Tracer for nuclear fuel damage detection and nuclear fuel damage detection method

Abstract

The invention discloses a tracer for nuclear fuel damage detection and a nuclear fuel damage detection method, the tracer comprises at least one group of characteristic compounds, the characteristic compounds comprise at least two tracer elements, and the at least one tracer element has at least two isotopes; in different characteristic compounds, the contents of different isotopes in the tracer elements are different; the characteristic compound resists the temperature in the fuel assembly and the pressure outside the fuel assembly cladding; the method comprises the following steps: filling tracers in a plurality of fuel assemblies of a nuclear reactor, filling different characteristic compounds in the fuel assemblies at different positions, then sampling and detecting a primary loop of the nuclear reactor, and judging the damage condition of nuclear fuel according to a detection result. Characteristic compounds in the tracer comprise at least two tracer elements, and different isotope content ratios are adopted in the tracer elements; different fuel assemblies can be identified by filling the nuclear reactor fuel with tracers.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear fuel detection, and particularly to a tracer for nuclear fuel breakage detection and a nuclear fuel breakage detection method. Background Art

[0002] Civil nuclear reactors often adopt rod bundle type fuel assemblies. Each assembly consists of multiple fuel element rods and auxiliary facilities, and multiple groups of fuel assemblies are arranged orderly to form a reactor core for a controllable chain reaction. As the first line of defense for the safe operation of nuclear power, if the cladding of the fuel element rod is damaged for some reason, it will cause the harmful radioactive substances originally enclosed in the cladding to spill out and enter the coolant in the primary loop, thereby increasing the risk of further nuclear radiation leakage.

[0003] Existing tracers can usually only trace less than 10 fuel assemblies and cannot be used in an environment with a large number of fuel assemblies, and all fuel assemblies cannot be located in the core. In addition, the existing detection method samples and detects the radioactivity of the primary loop. Since there are dozens of chemical elements in the analysis results of the samples, plus the diversity of the causes of breakage and the wide range of the positions of the damaged assemblies, the current on-line detection means has great uncertainty in judging whether the assembly is damaged according to the radiochemical analysis results of the samples. And other technical means that can definitely detect breakage are required to be carried out after stopping the nuclear reaction, that is, power generation must be stopped first, resulting in huge economic losses. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a tracer for nuclear fuel breakage detection and a nuclear fuel breakage detection method.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a tracer for nuclear fuel breakage detection, the tracer includes at least one group of characteristic compounds, the characteristic compounds include at least two tracer elements, and at least one tracer element has at least two isotopes; in different characteristic compounds, the contents of different isotopes in the tracer elements are different; the characteristic compounds can withstand the temperature inside the fuel assembly and the pressure outside the cladding of the fuel assembly;

[0006] The tracer elements simultaneously meet the following conditions:

[0007] The tracer element is not a fission element;

[0008] The tracer element is not an original element of the nuclear reactor;

[0009] The tracer element is not an isotope generated by the nuclear reactor under irradiation.

[0010] In some embodiments, in the same group of characteristic compounds, each characteristic compound includes two tracer elements, namely tracer element A and tracer element B. Tracer element A has at least two isotopes, and tracer element B has no isotopes; each characteristic compound is composed of at least one isotope of tracer element A and tracer element B.

[0011] In some embodiments, in different characteristic compounds, the contents of at least two isotopes in tracer element A are different from each other.

[0012] In some embodiments, in the same group of characteristic compounds, each characteristic compound includes two tracer elements, and both tracer elements have at least two isotopes; each characteristic compound is composed of at least one isotope of each tracer element.

[0013] In some embodiments, in the same group of characteristic compounds, each characteristic compound includes at least three tracer elements, and at least one tracer element has at least two isotopes; each characteristic compound is composed of at least one isotope of each tracer element.

[0014] In some embodiments, in different characteristic compounds, the contents of at least two isotopes in the tracer elements are different from each other.

[0015] In some embodiments, in the same group of characteristic compounds, the content of the isotopes of each tracer element increases or decreases by 5-20% in mass percentage in different characteristic compounds.

[0016] In some embodiments, the tracer includes at least two groups of characteristic compounds, and at least one characteristic compound in at least one group of characteristic compounds and at least one characteristic compound in another group of characteristic compounds form a characteristic mixture.

[0017] In some embodiments, in different characteristic mixtures, the contents of at least two characteristic compounds are different from each other, and the contents of at least two tracer elements in the characteristic compounds are also different from each other.

[0018] In some embodiments, the characteristic compound is carbon dioxide, sulfur hexafluoride or carbon tetrafluoride.

[0019] In some embodiments, the temperature inside the fuel assembly is 400-500 °C, and the pressure outside the fuel assembly cladding is 12-20 MPa.

[0020] The present invention also provides a method for detecting nuclear fuel damage. Using the tracer for detecting nuclear fuel damage according to any one of the above, the method for detecting nuclear fuel damage includes the following steps: filling the tracer in several fuel assemblies of a nuclear reactor, filling different characteristic compounds in the fuel assemblies at different positions, then sampling and detecting the primary loop of the nuclear reactor, and judging the damage condition of the nuclear fuel according to the detection result.

[0021] In some embodiments, different characteristic compounds are filled in several fuel rods of a fuel assembly; one characteristic compound is filled in a fuel rod; or, at least two characteristic compounds are filled in a fuel rod, and the contents of the at least two characteristic compounds in different fuel rods are different from each other.

[0022] Advantages of the present invention:

[0023] The present invention uses at least two different tracer elements and different isotope content ratios in the tracer elements to combine and form different characteristic compounds in the same group. The physical and chemical properties of the characteristic compounds themselves are relatively stable. At least one group of characteristic compounds forms a tracer, which is suitable for the tracer of fuel breakage detection in a nuclear reactor and can also be used for other chemical environment tracers.

[0024] By filling a tracer in the nuclear reactor fuel, different characteristic compounds are filled in fuel assemblies at different positions, and then the primary loop is sampled and detected to determine whether the fuel assembly is damaged. Further, according to the isotopes of the tracer elements of the detected characteristic compounds and their content ratios, the damaged fuel assembly can be located. Detailed implementation manners

[0025] For a clearer understanding of the technical features, objectives, and effects of the present invention, the present invention will be further described in detail below in conjunction with specific implementation manners. It is only used to explain the present invention and does not constitute a limitation on the protection scope of the present invention.

[0026] The present invention provides a tracer for nuclear fuel breakage detection. The tracer includes at least one group of characteristic compounds. The characteristic compounds include at least two tracer elements, and at least one tracer element has at least two isotopes. The at least one tracer element and its isotopes are arranged and combined to form several characteristic compounds in the same group. The more the types of the tracer elements and their isotopes, the more the characteristic compounds formed by the combination. In addition, in different characteristic compounds in the same group, the contents of different isotopes in the tracer elements are different from each other. By using different content ratios for the isotopes of at least two tracer elements, several characteristic compounds in the same group can be formed.

[0027] The characteristic compound is resistant to the temperature inside the fuel assembly to ensure that the characteristic compound itself has sufficient stability under the normal operating conditions of the reactor and will not undergo chemical reactions or decomposition reactions under normal operating temperature and pressure. In some embodiments, the temperature inside the fuel assembly is 400 - 500 °C, such as 400 °C, 420 °C, 440 °C, 470 °C, 500 °C, etc. At the same time, the characteristic compound is resistant to the pressure outside the fuel assembly cladding to ensure that the expansibility of the characteristic compound itself meets the pressure resistance performance of the fuel assembly cladding under the normal operating conditions of the reactor. In some embodiments, the pressure outside the fuel assembly cladding is 12 - 20 MPa, such as 12 MPa, 13.5 MPa, 15.5 MPa, 18 MPa, 20 MPa, etc.

[0028] The tracer elements simultaneously satisfy the following conditions:

[0029] (1) The tracer element is not a fission element;

[0030] (2) The tracer element is not an original element of the nuclear reactor;

[0031] (3) The tracer element is not an isotope generated by the nuclear reactor under irradiation.

[0032] By the above conditions, it is ensured that the tracer element is not easily induced to fission by the irradiation environment in the reactor, and the tracer element does not overlap with the original or generated elements of the nuclear reactor itself. At the same time, the tracer element has sufficient stability under the normal operating conditions of the reactor.

[0033] According to the types and quantities of the tracer elements and their isotopes, the characteristic compounds in the same group have the following three implementation modes:

[0034] The first implementation mode: In the same group of characteristic compounds, each characteristic compound includes two tracer elements, namely tracer element A and tracer element B. Tracer element A has at least two isotopes, and tracer element B does not have isotopes or tracer element B is one of the isotopes of a certain element (having at least two isotopes). For example, tracer element A is carbon, and its isotopes are C-12, C-13, and C-14. Tracer element B is one of the isotopes of oxygen, O-16. The two tracer elements form the characteristic compound carbon dioxide. In this implementation mode, each characteristic compound is composed of at least one isotope of tracer element A and tracer element B. Further, in different characteristic compounds in the same group, the contents of at least two isotopes in tracer element A are different.

[0035] In some embodiments of this implementation mode, tracer element A has three isotopes, namely A 1 、A 2 and A 3 , then the elemental composition of the characteristic compound can be A1 B, A 2 B, A 3 B, A 1 A 2 B, A 1 A 3 B, A 2 A 3 B or A 1 A 2 A 3 B. Among them, for the characteristic compound with the element composition of A 1 A 2 B, the isotope A 1 and A 2 have different content ratios in the tracer element A, and A 1 and A 2 can have a mass ratio of 1:1, 1:4, 2:3, 3:2, 4:1, etc. The characteristic compound A 1 A 3 B, A 2 A 3 B is the same. For the characteristic compound with the element composition of A 1 A 2 A 3 B, the isotope A 1 , A 2 and A 3 have different content ratios in the tracer element A, and the isotope A 1 , A 2 and A 3 can have a mass ratio of 1:1:8, 1:3:6, 4:1:5, 7:2:1, 2:3:5, 3:5:2, etc.

[0036] The second implementation mode: In the same group of characteristic compounds, each characteristic compound includes two tracer elements, and both tracer elements have at least two isotopes. Each characteristic compound is composed of at least one isotope of each tracer element. Further, in different characteristic compounds, the contents of at least two isotopes in the tracer elements are different.

[0037] In some embodiments of this implementation mode, the characteristic compound includes two tracer elements, namely tracer element C and tracer element D. Tracer element C has two isotopes, namely C 1 and C 2 , and tracer element D has two isotopes, namely D 1 and D 2 , then the element composition of the characteristic compound can be C 1 D 1 、C 2 D 1 、C 1 D2 , C 2 D 2 , C 1 C 2 D 1 , C 1 C 2 D 2 , C 1 D 1 D 2 , C 2 D 1 D 2 or C 1 C 2 D 1 D 2 . Among them, for the characteristic compound whose element composition includes C 1 and C 2 , the content ratio of the isotopes C 1 and C 2 in the tracer element C is different. The mass ratio of C 1 and C 2 can be 1:9, 3:7, 5:5, 7:3, 9:1, etc. The content ratio of the isotopes D 1 and D 2 in the tracer element D is the same by analogy. For example, the tracer element C is carbon element, its isotopes are C-12 and C-13, the tracer element D is oxygen element, its isotopes are O-16 and O-18, and the characteristic compound is carbon dioxide composed of carbon element and oxygen element.

[0038] The third implementation mode: In the same group of characteristic compounds, each characteristic compound includes at least three tracer elements, and at least one tracer element has at least two isotopes. Each characteristic compound is composed of at least one isotope of each tracer element. Further, in different characteristic compounds, the contents of at least two isotopes in the tracer elements are different.

[0039] In some embodiments of this implementation mode, the characteristic compound includes three tracer elements, namely tracer element E, tracer element F, and tracer element G. Among them, tracer element E has two isotopes, namely E 1 and E 2 , tracer element F has three isotopes, namely F 1 , F 2 and F 3 , and tracer element G has no isotope. Then the element composition of the characteristic compound can be E 1 F 1 G, E 2 F 1 F 2 G, E 1 E 2 F2 G, E 1 E 2 F 1 F 2 G, E 1 E 2 F 1 F 2 F 3 G, etc. Among them, for the tracer element E, the mass ratio of the isotopes E 1 and E 2 can be 1:7, 2:11, 4:5, 7:2, 9:8, etc. For the tracer element F, the mass ratio of the isotopes F 1 , F 2 and F 3 can be 1:1:2, 1:4:5, 3:7:6, 5:2:8, 9:1:3, etc.

[0040] In the above three implementation manners, in the same set of characteristic compounds, the content of the isotopes of each tracer element increases or decreases by 5-20% in mass percentage in different characteristic compounds, and this mass percentage can be 5%, 10%, 15%, 20%, etc. In some embodiments, for the characteristic compound A 1 A 2 B of the first implementation manner above, the isotopes A 1 and A 2 of the tracer element A increase or decrease by 10% in mass percentage in different characteristic compounds. Then, in different characteristic compounds, the mass percentage of the isotopes A 1 and A 2 in the tracer element A can be 10%A 1 +90%A 2 , 20%A 1 +80%A 2 , 30%A 1 +70%A 2 , 40%A 1 +60%A 2 , 50%A 1 +50%A 2 , 60%A 1 +40%A 2 etc. Among them, the magnitude of the increasing or decreasing mass percentage depends on the precision of the tracer element detection instrument and the number of fuel elements, and can be specifically selected according to actual needs. If the instrument detection precision is high and the number of fuel elements is large, the increasing or decreasing mass percentage can be less than 5%, and vice versa, it can be higher than 20%.

[0041] Different from the above three embodiments, in some other embodiments, the tracer includes at least two groups of characteristic compounds. Each of the at least two groups of characteristic compounds is selected from one of the above three embodiments. At least one characteristic compound in at least one group of characteristic compounds and at least one characteristic compound in another group of characteristic compounds form a characteristic mixture. In different characteristic mixtures, the contents of at least two characteristic compounds (from different groups of characteristic compounds respectively) are different, and the contents of at least two tracer elements in the characteristic compounds are also different.

[0042] In some embodiments, the tracer compound includes two groups of characteristic compounds. The first group of characteristic compounds is the characteristic compounds of the first embodiment above, that is, including A 1 B, A 2 B, A 3 B, A 1 A 2 B and seven other characteristic compounds; the second group of characteristic compounds is the characteristic compounds of the second embodiment above, such as those including C 1 D 1 , C 2 D 1 , C 1 D 2 , C 2 D 2 , C 1 C 2 D 1 and nine other characteristic compounds. One characteristic compound in the first group of characteristic compounds and one characteristic compound in the second group of characteristic compounds form a characteristic mixture. The composition of this characteristic mixture can be A 1 B + C 1 D 1 , A 2 B + C 2 D 1 , A 3 B + C 1 C 2 D 1 , A 1 A 2 B + C 1 C 2 D 1 D 2 etc. Among them, for the characteristic mixture composed of A 3 B and C 1 C 2 D 1 composition, A 3 B and C 1 C 2 D 1The mass ratio can be 1:9, 3:7, 5:5, 7:3, 9:1, etc. For isotope C 1 and C 2 The mass ratio can be 1:9, 2:8, 3:7, 4:6, 5:5, etc. Similarly, for other characteristic mixtures, the content ratios of different characteristic compounds and different isotopes are the same.

[0043] For example, the tracer element H with 4 isotopes combines with the tracer element I with 3 isotopes to form a characteristic compound m H n I (m is the mass number of the tracer element H, and n is the mass number of the tracer element I), which can identify 12 different fuel assemblies; the characteristic compound formed by the tracer element J with 5 isotopes and the tracer element K with 4 isotopes x J y K (x is the mass number of the tracer element J, and y is the mass number of the tracer element K), which can identify 20 different fuel assemblies. If the characteristic compounds m H n I and x J y K are composed of several characteristic mixtures with different content ratios, and for the characteristic compound m H n I, the 4 isotopes of the tracer element H have different content ratios, and the 3 isotopes of the tracer element I have different content ratios. For the characteristic compound x J y K, the 5 isotopes of the tracer element J have different content ratios, and the 4 isotopes of the tracer element K have different content ratios. Then the characteristic mixtures composed of the characteristic compounds m H n I and x J y K can distinguish at least 32 different fuel assemblies, and even if at least 2 fuel assemblies are damaged simultaneously, they can be accurately identified.

[0044] The characteristic compound can be a gas or a salt. Since gases are easy to precipitate and salts need to be dissolved after being immersed in a liquid, the characteristic compound is preferably a gas. Specifically, the gas characteristic compound can be carbon dioxide (CO 2 ), sulfur hexafluoride (SF 6 ), or carbon tetrafluoride (CF 4 ). Among them, sulfur hexafluoride decomposes at about 400 °C, and carbon tetrafluoride decomposes at about 800 °C. According to reactors at different temperatures, gas characteristic compounds with different decomposition temperatures can be selected.

[0045] The present invention uses at least two different tracer elements and different isotope content ratios in the tracer elements to form different characteristic compounds in the same group. The physical and chemical properties of the characteristic compounds themselves are relatively stable. At least one group of characteristic compounds forms a tracer, which is suitable for the tracer of nuclear reactor fuel damage detection and can also be used for other chemical environment tracers.

[0046] The tracer for nuclear fuel damage detection of the present invention can achieve the characteristic calibration of several different fuel assemblies. If combined with high-precision detection equipment, by sampling at specific positions in the reactor and analyzing the isotope content ratio in the characteristic compounds, the precise positioning of the damaged fuel assembly can be achieved. The specific position refers to the nuclear sampling position suitable for gas, and the existing REN sampling system can be used for sampling.

[0047] The present invention also proposes a nuclear fuel damage detection method, which uses the above-mentioned tracer for nuclear fuel damage detection. The nuclear fuel damage detection method includes the following steps: filling the tracer in several fuel assemblies of the nuclear reactor, filling different characteristic compounds in the fuel assemblies at different positions, and then sampling and detecting the primary coolant circuit of the nuclear reactor, and judging the damage condition of the nuclear fuel according to the detection result.

[0048] In some embodiments, the same characteristic compound is filled in several fuel rods of the same fuel assembly. By sampling and detecting the primary coolant circuit of the reactor, if the fuel assembly is damaged, the position of the damaged fuel assembly can be located according to the tracer element of the leaked characteristic compound.

[0049] In other embodiments, different characteristic compounds are filled in several fuel rods of the same fuel assembly respectively, so as to be able to locate the damaged fuel rod during sampling and detection. The tracer includes a group of characteristic compounds, and a different characteristic compound is filled in each of several fuel rods respectively; or, the tracer includes at least two groups of characteristic compounds, and at least one characteristic compound in at least one group of characteristic compounds and at least one characteristic compound in another group of characteristic compounds form a characteristic mixture, and a different characteristic mixture is filled in each of several fuel rods respectively, that is, at least two characteristic compounds (from different groups of characteristic compounds) are filled in each fuel rod. Further, in different characteristic mixtures, the contents of at least two characteristic compounds are different, that is, the contents of at least two characteristic compounds in different fuel rods are different, and the contents of at least two tracer elements in the characteristic compounds are also different.

[0050] For the selection of the characteristic compounds for tracing the fuel assembly or fuel rod, the total number of fuel assemblies to be traced should be fully considered. This number is related to the refueling scheme of the nuclear reactor, and it should be ensured that the characteristic compounds of all fuel assemblies in the reactor do not repeat during any fuel cycle.

[0051] The selection of characteristic compounds needs to consider the generation of isotopes under reactor irradiation conditions. Other interfering isotopes may be generated under high-energy irradiation, and tracer elements should try to avoid duplication with interfering isotopes. If such duplication cannot be avoided, the interfering isotopes generated can be used as cumulative factors to correct the location of damaged fuel assemblies, that is, according to the reactor operation time and power level, the integrated power (burnup) is increased or decreased synchronously.

[0052] Since the flow rate of the primary coolant in a nuclear reactor is very fast during normal operation, a cycle can be completed in the coolant loop in tens of seconds. The half-life of the activated corrosion product nuclides in the coolant is much longer than the circulation time of the coolant in the loop. It can be assumed that the coolant will be quickly and evenly mixed in the loop, and then the coolant is considered to be the same everywhere along the loop. Therefore, the characteristic compounds leaked after the fuel is damaged can be quickly sampled and collected in the primary loop.

[0053] Sampling and testing the primary circuit of a nuclear reactor may be testing water samples or gases in the primary circuit, and the detection method may be a mass spectrometer. If a tracer element of a characteristic compound is detected in the primary circuit of the reactor, it is determined that the fuel assembly is damaged, and further based on the type of the tracer element and its isotope, and the content ratio between the isotopes in different tracer elements, the location of the damaged fuel assembly or fuel rod is located. If no tracer element is detected, the primary circuit of the reactor is resampled and tested.

[0054] The present invention fills tracers in nuclear reactor fuel, fills different characteristic compounds in fuel assemblies or fuel rods at different positions, then samples and detects a loop to determine whether the fuel assembly or fuel rod is damaged, and further locates the damaged fuel assembly or fuel rod based on the isotopes of the tracer elements of the detected characteristic compounds and their content ratios.

[0055] During the operation of a nuclear power plant, if the occurrence of a fuel damage event can be accurately determined, even if it is a minor damage event, the nuclear power plant can arrange a work plan for refueling and maintenance in advance, handle and inspect the damaged fuel in advance, and provide maintenance benefits. The nuclear fuel damage detection method of the present invention realizes the characteristic identification of fuel assemblies or fuel rods at different positions of a nuclear reactor by filling characteristic compounds with different characteristics in the fuel assembly. When damage occurs in the fuel assembly, the type of characteristic compound can be identified by sampling and analyzing in the primary circuit of the reactor, so that it can accurately determine whether the fuel assembly is damaged without stopping the reactor, and accurately locate the position of the damaged fuel assembly or fuel rod, reducing the economic losses caused by shutdown and maintenance due to misjudgment of damage, and has the dual important significance of ensuring nuclear safety and reducing huge economic losses.

[0056] The following is an example to illustrate:

[0057] A tracer for detecting nuclear fuel damage, the tracer includes a group of characteristic compounds. In the same group of characteristic compounds, each characteristic compound includes two tracer elements, namely carbon element and oxygen element. Among them, carbon element has two common isotopes, namely C-12 and C-13, and oxygen element has two common isotopes, namely O-16 and O-18. The characteristic compound is carbon dioxide composed of at least one isotope of carbon element and at least one isotope of oxygen element. The carbon dioxide characteristic compound can withstand the temperature inside the fuel assembly and the pressure outside the fuel assembly cladding. The temperature inside the fuel assembly is 440 °C, and the pressure outside the fuel assembly cladding is 15.5 MPa. The contents of C-12 and C-13 in different characteristic compounds are different, and the contents of O-16 and O-18 are also different. Specifically, the content of the isotope of each tracer element increases or decreases by 5% in mass percentage in different characteristic compounds.

[0058] The tracer elements and their content ratios of the carbon dioxide characteristic compounds of the tracer are shown in Table 1. Among them, the first content ratio of C-12 and C-13 in carbon element (i.e., 100% C-12 + 0% C-13) is numbered 01, and the second content ratio of carbon element (i.e., 95% C-12 + 5% C-13) is numbered 02, and so on. There are a total of twenty content ratios of carbon element. Similarly, there are a total of twenty content ratios of O-16 and O-18 in oxygen element, numbered 01-20 in sequence. The carbon dioxide characteristic compound composed of the first content ratio of carbon element and the first content ratio of oxygen element is numbered 0101; the carbon dioxide characteristic compound composed of the first content ratio of carbon element and the second content ratio of oxygen element is numbered 0201, and so on. There are a total of 400 carbon dioxide characteristic compounds.

[0059] Table 1 Element combinations of carbon dioxide characteristic compounds

[0060]

[0061] The present invention also provides a method for detecting nuclear fuel damage, which uses the above tracer. The method for detecting nuclear fuel damage includes the following steps: filling the tracer in several fuel assemblies of a nuclear reactor, filling different carbon dioxide characteristic compounds in the fuel assemblies at different positions, and then sampling and detecting the primary loop of the nuclear reactor, and judging the damage condition of the nuclear fuel according to the detection result.

[0062] Specifically, the same carbon dioxide characteristic compound is filled in several fuel rods of the same fuel assembly. Subsequently, the water in the primary loop of the nuclear reactor is sampled and detected and analyzed by a mass spectrometer. If the tracer elements (C-12, C-13, O-16 or O-18) of the carbon dioxide characteristic compound are detected, it is determined that the fuel assembly is damaged. Further, according to the types of the tracer elements and their isotopes and the content ratio between the isotopes in different tracer elements, the position of the damaged fuel assembly or fuel rod is located. If no tracer element is detected, the primary loop of the reactor is resampled and detected.

[0063] The present invention uses at least two different tracer elements and different isotope content ratios in the tracer elements to combine and form different characteristic compounds in the same group. The physical and chemical properties of the characteristic compounds themselves are relatively stable. At least one group of characteristic compounds forms a tracer, which can realize the characteristic calibration of several different fuel assemblies. By filling the fuel assembly with characteristic compounds having different characteristics, the fuel assemblies or fuel rods at different positions in the nuclear reactor can be characterized. When a fuel assembly is damaged, the types of the characteristic compounds can be identified by sampling and analyzing in the primary loop of the reactor. Therefore, without shutting down the reactor, it can accurately determine whether the fuel assembly is damaged and accurately locate the position of the damaged fuel assembly or fuel rod, reducing the economic losses of shutdown and maintenance caused by misjudgment of damage, and having double important significances of ensuring nuclear safety and reducing huge economic losses.

[0064] It can be understood that the above embodiments only express the preferred embodiments of the present invention, and the description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent; it should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can also be made, which all belong to the protection scope of the present invention; therefore, all equivalent transformations and modifications made to the scope of the claims of the present invention should fall within the scope covered by the claims of the present invention.

Claims

1. A tracer for nuclear fuel damage detection, characterized in that: The tracer comprises at least one group of characteristic compounds, the characteristic compounds comprise at least two tracer elements, at least one of the tracer elements has at least two isotopes; the contents of different isotopes in the tracer elements are different in different characteristic compounds; the characteristic compounds withstand the temperature inside the fuel assembly and the pressure outside the fuel assembly cladding; The tracer element satisfies the following conditions at the same time: The tracer element is not a fissile element; The tracer element is not an original element of the nuclear reactor; The tracer element is not an isotope produced by irradiation in a nuclear reactor.

2. The tracer for nuclear fuel damage detection according to claim 1, characterized in that: In the same group of characteristic compounds, each of the characteristic compounds includes two of the tracer elements, namely tracer element A and tracer element B, the tracer element A has at least two isotopes, and the tracer element B has no isotopes; each of the characteristic compounds is composed of at least one of the isotopes of the tracer element A and the tracer element B.

3. The tracer for nuclear fuel damage detection according to claim 2, characterized in that: In different characteristic compounds, the contents of at least two isotopes in the tracer element A are different.

4. The tracer for nuclear fuel damage detection according to claim 1, characterized in that: In the same group of characteristic compounds, each characteristic compound includes two tracer elements, and both of the tracer elements have at least two isotopes; each characteristic compound is composed of at least one isotope of each of the tracer elements.

5. The tracer for nuclear fuel damage detection according to claim 1, characterized in that: In the same group of characteristic compounds, each of the characteristic compounds includes at least three of the tracer elements, at least one of which has at least two isotopes; and each of the characteristic compounds is composed of at least one isotope of each of the tracer elements.

6. The tracer for nuclear fuel damage detection according to claim 4 or 5, characterized in that: In different characteristic compounds, the contents of at least two isotopes in the tracer element are different.

7. The tracer for nuclear fuel damage detection according to claim 1, characterized in that: In the same group of characteristic compounds, the content of the isotope of each tracer element increases or decreases in different characteristic compounds by 5 to 20% by mass.

8. The tracer for nuclear fuel damage detection according to claim 1, characterized in that: The tracer includes at least two groups of characteristic compounds, and at least one characteristic compound in at least one group of characteristic compounds and at least one characteristic compound in another group of characteristic compounds constitute a characteristic mixture.

9. The tracer for nuclear fuel damage detection according to claim 8, characterized in that: In different characteristic mixtures, the contents of at least two of the characteristic compounds are different, and the contents of at least two of the tracer elements in the characteristic compounds are also different.

10. The tracer for nuclear fuel damage detection according to claim 1, characterized in that: The characteristic compound is carbon dioxide, sulfur hexafluoride or carbon tetrafluoride.

11. The tracer for nuclear fuel damage detection according to claim 1, characterized in that: The temperature inside the fuel assembly is 400-500° C., and the pressure outside the fuel assembly cladding is 12-20 MPa.

12. A method for detecting nuclear fuel damage, characterized in that: The tracer for nuclear fuel damage detection according to any one of claims 1 to 11 is used, and the nuclear fuel damage detection method comprises the following steps: filling the tracer into several fuel assemblies of a nuclear reactor, filling different characteristic compounds into the fuel assemblies at different positions, then sampling and testing a circuit of the nuclear reactor, and judging the damage of the nuclear fuel based on the test results.

13. The method for detecting nuclear fuel damage according to claim 12, characterized in that: The fuel rods of the fuel assembly are respectively filled with different characteristic compounds; the fuel rods are filled with one characteristic compound; or the fuel rods are filled with at least two characteristic compounds, and the contents of the at least two characteristic compounds in different fuel rods are different.

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