Faby Sunny

AEROSOL STUDIES IN A NUCLEAR AEROSOL TEST FACILITY UNDER DIFFERENT TURBULENCE CONDITIONS

Abstract An experimental nuclear aerosol test facility has been built at the Bhabha Atomic Research Centre for validating the aerosol behavior computer codes used in nuclear reactor safety assessment. Its essential components are the 10-m3 stainless steel test vessel, plasma torch aerosol generator, and aerosol instrumentation to study the aerosol characteristics. Studies have been conducted with metal/metal oxide aerosols in dry environments under varying turbulence conditions and the results have been compared with the predictions of NAUA (Mod 5) code. The code predictions were found to differ from the experimental observations. To explain the differences under calm conditions, a gravity-induced spatial stratification model was formulated and solved. It was found that NAUA prediction agrees fairly well with the depletion of total airborne mass given by this model. In the presence of turbulence, the code overestimated the airborne concentrations. This is attributed to the noninclusion of particle removal by inertial impaction. Accordingly, the deposition velocity formula used in the code was modified based on the Crump-Seinfeld approach. With this modification, the results of airborne mass depletion agreed quite well with the measured data. On the whole, the study provides validated modifications in the NAUA (Mod 5) code to include turbulence effects and a formulation of gravity-induced stratification of aerosols under calm conditions.

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.

Estimation of daytime radiative and soil heat fluxes at Trombay, Bombay (19.1° N, 72.8° E) using routine weather data

SummaryThis note presents estimates of hourly averages of insolation, net radiation and soil heat flux during daytime from solar-elevation angle and routine weather data on cloud cover and screen level air temperature using a formulation procedure generally adopted in surface layer parametrisation schemes. The estimation procedure employs commonly used forms of empirical relationships and the estimates are compared with the concurrent field observations at Trombay site in Bombay (19.1° N, 72.8° E) India. Wherever possible site-specific empirical coefficients are derived. Using the observed insolation, the net radiation and soil heat flux are respectively estimated within ±18% and ±14% of their observed values. Estimated insolation was found to be within ±37% of the observed values and, when used to derive the fluxes, the uncertainty increases to ±25% and ±27%, respectively.

Source term evaluation model for high-level radioactive waste repository with decay chain build-up.

ABSTRACT A source term model based on two-component leach flux concept is developed for a high-level radioactive waste repository. The long-lived radionuclides associated with high-level waste may give rise to the build-up of activity because of radioactive decay chains. The ingrowths of progeny are incorporated in the model using Bateman decay chain build-up equations. The model is applied to different radionuclides present in the high-level radioactive waste, which form a part of decay chains (4n to 4n + 3 series), and the activity of the parent and daughter radionuclides leaching out of the waste matrix is estimated. Two cases are considered: one when only parent is present initially in the waste and another where daughters are also initially present in the waste matrix. The incorporation of in situ production of daughter radionuclides in the source is important to carry out realistic estimates. It is shown that the inclusion of decay chain build-up is essential to avoid underestimation of the radiological impact assessment of the repository. The model can be a useful tool for evaluating the source term of the radionuclide transport models used for the radiological impact 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...

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.

Estimation of actinic flux and photolysis rate constant of NO2 from aerosol size data

Abstract Aerosol mass measurements made using Andersen cascade impactor at different locations in an urban area were used to study the variation in power-law exponent in the Junge-type number distribution. The discrete mass size data were inverted by modified Twomey algorithm to obtain continuous mass size distribution from which number distributions were derived. These were used for evaluating actinic fluxes and hence NO 2 photolysis rate constants employing a radiative transfer model with delta-Eddington approximation. Results of the spatial variation of Junge power-law exponent over the urban region are presented. The relative magnitude of photolysis rate constants over regions with differing aerosol emission characteristics are illustrated. Parametric studies indicated the importance of considering fractional elemental carbon content of the aerosols in the atmosphere. Results of a limited validation study of the model are also presented using quartz crystal microbalance impactor data at one of the sites.