6.43.
Solid radioactive waste may be heterogeneous. Particular consideration should be given to representative sampling before processing so as to confirm compatibility of the waste with the intended process, and appropriate arrangements should be made for such sampling as far as practicable. Arrangements should be made for the systematic control of the final treatment products to verify compliance with established requirements.
6.44.
A great number of processes are available for producing acceptable waste forms. The processes to be employed should be selected on the basis of the characteristics of the waste concerned. If possible, processes that achieve high volume reduction factors and that use proven techniques, such as compaction or incineration, should be employed.
6.45.
Incineration of combustible solid waste normally achieves the highest reduction in volume as well as yielding a stable waste form. After combustion, radionuclides from the waste will be distributed between the ash, the products from cleaning the exhaust gases and the stack discharges. The distribution will depend on the design and operating parameters of the incinerator used and the nature of the radionuclides in the waste. Incineration will result in an increase of the activity concentration levels in the ash, which might result in a change of the waste class. In addition, other constituents in the waste may yield acidic gases and corrosive combustion products, which could lead to corrosion of the incinerator’s components and to acid releases to the atmosphere. Off-gas scrubbing to prevent the discharge of radioactive material and non-radioactive hazardous materials may be necessary and should be considered. Consideration should be given to the possibility of radionuclides accumulating in residues of the gas cleaning system and of radionuclides remaining in the ash, and to the need for further conditioning.
6.46.
Releases of radionuclides to the environment are largely determined by the operating conditions of the incinerator, in particular by control of the temperature and the types and amounts of waste treated and the radionuclide content. For incinerators processing significant amounts of radioactive waste, the operating organization should monitor the radionuclides in the stack discharge by appropriate means to ensure that the concentrations and amounts discharged are within the limits specified by the regulatory body and are consistent with the parameters modelled in the safety assessment. Certain products of incineration (acids, polychlorinated biphenyls and various other materials) present non-radiological hazards.
6.47.
Compaction is a suitable method for reducing the volume of certain types of waste. It may include the compaction of ash resulting from the incineration of waste. The characteristics of the material to be compacted and the desired volume reduction should be well defined and controlled. Consequences of compaction that should be given consideration in selecting or designing and operating a compactor include the following:
The possible release of volatile radionuclides and other airborne radioactive contaminants during compaction;
The possible release of contaminated liquid during compaction;
The chemical reactivity of the material during and after compaction;
Potential fire and explosion hazards due to pyrophoric or explosive materials or pressurized components;
Criticality hazards when waste that contains fissile material is compacted into a single waste package.
6.48.
Segmentation or disassembly and other size reduction techniques may be applied before the conditioning of waste that is bulky or oversized in relation to the intended processing (e.g. worn out components or structures). Processes for segmentation or disassembly typically use cutters with high temperature flames, various sawing methods, hydraulic shearing, abrasive cutting and plasma arc cutting. The need for means of preventing the spread of particulate contamination and for fire protection in case of pyrophoric waste should be considered in the selection of the method and in the operation of the equipment.
6.49.
For non-combustible and non-compressible solid waste, for which ‘delay and decay’ or decontamination is not a viable option, direct conditioning without prior treatment should be considered. Melting of metal scrap, with resultant homogenization of the radioactive material and its accumulation in the slag, may be considered as a means of achieving material that can be reused or cleared from regulatory control.