Spatial Distribution Of Radionuclides Research Articles

Influence of Precipitation on the Spatial Distribution of 210Pb, 7Be, 40K and 137Cs in Moss

Mosses have been widely used as biomonitors of a variety of atmospheric pollutants, including radionuclides. Here we determine the radionuclide activity concentration of 210Pb, 137Cs, 7Be, and 40K in moss tissue (Hylocomium splendens) collected from 24 sites across Ireland and assess the influence of precipitation on radionuclide spatial distribution. Lead-210 was the most abundant radionuclide (range: 226–968 Bq kg–1), followed by 7Be (range: <DL—604 Bq kg–1), 40K (range: <DL—155 Bq kg–1), and 137Cs (range: <DL—41 Bq kg–1). Albeit nearly thirty years since the Chernobyl disaster, 137Cs activity concentration was detected at 67% of the study sites; however, the spatial distribution was not fully consistent with the 1986 Chernobyl deposition pattern. Rather, 137Cs was weakly correlated with rainfall, with higher concentrations along the west coast, suggesting that the 2011 Fukushima Dai-ichi nuclear accident was also a potential source. Average annual rainfall was a significant predictor of 210Pb activity (linear regression, R2 = 0.63, p < 0.001). As such, the highest radionuclide activity was observed for 210Pb (average: 541 Bq kg–1), owing to the high levels of precipitation across the study sites (average: 1585 mm). In contrast, 7Be or 40K were not correlated with precipitation; rather, 40K and 7Be were significantly correlated to each other (rs = 0.7), suggesting that both radionuclides were transferred from the substrate or through soil re-suspension. Precipitation is widely reported as an important factor in the spatial distribution of radionuclides; however, only 210Pb activity concentrations in moss were strongly influenced by precipitation in the current study.

Dosimetric impact of natural terrestrial radioactivity on residents of lower Himalayas, India.

A comprehensive radio-ecological evaluation of soil samples of Solan and Shimla districts of Himachal Pradesh has been carried out for risk and dose assessment. Twenty-six randomly selected environmental soil samples were analysed for natural radionuclide concentrations (226Ra, 232Th and 40K) using NaI(Tl) scintillator detector. The average concentration of 226Ra, 232Th and 40K was observed as 37, 59 and 430Bqkg-1, respectively, which exceeded the worldwide average of 33, 45 and 412Bqkg-1 reported by UNSCEAR (Sources and effects of ionizing radiation. Report to the general assembly with scientific annexes, New York, 2008). Radium equivalent activity (Raeq), hazard indices (Hex, Hin) and radioactivity level indices (Iϒr, Iα, AUI) and Clark value were checked against their threshold limits, and their mean values were safely below the recommended criteria. This confirms the soil applicability for construction purposes. Indoor and outdoor dose rates (Ḋ), age-dependent annual effective doses (AED), organ-specific doses and lifetime attributable cancer risk (both cancer incidence and cancer mortality) were also computed. Strong positive correlation was established between radon/thoron exhalation rate and their parent radionuclides. Multivariate statistical technique was employed to explore spatial distribution of radionuclides and homogeneity between various radiological parameters.

Applied gamma-ray spectrometry for evaluating tropical soil processes and attributes

Geophysical methods, such as gamma-ray spectrometry, have great potential to enhance knowledge of the pedosphere (pedogenesis, pedogeochemistry and pedogeomorphology), helping to predict tropical soil attributes. We applied proximal gamma-ray spectrometry to evaluate tropical landscape dynamics, pedogenesis and spatial distribution of radionuclides and selected soil attributes. This study was carried out in southeast Brazil, where 79 soil samples (0–20 cm) along transects were collected to perform physical-chemical analysis coupled with collection of surface gamma-ray spectrometric data, allowing the detection of the radionuclides uranium (U238), thorium (Th232), and potassium (K40). Additionally, we analyzed soils in four toposequences, with varying lithology, relief, and hydrology. The radionuclide concentrations in soils showed a direct relationship with the parent material composition, either rocks or sediments. Weathering degree and the geochemical behavior of each radionuclide determines its permanence or removal in soils. Denudation processes along the toposequences also influence the distribution of radionuclides. On one hand, the radionuclide contents of mature, weathered soils are closely associated with advanced pedogenesis, with a higher clay contents and argic horizon formation, whereas in younger, less weathered soils the parent material exerts a greater influence than pedogenesis. Uranium decreased with altitude, and showed greater mobility compared with thorium. Thorium presented a higher correlation with clay content, and the opposite with sand content. Potassium detection increased with soil cation exchange capacity (CEC) and clay content. Gamma-spectrometry detected significant variations in some segments along the toposequences, undetectable by conventional soil survey techniques. This may indicate changes from one soil class to another or the continuity of a particular soil class, demonstrating the potential of this tool in digital soil mapping, pedogeochemical, pedogeomorphological and pedogenesis processes studies.

Development of calculation methodology for estimation of radionuclide composition in wastes generated at Fukushima Daiichi nuclear power station

ABSTRACT A calculation methodology for estimating the radionuclide composition in the wastes generated at the Fukushima Daiichi nuclear power station has been developed by constructing a skeleton overview of the distribution of radionuclides considering the material balance in the system and calculation flowcharts of the transportation of radionuclides into the wastes. The wastes have a distinctive feature that their level of contamination includes considerable uncertainties because the process behind the contamination with the radionuclides released from the damaged fuel during and after the accident is not yet fully understood. Here, the developed method can explicitly specify the intrinsic uncertainties as a band to be included in the estimated radionuclide composition in the wastes and can quantitatively describe the uncertainties by calibration using analytically measured data on actual waste samples collected at the site. Further studies to improve the quality of the calculation method, the introduction of a stochastic approach to describe uncertainties, and acquiring a quantitative understanding of the spatial distribution of radionuclides inside the reactor building are suggested as important steps toward reasonable and sustainable waste management as an integral part of the decommissioning of the Fukushima Daiichi nuclear power station.

Spatial distribution of radionuclides in agricultural soil in the vicinity of a coal-fired brick kiln

The spatial distributions of naturally occurring radionuclides (226Ra, 232Th, and 40K) in agricultural soils collected in the proximity of a coal-fired brick kiln located at Chittagong district were studied using HPGe γ-ray spectrometry. The obtained mean activity concentrations for 226Ra, 232Th, and 40K were slightly higher than the world average values, which indicate the contribution of radionuclides via the fly ash deposition from the kiln. The maximum activity concentrations of 226Ra, 232Th, and 40K in soil samples collected at a distance of 120 m from the kiln were found to be 54.3 ± 11.3 Bq kg−1, 62.1 ± 18.2 Bq kg−1, and 572 ± 123 Bq kg−1, respectively; the levels show further decreasing trend in all directions (towards and away from the kiln). Associated radiological hazard indices were calculated in order to assess the radiation effects to human health and compared with the world-recommended values. Basic multivariate statistical analysis was performed to describe the statistical characteristics of the radionuclides. Lower values of radiological indices indicate that there is no probability of immediate health effect on workers and public living around the kiln due to the presence of natural radioactivity in the agricultural soils.

Radiometric analysis and spatial distribution of radionuclides with-in the terrestrial environment of South-Western Nigeria using ERICA tool

Samples of soil, grass and organs of herbivore mammal were collected from different sampling locations in five states within the south-western area of Nigeria. The activity concentrations of natural radionuclides such as 40K, 238U and 232Th present in the collected samples were detected with a method of gamma spectrometry using High Purity Germanium detector. These activity measurements and other ecological (site-specific) data were loaded into ERICA Tool (Version 1.2) to examine the radioactivity level of terrestrial non-human biota. Basic statistics like kurtosis, skewness, histogram alongside spatial distribution calculation were performed in order to understand the radionuclide distribution pattern within the samples. The study also examined the radionuclide transfer factor between the soil and the grass samples. The highest activity concentration was recorded for samples collected from Abeokuta and lowest from samples from Iwo. The calculated concentration is in the order of 40K >238U >232Th. The transfer factor calculation revealed the uptake of 232Th by the collected grass samples is larger than that of 238U and 40K. The dose rates acquired with the use of the application of ERICA Tool indicates that higher contribution to the total dose is from internal exposure derived from exposure to 238U and 228Th with a joint contribution of 95.7% for mammals and 96.9% for grasses. The contribution of 40K corresponds to 4.3% for mammals and 3.1% for grass which is quite a low contribution to total dose. The RQexp value for sampled location is below unity while the RQcons exceeds unity for Lagos and Abeokuta. The result of this study would hearten the use of software application to a wide range of ecosystems and could also serve as a reference or pilot for further research regarding ionizing radiation on non-human biota.

Radionuclides in Irradiated Graphite of Uranium–Graphite Reactors: Decontamination of Sleeves Using Liquid Reagents

To examine the possibility of disposal of irradiated graphite in ground near-surface repositories, the concentration and spatial distribution of radionuclides in the volume of irradiated graphite sleeves of industrial uranium–graphite reactors was studied, and the efficiency of decontamination using liquid reagent treatment methods was evaluated. The radionuclide distribution in the graphite volume is extremely heterogeneous on the 10–100 μm scale. The degree of decontamination using solutions with high acid concentrations and fluoride ions added does not exceed 16–25% for 14C and 15–19% for 36Cl. Under these treatment conditions, no structural changes occur in graphite, and 14С bound with the graphite surface via sorption is removed. Significant differences in the efficiency of the reagent decontamination of irradiated graphite from various producers were revealed.

Determination of radioactivity levels and associated hazards of coastal sediment from south east coast of Tamil Nadu with statistical approach

The concentration of 238U, 232Th and 40K in sediment samples collected from Thazhankudato Kodiyakkarai along the east coast of Tamil Nadu, India was measured using γ-spectrometry. Measured mean activity concentrations are 3.3, 40.45 and 389.28 Bq kg−1 for 238U, 232Th and 40K, respectively. The average activity concentration of 232Th is slightly higher than the world average value. The radiation hazards such as radium equivalent activity, absorbed gamma dose rates in air, the annual gonadal dose equivalent, annual effective dose equivalent, external hazard index, internal hazard index, representative level index and excess lifetime cancer risk associated with the radionuclides were calculated. Heat production rate of sediments and spatial distribution of radionuclides is studied. The multivariate statistical analysis, such as Pearson correlation, principal component and cluster analysis were applied to know the existing relation between radiological variables. From the analysis, the radioactivity levels in sediment samples do not pose any environmental health problem. Thus, the presented data provide a general background of the detectable radionuclides for the study area and can be helpful in future epidemiological studies.

Spatial distribution of radionuclides in 3D models of SN 1987A and Cas A

AbstractFostered by the possibilities of multi-dimensional computational modeling, in particular the advent of three-dimensional (3D) simulations, our understanding of the neutrino-driven explosion mechanism of core-collapse supernovae (SNe) has experienced remarkable progress over the past decade. First self-consistent, first-principle models have shown successful explosions in 3D, and even failed cases may be cured by moderate changes of the microphysics inside the neutron star (NS), better grid resolution, or more detailed progenitor conditions at the onset of core collapse, in particular large-scale perturbations in the convective Si and O burning shells. 3D simulations have also achieved to follow neutrino-driven explosions continuously from the initiation of the blast wave, through the shock breakout from the progenitor surface, into the radioactively powered evolution of the SN, and towards the free expansion phase of the emerging remnant. Here we present results from such simulations, which form the basis for direct comparisons with observations of SNe and SN remnants in order to derive constraints on the still disputed explosion mechanism. It is shown that predictions based on hydrodynamic instabilities and mixing processes associated with neutrino-driven explosions yield good agreement with measured NS kicks, light-curve properties of SN 1987A and asymmetries of iron and 44Ti distributions observed in SN 1987A and Cassiopeia A.

Modelling of the spatial distribution of the induced activities in the RBMK-1500 reactor graphite blocks and rings/sleeves

There is one nuclear power plant (NPP) in Lithuania – the Ignalina NPP – which is under decommissioning now. The Ignalina NPP has two units with RBMK-1500 reactors, which are the most powerful and the most advanced versions of RBMK-type reactor design. Unit 1 of the Ignalina NPP was shut down at the end of 2004 and Unit 2 was shut down at the end of 2009. RBMK is a water-cooled graphite-moderated channel-type power reactor and the decommissioning of these reactors faces specific challenges for proper characterisation and disposal of irradiated reactor graphite.Apart from radiological inventory, the spatial distribution of radionuclides in the reactor graphite is also very important because it could indicate the possibilities for decontamination/treatment of the irradiated graphite. This is important for consideration of the near surface disposal option for irradiated graphite, as without treatment it usually does not meet the waste acceptance criteria.Based on that, the work presented in this paper is focused on the modelling of the induced activity spatial distribution in the Ignalina NPP RBMK-1500 reactor graphite components: blocks and rings/sleeves. The modelling was performed with MCNP and SCALE computer codes and consisted of two mains stages: modelling of the neutron flux in the reactor graphite components, and then modelling of the neutron activation in them using the already modelled neutron flux. In such a way, the spatial induced activity distribution in the analysed reactor components was obtained. Modelling results show that the thermal neutron flux is more intensive in the outer radial regions of the graphite components and this, in general, results in higher induced activities there.

Activity concentration and spatial distribution of radionuclides in marine sediments close to the estuary of Shatt al-Arab/Arvand Rud River, the Gulf

Tigris and Euphrates rivers both emerge in eastern Turkey and cross Syria and Iraq. They unite to Shatt al-Arab/Arvand Rud River and discharge in Arabic/Persian Gulf. The activity concentration of natural and anthropogenic radionuclides was measured during the August of 2011 in a number of surficial sediment samples collected from the seabed along an almost straight line beginning near the estuary mouth and extending seaward. The results exhibited low activity concentration levels and an almost homogeneous spatial distribution except locations where sediment of biogenic origin, poor in radionuclides, dilute their concentrations. Dose rates absorbed by reference marine biota were calculated by the ERICA Assessment Tool considering the contribution of 40 K. The results revealed a relatively low impact of 40 K mainly to species living in, on and close to the seabed. Also, statistical association of radionuclides with selected stable elements (Ca, Ba and Sr) did not indicate presence of by-products related with oil and gas exploitation and transportation activities. Moreover, a semi-empirical sedimentology model applied to reproduce seabed granulometric facies based entirely on radionuclides activity concentrations.

Natural radionuclides in soil profiles surrounding the largest coal-fired power plant in Serbia

This study evaluates the influence of the largest Serbian coal-fired power plant on radionuclide concentrations in soil profiles up to 50 cm in depth. Thirty soil profiles were sampled from the plant surroundings (up to 10 km distance) and analyzed using standard methods for soil physicochemical properties and gamma ray spectrometry for specific activities of natural radionuclides (40K, 226Ra and 232Th). Spatial and vertical distribution of radionuclides was determined and analyzed to show the relations between the specific activities in the soil and soil properties and the most influential factors of natural radionuclide variability were identified. The radiological indices for surface soil were calculated and radiological risk assessment was performed. The measured specific activities were similar to values of background levels for Serbia. The sampling depth did not show any significant influence on specific activities of natural radionuclides. The strongest predictor of specific activities of the investigated radionuclides was soil granulometry. All parameters of radiological risk assessment were below the recommended values and adopted limits. It appears that the coal-fired power plant does not have a significant impact on the spatial and vertical distribution of natural radionuclides in the area of interest, but technologically enhanced natural radioactivity as a consequence of the plant operations was identified within the first 1.5 km from the power plant.

Effect of nonlinear sorption on multispecies radionuclide transport in a coupled fracture-matrix system with variable fracture aperture: a numerical study

A one-dimensional numerical analysis on multispecies radionuclide transport in a single-horizontal coupled fracture-matrix system has been performed. Analysis considering linear and nonlinear adsorption cases with linear, Langmuir, and Freundlich adsorption models has been carried out. The results indicate that there is a significant change in the spatial distribution of radionuclides in a coupled fracture-matrix system when a nonlinear adsorption isotherm is considered as compared to the simplified linear sorption isotherm. Sensitivity analysis of Langmuir constant and Freundlich exponent has been performed, and the numerical results indicate that the behavior of radionuclide transport is strongly influenced by these nonlinear sorption isotherm parameters. In addition, an attempt has been made to consider the variation of fracture aperture thickness along its flow direction by introducing logarithmic distribution. A clear distinction in the spatial distribution of radionuclide concentration was observed when variable fracture aperture is considered as opposed to the conventional parallel plate model with a constant fracture aperture thickness. Further, the results suggest that there is an enhanced retardation of radionuclides within the high permeable fracture with varying fracture aperture.

Numerical Simulation of Dispersion of Radionuclides Released from the Fukushima NPP and the Assessment of their Nuclear Impact

A large number of radionuclides were discharged into oceans after the Fukushima nuclear crisis. In this paper, we employed ROMS to simulate the circulation of water around Japan. We evaluated the temporal and spatial distribution of radionuclides originated from Fukushima NPP, such as: Cs-137, Cs-134 and I-131. Then, we utilized MCNP 5 to assess the external nuclear impact of these nuclides in water and obtained the effective dose rate distribution in the coast water around Fukushima NPP.

Spatial distribution of radionuclides in seabed sediments off Ibaraki coast after the Fukushima Daiichi Nuclear Power Plant accident

Fifty-one seabed sediments were collected to estimate the influence of the Fukushima Daiichi Nuclear Power Plant accident on the area offshore from Ibaraki. The 134Cs and 137Cs radioactivity levels were 3.8–206.7 and 6.1–296 Bq/kg (dry wt), respectively, and the activity ratios of 134Cs/137Cs were 0.48–0.77. The 90Sr and 239,240Pu activity levels were ND–0.26 and 0.170–0.78 Bq/kg (dry wt), respectively. The ratios of 238Pu/239,240Pu activity were 0.014–0.019. The 90Sr radioactivity was increased by the accident and Pu isotopes radioactivity was not changed.

Activity concentrations and distribution of radionuclides in surface and core sediments of the Neretva Channel (Adriatic Sea, Croatia)

The activity concentrations and the distribution of manmade 137 Cs and naturally occurring radionuclides 40 K, 238 U and 232 Th in surface and core sediments of the semi enclosed, river-dominated marine environment of the Neretva Channel were investigated in relation to the sedimentological characteristics and the content of the total organic carbon (TOC). The activity concentrations of radionuclides were determined by gamma spectrometry. Distinct interrelations between sediment properties and spatial distribution of radionuclides were established. The highest accumulation of 137 Cs was found close to the river mouth, in the region of intensive deposition of organic matter of terrestrial origin. This finding implies that the river-borne organic material and its deposition processes should be considered as the most important factor controlling distribution of 137 Cs in this transitional land-sea environment. The sediment accumulation rates, estimated from distribution of 137 Cs in core sediments, were approximately 6 mm y -1 in front of the Neretva River mouth and 4 mm y -1 in the channel area. The spatial distribution of natural 40 K and 232 Th radionuclides indicates their distinct association with fine-grained sediments. The interrelation of 238 U with fine-grained particles was somewhat weaker but still present. The results obtained indicate that the accumulation pattern of natural radionuclides in the Neretva Channel sediments is mainly governed by the deposition of fine-grained material. This study scrutinizes the baseline level for occurring radionuclides and should be used for monitoring and assessing the radionuclide pollution record in the investigated transitional land-sea environment of the Adriatic.

Chemical speciation code CHEMSPEC and its applications

The adsorption and migration behavior of a radionuclide in geological media heavily depends on its chemical forms in a given chemical environment. In order to predict the temporal and spatial distribution of radionuclides around a disposal site when its canister is damaged, it is necessary to develop coupled chemical speciation-solute transport models and relevant software. For that reason, we wrote a new chemical speciation program CHEMSPEC. In this paper, the principles and structure of CHEMSPEC are briefly described, and the strategy and algorithms that were used in this code are interpreted in some detail, such as the measures adopted to prevent divergence in iteratively solving the mass balance equations, the “predictor-corrector” algorithm for calculation of the number and quantities of solid species formed, and the alternate use of “freezing” and “defreezing” oxidation states in handling of co-existent redox and precipitation equilibria. Four examples are given to illustrate CHEMSPEC’s features and capabilities.

Distribución espacial de radionucleídos en sedimentos marinos de Bahía Culebra y el Golfo de Nicoya, Pacífico, Costa Rica

Spatial distribution of radionuclides in marine sediments from Culebra Bay and the Gulf of Nicoya, Pacific coast, Costa Rica . Ten natural and artificial radionuclides (K40, Cs137, Bi212, Pb212, Bi214, Pb214, Ra226, Ac228, Pa234, U235) in marine sediments were studied in Culebra Bay and the Gulf of Nicoya, both on the Pacific coast of Costa Rica. A freshwater marsh and an offshore island (Coco Island) were used as reference sites. The concentration of radioactive elements from the time of Earth’s formation diminishes in older continental blocks. Higher concentrations are expected in the offshore island, as found in this study. The range of values of these elements are considered normal according to global reports. Some of them, like Potassium 40, seem to have an anthropogenic contribution in the Gulf of Nicoya, possibly related to the activities developed in the adjacent hydrographic basins. In all sampled sites, the artificial element Cesium-137 has been detected within normal ranges and values are very similar to those measured in the coast and in the interior of Costa Rica in previous studies. Rev. Biol. Trop. 56 (Suppl. 4): 83-90. Epub 2009 June 30.

Estimation of the Influence of Humic Acid on Radionuclide Binding to Solid Residuals in Deposits of Radioactive Waste

In contaminated water reservoirs, the sorption and binding of radionuclides to solids (SR) determines their bioavailability and transport and thus human and ecosystem exposure. In this work, the influence of organic matter (OM) on binding of the radionuclides 90Sr, 137Cs, sum of 235U, 238U, and sum of 239Pu, 240Pu to solids are investigated, using experimental data derived from ecological monitoring of radioactive waste deposits in South Ural (Russia). OM in several surface water reservoirs mainly consists of humic substance (HS) which forms humates and fulvates with radionuclides and binds to solids via different mechanisms, such as coordinating bond or covalent bond. These processes are strongly dependent on the phase of HS, which can be colloidal or soluble high-molecular compounds. Based on the spatial distribution of radionuclides, SR and OM in waste deposits, we assumed a specific influence of humic acids (HA) on the binding of radionuclides to SR, and quantified it with invariant values of a modified partitioning coefficient. The mathematical form of this invariant value emphasizes a significant impact of the local mass of HA (mHA/V) and local surface area of SR (s = Ssorb/V) per volume V on the processes involved in binding radionuclides to SR. These processes may retard radionuclide migration into groundwater.

RBS and micro-PIXE study of I and Cs Heterogeneous Retention on Concrete

AbstractA combination of two nuclear ion beam techniques, Rutherford Backscattering Spectrometry (RBS) and micro-Particle Induced X-Ray Emission (uPIXE) was tested to evaluate both diffusion profiles and radionuclide spatial distribution of radionuclides (RN) onto cement-based materials. The methodology was tested on a Spanish reference backfill concrete, used as engineering barrier in low-level radioactive waste repositories, using two elements (Cs and I) with different sorption behaviour onto the cement. The applicability and limitations of the selected methodology is discussed for both elements.