Radioactive wastes are generated by different kinds of facilities. The major contributor is the nuclear power industry but other users such as the defence industry, hospitals, manufacturing industries and educational facilities produce radioactive wastes in a variety of physical and chemical forms.
With the associated health and environmental risks associated with radioactivity, it is imperative that the radioactive waste is disposed off safely and responsibly. The methods employed in disposal of radioactive waste depend on several factors some of which are listed below:
- The activity and concentration
- The half life
- The chemical properties i.e. associated chemical hazards, reactivity and combustibility.
- The physical properties i.e. state (solid, liquid or gaseous), size and weight and solubility.
For example Plutonium-239 undergoes alpha decay. Alpha particles are relatively simple to provide protection against as their high ionisation means they cannot penetrate more than a few centimetres of air. However, Plutonium-239 has a half life of 24000 years and it is extremely toxic and corrosive therefore any disposal system for this radioactive isotope needs to be very secure for many thousands of years.
Radioactive waste has been categorised by a classification system. The categories are as follows:
High Level Waste (HLW)
This is radioactive waste produced by the chemical reprocessing of nuclear fuel. It contains mainly fission products and other heavy nuclei that are generated in the reactor core. Besides being radioactive it is thermally hot. Disposal methods for high level waste include solidifying the waste in a glass matrix and sealing it in a corrosion resistant steel lined drum. The drums are stored in specially engineered cooling pools or storage vaults.
Intermediate Level Waste (ILW)
This is radioactive waste with a radioactive content that requires shielding but requires no cooling as it is not thermally hot. Intermediate level waste includes the old components from a nuclear reactor, chemical residues and other support structures form a nuclear reactor core. Intermediate level wastes are mixed with cement and solidified in stainless steel drums which are stored in special facilities above ground or in shaft or trenches underground.
Low Level Waste (LLW)
This is radioactive waste with a low level of radioactivity requiring no shielding. Examples of low level waste include discarded protective clothing, packaging material and medical equipment such as syringes and needles. Other than nuclear power stations this waste is generated from hospitals and other industries. This type of waste is short lived and is stored on sites with special licences until it has decayed and is then disposed off as ordinary waste.
The table below summarises the categories of radioactive waste:
|Radioactive waste category||Examples||Disposal method|
|High Level Waste
|Fission products and other heavy nuclei that are generated in the reactor core.||Solidifying the waste in a glass matrix and sealing it in a corrosion resistant steel lined drum. Storing the drums in specially engineered cooling pools or storage vaults.|
|Intermediate Level Waste
|Old components from nuclear reactors, chemical residues and other support structures form a nuclear reactor core.||Mixed with cement and solidified in stainless steel drums which are stored in special facilities above ground or in shaft or trenches underground.|
|Low Level Waste
|Discarded protective clothing, packaging material and medical equipment such as syringes and needles.||Stored on sites with special licences until it radioactive decay complete and then disposed off as ordinary waste usually in landfills.|