P. M. Ravi

Soil to leaf transfer factor for the radionuclides 226Ra, 40K, 137Cs and 90Sr at Kaiga region, India

Transfer factors are the most important parameters required for mathematical modeling used for environmental impact assessment of radioactive contamination in the environment. In this paper soil to leaf transfer factor for the radionuclides ⁴⁰K, ²²⁶Ra, ¹³⁷Cs and ⁹⁰Sr is estimated for Kaiga region in Karnataka state, India. Among the plants in which study is carried out, ²²⁶Ra, ⁴⁰K, ¹³⁷Cs and ⁹⁰Sr activity in leaves of herbaceous plants is higher than that of tree leaves. Soil to leaf transfer factor for ²²⁶Ra, ⁴⁰K, ¹³⁷Cs and ⁹⁰Sr was found to be in the range of 0.03-0.65, 0.32-8.04, 0.05-3.03 and 0.42-2.67 respectively.

Spatial distribution and accumulation of 226Ra, 228Ra, 40K and 137Cs in bottom sediments of Mumbai Harbour Bay

The present work shows the activity levels of 226Ra, 228Ra, 40K and 137Cs in bottom sediments collected from eight locations of Mumbai Harbour Bay. The study has shown that 40K and 228Ra concentration is nearly uniform throughout the studied area while 226Ra and 137Cs are more concentrated in the southern regions of the bay. The significant variation in the activity levels of radionuclides within the study site might be due to their sorption/desorption processes onto the surface of sediment materials. The low mean value of 226Ra/228Ra ratio (0.72) in the sediments indicates that 238U has relatively greater solubility and mobility than 232Th. Similarly, low activity ratio (0.18) for 137Cs/40K reflects the presence of very high content of 40K in sediment due to presence of primary minerals in sediment. Silt and clay were reported to dominate the composition of the sediment. A significant positive correlation between 226Ra and 228Ra and 137Cs and 40K suggest a similar origin of their geochemical sources and identical behavior during transport in the sediment system.

Characterization of groundwater composition in Punjab state with special emphasis on uranium content, speciation and mobility

Abstract Groundwaters (borewell and handpump) were sampled from two districts (Bathinda and Mansa) of Punjab state and analyzed for their major ionic concentrations and uranium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The major ionic concentrations of waters were plotted on a Piper diagram and grouped into four dominant hydrochemical facies as (Na+K)-SO4+Cl type (69% – 73%), (Ca+Mg)-SO4+Cl type (6% – 21%), (Ca+Mg)–HCO3 type (4% – 6%) and (Na+K)-HCO3 type (2% – 19%). It was observed that mobility of uranium in groundwater was very much influenced by TDS (total dissolved solids). To investigate the various mechanisms for deriving the elevated uranium concentrations in groundwater, 234U/238U activity ratios (ARs) were calculated using the determined activity levels of 234U and 238U. The mean ARs was found to be near unity (i.e. secular equilibrium) in the study regions confirmed that uranium in groundwaters was mainly resulted from its host/parent rocks through weathering processes. The concentration of HCO3− in ground water showed one order of magnitude higher than the total dissolved SiO2 indicates that carbonate weathering was the dominant process due to major water–rock interaction. The uranium speciation in groundwaters was investigated by an equilibrium model calculation using MEDUSA (make equilibrium diagrams using sophisticated algorithms) under the influence of redox conditions and complexant concentration. At the observed range of pH values, the predominant redox speciation of uranium was observed as hydroxo-carbonato complexes of (UO2)2(CO3)(OH)3− and hydroxyl complexes of UO2(OH)3− which might be caused for increasing the solubility of uranium. Due to very low concentration of phosphate in groundwater, its effects on U(VI)-aqueous speciation was negligible.

Thermodynamic parameters of U (VI) sorption onto soils in aquatic systems

The thermodynamic parameters viz. the standard free energy (∆Gº), Standard enthalpy change (∆Hº) and standard entropy change (∆Sº) were determined using the obtained values of distribution coefficient (kd) of U (VI) in two different types of soils (agricultural and undisturbed) by conducting a batch equilibrium experiment with aqueous media (groundwater and deionised water) at two different temperatures 25°C and 50°C. The obtained distribution coefficients (kd) values of U for undisturbed soil in groundwater showed about 75% higher than in agricultural soil at 25°C while in deionised water, these values were highly insignificant for both soils indicating that groundwater was observed to be more favorable for high surface sorption. At 50°C, the increased kd values in both soils revealed that solubility of U decreased with increasing temperature. Batch adsorption results indicated that U sorption onto soils was promoted at higher temperature and an endothermic and spontaneous interfacial process. The high positive values of ∆Sº for agricultural soil suggested a decrease in sorption capacity of U in that soil due to increased randomness at solid-solution interface. The low sorption onto agricultural soil may be due to presence of high amount of coarse particles in the form of sand (56%). Geochemical modeling predicted that mixed hydroxo-carbonato complexes of uranium were the most stable and abundant complexes in equilibrium solution during experimental.

Base line radioactivity levels in Kaiga site soil and its migration to biosphere

The effects of variation in different parameters on the environmental distribution of base line 137Cs and 40K activities in Kaiga environment and their migration into biosphere are discussed. Transfer factors of these radionuclides from soil to different parts of commonly available plants in this region were estimated. Base line radioactivity levels in soil at Kaiga were higher as compared to pre-operational values reported from other power station sites in India and were mainly attributed to the very high precipitation rate prevailing in this area. Also, this area being an undisturbed forest land, fallout activities are re-circulated to the soil by the decay of parts of trees.40K and 137Cs activity levels in leaves of shallow rooted plants were found to be higher as compared to that in deep rooted trees. Transfer factors of soil to plant parts revealed that there is no major bio-accumulation of 137Cs in any parts of Colocassia esculenta (L.) and Chromolaena odorata (L.) King & Robinson. Comparison of 40K/137Cs ratio between soil and different parts of these plants has revealed that uptake of K is relatively more efficient as compared to that of Cs, presumably because of the faster kinetics of K due to its larger atom inventory in the soil.

A review of radio chemical analysis and estimation of 210Po in soil matrices

Abstract The naturally occurring radionuclide 210Po, arising from the uranium–radium decay series, provides a considerable contribution to the radiation exposure to humans. Polonium is analyzed for a variety of purposes, including for radiological impact assessment or as a tracer of environmental processes. Losses of polonium may occur at temperatures above 100°C, depending on conditions, requiring particular care in sample preparation and treatment. There has been little development regarding analysis of polonium in environmental samples since 1960 as radiochemical analysis of polonium is quite straight forward due to easy of source preparation through auto-deposition on to metal surfaces. In this paper a brief review of estimation of polonium in the soil samples have given emphasis.

Equilibrium isotherm and kinetics modeling of U(VI) adsorption by natural soil systems

This research examined the adsorption capability of natural soils of different origin for U(VI) at soil–water interface and the mechanism involved. Adsorption kinetics study indicates that adsorption followed the pseudo-second order kinetics irrespective of soil types and was not solely controlled by the diffusion step rather surface complexation and ion-exchange plays major role. Study of adsorption isotherms indicates adsorption involves chemisorption and soil with high Fe and Mn content better fit to Langmuir model. The study provides a better insight for site selection for radioactive waste (uranium) disposal facilities as well as soil suitable for back fill or permeable reactive barrier to inhibit migration of U(VI).

Studies on the rain scavenging process of tritium in a tropical site in India.

This study presents the results of one of the first systematic experiments on tritium ((3)H) concentrations in ground level air against that in rainwater near a pressurized heavy water reactor in a tropical region. The samples were collected over the rainy season of three years (2007, 2008 and 2010). For this study, 31 data sets were collected and interpreted based on the theoretical information available in the literature. The specific activity ratio of (3)H between rainwater and air moisture at ground level was calculated for each data set. The average specific activity ratio was found to be 1.96 ± 2.72. A correlation (r = 0.82, p < 0.001) was observed between the total rain hours in a day and the rainwater (3)H activity. Higher rain duration with slower rain rate yielded higher (3)H concentrations as more time was available for the scavenging/wash out process to take effect together with lower dilution. The present data also suggested the need to further investigate the influence of raindrop distribution and other local meteorological parameters on the (3)H wash out process. An attempt was also made to predict the (3)H concentration in air moisture samples using a Gaussian plume dispersion model and the values were compared with the measured (3)H activity. The measured values were generally lower than the predictions.

Transfer coefficient of 137Cs from feed to cow milk in tropical region Kaiga, India.

In the transport model for the prediction of the concentration of (137)Cs in milk, the transfer coefficient from feed to milk, F(m), is an important parameter. Site-specific transfer coefficient from feed to cows milk, for (137)Cs in the Kaiga environment, a nuclear power station site in India, determined over a period of 10 y is presented in this paper. The value is determined from (137)Cs concentration in milk and grass samples of the Kaiga region and the result ranged from 6.43E-03 to 1.09E-02 d l(-1) with a geometric mean value of 8.0E-03 d l(-1). The result is compared with that for (40)K, determined concurrently at the same region and ranged from 3.06E-03 to 3.48E-03 d l(-1) with a geometric mean value of 3.26E-03 d l(-1). This parameter is quite useful in decision-making for implementing countermeasures during a large area contamination with (137)Cs in tropical areas like Kaiga.

Speciation and estimation of radioiodine in reactor coolant water

The species of radioiodine in the primary coolant water of the heavy water moderated, heavy water cooled 100 MW research reactor have been identified. It was observed that IO3− was the major species in the reactor coolant during reactor operation and I− was the major species during shutdown. Organic and elemental forms amount only to less than 2% of total radioiodine. A simple method was developed for the estimation of gross iodine activity in reactor coolant water. The method involves the separation of all inorganic forms of iodine into a photographic film consisting of a thin layer of silver halide. The iodine in the film was estimated by gross counting of the film in a Geiger-Müller counter. Gross iodine activity in the reactor coolant samples estimated by the present method were in agreement with that obtained by direct γ-spectrometry with a Ge detector. It is concluded that the method can be used for the routine estimation of radioiodine in reactor coolant water.133I/131I and135I/131I ratios in the film were estimated and found to be useful in identifying split rod conditions in the reactor.