changes could possibly make some of them more acceptable. In addition, they are often brought up by members of the general public as options which appear, on the surface, preferable to geological disposal.

3.4.2. Politically blocked options: sub-seabed and Antarctic icecap disposal

3.4.2.1. Sea dumping and sub-seabed disposal

Although reprocessing plants (e.g., Sellafield and Cap de La Hague) and many reactors still release certain radionuclides from their waste streams into the sea, disposal of solid radwaste onto the seabed has effectively been blocked by international treaties (e.g., the London Dumping and OSPAR Conventions – see McCombie and Chapman, 2003a, for details). This results from concern over the final fate of the wastes and arguments that a few countries should not be able to contaminate the marine environment which is shared by all countries. Nevertheless, until relatively recently, many countries (e.g., Grover, 1984) disposed of LLW onto the seabed (even land-locked Switzerland) and it has been shown (NEA, 1985) that the disposal of some waste streams in this manner presents very low individual risk.

Technically, sub-seabed disposal (Fig. 3.8) is, in principle, directly equivalent to disposal on land with some clear advantages (high dilution of releases, low porewater

Fig. 3.8. Two potential methods for sub-seabed disposal. In the first, the waste is simply dropped over the side of the ship in specially designed penetrators which rely on their kinetic energy to bury themselves deeply into the seabed, the sediments re-sealing as the penetrator sinks. These were successfully tested in the Atlantic abyssal plane by the UKDOE in the 1980s. The second method is a paper study where the waste packages would have been lowered down a large diameter drill string which had penetrated the seabed. After the subseabed part of the hole had been filled with waste, it would have been sealed with concrete.