The use of narrow diameter boreholes for the disposal of disused sealed radioactive sources (DSRS) is being supported by the International Atomic Energy Agency (IAEA) in Malaysia and Ghana. In Malaysia, preparatory work borehole facility construction is currently in its final stages, and it is expected that the facility will soon be operational. Ghana is also at an advanced stage in its project, with construction of the borehole facility expected to begin upon completion of the licensing review process.
Quintessa has been actively supporting the associated IAEA programmes for more than 10 years through: hosting and providing training to staff from the implementing organisation in each country; undertaking expert missions to both countries; developing supporting IAEA documents such as a generic post-closure radiological safety assessment (GSA) and the application of the graded approach to the disposal of DSRS in boreholes; and developing the BDC Scoping Tool.
Integral to this work has been the application of Quintessa’s compartmental modelling tool, AMBER to borehole disposal concept. It has been used to carry out supporting calculations for the GSA with the aim of identifying the concept's key safety features under varying disposal system conditions. It has also been used in site-specific assessments in each country to support the associated design and licensing processes.
AMBER was used to implement the conceptual and mathematical models described in the GSA with the aim of minimising the number of input files to reduce input error, facilitate checking and updating, and avoid the replication of data. This was achieved by using of a series of NameSet options as switches to allow variant cases to be set up easily from a common "source" file. Two separate AMBER "source" files were developed: one for unsaturated cases; and one for saturated cases. The same saturated geosphere and biosphere was used for the two source files, but different near fields were implemented. By changing the item selected in each NameSet option, all case files for all scenarios can be directly created in batch mode from the two "source" files. The generic model for disposal in the saturated zone has subsequently been modified for country-specific application in both Malaysia and Ghana by taking account of each country’s inventory and site-specific characteristics. The resulting model output has been incorporated into the safety case developed for borehole disposal of DSRSs in each country.