Assessment of hydrologic transport of radionuclides from the Rio Blanco underground nuclear test site, Colorado

DOE is operating an environmental restoration program to characterize, remediate, and close non-Nevada Test Site locations used for nuclear testing. Evaluation of radionuclide transport by groundwater is part of preliminary risk analysis. These evaluations allow prioritization of test areas in terms of risk, provide a basis for discussions with regulators and the public about future work, and provide a framework for assessing site characterization data needs. The Rio Blanco site in Colorado was the location of the simultaneous detonation of three 30-kiloton nuclear devices. The devices were located 1780, 1899, and 2039 below ground surface in the Fort Union and Mesaverde formations. Although all the bedrock formations at the site are thought to contain water, those below the Green River Formation (below 1000 in depth) are also gas-bearing, and have very low permeabilities. The transport scenario evaluated was the migration of radionuclides from the blast-created cavity through the Fort Union Formation. Transport calculations were performed using the solute flux method, with input based on the limited data available for the site. Model results suggest that radionuclides from the test are contained entirely within the area currently administered by DOE. This modeling was performed to investigate how the uncertainty in various physical parameters affect radionuclide transport at the site, and to serve as a starting point for discussion regarding further investigation; it was not intended to be a definitive simulation of migration pathways or radionuclide concentration values. Given the sparse data, the modeling results may differ significantly from reality. Confidence in transport predictions can be increased by obtaining more site data, including the amount of radionuclides which would have been available for transport (i.e., not trapped in melt glass or vented during gas flow testing), and the hydraulic properties of the formation. 38 refs., 6 figs., 1 tab

Near-field modeling in Frenchman Flat, Nevada Test Site

The US Department of Energy (DOE) is investigating the effects of nuclear testing in underground test areas (the UGTA program) at the Nevada Test Site. The principal focus of the UGTA program is to better understand and define subsurface radionuclide migration. The study described in this report focuses on the development of tools for generating maps of hydrogeologic characteristics of subsurface Tertiary volcanic units at the Frenchman Flat corrective Action Unit (CAU). The process includes three steps. The first step involves generation of three-dimensional maps of the geologic structure of subsurface volcanic units using geophysical logs to distinguish between two classes: densely welded tuff and nonwelded tuff. The second step generates three-dimensional maps of hydraulic conductivity utilizing the spatial distribution of the two geologic classes obtained in the first step. Each class is described by a correlation structure based on existing data on hydraulic conductivity, and conditioned on the generated spatial location of each class. The final step demonstrates the use of the maps of hydraulic conductivity for modeling groundwater flow and radionuclide transport in volcanic tuffs from an underground nuclear test at the Frenchman Flat CAU. The results indicate that the majority of groundwater flow through the volcanic section occurs through zones of densely welded tuff where connected fractures provide the transport pathway. Migration rates range between near zero to approximately four m/yr, with a mean rate of 0.68 m/yr. This report presents the results of work under the FY96 Near-Field Modeling task of the UGTA program

Assessment of hydrologic transport of radionuclides from the Gasbuggy underground nuclear test site, New Mexico

The U.S. Department of Energy (DOE) is operating an environmental restoration program to characterize, remediate, and close non-Nevada Test Site locations that were used for nuclear testing. Evaluation of radionuclide transport by groundwater from these sites is an important part of the preliminary risk analysis. These evaluations are undertaken to allow prioritization of the test areas in terms of risk, provide a quantitative basis for discussions with regulators and the public about future work at the sites, and provide a framework for assessing data needs to be filled by site characterization. The Gasbuggy site in northwestern New Mexico was the location of an underground detonation of a 29-kiloton nuclear device in 1967. The test took place in the Lewis Shale, approximately 182 m below the Ojo Alamo Sandstone, which is the aquifer closest to the detonation horizon. The conservative assumption was made that tritium was injected from the blast-created cavity into the Ojo Alamo Sandstone by the force of the explosion, via fractures created by the shot. Model results suggest that if radionuclides produced by the shot entered the Ojo Alamo, they are most likely contained within the area currently administered by DOE. The transport calculations are most sensitive to changes in the mean groundwater velocity, followed by the variance in hydraulic conductivity, the correlation scale of hydraulic conductivity, the transverse hydrodynamic dispersion coefficient, and uncertainty in the source size. This modeling was performed to investigate how the uncertainty in various physical parameters affects calculations of radionuclide transport at the Gasbuggy site, and to serve as a starting point for discussion regarding further investigation at the site; it was not intended to be a definitive simulation of migration pathways or radionuclide concentration values

Three-dimensional mapping of equiprobable hydrostratigraphic units at the Frenchman Flat Corrective Action Unit, Nevada Test Site

Geological and geophysical data are used with the sequential indicator simulation algorithm of Gomez-Hernandez and Srivastava to produce multiple, equiprobable, three-dimensional maps of informal hydrostratigraphic units at the Frenchman Flat Corrective Action Unit, Nevada Test Site. The upper 50 percent of the Tertiary volcanic lithostratigraphic column comprises the study volume. Semivariograms are modeled from indicator-transformed geophysical tool signals. Each equiprobable study volume is subdivided into discrete classes using the ISIM3D implementation of the sequential indicator simulation algorithm. Hydraulic conductivity is assigned within each class using the sequential Gaussian simulation method of Deutsch and Journel. The resulting maps show the contiguity of high and low hydraulic conductivity regions

Assessment of hydrologic transport of radionuclides from the Gnome underground nuclear test site, New Mexico

The U.S. Department of Energy (DOE) is operating an environmental restoration program to characterize, remediate, and close non-Nevada Test Site locations that were used for nuclear testing. Evaluation of radionuclide transport by groundwater from these sites is an important part of the preliminary site risk analysis. These evaluations are undertaken to allow prioritization of the test areas in terms of risk, provide a quantitative basis for discussions with regulators and the public about future work at the sites, and provide a framework for assessing data needs to be filled by site characterization. The Gnome site in southeastern New Mexico was the location of an underground detonation of a 3.5-kiloton nuclear device in 1961, and a hydrologic tracer test using radionuclides in 1963. The tracer test involved the injection of tritium, {sup 90}Sr, and {sup 137}Cs directly into the Culebra Dolomite, a nine to ten-meter-thick aquifer located approximately 150 in below land surface. The Gnome nuclear test was carried out in the Salado Formation, a thick salt deposit located 200 in below the Culebra. Because salt behaves plastically, the cavity created by the explosion is expected to close, and although there is no evidence that migration has actually occurred, it is assumed that radionuclides from the cavity are released into the overlying Culebra Dolomite during this closure process. Transport calculations were performed using the solute flux method, with input based on the limited data available for the site. Model results suggest that radionuclides may be present in concentrations exceeding drinking water regulations outside the drilling exclusion boundary established by DOE. Calculated mean tritium concentrations peak at values exceeding the U.S. Environmental Protection Agency drinking water standard of 20,000 pCi/L at distances of up to almost eight kilometers west of the nuclear test

Risk-based screening analysis of ground water contaminated by radionuclides introduced at the Nevada Test Site (NTS)

The Nevada Test Site (NTS) is located in the southwestern part of Nevada, about 105 km (65 mi) northwest of the city of Las Vegas. Underground tests of nuclear weapons devices have been conducted at the NTS since late 1962 and ground water beneath the NTS has been contaminated with radionuclides produced by these tests. This concern prompted this examination of the potential health risk to these individuals from drinking the contaminated ground water either at a location on the NTS (assuming loss of institutional control after 100 y) or at one offsite (considering groundwater migration). For the purpose of this assessment, a representative mix of the radionuclides of importance and their concentrations in ground water beneath the NTS were identified from measurements of radionuclide concentrations in groundwater samples-of-opportunity collected at the NTS. Transport of radionuclide-contaminated ground water offsite was evaluated using a travel-time-transport approach. At both locations of interest, potential human-health risk was calculated for an individual ingesting radionuclide-contaminated ground water over the course of a 70-y lifetime. Uncertainties about human physiological attributes, as well as about estimates of physical detriment per unit of radioactive material, were quantified and incorporated into the estimates of risk. The maximum potential excess lifetime risk of cancer mortality estimated for an individual at the offsite location ranges from 7 {times} 10{sup {minus}7} to 1 {times} 10{sup {minus}5}, and at the onsite location ranges from 3 {times} 10{sup {minus}3} to 2 {times} 10{sup {minus}2}. Both the offsite and the onsite estimates of risk are dominated by the lifetime doses from tritium. For the assessment of radionuclides in ground water, the critical uncertainty is their concentration today under the entire NTS

The Interreg Project AdSWiM: Managed Use of Treated Wastewater for the Quality of the Adriatic Sea

The Italy-Croatia Cross Border Cooperation (CBC) Programme is the financial instrument supporting the cooperation between the two European Member States overlooking the Adriatic Sea. The first call for proposals was launched in 2017, identifying four priority axes of intervention. Subsequently, in 2019, the kick-off of the AdSWiM project “Managed use of treated urban wastewater for the quality of the Adriatic Sea” took place in Udine (IT). Adriatic marine waters are generally classified as good to excellent based on the Bathing Water Directive (2006/7/EC). Nevertheless, issues of low productivity or the lack of nutrients have been often suggested, especially on the Italian side. The project addresses the question of whether wastewater treatment plants (WWTPs) discharging to the sea, after applying appropriate pollution control and management technologies, can modulate the nutrient content of their effluents to support localized depleted areas. This idea is borrowed from one of the motivations that support the reuse of treated wastewater for irrigation, thus leading to the return of nutrients (nitrogen, phosphorus, potassium, etc.) to natural biogeochemical cycles. However, the hypothesis of modulating the nutrient composition of wastewater opens up to several critical aspects, including legislative and technological ones. Being aware of the delicate environmental implications, we have undertaken the project involving WWTPs, research centers, municipalities, and legal experts with the aim of investigating in detail the problems related to wastewater reuse, especially with regard to the content of nutrients. Our experimental approach aimed to evaluate appropriate and possibly new treatment technologies to reduce the microbial load and to implement chemical and microbiological tests on the treated wastewater. Results have shown that it can be tricky to draw decisive conclusions because (i) the wastewater management systems differ between the two sides of the Adriatic sea due to the different levels of technological development of WWTPs; (ii) the Italian and Croatian coasts deeply differ in geographic characteristics (i.e., topography, orography, current circuits, presence of rivers) and anthropogenic pressure (i.e., exploitation levels, population density); (iii) the new treatment technologies to lower bacterial contamination need further efforts to raise their technological level of readiness (TRL) and make them implementable in the existing WWTPs. However, in terms of chemical control methodologies, the proposed sensors and biosensors gave positive results, managing to decrease the detection limits for the measured parameters, and the tested technologies for microbiological monitoring were also effective. In particular, the latter was carried out by using recent molecular biology techniques, capable of resolving the microbiota in treated wastewater, which emerged to be strictly related to the features of the WWTPs

Transport of sorbing solutes in randomly heterogeneous formations: Spatial moments, macrodispersion, and parameter uncertainty

Expressions for the spatial moments and macrodispersion tensor for sorbing solutes in heterogeneous formations were presented using a probabilistic model of a fluid residence time coupled with the particle position analysis. The fluid residence time was defined as a fraction of the actual time during which the particle stayed in the mobile fluid phase of the aquifer. The fluid residence time is a random variable whose variability comes as a result of the non-equilibrium sorption properties. The sorbing solute was assumed to be governed with first-order linear kinetics. The closed-form expressions were based on the stationarity in the kinetic process and on the first-order approximation in the hydraulic conductivity field and in the fluid residence time. The non-equilibrium effects were presented as a function of the spatial variability in hydraulic conductivity and temporal variability in the fluid residence time. The importance of the non-equilibrium processes in the field scale was found to be dependent on reaction rates, retardation factor, mean velocity, and on variance and correlation scale of the hydraulic conductivity. The time needed to reach the asymptotic macrodispersivity is dependent on the degree of non-equilibrium processes and distribution coefficient. The impact from the uncertainty in parameters upon the spatial moments was examined and compared with the organic tracer used in the Borden field experiment

Carbon/Hybrid Perovskite Interfaces: From Light Emission to Radiation Detection

In this dissertation, carbon is proposed as an alternative electrode material to interface with semiconducting organic-inorganic metal halide perovskites in various optoelectronic applications. Carbon electrodes may offer, good device performance, while providing improved stability due to their inert nature. The focus will be on a special architecture of carbon nanotubes, called the vertically aligned carbon nanotube forest (VACNTs), in which the CNTs are self-assembled into a vertically oriented array during growth on a substrate. I start discussing, the unexpected discovery, namely, that single crystals of methylammonium lead perovskites (MAPbBr3 and MAPbCl3) grow directly on these VACNT forests. The peculiarity is that fast-growing single crystals engulfed the individual CNTs, as protogenetic inclusions, resulting in a three-dimensionally enlarged photosensitive interface. Sensitive photodetector devices were fabricated utilizing this ¿exotic¿ junction, detecting low light intensities (< 20 nW) from the UV range to 550 nm. Moreover, a photocurrent was recorded at zero external bias voltage, which points to a plausible formation of a p-n junction of the MAPbBr3 single crystal and VACNT forest interface. While, attempting to push the I-V characteristics of these photodetectors to the limits, we were granted with another unexpected discovery, the bright green electroluminescence of these devices, observed at room temperature. Under an applied electric field, charged ions in the crystal drifted and accumulated near the electrodes, resulting in an in operando formed p¿i¿n heterojunction. The decreased interface energy barrier and the strong charge injection due to the CNT tip enhanced electric field, resulted in a bright green light emission up to 1800 cd m-2 at room temperature. Furthermore, the possibility of designing perovskite-based ultrasensitive, low cost detectors for high-energy radiation was demonstrated. MAPbBr3 single crystal ¿-ray detectors, equipped with carbon electrodes, were fabricated allowing radiation detection by photocurrent measurements at room temperature with record sensitivities (333.8 µC Gy-1 cm-2). Importantly, the devices operated at low bias voltages (< 1.0 V), which may enable, future low-power operation in energy-sparse environments, including space. The detector prototypes were exposed to radiation from a 60Co source at dose rates up to 2.3 Gy h-1 under ambient and operational conditions for over 100 hours, without any sign of degradation. We postulate that the excellent radiation tolerance stems from the intrinsic structural plasticity of the organic-inorganic halide perovskites, which can be attributed to a defect-healing process by fast ion migration at the nanoscale level. Since, the sensitivity of the ¿-ray detectors is proportional to the volume of the employed MAPbBr3 crystals, a unique crystal growth technique was introduced, baptized as the `oriented crystal-crystal intergrowth¿ or OC2G method, yielding crystal specimens with a volume and mass of over 1¿000 cm3 and 3.8 kg, respectively. Large volume specimens have a clear advantage for radiation detection, however, the demonstrated kilogram scale crystallogenesis coupled with future cutting and slicing technologies may have additional benefits, for instance, enable the development for the first time crystalline perovskite wafers, which may challenge the status quo of present and future performance limitations in all optoelectronic applications

Robustheitsbewertung crashbelasteter Fahrzeugstrukturen

Zunächst werden im Rahmen der felddatenbasierten Robustheitsanalyse reale Unfallkonstellationen als Eingangsstreuungen aufgefasst und Anforderungen der Fahrzeugsicherheit in ihrer Robustheit gegenüber dem realen Unfallgeschehen untersucht. Die virtuelle Robustheitsanalyse bewertet in einem weiteren Schritt die Robustheit crashbelasteter Fahrzeugstrukturen gegenüber einer definierten Anforderung unter Berücksichtigung von aleatorischen Streueinflüssen aus der Fahrzeugentwicklung. Zur Auswertung der hierzu durchgeführten stochastischen Struktursimulationen wird ein neuer Robustheitsindex RI als skalare Bewertungsgröße eingeführt