This chapter presents a summary of the engineering studies which have been carried out into the disposal of heat-generating nuclear waste in the deep ocean sediments Two disposal methods, the penetrator option and the drilled emplacement option have been investigated on an international basis, while a third, the seabed repository option, has been studied in the UK only Before describing the three disposal methods, the chapter discusses the role of the engineered barrier in the disposal system and presents the various waste forms that have been considered for disposal The information gathered from the deep ocean sediments which is required for the engineering studies is also summarized The chapter concludes by assessing the engineering feasibility of deep ocean disposal and indicates areas where further confirmatory work is required.
A renew of international engineering studies into the disposal of heat-generating nuclear waste in the deep ocean sediments was carried out during late 1986, funded by the United Kingdom Department of the Environment. It culminated in a draft report for the Engineering Studies Task Group (ESTG) of the Seabed Working Group and the final report for the Department of the Environment Final versions have now been published (Hickerson et al, 1988, Ove Arup and Partners, 1988) and further details of the engineering studies together with a comprehensive list of references can be found in these reports The results of the renew for the Department of the Environment will be used in the formation of Government policy, but at this stage do not necessarily represent Government Policy.
Engineering research started in earnest in about 1982 when the ESTG formulated a five-year plan to co-ordinate International studies. Many countries and governments have participated with the following taking leading roles Commission of European Communities France, Italy, Japan, Netherlands, United Kingdom, United States
Heat-generating waste (HGW) disposed of in the deep oceans would be prevented from having harmful effects on living organisms by four barriers The first is the waste-form itself which prevents the radionuclides from escaping by physically and chemically locking them into a glass block The low leach rate of the block is discussed by Lanza (Chapter 8, this volume).
The second barrier, the engineered barrier, has been the subject of a large portion of the engineering studies reported in this chapter The ocean sediment surrounding the emplaced waste is the third barrier and the assessment of its effectiveness is the principal theme of this conference The fourth and final barrier which is outside the scope of this conference is the ocean itself, which will disperse and dilute any radionuclides which have penetrated the other three barriers.
The engineered barrier must fulfil certain functions. The performance is related to the age of the waste at disposal but in general terms, the barrier is required to prevent the release of radionuclides for 500 years. This period allows many of the short-lived rahonuclides to decay down to insignificant levels and the canister temperatures to drop down to near ambient.
The disposal package must obviously be capable of withstanding routine handling and emplacement loads and reasonable accidental loads US Federal Regulations may require the package to be retrievable for nearly 100 years but this requirement has not been clarified. There is no such stipulation at present from the CEC or European Governments.
