Compositions – Radioactive compositions
Patent
1991-07-18
1993-09-28
Nelson, Peter A.
Compositions
Radioactive compositions
252632, 2505061, G21F 916
Patent
active
052484530
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of processing a dry precursor material incorporating radioactive waste. The invention is particularly concerned with the incorporation of high level radioactive waste within an immobilising substance such as synthetic rock or glass.
BACKGROUND OF THE INVENTION
An existing arrangement for producing synthetic rock precursor incorporating high level radioactive waste involves the production of synthetic rock precursor using tetraisopropyltitanate and tetrabutylzirconate as ultimate sources of titanium oxide TiO.sub.2 and ZrO.sub.2. The components are mixed with nitrate solutions of other components, coprecipitated by addition of sodium hydroxide and then washed. The precursor thus produced is mixed in a hot cell with high level nuclear waste in the form of a nitrate solution to form a thick homogenous slurry. The slurry is then fed to a rotary kiln in which the slurry is heated, devolatilized and calcined to produce a powder which is then mixed with metallic titanium powder and poured into containers for hot pressing.
The containers which are used for this purpose have a generally cylindrical wall of bellows-like formation. Heat and pressure is applied to each container and its contents, and a synthetic rock product is formed within the container with the high level radioactive waste suitably immobilised therein.
A system for producing synthetic rock as described above has a number of deficiencies which will now be outlined.
The apparatus required to produce the synthetic rock requires that a slurry incorporating high level radioactive waste be fed into a calciner. The calciner must be free of oxygen by the use of a reducing gas and at the same time the slurry must be heated and dried.
A calciner which meets all these objectives is a large and cumbersome apparatus with numerous working parts on which it is difficult to perform maintenance on. Typically, a rabble bar is required within the calciner to prevent caking of the slurry and a filtration system is required to prevent escape of radioactive dust.
The present invention provides an alternative method for use in forming a substance incorporating immobilised radioactive waste.
DISCLOSURE OF THE INVENTION
According to the present invention, there is provided a method of processing a dry precursor material incorporating radioactive waste comprising: filling a container with dry precursor material incorporating radioactive waste and nitrate components, the container having a generally cylindrical shape with at least a partially corrugated side wall, a gas outlet, an outlet filter, a gas inlet and an inlet filter; sealing the container excepting the gas inlet and outlet; heating the container and its contents while feeding a gas through the gas inlet, inlet filter and dry precursor material; and collecting exhaust gas passing through the outlet filter and gas outlet; whereby a dry calcined material incorporating radioactive waste is produced in a form in which substantially all nitrate components have been decomposed and removed.
Preferably deleterious effects of the dried calcined material when in the form of a synthetic rock precursor are avoided by providing that the gas is a reducing gas such as H.sub.2.
Preferably, the method includes a step of hot isostatically or uniaxially pressing the container once substantially all the nitrate components have been decomposed and removed.
The gas inlet and outlet are preferably arranged at opposite ends of the container.
Alternatively, the gas inlet and outlet may be located on the side wall of the container or at the same end.
The gas inlet and outlet may both be connected with a perforated inlet and outlet pipe respectively which are located within the container and are separated from the dry precursor material by the inlet and outlet filters respectively.
Preferably, the container has a dumb-bell shape.
The container is preferably provided with a filling port which is arranged to permit filling of the container with dry precursor material.
It is prefe
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patent: 4626414 (1986-12-01), Baatz et al.
patent: 4642204 (1987-02-01), Burstrom et al.
patent: 4645624 (1987-02-01), Ramm et al.
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patent: 4778626 (1988-10-01), Ramm et al.
patent: 4808337 (1989-02-01), Ramm et al.
patent: 4834917 (1989-05-01), Ramm et al.
Australian Nuclear Science & Technology Organization
Mai Ngoclan T.
Nelson Peter A.
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