The emplacement of heat-generating radioactive waste (HGW) in the deep ocean bed, and the subsequent interaction between the waste and the surrounding sediments, would induce a number of changes to the sediments This chapter describes the processes that have to be modelled to define these changes, and briefly renews the models that have been developed as a part of the International Seabed Working Group's research programme The experiments that have been performed by the SWG to validate these models are discussed, and the results of penetrator tests performed in the Atlantic study areas are used to illustrate the application of in situ test data to model verification, a corollary of this work is that it is now possible to predict the final burial depth of a penetrator with a high degree of confidence
It is concluded that, while it has not been possible to quantify all the physical changes to the sediments, the theoretical models that have been developed (and the experiments that have been performed to validate these models) have shown many of the processes originally perceived as being potentially deleterious to the sediment barrier to be benign. Consequently, it is extremely likely that HGW could be emplaced in the deep ocean in such a way that the properties of the sediment barrier would not be significantly impaired. However, if it were decided to continue research on deep ocean disposal, considerable further effort would be required to quantify all the processes involved in the burial of HGW within the sediments of the deep ocean.
Because of their immobile pore waters andion retention properties, the sediments of certain areas of the deep ocean offer a potentially effective barrier for the containment of heat-generating radioactive waste (HGW). However, the emplacement of the waste, and the subsequent interaction between the waste and the surrounding sediments, would induce a number of physical changes to the sediments. These changes have to be understood, and where possible quantified, to ensure that the sediment barrier would not be disrupted. In addition, for ‘self-burying’ disposal techniques, such as the free-fall penetrator, the interaction with the sediments during emplacement has a direct influence on the final depth of burial and the sealing of the entry pathway.
Theoretical models provide the key to understanding the physical processes associated with emplacement of HGW in the deep ocean bed. While many of the characteristics of conceptual disposal techniques could be studied directly by performing in situ simulations, such observations in themselves do not demonstrate that the underlying processes are understood. Theoretical models are therefore needed to confirm that the observed results are predictable Moreover, the cost of performing experiments in the deep ocean, and the time-scales associated with some processes, may make it impractical to study all aspects of a particular disposal technique in situ The preliminary study of the feasibility of deep ocean HGW disposal, which has been addressed by an international research programme co-ordinated by the Nuclear Energy Agency's ‘Seabed Working Group’ (SWG), has therefore had to rely heavily on predictions based on theoretical models.
