Method and apparatus for analyzing nuclide composition of spent fuel assembly

Abstract

The application discloses a kind of nuclide composition analysis methods of spent fuel assembly, comprising: respectively obtaining the rod position data of AO control rod group and mechanical compensation control rod group in each fuel cycle in each burnup point in core.According to the rod position data of AO control rod group in each fuel cycle in each burnup point, obtain the calculation segmentation number N of AO control rod group.According to the rod position data of mechanical compensation control rod group in each fuel cycle in each burnup point, obtain the maximum burnup depth ratio Z of mechanical compensation control rod group k . According to the calculation segmentation number N of AO control rod group insertion and the maximum burnup depth ratio Z k , the burnup of each axial segmentation of the spent fuel assembly is calculated to obtain the nuclide composition of each axial segmentation of the spent fuel assembly.The present method can analyze the nuclide composition of spent fuel assembly, and the analysis result is accurate.The application also discloses a kind of nuclide composition analysis devices of spent fuel assembly.

Description

Technical Field

[0001] This invention belongs to the field of nuclear industry technology, specifically relating to a method and apparatus for analyzing the nuclide composition of spent fuel assemblies. Background Technology

[0002] Criticality safety analysis is a crucial aspect of spent fuel handling, transportation, and storage design, directly impacting nuclear safety. The burnup credit method, used for nuclear criticality safety analysis, differs from traditional methods that treat spent fuel as unirradiated, high-enrichment new fuel. The burnup credit method considers the overall decrease in reactivity due to increased core irradiation and cooling time, thus allowing for a computational margin and improving the economics of nuclear equipment or facilities designed using this method for nuclear criticality safety.

[0003] Currently, most nuclear power plants in China have adopted the burnup credit system in the design of their spent fuel storage systems, and the nuclear criticality safety design of spent fuel reprocessing plants is also gradually applying the burnup credit system.

[0004] To conduct criticality safety analysis of spent fuel using the burnup credit method, it is first necessary to determine a reliable and conservative nuclide composition of the spent fuel. Currently, the nuclide composition of spent fuel is mainly obtained through burnup calculations. Therefore, a set of parameters for burnup calculation of nuclide composition needs to be selected when analyzing the nuclide composition of spent fuel. This set includes, but is not limited to, the power of the spent fuel assembly, fuel temperature, coolant density and temperature, soluble boron concentration, and the type and quantity of combustible poisons. The insertion of control rods is also an important consideration. Control rods are typically inserted into spent fuel assemblies from top to bottom and are used to compensate for fuel consumption, adjust power distribution and power levels, and facilitate rapid core shutdown. The insertion of control rods affects the accuracy of burnup calculations, and consequently, the assessment of the reactivity of spent fuel.

[0005] Currently, some nuclear reactor types employ a mechanical compensation operation mode. In this mode, control rods are inserted into the reactor core in a specific order, with the insertion order periodically changed. Therefore, the insertion depth of the control rods varies periodically throughout a fuel cycle. However, the variation pattern is complex, posing significant challenges to considering the control rod insertion during spent fuel nuclide composition analysis. Previous analyses typically used the standard that each axial segment below a certain number of axial segments in the spent fuel assembly was calculated based on the insertion of gray control rods. However, in reality, only a small proportion of gray control rods are inserted into the lower axial segments of the spent fuel assembly. This method is overly conservative, overestimating the reactivity of the spent fuel assembly under a burnup credit system during storage, transportation, and reprocessing, which is detrimental to improving the economics of criticality safety design.

[0006] Currently, researchers have conducted research and application on the use of burnup credit system in spent fuel reprocessing facilities, but have not provided relevant methods or procedures for radionuclide composition analysis of spent fuel assemblies in mechanically compensated operation mode reactors. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art by providing a method and apparatus for nuclide composition analysis of spent fuel assemblies. This method can perform nuclide composition analysis on spent fuel assemblies with accurate results, which is beneficial to improving the economy of critical safety design.

[0008] According to an embodiment of a first aspect of the present invention, a method for analyzing the nuclide composition of spent fuel assemblies is provided, comprising:

[0009] S1: Obtain the rod position data of the AO control rod group and the mechanical compensation control rod group in the core at each burnup point in each fuel cycle.

[0010] S2: Based on the rod position data of the AO control rod group at each combustion point in each fuel cycle, obtain the calculated number of segments N of the AO control rod group.

[0011] S3: Based on the rod position data of the mechanical compensation control rod assembly at each combustion point in each fuel cycle, obtain the maximum combustion depth ratio Z of the mechanical compensation control rod assembly. k ,

[0012] S4: Based on the calculated number of segments N of the AO control rod assembly insertion and the maximum burn-out depth ratio Z of the mechanical compensation control rod assembly. k The burnup of each axial segment of the spent fuel assembly is calculated to obtain the nuclide composition of each axial segment of the spent fuel assembly.

[0013] Preferably, in step S1, obtaining the rod position data of each burnup point of the AO control rod group and the mechanical compensation control rod group in each fuel cycle includes the following steps: simulating the fuel cycle process of the core from the first cycle to the balance cycle in the mechanical compensation operation mode, so as to obtain the rod position data of each burnup point of the AO control rod group and the mechanical compensation control rod group in each fuel cycle.

[0014] Preferably, step S2 specifically includes: obtaining the number of axial segments of the spent fuel assembly; obtaining the maximum average insertion depth P of the AO control rod group based on the rod position data of each burnout point in each fuel cycle; and determining the calculated number of segments N of the AO control rod group based on the number of axial segments of the spent fuel assembly and the maximum average insertion depth P.

[0015] Preferably, the maximum average insertion depth P of the AO control rod assembly is obtained based on the rod position data at each burnout point in each fuel cycle, including the following steps: performing a burnout depth-weighted average calculation on the rod position data of the AO control rod assembly in each fuel cycle to determine the average insertion depth P of the AO control rod assembly in each fuel cycle. i Compare the average insertion depth P of the AO control rod assembly in each fuel cycle. i The maximum value among them is selected as the maximum average insertion depth P of the AO control rod group.

[0016] Preferably, determining the number of calculated segments N of the AO control rod group based on the number of axial segments of the spent fuel assembly and the maximum average insertion depth P includes the following steps: deriving the correspondence between the axial segments and the rod position data of the AO control rod group based on the number of axial segments of the spent fuel assembly; and obtaining the number of axial segments corresponding to the maximum average insertion depth P of the AO control rod group through the correspondence of the rod position data of the AO control rod group, which is the number of calculated segments N of the AO control rod group.

[0017] Preferably, in step S3, the maximum burn depth ratio Z of the mechanical compensation control rod assembly is obtained based on the rod position data of each burn point in each fuel cycle. k The process includes the following steps: Based on the rod position data of the mechanical compensation control rod assembly at each burnout point in each fuel cycle, the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle is determined; based on the number of axial segments of the spent fuel assembly, the correspondence between the axial segments and the rod position data of the mechanical compensation control rod assembly is determined; through the correspondence of the rod position data of the mechanical compensation control rod assembly, the number of axial segments corresponding to the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle is determined; based on the number of axial segments, a weighted average calculation of burnout depth is performed to obtain the burnout depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle. ik Compare the burnup depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle. ik The maximum value among them is selected as the maximum burn-out depth ratio Z of the mechanical compensation control rod assembly. k .

[0018] Preferably, the burn depth ratio Z ik The percentage increase in burn-out depth relative to the total burn-out depth when the mechanical compensation control rod is inserted into each axial segment of the spent fuel assembly.

[0019] Preferably, in step S4, the calculated number of segments N of the AO control rod assembly insertion and the maximum burn-out depth ratio Z of the mechanical compensation control rod assembly are used as the basis for the calculation.k The burnup calculation for each axial segment of the spent fuel assembly includes the following steps: determining whether the axial segment is the first N segments at the upper end of the spent fuel assembly; if yes, then the burnup of the axial segment is calculated according to the calculation parameters of the inserted AO control rod; if no, then it is further determined whether the burnup depth ratio of the axial segment is within 100%-Z. k Within the specified range: if yes, then the fuel consumption of the axial segment is calculated according to the calculation parameters without the insertion of the control rod; if no, then the fuel consumption of the axial segment is calculated according to the calculation parameters with the insertion of the mechanical compensation control rod.

[0020] Preferably, the method further includes the step: S5: obtaining the total proportion of each nuclide component in the spent fuel assembly by the nuclide composition of each axial segment.

[0021] According to an embodiment of a second aspect of the present invention, a radionuclide composition analysis apparatus for spent fuel assemblies is provided, comprising a rod position data module, an AO rod group segmentation module, a burnup ratio module, and a burnup calculation module. The rod position data module is used to acquire rod position data of the AO control rod group and the mechanically compensated control rod group in the reactor core at each burnup point in each fuel cycle. The AO rod group segmentation module, connected to the rod position data module, is used to acquire the calculated segment number N of the AO control rod group based on the rod position data of the AO control rod group at each burnup point in each fuel cycle. The burnup ratio module, connected to the rod position data module, is used to acquire the maximum burnup depth ratio Z of the mechanically compensated control rod group based on the rod position data of the mechanically compensated control rod group at each burnup point in each fuel cycle. k The fuel consumption calculation module, connected to the AO rod group segmentation module and the fuel consumption ratio module, is used to calculate the number of segments N inserted into the AO control rod group and the maximum fuel consumption depth ratio Z of the mechanical compensation control rod group. k The burnup of each axial segment of the spent fuel assembly is calculated to obtain the nuclide composition of each axial segment of the spent fuel assembly.

[0022] Preferably, the AO rod assembly segmentation module includes an axial segmentation unit, an average insertion depth unit, and a determination unit. The axial segmentation unit is used to obtain the number of axial segments of the spent fuel assembly. The average insertion depth unit is connected to the rod position data module and is used to determine the maximum average insertion depth P of the AO control rod assembly based on the rod position data of each burnup point in each fuel cycle. The determination unit is connected to the axial segmentation unit and the average insertion depth unit and is used to determine the calculated number of segments N of the AO control rod assembly based on the number of axial segments of the spent fuel assembly and the maximum average insertion depth P.

[0023] Preferably, the fuel consumption ratio module includes a maximum insertion depth unit, a corresponding unit, a segment determination unit, a fuel consumption depth ratio unit, and a value selection unit. The maximum insertion depth unit is used to determine the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle based on the rod position data at each fuel consumption point within each fuel cycle. The corresponding unit is used to determine the correspondence between the axial segments and the rod position data of the mechanical compensation control rod assembly based on the number of axial segments of the spent fuel assembly. The segment determination unit, connected to the corresponding unit, is used to determine the number of axial segments corresponding to the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle through the correspondence. The fuel consumption depth ratio unit, connected to the segment determination unit, is used to determine the fuel consumption depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle based on the number of axial segments. ik The selection unit, connected to the fuel consumption depth ratio unit, is used to compare the fuel consumption depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle. ik The maximum value among them is selected as the maximum burn-out depth ratio Z of the mechanical compensation control rod assembly. k .

[0024] Preferably, the fuel consumption calculation module includes a judgment unit and a calculation unit. The judgment unit is connected to the calculation unit and is used to determine whether the axial segment is the first N segments of the upper end of the spent fuel assembly. If yes, a first signal is sent to the calculation unit; if no, it determines whether the fuel consumption depth ratio of the axial segment is within 100%-Z. k Within the range: if yes, a second signal is sent to the calculation unit; if no, a third signal is sent to the calculation unit. The calculation unit is used to perform fuel consumption calculation on the axial segment according to the calculation parameters for inserting the AO control rod when receiving the first signal; or, to perform fuel consumption calculation on the axial segment according to the calculation parameters for not inserting the control rod when receiving the second signal; or, to perform fuel consumption calculation on the axial segment according to the calculation parameters for inserting the mechanical compensation control rod when receiving the third signal.

[0025] The nuclide composition analysis method for spent fuel assemblies in this invention obtains the rod position data of the AO control rod group and the mechanical compensation control rod group respectively. Based on the rod position data of the AO control rod group and the mechanical compensation control rod group, the calculated number of segments of the AO control rod group and the maximum burn-off depth ratio of the mechanical compensation control rod group are obtained. Then, the calculation parameters of each axial segment are determined according to the calculated number of segments and the maximum burn-off depth ratio, and burn-off is calculated based on the calculation parameters to obtain the nuclide composition of each axial segment of the spent fuel assembly. Therefore, this spent fuel nuclide composition analysis method can perform nuclide composition analysis on spent fuel assemblies, reasonably and conservatively considers the actual core operation conditions, and the analysis results are accurate. It can accurately determine the reactivity of spent fuel assemblies, thereby improving the economy of critical safety design.

[0026] The radionuclide composition analysis method for this spent fuel assembly is particularly suitable for radionuclide composition analysis of spent fuel assemblies in nuclear reactors operating under mechanical compensation mode. Attached Figure Description

[0027] Figure 1 This is a flowchart of a spent fuel nuclide analysis method in some embodiments of the present invention;

[0028] Figure 2a This is a data diagram of the AO control rod group at each burnup point in the core balancing cycle in some embodiments of the present invention.

[0029] Figure 2b This is a data diagram of the position of the ash rod control rod group 1 and ash rod control rod group 2 at each burnup point in the core balance cycle in some embodiments of the present invention.

[0030] Figure 2c This is a data diagram of the position of the ash rod control rod group 3 and ash rod control rod group 4 at each burnup point in the core balance cycle in some embodiments of the present invention. Detailed Implementation

[0031] The technical solutions of the invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without creative effort are within the scope of the invention.

[0032] In the description of this invention, it should be noted that the terms "upper", "lower", "upstream", "downstream", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience and simplification of the description and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0033] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connection," "setting," "installation," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0035] In the description of this invention, each unit or module may correspond to only one entity structure, or may be composed of multiple entity structures, or multiple units or modules may be integrated into one entity structure; the units or modules may be implemented by software or by hardware, for example, the units or modules may be located in a processor.

[0036] In the description of this invention, unless otherwise specified, the functions and steps marked in the flowcharts and block diagrams of this invention may occur in a different order than that marked in the accompanying drawings.

[0037] Example 1

[0038] Please see Figure 1 This invention discloses a method for radionuclide composition analysis of spent fuel assemblies, comprising the following steps:

[0039] S1: Obtain the rod position data of each burnup point of the AO control rod group and the mechanical compensation control rod group in the core during each fuel cycle.

[0040] S2: Based on the rod position data of each combustion point of the AO control rod group in each fuel cycle, obtain the calculated number of segments N of the AO control rod group.

[0041] S3: Based on the rod position data of the mechanical compensation control rod assembly at each flammability point in each fuel cycle, obtain the maximum flammability depth ratio Z of the mechanical compensation control rod assembly. k .

[0042] S4: Based on the calculated number of segments N for the AO control rod assembly insertion and the maximum burn-out depth ratio Z of the mechanical compensation control rod assembly. k Burnup calculations were performed on each axial segment of the spent fuel assembly to determine the nuclide composition of each axial segment.

[0043] It should be noted that the AO control rod group includes several black rod control rod groups, and the mechanical compensation control rod group includes several gray rod control rod groups. In this embodiment, the AO control rod group in the reactor core under mechanical compensation operation mode is one black rod control rod group. The mechanical compensation control rod group includes four gray rod control rod groups, namely gray rod control rod group 1, gray rod control rod group 2, gray rod control rod group 3, and gray rod control rod group 4.

[0044] The core's mechanical compensation control rod assembly, together with the AO control rod assembly capable of independently controlling axial power distribution, enables load tracking operation without boron adjustment. Specifically, the value of the four gray rod control rod assemblies and the design of the overlapping rod lifting procedure ensure that the insertion of the AO control rod assemblies causes a monotonically decreasing axial offset factor. In mechanical compensation operation mode, the average coolant temperature under the designed power conditions is maintained by using the four gray rod control rod assemblies. The control of the AO control rod assemblies by the rod control system ensures that the axial offset factor remains essentially constant throughout the entire load tracking operation period. Considering long-term core burnup, the operator adjusts the boron concentration in the reactor coolant system. Adjusting the boron concentration also allows two gray rod control rod assemblies to be held in a near-fully-lifted position, the initially moved two gray rod control rod assemblies to be fully-inserted, and the AO rod assembly to be in a slightly-inserted position.

[0045] Furthermore, when conducting criticality safety analysis on spent fuel assemblies, it is necessary to determine reliable and conservative nuclide composition. However, existing nuclide analysis methods are too conservative. When calculating burnup for spent fuel assemblies, these methods assume the insertion of gray control rods in each axial segment below a certain number of axial segments, overestimating the reactivity of the spent fuel assemblies and hindering the economic efficiency of criticality safety design. Our proposed nuclide composition analysis method, however, requires consideration of the calculated number of segments N for the insertion of AO control rod groups (black rods) and the maximum burnup depth ratio Z of the mechanically compensated control rod groups (gray rods). k The calculation parameters for each axial segment are determined separately, and fuel consumption is calculated accordingly.

[0046] Therefore, this method can perform radionuclide composition analysis on spent fuel assemblies and accurately determine the reactivity of spent fuel assemblies while ensuring safety, thereby improving the economy of critical safety design.

[0047] In this embodiment, step S1 specifically includes the following steps: simulating the fuel cycle process from the first cycle to the balance cycle of the reactor core in the mechanical compensation operation mode, so as to obtain the rod position data of each burnup point of the AO control rod group and the mechanical compensation control rod group in each fuel cycle.

[0048] It should be noted that after startup, the reactor core typically undergoes three transition cycles before entering the balancing cycle. Therefore, in this embodiment, the period from the initial cycle to the balancing cycle is referred to as cycles 1 to 5. To determine the rod position data for the AO control rod group and the mechanical compensation control rod group inserted into the spent fuel assembly, the core calculation program can be used to simulate the core's operation from the initial cycle to the balancing cycle in mechanical compensation mode. Specifically, in the core calculation program, the AO control rod group and the mechanical compensation control rod group are set to operate under the basic load of the mechanical compensation mode, thereby obtaining the rod position data for each burnup point of the AO control rod group and the mechanical compensation control rod group in each burnup cycle (i.e., cycles 1 to 5).

[0049] For example, such as Figure 2a , Figure 2b and Figure 2c As shown, where, Figure 2a It provides rod position data for the AO control rod group at each burnup point in the core balance cycle (i.e., the 5th cycle) under basic load control in mechanical compensation operation mode; Figure 2b Data on the position of ash rod control rod group 1 and ash rod control rod group 2 at each burnup point in the core balance cycle under basic load control in mechanical compensation operation mode are provided. Figure 2c Data on the position of ash rod control groups 3 and 4 at various burnup points during core balancing cycles are provided under the basic load control of the mechanical compensation operation mode.

[0050] More specifically, the core calculation program can be either ANC or Bamboo.

[0051] In this embodiment, step S2 specifically includes the following steps:

[0052] Obtain the number of axial segments in the spent fuel assembly.

[0053] Based on the rod position data of the AO control rod assembly at each burnout point in each fuel cycle, the maximum average insertion depth P of the AO control rod assembly is determined.

[0054] The calculated number of segments N for the AO control rod assembly is determined based on the number of axial segments of the spent fuel assembly and the maximum average insertion depth P.

[0055] The maximum average insertion depth P of the AO control rod assembly is obtained based on the rod position data at each burnup point in each fuel cycle, specifically including the following steps:

[0056] The average insertion depth P of the AO control rod assembly in each fuel cycle is calculated by performing a burnup depth-weighted average of the rod position data within each fuel cycle. i ,

[0057] Compare the average insertion depth P of the AO control rod assembly in each fuel cycle. i The maximum value among them is selected as the maximum average insertion depth P of the AO control rod group.

[0058] Furthermore, based on the number of axial segments of the spent fuel assembly and the maximum average insertion depth P, the calculated number of segments N for the AO control rod assembly is determined, specifically including the following steps:

[0059] Based on the number of axial segments in the spent fuel assembly, the correspondence between the axial segments and the rod position data of the AO control rod assembly is derived.

[0060] By using the correspondence between the rod position data of the AO control rod group, the axial segment number corresponding to the maximum average insertion depth P of the AO control rod group can be obtained, which is the calculated segment number N of the AO control rod group.

[0061] It should be noted that, according to the critical safety analysis requirements of spent fuel, the axial direction of the spent fuel assembly is divided into several axial segments, each with the same axial length. For example, according to the critical safety analysis requirements of the spent fuel assembly, the axial direction of the spent fuel assembly is divided into 18 segments to establish the correspondence between the rod position data of the AO control rod group and the axial segments. Specifically, if the rod position of the AO control rod group in the active section of the core is 264 steps, then each axial segment of the spent fuel assembly corresponds to 14.67 steps of the control rod group position, where the height of each segment accounts for 5.56%. Based on the rod position data of the AO control rod group (black rod) at each burnup point in each fuel cycle under the basic load control of the mechanically compensated operation mode, its average insertion depth P in each cycle is calculated by weighted averaging of burnup depth. i (Percentage, where i represents the cycle number). Average insertion depth P for cycles 1-5. i The percentages were 6.8%, 8.5%, 8.9%, 4.7%, and 4.8%, respectively. Among them, P... i The maximum value is recorded as 8.9%. Based on the correspondence between the control rod position data in the core and the axial segments, the number of axial segments for the AO control rod (black rod) insertion to be considered in the burnup calculation of the spent fuel assembly is determined to be 2 by rounding up. That is, the number of segments N is recorded as 2.

[0062] In this embodiment, step S3 specifically includes the following steps:

[0063] Based on the rod position data of the mechanical compensation control rod assembly at each combustion point in each fuel cycle, the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle is determined.

[0064] Based on the number of axial segments in the spent fuel assembly, the correspondence between the axial segments and the rod position data of the mechanical compensation control rod assembly is derived.

[0065] By analyzing the correspondence between the rod position data of the mechanical compensation control rod assembly, the number of axial segments corresponding to the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle can be determined.

[0066] Based on the number of axial segments, a weighted average calculation of burn-off depth is performed to obtain the burn-off depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle. ik ,

[0067] Compare the burn depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle. ik The maximum value among them is selected as the maximum burn depth ratio Z of the mechanical compensation control rod assembly. k .

[0068] It should be noted that the rod position data of the mechanical compensation control rod assembly at each combustion point in each fuel cycle refers to the rod position data of the mechanical compensation control rod assembly at each combustion point in each cycle (i.e., cycles 1 to 5) under the basic load control of the mechanical compensation operation mode. Based on the rod position data, the maximum insertion depth (percentage) of the mechanical compensation control rod assembly (i.e., the ash rod control rod assembly) at each combustion point in each cycle is obtained. Then, the correspondence between the rod position data of the mechanical compensation control rod assembly and the axial segment is established. The process is the same as that of the AO control rod assembly, and will not be elaborated further here.

[0069] Furthermore, based on the correspondence between rod position data and axial segments, the number of axial segments requiring the insertion of the mechanical compensation control rod group in the burnup calculation of the spent fuel assembly at each burnup point in each fuel cycle is determined by rounding up. The mechanical compensation control rod group contains several ash rod control rods. Then, the burnup depth ratio Z of the ash rod control rod group insertion in each axial segment of each cycle is calculated. ik (Percentage, where i represents the cycle number and k represents the axial segmentation of the active region of the fuel assembly), and the maximum Z-value of each cycle is... ik The value is denoted as Z. k .

[0070] It should also be noted that the fuel consumption depth ratio Z ik This represents the proportion of the increased burn-down depth relative to the total burn-down depth when mechanical compensation control rods are inserted into each axial segment of the spent fuel assembly. It is specifically calculated using a weighted method based on burn-down depth. When calculating the burn-down depth, it's necessary to determine whether to consider the axial burn-down distribution of the spent fuel assembly based on the application scenario. If so, the axial burn-down envelope curve needs to be determined first to obtain the burn-down normalization factor Bk for each axial segment. Then, based on the average burn-down depth Bu of the spent fuel assembly, the burn-down depth to (Bu·Bk) for each axial segment is obtained. If not, each axial segment burns to a burn-down depth of Bu.

[0071] Here, we take a spent fuel assembly with an initial enrichment of 4.95% and an average burnup of 42,000 MWd / tU as an example. In this embodiment, the nuclide composition analysis of each axial segment considers the axial envelope burnup distribution of the spent fuel assembly. From top to bottom, the burnup depths of each axial segment are 21,504, 33,600, 41,202, 43,050, 46,368, 46,494, 46,242, 46,242, 46,494, 46,368, 46,788, 46,872, 46,704, 47,040, 43,890, 42,840, 38,556, and 25,830 MWd / tU. In this embodiment, the burnup depth ratios corresponding to each axial segment are shown in Table 1.

[0072] Table 1 shows the burn depth ratio of each axial segment where the mechanical compensation control rod assembly is inserted in each fuel cycle.

[0073]

[0074]

[0075] In this embodiment, step S4: Based on the calculated number of segments N of the AO control rod assembly insertion and the maximum burn-out depth ratio Z of the mechanical compensation control rod assembly. k The burnup of each axial segment of the spent fuel assembly is calculated. This includes the following steps:

[0076] Determine if the axial segment is the first N segments at the top of the spent fuel assembly:

[0077] If so, fuel consumption is calculated for the axial segments according to the calculation parameters of the inserted AO control rod;

[0078] If not, then continue to determine whether the fuel consumption depth ratio of the axial segment is within 100%-Z. k Within the specified range: If yes, then the fuel consumption of the axial segment is calculated according to the calculation parameters without the control rod; if no, then the fuel consumption of the axial segment is calculated according to the calculation parameters with the mechanical compensation control rod inserted.

[0079] It should be noted that for spent fuel assemblies requiring criticality safety analysis, the nuclide composition calculation parameters must employ a conservative combination suitable for criticality safety analysis to perform burnup calculations at a given burnup depth. This conservative combination of nuclide composition calculation parameters refers to a conservative analysis method based on burnup credits, using a conservative approach that considers the reactivity of the spent fuel assembly for criticality safety analysis as a measure, and determining a conservative combination of relevant irradiation history parameters. This conservative combination includes, but is not limited to, assembly power, fuel temperature, coolant density and temperature, soluble boron concentration, and the type and quantity of combustible poisons.

[0080] Specifically, after determining the calculation parameter types for each axial segment, fuel consumption calculations can be performed on each axial segment using existing fuel consumption calculation programs. More specifically, the fuel consumption calculation program can be RMC or CASMO. For fuel consumption calculations with different AO control rod insertion states, different component calculation models are established in the fuel consumption calculation. For example, in the component model for fuel consumption calculation based on the calculation parameters of inserted AO control rods, the AO control rods are inserted into the guide tube of the component. However, for fuel consumption calculations within different fuel consumption depth ratios based on whether mechanical compensation control rods are inserted or not, it is necessary to achieve this through the component calculation model's function of changing the insertion state or restarting the calculation after changing the calculation model. Appropriate calculation functions can be selected according to the functional characteristics of different programs.

[0081] Continuing with the example of a spent fuel assembly with an initial enrichment of 4.95% and an average fuel consumption of 42,000 MWd / tU, in this embodiment, the number of calculated segments N for the AO control rod insertion is 2. Therefore, the top 1-2 segments of the spent fuel assembly are calculated for fuel consumption using the parameters for inserting the AO control rod (black rod). The remaining segments are calculated before their combustion depth (100% - Z). k Within the range of ) without inserting any control rods, the final Z of the burn depth k Within the specified range, mechanical compensation control rod groups (gray rod control rod groups) are inserted to perform fuel consumption calculations, thereby obtaining the axial nuclide composition of each segment that can be used for critical safety analysis. In this embodiment, from top to bottom, fuel consumption calculations are performed with gray rod control rods inserted for the entire fuel consumption range of segments 2 to 8; for segments 9 to 18, fuel consumption calculations are performed without inserting any control rods for the first fuel consumption range of 3035, 6224, 8105, 12328, 16718, 21123, 23889, 26379, 27176, and 21329 Wd / tU, respectively; and for the subsequent fuel consumption ranges of 43459, 40144, 38683, 34544, 29986, 25917, 20001, 16461, 11380, and 4501 Wd / tU, fuel consumption calculations are performed with gray rod control rods inserted. Concentrating the control rods inserted into the last part of the burn-out depth can make the nuclide composition calculation results conservative.

[0082] In this embodiment, the nuclide composition analysis method for the spent fuel assembly further includes step S5: obtaining the total proportion of each nuclide component in the spent fuel assembly by analyzing the nuclide composition of each axial segment.

[0083] Specifically, the average uranium and plutonium isotope ratio in the spent fuel assembly is used as a conservative criterion for judging the reactivity of the spent fuel assembly. This is illustrated by an application scenario in a spent fuel reprocessing plant where the critical safety design of the dissolved liquid after the spent fuel assembly dissolves is used. The calculated fuel composition of each axial segment of the spent fuel assembly is added together to obtain the average uranium and plutonium isotope ratio of the assembly. The remaining percentage of U-235 in the total U is 1.870%; the mass ratio of Pu-239, Pu-240, Pu-241, and Pu-242 is 61.773:19.152:13.675:3.769.

[0084] In contrast, existing radionuclide composition analysis methods use burnout calculations based on the insertion of gray control rods across the entire burnout range of segments 2 to 18. Similarly, the calculated compositions of the fuel in each axial segment are summed to determine the average uranium and plutonium isotope ratio of the assembly. The results show that the remaining percentage of U-235 in the total U is 1.941%; the mass ratios of Pu-239, Pu-240, Pu-241, and Pu-242 are 63.328:18.178:13.475:3.389.

[0085] Comparing the above analysis results, it can be seen that in the average uranium-plutonium isotope ratios of spent fuel assemblies calculated by this method, U-235 has a lower remaining percentage in total U, Pu-239 has a higher mass proportion in total Pu, and Pu-240 has a lower mass proportion in total Pu. Therefore, under the same critical safety analysis conditions, the average uranium-plutonium isotope ratios of spent fuel assemblies calculated using this method result in lower reactivity of the solution while ensuring critical safety, thus making critical safety design more economical.

[0086] Furthermore, under the same critical safety analysis conditions of uranium and plutonium concentrations and the same uranium and plutonium isotope ratios, using this method to conduct nuclide composition analysis of spent fuel assemblies and determine the minimum burnup limit of spent fuel assemblies will allow the minimum burnup limit of spent fuel assemblies to be smaller. This will enable spent fuel reprocessing plants to process spent fuel assemblies with a wider burnup range, thereby increasing the processing capacity of spent fuel reprocessing plants.

[0087] For example, this nuclide composition analysis method can be applied to the nuclide composition analysis of spent fuel assemblies in a nuclear reactor operating under mechanical compensation mode, thereby helping to complete the critical safety design of the nuclear reactor.

[0088] Example 2

[0089] The present invention also discloses a radionuclide composition analysis device for spent fuel assemblies, comprising: a rod position data module, an AO rod segmentation module, a burnup ratio module, and a burnup calculation module.

[0090] The rod position data module is used to acquire the rod position data of the AO control rod group and the mechanical compensation control rod group at each burnup point in each fuel cycle. The AO rod group segmentation module is connected to the rod position data module and is used to obtain the calculated segment number N of the AO control rod group based on the rod position data of each burnup point in each fuel cycle. The burnup ratio module is connected to the rod position data module and is used to obtain the maximum burnup depth ratio Z of the mechanical compensation control rod group based on the rod position data of each burnup point in each fuel cycle. k The fuel consumption calculation module is connected to the AO rod assembly segmentation module and the fuel consumption ratio module. It is used to calculate the number of segments N inserted into the AO control rod assembly and the maximum fuel consumption depth ratio Z of the mechanical compensation control rod assembly. k Burnup calculations were performed on each axial segment of the spent fuel assembly to determine the nuclide composition of each axial segment.

[0091] Specifically, the rod position data module can be a core calculation program, such as ANC or Bamboo. The core is modeled using the rod position data module, and the fuel cycle process from the first cycle to the equilibrium cycle in mechanical compensation operation mode is simulated to obtain the rod position data for each burnup point of the AO control rod group and the mechanical compensation control rod group in each fuel cycle. Then, the rod position data module transmits this rod position data to the AO rod group segmentation module.

[0092] In this embodiment, the AO rod assembly segmentation module includes an axial segmentation unit, an average insertion depth unit, and a determination unit. The axial segmentation unit is used to obtain the number of axial segments of the spent fuel assembly. Specifically, the operator can determine the number of axial segments of the spent fuel assembly and then input the number of axial segments into the axial segmentation unit. The axial segmentation unit then sends the number of axial segments to the determination unit.

[0093] The average insertion depth unit is connected to the rod position data module and is used to determine the maximum average insertion depth P of the AO control rod group based on the rod position data at each burnout point in each fuel cycle. Specifically, after receiving the rod position data of the AO control rod group at each burnout point in each fuel cycle, the average insertion depth unit performs a burnout depth-weighted average calculation on the rod position data of the AO control rod group in each fuel cycle to determine the average insertion depth P of the AO control rod group in each fuel cycle. i Then, the average insertion depth unit compares the average insertion depth P of the AO control rod assembly in each fuel cycle. i The maximum value among them is selected, which is the maximum average insertion depth P of the AO control rod group. The average insertion unit is also used to send the maximum average insertion depth P of the AO control rod group to the decision unit.

[0094] Furthermore, the determination unit is connected to the axial segmentation unit and the average insertion depth unit, and is used to determine the calculated number of segments N of the AO control rod group based on the number of axial segments of the spent fuel assembly and the maximum average insertion depth P. Specifically, the determination unit derives the correspondence between the axial segments and the rod position data of the AO control rod group based on the number of axial segments of the spent fuel assembly. Then, the determination unit uses the correspondence to determine the number of axial segments corresponding to the maximum average insertion depth P of the AO control rod group, which is the calculated number of segments N of the AO control rod group.

[0095] In this embodiment, the fuel consumption ratio module includes a maximum insertion depth unit, a corresponding unit, a segment determination unit, a fuel consumption depth ratio unit, and a value selection unit. The maximum insertion depth unit is connected to the rod position data module and is used to determine the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle based on the rod position data at each fuel consumption point within each fuel cycle. The corresponding unit is used to determine the correspondence between the axial segments and the rod position data of the mechanical compensation control rod assembly based on the number of axial segments of the spent fuel assembly. The segment determination unit is connected to the corresponding unit and is used to determine the number of axial segments corresponding to the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle based on the correspondence. The fuel consumption depth ratio unit is connected to the segment determination unit and is used to determine the fuel consumption depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle based on the number of axial segments. ik The selection unit is connected to the fuel consumption depth ratio unit and is used to compare the fuel consumption depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle. ik The maximum value among them is selected as the maximum burn depth ratio Z of the mechanical compensation control rod assembly. k .

[0096] In this embodiment, the fuel consumption calculation module includes a judgment unit and a calculation unit. The judgment unit is connected to the calculation unit and is used to determine whether the axial segment is the first N segments of the upper end of the spent fuel assembly: if yes, a first signal is sent to the calculation unit; if no, it determines whether the fuel consumption depth ratio of the axial segment is within the range of 100%-Zk: if yes, a second signal is sent to the calculation unit; if no, a third signal is sent to the calculation unit.

[0097] The calculation unit is used to calculate the fuel consumption of the axial segment according to the calculation parameters of inserting the AO control rod when receiving the first signal, or to calculate the fuel consumption of the axial segment according to the calculation parameters of not inserting the control rod when receiving the second signal, or to calculate the fuel consumption of the axial segment according to the calculation parameters of inserting the mechanical compensation control rod when receiving the third signal.

[0098] In summary, the radionuclide composition analysis device for this spent fuel assembly can perform radionuclide composition analysis on the spent fuel assembly and accurately determine the reactivity of the spent fuel assembly while ensuring safety, thereby improving the economy of critical safety design.

[0099] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for radionuclide composition analysis of spent fuel assemblies, characterized in that, include: S1: Obtain the rod position data of the AO control rod group and the mechanical compensation control rod group in the core at each burnup point in each fuel cycle. S2: Based on the rod position data of the AO control rod group at each combustion point in each fuel cycle, obtain the calculated number of segments N of the AO control rod group. Step S2 specifically includes: Obtain the number of axial segments of the spent fuel assembly. Based on the rod position data of each burnout point of the AO control rod group in each fuel cycle, the maximum average insertion depth P of the AO control rod group is obtained. Based on the number of axial segments of the spent fuel assembly and the maximum average insertion depth P, the calculated number of segments N of the AO control rod group is determined. S3: Based on the rod position data of the mechanical compensation control rod assembly at each combustion point in each fuel cycle, obtain the maximum combustion depth ratio Z of the mechanical compensation control rod assembly. k , S4: Based on the calculated number of segments N of the AO control rod assembly insertion and the maximum burn-out depth ratio Z of the mechanical compensation control rod assembly. k The burnup of each axial segment of the spent fuel assembly is calculated to obtain the nuclide composition of each axial segment of the spent fuel assembly. Step S4 specifically includes: determining whether the axial segment is the first N segments of the upper end of the spent fuel assembly. If so, the fuel consumption of the axial segment is calculated according to the calculation parameters of the inserted AO control rod; If not, then continue to determine whether the burn depth ratio of the axial segment is within 100%-Z. k Within the specified range: if yes, then the fuel consumption of the axial segment is calculated according to the calculation parameters without the insertion of the control rod; if no, then the fuel consumption of the axial segment is calculated according to the calculation parameters with the insertion of the mechanical compensation control rod.

2. The method according to claim 1, characterized in that, In step S1, acquiring the rod position data of the AO control rod group and the mechanical compensation control rod group in the reactor core at each burnup point in each fuel cycle includes the following steps: The fuel cycle process from the first cycle to the balance cycle of the reactor core in mechanical compensation operation mode is simulated to obtain the rod position data of the AO control rod group and the mechanical compensation control rod group at each burnup point in each fuel cycle.

3. The method according to claim 1, characterized in that, Based on the rod position data of the AO control rod assembly at each combustion point in each fuel cycle, the maximum average insertion depth P of the AO control rod assembly is obtained, including the following steps: The average insertion depth P of the AO control rod assembly in each fuel cycle is calculated by performing a burnup depth-weighted average calculation on the rod position data of the AO control rod assembly in each fuel cycle. i , Compare the average insertion depth P of the AO control rod assembly in each fuel cycle. i The maximum value among them is selected as the maximum average insertion depth P of the AO control rod group.

4. The method according to claim 1, characterized in that, The calculated number of segments N of the AO control rod assembly is determined based on the number of axial segments of the spent fuel assembly and the maximum average insertion depth P, including the following steps: Based on the number of axial segments in the spent fuel assembly, the correspondence between the axial segments and the rod position data of the AO control rod group is determined. By using the correspondence of the rod position data of the AO control rod group, the axial segment number corresponding to the maximum average insertion depth P of the AO control rod group can be obtained, which is the calculated segment number N of the AO control rod group.

5. The method according to claim 1, characterized in that, In step S3, the maximum burn depth ratio Z of the mechanical compensation control rod assembly is obtained based on the rod position data of each burn point in each fuel cycle. k It includes the following steps: Based on the rod position data of the mechanical compensation control rod assembly at each combustion point in each fuel cycle, the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle is determined. Based on the number of axial segments in the spent fuel assembly, the correspondence between the axial segments and the rod position data of the mechanical compensation control rod assembly is determined. By using the correspondence between the rod position data of the mechanical compensation control rod assembly, the number of axial segments corresponding to the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle can be obtained. Based on the number of axial segments, a weighted average calculation of the burn-out depth is performed to obtain the burn-out depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle. ik , Compare the burn depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle. ik The maximum value among them is selected as the maximum burn-out depth ratio Z of the mechanical compensation control rod assembly. k .

6. The method according to claim 5, characterized in that, The burn-out depth ratio Z ik The percentage increase in burn-out depth relative to the total burn-out depth when the mechanical compensation control rod is inserted into each axial segment of the spent fuel assembly.

7. The method according to any one of claims 1-6, characterized in that, The method further includes the following steps: S5: By analyzing the nuclide composition of each axial segment, the total proportion of each nuclide in the spent fuel assembly is obtained.

8. A device for analyzing the radionuclide composition of spent fuel assemblies, characterized in that, It includes a rod position data module, an AO rod segmentation module, a fuel consumption ratio module, and a fuel consumption calculation module. The rod position data module is used to acquire the rod position data of the AO control rod group and the mechanical compensation control rod group in the reactor core at each burnup point in each fuel cycle. The AO rod group segmentation module, connected to the rod position data module, is used to obtain the calculated number of segments N of the AO control rod group based on the rod position data of each combustion point in each fuel cycle. The AO rod segmentation module includes an axial segmentation unit, an average insertion depth unit, and a determination unit. The axial segmentation unit is used to obtain the number of axial segments of the spent fuel assembly. The average insertion depth unit, connected to the rod position data module, is used to determine the maximum average insertion depth P of the AO control rod group based on the rod position data at each burnup point in each fuel cycle. The determination unit, connected to the axial segmentation unit and the average insertion depth unit, is used to determine the calculated number of segments N of the AO control rod group based on the number of axial segments of the spent fuel assembly and the maximum average insertion depth P. The fuel consumption ratio module is connected to the rod position data module and is used to obtain the maximum fuel consumption depth ratio Z of the mechanical compensation control rod group based on the rod position data of each fuel consumption point in each fuel cycle. k , The fuel consumption calculation module is connected to the AO rod group segmentation module and the fuel consumption ratio module, and is used to calculate the number of segments N inserted by the AO control rod group and the maximum fuel consumption depth ratio Z of the mechanical compensation control rod group. k The burnup of each axial segment of the spent fuel assembly is calculated to obtain the nuclide composition of each axial segment of the spent fuel assembly. The fuel consumption calculation module includes a judgment unit and a calculation unit. The judgment unit, connected to the calculation unit, is used to determine whether the axial segment is the first N segments of the upper end of the spent fuel assembly. If so, a first signal is sent to the computing unit. If not, determine whether the fuel consumption depth ratio of the axial segment is within the range of 100%-Zk: if yes, send a second signal to the calculation unit; if no, send a third signal to the calculation unit. The calculation unit is used to calculate the fuel consumption of the axial segment according to the calculation parameters of the inserted AO control rod when the first signal is received. Alternatively, upon receiving the second signal, fuel consumption calculations can be performed on the axial segments using the calculation parameters without inserting a control rod. Alternatively, upon receiving a third signal, fuel consumption calculations can be performed on the axial segments according to the calculation parameters of the inserted mechanical compensation control rod.

9. The apparatus according to claim 8, characterized in that, The fuel consumption ratio module includes a maximum insertion depth unit, a corresponding unit, a segment determination unit, a fuel consumption depth ratio unit, and a value selection unit. The maximum insertion depth unit is used to determine the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle based on the rod position data at each burnout point within each fuel cycle. The corresponding unit is used to determine the correspondence between the axial segments and the rod position data of the mechanical compensation control rod assembly based on the number of axial segments of the spent fuel assembly. The segmentation determination unit, connected to the corresponding unit, is used to determine the number of axial segments corresponding to the maximum insertion depth of the mechanical compensation control rod assembly in each fuel cycle through the correspondence. The burn-out depth ratio unit is connected to the segmentation determination unit and is used to determine the burn-out depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle based on the axial segmentation number. ik , The selection unit, connected to the fuel consumption depth ratio unit, is used to compare the fuel consumption depth ratio Z of the mechanical compensation control rod assembly in each fuel cycle. ik The maximum value among them is selected as the maximum burn-out depth ratio Z of the mechanical compensation control rod assembly. k .

Images