Since 1977 the International Seabed Working Group, under the auspices of the OECD Nuclear Energy Agency, has been carrying out a coordinated research programme to investigate the feasibility and safety of the disposal of heat-generating wastes into deep ocean abyssal plain formations The main objectives of the research are to assess the long-term safety of the option, to identify characteristic study zones in the North Atlantic and Pacific Oceans, and to demonstrate the necessary engineering emplacement capability within oceanic geological formations.

The production of energy by nuclear power plants covers about 20% of the electricity generation of the European Community member states One of the larger Community countries, France, has reached the-point of producing over half of its electricity consumption by nuclear sources As happens with all types of industrial production, waste is produced at all stages of the process, from uranium mining and refining to the final dismantling of the power plant after having reached the end of its service life However, radioactive waste is not only generated by power production industrial and medical uses of radioisotopes generate in the order of 15% of the amount of low level waste, and military radioactive waste production is probably in the same order of magnitude as the civil nuclear one in the countries having a nuclear defence weapon system.

Methods for the safe disposal of solid low, medium and high level radioactive wastes are therefore the subject of investigations in many countries.

A number of options for the final disposal of high level wastes in different kinds of deep geological continental formations using the concept of a mined repository are being actively studied To assess the technical feasibility and long-term safety of these options a major effort is being placed on studying the natural and artificial barriers that isolate the wastes from man A demonstration of engineering capability is also required at sites which have the required characteristics of isolation and long-term stability The types of formations being considered for high level radioactive wastes within the European Communities are salt formations, clay and hard rock (granite), and sub-sea bed sediments.

Since 1977 an international coordinated programme has been developed under the auspices of the OECD Nuclear Energy Agency to study the feasibility and safety of emplacing vitrified nuclear wastes or unreprocessed fuel elements into deep ocean sedimentary formations (Fig 1) The objective of the research programme of the Seabed Working Group is to provide scientific and technical information to enable international and national authorities to assess the long-term safety and engineering feasibility of emplacing high level radioacties wastes packaged in suitable containers at some depth into the sedimentary geological formations of the deep ocean floor.

The characteristics that potentially make this option attractive are that the formations under investigation are stable and large in extent, they contain little or no strategic materials and consist of sedimentary material which has been shown to strongly retain most radionuclides The nature of this material is such that it tends to seal itself after natural or artificial disturbances

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