A method for generating a thermal safety envelope curve for a candu core irradiated target

Abstract

The present application belongs to the technical field of nuclear reactor core thermal safety analysis, and particularly relates to a thermal safety envelope curve generation method for a candu reactor core irradiation target. The method comprises the following steps: step 1, data collection and arrangement; step 2, calculation of irradiation heat release rate; step 3, establishment of a CFD analysis model; step 4, preparation of temperature limit criteria; step 5, preparation of a thermal calculation sequence; step 6, two-dimensional large-scale calculation screening; step 7, three-dimensional detailed calculation statistics; step 8, generation of an envelope curve; and step 9, envelope curve-based evaluation. The CFD calculation model used is more accurate than the theoretical calculation or numerical calculation method used in conventional methods, and fully considers external fluid flow heat transfer, non-uniform power distribution on the circumference of the VFD component outer surface, and internal asymmetric heat transfer processes.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear reactor core thermal safety analysis, and particularly relates to a thermal safety envelope curve generation method for a candu reactor core irradiation target. BACKGROUND

[0002] The candu reactor is a reactor design using heavy water as a moderator and coolant. Its high neutron flux and online refueling characteristics make it have significant advantages in the production of radionuclides. The target can be placed into the core area through the detector hole (TFD) of the VFD center for efficient irradiation to produce valuable nuclides, which are widely used in medical, industrial and scientific fields.

[0003] Different targets have potential thermal safety risks to the core when irradiated in the core, so the selection of new targets or changes in the loading amount need to be analyzed in detail to ensure that they meet the safety criteria of the core operation. With the increasing demand for the production of nuclides using candu reactors, the replacement of targets and the increase in loading amount also increase. Under this background, the conventional operation process of the past has become a bottleneck for the improvement of nuclide production, which mainly includes the following three points:

[0004] First, the rapid evaluation of pre-irradiated targets. The conventional method needs to perform neutron calculation on the pre-irradiated target in the reactor to obtain the heat release, and then evaluate the material temperature distribution to examine the thermal safety of the target in the reactor. It cannot quickly provide the heat release rate envelope limit of the pre-irradiated target.

[0005] Second, the theoretical calculation method is used in the existing target thermal safety evaluation method, which is too conservative in model establishment and calculation method, leaving too much margin, which limits the improvement of target loading amount.

[0006] Third, the evaluation period is long and the cost is high. When designing new irradiation targets or changing the loading amount, detailed thermal evaluation is needed to determine whether it meets the safety acceptance criteria. The whole method process is high in cost and long in period, which limits the increasing demand for irradiation production.

[0007] Overall, in the process of thermal safety evaluation of candu reactor core irradiation targets, the existing method mainly has the problems of insufficient accuracy, limited material types covered, and low evaluation efficiency. SUMMARY

[0008] The application aims to provide a method for generating a thermal safety envelope curve of a candu reactor core irradiation target, which introduces reasonable conservative assumptions while ensuring calculation accuracy, ensures that the evaluation result has a thermal safety margin, expands the range of applicable target materials and thermal physical parameters, and enhances the universality and inclusiveness of the method.

[0009] The technical solution of the application is as follows: a method for generating a thermal safety envelope curve of a candu reactor core irradiation target, comprising the following steps:

[0010] Step 1: data collection and arrangement;

[0011] Step 2: calculation of irradiation heat release rate;

[0012] Step 3: establishment of a CFD analysis model;

[0013] Step 4: preparation of temperature limit criteria;

[0014] Step 5: preparation of a thermal calculation sequence;

[0015] Step 6: two-dimensional large-scale calculation screening;

[0016] Step 7: three-dimensional detailed calculation statistics;

[0017] Step 8: generation of an envelope curve;

[0018] Step 9: evaluation based on the envelope curve.

[0019] The step 1 comprises:

[0020] Step 11: arrangement of the internal geometry of the VFD component, including the diameter, height and gap size between the internal channels, material data information containing the main component composition of the component, obtaining detailed radial and axial size information and the specific material name and composition of all existing solids, gases and liquids in the channel by querying the design report of the candu reactor;

[0021] Step 12: collection of the thermal physical property table of the material involved According to all the material data information collected in step 11, the thermal physical property table is one-to-one corresponding to the density, thermal conductivity, specific heat capacity, melting point, dynamic viscosity of each substance, and the density, thermal conductivity, specific heat capacity, dynamic viscosity of the material involved, and the limit temperature of the material in engineering application based on safety consideration are obtained;

[0022] Step 13: selection of irradiation target materials and physical parameters, obtaining alternative target materials in the actual irradiation process, arranging the density, thermal conductivity and specific heat capacity parameters of each material, and the limit temperature in engineering application.

[0023] The step 2 comprises:

[0024] Step 21: Instantaneous heat release rate calculation;

[0025] The step 21 comprises:

[0026] Step 211: Perform neutron and photon coupled transport calculation on the two-rod bundle model of the heavy water reactor at a given target loading amount, to obtain the total neutron and photon deposition energy in the entire two-rod bundle calculation region, and the neutron and photon deposition energy in the cladding, quartz tube and target material in the irradiation target;

[0027] Step 212: Obtain the instantaneous neutron and photon heat release rate in the cladding, quartz tube and target material in the irradiation target at different neutron flux density levels by the normalization method;

[0028] Step 213: Establish the relationship between the instantaneous heat release rate of the cladding, quartz tube and target material in the irradiation target and the neutron flux density and target loading amount;

[0029] Step 22: Delayed heat release rate calculation;

[0030] The step 22 comprises:

[0031] Step 221: Perform neutron and photon coupled transport calculation on the two-rod bundle model of the heavy water reactor at a given target loading amount, to obtain the two-group effective microscopic cross section of various isotopes in the target;

[0032] Step 222: According to the normalized neutron flux density and two-group effective microscopic cross section of the isotopes, obtain the nuclear density of the activated product in unit volume after irradiation by solving the burnup equation;

[0033] Step 223: According to the decay rate and decay energy of the activated product, the delayed heat release rate can be obtained. In the calculation process, the neutron activation of all materials in the VFD assembly is calculated, and the heat release rate of each material in the specific irradiation process in the reactor is sorted out.

[0034] The step 3 comprises:

[0035] Step 31: Model simplification processing includes three aspects

[0036] First, model the VFD assembly based on the cold state geometric size;

[0037] Second, in the modeling of the structure of the VFD assembly, it is simplified as an equal quality and uniform structure during the modeling process;

[0038] Third, in the modeling process of the internal channel of the VFD assembly, the gap between the walls is enlarged;

[0039] Step 32: The specific material property selection setting is to specify the thermal properties of each material in the model after the CFD model is established. In the property selection process, the inlet temperature of the slow reactor container is set to 46℃ and the slow reactor container top pressure is set to 0.13MPa as the condition, and the density, specific heat capacity, thermal conductivity and dynamic viscosity of the VFD component solid, gas and fluid are queried in the thermal property table collected in step 1;

[0040] Step 33: The boundary condition and solution setting includes the boundary condition and program setting when the model is solved. The pressure boundary condition of the inlet and outlet is set, and the SST k-ω turbulence model is selected. For the heat release rate of each material in the VFD component, an uncertainty factor of 1.15 is selected. After the model is established, mesh independence analysis needs to be performed on the three-dimensional model and the two-dimensional model.

[0041] Step 4: Before numerical simulation, according to the limit temperature of the material in the VFD component and the limit condition that the heavy water in the gap between the sealing sleeve and the guide pipe cannot occur bubble nucleate boiling, combined with the property table, the material limit and the empirical relationship, the vanadium probe limit temperature, the target material limit temperature and the bubble nucleate boiling start temperature of the sealing sleeve wall surface are determined as the criterion of the thermal safety temperature limit. According to the selected target material properties, the heat conductivity coverage range of the envelope curve and the sparse and dense distribution of the calculation points in the interval are determined. For the heat release rate, the interval of 0.1W / cm³~500 W / cm³ is given, and the calculation points are set at equal intervals in the interval. The heat conductivity and the heat release rate are cross-matched to generate a set of calculation points.

[0042] The bubble nucleate boiling start temperature of the wall surface T ONB In calculation, Thom empirical relationship is selected, and the specific form is as follows:

[0043]

[0044] In the formula, T sat The fluid saturation temperature is T, q″ The surface heat flux is q, P The fluid pressure is p, all of which use the conservative value in step 3.

[0045] Step 5 includes:

[0046] Step 51: The heat conductivity range of the irradiated target material is set by arranging the preselected target material heat conductivity collected in step 1;

[0047] Step 52: The heat release rate calculation range of the irradiated target material is selected, which is 0.1W / cm³~500 W / cm³, and the interval range is set by equal interval distribution;

[0048] Based on the above irradiation target material thermal conductivity and heat release rate range selection, cross matching setting calculation point.

[0049] The step 6 comprises:

[0050] Step 61: For large-scale two-dimensional calculation results, feature screening is performed;

[0051] Step 62: Eliminate the calculation points of the screening method exceeding the temperature limit value in step 4, which is based on the following criteria,

[0052]

[0053] Among them, q The volume heat release rate of the material, k The thermal conductivity of the material. By arranging the temperature distribution of all calculation points, the maximum temperature of the outer wall of the sleeve T wall ( q, k ), the maximum temperature of the irradiation target T center ( q, k ) and the maximum temperature of the resident vanadium detector T detector ( q, k ) are obtained, and compared with the corresponding temperature limit value, the calculation points exceeding the limit value are eliminated; q The volume heat release rate of the material, k The thermal conductivity of the material.

[0054] The step 7 comprises: matching the simplified calculation point set of the screened target material thermal conductivity and heat release rate, calculating the target material properties in the three-dimensional model through batch processing, completing the detailed three-dimensional flow-heat coupled heat transfer calculation of all screened calculation points, and obtaining the temperature distribution of the VFD assembly under the detailed three-dimensional heat transfer calculation condition;

[0055] Complete the three-dimensional heat transfer simulation of the simplified calculation point set of all screened calculation points, again statistic the maximum temperature of the outer wall of the sleeve T wall ( q, k ), the maximum temperature of the irradiation target T center ( q, k ) and the maximum temperature of the resident vanadium detector T detector ( q, k ), and compared with the corresponding temperature limit value, the calculation points exceeding the limit value are eliminated;

[0056] For all remaining calculation point data, the thermal conductivity of the target material k The heat release rate q of the target material and the highest temperature of the target material TCorrelation table of the change k - q - T Correlation table.

[0057] The step 8 comprises: according to the limit temperature distribution of the preselected target material investigated in step 1, selecting a series of limit temperature points of the target material, so as to k - q - T Based on the correlation table, the corresponding heat release rate is obtained by interpolation calculation under the condition of different target thermal conductivities, and a one-to-one corresponding relationship table is formed, so that the heat release rate under the condition of different target temperatures can be sorted out. k - q The envelope curve is obtained, after obtaining the new target thermal conductivity and limit temperature, the horizontal coordinate of the thermal conductivity in the k-q series curve is found, and the intersection of the straight line and the limit temperature interval line is made, so that four intersection points are obtained, and the maximum heat release rate corresponding to the current target limit temperature is obtained by two-dimensional interpolation calculation of the thermal conductivity, heat release rate and temperature curve value of the four points, and the heat release rate of the current target is evaluated based on the maximum heat release rate whether it meets the thermal safety criterion.

[0058] The step 9 comprises: after obtaining the thermal conductivity and limit temperature of the irradiated target material, according to the thermal conductivity k The envelope curve sorted out in step 8 k - q The corresponding horizontal coordinate interval is found in the envelope curve graph k 1 And k 2 At the same time, based on the limit temperature T , the corresponding target temperature value curve interval T 1 and T 2 is found, and linear interpolation calculation is carried out in the interpolation interval, and the specific calculation method is as follows:

[0059]

[0060] Wherein, the first number of the subscript represents the temperature curve corresponding to T, and the second number represents the thermal conductivity straight line corresponding to k, such as q 11 In the first 1 of q 11 , the second 1 corresponds to the thermal conductivity k1, that is, the vertical coordinate q11 of the point intersected with the horizontal coordinate k1 on the T1 temperature limit value curve, so that the heat release rate under the condition of the new target thermal conductivity and limit temperature is obtained, and the heat release rate obtained by interpolation is the maximum heat release rate corresponding to the limit temperature, and whether the heat release rate of the pre-irradiated material meets the safety limit is judged.

[0061] The beneficial effects of the present application are as follows:

[0062] 1. Considering accuracy and conservatism

[0063] Compared with the theoretical calculation or the method combined with numerical calculation used in the conventional method, the CFD calculation model used in the method is more accurate, fully considers the external fluid flow heat transfer, the non-uniform power distribution on the outer surface of the VFD assembly in the circumferential direction, and the internal asymmetric heat transfer process, etc.

[0064] 2, sufficient coverage

[0065] In the envelope curve generation process of the method, more than twenty target materials that can be irradiated in the reactor to produce nuclides are selected, and the thermal properties of these target materials are fully covered when the target thermal conductivity and heat release rate interval and calculation points are determined, so that the selected target materials can be queried in the envelope curve. At the same time, when the calculation range is selected, the thermal conductivity exceeds the highest thermal conductivity investigated, and a certain amount of surplus is added, and the heat release rate is based on the temperature limit value, so that the target material selection can cover a wider range.

[0066] 3, fast thermal safety evaluation

[0067] The method relies on sufficient coverage, sufficient calculation points, and a wide range of calculations combined with multiple temperature limits to form a feature that can accurately capture the changes in thermal conductivity, heat release rate and target temperature of the irradiated target material in each range. The envelope curve is set differently in density according to the change characteristics during the generation process, and the corresponding thermal conductivity and maximum heat release rate under the limit temperature can be accurately and quickly interpolated. Without the need for complex calculations, only the thermal conductivity and limit temperature of the irradiated target material provided by the experimental data or the production party can quickly evaluate the thermal safety of the irradiated target material, greatly simplifying the operation steps in the initial stage and saving a lot of cost. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 is a simplified structure diagram of a VFD assembly;

[0069] Figure 2 is a flow chart of a thermal safety envelope curve generation method for a CANDU reactor core irradiated target material provided by the present application;

[0070] Figure 3 is a three-dimensional geometric model of a VFD assembly;

[0071] Figure 4 is a radial grid distribution of a VFD assembly;

[0072] Figure 5 is a schematic diagram of the change curve of the thermal conductivity of the target material and the heat release rate of the target material;

[0073] Figure 5 T1, T2, T3, T4 are schematic representation of different target temperature points selected, each curve is isothermal point, matching different thermal conductivity ( k ) and heat release rate ( q ).

[0074] Figure 6 Based on the target thermal conductivity and limit temperature interpolation to get the maximum heat release rate diagram.

[0075] Figure 6 (k, T) are the thermal conductivity and limit temperature of the pre-irradiated target, respectively; k1 and k2 are the upper and lower limit values of the thermal conductivity based on the pre-irradiated target; T1 and T2 are the upper and lower limit values of the target temperature based on the limit temperature; q11 and q12 are the intersection heat release rates of k1 and k2 with T1 isothermal line, q21 and q22 are the intersection heat release rates of k1 and k2 with T2 isothermal line, and q is the maximum heat release rate obtained by final interpolation.

[0076] In the figure: 101 guide tube, 102 helium, 103 air, 104 quartz tube, 105 target, 106 target cladding, 107 sealing sleeve, 108 emitter, 109 insulator, 110 collector, 111 heavy water, 112 detector channel. DETAILED DESCRIPTION

[0077] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0078] A method for generating a thermal safety envelope curve of a candu reactor core irradiation target, based on a finite volume computational fluid dynamics (CFD) software, a detailed flow-thermal coupling numerical analysis model is established for the VFD assembly, including the detailed structure of the irradiation target and the resident vanadium detector, but all the material thermal properties, boundary conditions, flow model selection, etc. in the VFD are set conservatively, such as querying the material thermal properties with the inlet fluid temperature, considering the natural convection form for wall flow, etc.

[0079] Based on this numerical analysis model, a conservative thermal envelope curve under a specific irradiation scenario is obtained based on multiple temperature limit criteria, which is mainly a series of curves corresponding to the thermal conductivity and irradiation heat release rate at different target temperatures. In the screening process of the curve data points, the target limit temperature (Tcenter, limit), the vanadium detector limit temperature (Tdetector, limit) and the sealing sleeve outer wall nucleate boiling initiation temperature (T ONB ) are selected as temperature limit criteria, among which the target limit temperature will change according to different materials.

[0080] After obtaining the thermal conductivity and limit temperature of the new irradiated target, interpolation calculation can be quickly performed in the target thermal conductivity and heat release rate envelope curve to obtain the maximum heat release rate of the target at the limit temperature, and then it is quickly judged whether the heat release of the pre-irradiated target meets the thermal safety requirement.

[0081] As shown in Figure 2 The present application provides a kind of for the thermal safety envelope curve generation method of Candu reactor core irradiation target, and the conservative thermal envelope curve generation under specific irradiation scenario is obtained based on multiple temperature limit criterion, and specific steps include as follows:

[0082] Step 1: data collection and arrangement

[0083] Determine the VFD component (as shown in Figure 1 The irradiation target is located in the geometric information and material information, and the material thermal property table is obtained based on experimental measurement data, literature data and material property software, and the interval range and distribution of the material property of the selected irradiation target are determined, including the following:

[0084] Step 11: arrange the geometric structure including the diameter, height and gap size of the internal hole of the VFD component, and the material data information contains the main component of the component. Obtain detailed radial and axial size information and the specific material name and composition of all existing solids, gases and liquids in the hole by querying the design report of Candu reactor;

[0085] Step 12: collect the thermal property table of the material involved According to the material data information collected in step 11, the thermal property table is the information of each substance such as density, thermal conductivity, specific heat capacity, melting point and dynamic viscosity, which is one-to-one corresponding to the material data. Through experimental measurement, material manual, literature data and material property query software, the density, thermal conductivity, specific heat capacity, dynamic viscosity and other thermal properties of the material involved are obtained, as well as the limit temperature of the material in engineering application based on safety consideration;

[0086] Step 13: optional irradiation target and material property parameter Through public literature or viewing irradiation target evaluation report, more than 20 kinds of target materials that can be selected in actual irradiation process are obtained, which include metal, oxide and salt, and the thermal property parameters such as density, thermal conductivity and specific heat capacity of each material are arranged, as well as the limit temperature in engineering application.

[0087] Step 2: calculation of irradiation heat release rate

[0088] Based on the material information of the VFD assembly and the target material obtained, the assembly is modeled by the Monte Carlo program, and neutron calculation is performed at the full power level of the core, so as to obtain the irradiation heat release rate of all materials in the VFD assembly under this condition. The materials involved in the VFD assembly, such as structural fixtures, irradiation targets and resident vanadium detectors, will directly generate heat release rate through long-term interaction with neutrons and photons, which includes prompt heat release rate and delayed heat release rate.

[0089] Step 21: prompt heat release rate calculation

[0090] Step 211: neutron and photon coupling transport calculation is performed on the two-rod bundle model of the heavy water reactor under a given target material loading, so as to obtain the total neutron and photon deposition energy in the entire two-rod bundle calculation region, and the neutron and photon deposition energy in the cladding, quartz tube and target material in the irradiation target;

[0091] Step 212: the prompt neutron and photon heat release rate in the cladding, quartz tube and target material in the irradiation target under different neutron flux density levels is obtained by the normalization method;

[0092] Step 213: the relationship between the prompt heat release rate of the cladding, quartz tube and target material in the irradiation target and the neutron flux density and target material loading is established.

[0093] Step 22: delayed heat release rate calculation

[0094] Step 221: neutron and photon coupling transport calculation is performed on the two-rod bundle model of the heavy water reactor under a given target material loading, so as to obtain the two-group effective microscopic cross section of various isotopes in the target;

[0095] Step 222: according to the normalized neutron flux density and two-group effective microscopic cross section of the isotopes, the nuclear density of the activated products in unit volume after irradiation is obtained by solving the burnup equation;

[0096] Step 223: the delayed heat release rate can be obtained according to the decay rate and decay energy of the activated products. In the calculation process, the neutron activation of all materials in the VFD assembly is calculated, and then the heat release rate of each material in the specific irradiation process in the reactor can be sorted out.

[0097] Step 3: establish CFD analysis model

[0098] Based on the size and material information of the VFD assembly and the target material, the finite volume analysis tool Comsol, Ansys is selected to establish a three-dimensional flow-thermal coupling model, and a fluid domain is added externally to calculate the natural convection heat transfer on the wall surface. In the modeling process, material properties and boundary condition setting, the principle of conservation is followed. At the same time, a two-dimensional simplified heat transfer model is established based on the three-dimensional model, and the external boundary condition is selected as a fixed temperature boundary. After the model is established, grid independence analysis is performed in the grid generation process to find the best calculation grid distribution. The key steps in the modeling process include model simplification, material property selection and setting, boundary condition and solution setting, etc., as follows:

[0099] Step 31: The specific model simplification mainly includes three aspects

[0100] First, based on the cold-state geometric size, the VFD assembly is modeled, and the thermal expansion effect in the heat release process is ignored. The conservative ignores the improvement of the VFD assembly heat transfer due to thermal expansion effect;

[0101] Second, in the modeling of VFD assembly structure, for structures such as probes with small size that have little effect on the calculation results, they are simplified by being uniformly distributed to the surrounding material in the modeling process;

[0102] Third, in the modeling process of the internal channel of the VFD assembly, considering that the linear contact between the outer wall of the channel will cause great challenges to the model grid generation, the gap between the walls is appropriately enlarged according to the principle of conservation in actual modeling, which not only ensures the conservation of the heat transfer process, but also simplifies the model grid generation;

[0103] Step 32: The specific material property selection setting is to specify the thermal properties of each material in the model after the CFD model is established. In the property selection process, the principle of conservation is also followed, and the inlet temperature of the pipe container moderator (46℃) and the top pressure of the pipe container moderator (0.13MPa) are selected as conditions. The thermal properties of the VFD assembly solid, gas and fluid such as density, specific heat capacity, thermal conductivity and dynamic viscosity are queried in the thermal property table collected in step 1;

[0104] Step 33: The specific boundary condition and solution setting includes the boundary condition and program setting when the model is solved. For the fluid domain built outside the VFD assembly as shown in Figure 4 , and the outlet temperature of the pipe container moderator (69℃) is selected as the boundary condition. In the wall flow heat transfer, the principle of conservation is followed to consider the natural convection heat transfer, so the inlet and outlet pressure boundary conditions are set, and the SST k-ω turbulent flow model is selected. The heat release rate of each material in the VFD assembly is based on the calculation results of step 2, but considering the uncertainty of the heat release rate in a conservative manner, an uncertainty factor of 1.15 is selected.

[0105] After the model is established, the grid independence analysis of three-dimensional model and two-dimensional model is needed, and the specific method is mainly to encrypt the grid generation to the point that it will not affect the calculation results.

[0106] Step 4: Prepare temperature limit criterion

[0107] Before numerical simulation, according to the limit temperature of materials in VFD assembly and the condition that the heavy water in the gap between the sealing sleeve and the guide tube cannot occur bubble nucleate boiling, combined with the material property table, the material limit and the empirical relationship, the limit temperature of vanadium detector (Tdetector, limit), the limit temperature of target material (Tcenter, limit) and the bubble nucleate boiling start temperature of sealing sleeve wall (T ONB ) are determined as the criterion of thermal safety temperature limit. According to the selected twenty kinds of target material properties, the heat conductivity coverage range of envelope curve and the sparse and dense distribution of calculation points in the range are determined. For the heat release rate, the interval of 0.1 W / cm³~500 W / cm³ is preliminarily given, and the calculation points are set at equal intervals in the interval. The heat conductivity and heat release rate are cross matched to generate the calculation point set.

[0108] According to the limit temperature of all materials collected in step 1 as the unbreakable condition of solid materials. By comparing the limit temperature of all materials in VFD assembly, since the target material needs to be replaced, its limit temperature will change accordingly, so the limit temperature of vanadium detector (Tdetector, limit) with the lowest limit temperature among the unchanged materials and the limit temperature of the variable target material (Tcenter, limit) are selected as the temperature limit of solid part. T detector,limit T center,limit

[0109] For the fluid part, the condition that the heavy water in the gap between the sealing sleeve and the guide tube cannot occur bubble nucleate boiling needs to be considered as the unbreakable condition. In the calculation of bubble nucleate boiling start temperature (T T ONB ), Thom empirical relationship is selected, and the specific form is as follows:

[0110]

[0111] In the formula, T sat is the saturation temperature of fluid, q″ is the surface heat flux, P is the fluid pressure, all of which adopt the conservative values in step 3.

[0112] Based on the above process, the temperature limit criterion of the components in VFD assembly, the irradiation target material and the resident vanadium detector in the reactor core is fully considered, that is, the limit temperature of vanadium detector Tdetector, limit, the limit temperature of target material Tcenter, limit and the bubble nucleate boiling start temperature of sealing sleeve wall T T detector,limit ​​, target material limit temperature T center,limit and wall surface bubble nucleate boiling inception temperature T ONB .

[0113] Step 5: Prepare thermal calculation sequence

[0114] After the preparation of step 1 to step 4 is completed, all settings of the CFD model are completed except for the thermal properties of the replaceable irradiation target. For the replaceable irradiation target, it is necessary to cover the thermal conductivity range of all pre-selected irradiation targets collected in step 1, and the heat release rate within the temperature limit range.

[0115] Based on the above set of calculation points, a rapid calculation simulation is performed through a two-dimensional model to obtain the preliminary temperature distribution of each part of the VFD and the target. The maximum temperature of the vanadium detector, the maximum temperature of the target, and the maximum temperature of the outer wall of the sealing sleeve of each calculation point are counted and compared with the prepared temperature safety limit to eliminate the calculation points that exceed the limit. In addition, if it is found during the statistical process that the preliminary set heat release rate range does not reach the temperature limit, the heat release range needs to be expanded until the temperature safety limit is reached.

[0116] During this process, according to the statistical results of the two-dimensional calculation, when the thermal conductivity or heat release rate changes, it will cause a large range of target temperature changes. Therefore, it is necessary to increase the calculation points to ensure that the envelope curve generated can fully reflect the change characteristics at this place. The new simplified calculation point set is formed through screening and encryption by this method, which specifically includes the following:

[0117] Step 51: The thermal conductivity range of the irradiation target is set by arranging the thermal conductivity of the pre-selected target collected in step 1, and approximately selecting the thermal conductivity that can cover all materials, such as 0.1 W / (m·K)~350 W / (m·K) range. However, when generating calculation points, it is necessary to set the density of the calculation points according to the distribution of the thermal conductivity of all pre-selected targets, that is, to increase the calculation points in the thermal conductivity interval with dense distribution, and to reduce the calculation points in the thermal conductivity interval with sparse distribution.

[0118] Step 52: The heat release rate calculation range of the irradiation target is selected, which needs to meet the temperature limit. However, before the heat transfer calculation, the temperature distribution of the materials in the VFD assembly under different heat release rates is not known, so it is necessary to preliminarily select the heat release rate range, such as 0.1 W / cm³~500 W / cm³ range, and set the interval range with equal interval distribution.

[0119] Based on the above irradiation target material thermal conductivity and heat release rate range selection, cross matching setting calculation points, for example, at thermal conductivity 0.1 W / (m·K), respectively with 0.1 W / cm³~500 W / cm³ interval set all heat release rate calculation points continue to match, so as to build a large range of calculation point set.

[0120] Step 6: two-dimensional large-scale calculation screening

[0121] Based on the selected irradiation target material thermal conductivity and heat release rate matching calculation point set in step 5, through the development of batch processing calculation file, drive two-dimensional numerical model to carry out large-scale rapid preliminary calculation, for screening out the calculation points which can cover the thermal conductivity, heat release rate and target temperature variation characteristics, at the same time, eliminate the calculation points which exceed the temperature limit value prepared in step 4.

[0122] Based on the two-dimensional screening of the simplified calculation point set which can fully grasp the thermal conductivity, heat release rate and temperature variation characteristics of the target, put it into the three-dimensional model one by one for numerical simulation, and obtain the accurate three-dimensional flow condition VFD component temperature distribution.

[0123] Similarly, the maximum temperature of vanadium detector, the maximum temperature of target and the maximum temperature of sealing sleeve outer wall of each calculation point are counted, and compared with the prepared temperature safety limit value, and the calculation points exceeding the limit are eliminated, including the following:

[0124] Step 61: for the large-scale two-dimensional calculation results, the highest temperature of the target changes slightly under the condition of thermal conductivity change and constant heat release rate, so the calculation points can be reduced, and the points which can reflect the temperature change in the interval can be selected. The same method is also applicable to the case of constant thermal conductivity and changing heat release rate. For the case where the temperature changes greatly in the interval, the calculation points can be appropriately encrypted.

[0125] Step 62: the screening method of eliminating the calculation points exceeding the temperature limit value in step 4 is based on the following criteria,

[0126]

[0127] Among them, q is the volumetric heat release rate of the material, k is the thermal conductivity of the material. By sorting all the temperature distribution of the calculation points, the maximum temperature of the sleeve outer wall of each calculation point T wall ( q, k ), the maximum temperature value of the irradiation target T center ( q, k ) and the maximum temperature value of the resident vanadium detector T detector ​q, k ) and compare it with the corresponding temperature limit, and the calculation points that exceed the limit can be eliminated; q is the volume heat release rate of the material, k is the thermal conductivity of the material.

[0128] Since the heat release rate selection in step 5 is a rough range, there is a possibility that all calculation points do not exceed the temperature limit. Therefore, if this is the case, it is necessary to repeat step 5 to expand the calculation area and perform two-dimensional calculation screening again until the temperature limit can be covered.

[0129] Step 7: 3D detailed statistics calculation

[0130] With the help of the two-dimensional large-scale rapid calculation screening in step 6, a streamlined calculation point set that can reflect the response characteristics of the irradiated target material temperature, thermal conductivity, and heat release rate and that covers a sufficiently large range to match the target material thermal conductivity and heat release rate can be sorted out.

[0131] The simplified calculation point set that matches the thermal conductivity and heat release rate of the screened target material is used to set the target material properties in the 3D model through a batch calculation script, and the detailed 3D fluid-thermal coupling heat transfer calculation of all the screened calculation points is automatically completed, thereby obtaining the temperature distribution of the VFD component under the detailed 3D heat transfer calculation conditions;

[0132] After completing the heat transfer simulation of the three-dimensional model of all the filtered simplified calculation point sets, it is necessary to count the maximum temperature of the outer wall of the casing of all calculation points again. T wall ( q, k ), the maximum temperature of the irradiated target T center ( q, k ) and the maximum temperature of the resident vanadium detector T detector ( q, k ), and compare it with the corresponding temperature limit, and eliminate the calculation points that exceed the limit.

[0133] For all remaining calculation point data, the thermal conductivity of the target material is sorted out. k , the heat release rate q of the target and the maximum temperature of the target T Change association table k - q - T Relation table.

[0134] Step 8: Generate Envelope Curve

[0135] Since the irradiation target needs to be replaced, the purpose of the present invention is to quickly query the thermal safety of the replacement target, so the step 7 finally sorts out the interpolation calculation. k - q - TBased on the correlation table, the target temperature under different conditions can be generated by interpolation. k - q Curve (such as Figure 5 ).

[0136] The specific method is to select a series of target limit temperature points based on the limit temperature distribution of the pre-selected target material investigated in step 1. k - q - T Based on the correlation table, the corresponding heat release rate is obtained by interpolation calculation under different target thermal conductivity conditions, forming a one-to-one corresponding relationship table, which can be used to sort out the heat release rate under different target temperature conditions. k - q The envelope curve of Figure 5 The envelope curve shown is distributed.

[0137] After obtaining the new target material's thermal conductivity and limit temperature, the kq series curve's horizontal axis (k-axis) can be used to find the interval where the thermal conductivity lies. A straight line can be drawn at the interval boundary to intersect the line of the limit temperature interval. This will result in four intersection points. Using the thermal conductivity, heat release rate, and temperature curve values ​​at these four points, a two-dimensional interpolation calculation can be performed to determine the maximum heat release rate corresponding to the current target material's limit temperature. This maximum heat release rate can be used to quickly assess whether the current target material's heat release rate meets thermal safety standards.

[0138] Step 9: Evaluation based on the envelope curve

[0139] In the actual irradiation process, the target material may be replaced or the target loading may be changed. In both cases, the thermal safety of the target needs to be re-evaluated. In the present invention, after obtaining the thermal conductivity and limit temperature of the new irradiation target, the target material can be re-evaluated according to the thermal conductivity. k In step 8, k - q Find the corresponding horizontal axis interval in the envelope curve diagram k 1 and k 2 , and based on this limit temperature T , find the corresponding target temperature value curve interval T 1 and T 2. Specific interpolation methods are as follows Figure 6 As shown. Since the calculation points are set densely enough, linear interpolation calculation can be performed within the interpolation interval. The specific calculation method is as follows:

[0140]

[0141] The first number in the subscript represents the temperature curve corresponding to T, and the second number represents the thermal conductivity line corresponding to k, such as q 11The first 1 corresponds to the T1 temperature limit value, and the second 1 corresponds to the k1 thermal conductivity, i.e. the ordinate q11 corresponding to the point of intersection of the T1 temperature limit value curve with the abscissa k1.

[0142] Thus, the new target material thermal conductivity and the heat release rate under the limit temperature condition can be obtained, and the heat release rate obtained by interpolation is the maximum heat release rate under the limit temperature, so the heat release rate generated by the new target material loading cannot exceed this value, thereby it can be determined whether the heat release rate of the pre-irradiated material meets the safety limit.

Claims

1. A method for generating a thermal safety envelope curve for a candu core irradiated target material, the method comprising: determining a plurality of thermal safety envelope curves for a plurality of different irradiated target materials; and determining a thermal safety envelope curve for the irradiated target material based on the plurality of thermal safety envelope curves. The method comprises the following steps: Step 1: data collection and arrangement; Step 2: calculation of irradiation heat release rate, including calculation of prompt heat release rate and calculation of delayed heat release rate; Step 3: establishment of a CFD analysis model; The step 3 comprises: Firstly, modeling of the VFD assembly based on cold-state geometric dimensions; Secondly, simplification of the VFD assembly structure modeling by homogenizing the VFD assembly into surrounding materials; Thirdly, expansion of the gap between the walls in the modeling process of the internal channels of the VFD assembly; Step 4: preparation of temperature limit criteria; Step 5: preparation of thermal calculation sequence; Step 6: two-dimensional large-scale calculation screening; The step 6 comprises: Step 61: feature screening of the large-scale two-dimensional calculation results; Step 62: screening method for eliminating the temperature limits in step 4, which is based on the following criteria, T wall (q,k)≤T ONB T center (q, k) < T center,limit T detector (q, k) < T detector,limit Among them, q is the volume heat release rate of the material, k is the thermal conductivity of the material, and by sorting out the temperature distribution of all calculation points, the maximum temperature T of the outer wall of the casing at each calculation point is obtained. wall (q,k), maximum temperature of the irradiated target T center (q, k) and the maximum temperature of the resident vanadium detector T detector (q, k), and compare it with the corresponding temperature limit, and eliminate the calculation points that exceed the limit; q is the volume heat release rate of the material, and k is the thermal conductivity of the material; Step 7: three-dimensional detailed calculation and statistics; The step 7 comprises: matching the screened target material thermal conductivity and heat release rate with the simplified calculation point set, calculating the target material properties in the three-dimensional model through batch processing, completing the detailed three-dimensional flow-heat coupled heat transfer calculation of all screened calculation points, and obtaining the temperature distribution of the VFD assembly under the condition of detailed three-dimensional heat transfer calculation; All the simplified calculation point sets are simulated by heat transfer simulation software, and the maximum temperature of the outer wall of the sleeve T wall (q, k) and the maximum temperature of the irradiation target T center (q, k) and the maximum temperature of the resident vanadium detector T detector (q, k) and the maximum temperature of the irradiation target T wall (q, k) and the maximum temperature of the irradiation target T center (q, k) and the maximum temperature of the resident vanadium detector T detector (q, k) and the maximum temperature of the irradiation target T wall (q, k) and the maximum temperature of the irradiation target T center (q, k) and the maximum temperature of the resident vanadium detector T detector (q, k) and the maximum temperature of the irradiation target T wall (q, k) and For all the remaining calculation point data, the target material thermal conductivity k, the target material heat release rate q and the target material highest temperature T are arranged into a k-q-T correlation table; Step 8: generation of envelope curve; The step 8 comprises: According to the preselected target material limit temperature distribution in step 1, a series of target material limit temperature points are selected, and the corresponding heat release rate is obtained by interpolation calculation under different target material thermal conductivity conditions based on the k-q-T correlation table, to form a one-to-one corresponding relationship table, thereby arranging the k-q envelope curve under different target material temperature conditions; after obtaining the new target material thermal conductivity and limit temperature, the thermal conductivity is found in the horizontal coordinate of the k-q series curve, and a straight line is drawn on the interval boundary value to intersect with the interval line of the limit temperature, so that four intersection points will appear, and the maximum heat release rate corresponding to the current target material limit temperature is obtained by two-dimensional interpolation calculation of the thermal conductivity, heat release rate and temperature curve value of the four points, and whether the current target material heat release rate meets the thermal safety criteria is evaluated based on the maximum heat release rate; Step 9: envelope curve-based evaluation.

2. A method of generating a thermal safety envelope curve for a candu core irradiated target as defined in claim 1, wherein, The step 1 comprises: Step 11: arrangement of the geometric structure in the VFD assembly, including the diameter, height and gap size between the channels, arrangement of material data information, and query of the design report of the candu reactor to obtain detailed radial and axial size information and the specific material name and composition of all existing solids, gases and liquids in the channels; Step 12: collection of the thermal physical property table of the materials involved, wherein the thermal physical property table is one-to-one corresponding to the density, thermal conductivity, specific heat capacity, melting point and dynamic viscosity of each substance, and the density, thermal conductivity, specific heat capacity and dynamic viscosity of the materials involved are obtained, as well as the limit temperature of the materials in engineering application based on safety consideration; Step 13: Select irradiation target material and physical property parameters, obtain alternative target materials in actual irradiation process, and arrange density, thermal conductivity and specific heat capacity parameters of each material, as well as limit temperature in engineering application.

3. A method of generating a thermal safety envelope curve for a candu core irradiated target as defined in claim 1, wherein, The step 2 comprises: Step 21: Instantaneous heat release rate calculation; The step 21 comprises: Step 211: Perform neutron and photon coupling transport calculation on the two-rod bundle model of the heavy water reactor under the given target material loading, and obtain neutron and photon deposition energy in the entire two-rod bundle calculation region and in the cladding, quartz tube and target material in the irradiation target; Step 212: Obtain the instantaneous neutron and photon heat release rate in the cladding, quartz tube and target material in the irradiation target under different neutron flux density levels by the normalization method; Step 213: Establish the relationship between the instantaneous heat release rate of the cladding, quartz tube and target material in the irradiation target and the neutron flux density and target material loading; Step 22: Delayed heat release rate calculation; The step 22 comprises: Step 221: Perform neutron and photon coupling transport calculation on the two-rod bundle model of the heavy water reactor under the given target material loading, and obtain two-group effective microscopic cross sections of various isotopes in the target; Step 222: According to the normalization of the neutron flux density and the two-group effective microscopic cross sections of the isotopes, obtain the nuclear density of the activated products per unit volume after irradiation by solving the burnup equation; Step 223: According to the decay rate and decay energy of the activated products, obtain the delayed heat release rate. In the calculation process, the neutron activation of all materials in the VFD assembly is calculated, and the heat release rate of each material in the specific irradiation process in the reactor is arranged.

4. A method of generating a thermal safety envelope curve for a candu core irradiated target as defined in claim 1, wherein, The step 3 comprises: The specific material property selection setting is to specify the thermal properties of each material in the model after the CFD model is established. In the property selection process, the inlet temperature of the tube container moderator is selected as 46℃ and the top pressure of the tube container moderator is selected as 0.13MPa as the conditions. The density, specific heat capacity, thermal conductivity and dynamic viscosity of the VFD assembly solid, gas and fluid are queried in the thermal property table collected in step 1; The boundary condition and solution setting includes the boundary condition and program setting when the model is solved. The pressure boundary condition of the inlet and outlet is set, and the SST k-ω turbulence model is selected. The heat release rate of each material in the VFD assembly is selected as 1.15 as the uncertainty factor. After the model is established, the grid independence analysis of the three-dimensional model and the two-dimensional model needs to be performed.

5. The method for generating a thermal safety envelope curve of an irradiation target for a CANDU reactor core according to claim 1, characterized in that: Before performing the numerical simulation, in step 4, the material limit temperature in the VFD assembly cannot be exceeded and the heavy water in the gap between the sealing sleeve and the guide tube cannot undergo nucleate boiling. In combination with the physical property table, material limit values, and empirical relationship, the vanadium detector limit temperature, the target material limit temperature, and the sealing sleeve wall nucleate boiling starting temperature are determined as the criterion for the thermal safety temperature limit. Based on the physical properties of the selected target material, the thermal conductivity coverage range of the envelope curve and the density distribution of the calculation points within the interval are determined, and a heat release rate of 0.1 W / cm is given. 3 ~500W / cm 3 The interval is set, and calculation points are set at equal intervals within the interval. The thermal conductivity and heat release rate are cross-traversed and matched to generate a calculation point set. In the wall nucleate boiling inception temperature T ONB In the calculation, the Thom empirical relationship is selected, and the specific form is as follows: T ONB = T sat + 0.02253(q") 0.5 e -P / 8.69 where T sat is the fluid saturation temperature, q" is the surface heat flux density, and P is the fluid pressure, all using conservative values from Step 3.

6. A method of generating a thermal safety envelope curve for a candu core irradiated target as defined in claim 1, wherein, The step 9 comprises: After obtaining the thermal conductivity and limit temperature of the new irradiation target, the corresponding abscissa interval k1 and k2 are found in the k-q envelope curve graph arranged in step 8 according to the thermal conductivity k, and the corresponding target temperature value curve interval T1 and T2 are found based on the limit temperature T. Linear interpolation calculation is performed in the interpolation interval. The specific calculation method is as follows: wherein the first number of the subscript indicates the temperature limit value corresponding to T, the second number indicates the thermal conductivity corresponding to k, q 11 wherein the first 1 corresponds to the T1 temperature limit value, the second 1 corresponds to the k1 thermal conductivity, q 12 wherein the 1 corresponds to the T1 temperature limit value, the 2 corresponds to the k2 thermal conductivity, q 21 wherein the 2 corresponds to the T2 temperature limit value, the 1 corresponds to the k1 thermal conductivity, q 22 wherein the first 2 corresponds to the T2 temperature limit value, the second 2 corresponds to the k2 thermal conductivity, thereby obtaining the heat release rate of the new target material under the thermal conductivity and limit temperature condition, at this time the heat release rate obtained by interpolation is the maximum heat release rate under the limit temperature, and it is judged whether the heat release rate of the pre-irradiated material meets the safety limit.

7. The method for generating a thermal safety envelope curve for a CANDU reactor core irradiation target according to claim 1, wherein: The step 5 comprises: Step 51: The thermal conductivity range of the irradiation target is arranged by arranging the preselected target thermal conductivity collected in step 1; Step 52: irradiation target material heat release rate calculation range selection, 0.1 W / cm 3 ~ 500 W / cm 3 Range, interval range is set with equal interval distribution; Based on the above irradiation target material thermal conductivity and heat release rate range selection, cross matching setting calculation point.

Images