GB2145650A - Device and method for storing radioactive wastes - Google Patents

Abstract

Surrounding walls of a concrete caisson are given sufficient strength to withstand the seismic wave, the earthquake, or the crustal movement, and sufficient thickness to exhibit high shielding performance against the radioactive radiation, and a cavity to be formed within said surrounding wall is made tightly sealable so as to be able to confine the radioactive wastes within the cavity in the hermetically sealed condition.

Description

SPECIFICATION Device and method for storing radioactive wastes The present invention relates to a device and a method for storing radioactive wastes.

A great deal of radioactive wastes come out of various working sites such as, for example, nuclear power plants, etc. where a large amount of radioactive substances are handled. Of various radioactive wastes, since those having high intensity of radioactivity, i.e. the so-called "high level radioactive wastes" are not so much in quantity, though the danger to be derived from them is still high, they can be stored without difficulty over a long period of time (i.e., until the radioactivity will have attenuated) at, for example, a certain definite isolated place on the land with utmost of the cautionary measures being taken.On the other hand, while low level radioactive wastes should also be put under custody with strict care, the producing quantity of such low level radioactive wastes is enormous, because they are mostly waste cloths used for wiping those contaminated parts of the nuclear power plant, or filtered substances from contaminated water which has been used for washing such contaminated parts at the time of handling the radioactive substances, or ashes and the like after burning of such filtered substances. On account of this, the present situation in disposition of the radioactive wastes is such that acquisition of the storage site is becoming more and more difficult.

Figure 1 of the accompanying drawing is a longitudinal cross-sectional view showing one method of abandoning (or throwing off) this kind of radioactive wastes into the ocean floor, etc. in a safer manner, which has so far been studied and researched. In the drawing, a reference numeral 1 designates a drumshaped can (or barrel) made of steel, a numeral 2 refers to a protective wall made of ferro-concrete (hereinafter simply referred to as "protective wall"), 3 indicates a wastes storing chamber, and 4 denotes the radioactive wastes.

The protective wall 2 has sufficient wall thickness to prevent radioactivity from leaking outside, and has strength such that the drum-shaped can 1 may not be fractured, even when it is thrown off into the ocean bottom of 10,000 meters deep. It may occur from time to time that cement or water glass is filled in the wastes storing chamber 3 together with the radioactive wastes 4.

Figure 2 illustrates one example of the drumshaped can 1 in Figure 1 which has been thrown off into the deep sea bed, wherein a reference numeral 5 designates the surface or level of the sea and a numeral 6 refers to the bottom of the sea. The drum-shaped can 1 which has been thrown off into the sea will soon be buried in the bottom thereof, and will not come outside of the sea bed permanently or at least until the level of the radioactivity from the wastes will have sufficiently attenuated.

Such waste-containing drum-shaped can which has thus been given adequate safety measures is perfectly safe and not considered to possibly give rise to any environmental pollution, even when it is abandoned into the ocean. However, all the deep seas belong to the high seas, and from the standpoint of emotion and sentiment of those inhabitants near or surrounded by such high seas, it has not yet come to a point that there is no difficulty in finding the sites for abandonment of such radioactive wastes, even if the method as shown in Figure 1 is followed exactly. That is to say, while the method of Figure 1 serves to relax the restriction imposed on selection of the location for abandonment or storage of the radioactive wastes, it does in no way perfectly solve the difficulty in finding the sites for such abandonment or storage.

The present invention has been made with a view to solving the abovementioned disadvantages inherent in the conventional technique of storing the radioactive wastes and the device for it, and is to provide a safer and less expensive device for storing the radioactive wastes by utilization of embankment for breakwater to be installed at harbours, etc., thereby eliminating the abovementioned disadvantages in the known techniques which have been practiced heretofore.

According to the present invention, in one aspect of it, there is provided a device for storing radioactive wastes, characterized in that a tightly sealable cavity for storing the radioactive wastes is formed in the interior of a concrete caisson for breakwater.

Accoring to the present invention, in another aspect of it, there is provided a method for storing radioactive wastes, characterized in that, when constructing breakwater embankment at harbours, etc., surrounding walls of a concrete caisson is given sufficient strength to withstand the seismic wave (or tsunami), the earthquake, or the crustal movement, and sufficient thickness to exhibit high shielding performance against radioactivity, and that a cavity to be formed within said surrounding wall is made tightly sealable so as to be able to confine the radioactive wastes within the cavity in the hermetially sealed condition.

The foregoing object, other objects as well as the specific construction of the storage device for the radioactive wastes and manner of storing such radioactive wastes in the storage device according to the present invention will become more apparent and understandable from the following detailed description thereof, when read in conjunction with the accompanying drawing.

In the drawing: Figure 1 is a longitudinal cross-sectional view of a drum-shaped can as one example of a conventional device for storing radioactive wastes; Figure 2 is a general view for explaining the manner of abandoning the drum-shaped can shown in Figure 1 into the bottom of the ocean; Figure 3 is a longitudinal cross-sectional view for explaining the manner of installing an ordinary concrete caisson for the breakwater; Figure 4 is also a longitudinal cross-sectional view showing one embodiment of the radioactive wastes storing device according to the present invention and Figure 5 is a cross-sectional view showing another embodiment of the radioactive waste storing device according to the present invention.

In the following, the present invention will be described in detail with reference to a preferred embodiment thereof shown in Figures 3 to 5.

Figure 3 illustrates one embodimental structure of an ordinary concrete caisson for the breakwater according to the conventional technique, which is presented to assist understanding of the readers of this specification prior to explanation of the embodiment according to the present invention.

In the drawing, a reference numeral 7 designates a body of the bank (concrete caisson), a numeral 8 refers to earth and sand filling the interior of the bank 7, a numeral 9 refers to foundation gravel, and 10 denotes a man-hole, through which workers pass for embedding the bottom foundation, and other works at the time of installing the bank 7.

While there are various types of the concrete caisson for the breakwater and various methods for installing the concrete caisson, the most general and typical way of the installation is that the ground leveling of the sea bottom is first carried out, and, in parallel with this, the body of the bank 7 is manufactured on land.

The bank 7 is then transported by a large-scaled crane and other conveying apparatuses to the site of the sea surface where the sea bottom has been levelled and sunken into the sea bottom, followed by filling earth and sand 8, etc. inside the cavity of the bank (concrete caisson) 7. The earth and sand serve as the weight for stabilizing the bank body 7 after it has been installed. Finally, the man-hole 10 on the top part of the bank body 7 is closed by filling concrete, etc. to prevent the earth and sand 8 from running out of the caisson. The dimension of the bank body 7 is generally of an order of 10 meters long at its one side, and its total volume usually amounts to 1,000 m3 and more.

Figure 4 illustrates one embodiment of the preseant invention. In the drawing, a reference numeral 11 designates a concrete caisson for the breakwater, which constitutes the bank body 7 and serves as the concrete shielding wall with its wall thickness being particularly made thick to increase the stgrength against earthquake, crustal movement, etc., and to heighten the radioactivity shielding performance.

At the middle portion within the bank body 7, there is formed a wastes storing chamber 3 as a tightly sealable cavity for confining therein the radioactive wastes, in which a plurality of drum-shaped cans 1 containing therein radioactive wastes are placed.

The space intervals among these drum-shaped cans 1 are filled with cement 12, etc. so as to prevent them from colliding one another due to displacement.

A long hole 13 is formed in the concrete wall 11 for permitting insertion of a sensor (not shown in the drawing) to measure the quantity of radiation from the radioactive wastes. The hole 13, however, is not in direct communication with the waste storing chamber 3, and measurement of the radiation quantity is carried out by way of the shielding wall 11. The top of the hole 13 is closed with a cap 14 so as not to let any living creatures or foreign substances into it.

The bank 7 shown in Figure 4 can be manufactured in such a construction that it has itself a high strength which is liable to cause shear and fracture, even though it might be turned over, in case there should arise transformation in the sea bed owing to the earthquake, the seismic wave, and the crustal movement. Further, the technique of preventing it from overturn has already been achieved by setting a length-to-breadth ratio of the bank body at an appropriate value to meet the need, and others, hence no problem arises at all in this respect.

As to the procedures for installing such concrete caisson (or bank body) 7, a plurality of the wastescontaining barrels 1 in bunch are confined inside the caisson at the site of its manufacturing on land, and, after the entire caisson has been solidified, it may be carried to a designated site. In another way, depending on the circumstances in the installation work, the bank body 7 having the wastes storing chamber 3 is first embedded in the sea bed with its top part being kept open as shown in Figure 5, and then the wastes are confined inside it, followed bytight-sealing of the same. In short, it is sufficient if the tight-sealing work be effected to a satisfactory degree and without failure.

While the abovementioned concretge caisson should be designed by taking into account much more safety than the general design standard of the conventional bank body for the breakwater, it should be noted that the domestic demands for the installation of the breakwater embankment may be higher, if the sufficient strength is ensured with the bank body, hence there will be no troublesome situation to occur in finding out appropriate sites for abandonment of the radioactive wastes. Incidentally, it is to be noted that the hole 13, etc. for measuring the radiation quantity in Figure 4 is not essential to the purpose of the present invention.

As stated in the foregoing, the method and device for storing radioactive wastes according to the present invention have well taken into consideration the high domestic demands for installation of the breakwater embankments, pay attention to the concrete caisson (or bank body) in huge volume, and utilize such large volume of the embankment for storing the radioactive wastes, in particular, the low level radioactive wastes, so that the invention has the advantage of being able to secure the safe storage site with less expense and trouble.

While, in the foregoing, the present invention has been described with particular reference to the preferred embodiments thereof, it should be noted that the invention is not limited to these embodiments alone, which are merely illustrative, and that any changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention as recited in the appended claims.

Claims (8)

1. A device for storing radioactive wastes, characterized in that a tightly sealable cavity for storing the radioactive wastes is formed in the interior of a concrete caisson for breakwater.

2. The device for storing radioactive wastes according to Claim 1, wherein said concrete caisson has a shielding wall of sufficient strength and radioactivity shielding performance.

3. The device for storing radioactive wastes according to Claim 1, wherein said shielding wall has a radiation measuring hole formed therein, which is not communicated with said tightly sealable cavity.

4. A method for storing radioactive wastes, characterized in that, when constructing a breakwater embankment at harbours, etc., surrounding walls of a concrete caisson are given sufficient strength to withstand the seismic wave (or tsunami), the earthquake, or the crustal movement, and sufficient thickness to exhibit high shielding performance against the radioactive radiation, and that a cavity to be formed within said surrounding wall is made tightly sealable so as to be able to confine the radioactive wastes within the cavity in the hermetically sealed condition.

5. The method for storing radioactive wastes according to Claim 4, wherein said wastes are confined inside the concrete caisson at its manfacturing site and tightly closed, and transported to an installatjion site of the embankment after the entire caisson has been solidified.

6. The method for storing radioactive wastes according to Claim 4, wherein said concrete caisson is moved to an installation site with its top part of said cavity being kept open, after which said wastes are placed inside said cavity followed by tight closure of the top part thereof.

7. A device for storing radioactive wastes, substantially as described with reference to the drawings.

8. A method for storing radioactive wastes, substantially as described with reference to the drawings.