Reconceptualization of the extended groundwater regime of the Vaalputs radioactive waste site
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Date
2015-08
Authors
Mandaba, Mbuthokazi
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
Vaalputs Radioactive Waste Site is the only nuclear waste facility in South Africa that stores Low- and Intermediate Level Radioactive Waste. Disposal of waste is carried out under the authorization granted by the National Nuclear Regulator (NNR) under the Act (Act 47 of 1999). The disposal Site is managed and owned by a state company called South African Nuclear Energy Corporations (Necsa). The NNR reviews its license periodically to update information required by the NNR regulation.
The method of disposal at Vaalputs can be described as both engineer and natural barrier concept. The metal drums are for LLW and concrete drums for ILW, these drums are buried in trenches 8m deep. These trenches consist of mixtures of clay, e.g. smectite, Kaolinite and illite. These clays act as a secondary barrier in the prevention of nuclear migration.
Environmental isotopes can be used as tracers for natural groundwater movement. At the Vaalputs Site and surrounding farms, analysis of 3H, 14C, 2H and 18O were performed on two occasions which yielded significant results concerning groundwater recharge. The initial standard for this study was established by studying dataset for year 1988 and 2000. Not enough radioisotope data is available on the western side of Vaalputs Site where the granite gneiss is weathered. This study aims to address that inadequate. Recharge plays a crucial role in updating the safety case assessment and potentially identifying the preferential groundwater pathways.
The second standard for the base of this study was established by studying the analytical chemistry results collected over 27 years. Systems of monitoring boreholes were drilled to a level below the water table on the perimeter security fence around the disposal Site. In total there are 19 boreholes situated on or just outside the security fence, evenly distributed around the trench. A total of 54 monitoring and extraction boreholes exist within the 20-km radius of the Site. Some of these boreholes will be used in this study. Bi annual sampling and monitoring results at the Vaalputs Site has been studied. Cations and anions behavior was assessed to determine any detectable contaminants on the groundwater system.
Pump test results for the study area revealed a great decrease in hydraulic conductivity in the matric with depth. Four boreholes (GWB1, GWB3, GWB5 and PBH16) adjacent to the repository were subjected to aquifer tests. Fracture zones in these boreholes yielded from 0.75 ℓ/s to 3.6 ℓ/s. this indicated the fracture zone of the study area has different variable conductivity. These aquifer tests were conducted on the eastern side of the Vaalputs Site.
The conceptual model for the study area revealed the Vaalputs aquifer is bounded in the west by Kamiebees shear zone and in the south by a Platbakkies shear zone. In the east a physical boundary is formed by the Koa River valley drainage system. The regional fault zone the Garing fault influences the piezometric head elevation, groundwater chemistry and flow. The purpose of this report is to re-conceptualise the groundwater regime using recent updated data.
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Keywords
Dissertation (M.Sc. (Geohydrology))--University of the Free State,2015, Radioactive waste disposal, Radioactive waste disposal in the ground, Radioactive waste disposal -- South Africa