Environmental transfer of radionuclides in a Sub-Saharan Africa setting

Doroh, RM

Abstract

In the last two decades, interest in the development of nuclear programmes in Sub-Saharan Africa (SSA) has increased. To ensure that the potential human and environmental ionising radiation exposure from nuclear developments within SSA can be adequately assessed, knowledge of radionuclide transfer within SSA ecosystems is required. Most of the research undertaken to date on radionuclide transfer to humans and wildlife has focused on studies within Europe and North America. These studies have provided data which form the basis of the generic transfer parameters used within the international system of radiological protection. Given that agricultural practices, diet, soils, food crops, wildlife and climatic conditions in SSA are very different to those in Europe and North America, the present study focuses on environmental radionuclides transfer in SSA and evaluates the extent to which the current generic transfer parameters derived from international data compilations are applicable in a SSA setting.
A systematic review of literature on radionuclide and stable element concentrations in SSA species (wildlife and agricultural food crops) and associated environmental media (soil, water, sediment) was conducted. Elemental concentration data were compiled for marine, freshwater and terrestrial ecosystems and these data were used to derive transfer parameter values that were reported within the Sub-Saharan Africa Database (SSAD) of transfer parameters.
A review of the SSAD data highlighted a lack of transfer parameter values for various radionuclide-organism combinations. Therefore, a sampling campaign was undertaken at two case study locations in SSA to help to address some of the SSAD data gaps. The case study locations were Geregu in Kogi State and Itu in Akwa-Ibom state, both are proposed locations for nuclear power plant construction in Nigeria. The sampling campaign involved the collection of soil, agricultural food crops, and wildlife samples. Animal sampling focused on the Reference Animals & Plants (RAPs) defined by the International Commission on Radiological Protection and was conducted in accordance with Schedule 1 of the Home Office guidelines for animal use in research. Agricultural food crops and wildlife samples were prepared and analysed to determine the concentration of stable elements using Microwave Plasma Atomic Emission Spectrometry (MP-AES); transfer for a given stable element was assumed to be representative of the transfer of radioisotopes of that element. Dose assessment was undertaken using site specific concentrations obtained from the case study location to determine the potential environmental impact of the planned nuclear power plant in Nigeria. To facilitate emergency preparedness planning for the planned nuclear power plant in an SSA setting, a study on Radiocaesium Interception Potential (RIP) of the principal soil types in Nigeria was undertaken. The resultant RIP data were used to test the applicability of the Absalom (also known as the “SAVE”) approach to predicting radiocaesium transfer at two case study locations in Nigeria.
The results of the mean concentration ratios obtained from the database of radionuclide transfer parameter values compiled by the International Atomic Energy Agency (i.e. for non SSA sites (Europe and North America)) and those of the SSAD are different. However, differences in mean concentration ratio values are not consistent in the different wildlife-element combinations. The results of the concentration ratios from the field campaign were comparable to those of the SSAD. For food crops, SSAD transfer parameters were consistently higher than generic transfer parameters obtained from IAEA. The dose assessment results obtained for potential radiation exposure of wildlife using the Environmental Risks from Ionising Contaminants: Assessment & Management (ERICA) Tool and predicted discharges from a planned nuclear power station at Geregu, Nigeria, revealed the risk quotient (RQ) to be less than one and the predicted dose rate was below the screening dose rate of 10µGyh-1 for each of the organisms considered within the assessment. The RIP measurements for Nigerian soils were low compared to RIP results from other parts of the world. The mean of the measured Cs transfer factor for grass (1.67E-02) growing on nitisol at Geregu was an order of magnitude higher than the Absalom model predicted transfer factor for nitisol (1.66E-03). For Itu, the mean of the measured Cs transfer factor (0.09) for grass growing on gleysol was comparable to the Absalom model predicted transfer factor (0.11) for gleysol. Despite an order of magnitude under-prediction for nitisol, the overall, the Absalom model prediction was good, and this suggests that the model would be applicable to SSA.
A dose assessment undertaken using predicted releases from the reactor type being considered for Nigeria suggested that routine releases were highly unlikely to result in dose rates that exceeded the benchmark value (ERICA screening dose rate equals 10µGyh-1). This finding provided confidence that the environmental impact of this proposed nuclear development in Nigeria would be negligible from a radiological perspective.

Citation

Doroh, R. Environmental transfer of radionuclides in a Sub-Saharan Africa setting. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Jun 15, 2020
• Publicly Available Date: Jun 15, 2020
• Award Date: Jan 1, 2020