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PubMed2001

The CEEF, closed ecosystem as a laboratory for determining the dynamics of radioactive isotopes.

Nuclear power generation is now confronted with a very difficult situation all over the world because of the problems of radioactive waste disposal and of the accidents, which have occurred. Nuclear power generation now supplies nearly 30% of total electric power demand in Japan. Therefore it is very difficult to change quickly the construction plans of nuclear facilities already designed. A nuclear fuel reprocessing center is now under construction in Rokkasho-Mura in Aomori Prefecture. If this center starts its operation, small amounts of 14CO2 are expected to be released into the atmosphere and will enter the global cycle. The simulation experiment of 14C trace amounts which enter into ecosystems is now being planned using stable isotope 13C within CEEF (Closed Ecology Experiment Facilities).

Air Pollution, Radioactive↗
PubMed1997

A study of radioactivities in six types of fish consumed in Hong Kong.

The contents of natural and artificial radionuclides in two types of fresh water fish and four types of marine fish commonly consumed by the Hong Kong population have been measured using HPGe gamma-ray spectrometry. The two types of fresh water fish are grey mullet (mugil cephalus) and grass carp (ctenopharyngodon idellus). The four types of marine fish are white pomfret (pampus argenteus), red bullseye (priacanthus macracanthus), golden thread (nemipterus) and ginkgo (gymnocranius griseus). All measurements of U and Th chain radionuclides in the samples have yielded values below MDA except for positive detection of 228Ra (assuming 228Ra to be in equilibrium with 228Ac) in grey mullet and bullseye perch. The 40K and 137Cs radionuclides were detectable in all samples, with values of 0.01-0.2 and 41.23-111.47 Bq/kg fresh respectively. The different levels of radioactivity in different species of fish is suggested to be due to differences in metabolism and feeding patterns. The radionuclide 60Co, the only other artificial radionuclide to be investigated herein, recorded values below MDA for most of the samples; observable values ranged from 0.01 to 0.04 Bq/kg fresh. Committed effective doses due to ingestion of radionuclides from fish have been estimated to be 1.2 (male) and 6.4 (female) microSv/yr for natural radionuclides; 0.027 (male) and 0.026 (female) microSv/yr for artificial radionuclides.

Animals↗
PubMed1999

Historical relationship between performance assessment for radioactive waste disposal and other types of risk assessment.

This article describes the evolution of the process for assessing the hazards of a geologic disposal system for radioactive waste and, similarly, nuclear power reactors, and the relationship of this process with other assessments of risk, particularly assessments of hazards from manufactured carcinogenic chemicals during use and disposal. This perspective reviews the common history of scientific concepts for risk assessment developed until the 1950s. Computational tools and techniques developed in the late 1950s and early 1960s to analyze the reliability of nuclear weapon delivery systems were adopted in the early 1970s for probabilistic risk assessment of nuclear power reactors, a technology for which behavior was unknown. In turn, these analyses became an important foundation for performance assessment of nuclear waste disposal in the late 1970s. The evaluation of risk to human health and the environment from chemical hazards is built on methods for assessing the dose response of radionuclides in the 1950s. Despite a shared background, however, societal events, often in the form of legislation, have affected the development path for risk assessment for human health, producing dissimilarities between these risk assessments and those for nuclear facilities. An important difference is the regulator's interest in accounting for uncertainty.

Decision Theory↗
PubMed2000

Thyroid cancer following exposure to radioactive iodine.

The thyroid gland is one of the most sensitive organs for radiation-induced oncogenesis and the magnitude of the risk from external radiation is well understood. This is not the case for internal radiation derived from the radioiodines, a matter of practical importance because of medical use and potential accidental exposure. This article reviews current knowledge derived from the follow-up of patients receiving diagnostic or therapeutic 131I and populations exposed to radioactive fallout. The latter includes the nuclear power station accident at Chernobyl and the results of atomic bomb development and testing at Hanford, the Nevada Test Site and the Marshall Islands. The most cogent information comes from Chernobyl where an epidemic of childhood thyroid cancer has followed exposure to radioiodine that was mainly 131I. Although much has been learned from this experience about the nature of radioiodine induced thyroid cancer in young children, the reconstruction of thyroid radiation doses is too preliminary to provide accurate knowledge of the risk in comparison to that from external radiation. In the Marshall Islands, much of the exposure was from short-lived radioiodines as well as external radiation, obviating the possibility to determine the risk from 131I. Exposure to 131I in the continental United States from atomic bomb testing is expected to have caused some thyroid cancers, but only in the immediate vicinity of the Nevada Test Site has any evidence of radiation-induced thyroid neoplasms been adduced. This evidence is minimally significant statistically, and not significant for thyroid cancer per se. Medical use of radioiodine has not been observed to cause thyroid cancer but very few of the patients studied were young children, the group most sensitive to thyroid radiation. Despite these limitations, this information is sufficient to make some suggestions concerning protective measures in the case of nuclear accidents and the follow up of individuals who have been exposed.

Humans↗
PubMed1998

Engineering a recombinant Deinococcus radiodurans for organopollutant degradation in radioactive mixed waste environments.

Thousands of waste sites around the world contain mixtures of toxic chlorinated solvents, hydrocarbon solvents, and radionuclides. Because of the inherent danger and expense of cleaning up such wastes by physicochemical methods, other methods are being pursued for cleanup of those sites. One alternative is to engineer radiation-resistant microbes that degrade or transform such wastes to less hazardous mixtures. We describe the construction and characterization of recombinant Deinococcus radiodurans, the most radiation-resistant organism known, expressing toluene dioxygenase (TDO). Cloning of the tod genes (which encode the multicomponent TDO) into the chromosome of this bacterium imparted to the strain the ability to oxidize toluene, chlorobenzene, 3,4-dichloro-1-butene, and indole. The recombinant strain was capable of growth and functional synthesis of TDO in the highly irradiating environment (60 Gy/h) of a 137Cs irradiator, where 5x10(8)cells/ml degraded 125 nmol/ml of chlorobenzene in 150 min. D. radiodurans strains were also tolerant to the solvent effects of toluene and trichloroethylene at levels exceeding those of many radioactive waste sites. These data support the prospective use of engineered D. radiodurans for bioremediation of mixed wastes containing both radionuclides and organic solvents.

Chromosome Mapping↗
PubMed1992

Post-Chernobyl accident radioactivity measurements in the Comunidad Autonoma de Valencia, Spain.

Increased atmospheric radioactivity after the accident in Chernobyl was first detected on air filters. Measurements were begun in Valencia on May 2, 1986, with the maximum activity being observed around May 3-4, 1986. As a consequence of this accident, annual campaigns of measurements on migrating birds (several species of aquatic birds and song-thrushes) were started. The data corresponding to the campaign immediately after the accident (1986/87) show a generalized contamination (approximately 50% of the measured specimens). Significant levels of 134Cs, 137Cs and 110Agm were found. It is important to note that 110Agm is only present in Aythya ferina. In the successive campaigns in 1988/89 and 1989/91 few samples were found to be contaminated and only 137Cs was identified. Strontium-90 was measured and identified in some specimens, mainly in their bones.

Accidents↗
PubMed2002

Analysis and processing of samples for a carbon-14 monitoring program at a radioactive waste storage site.

A monitoring program was undertaken to determine the levels of airborne radioactive 14CO2 in an operating waste management area, and it its vicinity. As a part of this program, alkaline microporous pellets, recently developed, were used to sample the 14CO2 in air near waste storage structures and near the waste management area. These pellets were never fully characterized for their ability to capture high levels of 14CO2, and the processing and analysis needed to be improved to provide data on recoveries and consistencies, for an eventual method validation, with independent calibrations and standards. The sample analysis scheme also had to accommodate 14CO2 levels varying from near the natural background (250 Bq kg-1 C), to potentially three to four orders of magnitude above this value, near the wastes. The porous alkaline solid pellets were used for the passive capture of airborne 14CO2 over a period of weeks, to a few months. The pellets were processed to release the captured CO2 (14CO2 and 12CO2) into a NaOH solution, which was subsequently analyzed by liquid scintillation. Processing of the pellets yielded a 14C recovery of 96.0 +/- 4.2% and a lower, but consistent total carbon recovery, i.e., 85.9 +/- 2.7 and 86.9 +/- 2.6%, for procedural blanks and standards, respectively. The detection limits for the pellet sampling and processing was sufficient to reach environmental levels. For the higher levels of 14CO2 and for 'spot' sampling, we also used air samples, pumped into a NaOH solution to trap the 14CO2. These NaOH solutions were counted directly for 14C, also by liquid scintillation. The method limits of this latter technique, although much higher than for pellet samples, also achieved the performance objective for detecting airborne 14CO2. Both sampling and processing techniques, when used together, provided sufficient flexibility to be used for low (environmental) levels and high levels, near the wastes.

Air Pollutants, Radioactive↗
PubMed2005

A comparative radiological assessment of five European biosphere systems in the context of potential contamination of well water from the hypothetical disposal of radioactive waste.

In the framework of the BioMoSA project for the development of biosphere assessment models for radioactive waste disposal the Reference Biosphere Methodology developed in the IAEA programme BIOMASS was applied to five locations, situated in different European countries. Specific biosphere models were applied to assess the hypothetical contamination of a range of agricultural and environmental pathways and the dose to individuals, following contamination of well water. The results of these site-specific models developed by the different BioMoSA partners, and the individual normalised dose to the exposure groups were compared against each other. Ingestion of drinking water, fruit and vegetables were found to be among the most important pathways for almost all radionuclides. Stochastic calculations revealed that consumption habits, transfer factors, irrigation rates and distribution coefficients (Kd(s)) were the most important parameters that influence the end results. Variations in the confidence intervals were found to be higher for sorbing elements (e.g. (36)Cl, (237)Np, (99)Tc, (238)U, (129)I) than for mobile elements (e.g. (226)Ra, (79)Se, (135)Cs, (231)Pa, (239)Pu). The influence of daughter products, for which the distribution into the biosphere was calculated individually, was also shown to be important. This paper gives a brief overview of the deterministic and stochastic modelling results and the parameter sensitivity. A screening methodology was introduced to identify the most important pathways, simplify a generic biosphere tool and refine the existing models.

Adult↗
PubMed1997

Lessons from Chernobyl: the event, the aftermath fallout: radioactive, political, social.

The accident at the Chernobyl nuclear power station on April 26, 1986, released about 300 MCi of radioactive substances, including about 40 MCi of 131I and 100 MCi of short-lived radioiodines. In the immediate surroundings there were 143 cases of acute radiation syndrome, 34 deaths, and hundreds of thousands of people displaced from their homes, many permanently. The social and psychologic stresses that followed have been enormous and long-lasting. This article focuses on the rising incidence of thyroid cancer in exposed children. Radiation-induced thyroid cancer following external radiation is well documented but there is little evidence in humans of thyroid cancer from internal radiation and the risk coefficient for radioiodine exposure is known. To achieve this, thyroid dose reconstruction and prospective follow-up of about 50,000 persons who were children in 1986 will be required. Thyroid cancer in children of southern Belarus began to increase in 1990 and there now are about 1,000 cases in Belarus and northern Ukraine. These aggressively growing tumors, almost all variants of papillary thyroid cancer, are typical for thyroid cancer in children not exposed to radiation, and a low mortality rate is to be expected. It also is expected, however, that malignant as well as benign thyroid neoplasms will continue to arise in these exposed children well into their adult life.

Adult↗
PubMed2004

Kalman filtration of radiation monitoring data from atmospheric dispersion of radioactive materials.

A Kalman filter method using off-site radiation monitoring data is proposed as a tool for on-line estimation of the source term for short-range atmospheric dispersion of radioactive materials. The method is based on the Gaussian plume model, in which the plume parameters including the source term exhibit a 'random walk' process. The embedded parameters of the Kalman filter are determined through maximum-likelihood estimation making the filter essentially free of external parameters. The method is tested using both real and simulated radiation monitoring data. For simulated data, the method is shown to retrieve the embedded parameters employed in generating the data and to reconstruct the plume model parameters, including the source term. When tested against experimental radiation monitoring data the method is found accurately to uncover the known source term.

Air Movements↗
PubMed2005

Study on external exposure doses from terrestrial radioactivity in Southern Vietnam.

This paper presents the radioactivity concentrations of 226Ra, 232Th and 40K for 106 samples of surface soil collected in Southern Vietnam. The mean values of mass activity of radionuclides 226Ra, 232Th and 40K for Southern Vietnam are 28.6, 50.7 and 292.6 Bq kg(-1), respectively, which lead to the population-weighted absorbed dose rate of 54.5 nGy h(-1). The average annual effective doses outdoors, indoors and in total of Southern Vietnam are estimated to be 0.067, 0.374 and 0.441 mSv, respectively. The radium equivalent activity and the external hazard index of soil in Southern Vietnam are in the range 23.2-254.1 Bq kg(-1) and 0.06-0.69, respectively.

Air Pollution, Indoor↗
PubMed1984

Ambient monitoring of airborne radioactivity near a former thorium processing plant.

Twenty-four hour sampling for airborne radioactivity near a former thorium and rare-earth extraction facility was conducted for approx. 2 months with high-volume and dichotomous air samplers. Thoron ( 220Rn ) daughters were identified in the air and confirmed to be originating from the waste storage site. High-volume samplers near the facility measured average 212Pb concentrations of 177, 43, and 237 pCi/m3 with corresponding ranges of (1.9-1351), (1.5-301) and (0.73-2201)pCi/m3. Simultaneous measurements with dichotomous samplers at the same sites measured average 212Pb concentrations on coarse particulates (2.5-15 microns dia.) of 14, 4 and 10 pCi/m3 and on fine particulates (less than 2.5 microns dia.) of 94, 9 and 214 pCi/m3, respectively. Corresponding ranges were (0.2-109), (0.1-63) and (0.1-94) pCi/m3 for coarse particulates and (0.7-1094), (0.4-101) and (0.5-2685) pCi/m3 for fine particulates. Uranium, thorium and radium radionuclides were not identified as being present in significant concentrations in the particulate samples.

Air Pollutants↗
PubMed1984

Ingestion pathway factor in dose assessment for annual airborne releases of radioactivity.

An analytic model is derived for use in a simplified assessment of the committed effective dose equivalent to the public due to routine airborne releases of radioactive materials. The model uses the dosimetry in ICRP Publication 30 and determines the ratio of the committed effective dose equivalent (CEDE) via a specified ingestion pathway relative to that CEDE by inhalation per annual airborne release of a radionuclide. This ratio is defined as the ingestion pathway factor (IPF) and is shown to depend upon the radionuclide annual limits of intake, the atmospheric deposition velocity, and an ingestion parameter, the effective contamination intake area. The IPF values are tabulated for several radionuclides. These resultant IPF values often exceed unity, suggesting that the ingestion path is often the critical or limiting pathway for off-site CEDE to an individual. An application of this assessment is demonstrated in a review of a hypothetical nuclear facility to determine the appropriate extent of radiologic effluent and environmental monitoring at the facility.

Air Pollutants↗
PubMed1985

Treatment, waste management and cost for removal of radioactivity from drinking water.

The processes (costs, efficiencies and reliability) used in treating drinking water for removal of radioactive contaminants and the disposal of wastes generated by the treatment processes are analyzed and discussed. The study was limited to U, Ra and Rn. Initially concepts of water and waste treatment in terms of their applicability to the drinking water industry were established. The alternative processes for treatment of Ra, U, Rn, water and sludges were described and evaluated, in terms of cost, efficiency, reliability, process control and feasibility.

Adsorption↗
PubMed1986

RADFOOD--a dynamic model for radioactivity transfer through the human food chain.

Radioactive fallout presents a short-term risk due to its direct deposition on agricultural crops, as well as a long-term risk resulting from its deposition on soil and subsequent uptake by crops. A dynamic model, RADFOOD, was developed, based on different existing models. It simulates transport of fallout radionuclides through agricultural food chains to man and evaluates the radiation doses resulting from consumption of contaminated food. Transport was modeled through compartments representing various environmental elements of food products. Internal radiation doses (whole-body weighted doses) following ingestion of contaminated foodstuffs were then estimated. Specific types of crops, soils and diet of man and livestock were considered. A sample calculation was performed in which individual and collective radiation doses, as well as associated health effects, resulting from fallout contamination were evaluated. They were estimated for food consumption beginning at various times after the fallout deposition and for different consumption durations. A sensitivity analysis, performed for the main model parameters, showed that the radiation dose is sensitive, for the short-term period, to changes in initial deposition levels and in the parameters characterizing initial fallout interception and resuspension.

Food Contamination, Radioactive↗
PubMed1987

Trees as indicators of subterranean water flow from a retired radioactive waste disposal site.

Tree sampling helped locate a subterranean flow of tritiated water from a low-level radioactive waste disposal site that had not been detected by well water monitoring alone. Deciduous trees growing in a natural forest on the hillsides downslope from the site were sampled for the presence of tritiated water in sap of maple trees and in leaf water extracted from oak and hickory trees. Elevated concentrations of 3H were detected in the leaf water extracted from several trees located 50 m downslope from the western boundary of the fenced exclusion zone. A 3-m-deep well drilled near these trees indicated that the source of tritiated water was a narrow zone of subterranean flow.

Radioactive Waste↗
PubMed1988

Feeding green-cut forage contaminated by radioactive fallout to dairy cows.

Grass contaminated by radioactive fallout from the Chernobyl accident was cut with 150 mm (Treatment 1) and 50 mm (Treatment 2) stubble height and fed to 20 dairy cows. The transfer of 137Cs and 131I from the greencut forage to milk was studied during a four-week and a two-week period, respectively. The four-week period was followed by a three-week period with nearly uncontaminated feeds. Cutting with high stubble height significantly reduced the activity concentration in forage compared with low stubble cutting, the average contents kg-1 dry matter being 385 Bq 137Cs and 24 Bq 131I in Treatment 1 versus 6656 Bq 137Cs and 249 Bq 131I in Treatment 2. Apparent treatment effects were also demonstrated by the 137Cs concentration in milk, with maximum weekly means of 23 Bq kg-1 (Treatment 1) and 92 Bq kg-1 (Treatment 2). Single day maximum concentrations of 131I in milk were 4 Bq kg-1 (Treatment 1) and 9 Bq kg-1 (Treatment 2). The mean transfer coefficients (d kg-1) were calculated to be 0.67 X 10(-2) and 0.19 X 10(-2) for 137Cs (weeks 2-4) and 1.8 X 10(-2) and 0.2 X 10(-2) for 131I (week 2) in Treatments 1 and 2, respectively. The lower value for 137Cs might possibly be associated with an enhanced ash content of the forage. Feeding nearly uncontaminated rations rapidly decreased the 137Cs levels in milk in both treatments with calculated effective half-times over the three-week period of 10 and 7 d, respectively.

Accidents↗
PubMed1990

Radioactive fallout reconstruction from contemporary measurements of reservoir sediments.

The temporal history of atmospheric deposition to a watershed area can be preserved in the sediment of a lake or reservoir that is supplied by the watershed. The 137Cs and isotopic Pu concentrations with depth were determined in the sediments of two reservoirs, Enterprise and Deer Creek, which are located in widely separated regions of the state of Utah. Our data not only reconstruct the history of the total radioactive fallout in the area, but also permit estimating the contributions from global sources and from the Nevada Test Site detonations in the 1950s.

Cesium Radioisotopes↗