surrounding rock and allow the package to sink deeper (e.g., Ojovan and Gibb, 2005). In this concept, the waste is completely contained within the overpack during melting and hence it may avoid some of the problems listed above. Apart from requiring considerable technological development, however, such an option is likely to be extremely costly and would probably be incompatible with some of the volatile nuclides which are actually the greatest challenge for waste management (i.e., it needs to be combined with a reprocessing and waste conditioning strategy).

Despite such options having been around for some time (see, e.g., comments in Chapman and McKinley, 1987) and more detailed assessments recently (see, e.g., Gibb, 2000, 2004; Sizgek, 2001; Ojovan et al., 2004), concerns of the type listed above lead to rock melting options being currently excluded by all national programmes on the basis of practicality or the limitations of existing technology to develop a robust safety case.

3.5.3. The international option: technical aspects

Although regional or international disposal projects are considered in some detail in Chapter 7.5.3, it is worth mentioning some technical issues associated with different variants of this particular option. In its simplest form, such regional facilities represent a simple optimisation process – spreading the costs of an expensive facility among users. This is, of course, particularly attractive for counties with relatively small quantities of waste – particularly if they are located in geographical proximity. In effect, this is similar to the LLW disposal ‘‘compacts’’ in the USA, where several states share a regional facility (an analogy which is reasonable, given that many such states are comparable in size and resources to smaller European countries). A similar idea is being implemented for disposal of radiation sources in Africa. For all such options, apart from socio-political issues, the resulting repository would be comparable to any other geological disposal facility.

Somewhat different to such ‘‘compacts’’ are international options focused on the selection of sites which are particularly suitable for waste disposal – generally due to their remoteness and perceived potential for waste isolation. Such projects have emerged repeatedly over the last few decades (e.g., Sahara, Gobi, Siberia, etc. – see www.ariusworld.org for details). More recently, however, the technical justification for such projects has improved significantly – typified by the Pangea ‘‘high isolation’’ concept which focused on areas where very long term immobilisation could be assured by the geological setting (see, for example, McCombie and Chapman, 2003b). This approach aims to remove many of the uncertainties associated with the characterisation of deep geological environments by choosing suitable sites where these are unimportant. With a starting-point which considered the entire world, such sites are likely to exceed in performance any which might be found in most national programmes. Nevertheless, benefits in terms of long-term safety needs to be balanced against the costs and risks associated with the more extensive transportation of radwaste which is required and the socio-political ramifications of such an approach in any potential host country (see also Nirex, 2005b, for further reading on this topic).

3.5.4. Alternative concepts: fitting the management option to future boundary conditions

In recent years, studies of ‘‘alternatives’’ have tended to be rather superficial analyses which fall into a number of classes:

Recycling the old studies of 2–3 decades ago, without proper consideration of the changing boundary conditions involved.

Rewriting history, showing that national programmes developed based on a structured repository concept development process (they rarely actually did) and that the previously selected design is the best available.

Attempting to obtain funding from the nuclear industry by adding ‘‘and its relevance to radwaste disposal’’ to an otherwise irrelevant academic study.

There is no doubt that many simple ideas from the past have been overtaken by technology development or environmental sensitivity. Examples here would include deep injection of liquid wastes and disposal into ‘‘permanent’’ ice fields or permafrost; the former due to concerns about long-term environmental contamination and the latter due to the awareness that, with uncertainties associated with global warming, such features can no longer be confidently assumed to be permanent (or even particularly long-lasting).

Other concepts may be currently excluded in terms of national or international laws and conventions. Nevertheless, developments in the future are hard to predict. In a scenario with increasing global affluence, restrictions on an option like sub-sea disposal might well continue – or even become stringent. Technically, however, such an option provides very high levels of safety and it is not inconceivable that socio-political constraints could change dramatically during the rest of this century – e.g., if alternatives to nuclear fission power generation fail to emerge and/or greenhouse perturbations lie on the upper limit of the present model envelope.

An important constraint on the management option chosen is the economics involved – even if this is rarely emphasised. Based on existing technology, this completely excludes some variants – e.g., space disposal or partitioning and transmutation of long-lived radionuclides (even if they are not excluded by other legal or safety issues). For other options, the economic constraints may be very sensitive to boundary conditions. Thus, despite all the caveats with respect to operational safety, a national programme with few (or no) nuclear power plants and hence a small waste inventory may well conclude that the cost/risk analysis favoured a deep borehole disposal concept over a conventional repository – even if a programme with a large number of NPPs came to exactly the opposite conclusion.

Deep borehole variants represent cases where it is difficult to build a robust concept based on existing technology – but it could be argued that the additional requirements for deep characterisation and operational robustness are within the limits of technological development which can be reasonably expected to occur over the next few decades. Such a situation can be contrasted to space disposal or complete transmutation, which do not appear feasible based on reasonably expected developments of any existing technology.

Overall, however, it must be accepted that technology has developed in unpredictable ways over the half century in which radwaste management has been an issue and major new developments cannot be precluded. To make these ‘‘super-science’’ options practical, however, such progress would effectively have to involve completely new science (anti-gravity, cold fusion, isotope chromatography, . . .) which may or may not ever develop. At the present moment, even major advances would appear to be capable of dealing only with a small amount of the least technically problematic waste (see also comments in Chapter 10). Nevertheless, the huge value of the nuclear industry could make even very expensive options feasible. It would, however, also have to be considered