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At least 1,477 records · Page 82Linked to original sources
PubMed1999

Carbonate induced dissolution of uranium containing precipitates under cement leachate conditions.

The effects of carbonate on uranium (VI) solubility under aerobic and cementitious conditions have been investigated. The information is of relevance to low level nuclear waste disposal. Aqueous NaOH, KOH, Ca(OH)2 and a cement leachate solution were added to uranyl nitrate solution. Afterwards, increasing amounts of ammonium carbonate were added to re-dissolve the precipitates. The precipitates were characterised by means of X-ray powder diffraction (XRPD) measurements and modelling studies. The model calculations were performed using the MINTEQA2 speciation code, with an expanded database incorporating uranium stability constants taken from the HATCHES database. The measured and predicted amounts of CO3(2-) needed to dissolve the precipitates were compared. The knowledge gained from the 'pure' systems was used to rationalise the precipitation and re-dissolution behaviour observed in the leachate system. The lack of uranium solubility at low carbonate levels brought into question literature formation constants for UO2(OH)3- and UO2(OH)4(2-). An approximate log K value of 26.8 for K2U2O7 formation was estimated from the KOH results at pH 12. Generally, uranium solubilities are expected to be insignificant at low level nuclear waste sites because anaerobic conditions should persist. However, this study has demonstrated that solubility in leachate could rise at high pH and high carbonate levels, if aerobic conditions were to develop. Soluble U(VI) species would be formed. The novel part of the study has been to reproduce the effects and to correlate enhanced solubilities with model predictions. Consequently, the study has re-emphasised the need for appropriate environmental monitoring of such sites.

Carbonates↗
PubMedDate not supplied

Analysis of thermal-hydrologic-mechanical behavior near an emplacement drift at Yucca Mountain.

A coupled thermal, hydrologic and mechanical (THM) analysis is conducted to evaluate the impact of coupled THM processes on the performance of a potential nuclear waste repository at Yucca Mountain, Nevada. The analysis considers changes in rock mass porosity, permeability, and capillary pressure caused by rock deformations during drift excavation, as well as those caused by thermomechanically induced rock deformations after emplacement of the heat-generating waste. The analysis consists of a detailed calibration of coupled hydraulic-mechanical rock mass properties against field experiments, followed by a prediction of the coupled thermal, hydrologic, and mechanical behavior around a potential repository drift. For the particular problem studied and parameters used, the analysis indicates that the stress-induced permeability changes will be within one order of magnitude and that these permeability changes do not significantly impact the overall flow pattern around the repository drift.

Mechanics↗
PubMed2006

Plutonium oxidation and subsequent reduction by Mn(IV) minerals in Yucca Mountain tuff.

Plutonium oxidation state distribution on Yucca Mountain tuff and synthetic pyrolusite (beta-MnO2) suspensions was measured using synchrotron X-ray micro-spectroscopy and microimaging techniques as well as ultrafiltration/solventextraction techniques. Plutonium sorbed to the tuff was preferentially associated with manganese oxides. For both Yucca Mountain tuff and synthetic pyrolusite, Pu(IV) or Pu(V) was initially oxidized to more mobile Pu(V/VI), but over time, the less mobile Pu(IV) became the predominant oxidation state of the sorbed Pu. The observed stability of Pu(IV) on oxidizing surfaces (e.g., pyrolusite), is proposed to be due to the formation of a stable hydrolyzed Pu(IV) surface species. These findings have important implications in estimating the risk associated with the geological burial of radiological waste in areas containing Mn-bearing minerals, such as at the Yucca Mountain or the Hanford Sites, because plutonium will be predominantly in a much less mobile oxidation state (i.e., Pu(IV)) than previously suggested (i.e., Pu(V/VI).

Hydrogen-Ion Concentration↗
PubMed2002

Dose rate prediction methodology for remote handled transuranic waste workers at the waste isolation pilot plant.

An approach is described for estimating future dose rates to Waste Isolation Pilot Plant workers processing remote handled transuranic waste. The waste streams will come from the entire U.S. Department of Energy complex and can take on virtually any form found from the processing sequences for defense-related production, radiochemistry, activation and related work. For this reason, the average waste matrix from all generator sites is used to estimate the average radiation fields over the facility lifetime. Innovative new techniques were applied to estimate expected radiation fields. Non-linear curve fitting techniques were used to predict exposure rate profiles from cylindrical sources using closed form equations for lines and disks. This information becomes the basis for Safety Analysis Report dose rate estimates and for present and future ALARA design reviews when attempts are made to reduce worker doses.

Algorithms↗
PubMed1997

Capillary zone electrophoresis and ion-exchange capillary electrochromatography: analytical tools for probing the Hanford nuclear site environment.

Ion-exchange capillary electrochromatography (IE-CEC) is a relatively new separation technique based on the combination of ion-exchange chromatographic and electrophoretic separation mechanisms. IE-CEC offers both the efficiency of capillary electrophoresis and the selectivity and sample capacity of ion-exchange chromatography. The utility of the method was examined with I- and IO3-, which are common constituents of nuclear wastes at Hanford, Washington and other U.S. Department of Energy (DoE) sites, and ReO4-, a surrogate for TcO4-. The advantages and limitations of IE-CEC relative to capillary zone electrophoresis (CZE) are explored. The chief advantages are increased loading capacity and an alternative selectivity to that of CZE, in addition to increased efficiency (relative to conventional ion-exchange chromatography). The run-to-run reproducibility of IE-CEC, however, was found to be a limitation of the technique.

Chromatography, Ion Exchange↗
PubMed2002

Local and interregional economic analysis of large US Department of Energy waste management projects.

An economic simulation model was used to understand the local and interregional economic impacts of four alternative waste management technologies proposed for the US Department of Energy's Savannah River nuclear weapons site. The simulations of the four technologies, each of which will cost at least a billion dollars, were done for the period 2000-2015. The analyses show that differences in project costs are not directly reflected in local economic impacts because of differences among the technologies during the design, testing and construction phases; differences in locations where the design and pilot-testing would occur; and choices about how any of the technologies would be funded.

Costs and Cost Analysis↗
PubMedDate not supplied

Validation of the multiscale thermohydrologic model used for analysis of a proposed repository at Yucca Mountain.

Performance assessment and design evaluation of the proposed repository at Yucca Mountain are facilitated by a thermohydrologic modeling tool that simultaneously accounts for processes occurring at a scale of a few tens of centimeters around individual waste packages and emplacement drifts, and accounts for processes at the multi-kilometer scale of the mountain. The most straightforward approach is to account for the 3-D drift- and mountain-scale dimensionality all within a single monolithic thermohydrologic model. This approach is too computationally expensive to be a viable simulation tool capable of addressing all waste-package locations in the repository. The Multiscale Thermohydrologic Model (MSTHM) is a computationally efficient alternative to addressing these modeling issues. In this paper, we describe the principal calculation stages to predict temperature, relative humidity, and liquid-saturation, as well as other thermohydrologic variables, in the drifts and in the host rock. Using a three-drift repository example (which is a scaled-down version of the proposed repository), we demonstrate the validity of the MSTHM approach against a nested monolithic thermohydrologic model.

Forecasting↗
PubMed2001

Gamma radiation effects on potassium pertechnetate in carbonate media.

Gamma radiation effects on the stability of the oxidation state of radioelements and diffusion within the framework of nuclear waste repositories are often neglected, although it may influence physicochemical processes and thus transfer to biosphere and geosphere. This knowledge is essential to model transport phenomena. This study reports on effects of gamma irradiation on technetium in carbonate media, which is representative of natural systems. Depending on media compositions, the gamma irradiation on pertechnetate leads to formation of Tc(IV) only in the absence of carbonate. CO3*- radicals are able to re-oxidise technetium intermediate oxidation states to the +7 state.

Carbonates↗
PubMed2001

Estimation of the radionuclide distribution in sediment in coast area.

The study of the radionuclide distribution in sediment is a very important aspect in environmental impact of the low level radioactive liquid waste (LLW) from coastal nuclear facilities or nuclear power plant. Even now we do not know much about it. In this paper, a simple and useful method is put forward and it is used to estimate the nuclide distribution in sediment. The result showed that the LLW from nuclear facility or nuclear power plant will do a little harm to the sediment nearby. But the harm is not very serious. Much works have to be done before full understanding of the situation.

Environmental Monitoring↗
PubMed1996

Health conditions among workers who participated in the cleanup of the Chernobyl accident.

People who took part in the Chernobyl accident cleanup have been registered upon their return to Kyrgyzstan since 1991, and their children since 1992. Later, citizens affected by the Semipalatinsk and Chelyabinsk contamination incidents were included for registration and health care purposes. The effects of the nuclear waste depositories in the Mailuu-Suu region were examined with the assistance of the Kansas University Medical Center (United States of America). All these investigations of affected people indicate apparent increases in a number of symptoms and illnesses when compared to the rest of the population. Sample sizes ranged from several hundred to several thousand. Above-normal radiation levels and/or the stress and fear of living in contaminated area can lead to significant increases in nervous disorders, cardiovascular diseases and other problems. The most significant increase was in the suicide rate.

Adult↗
PubMed2003

Large-scale purification of 90Sr from nuclear waste materials for production of 90Y, a therapeutic medical radioisotope.

A major limitation on the supply of the short-lived medical isotope 90Y (t1/2 = 64 h) is the available quantity of highly purified 90Sr generator material. A radiochemical production campaign was therefore undertaken to purify 1,500 Ci of 90Sr that had been isolated from fission waste materials. A series of alkaline precipitation steps removed all detectable traces of 137Cs, alpha emitters, and uranium and transuranic elements. Technical obstacles such as the buildup of gas pressure generated upon mixing large quantities of acid with solid 90Sr carbonate were overcome through safety features incorporated into the custom-built equipment used for 90Sr purification. Methods are described for analyzing the chemical and radiochemical purity of the final product and for accurately determining by gravimetry the quantities of 90Sr immobilized on stainless steel filters for future use.

Cesium Radioisotopes↗
PubMedDate not supplied

Incidence of leukaemia in young people around the La Hague nuclear waste reprocessing plant: a sensitivity analysis.

The objectives are to investigate the incidence of childhood leukaemia in young people around the French nuclear waste reprocessing plant (La Hague, Normandy) for the period 1978-1992, and to check the sensitivity of the results to the choice of disease clustering tests and reference rates. The performance of three statistical procedures are compared: a conventional approach; a Poisson maximum test, and an extraction mapping technique. On the whole, the results are in general agreement and demonstrate the apparent existence of a distinct cluster of childhood leukaemia, contiguous and south-east of the La Hague nuclear facility.

Adolescent↗
PubMed1997

The vulnerability of the Nevada visitor economy to a repository at Yucca Mountain.

This article reviews the studies commissioned by the Nevada Nuclear Waste Project Office to estimate the economic impact of a high-level nuclear waste repository at Yucca Mountain. Case studies found that visitor impacts occur for some analogous facilities, but not for others. Assessments of behavioral intent indicate that at least some economic agents would avoid visiting Nevada under repository scenarios. A third set of studies tested the risk-aversion and negative-imagery models of visitor decision making; people avoid visiting places associated with either a significant health risk or negative imagery, but it has yet to be shown that a repository would induce these perceptions in nearby places. In sum, the NWPO-sponsored studies suggest the potential for visitor impacts, but do confirm that these effects will occur.

Humans↗
PubMed1982

Effects of ICRP Publication 30 and the 1980 BEIR Report in hazard assessments of high-level waste.

ICRP Publication 30 (ICRP30) gives the radiation dose to various body organs in Sv per Bq, which are readily translated into rad per curie ingested for various radioisotopes; the 1980 BEIR Report (BEIR III) gives the risk of fatal cancer per rad of dose to each body organ; the ORIGEN 2 Code gives the curies per tonne of initial uranium fuel in high level waste and in spent fuel. The product of these, Ci/tonne x rad/Ci x risk/rad gives the risk/tonne in terms of fatal cancer doses, if ingested, per tonne of uranium. When the resulting curves are compared with those calculated previously (based on ICRP Publication 2 and the 1972 BEIR Report), the hazard is less for the first century but much more thereafter. The principal sources of this greatly increased hazard is the 100-fold increase in absorption through the gut for 237Np in ICRP 30, plus the high cancer risk from radiation to liver in BEIR III. Some consequences of these changes and some scientific questions relevant to ascertaining their validity are discussed.

Humans↗
PubMedDate not supplied

Effect of heterogeneity in fracture permeability on the potential for liquid seepage into a heated emplacement drift of the potential repository.

A numerical model was used to investigate the effect of spatial variability in fracture permeability on liquid seepage and moisture distribution in the vicinity of a waste emplacement drift in the unsaturated zone (UZ) of Yucca Mountain. The model is based on a two-dimensional, cross-sectional, dual-permeability model of the unsaturated zone at Yucca Mountain and uses a stochastic approach to investigate the effect of small-scale heterogeneous features. The studies were conducted using one uniform fracture permeability case, three realizations of stochastically generated fracture permeability, one discrete permeability feature case, and one increased ambient liquid flux case. In all cases, the models predict that completely dry drift conditions will develop above and below the drift in 10-100 years and remain dry for 1000-2000 years. During this period, the models predict no seepage into drifts, although liquid flux above the drifts and within the drift pillars may increase by up to two orders of magnitude above ambient flux. This is because the heat released by the emplaced waste is sufficient to vaporize liquid flux of one to two orders of magnitude higher than present-day ambient flux for over 1000 years. The results also show that unsaturated zone thermal-hydrological (TH) models with uniform layer permeability can adequately predict the evolution of seepage and moisture distribution in the rock mass surrounding the repository drifts. The models further show that although variability in fracture permeability may focus and enhance liquid flow in regions of enhanced liquid saturation (due to condensation above the drifts), vaporization and vapor diffusion can maintain a dry environment within the drifts for thousands of years.

Geological Phenomena↗
PubMed2004

Regulatory off-gas analysis from the evaporation of Hanford simulated waste spiked with organic compounds.

After strontium/transuranics removal by precipitation followed by cesium/technetium removal by ion exchange, the remaining low-activity waste in the Hanford River Protection Project Waste Treatment Plant is to be concentrated by evaporation before being mixed with glass formers and vitrified. To provide a technical basis to permit the waste treatment facility, a relatively organic-rich Hanford Tank 241-AN-107 waste simulant was spiked with 14 target volatile, semi-volatile, and pesticide compounds and evaporated under vacuum in a bench-scale natural circulation evaporator fitted with an industrial stack off-gas sampler at the Savannah River National Laboratory. An evaporator material balance for the target organics was calculated by combining liquid stream mass and analytical data with off-gas emissions estimates obtained using U.S. Environmental Protection Agency (EPA) SW-846 Methods. Volatile and light semi-volatile organic compounds (<220 degrees C BP, >1 mm Hg vapor pressure) in the waste simulant were found to largely exit through the condenser vent, while heavier semi-volatiles and pesticides generally remain in the evaporator concentrate. An OLI Environmental Simulation Program (licensed by OLI Systems, Inc.) evaporator model successfully predicted operating conditions and the experimental distribution of the fed target organics exiting in the concentrate, condensate, and off-gas streams, with the exception of a few semi-volatile and pesticide compounds. Comparison with Henry's Law predictions suggests the OLI Environmental Simulation Program model is constrained by available literature data.

Air Pollutants↗
PubMed2001

Waste form corrosion modeling: comparison with experimental results.

Results of leaching experiments using active and inactively simulated HLW glass in concentrated NaCl solution are described. Measured solution concentrations of glass components, fission products and actinides are compared with computed data. The computed pH value corresponds with the findings from experiments with inactively simulated glass samples. Moreover, the concentrations of silica and strontium can be described adequately by reaction path modelling. The computed U concentration is explained by the precipitation of schoepite or Na2U2O7. The computed Am concentration significantly exceeds the measured data. This may be attributed to sorption processes on corrosion products of the glass, which are relevant also for lanthanide elements under the conditions of the experiments. This hypothesis is tested by solid solution approaches and by computing sorption of Am onto SiO2 precipitates.

Actinoid Series Elements↗
PubMed1988

The future of the de minimis concept.

How low is low enough? Is "close to zero? Does detectability define importance? These and similar questions are addressed in this paper, which considers the concept of a "practical zero" or de minimis level of radiation and the future applications of that concept. After defining the concept and some widely used terms and summarizing the current status of the de minimis approach, this article surveys the activities of standards-setting and regulatory bodies throughout the world and their possible future approaches to applying the de minimis concept. Applications include conventional disposal of very-low-level wastes, ocean dumping, decontamination and decommissioning guidelines, and truncation of as low as reasonably achievable and collective dose calculations. Implications in areas beyond low-level radiation control are also addressed. These areas include nuclear accident risks and the risks associated with use of hazardous materials. The application of the de minimis concept to risks of all types is discussed, with a particular emphasis on the risks of carcinogenesis. The paper also presents a summary of methods for quantitatively setting actual levels that are deemed de minimis in specific cases. Finally, the problems inherent in a de minimis approach are discussed and an attempt is made to predict future developments.

Government Agencies↗