Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste – Surrounding with specified material or structure
Patent
1997-09-30
2000-03-21
Popovics, Robert J.
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
Surrounding with specified material or structure
588 20, 588900, 976DIG380, 976DIG385, 976DIG395, 210770, 210805, 210808, 210406, 2104161, 210484, 210237, 210248, 294 77, G21F 900, G21F 904
Patent
active
060404914
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention generally relates to the handling and disposal of radioactive waste, in particular low-level and intermediate-level waste, from nuclear power plants.
To be more specific, the invention concerns a method for dawatering and containing aqueous, low-level or intermediate-level waste, as well as an apparatus for implementing this method.
DESCRIPTION OF THE PRIOR ART
Low-level waste from nuclear power plants occurs, inter alia, in the form of contaminated ion-exchange material obtained when cleaning the aqueous phase of the secondary side of leaking steam generators. Such cleaning may be performed in what is commonly referred to as ion-exchange beds containing a suitable amount of ion-exchange material, for instance in the order of 2000 kg per bed. As the ion-exchange material is spent and replaced with fresh material, the spent, low-level and aqueous ion-exchange material has to be taken care of in some suitable fashion. The activity of this material may be in the order of, say, 25.times.10.sup.3 Bq/kg, for which reason this material cannot be deposited as it is on the ground.
In a conventional method for handling such aqueous, low-level ion-exchange material, the material is embedded in a concrete or sheet-metal chill mould having an external volume of 1.7 m.sup.3. To this and, the aqueous, low-level ion-eaxchange material is mixed with cement under agitation in an empty chill mould in order to form a solid matrix having a volume in the order of 1 m.sup.3. The ion-exchange material proper then makes up, say, only 0.7 m.sup.3. Finally, a concrete lid is cast over the matrix in order to seal the chill mould. The finished chill mould is then ultimately disposed of in some suitable deposition compartment.
However, the containment technique described above is inconvenient in many respects. First, this technique is far too expensive. The material cost for making a single concrete chill mould of the above type may amount to SEK 10,000. Second, this technique means that the deposition compartment in which the chill moulds are to be placed is poorly utilised as to volume. Thus, but a small amount of the total volume of the chill mould is made up of radioactive waste, the remainder consisting of the concrete shell, the cement in the core as well as socalled void water accompanying the contaminated ion-exchange material from the bed. Accordingly, this prior-art technique is anything but cost-effective.
A further inconvenience of the prior-art technique is that the ion-exchange material will, owing to its content of various chemical additives serving to improve the ion-exchange function, exhibit an unfavourable pH value rendering the embedment procedure more complicated.
GB-A-2,216,034 teaches a disposable container structure for dewatering radioactive, aqueous waste by means of centrifugation. The container structure comprises a cylindrical, rigid inner container, which is integrated with a top lid and whose cylindrical circumferential wall and bottom both are water-permeable but not permeable to solid material, as well as a cylindrical, watertight and rigid outer container, in which the inner container is accommodated with a small gap towards the inner surface of the outer container, which is sealingly applied against the top lid of the inner container. The aqueous waste is supplied to the inner container through an opening in the top lid while the entire container structure, i.e. both the inner and the outer container, is rotated in a frame about a vertical centre axis of the container structure. As a result, water is by centrifugal action expelled radially through the filtrating circumferential wall of the inner container and introduced into a gap between the inner and the outer container, whence it is conducted through a lateral opening in the upper end of the outer container to be further disposed of. The centrifugation is carried out during the filling operation as well as for some time (5-10 min) after the filling operation has been completed. After the centrifugati
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Popovics Robert J.
Vattenfall AB
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