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PubMed2001

Present state and future directions of modeling of geochemistry in hydrogeological systems.

A first step towards understanding and controlling the fate and dissemination of radioactive waste is to create a concise and comprehensive theoretical framework for the rather non-linear processes involved--hence, the need for geochemical models. Two classes of geochemical models are commonly used, i.e., static and hydrodynamic models. In contrast to static models, hydrodynamic models combine geochemical reactions with hydrogeological processes such as ground-water flow, diffusion and dispersion. In this review, we examine the present state of geochemical models in terms of included processes, thermodynamic databases, missing phenomena, numerical behavior and performance. It is shown that over the past decade, significant progress has been made with respect to modeling of geochemistry in hydrodynamic systems: this is illustrated by describing several applications. Finally, we focus on the perspectives of geochemical modeling in the assessment of the safety of nuclear waste disposal.

Colloids↗
PubMedDate not supplied

[Accumulation of uranium, plutonium and americium by granulated microbial biosorbent].

A possibility of efficient extraction of 238U, 239Pu and 241Am by microorganisms from solutions with activity 520-3200 Bq/l has been shown on the example of microbial biosorbent (MBS). MBS presents water-resistant granules consisting of living microorganisms and nutrient substances. The ratio MBS:solution being equal to 1:100 and 1:20, microorganisms extracts 98.9 and 99.8% of 238U; 99.1 and 99.8% of 239Pu, 241Am, respectively. The worked out MBC granules may be utilized by burning with the 4-8 decrease of the volume. It is foreseen to use MBS in industrial processes of treatment of liquid radioactive waste (LRW) for uranium and transuranium elements.

Absorption↗
PubMed1993

Radioactive contamination of the Techa River, the Urals.

The Techa River in the Urals was contaminated with high-level radioactive waste from the MAJAK nuclear installation around 1950. The total discharge to the river amounted to 100 PBq with 90Sr and 137Cs contributing approximately 10 PBq each. This study has shown that the river presently contains approximately 0.3 TBq 90Sr, > 6 TBq 137Cs, and approximately 8 GBq 239,240Pu. The estimates were made for the part of the river starting 50 km from the point of discharge and ending 240 km downstream at the confluence with the Iset River. Radioactivity was measured only in the upper 0.10-m sediments layer. The external dose rates from the contamination range from 0.1-30 microGy h-1. The activity concentrations decrease exponentially or by power functions with distance.

Nuclear Energy↗
PubMed2000

The basic directions and results of activities of branch no. 1 of the state research center of the Russian Federation "Biophysics Institute" (FIB-1).

During the 1950's, in the early years at the Mayak Production Association (MAYAK) in the Southern Urals, there was a rapid expansion of plutonium output. This was carried out when nuclear technology was still being developed and knowledge of the effects of radiation exposure on humans was not well understood. As result of the discharge of liquid waste into the Techa River, there was large scale overexposure to both the workers at the facility and the population of riverside localities on the Techa River. There were also other environmental discharges, due to an accident and problems of waste storage, which contributed to exposure of other populations around MAYAK. Although all information on the MAYAK operation and its consequences for both workers and population was kept secret, studies on nuclear technology improvement, the handling of radioactive waste, of medical sequence of radiation exposure, radiation safety improvement, and prevention and treatment of radiation injuries were initiated virtually from the onset the of nuclear weapons production program.

Academies and Institutes↗
PubMed2005

Investigating Pu and U isotopic compositions in sediments: a case study in Lake Obuchi, Rokkasho Village, Japan using sector-field ICP-MS and ICP-QMS.

The objectives of the present work were to study isotope ratios and the inventory of plutonium and uranium isotope compositions in sediments from Lake Obuchi, which is in the vicinity of several nuclear fuel facilities in Rokkasho, Japan. Pu and its isotopes were determined using sector-field ICP-MS and U and its isotopes were determined with ICP-QMS after separation and purification with a combination of ion-exchange and extraction chromatography. The observed (240)Pu/(239)Pu atom ratio (0.186 +/- 0.016) was similar to that of global fallout, indicating that the possible early tropospheric fallout Pu did not deliver Pu from the Pacific Proving Ground to areas above 40 degrees N. The previously reported higher Pu inventory in the deep water area of Lake Obuchi could be attributed to the lateral transportation of Pu deposited in the shallow area which resulted from the migration of deposited global fallout Pu from the land into the lake by river runoff and from the Pacific Ocean by tide movement and sea water scavenging, as well as from direct soil input by winds. The (235)U/(238)U atom ratios ranged from 0.00723 to 0.00732, indicating the natural origin of U in the sediments. The average (234)U/(238)U activity ratio of 1.11 in a sediment core indicated a significant sea water U contribution. No evidence was found for the release of U containing wastes from the nearby nuclear facilities. These results will serve as a reference baseline on the levels of Pu and U in the studied site so that any further contamination from the spent nuclear fuel reprocessing plants, the radioactive waste disposal and storage facilities, and the uranium enrichment plant can be identified, and the impact of future release can be rapidly assessed.

Environmental Monitoring↗
PubMed2000

A custom-built shielded storage cabinet for LLRW.

A shielded storage cabinet has been designed to eliminate the problems associated with the use of storage pits for the decay-in-storage of short-lived low-level radioactive waste (LLRW).

Equipment Design↗
PubMed1989

Medical waste: socioeconomic impact.

The proper disposal and management of medical waste is a never-ending problem and one which is of grave concern to the general public. The amounts that are produced each day by hospitals and other small-generators are staggering, e.g., in the U.S. ca. 6000 tons per day. Approximately fifteen (15%) percent of this waste is considered infectious. This latter type of waste is usually incinerated or autoclaved (steam sterilization). In addition to the daily accumulation of solid waste, chemical wastes (liquids) and low-level radioactive wastes are generated. The proper disposal of all types of wastes is discussed as well as the overall cost and its impact on society.

Medical Waste↗
PubMed1993

Some safety procedures for handling 32P during postlabelling assays.

32P is a high-energy (1.7 MeV) beta-emitter. Its handling is therefore subject to regulation and very strict control. During the postlabelling procedure, numerous steps involve exposure to 32P. The main risk from exposure is through irradiation, but direct accidental contamination can occur. The various manipulation steps (ATP synthesis, labelling, chromatography, quantification) have been analysed for their contribution to potential radiation exposure. Several measures have been taken in the IARC laboratories to minimize exposure of all personnel involved, including those who handle radioactive wastes, since most of the initial radioactivity is eventually discarded. The various steps to be taken for minimizing exposure, such as the training of personnel using fluorescent compounds instead of radioactivity, the use of protective screens and of equipment specially adapted for this work, are reviewed.

Equipment and Supplies↗
PubMed1997

Current and potential doses from Arctic seafood consumption.

Current collective and individual dose rates to humans are estimated from the consumption of seafood harvested in the Arctic Seas. Statistical data on catches are used for the dose assessment, as well as observed data (1991-1994) on the radioactivity of marine biota. The actual collective dose rates to the world population are estimated to be: 2.7-4.5 manSv/year due to consumption of seafood from the Barents Sea, and 0.03 manSv/year-due to seafood from the Kara Sea. The contribution of 137Cs to the collective dose rate is about 90%. Current individual dose rates to high-rate consumers are estimated to be: 2.6 x 10(-6) Sv/year due to seafood from the Barents Sea; and 4.2 x 10(-6) Sv/year-due to seafood from the Kara Sea. The future radiological impact of the radioactive waste (RW) disposals in the Kara Sea is simulated for the period over 1000 years, using the regional box model of the Arctic Seas. The model predictions are made for three hypothetical scenarios of long-term radionuclide releases, prepared within the framework of the International Arctic Seas Assessment Project. The potential collective dose to world population truncated to 3000 AD is shown to be not higher than 0.13 manSv. The maximum individual dose rates from Arctic seafood consumption are estimated to be about 1.2 x 10(-7) Sv/year. The predicted doses are much smaller than the actual doses due to the current radioactive contamination of the Arctic Seas.

Animals↗
PubMed2004

In situ bioreduction of technetium and uranium in a nitrate-contaminated aquifer.

The potential to stimulate an indigenous microbial community to reduce a mixture of U(VI) and Tc(VII) in the presence of high (120 mM) initial NO3- co-contamination was evaluated in a shallow unconfined aquifer using a series of single-well, push-pull tests. In the absence of added electron donor, NO3-, Tc(VII), and U(VI) reduction was not detectable. However, in the presence of added ethanol, glucose, or acetate to serve as electron donor, rapid NO3- utilization was observed. The accumulation of NO2-, the absence of detectable NH4+ accumulation, and the production of N2O during in situ acetylene-block experiments suggest that NO3- was being consumed via denitrification. Tc(VII) reduction occurred concurrently with NO3- reduction, but U(VI) reduction was not observed until two or more donor additions resulted in iron-reducing conditions, as detected by the production of Fe(II). Reoxidation/remobilization of U(IV) was also observed in tests conducted with high (approximately 120 mM) but not low (approximately 1 mM) initial NO3- concentrations and not during acetylene-block experiments conducted with high initial NO3-. These results suggest that NO3(-)-dependent microbial U(IV) oxidation may inhibit or reverse U(VI) reduction and decrease the stability of U(IV) in this environment. Changes in viable biomass, community composition, metabolic status, and respiratory state of organisms harvested from down-well microbial samplers deployed during these tests were consistent with the conclusions that electron donor additions resulted in microbial growth, the creation of anaerobic conditions, and an increase in activity of metal-reducing organisms (e.g., Geobacter). The results demonstrate that it is possible to stimulate the simultaneous bioreduction of U(VI) and Tc(VII) mixtures commonly found with NO3- co-contamination at radioactive waste sites.

Biodegradation, Environmental↗
PubMed1999

129I in the oceans: origins and applications.

The quantity of the long lived (half-life 15.7 million years) radioactive isotope 129I in the pre-nuclear age ocean was approximately 100 kg. Various nuclear related activities, including weapons testing, nuclear fuel reprocessing, Chernobyl and other authorized or non-authorized dumping of radioactive waste have increased the ocean inventory of 129I by more than one order of magnitude. The most important of these sources are the direct marine discharges from the commercial reprocessing facilities at La Hague (France) and Sellafield (UK) which have discharged approximately 1640 kg in the English Channel, and approximately 720 kg in the Irish Sea, respectively. We discuss how this 129I can be used as both a 'pathway' and 'transit time' tracer in the North Atlantic and Arctic oceans, as well as a parameter for distinguishing between reprocessed and non-reprocessed nuclear waste in the ocean, and as a proxy for the transport and dilution of other soluble pollutants input to the North Sea.

Environmental Monitoring↗
PubMed2000

Environmental radioactivity: experience from the 20th century--trends and issues for the 21st century.

Environmental radioactivity has been an important area of research throughout the 20th century, with recent work having been stimulated mainly by: (i) the remarkable power of radionuclides as tracers of the rates and mechanisms of environmental processes and (ii) the potential health implications of contaminant radionuclides in the environment. A review is presented of salient aspects of environmental radioactivity, including consideration of tracer applications, sources and environmental impact of anthropogenic radionuclides, radioactive waste disposal and future exploitation of nuclear energy.

Cosmic Radiation↗
PubMed1997

Radioactive contamination in the environment of the nuclear enterprise 'Mayak' PA. Results from the joint Russian-Norwegian field work in 1994.

A brief overview of the radioactive waste inventory of the 'Mayak' PA reprocessing plant, Chelyabinsk Region, Russia is given together with a description of the environmental contamination caused by its activities and the origins of contamination. The joint Russian-Norwegian field work in 1994 is described, together with the major analytical results. The field work was of a limited extent, and was not designed to include a complete mapping of the environmental contamination around the plant. The results are, however, in good agreement with the very extensive previous Russian investigations. The highest concentrations of radioactivity were found in Reservoirs 10 and 11 and at the floodplain of the upper Techa River (Asanov Swamp). Also high concentrations are found in biota, especially fish from Reservoir 10.

Arctic Regions↗
PubMed2005

On the possible leakage of ET-RR1 liquid waste tank: hydrological and migration modes studies.

The first Egyptian (ET-RR1) research reactor has been in operation since 1961 at the Egyptian Atomic Energy Authority (EAEA) Inshas site. Therefore, at present, it faces a serious problem due to aging equipment, especially those directly in contact with the environment such as the underground settling tanks of nuclear and radioactive waste. The possible leakage of radionuclides from these aging tanks and their migration to the aquifer was studied using instantaneous release. This study was done based on the geological and hydrological characteristics of the site, which were obtained from the hydrogeological data of 25 wells previously drilled at the site of the reactor[1]. These data were used to calculate the trend of water levels, hydraulic gradient, and formulation of water table maps from 1993-2002. This information was utilized to determine water velocity in the unsaturated zone. Radionuclides released from the settling tank to the aquifer were screened according to the radionuclides that have high migration ability and high activity. The amount of fission and activation products of the burned fuels that contaminated the water content of the reactor pool were considered as 10% of the original spent fuel. The radionuclides considered in this case were H-3, Sr-90, Zr-93, Tc-99, Cd-113, Cs-135, Cs-137, Sm-151, Pu-238, Pu-240, Pu-241, and Am-241. The instantaneous release was analyzed by theoretical calculations, taking into consideration the migration mechanism of the various radionuclides through the soil space between the tank bottom and the aquifer. The migration mechanism through the unsaturated zone was considered depending on soil type, thickness of the unsaturated zone, water velocity, and other factors that are specific for each radionuclide, namely retardation factor, which is the function of the specific distribution coefficient of each radionuclide. This was considered collectively as delay time. Meanwhile, the mechanism of radionuclide migration during their passage in the water body of the aquifer was the main focus of this study. The degree of water pollution in the aquifer at a point of contact with the main water body of Ismailia Canal 1000 m from the reactor site was assessed for the instantaneous release by comparing the results obtained with the regulations of the standard limit of radionuclides in drinking water.

Egypt↗
PubMed1991

[Nuclear medicine--personnel exposure and release of radioactivity].

The Nuclear Medicine Division and 30 other groups at the University of Hannover School of Medicine are taken as examples to describe the diagnostic, therapeutic and research uses of radioactivity and the effectiveness of the associated radiation protection. The evolution of radiation exposures of 520 employees followed over the last six years and the methods used for the disposal of radioactive waste are explained. The adaptation of protective measures to individual and, in particular, specific working conditions has led to approximately 90% of all exposures remaining under the detection limit of the personal dosimeters during the entire observation period. Only a few people contributed to the collective radiation dose. In 1990, the average annual dose equivalent among personnel in the Nuclear Medicine Division was 0.12 mSv/person. By the installation of facilities for the storage of isotopes with short half-lives and of filters in the air circulation system, environmental contamination could be held much below the legal limits. Combustible and liquid waste containing radionuclides with long half-lives such as tritium and 14C had to be disposed of separately. However, they were a small fraction of the total radioactivity used.

Environmental Pollutants↗
PubMed1996

Cancer mortality among Techa River residents and their offspring.

This paper analyzes the data on leukemia and solid cancers of all types among 28,000 people exposed due to discharges of radioactive waste into the Techa River in the South Urals. Cancer mortality rates for the 33-y period since the beginning of the exposure have been estimated. In addition, the paper discusses malignancy cases among the first generation offspring of the exposed people. In comparison with matched control groups, an increased incidence of malignant neoplasms was observed among the exposed population. The leukemia risk, estimated on the basis of the linear model of absolute risk, was 0.85 per 10,000 person-y Gy of the dose accumulated in red bone marrow. Solid cancer risk (except osteosarcoma), estimated using linear model of relative risk, was 0.65 per Gy of dose accumulated in soft tissues. No increase in cancer mortality has been documented for the offspring of the exposed individuals.

Adolescent↗
PubMed1996

Nuclear waste repositories in salt mines: a new approach to safety assessment.

The long-term safety of radioactive waste repositories in rock-salt mines in the deep underground benefits significantly from the barrier effect of overlying rocks. The concentrations of radioactive substances released from the repository and migrating in the aquifer up to the biosphere are greatly reduced during passage through these rocks. In former safety analyses of waste repositories this transport has generally been modelled as a combination of the involved phenomena, e.g. convection, dispersion, adsorption, etc. The data required for a numerical evaluation of the overall effect are obtained either as (conservative) estimates based on experience or are empirical, based mainly on laboratory experiments. The approach presented here is much simpler and entirely empirical, and therefore more transparent. It makes use of the fact that the groundwater in the overlying rocks always contains dissolved salt from the salt formation and carries it continuously into the receiving channels or the drainage system. The relation between the total amount of dissolved solids present in a certain subsurface catchment area and their steady-state concentration in the receiving channels is assumed to be equivalent to the relation between the given amount of radionuclides released from the repository and their concentration in the receiving channels, the latter leading to a certain radiation exposure of the population. Two versions of this approach are discussed: version (a) assumes a continuous stream of radionuclides released from the repository, and version (b) assumes a pulse release of radionuclides from the repository. A simple calculation using data from the Gorleben exploration leads to the inequality [equation: see text] where Cmax is the maximum radionuclide concentration (with respect to time) in the receiving channels and W (Bq) is the amount of radionuclides released from the respository in a very short time. Cmax obtained from (1), is supposed to be an upper limit of the radionuclide concentration in the receiving channel and, therefore, a conservative estimate. In some catchment areas the salt concentration in a small region near the surface is higher by a factor of < 2 to 3 than the concentration in the receiving channel. In order to be conservative, this empirical factor may be used to calculate the concentration of radioactive substances. Surprisingly, the values of radiation exposure resulting from both versions of the new approach are far below those calculated by applying elaborated models of the transport processes. The respective factors are 10-100 in case (a) and as much as 1000 in case (b). The reasons for these significant differences are discussed.

Radioactive Waste↗
PubMed2005

Mortgaging the future: dumping ethics with nuclear waste.

On August 22, 2005 the U.S. Environmental Protection Agency issued proposed new regulations for radiation releases from the planned permanent U.S. nuclear-waste repository in Yucca Mountain, Nevada. The goal of the new standards is to provide public-health protection for the next million years - even though everyone admits that the radioactive wastes will leak. Regulations now guarantee individual and equal protection against all radiation exposures above the legal limit. Instead E.P.A. recommended different radiation exposure-limits for different time periods. It also recommended using only the arithmetic mean of the dose distribution, to assess regulatory compliance during one time period, but using only the median dose to assess compliance during another period. This piece argues that these two changes - in exposure-limits and in methods of assessing regulatory compliance - have at least four disturbing consequences. The changes would threaten equal protection, ignore the needs of the most vulnerable, allow many fatal exposures, and sanction scientifically flawed dose calculations.

Ethics↗