JPH09264992A - Method for radiating radioactive ray and cask vessel for storing spent nuclear fuel used for the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to improve the preventing effect of abnormally high temperature at a center in a cask vessel by radiating the radioactive ray from spent nuclear fuel in a storage chamber to sample to be radiated in a cavity. SOLUTION: A cask vessel 1 is located at the spent fuel storage site of a nuclear power plant, bolts 8 are removed, an upper cover 5 is opened, spent fuel assembly is contained in a storage chamber A, the cover 5 is closed, and sealed by the bolts 8. The radiation heat due to the heat of the assembly 6 in the chamber A is radiated to the cavity 7 at the inside of the inner peripheral wall 3 in this state. Since the vessel 1 has such a constitution, γ-ray and radiation heat from the assembly 6 can not only be used for the radiation of various samples but also the center area of the vessel can be formed in a cavity in the non-disposed area of the assembly, and the effect of preventing the abnormal rise of the temperature in the cast can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation irradiation method that effectively uses spent nuclear fuel and a cask container used for the method.

[0002]

2. Description of the Related Art Spent nuclear fuel generated from a nuclear power plant still generates radiation and heat due to residual radioactivity, and it is necessary to prevent environmental pollution due to these. It is stored by a wet storage method in which it is immersed in water in a storage pool, or a dry storage method in which it is stored in a radiation shielded heat insulating container device (cask system).

Of these, if the storage scale is small, it is economically advantageous to use the cask system, and in this case, the spent nuclear fuel storage cask system is also used for storage in the nuclear power plant.

Conventionally, various structures have been proposed as a spent nuclear fuel storage cask system, but in general, a concrete cask system is often used. Not only is concrete excellent as a neutron shield, it is cheaper than other barriers, and it also provides the necessary strength and heat insulation as a structure, so it is widely used as a radiation shield for nuclear facilities.

However, the strength of concrete is apt to be lowered due to the influence of heat, and there is a problem that the strength is locally lowered in the heat-affected zone to cause cracks and the like particularly when it is placed locally at a high temperature.

For this reason, when the spent nuclear fuel that still generates heat is stored in the concrete cask system, a heat removal system is attached to avoid an abnormal temperature rise inside the cask. Special measures are needed to eliminate adverse effects.

For example, FIG. 5 shows an example of a concrete cask system including a ventilation type heat removal system which has been generally used conventionally. This cask system is a cylindrical multi-shielded sealed cask container (MSB) 51 in which a spent nuclear fuel storage chamber partitioned by a sleeve into a plurality of compartments is formed for stable storage of a plurality of spent fuel assemblies. And a cylindrical concrete outer container 5 for accommodating the sealed cask container 51 therein.
2 is provided, and an air flow path is formed between the sealed cask container 51 and the concrete outer container 52 that covers the outer periphery thereof,
In this air flow path, a lower air inlet 53 and an upper air outlet 5 are provided.
The structure is such that natural convection is generated via

[0008]

In the conventional concrete cask system as shown in FIG. 5, a hermetically-sealed cask container 51 has a multi-shield structure and a concrete outer container 52 has a concrete shell having a sufficient thickness. Although the leakage of radiation to the outside is suppressed below the safety standard level, a plurality of fuel assemblies are densely arranged in a cylindrical sealed cask container 51 housed in a closed space inside a concrete outer container 52. Because of this structure, the density of radiation generated from the fuel assembly during storage is considerably high in the central portion of the sealed cask container 51, and the heat generated thereby causes the temperature of the central portion of the cask container 51 to be abnormally high. May be.

For this reason, it is unavoidable to install a radiation shielding member or the like inside the sealed cask container 51. However, since the sealed cask container 51 is only cooled at its outer peripheral portion by natural convection, the cask is not sealed. There is a problem in that it is difficult to effectively cool the central region of the container 51, which limits the number of fuel assemblies that can be accommodated in the sealed cask container 51.

The object of the present invention is to effectively prevent the temperature rise in the central portion of the cask container, and at the same time, to effectively utilize the radiation from the spent nuclear fuel in the cask, which has conventionally only shielded wastefully. A radiation irradiation method and a cask container for storing spent nuclear fuel used therefor are provided.

[0011]

In order to solve the above-mentioned problems, a radiation irradiation method according to the invention of claim 1 is a cavity opened to the outside so as to be surrounded by a spent nuclear fuel storage chamber through a partition wall. Using a cask container for storing spent nuclear fuel having, the irradiation target sample is positioned in the cavity with the spent nuclear fuel stored in the storage chamber, and the radiation emitted from the spent nuclear fuel in the storage chamber is stored. Irradiation is performed on the sample to be irradiated in the cavity.

A spent nuclear fuel storage cask container according to a second aspect of the present invention is provided with a cavity surrounded by a spent nuclear fuel storage chamber via a partition wall, and a sample to be irradiated is introduced into the cavity. It is characterized in that an opening for is provided.

A spent nuclear fuel storage cask container according to a third aspect of the present invention is the spent nuclear fuel storage cask container according to the second aspect of the present invention, wherein the storage chamber has an annular storage by an inner peripheral partition wall and an outer peripheral partition wall. A space is formed, and the hollow portion forms a concentric central inner hole surrounded by the inner peripheral partition wall of the annular storage space.

Further, the spent nuclear fuel storage cask container according to the invention of claim 4 is the spent nuclear fuel storage cask container according to the invention of claim 2 or 3, wherein the cartridge container for accommodating an irradiation target sample therein is the cavity. It is characterized in that it is detachably inserted into the section.

Furthermore, the spent nuclear fuel storage cask container according to the invention of claim 5 is the spent nuclear fuel storage cask container according to the invention of claim 4, wherein an auxiliary radiation source is provided inside the cartridge container. It is a feature.

The present invention is effective for the purpose of irradiating various kinds of samples to be irradiated with γ-rays. Examples of such applications include sterilization and sterilization of medical tools and instruments, packaging containers for biochemistry, raw materials for preparations, crosslinking reaction of plastic materials, suppression of germination or growth of plants, and insecticidal activities.

That is, according to the present invention, the cask container for storing spent nuclear fuel is not used only as a waste storage container, but is effectively utilized as a radiation irradiation device for γ-rays, etc. The cask container is provided with a cavity open to the outside so that the cavity is used as a region for radiation irradiation and a non-nuclear fuel arrangement region to prevent abnormal temperature rise in the spent nuclear fuel storage chamber. The basic idea is to do.

The spent nuclear fuel storage cask container according to the present invention is externally surrounded by a bulkhead by a spent nuclear fuel storage chamber when compared with a multiple shield (MSB) type sealed cask container in a conventional concrete cask system. It is unique in that it has an open cavity.

That is, in the spent nuclear fuel storage cask container according to the present invention, the partition wall separating the spent nuclear fuel storage chamber and the cavity from each other irradiates at least the cavity opened to the outside with the radiation from the vessel. It has a material structure that allows it to pass therethrough with a strength that satisfies the purpose, and the outer shell excluding this partition has a radiation shielding structure such as a multiple shielding (MSB) type.

In this case, specifically, for example, the partition wall is generally made to have a γ-ray transmissive partition wall structure having a neutron shielding function, and the cavity portion isolated from the spent nuclear fuel storage chamber by such partition wall is used. By providing it, the inside of this cavity can be used as a γ-ray irradiation space.

One or a plurality of cavities may be provided, and the location of the spent nuclear fuel storage cask container may be selected depending on the shape of the cask container to a portion where concentration of radiation density inside should be avoided. For example, in the case of a tubular spent nuclear fuel storage cask container intended for a fuel assembly of a normal light water reactor, it is provided as a concentric cavity portion extending along the central axis of the cask container.

In any case, since the cavity portion is surrounded by the spent nuclear fuel storage chamber through the partition wall, the cavity portion in which the spent nuclear fuel does not exist is secured in the inner region of the spent nuclear fuel storage chamber. Therefore, the inside of the spent nuclear fuel storage chamber will not have an abnormally high temperature. Although the cavity is not exposed to abnormally high temperatures, it still receives radiant heat from the surrounding spent nuclear fuel storage chamber. Alternatively, when irradiation with heat is not necessary, the sample to be irradiated may be introduced into the cavity while being covered with a radiation-transparent heat insulating material or in a container.

The cavity can be a bottomed or through hole having an opening located on the outer surface of the cask container at least at one end thereof, and the sample to be irradiated can be taken in and out through this opening. When the hollow portion is open at both end surfaces of the cylindrical cask container and penetrates in the axial direction, the irradiation target sample can be passed in one way from the opening at one end to the opening at the other end.

For example, in a cask container in which such a hollow portion is concentrically provided on the central axis, the spent nuclear fuel storage chamber has an annular storage space having the hollow portion as a central inner hole. . When this cask container is stored in a concrete outer container, an opening is also provided in the outer container at a location corresponding to the opening of the cavity so that the irradiation target sample can be put in and out of the cavity through both openings. When it is not used for irradiation, it is advisable to seal the opening of the outer container with a radiation shielding lid.

The sample to be irradiated can be put in and taken out of the cavity by various methods such as a method of suspending the sample to be irradiated by its own weight and a method of using a conveying means such as a conveyor device or a pulley device. Further, the sample to be irradiated may be put in or out of the cavity after being covered or wrapped in a package such as a container. Generally, the cartridge container containing the sample to be irradiated is removably inserted into the cavity. A method can be adopted.

The advantage of this method is that the irradiation time can be easily controlled by controlling the insertion time of the cartridge container into the cavity, and the end cover of the cartridge container is constructed as a radiation shielding structure. Therefore, by designing the end lid to close the opening of the cavity closely when the cartridge container is installed in the cavity, it is possible to empty the cask container when the cartridge container is installed. One of the advantages is that the amount of radiation that leaks from the body opening to the outside is limited to a very small amount.

When the sample to be irradiated is relatively densely placed in the cartridge container for irradiation, the dose in the central part of the cartridge container may be lower than that in the peripheral part. When irradiation of the sample to be irradiated in the cartridge container is required to be as uniform as possible, various auxiliary radiation sources, such as cobalt 60, are preferably provided in the cartridge container, preferably in substantially the center thereof, depending on the purpose of irradiation. It is also effective to arrange them.

As another method, it is also effective to dispose a reflecting member made of a desired radiation reflecting material such as a γ-ray reflecting material in the center of the cartridge container. The interior may be radially divided to form a plurality of parallel sample storage compartments, each along the axial direction.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an embodiment of the present invention. 1 (a) is a schematic vertical cross-sectional view of a spent nuclear fuel storage cask container in this example, and FIG. 1 (b) is FIG.
FIG. 2A is a cross-sectional view taken along line XX of FIG.
Corresponds to the vertical sectional view taken along the line YY of FIG. In all the drawings described below, the same or corresponding parts are designated by the same reference numerals.

The cask container 1 has an annular disc-shaped bottom wall 4 having a through-opening at its center, an outer peripheral wall 2 joined to the outer edge of the bottom wall 4, and a peripheral edge of the through-opening of the bottom wall 4. The container main body 1 has a concentric bottomed double-cylinder structure constituted by the inner peripheral wall 3 and the annular space between the outer peripheral wall 2 and the inner peripheral wall 3 of the container main body 1 is a plurality of used bodies. A spent nuclear fuel storage chamber A for storing the fuel assembly 6 in parallel with the axis is formed, and the inner hole surrounded by the inner peripheral wall 3 irradiates the irradiation target sample with radiation from the fuel assembly in the storage chamber A. A hollow portion 7 for forming is formed.

The inner peripheral wall 3 is provided with an inward flange protruding inward in the radial direction at the upper opening edge of the cavity 7, while the outer peripheral wall 2 is provided at the upper edge of the outer peripheral surface thereof. An outward flange is provided that projects radially outward. These flanges are provided with a plurality of bolt through holes at predetermined circumferential intervals.

On the upper edge of the container body 1 having such a flange structure, an annular disk-shaped upper cover 5 having a corresponding inward and outward flange structure is removably stacked with bolts 8, and the upper cover 5 is also attached. A seal ring 9 is provided between the container body 1 and the container body 1 at the bases of the inward and outward flanges, so that the storage chamber A is sealed by the upper lid 5 by tightening the bolt 8. ing. The hollow portion 7 of the cask container with the upper lid 5 attached is pierced in the axial direction by the central openings of the bottom wall 4 and the upper lid 5.

The outer peripheral wall 2, the bottom wall 4 and the upper lid 5 of the cask container 1 are radiation shielding walls for shielding radiation such as neutrons and γ rays from the inside of the storage chamber, while the inner peripheral wall 3 is A partition wall that blocks neutrons but allows γ-rays to pass through with an intensity at least according to the purpose of irradiation.

Although the specific structures of the lid and the wall are not particularly limited in the present invention, for example, the outer peripheral wall 2
As shown in FIG. 1 (b), each is an outer cylinder 10 made of steel.
It has a triple tube structure in which an intermediate tube 12 is concentrically arranged between the inner tube 11 and the inner tube 11, a neutron shielding material 13 is provided between the outer tube 10 and the intermediate tube 12, and a intermediate tube 12 is provided between the intermediate tube 12 and the inner tube 11. It has a multi-layered shielding structure (MSB) in which the γ-ray shielding materials 14 are respectively loaded. Further, the inner peripheral wall 3 is a steel inner cylinder 1 facing the cavity 7.
1a and a neutron shielding material 13 that covers the surface of the storage chamber A
It has a laminated structure with a.

The cask container 1 having such a structure is placed at a spent fuel storage site of a nuclear power plant, for example, and the bolt 8 is removed and the upper lid 5 is opened to store the spent fuel assembly 6 in the storage chamber A. It is housed inside, and the upper lid 5 is closed and sealed with bolts 8.

In this state, the cavity 7 inside the inner peripheral wall 3 is irradiated with γ-rays from the spent fuel assembly 6 in the storage chamber A, and the radiation heat generated by the spent fuel assembly 6 is also radiated. 7 is irradiated. The sample to be irradiated may be introduced into the cavity 7 through the central opening of the upper lid 5, and the sample to be irradiated may be subjected to γ-ray irradiation for a necessary time. For the introduction of this sample, for example, suspension by a bucket container or continuous conveyance by a conveyor can be adopted.

Since the cask container 1 of this example is provided with such a structure, it is possible not only to utilize γ-rays and radiant heat from the spent fuel assembly for irradiation of various samples, but also to use the conventional cask. In the system, the central region of the cask container where the temperature is abnormally high can be hollowed out as a region where the fuel assemblies are not arranged, and an effect of preventing an abnormal rise in the temperature inside the cask can be obtained.

2 and 3 show another example of the embodiment of the present invention. 2 (a) is a cross-sectional view of the cask container, FIG. 2 (b) is a vertical cross-sectional view of the irradiation target sample cartridge container mounted in the cavity of the cask container, and FIG. It is a longitudinal cross-sectional view of a state in which a cartridge container is mounted.

The cask container 1 of this example has almost the same structure as that shown in FIG. 1, but the inner peripheral wall 3 thereof is composed only of a steel inner cylinder such as stainless steel having no neutron shielding layer, It is also different in that the bottom wall 4 is disk-shaped giving a closed surface without a central opening. Therefore, the hollow portion in this case is a bottomed inner hole, and the cartridge container 20 is put into and taken out of the hollow portion through the central opening of the upper lid 5.

The cartridge container 20 comprises a cylinder whose main body has an outer diameter smaller than the inner diameter of the inward flange of the cask container 1. The main body cylinder is made of steel as shown in FIG. 2 (b). Inside the cylindrical body 23 made of neutron shielding material 13b
, The bottom part of which is closed with the neutron shielding material 13c as well, and the lid 22 of the neutron shielding structure can be detachably closed with the bolt 8 in the upper opening, and the handle 21 is provided on the upper portion of the lid 22. The protrusion 21a is attached to the lower surface of the handle 21.

Inside the cartridge container 20, the lid 22 is opened and the sample to be irradiated is put therein. After this, the lid 2
The cartridge container in which 2 is closed and sealed with bolts 8 is inserted into the cavity 7 from the bottom through the upper opening of the cask container 1.

At this time, the protrusion 21a provided on the lower surface side of the handle 21 is placed on the upper surface of the inward flange of the upper lid 5,
As a result, the load of the cartridge container 20 is supported by the cask container 1. In this way, the sample in the cartridge container 20 is irradiated with γ rays for a desired time. When the irradiation process is completed, the handle 21 is pulled upward to take out the cartridge container 20 from the cavity 7,
Another cartridge container is inserted into the cavity 7 instead.

In the case of this example, the upper lid 5 of the cask container 1
Since the opening of the cartridge container 20 is shielded by the lid 22 of the cartridge container 20, there is an effect that radiation leakage to the outside of the cask with the cartridge container 20 attached can be prevented, and like the example of FIG. Γ from fuel assembly
In addition to being able to irradiate the sample to be irradiated in the cartridge container 20 with radiation or radiant heat, the central region of the cask container, which has an abnormally high temperature in the conventional cask system, can be hollowed out as a non-arrangement region of the fuel assembly, and the temperature inside the cask becomes abnormal The effect of preventing the rise is also obtained.

FIG. 4 shows the cartridge container 2 shown in FIG.
A modified example in which the auxiliary radiation source 40 is provided in 0 will be described. In this case, a column-shaped auxiliary radiation source 40 made of cobalt 60 is attached at a position on the axial center of the cartridge container 20. The configuration other than this is the same as the example described in FIGS.

In the example of FIG. 4, with respect to the sample to be irradiated in the cartridge container 20, γ rays from the storage chamber A of the cask container 1 from the outer periphery and auxiliary radiation source 4 from the center side.
Since the gamma ray from 0 is irradiated, the cartridge container 20
Irregularity of irradiation intensity inside is alleviated.

FIG. 4 shows the case where the auxiliary radiation source 40 is attached on the axial center of the cartridge container 20, but the auxiliary radiation source 40 is assumed to extend over the entire inner length of the cartridge container 20. The present invention is not limited to this, and may be appropriately arranged at a position where the dose needs to be supplemented according to the loading state of the sample in the cartridge container 20.

In any case, the cartridge container 20
Has a primary purpose of using a sample to be irradiated for γ-ray irradiation. However, for example, an empty cartridge container 20 containing nothing therein is properly mounted in the cavity 7 It is needless to say that it can also be used exclusively for blocking the leakage of radiation from the opening of the above, and thereby the effect of preventing abnormal high temperature at the center of the cask can be obtained.

Further, in the example of FIG. 4, the cartridge container 20
Although the case where the auxiliary radiation source 40 is arranged inside is described, the γ-ray reflecting member may be arranged in a column shape instead of or in addition to this auxiliary radiation source 40, which is effective for alleviating the uneven dose distribution. is there.

[0049]

Example A cask container having the same structure as shown in FIG. 1 was used, and the γ-absorbed dose in the cavity when twelve spent fuel assemblies were loaded in the storage chamber was evaluated.
The spent fuel assemblies used are 12 types of 4 types of extracted burnups with 4 years of extraction cooling period. ORIGEN2 code is used for radiation source calculation and ANISN- is used for shielding calculation.
It was done with the JR code. Table 1 shows the evaluation results of the γ-absorbed dose with respect to the enrichment type of the loaded fuel assembly and the extracted burnup, together with the time T [hr] required to obtain the irradiation dose of 1 [kGy] in the cavity.

[0050]

[Table 1]

From the results in Table 1, the relationship between the γ dose in the cavity and the irradiation time can be understood depending on the type of the spent fuel assembly. Therefore, the irradiation process based on such evaluation results or actual measurement results can be performed. By performing process control, it is possible to determine the irradiation time corresponding to the required irradiation amount.

[0052]

As described above, according to the present invention, the cask container for storing spent nuclear fuel is not treated as a waste storage container, but is effectively utilized as a radiation irradiation device for γ-rays or the like from a new viewpoint. Since the cask container was provided with a cavity opened to the outside so as to be surrounded by the spent nuclear fuel storage chamber through the partition wall, this cavity was used as an area for radiation irradiation and spent nuclear fuel storage. It can be used as a nuclear fuel non-arrangement region for preventing an abnormal temperature rise in the chamber.

Therefore, by making a part of the cask container hollow, there is no abnormally high temperature inside the cask,
It can be applied to a concrete cask system to effectively prevent thermal deterioration of the concrete shielding shell, and moreover, irradiation of various materials can be performed with simple equipment.

[Brief description of drawings]

1A and 1B are explanatory views showing a cask container for spent nuclear fuel storage according to an example of an embodiment of the present invention, in which FIG. 1A is a schematic vertical cross-sectional view, and FIG. It is a cross-sectional view in the X-ray.

2A and 2B are explanatory views showing a cask container for spent nuclear fuel storage according to another example of the embodiment of the present invention, wherein FIG. 2A is a schematic cross-sectional view, and FIG. 2B is a schematic vertical section of a cartridge container. It is a side view.

FIG. 3 is a schematic vertical cross-sectional view of the cask container of FIG. 2A with the cartridge container of FIG. 2B attached.

4 is a schematic cross-sectional view showing a modified example in which an auxiliary radiation source is provided in the cartridge container of the example of FIG.

FIG. 5 is a partially cutaway perspective view showing an example of a concrete cask system having a conventional ventilation type heat removal system.

[Explanation of symbols]

 1: Cask container for spent nuclear fuel storage 2: Outer peripheral wall 3: Inner peripheral wall 4: Bottom wall 5: Top cover 6: Fuel assembly 7: Cavity part 8: Bolt 9: Seal ring 10: Outer cylinder 11, 11a: Inner cylinder 12: Intermediate cylinder 13, 13a, 13b, 13c: Neutron shielding material 14: γ-ray shielding material 20: Cartridge container 21: Handle 21a: Protrusion 22: Lid 40: Auxiliary radiation source

Claims (5)

[Claims] 1. A spent nuclear fuel storage cask container having a cavity opened to the outside so as to be surrounded by a spent nuclear fuel storage chamber through a partition wall, and the spent nuclear fuel is stored inside the storage chamber. In the state, the irradiation target sample is positioned in the cavity, and the irradiation target sample in the cavity is irradiated with the radiation emitted from the spent nuclear fuel in the storage chamber. 2. A spent nuclear fuel storage chamber is provided with a cavity surrounded by a partition wall, and the cavity has an opening for introducing a sample to be irradiated. Cask container for nuclear fuel storage. 3. The storage chamber forms an annular storage space by an inner peripheral partition wall and an outer peripheral partition wall, and the cavity portion forms a concentric central inner hole surrounded by the inner peripheral partition wall of the annular storage space. The spent nuclear fuel storage cask container according to claim 2, wherein 4. The spent nuclear fuel storage cask container according to claim 2 or 3, wherein a cartridge container for accommodating a sample to be irradiated is removably inserted into the cavity. 5. The spent nuclear fuel storage cask container according to claim 4, wherein an auxiliary radiation source is provided inside the cartridge container.