Method and system for calculating uranium contamination fission products of reactor core fuel assembly of nuclear power plant

Abstract

The invention discloses a nuclear power plant reactor core fuel assembly uranium contamination fission product calculation method and system, and the method comprises the following steps: monitoring the characteristic nuclide of a loop coolant of a reactor core fuel assembly in real time, and judging whether the surface of the reactor core fuel assembly has uranium contamination; if the uranium contamination exists, calculating the uranium contamination amount of the uranium contamination distributed in the primary loop coolant on the surface of the reactor core fuel assembly; and calculating uranium contamination fission product distribution of the reactor core fuel assembly according to the uranium contamination amount. According to the method, the uranium contamination fission product distribution in the primary loop coolant is collected, so that the risk of erroneous judgment of the damage of the reactor core fuel assembly caused by uranium contamination can be remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of core fuel damage monitoring, and in particular to a method and system for calculating uranium-contaminated fission products of a core fuel assembly in a nuclear power plant. Background Art

[0002] By analyzing the activity concentration of fission product nuclides in the primary coolant of the reactor core of a nuclear power plant, the damage of the core nuclear fuel assembly can be effectively determined. However, the fission products generated by uranium contaminated on the outer surface of the core fuel assembly cladding under neutron irradiation will enter the coolant and interfere with the determination of the source of the fission products. Therefore, the fission product nuclides in the coolant caused by uranium contamination of the core fuel assembly cladding become an important interference factor in determining whether the fuel assembly cladding is damaged.

[0003] Typically, methods such as gas-flow multi-wire proportional counters and surface contamination testers are used to measure the total alpha activity concentration on the fuel surface. Alternatively, alpha particle detectors (such as silicon detectors) combined with energy spectrum analysis can be used to identify characteristic alpha peaks of uranium isotopes (such as U-234, U-235, and U-238) and calculate the activity concentration of characteristic nuclides. This is then used to estimate the amount of uranium contamination in the core fuel assemblies. However, this method is complex and only suitable for localized contamination screening during outages. If the core fuel assemblies are inspected online, the characteristic nuclides released by the damaged core fuel assemblies overlap with those of the uranium contamination fission products outside the fuel assemblies, making it difficult to distinguish their sources. Furthermore, the transient signals of short-lived nuclides (such as Rb-90) are easily overlooked by conventional detection methods, resulting in missed detections. This makes it difficult to calculate the amount of uranium contamination remaining on the surface of the core fuel assemblies and the concentration of fission nuclides in the primary coolant caused by uranium contamination difficult to calculate. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for calculating the fission products of uranium contamination in the core fuel assemblies of a nuclear power plant, in response to at least one defect of the related technology mentioned in the above background technology: it is difficult to calculate the uranium contamination residue on the surface of the core fuel assembly and the concentration of fission nuclides in the primary coolant caused by uranium contamination.

[0005] The technical solution adopted by the present invention to solve the technical problem is to construct a method for calculating uranium contaminated fission products of nuclear power plant core fuel assemblies, which includes the following steps:

[0006] By real-time monitoring of the characteristic nuclides of the primary coolant of the core fuel assembly, it is possible to determine whether there is uranium contamination on the surface of the core fuel assembly;

[0007] If uranium contamination exists, calculate the amount of uranium contamination distributed on the surface of the core fuel assembly in the primary coolant;

[0008] The distribution of uranium contamination fission products in the core fuel assembly is calculated based on the uranium contamination amount.

[0009] In some embodiments, determining whether there is uranium contamination on the surface of the core fuel assembly by real-time monitoring of characteristic nuclides in the primary coolant of the core fuel assembly includes:

[0010] Real-time monitoring of multiple nuclides in the primary coolant circuit is carried out to establish a dynamic database of characteristic nuclides corresponding to the characteristic nuclides in the multiple nuclides;

[0011] Extract nuclide information from the dynamic database of characteristic nuclides to determine whether there is uranium contamination on the surface of the core fuel assembly.

[0012] In some embodiments, extracting nuclide information from a dynamic database of characteristic nuclides includes:

[0013] The nuclide information including at least the specific activity ratio of the preset characteristic nuclide, the measured yield of the preset characteristic nuclide and the short-lived nuclide is extracted from the characteristic nuclide dynamic database.

[0014] In some embodiments, determining whether uranium contamination exists on the surface of the core fuel assembly includes:

[0015] According to a preset adaptive ratio model, determining whether the specific activity ratio of the preset characteristic nuclide is less than a preset value;

[0016] If so, determine whether the deviations between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides are both no greater than the preset values;

[0017] If so, determine whether there are short-lived nuclides;

[0018] If so, there is uranium contamination on the surface of the core fuel assembly.

[0019] The formula for calculating the amount of uranium contamination on the surface of the core fuel assembly and its distribution in the primary coolant is:

[0020]

[0021] Where w is the mass of uranium contamination per unit mass of primary coolant, m is the mass of uranium in a single fuel rod in the core fuel assembly, M is the total mass of coolant in the core area, and R / B is the ratio of uranium nuclides released to generated.

[0022] In some embodiments, the formula for calculating the uranium nuclide release and production ratio is:

[0023]

[0024] Where R / B is the ratio of uranium nuclide release to production, A is the specific activity of uranium nuclides, V is the volume of the primary coolant, G is the thermal power of the nuclear reactor, n is the number of fuel rods in the core fuel assembly, and Ef is the fission yield of uranium nuclides.

[0025] In some embodiments, the calculation formula for the concentration of uranium contamination fissile nuclides in the core fuel assembly is:

[0026]

[0027] Where φ is the neutron flux, σ is the fission cross section of uranium, w is the uranium contamination mass per unit mass of the primary coolant, N is the uranium atomic density, Y is the fission nuclide yield, η is the fission nuclide release efficiency, v is the primary coolant flow rate, S 管 is the cross-sectional area of ​​the primary circuit pipeline, U is the molar mass of the fission nuclide, S 铀 is the uranium contamination area, λ is the decay time of the fission nuclide, and t is the neutron irradiation time.

[0028] The present invention also constructs a nuclear power plant core fuel assembly uranium contamination fission product calculation system, comprising:

[0029] The monitoring and judgment module is used to determine whether there is uranium contamination on the surface of the core fuel assembly by real-time monitoring of the characteristic nuclides of the primary coolant of the core fuel assembly;

[0030] A uranium contamination amount calculation module is used to calculate the uranium contamination amount of the uranium contamination distribution on the surface of the core fuel assembly in the primary coolant circuit if uranium contamination exists;

[0031] The fission product calculation module is used to calculate the distribution of uranium contamination fission products in the core fuel assembly based on the uranium contamination amount.

[0032] In some embodiments, the monitoring and judgment module includes:

[0033] A monitoring unit is used to monitor multiple nuclides in the primary coolant in real time and establish a dynamic database of characteristic nuclides corresponding to the characteristic nuclides in the multiple nuclides;

[0034] The judgment unit is used to extract nuclide information from the dynamic database of characteristic nuclides and judge whether there is uranium contamination on the surface of the core fuel assembly.

[0035] In some embodiments, the determining unit includes:

[0036] a characteristic nuclide extraction subunit, configured to extract nuclide information including at least the specific activity ratio of a preset characteristic nuclide, the measured yield of the preset characteristic nuclide, and short-lived nuclides from a characteristic nuclide dynamic database; and / or

[0037] The ratio dynamic analysis subunit is used to determine whether the specific activity ratio of the preset characteristic nuclide is less than a preset value according to a preset specific activity ratio model;

[0038] The fission yield matching subunit is used to determine that the deviation between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides is not greater than the preset value if the specific activity ratio of the preset characteristic nuclides is less than the preset value;

[0039] The short-lived nuclide analysis subunit is used to determine whether there are short-lived nuclides if the deviations between the measured yield ratio and the theoretical yield ratio are not greater than the preset value;

[0040] The judgment subunit is used to determine that if the specific activity ratio of the preset characteristic nuclides is less than the preset value, and the deviation between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides is greater than the preset value, and there are short-lived nuclides, then there is uranium contamination on the surface of the core fuel assembly.

[0041] By implementing the present invention, the following beneficial effects are achieved:

[0042] The present invention monitors the characteristic nuclides of the primary coolant of the core fuel assembly in real time to determine whether there is uranium contamination on the surface of the core fuel assembly. If uranium contamination is present, the uranium contamination amount of the uranium contamination on the surface of the core fuel assembly in the primary coolant is calculated. Finally, the distribution of uranium contamination fission products of the core fuel assembly is calculated based on the uranium contamination amount, and the distribution of uranium contamination fission products in the primary coolant is collected. This can significantly reduce the risk of misjudging core fuel assembly damage caused by uranium contamination. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0044] Figure 1 A flow chart of an embodiment of a method for calculating uranium-contaminated fission products in a nuclear power plant core fuel assembly according to the present invention is shown;

[0045] Figure 2 The present invention shows a flow chart of determining whether there is uranium contamination on the surface of a core fuel assembly in an embodiment of a method for calculating uranium contamination fission products of a core fuel assembly of a nuclear power plant according to the present invention. DETAILED DESCRIPTION

[0046] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0047] It should be noted that the flowcharts shown in the accompanying drawings are for illustrative purposes only and do not necessarily include all content and operations / steps, nor must they be executed in the order described. For example, some operations / steps may be decomposed, while others may be combined or partially combined. Therefore, the actual execution order may vary depending on the actual situation.

[0048] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically separate entities. That is, these functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0049] like Figure 1 As shown, some embodiments of the present invention disclose a method for calculating uranium-contaminated fission products in a nuclear power plant core fuel assembly, the method comprising the following steps:

[0050] By real-time monitoring of the characteristic nuclides of the primary coolant of the core fuel assembly, it is possible to determine whether there is uranium contamination on the surface of the core fuel assembly;

[0051] If uranium contamination exists, calculate the amount of uranium contamination distributed on the surface of the core fuel assembly in the primary coolant;

[0052] The distribution of uranium contamination fission products in the core fuel assembly is calculated based on the uranium contamination amount.

[0053] In some embodiments, determining whether there is uranium contamination on the surface of the core fuel assembly by real-time monitoring of characteristic nuclides in the primary coolant of the core fuel assembly includes:

[0054] Real-time monitoring of multiple nuclides in the primary coolant circuit is carried out to establish a dynamic database of characteristic nuclides corresponding to the characteristic nuclides in the multiple nuclides;

[0055] Extract nuclide information from the dynamic database of characteristic nuclides to determine whether there is uranium contamination on the surface of the core fuel assembly.

[0056] The core fuel online monitoring gamma spectroscopy system monitors multiple nuclides in the primary coolant in real time, establishing a dynamic database of characteristic nuclides corresponding to the characteristic nuclides in the multi-nuclides. The dynamic database includes information on preset characteristic nuclides and other nuclides that are not characteristic nuclides. Characteristic nuclides include, for example, Xe-133, Xe-135, I-131, and Kr-85m. The characteristic nuclides Xe-133, Xe-135, I-131, and Kr-85m are provided for illustrative purposes only and are not intended to limit the present application. Other nuclides may also be included.

[0057] The nuclide information is extracted from the dynamic database of characteristic nuclides, and then the presence of uranium contamination on the surface of the core fuel assembly is determined based on the multimodal uranium contamination analysis method of typical fission products.

[0058] In some embodiments, extracting nuclide information from a dynamic database of characteristic nuclides includes:

[0059] The nuclide information including at least the specific activity ratio of the preset characteristic nuclide, the measured yield of the preset characteristic nuclide and the short-lived nuclide is extracted from the characteristic nuclide dynamic database.

[0060] Specific activity refers to the activity of a radioactive substance per unit mass or volume, or the number of decays that occur per unit time. The specific activity ratio is the ratio of the specific activities of two different radioactive substances, for example, the ratio of the specific activity of Xe-133 to the specific activity of Xe-135.

[0061] Yield refers to the amount of a specific fission product nuclide produced during the fission process. When a nuclide fissions, it produces a variety of fission products. For example, the fission of U-235 (uranium-235) may produce Kr-92 (krypton-92) and Ba-141 (barium-141). If 200 Kr-92 nuclei are produced in 1,000 U-235 fission events, the Kr-92 yield can be expressed as 200. Measured yield refers to the actual measured yield of fission products.

[0062] like Figure 2 As shown, in some embodiments, determining whether there is uranium contamination on the surface of the core fuel assembly includes:

[0063] According to a preset adaptive ratio model, determining whether the specific activity ratio of the preset characteristic nuclide is less than a preset value;

[0064] If so, determine whether the deviations between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides are both no greater than the preset values;

[0065] If so, determine whether there are short-lived nuclides;

[0066] If so, there is uranium contamination on the surface of the core fuel assembly.

[0067] The typical fission product multimodal uranium contamination analysis method integrates: the typical nuclide ratio dynamic analysis method, which is to determine whether the deviation between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides is no more than the preset value; the fission yield matching verification method, which is to determine whether the deviation between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides is no more than the preset value; and the short-lived nuclide existence analysis method, which is to determine whether short-lived nuclides exist.

[0068] The typical nuclide ratio dynamic analysis method uses a method that uses historical data and a nuclide database to establish an adaptive ratio model based on factors such as the fuel cycle and fuel burnup depth, as the specific activity ratio threshold of two preset characteristic nuclides varies across different fuel cycles and burnups. This model is used to adaptively determine the specific activity ratio threshold. If uranium contamination and fission dominate on the fuel assembly surface, and the specific activity ratio of the preset characteristic nuclides is less than the preset value, uranium contamination is likely present on the core fuel assembly surface, requiring further analysis using the fission yield matching verification method.

[0069] The fission yield matching verification method establishes a theoretical fission yield value by referencing a nuclide database, such as the Evaluation Nuclear Data File (ENDF / B). If the measured yield percentages of pre-set characteristic nuclides deviate from the theoretical yield percentages by no more than 5%, for example, a theoretical yield of 2.558% for Kr-87, 6.539% for Xe-135, and 6.188% for Cs-137, and the deviations from the theoretical yield percentages for these three characteristic nuclides are all within 5%, then there is a high probability of uranium contamination on the fuel assembly surface, necessitating further analysis using the short-lived nuclide presence analysis method. The measured yield percentage refers to the ratio of the measured yield of a particular fission product to the total measured yield of all fission products. The theoretical yield percentage refers to the ratio of the theoretical yield of a particular fission product to the total theoretical yield of all fission products under ideal conditions.

[0070] The presence of short-lived nuclides is analyzed. The presence of short-lived nuclides indicates that uranium decay is ongoing. Short-lived nuclides have short half-lives and typically decay completely within a few days to hours. Therefore, the detection of these short-lived nuclides indicates that the uranium decay activity is recent, rather than residual from a long time ago. The detection of short-lived nuclides such as Rb-90 and Rb-91 indicates uranium contamination on the fuel assembly surface. Rb-90 and Rb-91 are used for illustrative purposes only and are not intended to limit this application; other short-lived nuclides may also be present.

[0071] In some embodiments, the formula for calculating the amount of uranium contamination distributed on the surface of the core fuel assembly in the primary coolant is:

[0072]

[0073] Where w is the mass of uranium contamination per unit mass of primary coolant, m is the mass of uranium in a single fuel rod in the core fuel assembly, M is the total mass of coolant in the core area, and R / B is the ratio of uranium nuclides released to generated.

[0074] The amount of uranium contamination in the primary coolant can be quantitatively calculated. The amount of uranium contamination is closely related to the uranium contamination mass per unit mass of the primary coolant, the uranium mass of a single fuel rod in the core fuel assembly, the total coolant mass in the core area, and the uranium nuclide release and generation ratio.

[0075] In some embodiments, the formula for calculating the uranium nuclide release and production ratio is:

[0076]

[0077] Where R / B is the ratio of uranium nuclide release to production, A is the specific activity of uranium nuclides, V is the volume of the primary coolant, G is the thermal power of the nuclear reactor, n is the number of fuel rods in the core fuel assembly, and Ef is the fission yield of uranium nuclides.

[0078] In some embodiments, the calculation formula for the concentration of uranium contamination fissile nuclides in the core fuel assembly is:

[0079]

[0080] Where φ is the neutron flux, σ is the fission cross section of uranium, w is the uranium contamination mass per unit mass of the primary coolant, N is the uranium atomic density, Y is the fission nuclide yield, η is the fission nuclide release efficiency, v is the primary coolant flow rate, S 管 is the cross-sectional area of ​​the primary circuit pipeline, U is the molar mass of the fission nuclide, S 铀 is the uranium contamination area, λ is the decay time of the fission nuclide, and t is the neutron irradiation time.

[0081] The calculation formula for the concentration of fission nuclides in uranium contamination of the core fuel assembly is used to quantitatively calculate the distribution and concentration changes of fission products in the primary coolant after uranium contamination of the core fuel assembly surface.

[0082] For example, this embodiment provides a method for calculating uranium-contaminated fission products in a nuclear power plant core fuel assembly. This method is for illustrative purposes only and is not intended to limit this application. Other methods are also possible. The specific steps are as follows:

[0083] The fissile nuclides in the primary coolant of a domestic nuclear power plant were monitored in real time using the core fuel online monitoring gamma spectroscopy system. A dynamic database of characteristic nuclides in the primary coolant (such as Xe-133, Xe-135, I-131, and Kr-85m) was established, as shown in Table 1.

[0084] Table 1 Activity concentrations of major fission nuclides in the primary coolant of a nuclear power plant

[0085] Serial number Nuclide type Activity concentration 1 Xe-133 <![CDATA[1.5×10 9 Bq / m 3 ]]> 2 Xe-135 <![CDATA[2.1×10 9 Bq / m 3 ]]> 3 I-131 <![CDATA[1.9×10 9 Bq / m 3 ]]> 4 Kr-85m <![CDATA[1.3×10 9 Bq / m 3 ]]> 5 Rb-90 <![CDATA[1.2×10 9 Bq / m 3 ]]> 6 Rb-91 <![CDATA[6.0×10 8 Bq / m 3 ]]>

[0086] Then, using a typical fission product multimodal uranium contamination analysis method, calculations revealed a Xe-133 / Xe-135 specific activity ratio of 0.71, less than 1. Furthermore, the activity concentrations of Kr-87, Xe-135, and Cs-137 accounted for 2.65%, 6.15%, and 6.58%, respectively. These values ​​all deviated significantly less than 5% from their theoretical yields. Furthermore, the short-lived nuclides Rb-90 and Rb-91 were detected, indicating uranium contamination on the fuel assembly surface.

[0087] Based on the fission and release laws of fissile nuclides, the dynamic uranium contamination amount calculation method in the primary coolant is adopted. and formula The calculation shows that the uranium contamination per unit mass of water in the first circuit coolant is 10 μg / cm 2 Finally, the formula The concentration of Xe-133 nuclides in the primary coolant of the reactor core fuel assembly surface contaminated with uranium is calculated to be 1.8×10 8 Bq / m 3 . The concentration calculations of other fission products are not listed here.

[0088] Some embodiments of the present invention disclose a system for calculating uranium contamination fission products in a nuclear power plant core fuel assembly, comprising:

[0089] The monitoring and judgment module is used to determine whether there is uranium contamination on the surface of the core fuel assembly by real-time monitoring of the characteristic nuclides of the primary coolant of the core fuel assembly;

[0090] A uranium contamination amount calculation module is used to calculate the uranium contamination amount of the uranium contamination distribution on the surface of the core fuel assembly in the primary coolant circuit if uranium contamination exists;

[0091] The fission product calculation module is used to calculate the distribution of uranium contamination fission products in the core fuel assembly based on the uranium contamination amount.

[0092] In some embodiments, the monitoring and judgment module includes:

[0093] A monitoring unit is used to monitor multiple nuclides in the primary coolant in real time and establish a dynamic database of characteristic nuclides corresponding to the characteristic nuclides in the multiple nuclides;

[0094] The judgment unit is used to extract nuclide information from the dynamic database of characteristic nuclides and judge whether there is uranium contamination on the surface of the core fuel assembly.

[0095] In some embodiments, the determining unit includes:

[0096] a characteristic nuclide extraction subunit, configured to extract nuclide information including at least the specific activity ratio of a preset characteristic nuclide, the measured yield of the preset characteristic nuclide, and short-lived nuclides from a characteristic nuclide dynamic database; and / or

[0097] The ratio dynamic analysis subunit is used to determine whether the specific activity ratio of the preset characteristic nuclide is less than a preset value according to a preset specific activity ratio model;

[0098] The fission yield matching subunit is used to determine whether the deviations between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides are both no greater than the preset value if the specific activity ratio of the preset characteristic nuclides is less than the preset value;

[0099] The short-lived nuclide analysis subunit is used to determine whether there are short-lived nuclides if the deviation between the measured yield ratio and the theoretical yield ratio is not greater than the preset value;

[0100] The judgment subunit is used to determine that if the specific activity ratio of the preset characteristic nuclides is less than the preset value, and the deviation between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides is greater than the preset value, and there are short-lived nuclides, then there is uranium contamination on the surface of the core fuel assembly.

[0101] It is understandable that the above embodiments only express some of the implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, the above embodiments or technical features can be freely combined, and several deformations and improvements can be made, which all fall within the scope of protection of the present invention, that is, the embodiments described in "some embodiments" can be freely combined with any of the above and below embodiments. Therefore, all equivalent transformations and modifications made to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for calculating uranium contaminated fission products in nuclear power plant core fuel assemblies, characterized in that: The method comprises the following steps: By real-time monitoring of the characteristic nuclides of the primary coolant of the core fuel assembly, it is possible to determine whether there is uranium contamination on the surface of the core fuel assembly; If uranium contamination exists, calculate the amount of uranium contamination distributed on the surface of the core fuel assembly in the primary coolant; The distribution of uranium contamination fission products in the core fuel assembly is calculated based on the uranium contamination amount.

2. The method for calculating uranium-contaminated fission products in a nuclear power plant core fuel assembly according to claim 1, characterized in that: By real-time monitoring of the characteristic nuclides of the primary coolant of the core fuel assembly, it is determined whether there is uranium contamination on the surface of the core fuel assembly, including: Real-time monitoring of multiple nuclides in the primary coolant circuit is carried out to establish a dynamic database of characteristic nuclides corresponding to the characteristic nuclides in the multiple nuclides; Extract nuclide information from the dynamic database of characteristic nuclides to determine whether there is uranium contamination on the surface of the core fuel assembly.

3. The method for calculating uranium-contaminated fission products in a nuclear power plant core fuel assembly according to claim 2, characterized in that: Extract nuclide information from the dynamic database of characteristic nuclides, including: The nuclide information including at least the specific activity ratio of the preset characteristic nuclide, the measured yield of the preset characteristic nuclide and the short-lived nuclide is extracted from the characteristic nuclide dynamic database.

4. The method for calculating uranium-contaminated fission products in a nuclear power plant core fuel assembly according to claim 3, characterized in that: Determine whether there is uranium contamination on the surface of the core fuel assembly, including: According to a preset adaptive ratio model, determining whether the specific activity ratio of the preset characteristic nuclide is less than a preset value; If so, determine whether the deviations between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides are both no greater than the preset values; If so, determine whether there are short-lived nuclides; If so, there is uranium contamination on the surface of the core fuel assembly.

5. The method for calculating uranium-contaminated fission products in nuclear power plant core fuel assemblies according to claim 1, characterized in that: The formula for calculating the amount of uranium contamination on the surface of the core fuel assembly and its distribution in the primary coolant is: Where w is the mass of uranium contamination per unit mass of primary coolant, m is the mass of uranium in a single fuel rod in the core fuel assembly, M is the total mass of coolant in the core area, and R / B is the ratio of uranium nuclides released to generated.

6. The method for calculating uranium-contaminated fission products in nuclear power plant core fuel assemblies according to claim 5, characterized in that: The formula for calculating the uranium nuclide release and production ratio is: Where R / B is the ratio of uranium nuclide release to production, A is the specific activity of uranium nuclides, V is the volume of the primary coolant, G is the thermal power of the nuclear reactor, n is the number of fuel rods in the core fuel assembly, and Ef is the fission yield of uranium nuclides.

7. The method for calculating uranium-contaminated fission products in nuclear power plant core fuel assemblies according to claim 1, characterized in that: The calculation formula for the concentration of uranium contaminated fissile nuclides in the core fuel assembly is: Where φ is the neutron flux, σ is the fission cross section of uranium, w is the uranium contamination mass per unit mass of the primary coolant, N is the uranium atomic density, Y is the fission nuclide yield, η is the fission nuclide release efficiency, v is the primary coolant flow rate, S 管 is the cross-sectional area of ​​the primary circuit pipeline, U is the molar mass of the fission nuclide, S 铀 is the uranium contamination area, λ is the decay time of the fission nuclide, and t is the neutron irradiation time.

8. A system for calculating uranium contamination fission products in a nuclear power plant core fuel assembly, characterized in that: include: The monitoring and judgment module is used to determine whether there is uranium contamination on the surface of the core fuel assembly by real-time monitoring of the characteristic nuclides of the primary coolant of the core fuel assembly; A uranium contamination amount calculation module is used to calculate the uranium contamination amount of the uranium contamination distribution on the surface of the core fuel assembly in the primary coolant circuit if uranium contamination exists; The fission product calculation module is used to calculate the distribution of uranium contamination fission products in the core fuel assembly based on the uranium contamination amount.

9. The nuclear power plant core fuel assembly uranium contamination fission product calculation system according to claim 8, characterized in that: The monitoring and judgment module includes: A monitoring unit is used to monitor multiple nuclides in the primary coolant in real time and establish a dynamic database of characteristic nuclides corresponding to the characteristic nuclides in the multiple nuclides; The judgment unit is used to extract nuclide information from the dynamic database of characteristic nuclides and judge whether there is uranium contamination on the surface of the core fuel assembly.

10. The nuclear power plant core fuel assembly uranium contamination fission product calculation system according to claim 9, characterized in that: The judgment unit includes: a characteristic nuclide extraction subunit, configured to extract nuclide information including at least the specific activity ratio of a preset characteristic nuclide, the measured yield of the preset characteristic nuclide, and short-lived nuclides from a characteristic nuclide dynamic database; and / or The ratio dynamic analysis subunit is used to determine whether the specific activity ratio of the preset characteristic nuclide is less than a preset value according to a preset specific activity ratio model; The fission yield matching subunit is used to determine whether the deviations between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides are both no greater than the preset value if the specific activity ratio of the preset characteristic nuclides is less than the preset value; The short-lived nuclide analysis subunit is used to determine whether there are short-lived nuclides if the deviation between the measured yield ratio and the theoretical yield ratio is not greater than the preset value; The judgment subunit is used to determine that if the specific activity ratio of the preset characteristic nuclides is less than the preset value, and the deviation between the measured yield ratio and the theoretical yield ratio of the preset characteristic nuclides is greater than the preset value, and there are short-lived nuclides, then there is uranium contamination on the surface of the core fuel assembly.

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