Simulation of the Stability of the Engineered Barrier System of the Borehole Disposal System for the Disposal of Disused Sealed Radioactive Sources in Ghana

Abstract

Ghana has opted for the Borehole Disposal System (BDS) as the long-term management solution for disused sources in storage. Confidence in the ability of the BDS to provide containment of the radionuclides for the requisite timescale rests on an adequate understanding of the behaviour of the engineered barrier system (EBS) on the host environmental conditions. The stability of the EBS to augment the natural barriers to ensure the long-term safety of the BDS had been demonstrated with the aid of a scoping tool. The failure times of the EBS were calculated based on hydro-chemical data determined at the site. The failure times which indicated the stability were influenced by the variations in the thickness of the engineered barriers. The results indicated faster failure times in aerobic environment compared to anaerobic environment. At the end of the failure times of the engineered barriers, the short-lived disused sources had decayed to negligible activities levels for all the scenarios considered. However, the activities of the long-lived disused sources at the end of the failure times had decayed by a factor of two as compared to the initial activities. The study thus demonstrated that with the required thickness for the proposed materials, the engineered barriers evaluated appeared stable on the host environmental conditions for a period commensurate to contain the disused sources for them to decay to their exemption levels. The disused sources could therefore be disposed using the BDS, particularly in anaerobic zone based on the engineered barriers evaluated. The results of the study could serve as reference data for the Nuclear Regulatory Authority when granting authorisation to the applicant. The implementer of the project could also use the results as a supplementary data in developing their safety case and in the fabrication of the waste packages.