Hazardous or toxic waste destruction or containment – Containment
Patent
1993-06-10
1995-05-09
Taylor, Dennis L.
Hazardous or toxic waste destruction or containment
Containment
100 37, 100249, 110346, A62D 300
Patent
active
054142083
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the formation of densified material and more particularly is concerned with producing blocks of densified material formed from particulate solid material. The invention will be exemplified with particular reference to the problem of a system for providing a synthetic rock structure in which high level radioactive waste is to be immobilised in a manner suitable for safe long term storage.
The present applicants through their prior published patent specifications have disclosed systems for immobilising high level radioactive waste. Synthetic rock precursor material is impregnated with liquid high level radioactive waste, and a pourable granulated solid is formed. This solid is then poured into a suitable container which, after closure, can undergo a pressure process at elevated temperature in order to produce a uniform densified block of synthetic rock which has extraordinarily high leach resistance.
Such processes must be conducted in active cells which are very expensive to build and the process must be operated with remote manipulators. Commercial factors dictate that the process must be capable of being operated for a large number of years with just simple maintenance by remote manipulators. Exceedingly high reliability is required. Thus there has been a longstanding need to conceive of and develop elegant engineering solutions aimed at providing the highest possible through-put of processed material in the smallest volume of active cell space.
The present invention is directed to providing new and useful alternatives to previous proposals. It will be appreciated that although the invention has particular application to processing nuclear waste into synthetic rock form, the process arrangements may be equally valuable for other purposes such as the formation of sophisticated ceramic materials of non-radioactive character. For machining into components of different types, there is a need to be able to produce efficiently cylindrical blocks of ceramic and embodiments of the invention can be useful in this field.
According to a first aspect of the present invention, there is provided a method of forming a densified block of material from a particulate solid, the method comprising (a) arranging a vertically extending tubular furnace with open ends for providing an entry and a discharge for processing elements to be passed in a stream through the furnace, the processing elements comprising canisters and spacer elements, pressure means being provided to be selectively operable to exert a compressive force only along the axis of the furnace and onto the stream of processing elements, (b) supplying the particulate solid in the canisters, each canister being of generally cylindrical form and a clearance fit in the furnace, each canister having axial end walls and a bellows-like convoluted side wall extending between the end walls, each canister being formed to retain the solid and to compress axially with no substantial radial expansion in the process, (c) supplying spacer elements to co-operate with the supplying of canisters whereby the stream is formed as a vertical column extending through the furnace, each spacer element being a rigid, refractory, cylindrical element dimensioned to move along the tubular furnace during the process and having end walls each shaped to engage with an axial end wall of a canister for controlling the location of the canister so as to be spaced from the wall of the furnace and for controlling uniaxial compression of the canisters, (d) operating the pressure means to compress the column and after sufficient residual time to displace a processing element through the discharge end of the furnace, (e) removing the applied pressure from time to time and either or both (i) removing a processing element from the discharge end and (ii) inserting a new processing element at the entry end of the furnace, and (f) activating holding means to support the column of processing elements to enable substitution of the lowermost processing element in the column.
The
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Australian Nuclear Science & Technology Organisation
Taylor Dennis L.
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