The need to protect humans and the environment from the potentially adverse effects of radioactive wastes is clearly recognized, particularly for long-lived wastes such as nuclear spent fuels or wastes from spent fuel reprocessing. In fact, consideration of the very long-term and future generations became at an early stage a fundamental concern in the management of radioactive wastes, arising from the principle that current generations producing the wastes should bear, to the extent possible, the responsibility to manage it . Accordingly, a strategy was developed for the isolation of radioactive wastes from humans and the environment for times sufficiently long to ensure that any future releases of radioactive substances to the environment be at a level that would not be unacceptable today. This strategy, which explicitly acknowledges the potential long- term radiological hazard, has the objective of ensuring that future populations are protected at a level at least equal to that acceptable for ourselves and are not committed to the continued expenditure of resources to ensure that this is so.
This objective should be achieved in a way which reconciles the various factors underlying our responsibilities to current and future generations. Broadly these factors are:
It is evident that these responsibilities are taken very seriously in OECD countries in the late 20th century. There is increasing distrust of the "out of sight - out of mind" philosophy which seemed to underlie some early hazardous waste management practices.
In a recent review of the principles of safe management of radioactive wastes (Annex I) the International Atomic Energy Agency provided confirmation of these basic responsibilities.
In technical and economic terms the exact measures preferred to achieve isolation of the different types of waste depend upon their physical and chemical characteristics. The types of processing, packaging and transportation required also vary between wastes. It is characteristic of radioactive wastes, with the exception of the natural radioactive residues from uranium mining, that their volume is relatively very small. In the case of some wastes from power stations, medical applications and research, the half-lives of the radioactive substances in the wastes are short enough that effective isolation is achievable by deposition in supervised near-surface vaults, or by other means of storage, whilst decay takes place. The present discussion concerns those longer-lived radioactive wastes which, like wastes containing unavoidable, non-recyclable toxic chemical elements, require isolation for times beyond the surveillance capability of current generations.
In comparison with many chemicals the toxicity of radioactive substances is well understood. However, unlike some industrial chemical wastes, most of the radioactive inventory of nuclear wastes is the inevitable by-product of power generation by nuclear fission and, except in the sense of packaging into a small volume, is not very amenable to further reduction by recycling or process improvement.
In the management of long-lived radioactive substances, as for other hazardous substances, there are essentially three options for wastes which cannot be recycled or eliminated by alternative technologies. The first is to dilute and disperse, the second is to store and monitor, and the third is to dispose by containment and isolation . It has been argued that another option is the actual destruction of the toxic atoms by nuclear transmutation but for many wastes this is certainly impractical for the foreseeable future. In any case, the efficiency of the nuclear transmutation process would not be sufficient to eliminate all long-lived radioactive wastes and thereby avoid the need for a long-term isolation strategy .
The dilution and dispersal of wastes in the air and water of the biosphere is now approached with great caution and is subject to strict regulatory control. The emergence of global warming as a possible consequence of CO2 dispersal in the atmosphere is a good example of the unexpected risks that may appear. In the nuclear industry, and increasingly in the more traditional chemical industries, it is normal practice to decontaminate aqueous and gaseous waste streams to a high degree before dispersal; the product of this action is a solid material for disposal or re-use.
The objective of disposal is to isolate the wastes from the biosphere for extremely long periods of time, ensure that residual radioactive substances reaching the biosphere will be at concentrations that are insignificant compared, for example, with the natural background levels of radioactivity, and provide reasonable assurance that any risk from inadvertent human intrusion would be very small . Geological disposal, which is discussed in more detail in the next section, is the method widely proposed for achieving this.
In almost all countries with nuclear activities, specific planning and project work leading towards geological disposal is underway. Nevertheless, in many countries there is a continuing public debate on the ethical case for geological disposal as a preferred means of passively safe isolation, and also on the question of when to implement the strategy and of its reversibility. Is the ethical course of action one in which the current generation, which has the use of the nuclear power, disposes of the associated wastes now in a way which is predicted to require no action by succeeding generations? Or should the current generation leave the wastes in supervised, retrievable stores so that future generations of technologists have all options for action open to them?
The indefinite storage and monitoring strategy has indeed a number of technical and ethical arguments in its favour, particularly if it were to be accompanied by suitable efforts to ensure continued development or improvement of options for final solutions and to ensure that financial resources would be available when needed at all times in the future. One interpretation of the concept of sustainability would support such an approach, wherein one generation would pass on to the next generation a world with "equal opportunity", and so on for the generations coming after, thus preserving options and avoiding the difficulty of predicting the far future. According to this idea of a "rolling present" the current generation would have a responsibility to provide to the next succeeding generation the skills, resources and opportunities to deal with any problem the current generation passes on. However, if the present generation delays the construction of a disposal facility to await advances in technology, or because storage is cheaper, it should not expect future generations to make a different decision. Such an approach in effect would always pass responsibility for real action to future generations and for this reason could be judged unethical.
A most significant deficiency of the indefinite storage strategy is related to the presumption of stability of future societies and their continuing ability to carry out the required safety and institutional measures. There is also a natural tendency of society to become accustomed to the existence and proximity of storage facilities and progressively to ignore the associated risks. Such risks would actually increase with time in the absence of proper surveillance and maintenance, leading at some indefinite future time to possible serious health and environmental damage. There are many well- known examples of bad environmental situations inherited from the past which show that this deficiency of a waiting strategy should not be underestimated.
What is needed is an evaluation of the good and bad aspects of alternative courses of action, given the principles listed earlier. One important factor is the argument that we cannot be sure that future society will maintain the knowledge and the institutions necessary for the protection of humans and the environment from hazards inherent in a strategy of supervised storage. Perhaps more important is the assertion that present generations have the direct benefits of nuclear power production and applications of radioisotopes in medicine and industry, and should not leave future generations to bear burdens of responsibility and resource cost if that can be avoided by action during the lifetime of current generations. Action can nevertheless be spread over several decades to resolve technical uncertainties about long-term waste isolation methods, or issues of social acceptability.
A variety of motivations influence social acceptability. Some of them are of an ethical nature, whilst others concern public opinion, trends and fashions. It is important in this respect to make a distinction between social convictions and ethical justifications, in order to avoid reducing the question of morality to one of acceptability or the question of acceptance to what can be justified ethically.
Today, the question is whether the proposed course of action is sufficiently safe and whether, given todays alternatives, it best meets the ethical principles discussed above. The answer is neither simple nor unequivocal. Existing methods, such as cost-benefit analysis and cost discounting (which cannot reasonably be applied over times longer than 20-30 years) have been considered for evaluation of intergenerational liabilities involved in different management strategies. None of them, however, can take account, quantitatively or qualitatively, of the ethical questions involved in bequeathing liabilities over many generations. In such circumstances, it should be the role of decision-makers to consider all issues, including ethics and public acceptability, to arrive at a balanced appreciation of the responsibilities of current generations to posterity.
In this context, it is important to remember that the health and environment detriment from disposed radioactive wastes is planned and regulated to be always at an acceptable level, and should not therefore be seen as one of the larger liabilities which are passed to future generations. There are issues of population control, depletion of natural resources and the dispersal of chemical by-products such as carbon dioxide, sulphur oxides and nitrogen oxides which potentially have much greater global consequences.