Patent Number: 048062790
Section: summary

FIELD OF THE INVENTION The present invention relates to vibratory processing arrangements and is particularly concerned with such a processing arrangment applicable to impregnating solid particulate synthetic rock precursor in an active cell with high level radioactive waste. Subsequent hot pressing will cause the formation of synthetic rock in which the waste is immobolised. BACKGROUND OF THE INVENTION The present applicant and The Australian National University are the proprietors of a series of inventions in this field. Australian patent application No. AU-B65176/80 (now Pat. No. 531,250) describes a hot uniaxial pressing process including embodiments in which a canister having a generally cylindrical wall of bellows like formation is used to contain the supply material to be pressed and while heating is maintained pressure is applied by a hydraulic press. The synthetic rock product is formed as the bellows like canister is axially compressed. A further patent application no. AU-72825/82 (now U.S. Pat. No. 524,883) describes a development of the hot uniaxial pressing in which the pressing is conducted in an upward direction against a fixed top abutment in the press. The prior art referred to in the above specifications includes prior art of The Australian National University describing the formation of synthetic rock from selected phases and suitable for the immobilisation of radioactive waste. Typically, synthetic rock precursor is in the form of a fine powder and high-level radioactive waste is a liquid which must be impregnated into the powder in the active cell and pressing must also take place in an active cell. Extremely reliable mechanical handling methods and equipment are required since it is desired for the equipment to operate for tens of years with servicing and repairs conducted only through remote manipulators. SUMMARY OF THE INVENTION The present invention is directed to processing arrangements and corresponding apparatus which can facilitate active cell processes which are highly reliable and conducted with equipment which is intrinsically relatively simple so that long working life and maintenance with remote manipulators can be provided. According to a first aspect of the invention there is provided a method of producing impregnated synthetic rock precursor comprising: feeding particulate synthetic rock precursor into a vibratory conveying means having an elongated path along which the particulate material is progressively moved under vibration, PA1 spraying the particulate material with a liquid incorporating radioactive waste over an extended region of the elongated path such that the liquid is absorbed into the particulate material which continues to advance to the discharge end of the device, and PA1 discharging the impregnated synthetic rock precursor. According to a second aspect of the invention, there is provided a method of preparing synthetic rock precursor for a hot uniaxial pressing process, the precursor being of particulate form and having impregnated therethrough radioactive waste, the method comprising passing the material into an upstream end of an elongated downwardly inclined tubular duct, establishing vibration of the tubular duct whereby the particulate material advances progressively and applying high level heating so as to calcine the particulate material, and discharging the calcined material at the downstream end of the apparatus. According to the third aspect of the invention, there is provided an arrangement for mixing a titanium powder into a calcined synthetic rock precursor incorporating therein radioactive waste; the arrangement comprises using a tubular vibratory conveyor which is downwardly inclined in the downstream direction and the titanium powder is introduced just downstream of the synthetic rock precursor inlet to the vibratory tube, whereby intimate mixing of the particulate material occurs in a well controlled and continuous manner. The discharge can be to a receiving hopper and/or to a bellows-like container whereby the poured material is ready for a hot uniaxial pressing process. PREFERRED FEATURES OF THE PRESENT INVENTION Although preferably the invention is implemented in a continuous process in which the elongated path extends from spaced upstream and downstream ends. the process can also be operated with paths of different configuration and indeed can be operated in a batch process in which the vibratory conveying means causes the particulate precursor to move around within a suitable vessel as it is being sprayed with radioactive waste liquid. For example, a generally square trough-like vessel may be used and the vibratory conveyor means can cause the particulate material to circulate around the trough. One very important embodiment of the invention is one in which heat is applied to the impregnated synthetic rock precursor thereby maintaining a substantially dry state and causing evaporation of water thereby leaving the radioactive material impregating the waste. The level of heating is preferably relatively low e.g. 300.degree. C. whereby the powder can remain in a flowable state and components of the radioactive waste which are volatile at higher temperatures remain substantially in the synthetic rock. The conveyor may be inclined either upwardly or downwardly or may be horizontal. This is dictated by the physical form of the precursor. Preferably the invention is implemented in a generally trough-like vibratory conveyor and has a vibrating element applied near its upstream end, its downstream end being supported in a flexible mounting and remaining substantially stationary. Preferably a series of spray heads are spaced along the trough-like conveyor. In a preferred embodiment, the synthetic rock precursor is formed into granules having an improved pourability and packing density compared with the particles of synthetic rock precursor; it has been found that use of this aspect of the invention permits very effective impregnation of such granules with highly uniform dispersion of radioactive components through the final synthetic rock produced after a hot uniaxial pressing process. Preferably, the apparatus is arranged to provide an operating temperature of about 750.degree. C. The calcining apparatus preferably has a variable frequency vibration unit which preferably is directed to actuate vibrations at the downstream end of the tube, the upstream end being mounted in suitable flexible mountings and substantially not moving. With advantage, induction heating can be used for the furnace which can be surrounded by insulating material. Furthermore, in the second aspect of the invention a most advantageous embodiment is one in which the tubular duct is connected to a gas circulation system whereby a controlled atmosphere can be passed preferably in a counter current arrangement through the tubular duct, whereby volatile radioactive components from the waste can be taken up and removed through suitable filtering arrangements. This aspect of the invention permits a reliable and very compact capital effective plant to be devised thereby obviating the complexity and very considerable volume required for an apparatus such as a rotary calciner. The capital cost per cubic meter of an active cell is very high and therefore a major impact on the economics of safe disposal of radioactive material may result from use of embodiments of the present invention. Various embodiments of the invention can contribute substantially to a most effective plant for high level waste immobilisation in synthetic rock by providing a compact and reliable process substantially avoiding the handling of any solids other than dry pourable solids at each stage. In a most effective and important embodiment all three of the above aspects of the invention are used in combination in sequence and furthermore a further inventive combination is one in which the above three aspects are used in combination with the further inventive step the subject of the present applicant's co-pending application entitled "Formation of Ceramics" and which is directed to an invention consisting in an apparatus for hot uniaxial pressing of heat resistant metal canisters containing synthetic rock components, the canisters having a generally cylindrical wall incorporating bellows-like formations, the apparatus comprising a hydraulic press having an upwardly acting ram with a refractory facing thereon for supporting the bottom of the canister, a fixed top abutment, a heating zone immediately below the abutment and adapted to surround the bellows container during the hot uniaxial pressing process and a retractable platen adapted to be inserted laterally into the press below the heating zone such that a bellows canister can be placed on the refractory facing and partially compressed at ambient temperature by upward displacement of the hydraulic press, the platen being removable to permit the press to be displaced upwardly to a higher level whereby the bellows-like canister is inserted within the heating zone and abuts against the top abutment.