GB1598355A

GB1598355A - System for the storage of radioactive material in rock

Info

Publication number: GB1598355A
Application number: GB5140777A
Authority: GB
Original assignee: WP System AB
Current assignee: WP System AB
Priority date: 1976-12-13
Filing date: 1977-12-09
Publication date: 1981-09-16
Also published as: MX4571E; JPS57480B2; FI773751A; JPS5387000A; FI63091C; ES464822A1; IT1088531B; FI63091B; DE2755554C2; CA1096644A; BR7708254A; FR2373861B1; FR2373861A1; DE2755554A1

Description

(54) SYSTEM FOR THE STORAGE OF RADIOACTIVE MATERIAL IN ROCK (71) We, WP-SYSTEM AKTIEBO LAG of Esplanaden 23, 852 32 Sundsvall, Sweden, a Swedish Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a system for the storage of radioactive material in rock and more particularly to a repository for the long-term storage of spent fuel from nuclear reactors and radioactive waste that is produced by reprocessing used nuclear fuel.

The fuel elements of a nuclear reactor must be removed after some time and replaced by new fuel. The spent fuel contains uranium, plutonium and fission products. The uranium and plutonium can be recovered by a reprocessing operation and used again as fuel. However, the present methods of reprocessing do not allow the recovery of all uranium and plutonium, and in the reprocessing operation a waste is produced which in addition to a large number of fission products also contains small amounts of uranium and plutonium and other transuranic elements. Most of the wastes are highly radioactive and disintegrate under gradual transformation into stable elements. During the disintegration radiation of various kinds is emitted. The disintegration rate of different wastes is highly different and may vary from fractions of seconds to millions of years.Plutonium242 e.g. has a half-life of 380 000 years.

Since intense radioactive radiation is dangerous to living organisms it is necessary to store this high-level waste during a long period (thousands of years) in such a way that it is kept isolated from all life.

In the reprocessing operation the high level waste is separated in the form of an aqueous solution which is concentrated as much as possible. However, this solution is not suited for final storage, and after a certain cooling period it is therefore converted into solid form. It is thought that the best method of converting the waste to solid form is to vitrify the waste. This means that the waste solution is evaporated and calcinated and then heated to a suitable temperature with an addition of glass making substances. By this process a fused glass mass is obtained which is filled into containers or canisters. These canisters are then placed in a suitable repository.

It has been proposed that the solidified high-level waste should be finally stored in rock cavities located at a great depth in bedrock. One proposed storage system Qf this kind consists of a receiving station located on the ground surface for receiving the waste. A vertical transport tunnel is bored from this receiving station to a great depth into the bedrock, and from the bottom part of this vertical tunnel a horizontal transport tunnel is extended in the bottom of which is taken up a number of vertical holes. By means of automatic. transport vehicles the waste canisters are transported through said tunnels and are lowered like plugs into the vertical holes in the bottom of the horizontal tunnel. As the holes are filled with waste canisters they are sealed at the top e.g. with concrete.

Such a repository provides an effective screening of the radioactive radiation.

However, the bedrock does not constitute any homogenous material but usually contains crevices and cavities and often contains ground water. The rock may also be subjected to deformations e.g. by earthquakes.

Also, for various reasons the bedrock may undergo slowly proceeding deformations. In a repository of the kind described above there is a risk that such deformations of the rock may cause the breaking of the waste canisters stored in the rock. Also there is a risk that ground water comes into contact with the radioactive waste which may thereby be dispersed in an uncontrollable manner. The radioactive disintegration also generates heat which gives rise to convection currents in the ground water. The radioactive radiation may also cause a chemical disintegration, so called radiolysis, of material exposed to the radiation.The radiolysis makes the surrounding water attain a much higher content of oxygen than ordinary water whereby the water becomes highly corrosive so that there is a risk that the casing of the radioactive waste will corrode away leaving the waste in direct contact with the ground water.

The object of the present invention is to provide a system for the storage of radioactive material in rock in which the abovementioned hazards are eliminated. Thus, the invention relates to a repository fulfilling the following requirements: 1) It shall not be possible for the radioactive material to come into contact with ground water and to be spread by this.

2) It shall not be possible for the radioactive material to escape into the environment due to deformations of the rock, e.g. deformations caused by seismic activity (earth quakes).

3) The heat generated by the disintegration of the radioactive material shall be dissipated without any dangerous rise in temperature in the environment.

The repository of this invention is primarily intended for the final storage of the radioactive waste produced by reprocessing spent nuclear fuel. However, the repository of the invention could also be used for the interim storage of spent nuclear fuel before this is reprocessed. The repository of the invention namely permits the material stored therein to be easily removed if so desired.

The present invention consists in an underground repository for the storage of radioactive material and other materials in a rock formation, comprising a first cavity in said rock formation, a first body of rock derived from said rock formation by having been left at the excavation of said first cavity so as to be surrounded on all sides by said first cavity, said first cavity being filled with a plastically deformable material supporting said first body of rock in spaced relationship relative to the outer wall of said first cavity, said first body of rock being hollow and containing in its interior storage space for the material to be stored, and shaft means extending through said rock formation, through said space filled with plastically deformable material and through said first body of rock to said storage space for the transfer of the material to be stored into said storage space.

The plastically deformable material surrounding the first body of rock preferably is clay. Clay is particularly suited for this purpose because it is capable of absorbing ions, has a small permeability to water and can be deformed without cracking due to its plasticity.

The first body of rock will be wholly embedded in the plastically deformable material. This material may have a sufficient supporting capacity to prevent the body of rock from sinking in it, but to make sure that such sinking shall not occur it may be advisable to stabilize the material by the addition of some suitable stabilizing agent in the area under the body of rock.

Other objects and features of the invention will become apparent from the following description with reference to the accompanying drawings which show preferred embodiments of the invention.

Figure 1 shows a vertical section of a repository in accordance with a first embodiment of the invention.

Figure 2 shows on a larger scale and in section the inner cavity and the hollow body located therein.

Figure 3 shows a section taken along line 1-1 in Figure 1.

Figure 4 shows a vertical section of a modification of the embodiment shown in Figures 1-3. 1 - vertical section 3.

Figure 5 shows a vertical section of another embodiment of the invention.

Figure 6 shows a half horizontal section taken along line VIlI-VIlI in Figure 5.

Figure 7 shows a half horizontal section taken along line IX-IX in Figure 5.

Figure 8 shows in a vertical section still another embodiment of the invention, Figure 9 shows on a larger scale the central part of the embodiment according to Figure 8.

Figure 10 shows in perspective view a tubeshaped member contained in the interior of the hollow body of Figure 9.

Figure 11 shows one of a plurality of concrete balls filling the interior of the hollow body of Figure 9.

Referring now to Figures 1 - 3 numeral 1 designates the bedrock in which the repository is situated at a certain depth under the ground surface 2. In the rock is excavated an inner cavity the outline of which is designated 3. A hollow body 4 which is made of concrete and the interior of which constitutes the space for accommodating the radioactive material is placed within the cavity 3 in such manner that the outside of the concrete body 4 everywhere is spaced from the wall of the cavity 3. The space between the wall of cavity 3 and the concrete body 4 is filled with clay 5.

The cavity 3 is wholly surrounded by rock mass 6 and this is surrounded by an outer cavity the boundary lines of which are designated 7. The outer cavity 7 is also filled with clay 8.

The cavities 3 and 7 as seen in a horizontal section preferably have a circular form. The boundary walls 7 of the outer cavity as seen in a horizontal section taken along line I-I in Figure 1 thus form two concentric circles as shown in Figure 3.

The concrete body 4 which has an ellipsoidal form is provided with an opening at its top which is in communication with a horizontal tunnel 10 through a shaft 9.

Through the tunnel 10 and the shaft 9 the radioactive material can be transported into the hollow concrete body 4. In Figure 2 the hollow concrete body 4 is shown in section.

Its interior is divided by means of horizontal partitions 11 into several apartments located above each other. The partitions 11 are provided with openings 12 which are situated straight under the bottom opening of shaft 9. The radioactive material is successively introduced into these apartments beginning with the bottom one. In Figure 2 some containers 13 for the radioactive waste are shown in the bottom apartment. When the whole volume of an apartment is fully utilized, the opening 12 can be closed with a lid 14 or be permanently sealed.

As shown in Figure 2 the concrete body 4 is at one side provided with inspection openings 15 into which are fitted windows 16 of lead glass. The openings 15 open into a shaft 17 which extends upwards to the horizontal tunnel 10 (Figure 1). Supervision personnel can be hoisted down through the shaft 17 to inspect visually the interior of the concrete body 4. The supervision can also be effected by means of a television system having cameras placed in the openings 15 and monitors placed at a supervision site remote from the repository.

The outside of the concrete body 4 may be covered with a layer 18 of plastics which is heat insulating and water tight. The plastics layer 18 may be provided with cooling channels for the circulation of a suitable coolant.

The inner cavity 3 may also be provided with a layer 23 of a heat insulating material on its walls.

A vertical shaft or boring 19 extends through the rock mass 6 up to the horizontal tunnel 10. In the shaft 19 are mounted measuring devices (not shown) for the measurement of temperature, moisture and radioactive radiation. These measuring devices may be connected through wires in shaft 9 and tunnel 10 with indicating means at a supervision site.

Drainage tunnels 20 may be provided in the bedrock outside the repository extending circularly around the repository. The object of these drainage tunnels 20 is to lead away ground water that my exist in the bedrock outside the respository. A boring 21 extends from the drainage tunnels 20 to the ground surface.

The horizontal tunnel 10 shown in Figure 1 may communicate directly with a plant for reprocessing spent nuclear fuel. Hereby the hazards accompanying a transport of radioactive wastes are decreased. However, the tunnel 10 is not essential to the system of the invention. Thus, the shafts 9, 17, and 19 may open into some suitable building for the reception of the radioactive waste. This building may be situated on the ground surface or in a cavity in the rock.

The system is of course provided with suitable hoisting and transport means for the transport of the radioactive wastes through the shaft 9 and distribution of the wastes in the space within the concrete body 4. Such hoisting and transport means which are preferably remote controlled could be designed according to known techniques and will not be described more in particular.

The construction of the system can - be effected by the use of wellknown methods of rock excavation. At first working and transport tunnels are driven in the rock to the places where the two cavities are to be located. The excavation of the two cavities will take place from below and upwards.

The outer cavity 7 is filled with clay as the rock mass is removed. The clay is compressed so that no cavities will remain in it. In an area situated at the bottom of the outer cavity the clay could be stabilized by the addition of a suitable stabilizing agent to be capable of supporting more safely the load of the rock mass 6. Such a stabilized area is indicated in Figure 1 by dotted lines 22.

When the inner cavity 3 is excavated, clay is placed on the bottom of the cavity up to a certain height. Then the hollow concrete body and the connecting shafts 9 and 17 are cast. When the concrete has hardened and the insulating plastics layer 18 been placed on the outside of the concrete body, the space between the concrete body and the walls of the inner cavity is wholly filled with clay. When the structure is completed the said working and transport tunnels may be filled with concrete.

Cracks and fissures that may be present in the rock adjacent to the two cavities could be sealed by injection of concrete.

The repository according to the invention can be said to consist of a plurality of shells of different material arranged within each other, namely in the embodiment shown in Figures 1 - 3, an innermost concrete shell 4, a first shell 5 of clay, a shell 6 consisting of rock mass, and a second shell 8 of clay which is wholly surrounded by the rock.

If displacements and subsidences should occur in the rock outside the repository these movements of the rock will first cause a deformation of the outer clay shell 8. If this clay shell is sufficiently thick the deformation forces will not be transferred to the inner shells. If the deformations should be of such magnitude that even the shell 6 of rock is affected, the deformation forces will be further damped by the inner clay shell 5.

The innermost concrete shell 4 which has preferably an ellipsoidal or spherical form has a very high resistivity against pressure forces acting from the outside. Therefore, not even very extensive deformations, e.g.

deformations caused by earth quakes, can affect the system to such extent that even the innermost concrete shell 4 collapses.

The embodiment shown in Figure 4 differs from the embodiment shown in Figures 1 - 3 only in that the outer cavity the boundary walls of which are designated 7 extends up to the ground surface 2. Seen in horizontal section the cavity 7 has preferably the form of an annulus. Thus, the plastically deformable material 8, e.g. clay, which fills this cavity has the form of a cylindrical or tube shaped shell which is terminated by a conical bottom. This tube shaped shell of plastically deformable material 8 surrounds a core 6 of rock mass. The outside of the shell 8 is also surrounded by rock. At the ground surface the cavity 7 is sealed with a layer of concrete 29. The concrete layer 29 prevents precipitation from penetrating the plastically deformable material 8. The concrete layer 29 is made sufficiently thick to prevent deliberate damage to the system e.g. through actions of war.The top side of the concrete layer could be rounded convexly as shown in the figure so that missiles hitting the concrete layer will rebound away from it.

The embodiment shown in Figure 4 is particularly suitable if the ground water level in the surrounding rock is high. The core 6 of rock mass which is located inside the clay shell 8 can be drained so that it becomes free from ground water, and the clay shell 8 effectively prevents ground water in the outer rock from penetrating into the system.

Other parts shown in Figure 4 can be designed in the same manner as the corresponding parts of the embodiment described with reference to Figures 1- 3 and will not be described in particular.

Figures 5 to 7 show another embodiment of the invention in which there is provided only one layer or shell of plastically deformable material (e.g. clay) around the inner hollow body.

The repository shown in Figures 5 - 7 is assumed to be situated in a rock formation at a suitable depth, e.g. 300 to 600 meters below the ground surface.

In the rock is excavated a cavity the walls of which are designated 31. This cavity is so excavated that a core 32 of rock mass remains in its interior. The space between this core and the outer rock is filled with a plastically deformable material 33, e.g. clay.

In the core 32 is excavated an inner cavity 34 which has the form of a cylinder with a vertical axis. The walls of cavity 34 are provided with a large number of recesses 35 which extend radially from the cavity into the core 32. The recesses 35 are intended to form storage spaces for the radioactive material. If this material consists of fuel rods containing spent but not reprocessed nuclear fuel, the form of the recesses 34 is adapted to the form of these fuel rods, so that a fuel rod can be inserted in each recess 35. However, in the first hand the repository is to be used for the storage of the radioactive waste that is produced by reprocessing spent nuclear fuel. Such waste is converted by known methods to solid form, e.g. by vitrifying, and is filled in containers which preferably have an oblong cylindrical form.

The storage spaces 35 can be adapted to the form of these waste containers. Thus, the recesses 35 are preferably arranged in groups which are placed above each other, the recesses of each group extending radially outwards from the inside of the cavity 34 with equal angular spacing as seen in Figures 5 and 7.

The cavity 34 communicates through a vertical shaft 36 with a horizontal tunnel 37.

Through tunnel 37 and shaft 36 the radioactive material is transported into the cavity 34. The repository is of course provided with suitable hoisting and transport means for transporting the radioactive material through shaft 36 and for distributing the waste in the recesses 35. These hoisting and transport devices which are preferably remote controlled may be of a kind well known in the art and will not be described more in particular.

The core 32 is supported at its bottom by concrete pillars 38 which rest upon the rock outside the shell 33 of clay. The form and arrangement of these pillars is most clearly seen in Figure 6.

The repository is provided with an inner cooling system which consists of a plurality of conduits 39 containing a suitable coolant which is preferably water. Each conduit 38 forms a closed loop which is situated in a vertical plane and which extends along the inner wall of cavity 34 and along the outside of the core. In that part of the cooling loop 39 which is situated in the cavity 34, the coolant will be heated by the heat developed by the radioactive material in the recesses 35, and therefore the coolant is caused to circulate around the loop 39 and is cooled at the outside of core 32 where the temperature is lower.

The repository is also provided with an outer cooling system which consists of a tunnel which extends in a helix having a plurality of turns concentrically with the whole system and along its whole height.

The helix-shaped part 40 of this tunnel is connected at the top to a tunnel 41 for the removal of hot coolant and connected at the bottom to a tunnel 42 for the supply of cooler coolant. At some distance from the system the tunnels 41 and 42 are connected to each other (not shown in the drawing) so that a closed cooling system is formed which likewise operates according to the thermosiphon principle.

Cracks and crevices that may be present in the rock core 32 are sealed by injection of some suitable sealing material, e.g. sodium silicate which as time goes on is converted into silicium dioxide.

The construction of this repository can likewise be effected by the use of well known methods of rock excavation. At first working and transport tunnels are driven in the rock to the place where the cavity 35 is to be located. The excavation of the cavity will take place from below and upwards.

The cavity is filled with clay as the rock mass is removed. Before the cavity is filled with clay in its bottom part the concrete pillars 28 are cast.

If the repository is to be used for the final storage of radioactive waste, e.g. such waste that is produced in reprocessing spent nuclear fuel, the whole repository can be sealed when all recesses 35 are filled with radioactive waste. This sealing can be effected by filling the cavity 34, the shaft 36 and the tunnel 37 wholly or in part with clay or other suitable material.

The dimensions of the repository may of course vary within wide limits. The core 32 can e.g. have a largest diameter of 25 meters and a height of 60 meters, and the shell 33 of clay can have a thickness of 6 meters. These dimensions are given only by way of example and the invention is of course not restricted to these dimensions.

Figures 8-11 illustrate an embodiment of the invention in which the heat generated by the stored radioactive material is distributed and dissipated in a particularly simple and effective way.

The repository shown in Figures 8-11 can be located in the bedrock 1 at a certain depth below the ground level 2. This depth may be for instance 300 to 600 meters. In the bedrock 1 there is excavated an outer cavity the outline of which is designated 53 in Figure 8, and in this cavity there is left a core 54 of rock. The space between this core 54 and the outer rock is filled with clay 55 which forms a shell enclosing the core 54 of rock. The core 54 is positioned in relation to the outer bedrock 1 by means of supporting members 56 which may consist of reinforced concrete or of left rock.

The core 54 contains an inner cavity 57 of a spherical form. Thus, the core 54 forms a shell of rock around the cavity 57. The cavity 57 communicates through a vertical shaft 58 with a horizontal tunnel 59 which is located adjacent to the ground level. The cavity 57 and the shaft 58 are line with reinforced concrete 60.

The cavity 57 constitutes the storage space for the radioactive material. A vertically standing cylinder 61 of reinforced concrete is placed within the cavity 57. This cylinder is shown in detail in Figure 10. As seen in this figure the wall thickness of the cylinder may be larger in the central part of the cylinder and decrease towards the ends of the cylinder. At the lower end of cylinder 61 there are arranged two rows of ventilation holes 62 along the periphery of the cylinder. Adjacent to the top end of the cylinder there are also provided a row of holes 63 along the periphery of the cylinder wall. The cylinder 61 rests by its lower end on the bottom part of the cavity 57 while its upper end is at some distance from the top part of the cavity 57.Thus, the cylinder 61 divides the cavity 57 in an outer space between the outside of cylinder 61 and the wall of cavity 57 and an inner space formed by the interior of the cylinder. These spaces communicate with each other through the openings 62 in the lower end of the cylinder 61 and through the open upper end of the cylinder and the holes 63.

As shown in Figure 9 the space in cavity 57 which is not occupied by the cylinder 61 is filled with spherical bodies in the form of balls 64 of concrete which are all of the same diameter. Such a ball 64 is shown more in detail in Figure 11. The ball is provided with a plurality of through cylindrical openings 65. In the embodiment shown in Figure 11 there are three such openings. The openings 65 have the form of straight cylinders and seen in a cross-section at right angles to their axes they are so disposed that the center lines are at the corners of an equilateral triangle. Each ball 64 is provided with a hook or strap 66 which is anchored in the ball and by means of which the ball can be lifted and lowered. The balls 64 are so placed in the cavity 57 that the openings extend in a direction at a certain angle to horizontal plane.This angle should be such that the openings terminate in the spaces between the balls. The hook or strap 66 is so located in relation to the openings that when the ball is lowered into the cavity 57 hanging in the hook or strap 66, the openings 65 will automatically assume the desired direction.

All the balls 64, both those located outside and those located inside the cylinder 61, are provided with such openings 65. The purpose of these openings is to facilitate the circulation of air within the cavity 57. In Figure 9 those balls 64 which accommodate radioactive material have been indicated by circles crossed by oblique parallel lines, whereas balls 64 not containing radioactive material are indicated by empty circles.

The radioactive material to be stored in the repository is assumed to be solid and shaDed into rods. Thus, spent fuel rods and fuel assemblies from a nuclear reactor can be stored without any further treatment in the repository according to the invention.

The rods of radioactive material are entered into the openings 65 in some of the balls 64, namely those balls that are placed within the cylinder 61 and preferably only in those balls 64 which are at the lower part of the interior of cylinder 61. Preferably the cylinder 61 is filled with balls 64 containing radioactive material only to one third of its height. The rods of radioactive material are placed in the openings 65 in the balls 64 in such a way that the rods are spaced from the inside of the openings 65 so that air can freely circulate through the openings along the rods of radioactive material. Figure 11 shows some fuel assemblies 67 placed in the openings 65 in the ball 64. The rods are positioned within the openings 65 by means of suitable support means not shown).

The cavity 57 is closed by means of a seal 68 located in the shaft 58 near its opening into the cavity 57. The cavity 57 may contain sensing means sensing temperature, pressure and radioactive radiation. These sensing means could be connected with measuring instruments located outside the repository by means of cables 69 which are drawn through the seal 68 and the shaft 58.

The construction of the repository can be effected by the use of rock blasting methods well known in the art and will therefore not be described more in particular. The cavity 57 should be lined on its inside with heavily reinforced concrete. The concrete cylinder 61 is manufactured by casting on its place within the cavity 57. The space outside the cylinder 61 is filled with concrete balls 64 which are lowered through the shaft 58.

Concrete balls 64 containing radioactive material are palced at the bottom of cylinder 61 and above these balls are placed concrete balls 64 not containing radioactive material.

The shaft 58 opens straight above the upper opening of cylinder 61. If so desired the balls 64 can easily be removed from the interior of the cylinder, which may be desirable for instance if the stored radioactive material is to be removed for reprocessing.

In the repository according to Figures 8 11 air in the bottom part of the tubeshaped member 61 will be heated by the radioactive material and caused to rise upwards within the tubeshaped member to its top end where the air is forced through the openings at the top end against the wall of the cavity where the air is cooled and flows downwards in the outer space between the tubeshaped member and the wall of the cavity, whereupon the air again flows into the tubeshaped member through the openings at its bottom end and again comes in contact with the radioactive material and is heated anew so that the flow cycle is repeated. The air flows through the spaces between the spherical bodies 14 and through the openings in these bodies.Thus, the spherical bodies act as a porous mass which makes possible a relatively free and rapid air flow and simultaneously prevents the cavity from being compressed and collapsing under the action of high external forces.

The heat generated by the radioactive material is thus distributed by convection nearly uniformly over the whole cavity, and large temperature peaks in limited areas of the interior of the cavity are avoided.

The generated heat spreads through the rock surrounding the cavity and further on to the clay shell. Due to the spherical shape of the cavity it is relativelv simple to calculate the temperature distribution in the environment of the cavity. For a given amount of stored radioactive material it is thus possible to estimate the variation with time of the temperature in the rock and the clay shell and the resulting maximum temperatures. These temperatures will of course be dependent of the dimensions of the rock mass and the clay shell, and it is therefore possible to determine beforehand these dimensions so that the temperature cannot assume critical values. By "critical values" of the temperature are ment such values which may cause undesirable changes in the rock and the clay, e.g. crumbling of the rock and drying-up of the clay so that it loses its plasticity.

A repository for the storage of 350 metric tons of spent fuel from a reactor will for instance have the following dimensions: Radius of cavity 57 = 20 meters Distance from the center of cavity 57 to the inner side of the clay barrier 55 = 65 meters The maximum temperature in shell 54 of rock will then amount to about 200"C and the maximum temperature in the clay shell 55 to less than 50"C.

In the embodiment shown in Figure 8 the clay shell 55 and the space occupied by this shell in the rock has a spherical shape.

However, the clay shell 55 and the space occupied thereby could also have other shapes, e.g. cylindrical shape within the scope of the invention.

It is not necessary to locate the repository according to this invention at a very large depth. Thus, the repository could be located above the ground water level and even in less stable rock formations. It is also possible to locate the repository according to the invention in mountains rising above the surrounding ground.

Thus, a repository constructed according to this invention will make possible a safe storage of radioactive waste during a time period sufficiently long to allow the radioactive radiation to decrease to a harmless level.

However, it will be understood that a repository in accordance with this invention can also be used for the disposal of other materials than radioactive material.

WHAT WE CLAIM IS: 1. An underground repository for the storage of radioactive material and other materials in a rock formation, comprising a first cavity in said rock formation, a first body of rock derived from said rock formation by having been left at the excavation of said first cavity so as to be surrounded on all sides by said first cavity, said first cavity being filled with a plastically deformable material supporting said first body of rock in spaced relationship relative to the outer wall of said first cavity, said first body of rock being hollow and containing in its interior storage space for the material to be stored, and shaft means extending through said rock formation through said space filled with plastically deformable material and through said first body of rock to said storage space for the transfer of the material to be stored into said storage space.

2. A repository as claimed in claim 1, wherein said first body of rock has a substantially ellipsoidal form.

3. A repository as claimed in claim 1 or 2, wherein said plastically deformable material is clay.

4. A repository as claimed in claim 1, 2 or 3, wherein said first cavity is extended up to the ground level of said rock formation.

5. A repository as claimed in claim 4, wherein said first cavity is sealed with concrete at the ground level.

6. A repository as claimed in any one of claims 1 to 5, comprising a second cavity within said first body of rock, said second cavity serving, at least partially, as said storage space.

7. A repository as claimed in claim 6, wherein the walls of said second cavity are provided with recesses forming said storage space.

8. A repository as claimed in claim 7, in which said second cavity is substantially cylindrical with a substantially vertical axis, said recesses extending substantially radially outwards from the cylidrical wall of said second cavity.

9. A repository as claimed in any one of claims 1 to 8, comprising a cooling system including a plurality of closed conduit loops for the circulation of a coolant, each df said conduit loops having a first part extending through the interior of said first body of rock between the lower part and the upper part theredf and a second part extending outside said first body of rock in said-space between said first body of rock and the walls of said first cavity.

10. A repository as claimed in any one of claims 1 to 9, wherein said plastically deformable material is stabilized in the lower portion of said space.

11. A repository as claimed in claim 1, comprising a second cavity located within said first body of rock, a second body of a solid material disposed within said second cavity, said second body being hollow and containing said storage space in its interior, said shaft means extending into the interior of said second body so as to communicate with said storage space therein.

12. A repository as claimed in claim 11, wherein said second body is made of concrete.

13. A repository as claimed in claim 11 or 12, wherein said second body has a substantially ellipsoidal form.

14. A repository as claimed in claim 11, 12 or 13, wherein the space between said second body and the walls of said second cavity is filled with air and stay means are connected between said second body and the walls of said second cavity to suspend said second body in said spaced relationship relative the walls of said second cavity.

15. A repository as claimed in claim 11, 12 or 13, wherein the space between said second body and the wall of said second cavity is filled with a plastically deformable material supporting said second body in said spaced relationship relative the walls of said second cavity.

16. A repository as claimed in any one of claims 11 to 15, wherein said plastically deformable material is clay.

17. A repository as claimed in any one of claims 11 to 16, wherein said second hollow body contains several internal storage compartments vertically spaced within said second body and separated from each other by horizontal partition walls provided with openings for the transfer of the material to be stored into said storage compartments.

18. A repository as claimed in claim 1, in which said first body of rock is of a substantially spherical form and has a central cavity which contains a tube-shaped member of solid material, said tube-shaped member extending in a vertical direction and being open at both ends thereby dividing the cavity in said first body in an outer space and an inner space, said outer and inner spaces communicating with each other

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. above the ground water level and even in less stable rock formations. It is also possible to locate the repository according to the invention in mountains rising above the surrounding ground. Thus, a repository constructed according to this invention will make possible a safe storage of radioactive waste during a time period sufficiently long to allow the radioactive radiation to decrease to a harmless level. However, it will be understood that a repository in accordance with this invention can also be used for the disposal of other materials than radioactive material. WHAT WE CLAIM IS:

1. An underground repository for the storage of radioactive material and other materials in a rock formation, comprising a first cavity in said rock formation, a first body of rock derived from said rock formation by having been left at the excavation of said first cavity so as to be surrounded on all sides by said first cavity, said first cavity being filled with a plastically deformable material supporting said first body of rock in spaced relationship relative to the outer wall of said first cavity, said first body of rock being hollow and containing in its interior storage space for the material to be stored, and shaft means extending through said rock formation through said space filled with plastically deformable material and through said first body of rock to said storage space for the transfer of the material to be stored into said storage space.

at the top and bottom ends of said tubeshaped member, both said outer space and said inner space being filled with spherical bodies of a heat resistant material, said bodies being provided with through openings and being arranged so that these openings extend at an angle to the horizontal lane, and said openings in the spherical bodies located at the lower part of the interior of said tube-shaped member being adapted to accommodate solidified radioactive material formed into rods having a less diameter than said opening.

19. A repository as claimed in claim 18, in which said tube-shaped member consists of a cylindrical tube of concrete which is open at both ends and also provided with apertures around its periphery adjacent to both ends of the tube.

20. A repository as claimed in claim 18 or 19, in which said spherical bodies are made of concrete.

21. A repository as claimed in any one of claims 18 to 20, in which the spherical bodies are provided with hooks or straps for lifting the bodies.

22. An underground repository substantially as described with reference to the accompanying drawings.