What is nuclear waste?
What is nuclear waste?
Radioactive waste means a material, item or structure that contains radioactive substances, has no use and which, due to its radioactivity, must be rendered harmless.
Typically, radioactive waste cannot be disposed of; rather, it must be isolated from living environments and habitats in a reliable manner. The activity of the waste nevertheless diminishes by itself through radioactive decay, and the requirements set for the isolation of waste depend, in addition to the activity level, on the half-life of the prevalent radionuclides.
The use of nuclear energy and the production of nuclear weapons generate large amounts of radioactive waste, referred to as nuclear waste according to its origin. In Finland, nuclear waste is primarily generated in the nuclear power plants in Loviisa and Olkiluoto. Small amounts are also generated in the research reactor located in Otaniemi. Given that the Otaniemi research reactor is being decommissioned, it is generating decommissioning waste. Nuclear waste is subject to nuclear energy legislation.
Other radioactive waste accumulates in the context of extraction operations, the industrial sector, healthcare and in research facilities which use sources of radiation. The quantities and activity of such waste are minor compared to nuclear waste, with the exception of excavation wastes where the quantities may be high. They are subject to radiation legislation.
The maintenance alternatives in principle
The principled alternatives for taking care of nuclear waste are often summarised by the following slogans:
- Delay and decay
- Dilute and disperse
- Concentrate and confine
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.
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.
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.