Radionuclide concentrations in several seaweeds and their annual variations

To examine the radionuclide concentrations in the environment, seaweeds were collected once a year since 1976 at two different places. A marked change was observed in the number of radionuclides in seaweeds. The increase of radionuclides is attributed to contamination by radioactive fallout from Chinese nuclear explosion tests. The radionuclide concentrations were strongly dependent on the species of seaweeds. A gradual decrease of the¹³⁷Cs/⁴⁰K activity ratio was observed in spite of the input of additional¹³⁷Cs fallout from Chinese nuclear tests. This implies that the amounts of¹³⁷Cs introduced into seawater by these detonations were small in comparison with those already contained in seawater. The cesium content in seawater was estimated by using specific activities of¹³⁷Cs in seaweeds and¹³⁷Cs concentration in seawater. The results show good agreement with the reported values by direct analysis of seawater.     

A description of the DOE Radionuclide Aerosol Sampler/Analyzer for the Comprehensive Test Ban Treaty

Radionuclide monitoring, though slower than vibrational methods of explosion detection, provides a basic and certain component of Comprehensive Test Ban treaty (CTBT) verification. Measurement of aerosol radioactive debris, specifically a suite of short-lived fission products, gives high confidence that a nuclear weapon has been detonated in or vented to the atmosphere. The variable nature of wind-borne transport of the debris requires that many monitoring stations cover the globe to insure a high degree of confidence that tests which vent to the atmosphere will be detected within a reasonable time period. To fulfill the CTBT aerosol measurement requirements, a system has been developed at PNNL to automatically collect and measure radioactive aerosol debris, then communicate spectral data to a central data center. This development has proceeded through several design iterations which began with sufficient measurement capability (<30 μBq/m^{3 140}Ba) and resulted in a system with a minimal footprint (1 m×2 m), minimal power requirement (1600W), and support of network infrastructure needs. The Mark IV prototype (Fig. 1) is currently the subject of an Air Force procurement with private industry to partially fulfill US treaty obligations under the CTBT. It is planned that the system will be available for purchase from a manufacturer in late 1997.     

Fukushima-derived radionuclides in ground-level air of Central Europe: a comparison with simulated forward and backward trajectories

Results of forward and backward modeling of air mass transport from Fukushima Daiichi nuclear power plant to Slovakia were compared with aerosol radioactivity measurements. Several radionuclide maxima (¹³¹I, ¹³⁴Cs and ¹³⁷Cs) were observed in the Bratislava ground-level air in March–April 2011. The ¹³¹I/¹³⁷Cs activity ratio records showed the presence of two different fresh air masses in the Bratislava air, supported by simulations of forward and backward trajectories between Fukushima and Bratislava.     

Radioactivity in the Exclusive Economic Zone of east coast Peninsular Malaysia: distribution trends of <Superscript>137</Superscript>Cs in surface seawater

Large volumes of surface seawater samples were collected from thirty locations in the Exclusive Economic Zone (EEZ) of the east coast Peninsular Malaysia on June 2008 to study the activity concentrations of ¹³⁷Cs. The results will serve as additional information to the existing baseline data and is very useful for monitoring fresh input of anthropogenic radionuclide into Malaysian marine environment. In this study, the activity concentrations of ¹³⁷Cs were determined using co-precipitation technique, followed by Gamma Spectrometry measurement. The mean activity concentration of ¹³⁷Cs ranged between 3.40 and 5.89 Bq/m³. Higher activity concentrations were observed at the coastal and towards the south of Peninsular Malaysia and were aligned with the high turbidity. These may due to the rapid diffusion of ¹³⁷Cs from suspended particulates and fine sediments into surface seawater. The activity concentrations of ¹³⁷Cs observed in this study were slightly higher than the concentrations reported in seawater at the Straits of Malacca, Vietnam and Philippines. This might be because the study area received more input of ¹³⁷Cs that originated from global fallout and then deposited on land which later being transported subsequently into the coastal zone due to siltation and erosion processes. It could also be attributed to the intrusion of river waters containing higher concentrations of ¹³⁷Cs.     

Worldwide measurements of radioxenon background near isotope production facilities, a nuclear power plant and at remote sites: the “EU/JA-II” Project

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) specifies that radioxenon measurements should be performed at 40 or more stations worldwide within the International Monitoring System (IMS). Measuring radioxenon is one of the principle techniques to detect underground nuclear explosions. Specifically, presence and ratios of different radioxenon isotopes allows determining whether a detection event under consideration originated from a nuclear explosion or a civilian source. However, radioxenon monitoring on a global scale is a novel technology and the global civil background must be characterized sufficiently. This paper lays out a study, based on several unique measurement campaigns, of the worldwide concentrations and sources of verification relevant xenon isotopes. It complements the experience already gathered with radioxenon measurements within the CTBT IMS programme and focuses on locations in Belgium, Germany, Kuwait, Thailand and South Africa where very little information was available on ambient xenon levels or interesting sites offered opportunities to learn more about emissions from known sources. The findings corroborate the hypothesis that a few major radioxenon sources contribute in great part to the global radioxenon background. Additionally, the existence of independent sources of ^131mXe (the daughter of ¹³¹I) has been demonstrated, which has some potential to bias the isotopic signature of signals from nuclear explosions.     

Determination of the amount and retention efficiency of aerosols arising during the vitrification of medium-level activity wastes from nuclear power plants

During the vitrification of medium-activity liquid wastes simulating the wastes from nuclear power plant aerosols are formed that enter into the gas pumped off from the vitrification furnace. The dependence of solid-aerosol carryover on the parameters characterizing the glass composition and its eluability were investigated in laboratory scale experiments. The aerosol carryover was determined either gravimetrically or radiometrically using radioactive tracers.¹³⁷Cs with a carrier was added to the wastes and the aerosol carryover was determined by following the¹³⁷Cs activity. In the case of the¹³⁷Cs-labeled aerosol it was observed that a higher alkali content in the melted wastes results in a higher carryover of the¹³⁷Cs-labeled aerosol. Using a multicomponent laboratory gas cleaning system a decontamination factor of 6.7·10⁶ was achieved for the removal of the¹³⁷Cs-labeled aerosol from the gas pumped off from the vitrification furnace.     

Study on the preparation of a137Cs/137mBa radionuclide generator

^137mBa has been applied successfully to dynamic studies for diagnosis in nuclear medicine for a long time. A variety of inorganic exchangers have been employed for the separation of^137mBa from its parent¹³⁷Cs. In the present study, cupric cobaltic ferrocyanide and amorphous zirconyl phosphate were synthesized and compared for use in a¹³⁷Cs/^137mBa generator. The results show that the former can adsorb¹³⁷Cs more efficiently and provide high elution yield of^137mBa with greater than 99.99% radionuclide purity. A new generator involving multimillicuries of^137mBa, in connection with a computerized detection system, has been constructed.     

Temporal and spatial variations of <Superscript>137</Superscript>Cs in the waters off a nuclear fuel reprocessing facility in Rokkasho,Aomori, Japan

Five survey cruises were carried out from 2004 to 2007 to determine ¹³⁷Cs concentrations in the water columns off Rokkasho Village, Aomori Prefecture, Japan, where the spent nuclear fuel reprocessing plant of Japan Nuclear Fuel Ltd has been undergoing test operation since March 2006. Seawater samples were collected with a large volume in situ filtration and concentration system at different depths in the water column. ¹³⁷Cs in particulate form could not be detected in the survey area. Dissolved ¹³⁷Cs showed temporal variation, especially in the surface water. Based on the results, it was concluded that no observable ¹³⁷Cs contamination was present in the investigated area. The distribution of ¹³⁷Cs concentrations was influenced by the mixing between the Tsugaru and Oyashio Currents.     

Dispersion model of cesium-137 in surface oceanic waters

The¹³⁷Cs radionuclide dispersion in the marine environment through the compartmental model is reported. The model simulates the surface water contamination caused by routine or accidental radionuclide releases. For the simulation the OCEAN program was applied in the North Sea, near to Sellafield and adjacent areas, based on published transfer coefficient data. The results are in good agreement with the literature and the model developed can be applied to the brazilian coastal regions.     

Diffusion of 137Cs in compacted bentonite: Effect of pH and concentration

The effect of pH and concentration on the diffusion of ¹³⁷Cs in the compacted bentonite is studied with capillary method at the ionic strength of 0.1M NaClO₄. The apparent diffusion coefficient increases with increasing concentrations if the sorption of radionuclides is largely dependent on the radionuclide concentrations. The apparent diffusion coefficient decreases with increasing pH because most of the radionuclide sorption on the bentonite increases with increasing pH. The interlaminary space contributes significantly to the radionuclide diffusion and sorption in compacted bentonite. The relationship of the apparent diffusion coefficient and the effective diffusion coefficient of ¹³⁷Cs is also discussed.     

Source term estimation using air concentration measurements during nuclear accident

The focus of this paper is locating and quantifying the diffusion source of ¹³⁷Cs by using observation data collected from monitoring stations. The estimation method is firstly tested in synthetic experiments and then verified with real ¹³⁷Cs concentration data of Fukushima accident. An atmospheric dispersion simulation system is used to support particle diffusion model. Besides, ridge regression is applied to calculate release rate. In terms of location estimation, posterior function of the source location can be deduced according to Bayesian inference. particle swarm optimization (PSO) method is implemented to locate diffusion source.     

Natural radionuclides and 137Cs activity concentration in the bottom sediment cores from Kuwait Bay

Summary The activity concentration of natural radionuclides and ¹³⁷Cs in the bottom sediments cores from Kuwait Bay have been determined by γ-ray spectrometry. Particular attention was devoted to the exact determination of two uranium isotopes: ²³⁵U and ²³⁸U in order to find any presence of depleted uranium dispersed during the 1991 Gulf War. The calculated ²³⁸U/²³⁵U activity ratios for all the surface (15 cm) as well as the core profile (up to 70 cm in depth) samples were within the limit of one standard deviation close to the value of 21.5 for natural uranium. Simultaneous instrumental determination of the unsupported ²¹⁰Pb and ²²⁶Ra in a few sediment core profiles was used for quantification of sediment accumulation rates. The calculated sedimentation rates (for the constant atmospheric ²¹⁰Pb flux rate - CRS model) ranged from 0.2 to 0.6 cm ^. y^-1 and were close to the data calculated by the Weibull distribution of ¹³⁷Cs in undisturbed sediment cores.     

Resuspension processes controll variations of 137Cs activity concentrations in the ground-level air

The ¹³⁷Cs activity concentration in the surface air between 1977 and 2007 was decreasing with an ecological half-life of 3.4?years, however, during 2007?C2010 the yearly averaged ¹³⁷Cs activity concentrations were almost constant. The increased atmospheric ¹³⁷Cs and ⁴⁰K levels observed during the winter may be due to surface soil resuspension and radionuclide transport by winds, particularly from open agricultural areas, as confirmed by high correlation coefficient between ¹³⁷Cs and ⁴⁰K atmospheric levels (R?=?0.84), and similar ¹³⁷Cs/⁴⁰K activity ratios in aerosols (0.07) and soils (0.05).     

Radiometric dating of sediment records in Kuwait’s marine area

Six sediment cores collected from the Northwestern Arabian/Persian Gulf have been radiometrically dated by ²¹⁰Pb. Three cores were collected from stations within the Kuwait Bay, and three others were collected from stations outside the bay. Two models have been used for ²¹⁰Pb dating of sediment cores, i.e. Constant Flux: Constant Sedimentation (CF:CS) Model and the Constant Rate of Supply (CRS) Model. The average rates were found to vary significantly between 0.16 and 1.00 cm y^?1 for stations outside and within the bay respectively. The variability of the sedimentation rate was essentially physiographic characteristics and variable hydrodynamic condition. In this study, ¹³⁷Cs fallout radiotracer was also used to construct a realistic chronology. It was observed that the ¹³⁷Cs in the entire vertical profile has been continuously contributed by fluvial and atmospheric deposition.     

Radionuclide uptake in red macroalgae from the Bulgarian Black Sea coast

Summary Technogenic and natural radionuclide content in red macroalgae (Ceramium rubrum, Corallina officinalisand Callithamnion corymbosum) from the Bulgarian Black Sea coast, collected in the period 1992-2003, was studied by low-level gamma-spectrometry. The data show that the nuclide concentrations depend on macroalgae species and coast locations. The highest nuclide content was measured in Ceramium rubrumspecies. The ¹³⁷Cs mean value is 9.8 Bq/kg, 19.6 Bq/kg for ²²⁶Ra and 17 Bq/kg for ²¹⁰Pb. The radionuclide pollution is considerably small due to the absence of nuclear facilities along the Bulgarian Black Sea coast.     

Long-term transfer of <Superscript>137</Superscript>Cs from soil to mushrooms in a semi-natural environment

The radioactive contamination following the Chernobyl accident resulted in high concentrations of ¹³⁷Cs in several mushrooms species. Mushroom samples were collected in a forest environment between 1986 and 2007 and the transfer of ¹³⁷Cs to two edible species, Suillus variegatus and Cantharellus spp., was investigated. The ¹³⁷Cs uptake by the collected samples did not decrease over time and in Cantharellus spp. a significant increase was observed. Most of the ¹³⁷Cs in soil still appears to be available for uptake and radioactive decay of the radionuclide is likely the main factor for the reduction of ¹³⁷Cs in a forest ecosystem.     

Distribution of3H,137Cs and239,240Pu in the surface seawater around Korea

The concentrations of³H,¹³⁷Cs and^239,240Pu were determined in surface seawaters collected at 21 sampling stations around Korea from October of 1994 to May of 1995. The results were consistent with the past data observed in the North Pacific. The concentrations of³H and¹³⁷Cs did not show much difference no matter where the samples were taken. Due to the limited distribution of sampling points, no systematic change in³H and¹³⁷Cs levels with latitude was observed. On the other hand,^239,240Pu concentration in the East Sea (Japan Sea) was somewhat higher than that in the South and the Yellow Seas, although the data on^239,240Pu concentration were not enough to explain the reason. The activity ratios of^239,240Pu/¹³⁷Cs in surface seawater ranged from 0.13% to 0.44% with a mean of 0.25±0.08%. The activity ratios were lower than those of the global fall-out level, 1.1%. This result presumably arose from the different behavior of the two radionuclides in seawater.     

The study on radioactive contamination in foodstuffs imported from Japan after the Fukushima accident

During the Fukushima nuclear accident, a large number of radionuclides were released, causing direct radioactive contamination to the environment and the ecosystem, and eventually indirect contamination to the foodstuffs. The Radiation Monitoring Group, Office of Atoms for Peace (OAP) in cooperation with the Food and Drug Administration (FDA), has been monitoring the foodstuffs imported from Japan, especially the Fukushima and nearby areas. This monitoring program covered the potentially contaminated foodstuffs. The measurements were mainly conducted using Gamma spectroscopy systems in order to analyze the radioactive concentration of ¹³¹I, ¹³⁴Cs, and ¹³⁷Cs fission products. From 442 samples collected between after the nuclear accident to the end of September 2012, 28 of contaminated food products of fission isotopes have been found with the contamination ranges of 0.63–15.25 Bq/kg fresh, 1.45–44.70 Bq/kg fresh, and 0.45–51.10 Bq/kg fresh) for ¹³¹I, ¹³⁴Cs, and ¹³⁷Cs, respectively. However, the contamination levels are still well under the Thailand standard of food contaminated with radionuclide and the relevant international standards. Finally, the research also investigated the relationship between the times the samples were collected and the contamination levels.     

137Cs in Biota and Sediment Samples from Turkish Coast of the Black Sea, 1997–1998

During the periods of 1997–1998, macroalgae, sea snail, mussel, fish and sediment samples were collected from different stations at Turkish Black Sea coast in order to determine activity levels of ¹³⁷Cs radionuclide. ¹³⁷Cs activity in the tested algae species and in soft parts of mussel and sea snail, were found to be below the lower limit of detection. On the other hand, the ¹³⁷Cs concentration in muscle tissue of the sea snail samples were found from 6±2 to 19±7 Bq·kg^–1 dry weight. The range of the ¹³⁷Cs concentration in anchovy fish muscles were found between 4±2 – 10±5 Bq·kg^–1 dry weight. The ¹³⁷Cs concentration in the whiting fish muscle was found below the lower limit of detection. However, this activity found in shad fish muscle to be 25±10 Bq·kg^–1 dry weight. The concentrationsof the ¹³⁷Cs activity in the sediment samples proved that the eastern region of the Black Sea was affected by Chernobyl at a very high degree compared with the western part. The measured ²³⁸U, ²³²Th and ⁴⁰K concentrations in sediment samples are within the range of the cited values in the previous works at the Turkish Black Sea coast.     

Methodologies for the practical determination and use of method detection limits

Underwater NaI(T1) and HPGe detectors are used in the environmental measurements programs at the Savannah River Site (SRS). A 22.9 cm × 10.2 cm NaI(T1) detector on the Savannah River continuously monitors effluent releases from both SRS (DOE) and Plant Vogtle (Georgia Power). Correlations with known releases indicate a sensitivity of 4 mBq/l for⁵⁸Co with 1500 min spectra; such levels are well below those of hazardous or legal concern. A 30%-efficient HPGe detector has appraised radionuclides in SRS cooling pond sediments; the dominant gamma-emitting radionuclide detected was¹³⁷Cs, at levels ranging up to 2.0 MBq/m². The pond activities were adequately quantified by 1 min counts with the HPGe detector; resulting contour maps of sediment¹³⁷Cs provided guidance for partially draining the ponds for dam repairs.