Radioactive waste is normally divided into three categories: low-, intermediate- and high-level waste. Low-level waste is so safe that it can be treated as ordinary waste after being sorted and washed. It consists mostly of items such as used protective clothing and filters. Intermediate-level waste must be isolated and radiation-shielded for about 500 years before it is no longer considered hazardous.
High-level waste consists of spent nuclear fuel. This accounts for 99 per cent of the radiation but only around five per cent of the total volume of nuclear waste. Several metres of water or several decimetres of steel are needed to contain the nuclear fuel radiation. The half-life (the time it takes for radioactive material to lose half of its radioactivity) varies widely between different radionuclides, from less than a second to millions of years, and the waste must be isolated for a very long time. By some estimates at least 100,000 years.
The solutions vary between countries
Each country has to take care of its own nuclear waste. The solutions vary somewhat between countries, and planning has reached different stages.
The Swedish solution prescribes that the spent nuclear fuel, as a first step, is stored in deep water reservoirs for a minimum of 30 years. Until approximately 90 per cent of the radiation has dissipated.
The spent nuclear fuel is then put in geologic final storage. It is encased in various types of protective material such as copper and iron. These capsules are then stored, surrounded by bentonite clay, in vaults or tunnels drilled 400 to 1,000 metres underground.
Several countries have strategies similar to the Swedish solution, and this type of terminal storage is planned in several areas but is not yet operational. In some other countries, however, the strategies for final storage remain unclear.