Stainless steel - zirconium alloys were developed by the US Department of Energy Laboratories as metallic waste forms for noble metal fission products. This thesis evaluates iron-zirconium-rhenium alloys to establish a technical basis for using metal waste form alloys for technetium-99 immobilization. Rhenium is used as a surrogate for Tc-99 since Tc is not naturally available and Re is metallurgically similar to Tc. The iron-zirconium system has two eutectic compositions, Fe-15 wt % Zr and Zr- 16 wt% Fe. Ten test samples were successfully cast in yttrium oxide crucibles at 1600°C, half near each eutectic composition, with Re amounts varying from 2.5 to 12.5 weight percent. A scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS) capability was employed to determine the phase structure and phase composition of each sample. Iron rich samples were found to form up to three phases, with the rhenium content favoring the intermetallic phases: 1) an Fe solid solution phase, 2) an FeZr2-type intermetallic with 11 wt % or less Re, and 3) a second intermetallic with about 18 wt % Re. Zirconium rich samples formed as many as five distinct phases: 1) a Zr solid solution phase, 2) a Zr3Fe-type intermetallic with as much as 13 wt% Re, 3) a rhenium-zirconium intermetallic, 4) another Fe-Zr intermetallic with very little Re, and 5) a Fe-Re intermetallic. Potentiostatic and potentiodynamic electrochemical tests were performed using sulfuric acid to evaluate the corrosion resistance of each sample. These tests found that the zirconium rich samples were very corrosion resistant but became increasingly susceptible at higher rhenium concentrations. The iron rich samples were not very resistant to corrosion under the test conditions; there was no notable trend in corrosion behavior related to the introduction of rhenium.

A Deep Geologic Repository is proposed for a site on the eastern margin of the Michigan Basin at a depth of 680 metres in the Cobourg Formation. A study of the paleo-hydrogeolgical conditions for the area was conducted using numerical simulation of the distribution of natural tracers and the observed hydraulic head. To conduct the study, simulations of the groundwater flow systems were developed for hydraulic head generated from glacial loading cycles to study its effects on advective solute transport. The hydro-mechanical loading during the glacial cycles is assessed using numerical analysis of coupled stress and porewater pressure. The effect of density-dependent flow was assessed in a second study to estimate the degree of penetration of glacially-derived water driven into the basin during periods of glacial loading. Numerical simulations were used to explore the potential freshwater invasion pathways under a variety of conditions. Finally, profiles of 18O and 2H measured in porewater were combined with our understanding of the paleo-hydrogeological conditions derived from the studies above to test the hypothesis that solute transport was diffusion-dominated in this setting. A series of pure diffusion and advection-diffusion models were developed and the results were compared with profiles of natural water isotopes obtained from the study area. The results of the hydro-mechanical study of glacial impact show the development of significant underpressure during the interstadial periods, especially in the lowest permeability formations. The results also show that the formations have not reached hydrostatic conditions at the present time. These results were verified by comparison to measured environmental heads obtained from the study site. The density-dependent modeling showed that freshwater is capable of reaching the location of the study site through several permeable features. The transport simulations showed that the evolution time starting from a uniform initial condition, and using boundary conditions that are defined by freshwater invasion at several depths agrees with the hydro-geological history of this part of the Basin. The results also show the importance of advection on solute transport from the upper and lower boundaries even in rock of extremely low permeability. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2014-05-30 10:18:01.286

The generation of nuclear energy leads to the generation of contaminated, radioactive wastes. The current strategy in the UK is to dispose of high and intermediate level wastes to a geological disposal facility with no possibility for retrieval. The waste is contained in an encapsulation matrix, which is usually cement, however cement is unsuitable for certain waste types, for which epoxy resins have been proposed as an alternative. The radiation resistance of two candidate epoxy/amine resin formulations under repository conditions were tested with regards to the degradation of the backbone structure and the release of potential organic ligands from the polymer. The difference in the polymers was the choice of amine curing agent. Analysis of the polymer by infra-red spectroscopy and nuclear magnetic resonance spectroscopy revealed that the carbon nitrogen bonds are the most susceptible to radiation damage, regardless of the atmospheric and aqueous environment. The presence of an aqueous phase greatly reduces the availability of oxygen and reduces the rate of degradation when irradiated under an atmosphere of air. The properties of the aqueous phase has little effect on the degradation of the polymer. Thermal analysis revealed that the effects of the environment are limited to a thin surface layer of the polymer. Leachate analysis revealed that both organic and nitrogen containing compounds are leached from the polymer when irradiated in pure water. Under repository conditions however very little carbon and nitrogen is observed, suggesting that the calcium hydroxide present in repositories is capable of removing the leached species from solution. The generation of nitrate ions from air radiolysis over water is suppressed in the presence of the polymers, suggesting that nitrate is removed from solution by leached species or reaction with the polymer.

Glassy carbon is a disordered form of carbon with very high temperature resistance, high hardness and strength and chemical stability even in extreme environments. Glassy carbon is also unaffected by nearly all acids and cannot be graphitized even at very high temperature. Because of these characteristics, there is a possibility that glassy carbon can replace copper, iron, titanium alloys and other materials employed in making canisters used in nuclear waste storage. The modification of glassy carbon due to strontium ions implantation and heat treatment is reported. Glassy carbon (GC) samples were implanted with 200 keV strontium ions to a fluence of 2×1016 ions/cm2 at room temperature. Sequential isochronal annealing was carried out on the implanted samples at temperatures ranging from 200 oC - 900 oC for one hour. The influence of ion implantation and annealing on surface topography was examined by the scanning electron microscopy (SEM), while Raman spectroscopy was used to monitor the corresponding structural changes induced in the glassy carbon. The depth profiles of the implanted strontium before and after annealing were determined using Rutherford Backscattering Spectroscopy (RBS). Compared to SRIM predictions the implanted strontium profiles was broader. After annealing at 300 oC, bulk and surface diffusion of the strontium atoms took place. Annealing at 400 oC- 700 oC not only resulted in further diffusion of strontium towards the surface, the diffusion was accompanied with segregation of strontium on the surface of the glassy carbon substrate. Evaporation of the strontium atoms was noticed when the sample was annealed at 800 oC and 900 oC respectively. These annealing temperatures are higher than the melting point of strontium (~769 oC). The Raman spectrum of the virgin glassy carbon shows the disorder (D) and graphitic (G) peaks which characterize disordered carbon materials. Merging of these two peaks was observed when the virgin sample was implanted with strontium ions. Merging of these peaks is due to damage caused by the implantation of strontium. The Raman spectrum recorded after heat treatment showed that only some of the damage due to implantation was annealed out. Annealing at 20000C for 5 hours resulted in a Raman spectrum very similar to that of virgin glassy carbon indicating that the damage due to the ion implantation was annealed out. SEM showed large differences in the surface topography of the polished glassy carbon surfaces and those of as-implanted samples. Annealing did not significantly change the surface microstructure of the implanted samples. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Physics / unrestricted

see document / Master of Science

Tens of thousands of metric tons of highly radioactive, nuclear waste have been generated in the United States. Currently, there is no treatment or disposal facility for these wastes. Of the radioactive elements in high-level nuclear waste, neptunium (Np) is of particular concern because it has a long half-life and may potentially be very mobile in groundwaters associated with a proposed underground disposal site at Yucca Mountain, Nevada. Aqueous Np concentrations observed in previous, short-term solubility experiments led to calculated potential doses exceeding proposed long-term regulatory limits. However, thermodynamic data for Np at 25°C showed that these observed aqueous Np concentrations were supersaturated with respect to crystalline NpO 2 . It was hypothesized that NpO 2 is the thermodynamically stable solid phase in aqueous solution, but it is slow to form in an aqueous solution of NpO 2 + on the time scale of previous experiments. The precipitation of NpO 2 would provide significantly lower aqueous Np concentrations leading to calculated doses below proposed regulatory limits. To test this hypothesis, solubility experiments were performed at elevated temperature to accelerate any slow precipitation kinetics. Ionic NpO 2 + (aq) was introduced into very dilute aqueous solutions of NaCl with initial pH values ranging from 6 to 10. The reaction vessels were placed in an oven and allowed to react at 200°C until steady-state aqueous Np concentrations were observed. In all cases, aqueous Np concentrations decreased significantly from the initial value of 10 −4 M. The solids that formed were analyzed by x-ray powder diffraction, x-ray absorption spectroscopy, and scanning electron microscopy. The solids were determined to be high-purity crystals of NpO 2 . This is the first time that crystalline NPO 2 has been observed to precipitate from NpO 2 + (aq) in near-neutral aqueous solutions. The results obtained demonstrate that Np will precipitate as NpO 2 in aqueous solutions thereby leading to significantly lower aqueous Np concentrations.

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In this thesis, nuclear power plants and their role in sustaining peace or threatening it are described and, to some extent, analysed. Nuclear energy contributes to the economic development of the country it is built in by providing electricity with relatively inexpensive prices than that of other kinds of energy. However, the construction costs of nuclear power plants are very expensive and it is a potential threat for human health and the environment. Different arguments on how nuclear power plants might contribute to peace or threaten it are analysed. The analysis is done through Johan Galtung’s articles “Violence, Peace, and Peace Research” and “Cultural Violence”, as well as by recalling few known nuclear accidents as example, mainly the one happened at the Chernobyl nuclear power plant. Cooperation of different stakeholders at national, regional, and international level is among the most important tools to minimise the possibility of nuclear threat to peace. Nuclear waste and the uncertainties in best practices for the safe management is most probably the most severe problem that future generations will have to face.

The United States plans to bury high level radioactive waste from commercial power reactors and from nuclear weapons manufacturing in Yucca Mountain, Nevada. Yucca Mountain, located about 80 miles northwest of Las Vegas, consists of horizontally bedded tuff deposits. Although the region is very arid, enough water exists in the tuffs to create a vapor dominated geothermal system as the pore water evaporates, circulates and recondenses. This study examines how silica leaching might occur as a result of water-tuff interactions in Yucca Mountain after the emplacement of heat-producing nuclear waste canisters. A vertical thermal gradient experiment (VTGE) was designed and built in order to simulate the water cycling scenario where water in the tuff is vaporized by the heat from the canisters, moves to cooler regions along fractures and condenses as a liquid which flows downward toward the hot canisters. This experiment was used to measure the rate of silica leaching from Yucca Mountain tuff at various heat fluxes. The results show that under the experimental conditions silica is leached from the tuff sample very effectively (about 1.85 x 10 -8 g per Joule of heat transferred). With such a rate, significant amount of amorphous silica (135 kg per canister for the first 1,000 years after emplacement) could be leached, transported and deposited above the repository horizon; the resulting low permeability zone might change the geological and hydrological properties of the host rock. A significant amount of colloidal silica was formed in the solution soon after the water recycling began. Such colloidal silica could adsorb and transport radionuclides released from breached waste canisters more efficiently than that when radionuclides act alone. The results indicate that silica leaching is a potential problem for the current designs of the Yucca Mountain repository. / Master of Science

The thesis deals with nuclear waste deep repositories in the law. With exception of long- term storage the nuclear waste deep repositories represent the only technical solution currently available to deal with the increasing volume of highly radioactive waste and spent nuclear fuel. The planning and construction of nuclear waste deep repository entails number of problems and challenges, both from technical and legal perspectives. The thesis aims to describe current legislation regarding the management of radioactive waste and spent nuclear fuel within the territory of the Czech Republic with a particular focus on planning and construction of a nuclear waste deep repository. There is step by step described procedure of planning and constructing a nuclear waste deep repository under the current legislation. Within this description the author evaluates the current legislation and identifies its major issues. Subsequently, the author reflects on the cause of these issues and proposes their solutions.