Patent Number: 050227882
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT In respect of the following and previously set out description and explanation, it should be understood that while the information given is considered to be correct, such explanations are necessarily somewhat speculative since the amount of factual information relating to the earth's crust and deep mantle is limited. Applicant would not want to be bound, therefore, by the following explanations if, subsequently, new and better information becomes available. The explanations hereinafter given are made for the purpose of full and complete disclosure of the invention but the qualification given above should be borne in mind. With reference now to the drawings, FIG. 1 illustrates the locations of subduction zones and plates throughout the world. The Pacific Plate 10 subducts the Indo-Australian Plate 11 on the North Island of New Zealand 12. The Explorer Plate 13 subtends the North American Plate 14 opposite the Canadian located Brooks Peninsula and Scott Islands generally illustrated at 15. The Gorda Plate 20 subtends the North American Plate 14 opposite the United States site of Cape Mendecino generally shown at 16. The four locations set out above are the only naturally occurring sites where the topography would allow a viable tunnelled access using current technology to the subduction zone where the tectonic plate descends adjacent the non-descending earth's crust. All other subduction zones are associated with deep ocean trenches and/or are situated far enough from land, that accessing them by a tunnel would be impractical. One exception is the Himalayas Subduction Zone. The truncated nature of the Himalayas Subduction Zone 40, however, where the continental crust subtends another continental crust makes India a less desirable location to dispose of high-level radioactive waste than the four locations set forth above. A typical subduction zone generally illustrated at 30 is shown in FIG. 2. The descending tectonic plate generally illustrated at 21 includes the sedimentary layer 22, the oceanic crust 23, the continental crust 42 and some semi-plastic rock mass 24. The subduction zone 30 denotes the boundary between the tectonic plate 21 and the non-descending plate 31. The tectonic plate 21 descends at a rate of about 6 cm per year into the earth's mantle 32. This phenomena is a result of the generation of the oceanic crust 23 by the rising plume of low-viscosity asthenosphere 34 at an oceanic ridge 41. The oceanic crust 23 which forms into a portion of the tectonic plate 21 moves to the left as indicated by the arrows in FIG. 2. The continental crust 42 of the tectonic plate 21 does not exist off the North American coast but could represent, for example, the Hawaiian Islands as they move towards subduction at the Japan Trench 43 (FIG. 1), or the Mariana Islands as they move towards subduction at the Phillipine Trench (not shown). The tectonic plate 21 is covered with ocean water 50 and comprises the sedimentary layer 22, the oceanic crust 23 and the continental crust 42. It descends back into the center of the earth at the subduction zone 30. It is contemplated that tens of millions of years would pass for the material in the tectonic plate 21 at the subduction zone 30 to descend downwardly as a solid, melt at a depth of approximately 700 kilometers, mix and become part of the liquid rock currents in the mantle 32 and, thereafter, migrate and return to the surface of the earth at the oceanic ridge 41. This time, of course, is far in excess of the time required for nuclear or other toxic waste materials to become harmless. It is calculated, for example, that Plutonium 239 placed in repositories in the tectonic plate 21 at the subduction zone 30 will reach a depth 51 of about fifteen (15) kilometers when it becomes radioactively harmless at an estimated subduction rate of about 6 cm per year and the approximately 250,000 years needed for Plutonium 239 to become radioactively harmless. The heat and pressure within the earth are also effective in reducing the toxicity of non-nuclear waste. At the subduction zone 30, the abrasion of the tectonic plate 21 against the non-descending plate 31 will cause portions of the sedimentary layer 22 to be scraped off the tectonic plate 21 which sediment is added to the non-descending plate 31 although some sediment may later be dragged into the mantle 32 by the tectonic pate 21 by the same abrasive action. At a depth of 100 kilometers illustrated at 52, the subducted sediment undergoes a phase change as heat and pressure drive water from the crystal structure. Some of the sediment will malt and rise to the surface as andesitic volcanoes 53. As the tectonic plate 21 descends further into the earth, it thins due to partial plasticizing and an increase in the rate of descent due to the current flow within the mantle 32. A section illustrating the ocean 50, sediment 22 and oceanic crust 23 is shown in FIG. 3. The oceanic crust. 23 comprises the basalt lava 25, the basalt dykes 26, the gabbro 27, the layered peridotite 28 and the peridotite 29. The combination of the sedimentary layer 22 and the oceanic crust 23 comprises the tectonic plate 21. The illustration is based on seismic velocity interpretations, evidence from dredged samples and comparisons with outcrops of rocks thought to have once been parts of ocean floors. At most subductior zones, the ocean 50 is deep as subduction zones are typically associated with trenches which reach depths as great as seven (7) miles. The Cascadia Subduction Zone 54 (FIG. 1), however, lays typically beneath only one (1) mile of water and thus the subducting tectonic plate 21 could be accessed by a tunnel from the non-descending plate 31 which, in this event, for example, would be the Brooks Peninsula, the Scott Island or Cape Mendicino. The thickness of sedimentary layer 22 over the oceanic crust 23 ranges from zero at the oceanic ridge 41 where the oceanic crust 23 is formed from the rising plume of the mantle 32 to an average of 3 to 4 kilometers near continental edges where the oceanic crust 23 is typically subducted. The further a plate has spread from its originating oceanic ridge 41, the older it is assumed to be and thus the thicker is the sediment 22 overlaying it having regards to the fact that the sedimentary layer 22 is built up over millions of years by debris raining onto the ocean floor. The Cascadia Subduction Zone 54 (FIG. 1) is only 550 kilometers from the Juan de Fuca Ridge 60 at its widest point. It is assumed, therefore, that the sedimentary layer over the Explorer Plate 13, the Juan de Fuca Plate (not shown) and the Gorda Plate 20 which are all subducted at the Cascadia Subduction Zone 54 would be considerably thinner than three (3) kilometers in depth. Accordingly, the sedimentary layer 22 could be tunnelled through using a method similar to conventional mining techniques such as those which have operated in South Africa to a depth of 9300 feet. If the sedimentary layer 22 proves to be three (3) to four (4) kilometers thick at the Cascadia Subduction Zone 54, however, it is: contemplated that tunneling to the bottom of the sedimentary layer 22 and radiating repositories at that depth as set forth in more detail hereafter should allow a sufficient overlaying buffer from the effects of abrasion and volcanism suffered by the sediments in the upper regions of the sedimentary layer 22 during subduction. Preferably, however, a tunnel would be driven into the oceanic crust 23 beneath the sedimentary layer 22 before waste repositories are radiated from the tunnel access. The accessing tunnel 61 envisioned according to the invention in a first embodiment traverses the subduction zone 30 (FIG. 5) from the non-descending plate 31 and bores into the descending tectonic plate 21. Alternatively, and in a second embodiment, the tunnel 61 could originate from the continental crust 42, including a natural or man-made island, on the descending side of the subduction zone 30. In either case, repositories 63 radiate outwardly from the tunnel 61 as shown more clearly in FIG. 4. The repositories 63 would be filled with the most hazardous wastes 64 in the distal reaches of the respective repository and the least hazardous wastes 70 such as low-level radioactive waste could act as a buffer between the high level radiation and thermal heat of the high-level radioactive wastes 64 and the plug 39, thereby better isolating both types of waste from the biosphere. As viewed in FIG. 5 a caisson 62 could also be used to access the tectonic plate 21 via the access tunnel 61. It can also be seen in FIG. 5 that in a preferred embodiment of this invention, the access tunnel 61 would have a sufficiently large cross section to permit the simultaneous removal of tailings from repositories 63 undergoing excavation as well as importation of wastes into the repositories 63. The following describes the approximate volume of high level radioactive waste to be disposed of having in mind current waste stockpiles. If the amount of radioactive waste stockpiled at present is assumed to be approximately 135,000 feet, it is calculated that the repositories required would have a width and height of approximately 15 ft.times.15 ft, the repositories having a lineal distance of about 600 feet being required to dispose of the current U.S. stockpile. If the waste is shielded before being brought to the disposal site, and assuming this adds five (5) times the volume to the waste, approximately 3000 lineal feet of repository would be required which is well within current technological abilities. Besides the use of an access tunnel to allow the deposit of wastes in a subtending tectonic plate, it is also contemplated that the use of an access tunnel or borehole across the subduction zone could be utilized for installing and monitoring instrumentation which could be used to determine the movement of the subtending tectonic plate relative to the non-descending plate in the subduction zone. This possibly, could be useful for more accurately determining the onset of earthquakes at various locations on the earth's surface which could bear some relationship to the movement of the plates at the subduction zone. While a specific embodiment of the invention has been described, many modifications will readily occur to those skilled in the art to which the invention relates. Accordingly, such description should be taken as illustrative of the invention only and not as limiting its scope as defined in accordance with the accompanying claims.