Development of the Borehole Disposal Concept

The Nuclear Energy Corporation of South Africa (Necsa) initiated the Borehole Disposal Concept (BDC) with a view to improving radioactive waste management practices in Africa. An IAEA Technical Cooperation project was launched to investigate the technical feasibility and economic viability of a borehole for the disposal of disused sealed radioactive sources. Phase III of the project was completed by the end of 2004, and the main objective of this phase was to demonstrate the technical feasibility of the concept by means of a practical demonstration. The disposal concept consists of a 260 mm diameter borehole drilled to a depth of up to 100 m in which stainless steel disposal containers are emplaced and backfilled with cement. Each disposal container contains a source within a stainless steel capsule within a containment barrier. Included in the terms of reference of Phase III were the design and the evaluation of the disposal concept. The evaluation included container materials, backfill materials and a generic post-closure safety assessment. The post-closure safety assessment and the associated derivation of activity limits showed that, through the use of multiple physical and chemical barriers, the BDC provides an appropriate degree of long term safety. Furthermore, the safety of the disposal concept is not reliant on an extended period of institutional control, and owing to its small 'footprint', the likelihood of direct human intrusion into the borehole is small. An international peer review team positively assessed the technical feasibility, economic viability and overall safety of the concept, and thus concluded the development phase of the project. The Member States of the African Regional Cooperative Agreement for Research, Development and Training related to Nuclear Science and Technology (AFRA) have decided to proceed to Phase IV of the project with the main aim to implement the borehole disposal technology. (author)