Sixth report : nuclear power and the environment : presented to Parliament by command of Her Majesty, September 1976 / Chairman: Sir Brian Flowers.

  • Great Britain. Royal Commission on Environmental Pollution.
Date:
1976
Catalogue details

Licence: Open Government Licence

Credit: Sixth report : nuclear power and the environment : presented to Parliament by command of Her Majesty, September 1976 / Chairman: Sir Brian Flowers. Source: Wellcome Collection.

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    and Figure 16 shows where the main ones are believed to lie. All of them are regions of seismic activity in the form of earthquakes or volcanic eruptions. Some of the subduction zones are associated with the very deep trenches that exist in parts of the ocean. The proposal would be to place the blocks of vitrified waste either on or in the sea bed of such trenches, so that they would be drawn down into the mantle and permanently removed. The difficulty is that the time scale of the subduction process is fundamentally too long. It would probably take of the order of 250,000 years for the process to be complete; even plutonium—239 would have effectively decayed before this. Moreover, these areas are geologically unstable, and the blocks might be damaged while awaiting their final burial. The water is very deep—typically 10 km—and the technology for drilling in these depths has not been developed. 395. The ice sheets in Antarctica and covering most of Greenland are known to be of great antiquity—perhaps of the order of a million years. A proposal has been made(*®) that the vitrified canisters should be placed on the surface, where their heat would melt the ice under them. They would then sink down through the ice, which would refreeze above them. Eventually, after a delay which would be sufficient for the fission products (and curium) to decay to a significant extent, they would reach the bottom. But in 1973 it was suggested(*’) that underlying the ice sheets of Antarctica there were a number of lakes which are now believed to be in direct communication with each other and with the oceans. Thus the slow but inevitable grinding of the blocks by the ice on the basement rocks would lead to leaching and a pathway back to the biosphere for the actinides. Though the oceans would provide much dilution it seems unlikely that this proposal would be acceptable. Moreover, since operations in such inhospitable areas of the world would inevitably be both difficult and expensive, it might be simpler to provide the requisite period of delay by other means. 396. Of the three options that we regard as promising, disposal into the ocean directly would be much the cheapest. Moreover, there would be no need to provide interim cooling in an engineered facility except perhaps to reduce the hazards of handling very active blocks at sea and to provide buffer storage. But there are a number of uncertainties about the radiological consequences, and there is also the possibility of retrieval of the wastes by accident. At present such disposal would be prohibited under the London Convention, unless it could be conclusively demonstrated that the containment was so secure that the wastes would be effectively prevented from leaking into the ocean before the radioactivity was below the limits shown in Table 10. It appears unlikely that this could be satisfactorily guaranteed and we are very doubtful whether this method should be accepted as the preferred means of disposal on grounds of cheapness if other alternatives offering rather more convincing long-term security are available. The Institute of Oceanographic Sciences (IOS) in their evidence to us, with an admitted inbuilt bias in favour of preserving the ocean environment, argued that such a scheme was to be regarded as a decidedly inferior option as compared with emplacing the wastes beneath the ocean floor. 397. We have concluded that there are essentially two reasonable options for the permanent disposal of high level vitrified waste, namely geological