JP3083276B2 - Stir-cooled storage tank for uranium-plutonium mixed oxide powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage tank for storing uranium-plutonium mixed oxide (MOX: Mixed Oxide) powder, and more particularly, to a hollow stirring blade structure inside a cylindrical storage tank body. And a stir-cooling type storage tank for uranium-plutonium mixed oxide powder in which stored uranium-plutonium mixed oxide powder is stirred and cooled. This device is
Particularly, it is suitable for mass storage of powder having a relatively high ratio of plutonium or powder having a high calorific value of plutonium among uranium-plutonium mixed oxide powders.

[0002]

2. Description of the Related Art Conventionally, a simple cylindrical storage tank has been used for storing uranium-plutonium mixed oxide powder.

[0003]

However, since the uranium-plutonium mixed oxide powder has a low thermal conductivity, when stored in large quantities, the maximum temperature at the center of the powder depends on the heat generation density of the plutonium or the proportion of added plutonium. 20
Temperatures far above 0 ° C. Due to this temperature, the uranium-plutonium mixed oxide powder is gradually oxidized, and the added organic substance is volatilized, which has adverse effects such as insufficient sintering density and poor appearance during pellet production. To avoid this, the diameter of a conventional simple cylindrical storage tank becomes too small, and a large amount of uranium / plutonium mixed oxide powder cannot be stored.

In order to enhance the cooling efficiency, it is conceivable that the storage tank has a hollow structure. Certainly, in the storage tank having the hollow structure, the cooling effect is improved to some extent. However, when the powder having a high plutonium ratio or the heat generation density of plutonium increases, the cooling cannot always be performed sufficiently. Therefore,
There is a demand for the development of a storage tank with higher cooling efficiency and smaller size.

An object of the present invention is to suppress the temperature rise of the uranium-plutonium mixed oxide powder, and to store a large amount of uranium-plutonium mixed oxide powder having a relatively high ratio of plutonium or a high heat generation density of plutonium. An object of the present invention is to provide a storage tank having a structure that can be downsized.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a storage tank body having a cylindrical shape with a smooth inner surface and a cooling pipe wound around the outer surface, a lower portion being narrowed to form a discharge port, and an outer portion of the storage tank body. An outer heat insulating jacket that covers, a rotatable hollow stirring blade structure that is incorporated inside the storage tank body, and a cool air introduction pipe that feeds cooling air into each hollow blade.
An agitated and cooled uranium-plutonium mixed oxide powder storage tank comprising a lid for covering an upper surface of the storage tank main body and a rotary drive mechanism for the hollow stirring blade structure. Here before
The hollow stirring blade structure has a bottomed circular tubular shaft portion and an outer portion.
A hollow blade protruding laterally from a peripheral surface;
Is connected to the connecting part and the whole is one continuous cavity
The structure is as follows. The cold air inlet tube is
Inserted along the central axis and covered with thermal insulation,
Therefore, with a structure that branches off and reaches near the tip inside the hollow blade
Yes, the upper part of the cold air introduction pipe is connected to the free joint
ing. This gushes from the branch pipe through the cold air inlet pipe
The cold air reaches the inner tip of the hollow blade and
Return along the inner surface and pass through between the cool air inlet pipe and the shaft.
A cold air flow path is formed outside the hollow stirring blade structure.
It is configured to cool the entire surface from inside. Uranium-plutonium mixed oxide powder is stored in the storage tank body. Then, cooling air is supplied to the cooling pipe to cool it, and while rotating the hollow stirring blade structure in the uranium-plutonium mixed oxide powder, cooling air is supplied into the hollow stirring blade structure to stir and cool.

[0007]

In the present invention, fins may be attached to the outer surface of the storage tank body instead of the cooling pipe, and cooling air may be supplied from below to the gap between the storage tank body and the outer heat insulation jacket for cooling. In order to supply the cooling air, it is desirable to install a cool air generator that generates cooling air by utilizing the adiabatic expansion of the compressed air outside the outer heat insulating jacket and above the cold air introducing pipe. It is also effective to attach an air knocker to the storage tank main body or the outer heat insulation jacket to remove powder adhering and staying inside by vibration.

[0008]

FIG. 1 is an overall constitutional view showing an embodiment of a stirred and cooled uranium / plutonium mixed oxide powder storage tank according to the present invention, and FIG. 2 is an exploded explanatory view thereof. This device is
Basically, it is a combination of a cylindrical storage tank main body 10 and a hollow stirring blade structure 12 incorporated therein.

The storage tank body 10 has a cylindrical shape, and its lower portion is narrowed in an inverted conical shape, and a discharge port 14 is formed at the tip. The inner surface of the storage tank body 10 is smooth, and a cooling pipe 16 is spirally wound around the outer surface. The cooling pipe 16 is divided into a plurality of systems. Outside the storage tank body 10, an outer heat insulating jacket 18 is provided at intervals. The outer heat-insulating jacket 18 has a vertically split two-piece structure made of vinyl chloride, and covers the storage tank body 10 by being combined from both sides. At the upper ends of the storage tank main body 10 and the outer heat insulating jacket 18, a ring-shaped lid 20 is provided so as to cover the upper surfaces thereof. The lid 20 is provided with a powder supply pipe 22.

The hollow agitating blade structure 12 includes a closed-bottomed cylindrical shaft portion 24 having a narrowed lower portion, and a plurality of propeller-like hollow blades 26 projecting laterally from the outer peripheral surface thereof.
This is a structure in which the connecting portions of the respective hollow blades 26 communicate with each other to form a single continuous cavity. A cold air introduction pipe 28 is incorporated inside the hollow stirring blade structure 12. The cold air introduction pipe 28 is inserted along the central axis of the shaft portion 24 and covered with a heat insulating material 30, and is branched therefrom by a branch pipe 32 so as to reach the vicinity of the tip in each hollow blade 26. Structure. A free joint 34 is provided above the cold air introducing pipe 28. As a result, the cool air blown from the branch pipe 32 through the cool air introducing pipe 28 reaches the inner tip of the hollow blade 26 and returns along the inner surface of the hollow blade 26, and the space between the cool air introducing pipe 28 and the shaft 24 is formed. A cool air flow path is formed so as to be discharged through the air passage, and cools the entire outer surface of the hollow stirring blade structure 12 (the shaft portion 24 and each hollow blade 26) from the inside. Note that a spiral hollow blade may be used instead of the propeller-shaped hollow blade.

The hollow stirring blade structure 12 is rotatably supported by a bearing 36 fixed to the lid 20, and includes a drive motor 40 and a gear mechanism (a gear 42 on the hollow stirring blade structure side and a gear on the drive motor side). 44 combinations) so as to rotate at a predetermined speed (about several revolutions per minute).

Uranium-plutonium mixed oxide powder 50
Is stored in the storage tank body 10. And the storage tank body 10
The cooling air is supplied to each cooling pipe 16 of the storage tank main body 10.
Is cooled from the outside. In addition, while the hollow stirring blade structure 12 is rotated slowly (at a rotational speed of about several times per minute) to stir the uranium-plutonium mixed oxide powder 50, cooling air is supplied to the cold air introduction pipe 12 as well. The hollow stirring blade structure 12 is entirely cooled from the inside.

Here, a cool air generator 52 is installed in each cooling pipe 16, and a cool air generator 54 is also installed above the cool air introducing pipe 28. These cold air generators 52, 54
Is an apparatus of a system that generates cooling air by utilizing adiabatic expansion of compressed air. For example, 20 ° C pressurized to 4 atm
When the compressed air is instantaneously reduced to the atmospheric pressure, -70 ° C. of cooling air is theoretically obtained. Actually, the temperature is not so low because of the efficiency etc.
It is possible to obtain cooling air of about −30 ° C. Although a certain degree of cooling is possible only by flowing air of normal temperature instead of cooling air, it goes without saying that the lower the temperature of air, the higher the cooling efficiency (removal of heat). In that regard, the use of a cold air generator as described above is preferred. The removal of heat by the cooling air is more effective as the temperature of the cooling air is lower and the flow rate is higher, but it is also important that the flow rate of the cooling air is higher. Therefore, it is desirable that the space (the inner diameter of the cooling pipe) through which the cooling air flows is narrow.

In the present invention, cooling air is supplied to the cooling pipe 28 from below. The reason for flowing the cooling air from below is that the cooling air is heated and expanded on the way, thereby further increasing the flow velocity. In addition, the heat insulating material 30 of the outer heat insulating jacket 18 and the cold air introducing pipe 28 has a function of reducing a temperature rise of the cooling air due to heat input from the outside.

The inner surface of the storage tank body 10 and the outer surface of the hollow stirring blade structure 12 are smooth surfaces subjected to puff finishing. Originally, if these surfaces had irregularities, the efficiency of removing heat would be improved, but the reason for not providing irregularities was to reduce the retention in the storage tank due to powder adhesion and reduce the exposure due to the accumulation. It is. When vibration is applied to the storage tank body 10 by installing the air knocker 56 on the outer heat insulation jacket 18, the vibration can remove the powder adhering and staying inside. The inside of the storage tank is cleaned by the hollow stirring structure 12.
, And the lid 20 on the upper part of the storage tank main body 10 is opened to easily perform the operation.

In this embodiment, the cooling pipe 16 is wound around the outer surface of the storage tank main body 10. Instead, fins are spirally provided on the outer surface of the storage tank main body, and the fins are used as guides for cooling air and are connected to the storage main body. In the gap with the outer insulation jacket,
A method of cooling by supplying cooling air from below may be used.

The powder to be stored in the storage tank according to the present invention can be applied to powder having an arbitrary heat generation density of plutonium and a plutonium addition rate, but is particularly suitable for storing powder having a high heat generation density of plutonium or a high plutonium addition rate. Are suitable.

The heat generated by plutonium is Pu238, Pu
The heat density of plutonium differs greatly depending on the composition of these isotopes. By the way, plutonium having a heating density of 20 w / kg Pu corresponds to a plutonium obtained by processing 50,000 MWD / T of spent fuel and mixed with some fission products. The isotope ratio of plutonium varies depending on the burnup of spent fuel in a light water reactor, but is usually about 7 to 13 w / kg Pu.

The heat generation density of the uranium-plutonium mixed oxide powder is determined by the heat generation density of plutonium and the addition ratio of plutonium. If the heat density of the uranium-plutonium mixed oxide powder is the same and the density of the powder is the same, the temperature will be the same. For example, 10% plutonium at 20 w / kg Pu
Added uranium-plutonium mixed oxide powder and 10
If the uranium-plutonium mixed oxide powder to which 20% of w / kg Pu of plutonium is added has the same shape, the same temperature is obtained.

In the present invention, air is used as a cooling medium. If water can be used, the cooling efficiency will be higher, which is desirable. However, the presence of water works in a direction in which criticality is likely to occur in terms of criticality safety. Furthermore, the size and storage volume of the storage tank are limited,
Design becomes difficult. Further, it is difficult to secure the structure to prevent water from leaking into the storage tank, and it is not practical to use water for cooling the storage tank for uranium / plutonium mixed oxide powder. Also, even if a refrigerant such as freon is recycled, the cooling effect is greater than flowing the cooling air through one through. However, recycling of the refrigerant requires a device such as a compressor, and even if the cost and the installation space are compared with the cooling effect, the cooling effect as much as the cost and space cannot be expected.

The storage property of the uranium-plutonium mixed oxide powder in the case of using a storage tank incorporating the hollow stirring blade structure according to the present invention was determined by using a plutonium heat density of 10 w / kg Pu,
40 kg of powder with an added amount of plutonium of 30% and bulk density of 3 g / cc
As compared to the example of storage tanks of various shapes,
Table 1 shows the size, maximum temperature, calculated height when 40 kg of powder is put, and cooling conditions. It should be noted that the maximum temperature of the powder during storage is 100 ° C. or less, which is used as a criterion for evaluation. The calculations in Table 1 are based on physical property values obtained in experiments.

[0022]

[Table 1]

Here, the storage tank is made of stainless steel having a thickness of 0.3 mm, and the hollow blades are made of stainless steel having a thickness of 0.5 mm.
The cooling air inlet temperature is -10 ° C and the flow rate is 50
Liter / minute, 25 liter / minute in the hollow stirring blade.

The temperature of 100 ° C. is a temperature set to prevent oxidation of the uranium-plutonium mixed oxide powder and to prevent the organic additive added to the powder from disappearing due to volatilization. The lower the temperature, the better.

The results in Table 1 were evaluated under certain limited conditions, and there is room for reducing the maximum temperature by about 20 ° C. by changing the cooling air introduction temperature or the flow rate. However, there is a limit to the efficiency of removing heat even if the flow rate is increased, and even if a cooling mechanism that can obtain a remarkably low temperature and a large flow rate is installed, the cooling efficiency does not increase for the size and price of the device. . From the results shown in Table 1, if the storage tank is a solid storage tank as shown in FIG.
If you put kg of powder, it will be as high as 1m. Such a storage tank is actually close to 2 m in height because a powder supply / discharge mechanism is provided above and below. The installation of such a long object in the glove box greatly restricts the installation of other devices, and makes it extremely difficult to clean the inside of the storage tank.

In such a storage tank with hollow blades (same configuration as the present invention, but without rotating the hollow blades),
Even if the hollow blade does not rotate, it functions as a radiation fin, so that a certain degree of cooling effect is produced. However, in a storage tank with hollow stirring blades (a product of the present invention in which the hollow blades are rotated) as shown in (1), the temperature can be significantly reduced by stirring. The results in Table 1 indicate that the blade shape was not one that could completely agitate the powder by convection, but it was possible to further reduce the temperature by narrowing the gap between the blade tip and the inner surface of the storage tank or improving the blade shape. is there. It is theoretically possible to lower the temperature to about 50 ° C.

[0027]

As described above, according to the present invention, a stirring blade having a hollow inside is provided in a storage tank to perform rotational stirring, and a cooling pipe or the like is provided outside the storage tank to cool the storage tank from the outside. Is also configured to cool by supplying cooling air, so that a large amount of uranium-plutonium mixed oxide powder can be stored while suppressing a rise in temperature. The storage tank according to the present invention can be easily housed in a glove box because it can be downsized.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of the present invention.

FIG. 2 is an exploded view of the same.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Storage tank body 12 Hollow stirring blade structure 14 Discharge port 16 Cooling pipe 18 Outer heat insulation jacket 20 Lid 24 Shaft part 26 Hollow blade 28 Cold air introduction pipe 30 Insulation material 32 Branch pipe 40 Drive motor 42,44 Gear

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-192923 (JP, A) JP-A-9-239252 (JP, A) JP-A-2-153718 (JP, A) 66631 (JP, U) Japanese Utility Model 4-74536 (JP, U) Japanese Utility Model 2-25025 (JP, U) Japanese Utility Model Utility Model 2-20926 (JP, U) Japanese Patent Publication No. 26-995 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) G21C 21/02 B01F 15/06 G21C 3/62

Claims (4)

(57) [Claims] 1. A storage tank body having a smooth inner surface and a cooling pipe wound around an outer surface thereof, a lower portion of which is a constricted portion serving as a discharge port, an outer heat insulating jacket covering an outer surface of the storage tank body, A rotatable hollow stirring blade structure incorporated in the storage tank body, a cool air introduction pipe for feeding cooling air into each of the hollow blades, a lid covering an upper surface of the storage tank body, and the hollow stirring blade structure Body rotation drive mechanism, the hollow stirring blade structure, a bottomed circular tubular shaft,
A hollow blade protruding laterally from an outer peripheral surface;
One continuous sky, communicating even at the root connection
It is a structure that is a cave, and the cold air introduction pipe is inserted along the central axis of
Inside the hollow blades
The top of the cold air introduction pipe is
The cold air blown from the branch pipe through the cold air inlet pipe is connected to the
To reach the inner tip and return along the inner surface of the hollow blade,
The cold air flow path that is discharged between the wind introduction pipe and the shaft is shaped
The entire outer surface of the hollow stirring blade structure is cooled from the inside.
The uranium-plutonium mixed oxide powder is stored in the storage tank body, cooled by supplying cooling air to a cooling pipe, and the hollow stirring blade structure is cooled by the uranium-plutonium mixed oxide. A stirring / cooling type uranium / plutonium mixed oxide powder storage tank, characterized in that cooling air is supplied into the hollow stirring blade structure while being rotated in the powder to stir and cool. 2. A stirred and cooled uranium-plutonium mixed oxide according to claim 1, wherein fins are attached to the outer surface of the storage tank body instead of the cooling pipe, and cooling air is supplied from below to the gap between the storage tank body and the outer heat insulation jacket. Storage tank for powder. 3. A stirred cooling uranium generator according to claim 1, wherein a cold air generator for generating cooling air by utilizing adiabatic expansion of the compressed air is installed outside the outer heat insulating jacket and above the cold air introducing pipe. Storage tank for plutonium mixed oxide powder. 4. An agitated cooling type uranium / plutonium mixed oxide powder storage tank according to claim 1, wherein an air knocker for removing powder adhering and staying therein by vibration is attached to the storage tank main body or the outer heat insulation jacket. .