bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigations of Fracture Zones in Crystalline Rock by Borehole Radar
Authors: Olsson Olle , Falk Lars , Forslund Olof , Lundmark Lars , Sandberg Eric 
Published: March 2011

AbstractA borehole pulse radar system has been developed as part of the International Stripa Project with the objective to identify and characterize fracture zones at a considerable distance from boreholes. The radar uses very short pulses, which are transmitted and received by dipole antennas inserted into the boreholes. The pulses are extremely broadband with center frequencies of 25–60 MHz corresponding to wavelengths of a few meters in the rock. At 25 MHz the attenuation in the Stripa granite is 28 dB/100 m and the pulse velocity is approximately 128 000 km/s. Reflection measurements have been used to identify fracture zones and determine their position and orientation. The zones often cause strong and well-defined reflections. Improvements in the pulse form and numerical filtering of the data have consequently made the radar a very efficient instrument for locating fracture zones. During measurements in Stripa reflections from fracture zones have been observed more than 100 m from the borehole.
The Role of Groundwater Oxidation Potential and Radiolysis on Waste Glass Performance in Crystalline Repository Environments
Authors: Jantzen Carol M. , Bibler Ned E. 
Published: March 2011

AbstractLaboratory experiments have shown that groundwater conditions in a granite repository will be as reducing as those in a basalt repository. Chemical analysis of the reduced groundwaters confirmed that the Fe2+/Fe3+ couple controls the oxidation potential (Eh). The reducing groundwater conditions were found to decrease the time-dependent release of soluble elements (Li and B) from the waste glass. However, due to the lower solubility of multivalent elements released from the glass when the groundwaters are reducing, these elements have significantly lower concentrations in the leachates.Gamma radiolysis reduced the oxidation potential of both granitic and basaltic groundwater in the absence of both waste glass and oxygen. This occurred in tests at atmospheric pressure where H2 could have escaped from the solution. The mechanism for this decrease in Eh is under investigation but appears related to the reactive amorphous precipitate in both groundwaters. The results of these tests suggest that radiolysis may not cause the groundwaters to become oxidizing in a crystalline repository when abundant Fe2+ species are present.
Intergranular Films and Pore Surfaces in Synroc C
Authors: Myhra S. , Segall R. L. , Smart R. ST. C. , Turner P. S , White T. J. 
Published: March 2011

AbstractHigh resolution electron microscopy and scanning electron microscopy were used to determine the distribution of intergranular films and microvoids in Synroc C. Diffraction contrast derived from these films, which were 1–3 nm thick, showed then to be ill-defined crystallographically, and they may be described as glassy. Pores were usually several micrometers in extent and occurred principally in rutile-rich areas. The chemical composition of these structural features was obtained using analytical transmission electron microscopy, secondary ion mass spectrometry, x-ray photoelectron spectroscopy and scanning Auger microscopy. Within intergranular films, elemental enhancement of cesium, sodium, potassium and aluminium, and possibly silicon and molybdenum was observed. Enhancement of cesium, sodium, phosphorous, aluminium and silicon was found at triple points. Fracture faces preferentially expose grain boundaries, and dissolution of these surfaces proceeds rapidly at ambient temperatures. During the fabrication of Synroc C, microvoids trap cesium vapour, and after cooling this condenses onto pore surfaces. Recognition of the (simulated) waste species which segregate at grain boundaries and pores, permitted the reinterpretation of published leach data for monolithic and crushed Synroc C.
The Corrosion of Spent UO2 Fuel in Synthetic Groundwater
Authors: Forsyth R. S. , Werme L.O. 
Published: March 2011

AbstractLeaching of high burnup BWR fuel for up to 3 years showed that both U and Pu attain saturation rapidly at pH 8.1, giving values of 1–2 mg/l and 1 μg/l respectively. The leaching rate for Sr-90 decreased from about 10−5/d to 10−7/d but was always higher than the rates for U, Pu, Cm, Ce, Eu and Ru. Congruent dissolution was only attained at pH values of about 4.The hypothesis that alpha radiolytic decomposition of water is a driving force for UO2 corrosion even under reducing conditions has been examined in leaching tests on low burnup (low alpha dose-rate) fuel. No significant effect of alpha radiolysis under the experimental conditions was detected.
Derivation of a Waste Package Source Term for NNWSI from the Results of Laboratory Experiments
Authors: Oversby Virginia M. , Wilson Charles N. 
Published: March 2011

AbstractResults are presented for the dissolution of Turkey Point pressurized water reactor (PWR) spent fuel in J-13 well water at ambient hot cell temperatures. These results are compared with those previously obtained on Turkey Point fuel in deionized water, on H. B. Robinson PWR fuel in J-13 water, and by other workers using various fuels in dilute bicarbonate groundwaters. A model is presented that represents the conditions under which maximum dissolution of spent fuel could occur in a repository sited at Yucca Mountain, Nevada. Using an experimentally determined upper limit of 5 mg/l for uranium solubility in J-13 water, a fractional release rate of 6.4 × 10−8 per year is obtained by assuming that all water entering the repository carries away the maximum amount of uranium.
Radiation Damage in Natural Titanite by Crystal Structure Analysis
Authors: Fleet M. E. , Henderson G. S. 
Published: March 2011

AbstractStudy of radiation damage in natural titanite (CaTiSiO5) permits estimation of the long-term performance of titanite-bearing glass ceramics in the immobilization of radioactive waste. Single-crystal X-ray structure analyses have been made on two geologically old, U, Th-bearing titanites (sphenes), on an undamaged gem-quality titanite and on their annealed equivalents. The alpha-damaged titanite crystal structure is characterized by a marked increase in magnitude of the apparent thermal parameters of all structural positions, reflecting a general increase in positional disorder. The ratio of observed structure factors (F0-damaged/F0-annealed) may be used to estimate the overall structural damage.
Alpha-Radiolysis of Aqueous Solutions
Authors: Christensen Hilbert , Bjergbakke Erling 
Published: March 2011

AbstractThe effects of the radiolysis of water exposed to mixed alpha- and beta-radiation originating from spent fuel have been calculated. The water is assumed to have penetrated the copper canister and fuel cladding, and then to exist as a 30 μm thin surface film on the fuel pellets.The combined effects of alpha and beta-radiation, and the presence of iron in the water have been found to be important parameters. The beta-radiation will lower the yield of hydrogen, as will the presence of low concentrations of iron ions. The most likely conditions for water exposed fuel give rise to a total production of 1 mol H2per m2fuel surface after 1 million years. A stoichiometric amount of oxygen is also formed.Calculations have also been carried out in connection with experiments on alpha-radiolysis from Am-241 or from spent fuel pellets. In the case of alpha-radiolysis from Am-241 it was calculated that a 20 cm2thin layer of 4 mCi Am-241 produced 1.4 × 10−3cm3hydrogen per day.Calculations simulating the conditions of experiments on the leaching of spent fuel have shown that both alpha- and gamma-radiation accelerate the dissolution. The rate is strongly dependent on the dose rate and on the area of the water film covering the fuel surface and fuel fissures.
Corrosion Rate of Unalloyed Steels and Cast Irons in Reducing Granitic Groundwaters and Chloride Solutions
Authors: Simpson J. P. , Schenk R. , Knecht B. 
Published: March 2011

AbstractMeasurements of the corrosion rate of unalloyed steel have been made under conditions representative for repositories in the granitic bedrock of Northern Switzerland using two independent methods: (1) Immersion tests in two representative groundwaters, with and without bentonite; (2) Hydrogen evolution measurements in these groundwaters. The immersion tests were carried out at 80°C and 140°C. In both cases the corrosion rate was higher than 50 μm/a as determined at the end of the first observation period of about 500 h. Corrosion rates of under 10 μm/a were estimated after the first 500 h. The corrosion rates were similar in both groundwaters with mineralisations of approx. 3 g/11 and 14 g/11 respectively, and were generally higher at 80°C than at 140°C. The hydrogen evolution measurements allow an hourly determination of the corrosion rate, with a sensitivity expressed as a corrosion rate of better than 0.1 μm/a. The results generally confirm the observation made in the immersion testing; high corrosion rates were observed over the first few days but then decreased to values well below 10 μm/a. The steady state corrosion rates measured were 1.1 μm/a, 6.5 μm/a, and 2.5 μm/a at 25°C, 50°C, and 80°C respectively in the water with the higher mineralisation. The inverse temperature effect on corrosion rate above 50°C is attributed to a change in the nature of the passive film at higher temperatures.
Geochemical Modelling of the Alteration of a Granitic Rock Around a Repository for Spent Nuclear Fuel
Authors: Fritz Bertrand , Kam Marie , Tardy Yves 
Published: March 2011

AbstractThe alteration of a granitic rock around a repository for spent nuclear fuel has been simulated considering the geothermal effect through an increase of temperature. The results of the simulation were considered in terms of mass transfers and their volumic consequences. The dissolution of primary minerals by alteration tends to increase the porous volume due to fissures and cracks, while the precipitation of secondary minerals and particularly here calcite and clay minerals will tend to decrease the porosity by sealing the cracks. The results of the simulations show that an increase of temperature from 10 to 100°C will favour the alteration of the granitic rock by the solutions circulating today in the rock. This rock is characterized by a very low fissure porosity and the water velocity is consequently particularly low. These conditions favour intense water-rock interactions and the water-rock system will probably reach the stability field of secondary clay minerals predicted by the calculations: the porosity will decrease. A combination of these thermodynamic mass balance calculations and hydrodynamic considerations, with a kinetic approach of mineral dissolutions gives a first attempt to calibrate the modelling in the time scale.
Diffusion Mechanisms of Strontium, Cesium and Cobalt in Compacted Sodium Bentonite
Authors: Muurinen Arto , Rantanen Juha , Penttilä-Hiltunen Pirkko 
Published: March 2011

AbstractFor a porous water-saturated material where diffusion in the pore water, sorption on the solid material and diffusion of the sorbed ions (surface diffusion) occur, a diffusion equation can be derived where the apparent diffusivity includes two terms. One represents diffusion in the pore-water, the other surface diffusion.In this research diffusion mechanisms were studied. The apparent diffusivities of strontium, cesium and cobalt in compacted sodium bentonite were measured by a non-steady state method. The sorption factors were adjusted using different sodium chloride solutions, groundwater and addition of EDTA for saturation of the bentonite samples. The corresponding sorption factors were measured by a batch method.The results suggest that cations diffuse also while being sorbed. A combined pore diffusion-surface diffusion model has been used to explain the transport and the corresponding diffusivities have been evaluated. The surface diffusivities (Ds) of Sr and Cs were 8-9·10-12 m2/s and 4-7·10-13 m2 /s respectively. The pore diffusivity eD of Cs was 3.5.10-11 m2 /s which has been used also for Sr.The sorption mechanism of Co seems to be different from that of Sr or Cs and the results allow no specific conclusions of the diffusion mechanism of Co. The apparent diffusivity of Co ranged from 2·10-14 to 7·10-14 m2/s.The anionic Co-EDTA seems to follow some other diffusion mechanism than the cations.
The Solubility of Actinides in the Near-Field
Authors: Ewart F. T. , Howse R. M. , Thomason H. P. , Williams S. J. , Cross J. E. 
Published: March 2011

AbstractThe solubility of some of the radiologically important actinide elements have been determined in a water whose chemistry was representative of that believed to exist in potential repositories in the U.K. The solubilities of the actinides have been determined as a function of the pH of the water. The results of these experiments have been compared with the results of predictions made using the PHREEQE geochemical modelling code in order to test and validate the data base used in the model. In the light of these comparisons, suggestions are made for alternative values for the thermodynamic data and for further studies.
Mechanical Behaviour of Host Rock Close to H.L.W. Disposal Cavities in a Deep Granitic Formation
Authors: Hoorelbeke J. M. , Dourthe M. 
Published: March 2011

AbstractThe construction of a H.L.W. repository in a deep granitic formation creates mechanical disturbances in the rock on the scale of the massif and in the nearfield. Amongst all the disturbances noted in the nearfield, this study is concerned with examining the evolution of stresses linked with the excavation of the rock and the rise in temperature in the proximity of the waste packages. Several linear elasticity calculations were made using on the one hand finite element models and on the other simple analytical models. These calculations concern two different storage concepts -“in room” concept and “in floor” concept- whose differences in mechanical behaviour are analysed. A study of sensitivity with regard to the characteristics of the rock and to the initial geostatic stresses is presented. The comparison of the calculated stresses with three-dimensional failure criteria gives a clear indication of the satisfactory behaviour of granite for final storage. However, the need for experimental study and complementary calculation must be emphasised.
Numerical Calculation of the Time and Space Dependent Temperature Distribution in a HLW Repository of Finite Extension and Temporal Step-by-Step Disposal Procedure
Authors: Hahne K. , Schlich M. , Korthaus E. 
Published: March 2011

AbstractWith the program system FAST-STEP the temporal step-by-step disposal procedure of a HLW repository and its finite geometry can be taken into consideration in the calculation of the time and space dependent temperature distribution. This will be obtained through the application of a suitable coupling of calculation models treating both far field and near field phenomena.After the description of the single steps of the program system the influence of both aspects on the temperature distribution will be demonstrated with the aid of a test calculation. The possible fields of application of FAST-STFP will be pointed out at the end.
Overheating In Silicon During Pulsed-Laser Irradiation?
Authors: Larson B. C. , Tischler J. Z. , Mills D. M. 
Published: March 2011

ABSTRACTNanosecond resolution time-resolved x-ray diffraction measurements of thermal strain have been used to measure the interface temperatures in silicon during pulsed-laser irradiation. The pulsed-time-structure of the Cornell High Energy Synchrotron Source (CHESS) was used to measure the temperature of the liquid-solid interface of <111> silicon during melting with an interface velocity of 11 m/s, at a time of near zero velocity, and at a regrowth velocity of 6 m/s. The results of these measurements indicate 110 K difference between the temperature of the interface during melting and regrowth, and the measurement at zero velocity shows that most of the difference is associated with undercooling during the regrowth phase.
Time-Resolved Reflectivity Measurements of Silicon And Germanium Using A Pulsed Excimer Laser
Authors: Jellison G. E. , Lowndes D. H. , Mashburn D. N. , Wood R. F. 
Published: March 2011

ABSTRACTTime-resolved reflectivity measurements of silicon and germanium have been made during pulsed KrF excimer laser irradiation. The reflectivity was measured simultaneously at both 1152 and 632.8 nm wavelengths, and the energy density of each laser pulse was monitored. The melt duration and the time of the onset of melting were measured and compared with the results of melting model calculations. For energy densities just above the melting threshold, it was found that the melt duration was never less than 20 ns for Si and 25 ns for Ge, while the maximum reflectivity increased from the value of the hot solid to that of the liquid over a finite energy range. These results, along with a reinterpretation of earlier time-resolved ellipsometry measurements, indicate that, during the melt-in process, the near-surface region does not melt homogeneously, but rather consists of a mixture of solid and liquid phases. The reflectivity at the onset of melting and in the liquid phase have been measured at both 632.8 and 1152 nm, and are compared with the results found in the literature.
Raman Microprobe Analysis of Laser-Induced Microstructures
Authors: Fauchet P. M. 
Published: March 2011

ABSTRACTWe study the composition, stress and structure variations across periodic surface undulations produced by pulsed laser illumination of semiconductors, by explosive crystallization of amorphous films, and by laser-assisted CVD. These variations are mapped out with a one micron spatial resolution using a Raman microprobe. Similarities and differences between the three cases are pointed out. These results are also compared to those obtained by deliberately exposing the sample to interfering beams.
Pulsed Co2 Laser Induced Melting and Nonlinear Optical Studies of GaAs
Authors: James R. B. , Christie W. H. , Mills B. E. , Burcham H. L. 
Published: March 2011

ABSTRACTWe report new optical and structural properties of p-type GaAs that result from the absorption of high-intensity 10.6 μm radiation. Prior to the onset of surface melting, we find that the absorption coefficient decreases with increasing intensity in a manner predicted by an inhomogeneously broadened two-level model. As the energy density of the CO2 laser radiation is increased further, the surface topography shows signs of melting, formation of ripple patterns, and vaporization. Auger spectroscopy and electron-induced x-ray emission show that there is loss of As, compared to Ga, caused by the melting of the surface. Using plain-view TEM we find that Ga-rich islands are formed near the surface during the rapid solidification of the molten layer. Auger and SIMS measurements are used to study the incorporation of oxygen in the near-surface region, and the results show that oxygen incorporation can occur for GaAs samples that have been irradiated in air.
In Situ Time-Resolved Reflectivity Measurements of Growth Kinetics During Solid Phase Epitaxy: A Tool To Estimate Interface Non Planarity During Growth
Authors: Licoppe C. , Nissim Y.I. 
Published: March 2011

ABSTRACTThe time resolved reflectivity technique is shown to give informations on the amorphous-crystalline interface evolution during solid phase epitaxial (SPE) regrowth in semiconductors. Two specific cases have been treated here. The first case is encountered in laser annealing when the growth front exhibits a curvature due to the combination of an inhomogeneous temperature distribution and a steep dependence of SPE growth rates with temperature. A computer simulation is carried out from an analytical determination of the laser induced temperature profiles to shape up the resultinq reflectivity signal. The second case is obtained when there is an evolution of interface roughness during regrowth. In order to simulate this effect a simple model is developed to treat the influence of diffusion of the reflected light at the interface, on the reflectivity modulation during SPE regrowth.
Formation of AlxGa1-xAs Alloy on the Semi-Insulating GaAs Substrate by Laser Bean Interaction
Authors: Joshi N. V. , Lehman J. 
Published: March 2011

ABSTRACTAlxGal-xAs alloy was obtained on semi-insulating GaAs by laser beam interaction. For this purpose, thin layers (~150 A) of AlAs and GaAs were deposited by MICVD on the semi-insulating undoped GaAs substrate and irradiated with a high power laser beam. For a certain critical value of incident power (7.1 watts/mm2), a layer of AlxGal-xAs alloy was formed. The nature of the alloy was examined by Auger and Far infrared reflectance spectroscopy. The later technique reveals the characteristic mode of AlxGal-xAs confirming its formation. Disorder induced LA mode was also observed.
Time-Resolved Spectroscopy of Plasma Resonances In Highly Excited Silicon And Germanium
Authors: Malvezzi A. M. , Huang C. Y. , Kurz H. , Bloembergen N. 
Published: March 2011

ABSTRACTThe dynamics of the electron-hole plasma in silicon and germanium samples irradiated by 20 ps, 532 nm laser pulses has been investigated in the near infrared by time-resolved picosecond optical spectroscopy. The experimental reflectivities and transmissions are compared with the redictions of the thermal model for degenerate carrier distributions through the Drue iformalism. Above a certain fluence, a significant deviation between measured and calculated values indicates a strong increase of the recombination rate as soon as the plasma resonances become comparable with the band gaps. These new plasmon-aided recombination channels are particularly pronounced in germanium.
Dynamics of Elementary Processes At Surfaces: Nitric Oxide Scattered From A Graphite Surface
Authors: Vach H. , Häger J. , Simon B. , Flytzanis C. , Walther H. 
Published: March 2011

ABSTRACTMolecular beam scattering from solid surfaces has long been recognized as a powerful means for investigation of gas-surface reaction dynamics. With the help of the recently developed laser-induced fluorescence and ionization techniques for state-selective detection, one can now measure the angular and velocity distributions of the scattered molecules together with their internal energy distributions. Such measurements fully describe the average energy and momentum exchanges between molecules and surfaces and give thus full information on the dynamics of the interaction. Recently, also the scattering of vibrationally excited NO molecules was investigated. The paper gives a review of new experiments with emphasis on the investigation of the scattering of NO molecules from a pyrographite surface. A simple model using transport properties of the solid is presented which accounts surprisingly well for the observed features.