown in the cited area in Figure 4 . The hydraulic diameter and thermal diameter calculated according to the shaded area are the aforementioned thermal diameter D h and hydraulic diameter D e of the fuel rod to be simulated. Among them, D e = 4(P 2 -πd 2 / 4) / πd,

[0043] D h = 4A / P h , P is the grid pitch of the fuel rod bundle to be simulated, A is the area of the equivalent flow channel 6, and P h is the wetted perimeter of the fuel rod to be simulated, that is, the part participating in heat transfer with the coolant. Thus, the relationship of D h = D e =(D 2 -d 2 ) / d can be calculated. Based on the thermal perimeter equivalence, it can be ensured that the average power of the single-rod test section is the same as that of the full-length fuel rod bundle test section, and further ensure the consistency of key parameters such as the gas content rate and enthalpy rise in the coolant flow channel.

[0044] In a preferred embodiment, the diameter of the fuel rod in the pressurized water reactor fuel assembly (i.e., the diameter d of the heating rod) is 9.5 mm, the pitch P = 12.6 mm, and the calculated inner diameter D of the thermal insulation tube is 14.22 mm.

[0045] The ceramic grid 4 has a very low coefficient of thermal expansion and high rigidity, which can ensure that the heating rod 1 will not undergo radial deformation due to thermal stress or coolant impact during the test. In other embodiments, according to different test conditions, the ceramic grid 4 can also be replaced with other materials with low coefficients of thermal expansion. According to the different axial lengths of the heating rod 1, the ceramic grid 4 can be arranged at different positions along the axis of the heating rod 1, and the specific installation position can be determined by simulation calculation based on the axial force of the heating rod 1 under the test conditions. For example, it can be arranged at the position where the buckling radial deformation of the heating rod 1 is the largest.

[0046] In the preferred embodiment, the structure of the ceramic grid 4 is as Figure 2 shown. The ceramic grid 4 is integrally set as a rod, and an enlarged end contact 5 is provided at one end in contact with the heating rod 1. The end contact 5 is used to reduce the pressure at the contact position and avoid damage to the heating rod. In different embodiments, the cross-sectional shape of the ceramic grid 4 can be set to different shapes, such as circular, rectangular, or other polygons, etc.; the contact surface between the end contact 5 and the heating rod 1 can also be set to different shapes, such as circular or polygonal, etc. The maximum width of the end contact 5 can be set to 2.5 mm - 5 mm.

[0047] In the preferred embodiment, the ceramic grids 4 are evenly arranged along the circumference of the thermal insulation tube 2, and the pressure range generated by their contact with the heating rod 1 is 1 N - 50 N.

[0048] According to an embodiment of another aspect of the present invention, a single-rod CHF test method is provided, and this method includes the following steps:

[0049] Step a): Provide the geometric parameters of the fuel rods in the fuel rod bundle simulated by the single-rod CHF test and the simulated working conditions. Specifically, the geometric parameters of the fuel rods include length, diameter, and pitch; the simulated working conditions include the heating power of the fuel rods, the flow field environment (including the composition, temperature, flow rate, and pressure of the coolant), as well as the corresponding thermal diameter and the corresponding hydraulic diameter.

[0050] Step b): According to the geometric parameters of the fuel rods and the simulated working conditions, design and manufacture the single-rod CHF test device provided in the foregoing embodiments. Specifically, the diameter of the heating rod 1 is 9.5 mm, and the inner diameter of the thermal insulation tube 2 is 14.22 mm.

[0051] Step c): Use this single-rod CHF test device to conduct a single-rod CHF test on the simulated fuel rods.

[0052] Specifically, asFigure 3 As shown in the figure, it includes the following steps:

[0053] Step c1): Calibrate the single-rod CHF test device.

[0054] Select several flow rate, temperature, pressure, and gas content rate parameters in the LOOK UP TABLE (2006 or later version), conduct the CHF calibration test, compare the CHF test results (M value) with the look-up results (P value) in the LOOK UP TABLE. When the errors of most data points in the CHF power deviation are within ±10%, and the errors of individual data points are within ±15%, the calibration test results are considered correct and the test data is credible.

[0055] Step c2): Verify the consistency between the model characteristics and the test design scheme of the single-rod CHF test device.

[0056] The model characteristics include the heating rod structure, test channel structure, heating rod assembly and installation status, coolant temperature, coolant pressure, coolant flow rate, voltage and current of the single-rod CHF test device. Verify and confirm the specific values of the above model characteristics with the tester, and compare them with the acceptance criteria to determine the credibility of the data.

[0057] Step c3): Calibration and verification of key measurement channels.

[0058] Calibrate the key measurement channels installed in the single-rod CHF test device, specifically including flow sensors (such as flow meters), temperature sensors (such as thermocouples), and pressure sensors (such as pressure transmitters, differential pressure transmitters), as well as voltage and current signal sensors, etc. Check the accuracy of the sensors and formulate acceptance criteria.

[0059] Step c4): Conduct a preliminary experiment to determine the deviation range of measurement data and the stability of test conditions.

[0060] By conducting a preliminary experiment, test the deviation range of preset condition pressure point parameters, inlet temperature deviation range, inlet mass flow rate deviation range, temperature controllable change range, pressure controllable change range, compare the data results with the acceptance criteria, and judge the stability / controllability of the condition / action.

[0061] Step c5): Conduct a seal test to verify the thermal balance data.

[0062] Conduct an overall seal test of the test loop. Gradually increase the loop pressure to 5 MPa, 10 MPa, and 15 MPa by adjusting the valve opening and maintain the loop pressure and temperature for 30 minutes. If there is no leakage at all sites on site, it is determined that the test loop meets the mass balance requirements (sealing requirements).

[0063] Conduct the initial thermal equilibrium test of the test loop. If the thermal equilibrium data is above 92%, it can be considered that the test results meet the energy balance requirements.

[0064] Step c6): Conduct the repeatability verification of the preliminary experiment.

[0065] To ensure that the performance and important parameters of the test device do not change significantly during the test, set multiple repeated test points during the preliminary experiment, and quantitatively calculate the measured power deviation value. If the deviations of the outlet pressure, inlet coolant temperature, mass flow rate, and test power in the repeated tests do not exceed ±5%, it is determined that the test results meet the repeatability requirements, and the formal test can be carried out.

[0066] Step c7): Conduct the formal CHF test.

[0067] After the above steps are completed, conduct the formal test to obtain the single-rod CHF test data, analyze the variation law of the measured CHF value (M value) with the key parameters during the test, and complete the verification and extension of the CHF relational formula.

[0068] The purpose of the above embodiments is to further elaborate on the present invention with reference to the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope disclosed by the present invention, optimizing or equivalently replacing the component structures or method steps involved, and combining the implementation manners in different embodiments without conflict in structure and principle all fall within the protection scope of the present invention.

Claims

1. A single-rod CHF test device, including a heating rod, characterized in that, it further includes a heat preservation tube and a fixing grid; wherein, the heating rod is arranged coaxially with the heat preservation tube through the heat preservation tube, and the space between the inner wall of the heat preservation tube and the heating rod is filled with a cooling medium. The diameter d of the heating rod is the same as the diameter of the simulated fuel rod, and the inner diameter D of the heat preservation tube satisfies: D h = D e = (D 2 - d 2 ) / d, where D h is the thermal diameter corresponding to the fuel rod to be simulated, and D e is the hydraulic diameter corresponding to the fuel rod to be simulated; The fixing grid is fixedly arranged on the inner wall of the heat preservation tube and abuts against the surface of the heating rod to provide radial limitation for the heating rod.

2. The single-rod CHF test device according to claim 1, characterized in that The fixing grid is configured as a ceramic grid.

3. The single-rod CHF test device according to claim 2, wherein The fixing grid is configured as a rod, and an enlarged end contact is provided at one end of the fixing grid that abuts against the heating rod.

4. The single-rod CHF test device according to claim 2 or 3, characterized in that, The fixing grids are evenly arranged circumferentially along the heat preservation tube.

5. The single-rod CHF test device according to claim 2 or 3, characterized in that The pressure between the fixing grid and the heating rod is 1N - 50N.

6. A single-rod CHF test method, characterized in that, It includes the following steps: Step a): Provide the geometric parameters of the simulated fuel rod and the simulated working conditions; Step b): According to step a), provide a single-rod CHF test device corresponding to the simulated fuel rod, and the single-rod CHF test device adopts the single-rod CHF test device described in any one of claims 1 to 5; Step c): Use the single-rod CHF test device to conduct a single-rod CHF test on the simulated fuel rod.

7. The single-rod CHF test method according to claim 6, characterized in that, In step a), the geometric parameters include the size of the simulated fuel rod, and the simulated working conditions include the heating power, flow field environment, corresponding thermal diameter, and corresponding hydraulic diameter of the simulated fuel rod.

8. The single-rod CHF test method according to claim 6, wherein Step c) includes the following steps: Step c1): Calibrate the single-rod CHF test device; Step c2): Verify the consistency between the model characteristics and the test design scheme of the single-rod CHF test device; Step c3): Calibrate the flow sensor, temperature sensor, and pressure sensor used in the test; Step c4): Conduct a preliminary experiment to determine the deviation range of the test data and the stability of the test conditions; Step c5): Conduct a sealing test to verify the heat balance data; Step c6): Conduct a repeatability verification of the preliminary experiment; Step c7): Conduct a formal CHF test.

9. The single-rod CHF test method according to claim 8, characterized in that, In step c2), the model characteristics include the heating rod structure, test channel structure, heating rod installation state, coolant temperature, coolant pressure, coolant flow rate, voltage, and current of the single-rod CHF test device.

10. The single-rod CHF test method according to claim 8, characterized in that, In step c5), when the heat balance data is above 92%, it is determined that the verification result meets the test requirements.

11. The single-rod CHF test method according to claim 8, wherein In step c6), when the deviations of the outlet pressure, inlet coolant temperature, mass flow rate, and test power in multiple preliminary experiments do not exceed ±5%, it is determined that the verification result meets the repeatability requirements.

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