JPH05297189A - Receiving vessel of radioactive material - Google Patents

Abstract

PURPOSE:To provide a receiving vessel capable of minimizing the outer dimension and weight while keeping sufficient radiation shielding performance, or a receiving vessel capable of receiving a large quantity of a radioactive material under the same outer dimension or the same weight. CONSTITUTION:A cylindrical basket 13 arranged around a radioactive material such as a used nuclear fuel 4 or a high level radioactive waste is provided with radiation shielding effect, and the basket 13 is received in a cylindrical vessel body 12. As the material of the basket 13, a material having a concentration higher than that of the material of the vessel body 12, for example, uranium or an uranium alloy, is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radioactive substance storage container (hereinafter, simply referred to as a storage container) for storing, storing or transporting spent nuclear fuel, high level radioactive waste and other radioactive substances.

[0002]

2. Description of the Related Art Conventional storage containers usually have spent nuclear fuel (fuel assembly) and a high-level radioactive waste stored in a canister in a cylindrical container body 2 having cooling fins 1 formed on the outer periphery thereof. There is one in which a cylindrical basket 3 holding a radioactive substance 4 such as an object is inserted. As the container body 2, forged carbon steel, ductile cast iron, a multilayer body of lead and stainless steel, or the like is used.

[0003]

However, in the conventional storage container, the basket 3 physically holds the radioactive material 4 such as spent nuclear fuel and high-level radioactive waste, and the decay heat generated from the radioactive material 4 is retained. For the purpose of quickly dissipating nuclear fuel, and in the case of spent nuclear fuel, to suppress the nuclear critical state, radiation emitted from radioactive materials such as spent nuclear fuel and high-level radioactive waste, such as gamma rays. Since the container is shielded by the container body 2 itself, there are the following problems.

That is, the outer size or weight of the storage container is limited by the size of the entrance / exit of a nuclear power plant or the like that handles them, or the lifting capacity of a crane, etc. In order to provide sufficient shielding performance, there are problems that the outer dimensions of the container body 2 and thus the storage container become large, and the weight of the storage container becomes large.

Further, when storing radioactive materials such as spent nuclear fuel and high-level radioactive waste, which emit a large amount of radiation, the storage amount should be reduced below a predetermined value to ensure safety. It must be located on the center side, or another container body 2 having a large shielding function must be prepared to store the radioactive materials such as spent nuclear fuel and high-level radioactive waste in the storage container. However, there is a problem that not only a plurality of different storage containers are required, but also management thereof (for example, a dedicated transport trailer is required for each different type of storage container) becomes complicated.

Further, since the container body 2 is required to have not only radiation shielding performance but also mechanical performance and fire resistance performance,
There is a problem that the material used is limited, and in order to provide necessary and sufficient shielding performance, the thickness of the container main body 2 becomes large, and the external dimensions and weight increase.

The present invention has been made in view of the above circumstances, and has a storage container capable of reducing external dimensions and weight while having necessary and sufficient radiation shielding performance, or having the same external dimensions. An object is to provide a storage container capable of storing a large amount of radioactive material under the same weight.

[0008]

The container according to claim 1 of the present invention provides a radiation shielding effect to a cylindrical basket arranged around radioactive materials such as spent nuclear fuel and high level radioactive waste. It is characterized in that the basket is housed in a cylindrical container body.

A storage container according to a second aspect of the present invention is characterized in that, in the storage container according to the first aspect, a material having a density higher than that of the material of the container body is used as the material of the basket.

A storage container according to a third aspect of the present invention is the storage container according to the first aspect, characterized in that uranium or a uranium alloy is used as a material of the basket.

[0011]

According to the storage container of the first aspect of the present invention, since the basket is provided with the radiation shielding effect, it is possible to reduce the burden of the shielding performance required for the container body. The thickness of the container body can be reduced, and the outer dimensions and weight of the container body can be reduced. Moreover, one kind of container body is prepared, and a plurality of baskets having various radiation shielding functions are prepared, and the basket can be appropriately selected and used according to the radiation dose of the spent nuclear fuel. As compared to the case where a plurality of different storage containers are prepared as described above, the number of storage containers can be reduced and management becomes easy. Further, since the basket is provided with the radiation shielding performance, the radiation shielding performance of the container body may be supplementary, and the container body may be provided mainly with mechanical performance and fire resistance performance. Further, it is possible to perform material setting with priority given to fire resistance performance, to optimize the wall thickness of the container body, and to reduce the outer dimensions and weight of the container body.

According to the storage container of the second aspect of the present invention, since the material of the basket has a density higher than that of the material of the container body, the gamma ray shielding performance can be enhanced. Moreover, since a basket with high shielding performance is arranged inside the container body, when a container body with the same shielding performance with the same material as the basket is provided in the container body, In comparison, the weight of the storage container can be reduced.

According to the storage container of the third aspect of the present invention, since uranium or a uranium alloy is used as the material of the basket, the gamma ray shielding performance can be enhanced due to the high density of uranium. Moreover, the uranium used in the basket can be obtained by using, as a raw material, depleted uranium obtained in the uranium enrichment process, which has a low utility value at present. It does not increase the manufacturing cost.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

The storage container 10 of this embodiment is shown in FIGS.
As shown in FIG. 1, a cylindrical basket 13 in which a lattice 15 for accommodating the spent nuclear fuel 4 is formed, and this basket 1
3 has a cylindrical container body 12 housed therein. On the outer peripheral surface of the container body 12, fins 11 for cooling are formed as in the conventional case.

For the container body 12, the same material as the conventional one can be selected, but in this embodiment, forged carbon steel (density: 7.85 g / cubic centimeter) is exemplified.

Various relatively high density materials can be selected for the material of the basket 13, but in this embodiment, SU is used.
S304 (density 7.9 g / cubic centimeter),
Copper (density 8.9 grams / cubic centimeter), lead (density 11.34 grams / cubic centimeter), uranium (density 19.0 grams / cubic centimeter) or tungsten (density 19.3 grams / cubic centimeter).
Is illustrated.

The thickness of the basket 13 is set larger than that of the conventional basket 3 so that a predetermined shielding performance can be obtained, and the thickness of the container body 12 is predetermined mechanical. The thickness dimension is set smaller than that of the conventional container body 2 to the extent that strength and auxiliary shielding performance are obtained, but in the present embodiment, it is 1/2 of the thickness of the conventional container body. It is thick.

Next, in Table 1, the container outer diameter ratio and the container weight ratio when the above various materials were used as the materials of the basket 13 were determined and compared with the above-mentioned conventional storage container.

[0020]

[Table 1]

Here, as a conventional storage container, when the predetermined spent nuclear fuel is stored, the legal radiation shielding performance (2 millisievert per hour or less on the storage container surface, 100 micrometer at a position 1 m from the storage container surface) Sievert per hour or less), the diameter D1 of the lattice portion in which the spent nuclear fuel shown in FIG. 4 is stored is 120 cm, and the outer diameter D2 is 1
80 cm, that is, a container body having a thickness of 30 cm was used. Each example shown in Table 1 is
In addition to using the materials in the table for the basket 13, as shown in FIG. 2, the diameter of the lattice portion in which the spent nuclear fuel is stored is the same as the conventional D1, and a cast carbon with a constant thickness of 15 cm is provided outside the basket 13. The tubular container body 12 made of steel is arranged, and the outer diameter of the container body 12 is D2 'as shown in FIG.
It is what The required thickness T in the table indicates the thickness of the basket 13 when both the basket 13 and the container body 12 are intended to satisfy the same shielding performance as the conventional storage container. The outer diameter ratio of the container in the table means the outer dimension D of the container body 12 in each example with respect to the outer dimension D3 (see FIG. 4) of the container body in the comparative example.
3 '(see FIG. 2). Further, the container weight ratio in the table means the ratio of the weight of the storage container of each example to the weight of the storage container of the comparative example.

As shown in Table 1, the required thickness T generally decreases as the density of the material used increases. The tendency differs slightly depending on the difference in the attenuation coefficient for the gamma ray per mass of the material used. Therefore, the container outer diameter ratio also decreases as the density of the material used increases, and in this embodiment,
The container weight ratio is minimum when the material used is uranium. From the above results, it is understood that uranium is the most suitable material for the basket 13 in this embodiment.

In the above embodiment, the basket 1
Although uranium (metal) is used as the material of No. 3, a uranium alloy in which an additive having a neutron absorbing effect such as boron or cadmium is added to uranium can be used. With these additives, the basket 13 (including the lattice portion 15) can also function as an absorber that absorbs neutrons emitted from the spent nuclear fuel.

A uranium alloy obtained by adding additives such as lead, tin, copper and iron to uranium can also be used. These additives improve the structural strength of the basket, the corrosion resistance, the heat transfer characteristics, and the manufacturing method.

Further, in Table 2, a storage container using uranium as the material of the basket 13 (same condition as in Example 4 of Table 1)
And a conventional storage container using uranium of the same thickness in the central portion of the container body.

[0026]

[Table 2]

As shown in Table 2, when uranium having the same thickness has the same radiation shielding effect, when uranium is used for the basket, the weight of the container is larger than that when uranium is used for the container body. It turns out that can be reduced.
For example, when the weight of the conventional storage container is 100 tons, according to the present embodiment, the weight of 3 tons can be reduced, and the crane capacity can be increased by this amount, and the radioactive substance can be added in excess. Can be stored in.

[0028]

As described above, according to the first aspect of the present invention.
According to the storage container described above, a cylindrical basket disposed around radioactive materials such as spent nuclear fuel and high-level radioactive waste is provided with a radiation shielding effect, and the basket is provided in the cylindrical container body. Since it is stored, it has the following effects.

That is, since the basket is provided with a radiation shielding effect, it is possible to reduce the burden of the shielding performance required for the container body, and it is possible to reduce the thickness of the container body. The outer dimensions and weight of the storage container can be reduced.

Moreover, one kind of container main body is prepared and a plurality of baskets having various radiation shielding functions are prepared, and the basket is prepared according to the radiation dose of radioactive materials such as spent nuclear fuel and high level radioactive waste. Can be appropriately selected and used, and as compared with the case where a plurality of storage containers are conventionally prepared, the number of storage containers owned can be reduced and the management becomes easy.

Further, since the basket is provided with the radiation shielding performance, the container body may be provided mainly with the mechanical performance and the fire resistance performance as an auxiliary to the radiation shielding performance of the container body, It is possible to set materials with priority given to mechanical performance and fire resistance, to optimize the wall thickness of the container body, and to reduce the outer dimensions and weight of the storage container.

In the storage container according to claim 2 of the present invention, in the storage container according to claim 1, a material having a density higher than that of the material of the container body is used as the material of the basket. Have an effect.

That is, since the material of the basket has a density higher than that of the material of the container body, the gamma ray shielding performance can be enhanced.

Moreover, since the basket having a high shielding performance is arranged inside the storage container, the container body having the same material and the same thickness having the same shielding performance is provided in the container body. As compared with the case, the outer dimensions and weight of the storage container can be reduced.

In the storage container according to claim 3 of the present invention, in the storage container according to claim 1, since uranium or a uranium alloy is used as the material of the basket, the gamma ray shielding performance is improved by the high density of uranium. Can be increased. Moreover, the uranium used in the basket can be obtained by using, as a raw material, depleted uranium obtained in the uranium concentration step and having a low utility value at present.
Even if uranium, which is a rare material, is used, the manufacturing cost of the basket does not increase so much. In addition, since uranium alloy with additives added to uranium is used, it can also function as an absorber that absorbs neutrons emitted from radioactive materials such as spent nuclear fuel and high-level radioactive waste, and the structure of the basket. It is possible to improve strength, heat transfer characteristics, corrosion resistance performance or manufacturing method.

[Brief description of drawings]

FIG. 1 is a partially cutaway side view showing a storage container according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line EE in FIG.

FIG. 3 is a partially cutaway side view showing a conventional storage container.

FIG. 4 is a cross-sectional view taken along the line ROLL in FIG.

[Explanation of symbols]

 4 Spent nuclear fuel 10 Storage container 11 Cooling fins 12 Container body 13 Basket 15 Lattice (basket)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuaki Ota 1002 No. 1002, Mukaiyama, Naka-cho, Naka-cho, Naka-gun, Ibaraki Prefecture 14 Mitsubishi Materials, Ltd. Naka Nuclear Development Center

Claims (3)

[Claims] 1. A radiation protection effect is provided in a cylindrical basket arranged around radioactive materials such as spent nuclear fuel and high-level radioactive waste, and the basket is housed in a cylindrical container body. Storage container for radioactive material characterized by: 2. The radioactive substance storage container according to claim 1, wherein a material having a density higher than that of the material of the container body is used as a material of the basket. 3. The radioactive substance storage container according to claim 1, wherein uranium or a uranium alloy is used as a material of the basket.