JPH06279078A - Production of heavy concrete - Google Patents

Abstract

PURPOSE:To improve the shielding performance utilizing waste products by admixing water and aggregate of depleted uranium to cement. CONSTITUTION:Depleted uranium is obtained in the form of a powder or pellets. The depleted uranium is admixed to cement, water and sludge aggregate to produce heavy concrete of 3 to 6g/cm<3> density such as concrete cask comprising the lid 1, the inner lining made of stainless steel 2 and the depleted uranium- containing heavy concrete 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing heavy concrete which is suitable for use in, for example, a concrete cask which is a storage container for spent fuel and which has an excellent radiation shielding property. The heavy concrete can be used for a building in a nuclear power plant, etc. where the size is severely restricted, and can also be used when a heavy weight is required as a weight.

[0002]

2. Description of the Related Art A large amount of depleted uranium has been produced as a by-product from the uranium enrichment process in association with the uranium enrichment business by producing fuel for nuclear power generation. This depleted uranium is mainly used in the United States in the early days for pigments, catalysts, and other chemical products, and in some cases it is used for ammunition, but its demand is low, and most of it is in the form of UF ₆ . At present, it is stored as fuel for fast breeder reactors, which is expected to be put to practical use in the future. In addition, in Japan, in addition to storing highly concentrated waste by-produced by establishing a nuclear fuel cycle, because of the small land area, especially for the storage of the large amount of depleted uranium generated from the concentration process, It is a problem in terms of cost and cost.

On the other hand, the spent fuel used in nuclear power generation is stored in a storage rack in a dedicated storage pool. When the radiation is shielded by using concrete, there are two methods: a method of increasing the thickness to improve the shielding property and a method of increasing the weight to achieve the same purpose. Normally,
The shielding performance is ensured by increasing the thickness, but if heavy concrete (also called heavy concrete) is used, the wall thickness and floor thickness can be reduced.

Although this heavy concrete has been used conventionally, it was iron ore mainly composed of magnetite that was added to increase the specific gravity. That is, in this heavy-weight concrete, in order to increase the shielding ability, it is necessary to increase the iron ore as an aggregate, but there is a limit to the amount of addition, and as the specific gravity of concrete increases Becomes difficult. Generally, the specific gravity of ordinary concrete is about 2.1 g / cm ^3, weight concrete are conventionally used gravity is often that of 3 to 4 g / cm ^3.

[0005]

By the way, instead of storing spent fuel by the storage pool and a dedicated rack,
In the concrete spent fuel storage container called concrete cask, which is expected to be developed in the future, dimensional constraints on wall thickness and floor thickness are severe, and heavy concrete with improved shielding ability is required.

However, in the above-mentioned conventional heavy concrete, as described above, there is a problem such as workability in order to increase the specific gravity and increase the shielding property, and in consideration of this workability, the concrete thickness is increased. It becomes necessary to do so, which causes a problem that the number of fuels that can be stored is limited. The decrease in the number of fuel storage bodies leads to deterioration in economic efficiency as it is, and improvement of the shielding property of the concrete is an important issue in the future.

The present invention has been made in view of the above-mentioned circumstances, and as described above, paying attention to depleted uranium that is mostly stored as waste at present, and weighting it as an aggregate or a mixed material. The purpose of the present invention is to obtain heavy concrete having higher shielding performance by utilizing it for concrete.

[0008]

That is, the feature of the method for producing heavy concrete of the present invention which meets the above object is that concrete in which water and aggregate are added to cement and kneaded is mixed with depleted uranium as an aggregate or a mixture. It is in use. Further, in the above production method, other aggregate may be added in addition to the deteriorated uranium, and the form of the deteriorated uranium to be added is preferably a powder or pellet of uranium oxide. Furthermore, it is also preferable to control the addition amount of depleted uranium so that the specific gravity of the heavy concrete is in the range of about ^{3 to} 6 g / cm ³ . The specific gravity referred to here is the specific gravity of the concrete after hardening.

[0009]

By the production method of the present invention, heavy concrete containing depleted uranium is produced.
When comparing the dose rate of gamma rays under the same thickness (about 60 cm) with the conventional iron ore-containing heavy concrete of the same specific gravity and the conventional ordinary concrete, the gamma ray dose rate is the same as that of the conventional heavy concrete. When used, it could be about 1/1000 that of normal concrete, but in the case of heavy concrete containing depleted uranium according to the present invention, the gamma dose rate of 1/4 or less of this conventional heavy concrete. I was able to

Further, according to the heavy concrete of the present invention, if the specific gravity is, for example, 5 g / cm ³ , about 3 t of depleted uranium can be adopted per 1 m ^{3 of} heavy concrete, so that a large amount of surplus is produced. It is also extremely useful as a method of using this depleted uranium.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing a concrete cask manufactured by the method for manufacturing heavy concrete according to the present invention. In the drawing, 1 is a container lid, 2 is an inner lining made of stainless steel, and 3 is heavy concrete containing depleted uranium. Shows.

As a method for producing the heavy concrete containing depleted uranium, depleted uranium having a higher shielding performance than that of conventional iron ore is used as an aggregate to be mixed into cement when water is added and mixed. As a form of depleted uranium to be mixed, it is most preferable to use stable uranium oxide, and this uranium oxide is mixed into the cement in the form of pellets such as nuclear fuel pellets.

Depleted uranium oxide (UO ₂ or U ₃ O ₈ )
When using as a powder, it is also preferable to separately prepare general aggregate or iron ore such as magnetite and mix these with cement.

On the other hand, in the production of the above-mentioned heavy concrete, uranium itself contains radioactivity, so that it must be handled with caution. Further, although the mixing ratio of each element material differs depending on the specific gravity of the heavy concrete to be finally achieved, it is necessary to prepare an agitator such as an omni-mixer because there is a considerable difference in the specific gravity of each element material. Further, an admixture or the like is used if necessary.

On the other hand, when pellets of depleted uranium oxide (sintered body or pressed material) are used, the pellets can be used as a part of the aggregate, and the weight concrete having a higher specific gravity than the case of using powder. Can aim for. The handling precautions during manufacturing are the same as for powder. Since the thickness of concrete when used as heavy concrete is usually 50 cm or more, even if the uranium oxide is mixed with cement in the form of pellets or the like, a difference in the shielding ability may be partially caused. Absent.

Further, the gamma ray shielding ability is higher as the specific gravity of the concrete is higher and the atomic number of the substance to be mixed is higher, so that the present invention contains depleted uranium even if the specific gravity of the heavy concrete is the same. The heavy-weight concrete has a higher gamma-ray shielding ability than the conventional iron-containing heavy concrete.

As for the specific gravity of the above-mentioned heavy concrete, if it is too low, the shielding ability is deteriorated, and if it is too high, the workability and the like can be impaired, so a range of about ³ to 6 g / cm ³ is suitable.

[0018] Thus, the manufacturing method of the present invention, as examples, to produce a heavy concrete DU containing specific gravity 4.5 g / cm ^3, this conventional iron ore 4.5 g / cm ³ of the same specific gravity The dose rate of gamma rays was compared with the contained heavy concrete and conventional conventional concrete (specific gravity 2.1 g / cm ³ ) under the same thickness conditions.

The dose rate of gamma rays is about 1/10 of that of ordinary concrete by using conventional heavy concrete.
Although it could be set to 00 or less, in the case of the heavy concrete according to the present invention, further
The gamma dose rate was less than 1/4.

Further, according to the heavy concrete of the present invention, when the specific gravity is, for example, 4.5 g / cm ³ , about 2.4 tons of depleted uranium can be adopted per 1 m ^{3 of} the heavy concrete, so that a large amount can be adopted. It can be said that it is extremely effective as a method of utilizing this surplus depleted uranium.

The embodiments of the present invention have been described above. However, aggregates other than depleted uranium may or may not be added regardless of the form of depleted uranium mixed therein. The purpose of the period can be achieved.

[0022]

As described above, the method for producing heavy concrete according to the present invention uses depleted uranium as an aggregate to be mixed into cement when water is added and mixed with the conventional iron ore. By using depleted uranium with excellent shielding properties instead of stone, it is possible to reduce the gamma ray dose rate to 1/4 or less compared to conventional heavy concrete of the same specific gravity and the same thickness. It is possible to avoid the strict size restriction of the concrete cask without difficulty, and to maintain the shielding performance of the cask, and to construct the specified cask according to the specified design effect.

Furthermore, according to the above heavy concrete of the present invention, if the specific gravity is, for example, 5 g / cm ³ , about 3 t of depleted uranium is used per 1 m ^{3 of} heavy concrete, and a large amount is used. It can be said that it is extremely effective as a method for treating and utilizing this surplus depleted uranium.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a concrete cask manufactured by a method for manufacturing heavy concrete according to the present invention.

[Explanation of symbols]

 1 Container lid 2 Inner lining 3 Heavy concrete containing depleted uranium

Claims (4)

[Claims] 1. A method for producing heavy concrete, characterized in that depleted uranium is used as the aggregate in concrete in which water and aggregate are added to cement and mixed. 2. The method for producing heavy concrete according to claim 1, wherein another aggregate is added in addition to the depleted uranium. 3. The depleted uranium is mixed with cement in the form of oxide powder or pellets.
A method for producing the described heavy concrete. 4. The specific gravity of concrete is about ^{3 to 6} g / cm ^3.
The method for producing heavy concrete according to claim 1, wherein the heavy concrete is in the range.