R. N. Nair

Estimation of thoron concentration using scintillation cell

Two counting techniques are proposed in this paper to estimate thoron ((220)Rn) concentration using a Lucas scintillation cell. The alpha activity build-up inside the cell is calculated theoretically by using Bateman equations. The first method is having a minimum detection limit of 325 Bq m(-3) and can be used for thoron measurement in thorium-processing plants. In the second method, thoron concentration is calculated using the alpha counts from thoron progenies and is a reference to the first method. The results obtained by these techniques compare well with the double filter method.

Migration of radionuclides from a high-level radioactive waste repository in deep geological formations

The paper presents the development of an analytical model to estimate the migration of radionuclides through a single fracture with right circular cylinder geometry from a high-level radioactive waste repository in deep geological structures. The processes considered are advection, dispersion, surface sorption and radioactive decay for transport in the fracture; diffusive loss to the host rock; radial diffusion, adsorption and radioactive decay for transport in the host rock. The model is applied to a typical case of high-level radioactive waste repository in deep geological rock formations. The concentrations showed an increasing trend with increasing dispersion in fracture or reducing dispersion in the host rock or reducing porosity. It is shown that the models which do not consider the dispersion of radionuclides within the fracture underestimate the radionuclide concentrations in the fracture water. Also, the effect of dispersion reduces with increase in fracture water velocity. The concentration of radionuclides in the fracture water in general increases with increase in fracture radius until a critical radius is reached. The model development is targeted for the performance assessment of high-level radioactive waste repositories.

Source Term Evaluation Model for Uranium Tailings Ponds

AbstractA multicompartmental source term model, which is designed to assess the radionuclide leaching and transport in a saturated or unsaturated porous medium such as a uranium tailings pond (or near-surface radioactive waste disposal facility) is developed. The subsurface environment is assumed to be composed of a series of compartments. In the case of a uranium tailings pond, these compartments represent the natural evolution of several layers of uranium mill wastes due to their disposal into a tailings pond over a few decades. The bottommost layer forms at the beginning of the disposal, and the topmost layer develops at the flag end of the disposal. The model incorporates the ingrowths of progeny from the parent radionuclide. Upon entry of radionuclides into a layer, they mix, sorb, decay, and are eventually removed by the downward movement of water, ultimately reaching the aquifer below the bottommost layer. Each compartment may have its own unique properties. The primary outputs of the model are the...

Assessment of Background Uranium Concentration in Groundwater Around a Proposed Mining Area

This study was carried out in and around a proposed mining area (Lambapur and Peddagattu) located in Andhra Pradesh, India with the aim of assessing the spatio-temporal variation and the impact of rainfall on uranium concentration in groundwater. The concentration of uranium in groundwater varied from 0.2 to 77.4 ppb. There was significant increase in uranium concentration in groundwater after rainfall which was due to the leaching of uranium ions present in the unsaturated zone along with rainwater. The reason for the presence of uranium in groundwater of this region is highly localized that depend on the lithology inherent to this region.

Radiological Impact Assessment of the Uranium Tailings Pond at Turamdih in India

Groundwater flow and contaminant transport modeling has been carried out for the uranium tailings pond at Turamdih in Singhbhum district of Jharkhand, India using the finite element based FEFLOW software with a view to assess its radiological impact on human and the environment. Hydrogeological investigations; including laboratory and field based studies; have been carried out to collect site-specific data on geological settings, cross sections and aquifer characteristics of the site. Results indicate that the concentrations of U-238 and its progenies and the corresponding annual effective dose rates to members of the public through groundwater drinking pathway are less than the corresponding standards even at a distance of 500 m from the boundary of the tailings pond. The radiological impact in groundwater at this distance is practically nil up to a period of 4000 years and trivial beyond this period.

Radiological impact assessment of opencast uranium mining for large reservoirs-uncertainty analysis using Wilk's method

Opencast mining may lead to natural erosion of ore material due to overland flow of water accumulated from rainfall. The overland flow may ultimately reach the nearby surface water body. This process may lead to the release of U-238 and its daughter products into the surface water body. The present study is carried out to assess the radiological impact of the erosion in terms of dose due to U-238 and its progenies in the surface water body and to quantify the uncertainty associated with the dose due to consumption of the reservoir water. The in-growth of progenies is also taken into account. The properties like settling velocity, distribution coefficients etc. are having inherent uncertainty associated with their values. The uncertainty of various parameters involved is propagated to the model output. Hence, the uncertainty analysis becomes important to build confidence in the results. In this paper, Wilks method is used to calculate a value greater than 95th percentile value for the dose rate through drinking water pathway with 95 percent confidence level (95/95 value). In present study, the 95/95 value for the annual effective dose to the public due to U-238 and its progenies through drinking water pathway is found to be 12.5 times lower as compared to the WHO guidelines for drinking water.