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PubMed2005

Plutonium contamination in soils and sediments at Mayak PA, Russia.

The Mayak Production Association (Mayak PA) was established in the late 1940's to produce plutonium for the Soviet Nuclear Weapons Programme. In total, seven reactors and two reprocessing plants have been in operation. Today, the area comprises both military and civilian reactors as well as reprocessing and metallurgical plants. Authorized and accidental releases of radioactive waste have caused severe contamination to the surrounding areas. In the present study, [alpha]-spectrometry and inductively coupled plasma-mass spectrometry (ICP-MS) have been used to determine plutonium activities and isotope ratios in soil and sediment samples collected from reservoirs of the Techa River at the Mayak area and downstream Techa River. The objective of the study was to determine the total inventory of plutonium in the reservoirs and to identify the different sources contributing to the plutonium contamination. Results based on [alpha]-spectrometry and ICP-MS measurements show the presence of different sources and confirmed recent reports of civilian reprocessing at Mayak. Determination of activity levels and isotope ratios in soil and sediment samples from the Techa River support the hypothesis that most of the plutonium, like other radionuclides in the Techa River, originated from the very early waste discharges to the Techa River between 1949 and 1951. Analysis of reservoir sediment samples suggest that about 75% of the plutonium isotopes could have been released to Reservoir 10 during the early weapons production operation of the plant, and that the majority of plutonium in Reservoir 10 originates from discharges from power production or reprocessing. Enhanced 240Pu/239Pu atom ratios in river sediment upper layers (0-2 cm) between 50 and 250 km downstream from the plant indicate a contribution from other, non-fallout sources.

Environmental Monitoring↗

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↗

PubMed2001

The new millennium: values, perceptions of risk, and the key roles of science and technology.

Radiation protection and management of radioactive waste streams and products are certain to be important areas of public policy, worker education, and technology development in the new millennium. Overriding values of freedom, sustainability, transparency, and public participation in decision making about technology's benefits and risks will shape the public policy agenda. Early engagement of stakeholders in the identification and assessment of risks and in communications about risk management will be beneficial in most cases. Putting specific environmental problems into broader public health and ecologic context will be helpful to all parties and will improve decisions about how best to utilize precious resources and enhance public confidence in the process and the outcomes.

Humans↗

PubMed2003

Estimation of animal transfer factors for radioactive isotopes of iodine, technetium, selenium and uranium.

In post-closure radiological safety assessments of repositories for solid radioactive wastes, transfers of radionuclides to animal products are typically characterised using Transfer Factors (TFs), defined as the ratio of the concentration of the radionuclide in the animal product of interest to the rate of intake in diet. Such transfer factors can be measured directly in experimental studies, but they can also be estimated by use of biokinetic models for uptake and retention of radionuclides in animals. Based on a review of the literature, biokinetic models have been developed for the uptake and retention of iodine, technetium, selenium and uranium. These biokinetic models allow TF values to be estimated for different types of animals and for different animal lifetimes. For each radionuclide considered, reference values and ranges of TF values are estimated. These are summarised in Table 1.

Animals↗

PubMed1998

Stochastic dose/risk assessment uncertainty and the concept of potential exposures.

Assessments of future potential doses and risks (e.g. in connection with radioactive waste disposal) can be associated with substantial uncertainties. These uncertainties are often incorporated into assessments using stochastic models, and give rise to doses characterised in probabilistic terms. Questions about how doses should be related to risks arise even in the case of deterministic dose assessments. However, results of a probabilistic dose assessment may lead to additional issues when interpreting them or attempting to convert them to risk for regulatory purposes. Some problems are shown to originate from the difference between the meaning of a probabilistic dose value and the definition of potential exposure. Others relate to the appropriate choice of, or approach to compliance with, a regulatory limit. A possible method for setting limits on probabilistic (potential) doses or risks is proposed, based on an accepted technique for determining detection limits.

Computer Simulation↗

PubMedDate not supplied

Use of urease-bromothymol blue-agar method for large-scale testing of urine on grain and seeds.

The current AOAC method (963.28) for large-scale (50 g) testing of urine on grain is based on the reaction of sodium in urine with magnesium uranyl acetate. Detection of sodium suggests that urine is present and that a test for urea is appropriate. Urea is detected with urease-bromothymol blue-paper and is confirmed through its reaction with xanthydrol to form dixanthylurea crystals, which are detected microscopically. The initial nonspecific test for sodium can be influenced by the presence of salt or other sodium compounds. Furthermore, the magnesium uranyl acetate spray used in Method 963.28 potentially exposes the analyst to the aerosol of a volatile, toxic uranium compound. Excess reagents and analyzed test portions must be disposed of as radioactive waste. In addition, Method 963.28 requires several steps to determine the presence of urea. The alternative AOAC method (972.41) tests for the presence of urea from urine on individual seeds. Urea is enzymatically decomposed to ammonia and carbon dioxide by urease. Liberated ammonia shifts the pH, changing the color of the indicator in the agar from yellow to blue. This study adapts Method 972.41 to larger test samples. Up to 25 g grains and seeds are sprayed with urease test agar instead of being individually immersed in the urease test agar. The modified method was used to analyze urea on seeds and grains of 24 plants from 4 families. The method has a limit of detection of one seed contaminated with 1 microgram urea.

Aerosols↗

PubMed1993

Age-dependent variation of selenium-75 biokinetics in rat.

Substantial levels of selenium-79 (79Se) in radioactive waste from the nuclear fuel cycle, may result in a significant collective dose commitment following release into the environment. Few data are available from which the effective dose equivalent among subgroups of the general population can be made. Accordingly, whole body retention and organ content were studied in neonate, adult and pregnant rat following oral contamination with 75Se. The results for whole-body retention conformed to a two-component exponential with terminal biological half-time of about 40, 30 and 20 days in adult male, neonate and pregnant rat, respectively. The highest concentrations of Se occurred in the liver, kidney, and testis. Influence of Se kinetics as a function of age and physiological development on dose estimates are discussed. Results were consistent with current dosimetric models but suggested that the testis should also be included.

Administration, Oral↗

PubMed2002

Developing additional resources.

We briefly outline existing information about several cohorts in the Southern Urals, Semipalatinsk and the Altai regions, in addition to those discussed in the companion papers in this issue of Radiation and Environmental Biophysics. These include: (a) the East-Urals Radiation Trace (EURT) cohort of individuals (exposed to fallout from the September 1957 explosion of a storage tank containing liquid radioactive waste from the Mayak Production Association) as well as their offspring, (b) the cohort of exposed parents (i.e. workers of the Mayak facility) and their children, having been established with the aim of examining reproductive health, and (c) several additional cohorts in the Altai region and in Semipalatinsk, where investment of additional resources would greatly facilitate the progress of ongoing studies. Furthermore, we include a brief description of the Russian Human Radiobiology Tissue Repository, which has been established in the city of Ozyorsk and is in the process of making an inventory of autopsied tissues from 700 deceased Mayak workers and of collecting and storing donations of blood and tumor tissues from the members of the Mayak workers cohort currently residing in the city.

Cohort Studies↗

PubMed2003

The volatilisation and sorption of (129)I in coniferous forest, grassland and frozen soils.

129I is a potentially important radionuclide in safety assessments of proposed deep geological radioactive waste repositories due to its radiotoxicity, high mobility and long physical half-life (15.7 million years). In soils, iodine is present both in an inorganic form and in organohalide complexes, some of which are volatile under natural environmental conditions. This study has examined volatilisation, sorption and the effect of freezing on sorption and loss of (125)I (physical half-life 60.2 days), as a surrogate for (129)I, within coniferous forest and grassland soils. The results do not suggest that volatilisation from these soils is a significant pathway for the transport of (129)I. Strong and specific sorption of iodine to humic substances has been demonstrated, which is reduced at freezing temperatures. It is hypothesised that rapid sorption to soil humic substances can significantly reduce volatilisation rates. The effect of freezing conditions on iodine extractability from soils suggests a microbially mediated sorption process.

Ecosystem↗

PubMed2005

Operational health physics.

A review of the operational health physics papers published in Health Physics and Operational Radiation Safety over the past fifteen years indicated seventeen general categories or areas into which the topics could be readily separated. These areas include academic research programs, use of computers in operational health physics, decontamination and decommissioning, dosimetry, emergency response, environmental health physics, industrial operations, medical health physics, new procedure development, non-ionizing radiation, radiation measurements, radioactive waste disposal, radon measurement and control, risk communication, shielding evaluation and specification, staffing levels for health physics programs, and unwanted or orphan sources. That is not to say that there are no operational papers dealing with specific areas of health physics, such as power reactor health physics, accelerator health physics, or governmental health physics. On the contrary, there have been a number of excellent operational papers from individuals in these specialty areas and they are included in the broader topics listed above. A listing and review of all the operational papers that have been published is beyond the scope of this discussion. However, a sampling of the excellent operational papers that have appeared in Health Physics and Operational Radiation Safety is presented to give the reader the flavor of the wide variety of concerns to the operational health physicist and the current areas of interest where procedures are being refined and solutions to problems are being developed.

Computers↗

PubMed2005

Operational health physics.

Computers↗

PubMedDate not supplied

Modeling thermal-hydrological response of the unsaturated zone at Yucca Mountain, Nevada, to thermal load at a potential repository.

This paper presents a numerical study on the response of the unsaturated zone (UZ) system of Yucca Mountain to heat generated from decaying radioactive wastes emplaced at the proposed repository. The modeling study is based on the current thermal-hydrological (TH) mountain-scale model, which uses a locally refined 2D north-south cross-section and dual-permeability numerical approach. The model provides a prediction of the mountain-scale TH response under the thermal-load scenario of 1.45 kW/m, while accounting for future climatic changes and the effects of drift ventilation. The TH simulation results show that ventilation of the repository drifts has a large impact on thermal-hydrologic regimes and moisture-flow conditions at the repository. In both cases, with and without ventilation, the TH model predicts dry or reduced liquid saturation near the drifts for over 1000 years, during which liquid flux through the drifts is reduced to either zero or less than the ambient flux. Without ventilation, the model predicts higher temperatures at the repository, but no major moisture redistribution in the UZ except in the areas very near the heated drifts.

Air Movements↗

PubMed1982

The identification of critical groups and its application to fish and shellfish consumers in the coastal area of the North-East Irish Sea.

Control of radioactive waste disposal to the environment, based on the recommendations of the International Commission on Radiological Protection (ICRP), necessitates an identification of the critical group of members of the public exposed from a given practice. Criteria for identification of critical groups based mainly on ICRP recommendations are discussed. Methods existing up to 1974 are briefly reviewed in the light of these criteria. Two more recent methods are described and compared on the basis of previous data; these methods, which are complementary, are based on homogeneity considerations and satisfy the criteria generally rather better than do the earlier methods. The application of the newer techniques to recent surveys of fish and shellfish consumption in the coastal area of the North-East Irish Sea is described, in relation to discharges from the Windscale reprocessing plant. The results of this survey are presented, and estimates are given of the effective dose equivalent to members of these critical groups in recent years, to show the effect of liquid discharges from Windscale in terms of public radiation exposure.

Animals↗

PubMed2001

Development and testing of radionuclide transport models for fractured rock: examples from the Nagra/JNC Radionuclide Migration Programme in the Grimsel Test Site, Switzerland.

The joint Swiss National Co-operative for the Disposal of Radioactive Waste (Nagra)/Japan Nuclear Cycle Development Institute (JNC) Radionuclide Migration Programme has now been on-going for over a decade in Nagra's Grimsel Test Site (GTS). The main aim of the programme has been the direct testing of radionuclide transport models in as realistic manner as possible. Although it will never be possible to fully test these models due to the large time and distance scales involved, tests of the model assumptions in scaled down but otherwise realistic conditions will contribute to developing confidence in the predictive power of the models. In this paper, the Nagra/JNC approach is highlighted with examples from a large programme of field, laboratory and natural analogue studies based around the GTS. The successes and failures are discussed as in the general approach to the thorough testing of predictive transport codes which will be used in repository performance assessment (PA). Some of the work is still on-going and this represents the first presentation of a unique set of results and conclusions.

Geological Phenomena↗

PubMed2003

A possible approach for the assessment of radiation effects on populations of wild organisms in radionuclide-contaminated environments?

It is frequently asserted that measures to protect the biotic environment from increased radiation exposures arising from human activities should be focussed on the population rather than the individual. It is, however, difficult (if not impossible) to identify any population-specific attributes that can be affected by radiation exposure directly rather than through the mediation of direct, known and identifiable effects in individual organisms. Indeed, it is often conceded that this difficulty forces attention to be refocussed onto the effects in individuals. Regulatory controls on radioactive waste management and disposal could then be implemented to ensure that any radiation effects in individual native plants and animals remain at, or below, some acceptable level (yet to be defined). Nevertheless, the question remains as to whether such controls would also provide for the protection of the population. An answer to this question depends on the availability of a model that allows the integration of the known effects of radiation exposure on the mortality, morbidity, fertility and fecundity of individuals into an assessment of the possible impact at the population level. The utility of one such approach, the Leslie Matrix Model, is explored in respect of a fish population (the plaice, Pleuronectes platessa). This initial implementation of the population model is simplistic (and, certainly, environmentally unrealistic), but it is concluded that the output from the model does provide some insights into how the population might respond to radiation-induced changes in individual attributes, and that further development in the direction of increased realism is fully warranted.

Age Factors↗

PubMed2004

An airborne gamma-ray spectrometry survey of nuclear sites in Belgium.

As part of a wider study to define the existing background levels in Belgium an airborne gamma-ray survey was conducted in two areas associated with nuclear sites. In the Mol area, the survey zone included areas surrounding the SCK-CEN nuclear research centre, and its associated neighbourhood which includes radioactive waste stores, fuel manufacture and fabrication facilities and an international accelerator laboratory. In the vicinity of Fleurus, the survey included the IRE complex with radiochemical laboratories, irradiation facilities and stores, and isotope production accelerators. The survey was conducted using a twin engined helicopter equipped with a combined scintillation and semiconductor spectrometer. The system was installed and tested in the UK, and then transferred to Belgium for operations. The complete survey was conducted successfully within 1 week. The results provide a comprehensive record of the radiation environment of the nuclear sites at time of survey, and show a range of signals associated with the types of activity present in each area. They confirm that radiation fields are largely confined to the operational sites, and provide a traceable record against which future changes could be assessed. The demonstration of efficient deployment between two European countries, coupled with rapid mapping of many different radiometric signals around these sites confirms the utility of the airborne gamma spectrometry approach for accurate definition of enhanced radiation fields. This has important implications for emergency response.

Belgium↗

PubMed2003

Porewater chemistry in compacted re-saturated MX-80 bentonite.

Bentonites of various types are being investigated in many countries as backfill materials in high-level radioactive waste disposal concepts. Being able to understand the chemistry of the porewater in compacted bentonite is very important since it is critical to predicting radionuclide solubilities and to the synthesis of sorption data bases, and hence to repository safety studies. In this paper, porewater compositions in compacted bentonites are calculated, taking into consideration such factors as montmorillonite swelling, semi-permeable membrane effects, very low "free water" volumes, and the highly effective buffering characteristics of the exchangeable cations and the amphoteric edge sites. The former buffer the cation concentrations and the latter fix the pH in the porewater of a re-saturated bentonite. The above considerations are used in conjunction with previously measured physico-chemical characterisation data on MX-80 powder to calculate porewater compositions in compacted bentonites. For the MX-80 material specified, the porewaters calculated for initial dry densities between 1200 and 1600 kg m(-3) had relatively high ionic strengths (I approximately 0.3 M), similar cation concentrations and a pH equal to 8.0. The porewaters changed from being Na(2)SO(4)-rich at 1200 kg m(-3) to a NaCl/Na(2)SO(4) type water at 1600 kg m(-3).

Adsorption↗

PubMedDate not supplied

Radionuclide transport simulation and uncertainty analyses with the saturated-zone site-scale model at Yucca Mountain, Nevada.

Evaluation of radionuclide transport in the saturated zone (SZ) to the accessible environment is an important component of performance assessment for the proposed radioactive waste repository at Yucca Mountain. Simulations of radionuclide migration in the SZ have been performed using the calibrated three-dimensional (3-D) SZ site-scale flow and transport model. An innovative particle-tracking method was used to simulate transport that includes the processes of advection, dispersion, matrix diffusion, and sorption. The uncertainties in groundwater flow and radionuclide transport were quantitatively evaluated to develop uncertainty distributions for key model parameters, and multiple realizations of the SZ system were simulated using the SZ site-scale model. The results of multiple realizations of radionuclide transport indicate significant aggregate uncertainty in transport times through the SZ. The simulated radionuclide mass breakthrough curves in the SZ have been coupled with other components of the repository system in Total System Performance Assessment (TSPA) analyses and constitute the means by which uncertainty in the SZ is incorporated into regulatory analyses. Regression analysis has been used to determine the sensitivity of radionuclide transport simulation results to the uncertainty of individual model input parameters. Results of the sensitivity analysis indicate that median radionuclide transport times were dominantly controlled by uncertainty in the specific discharge in the SZ, with sorption and retardation in the alluvium playing important roles for some radionuclides.

Forecasting↗