Taking care of nuclear waste

The principled alternatives for taking care of nuclear waste are often summarised by following three choices

1. The ‘delay and decay’ approach, i.e. storing the waste until its activity level has dropped below the exemption value, is mainly useful when the halving times of the radionuclides contained by the waste are approximately 100 days in maximum. Most of the radioactive waste generated by hospitals can be made harmless in this way. As nuclear waste contains a large number of radionuclides of various ages, the delay method is not particularly effective to reduce the quantity of waste. This being said, by delaying it is often possible to facilitate the further processing of the waste by reducing the radiation levels and the easily released radioactive substances.
2. Many facilities subject to radiation control release radioactive substances to the air and waterways in a controlled manner. This is then subject to the ‘dilute and disperse’ approach: the initial dilution ensures that even the maximum concentrations will remain minor in the living environment and that the concentrations will be diluted further as the radioactive substances disperse into the atmosphere or waterways. The ‘dilute and disperse’ principle is often linked to the processing of gaseous or liquid radioactive substances: the low-activity but large-quantity percentage is released into the environment, whereas the majority of the activity is condensed into solid radioactive waste.
3. The third principle, ‘concentrate and confine’, means turning the radioactive waste material into a compact, permanent form, which is isolated from the living environment by means of the final disposal of the waste packages. The trend has been to consistently reduce radioactive substance emissions and collect more of the waste materials.

Treatment of nuclear waste

Pretreatment of waste may include waste collection, sorting, neutralisation or other chemical characterisation, decontamination and primary characterisation (see classification). For liquid wastes, volume reduction may include ion exchange, mechanical filtration, evaporation, chemical precipitation and centrifugation. Solid waste can be reduced by incineration, compression, shredding or melting. In the case of pre-treatment, some waste may be exempted from control for disposal as normal waste if it is found to be sufficiently low-active during initial characterisation.

Final treatment involves the waste being made stable and packaged in a container for storage, transport and disposal. Liquid and finely divided waste materials are usually brought to a more stable form by solidification with a suitable solidifying agent, such as cement or bitumen, in the waste package. Solid waste is packed in containers as such or with a cementitious filling.