fluxes, very low risk of human intrusion, etc.). Many studies of disposal variants have been carried out (e.g., Mobbs et al., 1989; Klett, 1997a,b) – the most extensive probably by the NEA (1988). Like on-seabed disposal (which is really a simple dumping option), however, most sub-seabed disposal options are also now banned by international convention (McCombie and Chapman, 2003a). An exception to this seems to be sub-seabed formations which are accessed from land. Although the legal situation here is certainly ambiguous, the existence of such repositories (e.g., Fig. 5.2a) indicates that they are, de facto, acceptable, although the recent EU ‘‘COMPASS’’ study (Dutton et al., 2004) is rather disingenuous in this regard – distinguishing only ‘‘on-shore disposal’’ and ‘‘offshore disposal in deep-sea sediments’’ – thus avoiding any discussion of coastal disposal options.

Basically, a coastal sub-seabed repository could be developed in a completely analogous way to an equivalent facility on land and hence will be implicitly included within the category of geological disposal. On the short term, such an option may have distinct advantages (as noted above) but, given the long timescales of interest, the effect of sealevel change on such coastal facilities needs to be considered very carefully. Advantages in ease of making a safety case over shorter timescales may be well compensated by much greater complexity at later times. Operationally, the safety concerns associated with massive construction projects below the sea also need to be carefully considered, but the existence of sub-seabed mines (e.g., the Durham (UK) coalfield under the North Sea) shows that this is feasible.

3.4.2.2. Antarctic icesheet disposal

Icesheet disposal is considered below but, as a special case, the Antarctic often receives particular attention due to its perceived great isolation from population centres. Disposal of all waste is, however, prohibited by the Antarctic Conservation Act and radwaste is explicitly excluded by Article 5 of the Antarctic Treaty.

3.4.3.Technically impractical options; partitioning and transmutation, space disposal and icesheet disposal

Discussions of the general problems of radwaste management with the general public inevitably drift onto the topics of ‘‘destruction’’ of the waste or simply shooting it into space. In principle, both are possible, but completely impractical based on existing technology or any currently imaginable development of it.

A point to be made at the outset is that these options are generally proposed for what are perceived by those unfamiliar with radwaste management to be the most problematic wastes – actinides and some of the longest lived fission products. As such, they are actually concentrated on wastes which could, in fact, be easily handled by geological disposal. From a purely technical viewpoint, some of the heterogeneous ILW-LL is most challenging for disposal (Hooper et al., 2005) and is not considered for such management options. Even worse, partitioning and transmutation (P&T) would probably significantly increase the inventory of this waste type.

For completeness, this section also considers icesheet disposal – an option increasingly seen as impractical due to the difficulty of assuring the longevity of ‘‘permanent’’ icesheets.

3.4.3.1. Partitioning and Transmutation

This is a proposed strategy for some actinides and fission products, which aims to reduce the need for long-term isolation of the waste by removing many of the long-lived isotopes. Note that P&T cannot eliminate the need for a geological repository, but it may change its design basis and, implicitly, its acceptability. This last point is rarely discussed, but a growing consensus is that most key stakeholder groups do not understand the subtle distinctions between HLW and ILW (see discussion of communication in Chapter 9) and hence this argument may be considerably over-played.

The basic principle behind P&T is straightforward – long-lived isotopes are irradiated to cause activation/fission reactions which produce shorter-lived products. In some concepts, the transmutation process itself may produce useable energy (e.g., Rubia et al., 1995). The great problem with this option is that additional nuclear facilities must be constructed and operated and enormous efforts are required in the separation of radionuclides before and after irradiation. This poses a risk to workers, is expensive and, in many cases, requires separation efficiencies which are far beyond existing technology. Based on present experience with reprocessing, the net result would be to replace a small quantity of homogeneous, very long-lived waste with a great quantity of different waste products containing isotopes with a wide range of half-lives.

The irradiation process, especially if using special reactors, particle accelerators, lasers, etc., also tends to be extremely expensive. For example, at a recent conference organised by SKB, Dr. Janne Wallenius (KTH, Stockholm) spoke in favour of P&T (Sains, 2004). However, Wallenius did admit that:

P&T would increase the cost of nuclear generated electricity by 25%

three to four new nuclear reactors with particle accelerators would need to be built for Sweden to use P&T

such a new technology would ‘‘. . . increase the risk for our generation (but would) reduce the risk for future generations.’’ because of decreased risk from SF

Note that this requires a huge nuclear infrastructure, all of which needs to be finally decommissioned – producing yet more secondary radwaste.

In principle, reprocessing with the extraction of U and Pu from spent fuel and the use of MOX in power reactors represent a kind of P&T (although it is not classified as such), which shows that the principle is feasible to some extent. The costs associated with even this very simple case, which have greatly limited its implementation, remove all credibility for the proposed option of transmuting minor actinides and long-lived fission products. To be brutal, claims for the value of exotic transmutation options must be seen more as a kind of funding hype for otherwise underemployed physicists rather than the basis for any kind of practical waste management options (e.g., Ninkovic and Raicevic, 2004; see also Box 3.2). Indeed, it has been argued by the Swedish safety regulators (SKI) that the advantage of reducing an extremely small (and hypothetical) risk from long-lived isotopes in the distant future has to be set against a major disadvantage of P&T, namely the increased risk of exposure to workers today due to significantly greater handling of short-lived, and hence high specific activity, isotopes; it could certainly be argued that the latter risk completely outweighs any potential gain.

Nevertheless, advances in partitioning technology could have clear practical applications in developing alternatives to the currently rather primitive wet chemistry approach to spent fuel reprocessing. It is thus not surprising that some of the countries which

Box 3.2. Exotic P&T options

A classic example of over-selling blue-sky physics research is laser transmutation. Demonstration of transmutation by an ultra-high power laser ( 5 1020 Watts cm 2) was quoted to show that ‘‘using lasers is a relatively cheap and very efficient way of disposing of nuclear waste’’ (Physicsweb, 2003). In fact, the picosecond laser pulse produces a relativistic plasma from a gold target, the ‘‘Bremsstrahlung’’ which causes the 129I ( , n) 128I reaction. Each shot produces about 3 106 128I nuclei – thus total conversion of the 50 g sample would require the laser to fire 1017 times. Not only would this require

an enormous amount of energy ( 107 GW h, assuming 100 per cent efficiency, for the laser power only), but would also take 1013 a (as the laser pulse rate is only once per hour). As 129I has a half-life

of a mere 16 Ma, it would have decayed away long before the transmutation process was completed. As noted above, the analysis assumed that all the chemical processing required can be carried out

extremely efficiently. Even if this was the case and the laser technology advanced to improve the firing rate by a factor of 1013, complete conversion of 50 g of 129I would not only require 103 GWa of power, it

would increase the specific activity of the waste by a factor of 5 1011. To put this 50 g in context, the annual production of 129I in spent fuel is in the order of 900 kg!

present P&T options prominently are those with a current investment in commercial/ military reprocessing and well established HLW disposal programmes (e.g., France, Japan, Russia and USA). With this wider viewpoint (e.g., RWMAC (2003)), the potential for a limited form of P&T involving advanced reprocessing and ‘‘actinide burning’’ reactors could be realised within a long-term nuclear fission programme (0100 a or so). In such a case, optimised fuel cycles which maximise power generation and minimise waste production are certainly possible and, in the right commercial environment, could even be financially attractive (Williams, 2000). There are no signs, however, that any conceivable decrease in toxicity of waste per unit power generation could remove the fundamental requirement for an associated waste disposal strategy.

3.4.3.2. Space disposal

This option gains most from its apparent ‘‘high-tech’’ complete solution to the problem as compared to the very ‘‘low-tech’’ approach of deep geological disposal (Rice and Priest, 1981). Although it may be contrary to national law in many countries (i.e., exporting of waste from national territory is not allowed) and to international conventions on the use of space, the situation is less clear than those options considered in section 3.4.2. However, implementing space disposal on the basis of existing technology can be rapidly ruled out as this is a very high-risk, high-consequence strategy. A short review of the world’s active space programmes clearly shows that the risk of catastrophic failure during spacecraft launch is significant (statistically, the chances of failure of a rocket lie in the 1–10 per cent range, depending on the maturity of the design) and the consequences of spreading a load of SF or HLW across the face of the earth following such a failure are potentially catastrophic.

Even with an emphasis on safety, the high cost of rocket launches severely constrains the measures which could be adopted if space disposal was to be seriously considered – e.g., for low earth orbit (LEO), launch costs are presently US$ 2 107 per tonne. Even without consideration of other requirements to remove the waste from earth’s orbit, this