Fuel assembly damage determination method and fuel assembly damage determination device

Abstract

To provide a fuel assembly damage determination technique that can conduct an inspection for every fuel assembly and can determine the presence or absence of damage even to a test object where FPs cannot be detected.SOLUTION: Provided is a fuel assembly damage determination method for determining the presence or absence of damage to a fuel assembly of nuclear fuel storing a plurality of fuel rods, the method including: placing the fuel assembly to be inspected in an airtight container in the atmosphere of tracer gas with a pressure higher than the internal pressure of the fuel rods assumed when the fuel rods are damaged for predetermined time; subsequently leaving the fuel assembly standing in the atmosphere with the tracer gas removed for the predetermined time; examining the presence or absence of the tracer gas in the atmosphere after the fuel assembly is left standing; and determining the presence of damage when the tracer gas is detected and determining the absence of damage when the tracer gas is not detected, or measuring the concentration of the tracer gas in the atmosphere immediately after the start of leaving and after the end of leaving; and determining the presence of damage when the concentration after the end of leaving is higher than that immediately after the start of leaving, and determining the absence of damage when the concentration is equal to or lower than that immediately after the start of leaving.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for detecting damage to a fuel assembly of nuclear fuel used for generating electricity in a nuclear power plant. The present invention relates to a method and device for determining damage to a fuel assembly, and can be applied not only to fuel assemblies in operating reactors and fuel assemblies stored in spent fuel pits at nuclear power plants, but also to determining whether or not damage has occurred in fuel assemblies that are stored in multiple units in a storage container and cooled for a long period of time for transport to a reprocessing facility. [Background technology]

[0002] In nuclear power generation, fission products (FPs) generated by the nuclear fission of uranium and other elements are usually contained within the fuel rods, which are the sealed boundary. If the fuel rods are damaged for some reason and lose their sealing function, gaseous FPs are released from inside the fuel rods through the damaged area, and water-soluble FPs are released to the outside as water enters, causing a so-called leak.

[0003] Fuel assemblies containing damaged fuel rods must be handled differently from healthy fuel assemblies in terms of operation. Therefore, inspection techniques have been developed to identify damaged fuel and determine whether or not the fuel assemblies are damaged.

[0004] One example is an inspection technique that uses ultrasonic waves (see, for example, Patent Document 1). This inspection technique is an inspection technique that determines the presence or absence of damage based on the difference in how ultrasonic waves are transmitted when water has entered the inside of a fuel rod and when it has not.

[0005] Another example is shipping inspection (see, for example, Patent Document 2). Shipping inspection is an inspection in which fuel assemblies are individually held in an environment isolated from the surroundings and FPs and the like released from inside the fuel rods are detected. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 5-84475 [Patent Document 2] Patent No. 6244126 Summary of the Invention [Problem to be solved by the invention]

[0007] However, ultrasonic inspection techniques require testing all of the fuel rods one by one to determine damage to the fuel assemblies, which takes a very long time to complete and is therefore inefficient.

[0008] On the other hand, with regard to shipping inspections, existing shipping inspections target radiation from radioactive isotopes such as xenon and krypton as FP gases, and iodine and cesium as water-soluble FPs.If the target nuclides are not present in the fuel rods, radiation cannot be detected, and even if damage is present, it cannot be detected.

[0009] And because damage to fuel rods occurs mainly during irradiation inside the reactor (power generation), reactor operators monitor the concentration of FP nuclides through gas and water monitoring of the entire core, and if there are signs of a leak, they conduct a shipping inspection immediately or at the time of the next regular inspection. If an inspection is conducted at this timing, it is unlikely that the above nuclides are not present in the fuel rods, so the above shipping inspection technology is sufficient to determine damage.

[0010] On the other hand, if fuel has been stored for a long period of time or is severely damaged, and the FP nuclides targeted by conventional shipping inspections have fallen below the detection limit due to radioactive decay, gas emission, leaching into water, etc., existing shipping devices cannot be applied.

[0011] Therefore, an objective of the present invention is to provide a fuel assembly damage determination technology that can perform inspection on a fuel assembly basis and determine the presence or absence of damage even for inspection objects in which FP cannot be detected. [Means for solving the problem]

[0012] The above problems can be solved by the means described below.

[0013] The invention described in claim 1 is A method for determining whether or not a fuel assembly containing a plurality of fuel rods is damaged, comprising: The fuel assembly to be inspected is placed in a sealed container for a predetermined period of time in an atmosphere of tracer gas at a pressure higher than the internal pressure of the fuel rod that would be expected if the fuel rod were damaged, and then the fuel assembly is left for a predetermined period of time in an atmosphere from which the tracer gas has been removed; After the test, the presence or absence of tracer gas in the atmosphere is checked. If tracer gas is detected, it is determined that there is damage, and if no tracer gas is detected, it is determined that there is no damage. Alternatively, the method for determining damage to a fuel assembly includes measuring the concentration of the tracer gas in the atmosphere immediately after the start of leaving it and after the end of leaving it, and determining that there is damage if the concentration after leaving it is higher than that immediately after the start of leaving it, and determining that there is no damage if the concentration is equal to or lower than that immediately after the start of leaving it.

[0014] The invention described in claim 2 is The method for determining damage to a fuel assembly as described in claim 1, characterized in that the internal pressure of the fuel rod assumed when the fuel rod is damaged is the same as the ambient pressure of the fuel assembly before the fuel assembly is placed in the tracer gas atmosphere in the sealed container.

[0015] The invention described in claim 3 is a fuel assembly containing step of containing the fuel assembly to be inspected in a sealable container; a tracer gas filling process in which, after the fuel assemblies are stored, a tracer gas is filled into the container to create a tracer gas atmosphere in the container at a pressure higher than the internal pressure of the fuel rods that would be assumed if the fuel rods were damaged; a step of leaving the sample in a tracer gas atmosphere for a predetermined period of time after filling the sample with the tracer gas; a gas replacement step of evacuating the tracer gas from the container after the container is left in the tracer gas atmosphere, and replacing the atmosphere in the container with a non-tracer gas atmosphere that does not contain the tracer gas; and a non-tracer gas atmosphere leaving step of leaving the non-tracer gas atmosphere for a predetermined period of time after replacing the non-tracer gas atmosphere. Investigate the presence or absence of tracer gas in a non-tracer gas atmosphere after leaving it in a non-tracer gas atmosphere. Alternatively, the method for determining damage to a fuel assembly according to claim 1 is characterized in that the tracer gas concentration in the non-tracer gas atmosphere is measured immediately after the start of exposure to the non-tracer gas atmosphere and after the end of exposure to the non-tracer gas atmosphere.

[0016] The invention described in claim 4 is The method for determining damage to a fuel assembly as described in claim 3, characterized in that the internal pressure of the fuel rod assumed when the fuel rod is damaged is the same as the pressure in the container before the tracer gas is filled into the container.

[0017] The invention described in claim 5 is a fuel assembly containing step of containing the fuel assembly to be inspected in a sealable first container; a tracer gas filling step of filling the first container with a tracer gas after the containment, and creating a tracer gas atmosphere in the first container at a pressure higher than the internal pressure of the fuel rod that would be assumed if the fuel rod were damaged; a step of leaving the sample in a tracer gas atmosphere for a predetermined period of time after filling the sample with the tracer gas; a fuel assembly transfer step of transferring the fuel assembly to a second container after being left in the tracer gas atmosphere, and making the atmosphere in the second container a non-tracer gas atmosphere not containing the tracer gas; and a step of leaving the device in a non-tracer gas atmosphere for a predetermined period of time after the device is moved. Investigate the presence or absence of tracer gas in a non-tracer gas atmosphere after leaving it in a non-tracer gas atmosphere. Alternatively, the method for determining damage to a fuel assembly according to claim 1 is characterized in that the tracer gas concentration in the non-tracer gas atmosphere is measured immediately after the start of exposure to the non-tracer gas atmosphere and after the end of exposure to the non-tracer gas atmosphere.

[0018] The invention described in claim 6 is The method for determining damage to a fuel assembly as described in claim 5, characterized in that the internal pressure of the fuel rod assumed when the fuel rod is damaged is the same as the pressure in the first container before the tracer gas is filled into the first container.

[0019] The invention described in claim 7 is 7. The method for determining damage to a fuel assembly according to claim 3, wherein the inside of the vessel or the first vessel is depressurized before the tracer gas filling step.

[0020] The invention described in claim 8 is 7. The method for assessing damage to a fuel assembly according to claim 1, wherein He gas is used as the tracer gas.

[0021] The invention described in claim 9 is 9. The method for determining damage to a fuel assembly according to claim 8, wherein N2 gas is used as the non-tracer gas.

[0022] The invention described in claim 10 is A fuel assembly damage determination device for determining whether or not a fuel assembly of a nuclear fuel having a plurality of fuel rods is damaged, The device for determining damage to a fuel assembly comprises a sealable container for storing the fuel assembly, a tracer gas supply means, a non-tracer gas supply means and an exhaust means, each of which is connected to the container by a vent pipe, a drainage means connected to the container by a water pipe, valves for opening and closing each of the vent pipes and a valve for opening and closing the water pipe, a pressurizing means installed in the tracer gas supply means for pressurizing the tracer gas, and a tracer gas detector connected to the container.

[0023] The invention described in claim 11 is A fuel assembly damage determination device for determining whether or not a fuel assembly of a nuclear fuel having a plurality of fuel rods is damaged, The device for determining damage to a fuel assembly comprises a sealable container for storing the fuel assembly, a tracer gas supply means, a non-tracer gas supply means, and an exhaust means, each of which is connected to the container by a vent pipe, a drainage means connected to the container by a water pipe, valves for opening and closing each of the vent pipes, and a valve for opening and closing the water pipe, a pressure reducing means installed in the exhaust means for reducing the pressure inside the container, and a tracer gas detector connected to the container.

[0024] The invention described in claim 12 is 12. The fuel assembly damage assessment device according to claim 10 or 11, wherein the container is equipped with a heater.

[0025] The invention described in claim 13 is The device for determining damage to a fuel assembly as described in claim 10 or 11 is further characterized in that it further comprises a second container that is sealable and stores a fuel assembly, the non-tracer gas supply means and the exhaust means are each connected to the second container by a vent pipe, each vent pipe is provided with a valve for opening and closing the vent pipe, and further comprises a tracer gas detector connected to the second container.

[0026] The invention described in claim 14 is 14. The device for determining damage to a fuel assembly according to claim 13, wherein the second container is equipped with a heater.

[0027] The invention described in claim 15 is 12. The device for determining damage to a fuel assembly according to claim 10 or 11, characterized in that a storage container for transporting the fuel assembly to a reprocessing facility is used as a container for storing the fuel assembly. Effect of the Invention

[0028] According to the present invention, a fuel assembly damage determination technique can be provided that can perform inspection on a fuel assembly basis and determine the presence or absence of damage even for inspection objects in which FP cannot be detected. [Brief description of the drawings]

[0029] [Figure 1] 1 is a diagram showing a configuration of a damage determination device for a fuel assembly according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In the present invention, the presence or absence of damage to a fuel assembly is determined not by the detection of FPs emitted from inside the fuel rods as in the conventional method, but by the detection of a tracer gas such as He.

[0031] Specifically, the fuel assembly to be inspected is placed in a sealed container in an atmosphere of tracer gas at a pressure higher than the internal pressure of the fuel rod that would be expected if the fuel rod were damaged, for a predetermined period of time, and then left in an atmosphere from which the tracer gas has been removed, for a predetermined period of time.

[0032] At this time, if the fuel rod is damaged, ventilation will occur between the inside and outside of the fuel rod through the damaged portion, whereas if there is no damage, there will be no ventilation between the inside and outside of the fuel rod. Therefore, by making the pressure of the tracer gas atmosphere higher than the internal pressure of the fuel rod that would be assumed if the fuel rod were damaged, the tracer gas will penetrate into the inside of the fuel rod if there is a damage, and if there is no damage, the tracer gas will not penetrate regardless of the pressure of the tracer gas atmosphere.

[0033] Thereafter, the fuel assembly is left in an atmosphere from which the tracer gas has been removed for a predetermined period of time, whereby the tracer gas filled inside the damaged fuel rod diffuses outside the fuel rod, i.e., into the atmosphere from which the tracer gas has been removed inside the sealed vessel.

[0034] After the sample is left as it is, the presence or absence of a tracer gas in the atmosphere is checked, and if a tracer gas is detected, it is determined that there is damage, and if no tracer gas is detected, it is determined that there is no damage.

[0035] Alternatively, the concentration of the tracer gas in the atmosphere is measured immediately after the start of leaving it and after the end of leaving it, and if the concentration after leaving it is higher than that immediately after leaving it, it is determined that there is damage, and if the concentration after leaving it is lower than that immediately after leaving it, it is determined that there is no damage.

[0036] In this way, the present invention utilizes the presence or absence of detection of a tracer gas such as He, so that it is possible to determine the presence or absence of damage to a fuel assembly even when it is difficult to detect FP. Also, since the inspection can be performed on a fuel assembly basis, the inspection can be performed efficiently.

[0037] Hereinafter, the present invention will be described based on an embodiment with reference to the drawings.

[0038] [1] First embodiment This embodiment relates to a technology for determining damage to a fuel assembly in which a step of leaving the fuel assembly in a tracer gas atmosphere and a step of leaving the fuel assembly in a non-tracer gas atmosphere are performed in one container.

[0039] 1.Damage determination device Fig. 1 is a diagram showing the configuration of a damage determination device for a fuel assembly according to this embodiment. In Fig. 1, 1 is a sealable container, 2 is a fuel assembly stored in the container 1, 3 is a vacuum pump as an exhaust means, 4 is a drainage pump as a drainage means, 5 is a pressurizer, 6 to 10 are valves for opening and closing the vent pipe, and 11 is a valve for opening and closing the water pipe. Although not shown in the figure, a tracer gas detector is provided outside the system. In this example, He gas is used as the tracer gas, and N2 gas is used as the non-tracer gas.

[0040] The tracer gas and non-tracer gas are not particularly limited as long as they are chemically stable with respect to the contents of the fuel assembly, but He gas is suitable as a tracer gas because it has excellent properties of passing through even very fine holes. In addition, N2 gas is a high-pressure gas that can be used as a general utility in nuclear power plants, so it is suitable as a non-tracer gas. These gases are supplied using known methods, such as adjusting the pressure to a specified level from a high-pressure cylinder.

[0041] The tracer gas supply means, the non-tracer gas supply means, and the vacuum pump 3 are each connected to the vessel 1 via a vent pipe. In addition, the pressurizer 5 is connected via a vent pipe between the vessel 1 and a valve 6 of the vent pipe connecting the tracer gas supply means and the vessel 1. In addition, the drainage pump 4 is connected to the vessel 1 via a water pipe.

[0042] 1, a water tank is used and the container 1 is placed in water, so that water is present in the container 1 at the stage of supplying the tracer gas, and this water must be drained. Therefore, for example, when the tracer gas is supplied into the container 1, the water present in the container 1 is drained by the drain pump 4, but the water in the container 1 may be drained by supplying a third gas (a gas other than the tracer gas) before the tracer gas is supplied.

[0043] However, when the height difference between the lower end of the fuel rods arranged in the vessel 1 and the drainage pump 4 exceeds 10 m, the suction force of the drainage pump 4 alone is not enough to suck up and drain the water in the vessel 1 until the fuel rods are exposed to the tracer gas, due to the relationship with the atmospheric pressure. Therefore, in such a case, it is preferable to apply pressure to the tracer gas, non-tracer gas or third gas by the pressurizer 5 to apply pressure to the water in the vessel 1, thereby pushing the water in the vessel 1 out to the suction side (suction side) of the drainage pump 4.

[0044] In Fig. 1, a water tank is used and the container 1 is placed in water, but it may be placed in air, although a water tank is preferable.

[0045] 2. Damage determination method (1) Fuel assembly containment process First, the container 1 is opened and the fuel assemblies 2 are stored in the container 1. After the storage is completed, the container 1 is closed. The container 1 is generally filled with water for cooling.

[0046] (2) Tracer gas filling process Next, after all the valves are closed, valves 6 and 11 are opened and the drainage pump 4 is started. This drains the water from the vessel 1 while filling it with He gas, and fills the entire area around the fuel assembly 2 with tracer gas (He gas). Next, valves 6 and 11 are closed and the drainage pump 4 is stopped, and then the pressurizer 5 is started to increase the pressure in the vessel 1 to a predetermined pressure higher than the internal pressure of the fuel rods.

[0047] (3) Tracer gas atmosphere exposure process After filling the fuel assembly with the tracer gas, the fuel assembly is left to stand for a specified period of time. The period of time is determined based on the results of an investigation into the time required for the tracer gas to be injected into the fuel assembly, using fuel assemblies that are known to be damaged.

[0048] (4) Tracer gas removal process After a predetermined time has elapsed, valves 8-10 are opened and vacuum pump 3 is started to remove the tracer gas from inside container 1 and the vent pipe. If the container is in a water tank, the container 1 may be opened and refilled with cooling water to remove the tracer gas. This operation is carried out until tracer gas is no longer detected in container 1 or for a predetermined time.

[0049] (5) Non-tracer gas filling process Next, valves 8 to 10 are closed, and after the vacuum pump 3 is stopped, the valve 7 is opened and non-tracer gas (N2 gas) is filled into the container 1. After filling is completed, the valve 7 is closed.

[0050] (6) Non-tracer gas atmosphere exposure process After the atmospheric gas replacement, the fuel assembly is left for a prescribed period of time. The period of time is determined as appropriate based on the results of an investigation into a fuel assembly known to be damaged, in order to determine the time required for the tracer gas injected into the fuel assembly 2 to leak out of the fuel assembly 2.

[0051] If the vessel 1 is equipped with a heater, it is preferable to operate the heater to heat the non-tracer gas during the exposure to the non-tracer gas atmosphere. By heating the non-tracer gas, the fuel assemblies are heated and the leakage of the tracer gas is promoted, thereby shortening the exposure time.

[0052] It is also preferable to equip the vessel with a circulation device and circulate the non-tracer gas in the vessel. This allows the entire fuel assembly to be heated to a constant temperature. This also prevents uneven distribution of leaked tracer gas and homogenizes the composition of the gas in the vessel, making it possible to determine the presence or absence of leakage with high accuracy.

[0053] (7) Damage determination process In the tracer gas removal process (4), when the tracer gas is removed until it is no longer detectable, after leaving it in a non-tracer gas atmosphere for a specified time, a tracer gas detector is used to check whether tracer gas is detected in the container 1, and if it is detected, it is determined that there is damage, and if it is not detected, it is determined that there is no damage. The presence or absence of tracer gas is determined by sampling the gas discharged from the container 1 with a syringe and then subjecting the sampled gas to a tracer gas detector.

[0054] On the other hand, in the tracer gas removal process, when the tracer gas is exhausted for a specified time, the concentration of the tracer gas in the atmospheric gas is measured using a tracer gas detector immediately after the start of leaving the non-tracer gas atmosphere and after the end of leaving it, and if the concentration after the end of leaving it is high, it is determined that there is damage, and if the concentration after the end of leaving it is lower than the concentration immediately after the start of leaving it, it is determined that there is no damage.

[0055] [2] Second embodiment This embodiment differs from the first embodiment in that the tracer gas atmosphere leaving step and the non-tracer gas atmosphere leaving step of the fuel assembly are performed in separate containers. Only the differences from the first embodiment will be described below.

[0056] 1.Damage determination device The damage assessment device of this embodiment is further provided with a second container in addition to the damage assessment device of the first embodiment, and is provided with two sealable containers. The damage assessment device of this embodiment differs from the first embodiment in that a tracer gas detector is connected to the second container. Note that a tracer gas supply means is not connected to the second container. Also, when the second container is placed in the air, a drainage pump is not connected to the second container.

[0057] It is preferable that the second container is equipped with a heater and a circulation device. By operating the heater in the non-tracer gas atmosphere standing step to heat the non-tracer gas, the standing time can be shortened, and by operating the circulation device, the tracer gas can be detected with higher accuracy.

[0058] It is also possible to store multiple fuel assemblies in a container for filling with tracer gas, pressurize multiple assemblies simultaneously, and then transfer each one to another container for measurement.

[0059] 2. Damage determination method Up to the stage of leaving in the tracer gas atmosphere, the same steps as in the first embodiment are carried out. After leaving in the tracer gas atmosphere, the container 1 is opened, the fuel assembly 2 is removed from the container 1, and transferred to a second container.

[0060] After the fuel assembly 2 is transferred to the second container, the second container is sealed and non-tracer gas (N2 gas) is supplied to the second container while the drainage pump 4 is started to drain the water, creating a non-tracer gas atmosphere inside the second container. Note that if the second container is placed in the air, drainage is not necessary.

[0061] After the second container is placed in a tracer gas-free atmosphere, the process of leaving the container in a non-tracer gas atmosphere and the process of determining whether or not there is damage are carried out in the same manner as in the first embodiment.

[0062] According to this embodiment, since it is not necessary to replace the atmospheric gas from a tracer gas atmosphere to a non-tracer gas atmosphere, the time required for the determination can be shortened.

[0063] [3] Third embodiment This embodiment differs from the first and second embodiments using a pressurizer 5 and the like in that a vacuum pump 3 is used to fill a tracer gas into a vessel 1 that contains a fuel assembly 2. That is, in this embodiment, as described below, by using a vacuum pump 3, it is possible to fill a damaged fuel rod with a tracer gas without applying high pressure to the vessel 1 and the like. Therefore, this embodiment has the advantage that it is not necessary to use a pressure vessel for the vessel 1 and the like.

[0064] In this embodiment, after draining the water from the vessel 1 in the same manner as in the first embodiment, the vessel 1 is depressurized by the vacuum pump 3 before introducing the tracer gas. The vessel 1 is evacuated until the internal pressure of the fuel rod is sufficiently low (for example, 0.1 atmA = -0.9 atmG) based on the exhaust speed that can be calculated from the expected size of the defect in the damaged fuel rod. After that, when the tracer gas is introduced into the vessel 1 at a not so high pressure (for example, 0.5 atmA = -0.5 atmG), the tracer gas is automatically filled into the damaged fuel rod because the internal pressure of the damaged fuel rod is lower.

[0065] [4] Effects of the present invention As described above, in the present invention, the presence or absence of damage to a fuel assembly is determined not by the presence or absence of detection of FPs emitted from inside the fuel rods as in the conventional method, but by the presence or absence of detection of a tracer gas such as He. Therefore, even when it is difficult to detect FPs, the presence or absence of damage to the fuel assembly can be determined.

[0066] Furthermore, since the inspection can be performed on a fuel assembly basis, the inspection can be performed efficiently.

[0067] Furthermore, when inspecting fuel assemblies that have been stored in a storage container for a long period of time and cooled for transportation to a reprocessing facility, the storage container can be used as the first pressurization container to simultaneously pressurize the multiple fuel assemblies, enabling efficient inspection.

[0068] Although the present invention has been described above based on the embodiment, the present invention is not limited to the above embodiment. Various modifications can be made to the above embodiment within the same and equivalent scope of the present invention. [Explanation of symbols]

[0069] 1 container 2 Fuel assembly 3. Vacuum pump 4. Drainage pump 5. Pressurizer 6 to 11 valves

Claims

1. A method for determining whether or not a fuel assembly containing a plurality of fuel rods is damaged, comprising: The fuel assembly to be inspected is placed in a sealed container for a predetermined period of time in an atmosphere of tracer gas at a pressure higher than the internal pressure of the fuel rod that would be expected if the fuel rod were damaged, and then the fuel assembly is left for a predetermined period of time in an atmosphere from which the tracer gas has been removed; After the test, the presence or absence of tracer gas in the atmosphere is checked. If tracer gas is detected, it is determined that there is damage, and if no tracer gas is detected, it is determined that there is no damage. Alternatively, a method for determining damage to a fuel assembly, which measures the concentration of a tracer gas in the atmosphere immediately after the start of leaving it alone and after the end of leaving it alone, and determines that there is damage if the concentration after leaving it alone is higher than that immediately after the start of leaving it alone, and determines that there is no damage if the concentration after leaving it alone is lower than that immediately after the start of leaving it alone.

2. 2. The method for determining damage to a fuel assembly according to claim 1, wherein an internal pressure of the fuel rod assumed when the fuel rod is damaged is the same as the pressure around the fuel assembly before the fuel assembly is placed in the tracer gas atmosphere in the sealed vessel.

3. a fuel assembly containing step of containing the fuel assembly to be inspected in a sealable container; a tracer gas filling process in which, after the fuel assemblies are stored, a tracer gas is filled into the container to create a tracer gas atmosphere in the container at a pressure higher than the internal pressure of the fuel rods that would be assumed if the fuel rods were damaged; a step of leaving the sample in a tracer gas atmosphere for a predetermined period of time after filling the sample with the tracer gas; a gas replacement step of evacuating the tracer gas from the container after the container is left in the tracer gas atmosphere, and replacing the atmosphere in the container with a non-tracer gas atmosphere that does not contain the tracer gas; and a non-tracer gas atmosphere leaving step of leaving the non-tracer gas atmosphere for a predetermined period of time after replacing the non-tracer gas atmosphere. Investigate the presence or absence of tracer gas in a non-tracer gas atmosphere after leaving it in a non-tracer gas atmosphere. Alternatively, the method for determining damage to a fuel assembly according to claim 1, further comprising the step of measuring the tracer gas concentration in the non-tracer gas atmosphere immediately after the start of exposure to the non-tracer gas atmosphere and after the end of exposure to the non-tracer gas atmosphere.

4. 4. The method for determining damage to a fuel assembly according to claim 3, wherein the internal pressure of the fuel rod assumed when the fuel rod is damaged is the same as the pressure in the container before the tracer gas is filled in the container.

5. a fuel assembly containing step of containing the fuel assembly to be inspected in a sealable first container; a tracer gas filling step of filling the first container with a tracer gas after the containment, and creating a tracer gas atmosphere in the first container at a pressure higher than the internal pressure of the fuel rod that would be assumed if the fuel rod were damaged; a step of leaving the sample in a tracer gas atmosphere for a predetermined period of time after filling the sample with the tracer gas; a fuel assembly transfer step of transferring the fuel assembly to a second container after being left in the tracer gas atmosphere, and making the atmosphere in the second container a non-tracer gas atmosphere that does not contain the tracer gas; and a step of leaving the device in a non-tracer gas atmosphere for a predetermined period of time after the device is moved. Investigate the presence or absence of tracer gas in a non-tracer gas atmosphere after leaving it in a non-tracer gas atmosphere. Alternatively, the method for determining damage to a fuel assembly according to claim 1, further comprising the step of measuring the tracer gas concentration in the non-tracer gas atmosphere immediately after the start of exposure to the non-tracer gas atmosphere and after the end of exposure to the non-tracer gas atmosphere.

6. 6. The method for determining damage to a fuel assembly according to claim 5, wherein the internal pressure of the fuel rod assumed when the fuel rod is damaged is the same as the pressure in the first vessel before the tracer gas is filled in the first vessel.

7. 7. The method for assessing damage to a fuel assembly according to claim 3, wherein the inside of the vessel or the first vessel is depressurized before the tracer gas filling step.

8. 7. The method for assessing damage to a fuel assembly according to claim 1, wherein He gas is used as the tracer gas.

9. The non-tracer gas is N ２ 9. The method for assessing damage to a fuel assembly according to claim 8, wherein a gas is used.

10. A fuel assembly damage determination device for determining whether or not a fuel assembly of a nuclear fuel having a plurality of fuel rods is damaged, a tracer gas detector connected to the container, the tracer gas detector being connected to the container through a water pipe; a valve for opening and closing each of the vent pipes; a pressure sensor connected to the tracer gas detector and a pressure sensor connected to the container;

11. A fuel assembly damage determination device for determining whether or not a fuel assembly of a nuclear fuel having a plurality of fuel rods is damaged, a tracer gas supply means, a non-tracer gas supply means and an exhaust means, each of which is connected to the container by a vent pipe; drainage means, which is connected to the container by a water pipe; valves for opening and closing the respective vent pipes and a valve for opening and closing the water pipe; pressure reduction means, which is installed in the exhaust means and which reduces the pressure inside the container; and a tracer gas detector, which is connected to the container.

12. 12. The fuel assembly damage assessment device according to claim 10, wherein the container is equipped with a heater.

13. 12. The fuel assembly damage determination device according to claim 10 or 11, further comprising a second container that is sealable and stores a fuel assembly, the non-tracer gas supply means and the exhaust means are each connected to the second container by a vent pipe, each vent pipe is provided with a valve for opening and closing the vent pipe, and further comprising a tracer gas detector connected to the second container.

14. The fuel assembly damage assessment device according to claim 13, wherein the second vessel is equipped with a heater.

15. 12. The device for determining damage to a fuel assembly according to claim 10 or 11, wherein a storage container for transporting the fuel assemblies to a reprocessing facility is used as a container for storing the fuel assemblies.

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