Radioactive wastes

Radioactive wastes present special public health problems that are not common to other wastes and are unfamiliar to many health authorities. Difficulties arise from the fact that there is no method of neutralizing or modifying the radioactivity of the wastes. Their decay rate is fixed, being a specific invariable property of each radionuclide. Furthermore, radioactive wastes containing very low concentrations of radionuclides are usually disposed of by dilution into the environment. Once they have been discharged into the environment, in accordance with statutory limitations, no significant further control can be practised; they undergo dilution, retention, and reconcentration through the operation of natural processes, and under special circumstances may constitute a potential hazard to man.

Liquid wastes create special problems of shielding, cooling and containment. In the case of solid wastes, the major problem is the sheer quantity which has to be disposed of, since its radioactivity is normally relatively low. Gaseous wastes create further complications.

Because a considerable part of this accumulated activity will be due to strontium-90 and other long-life radionuclides, methods for ultimate waste disposal of these wastes must provide containment and control for at least several hundred years. It is doubtful whether any man-made structure could be guaranteed to provide permanent containment, so that the use of deep geological formations (salt deposits, antarctic ice, ocean deeps, etc) seems more suitable. High-level wastes are at present stored mainly in liquid form, and some constituents will remain dangerously radioactive for several hundreds of thousands of years. There is at present no generally accepted means whereby high-level waste can be permanently isolated from the environment and remain safe for very long periods.

High-level radioactive waste contains uranium-235 and plutonium-239. It is highly toxic, can be used to make nuclear weapons, and is difficult to store because radioactivity keeps it hot and corrosive for hundreds of years. For example, plutonium has a half-life of 24,300 years, which means that it will remain a danger to human health for up to half a million years or 16,666 generations. Some studies conclude that high-level waste, isolation from the biosphere for 10 million years may have to be considered for spent fuel; and for reprocessed high-level waste, isolation time of 1 million to 10 million years are to be used for guidelines in developing appropriate disposal techniques. The least powerful but most plentiful form of high-level waste is uranium mine tailings. A ton of uranium ore yields only 4 lbs (1.8 kgs) of usable uranium: the rest is tailings, which emit radioactive radon gas and will remain radioactive for practically an indefinite period. Most of the high-level waste existing today is a product of nuclear weapons production. However, the nuclear waste from peaceful uses is a hundred times more concentrated, so that civilian waste in the USA already contains more radioactivity than military waste.

Low-level radioactive waste – which includes any material that has picked up induced radiation, such as uranium mining tools, uniforms of workers in reprocessing plants, medical wastes, and cooling water from nuclear reactors – is the next most plentiful form of nuclear waste.

Radioactive residue from power stations is a result of their production process, but that production technology has got very much ahead of the waste disposal technology. The result is a growing difficulty in finding ways to deal with the waste. Some of this, like strontium 90, caesium 137, carbon 14 and trans-uranic elements like plutonium, have very long half-lives. They will continue to be capable of radiating the environment for millions of years. No repository currently exists which can securely store such elements, although there are many potentially useful schemes in progress. Further, there is no known way at all to prevent the escape of radioactive gases, tritium or uranium byproducts.

USA military research and weapons production have produced 10 million cubic feet (280,000 cubic meters) of high-level waste and 50 million cubic feet (1.4 million cubic meters) of low-level waste; the former Soviet Union has probably produced an equivalent amount, and the other nuclear powers – France, UK, China, and India – proportionately smaller quantities. Each year these totals are growing. During 1979, the global operation of nuclear reactors (assuming an average capacity of 500 megawatts) resulted in 530 million cubic feet (15 million cubic meters) of mine tailings, 380,000 cubic feet (11,000 cubic meters) of low-level waste, and 140,000 cubic feet (4,000 cubic meters) of high-level waste containing almost 50,000 lbs (23,000 kgs) of plutonium.

It has been estimated that by the year 2000 high-level liquid wastes will be produced at the rate of 250,000 to 2,500,000 gallons per day. And by that time the total accumulated volume of high-level wastes will be of the order of 150,000 to 250,000 million gallons, and the total accumulated radioactivity will be more than 500,000 million curies. It is also estimated that by 1990 there will be 20,000 cubic metres of high-activity wastes arising from the reprocessing of spent fuel. Such wastes contain over 99% of the fission products present in the fuel, together with smaller quantities of actinides.

The USA Department of Energy estimates that $1.8 billion is needed every year for 20 years to assure safe storage of nuclear waste from production of weapons grade plutonium, another $14 billion to comply with modern pollution laws and a further $78 billion to clean up abandoned nuclear facilities in the USA alone. The estimates are revised regularly and appear to be rising. In the UK waste radioactive nuclear fuel totalled 6,219 tonnes in 1970: by 1985 it had grown to over 60,000 tonnes.