Radioactive wastes are radioactive materials and are by-products of nuclear power generate and other applications of nuclear fission or nuclear technology such as research and medicine.
Radioactive wastes comprise of a number of radioisotopes which are unstable configurations of elements that decay emitting ionizing, radiations which can be harmful to main and the environment.
Those isotopes emit different types and levels of radiation, which last for different periods of time.
Properties of Radioactive Wastes:
Radioactivity of all nuclear waste diminishes with passage of time. All radioisotopes contained in the waste have a half-life i.e. the time taken for any radionuclide to lose half of its radioactivity. Thus, all radioactive waste decays into non-radioactive elements i.e. stable isotopes.
The nuclei of radioactive substances spontaneously disintegrate to emit protons (α-particles), electrons (β-particles) and gamma rays (short electromagnetic waves).
Sources:
The sources of radiations are both natural and man-made. The natural radiations are cosmic rays that comes to earth from space and terrestrial radiations from radioactive elements present in earth crust such as radium-224, uranium-235 and 238, thorium-232, radon-222, potassium-40 and carbon-14. The man-made radiation arise due to mining and refining of plutonium and thorium; production and explosion of nuclear weapons; nuclear power plants and fuels and preparation of radioactive isotopes medical and industrial nuclear wastes.
Radioactive medical wastes contain beta particles and gamma rays emitters. In diagnostic nuclear medicine a number of short lived gamma emitters such as technetium-99, are used which decay within a short time.
Other isotoes used in medicine are:
(i) Y-90 used for treating lymphoma (half life period 2.7 days)
(ii) 1-131, used for thyroid function test and treatment of thyroid cancer (8.0 days)
(iii) Sr-89, used for treating bone cancer (52 days)
(iv) Ir-192 for brachytherapy (74 days);
(v) Co-60 used for brachytherapy and external radiotherapy (5.3 years)
(vi) Cs-137 used for brachytherapy and external radiotherapy (30 years).
Traces of radioactive elements occur in a number of products, e.g. polonium in tobaco, radon at the base of indoor walls several naturally occurring oars. Depending upon the amount of radioactivity the following three types of radioactive wastes have been identified.
Low Level Radiation:
Radioactive wastes are produced by testing laboratories, irradiation centres for introduction of mutations, study of metabolic pathways, radiotherapy and other centres using radioisotopes.
Extremely small amount of radioactivity enters coolant water used in atomic reactors and ponds used for quenching heat and radioactivity of spent fuel. But due to bio-magnification the level may go up to 75,000 times in birds.
Intermediate Level Radiation:
These are radioactive wastes not liberating much heat. There is not much problem in disposal of such wastes as they emit intermediate level of radiation. Small amounts of these radioactive wastes occur in all oars. They are separated during processing and refinement. If these wastes are not dumped properly they can damage vegetation and can cause irreparable injuries to animals including human being.
High Level Radiation:
These are high level wastes producing a lot of heat and large amount of radiations. Even short duration exposure to such high levels of radiations causes loss of hair and nails, subcutaneous bleeding and damage to all organs. The radiations cause turners, cancers and genetic deformities. They are highly destructive radiations which develop due to (z) accidental leakage or melt down of atomic reactors (e.g. Three Mile Island of Chernobyl mishap) (ii) spent fuel of atmomic reactors.
Control:
High level wastes, need to be cooled and require special protective shields during handling and transport. First of all the wastes are to be reduced in their bulk by concentration. Then they should be sealed property in concrete or steel containers. It should be ensured that the containers are thick walled and leak proof. These containers can be dumped for 50 to 100 years in small ponds in the premises of nuclear plants.
Their storage dissipates major part of both heat and radioactivity. The weakened radioactive wastes in shielded containers are then buried 500 metres down deep under the earth. The other method of disposal is by using sea bottom. However, both the methods of disposal have been opposed by environmentalists.