bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neptunium Solubility in the Near-Field Environment of a Proposed Yucca Mountain Repository
Authors: Sassani David C. , Van Luik Abraham , Summerson Jane 
Published: April 2011

ABSTRACTFor representing the source-term of a proposed repository at Yucca Mountain, NV, the performance assessment (PA) approach evaluates the disequilibrium degradation of the waste forms to capture a bounding rate for radionuclide source-term availability and use solubility constraints that are more representative of longer-term, equilibrium processes to limit radionuclide mass transport from the source-term. These solubility limits capture precipitation processes occurring either as the waste forms alter, or in the near-field environment as chemical conditions evolve. A number of alternative models for solubility controls on dissolved neptunium concentrations have been evaluated. These alternatives include idealized models based on precipitation of simple, discrete neptunium phases and more complex considerations of trace amounts of neptunium being incorporated into secondary uranyl phases that form during waste form alteration. Thermodynamic constraints for neptunium under oxidizing conditions indicate that tetravalent neptunium solids (e.g., NpO2) are more stable relative to pentavalent phases (e.g., Np2O5), and therefore have solubilities that set lower dissolved concentrations of neptunyl species. Within solution, the pentavalent neptunyl ion (NpO2+) and its complexes dominate. Data on solids and solutions from slow flow-through (dripping) tests on spent nuclear fuel (SNF) grains indicate that neptunium is tetravalent in the SNF and that, over the ∼9 years duration of the tests, the dissolved neptunium concentrations are near to, or below, calculated NpO2 solubility. Currently, the NpO2 solubility model is applied at the waste forms within waste packages because the degradation of SNF and corrosion of alloys ensures active reduction reactions. The more conservative Np2O5 solubility model is applied in environments distal to the waste forms (i.e., the invert below waste packages) where reduction of dissolved pentavalent neptunium is less certain. Consideration of Np incorporation into secondary uranyl phases suggests that both of these idealized models will provide conservative estimates of neptunium release to the geosphere.
Modeling of Groundwater Flow and Radionuclide Transport in a High-Level Radioactive Waste Repository with Multiple Canisters
Authors: Lim Doo-Hyun 
Published: April 2011

ABSTRACTA two-dimensional numerical model incorporating a multiple-canister configuration and a non-uniform flow field of the host rock is developed for more reliable performance assessment of a water-saturated high-level radioactive waste repository. A space-dependent flow velocity distribution is established numerically using the finite-element method. Transport of Cs-135 is simulated using the random-walk method. Numerical results for a source condition of instantaneous-pulse-input show that (i) migration of Cs-135 is influenced significantly not only by the canister configurations but also by flow boundary conditions, ii) effect of applied hydraulic gradient direction on Cs-135 migration becomes more significant as the number of canisters increases, while the effect is negligible for a single-canister configuration, (iii) the direction of the hydraulic gradient orthogonal to the orientation of the disposal tunnel is most advantageous with respect to the isolation of the radionuclide, and (iv) the single-canister configuration yields conservative results compared with multiple-canister configurations.
Studies on Sealing Performance of Clay Plug by the Tunnel Sealing Experiment
Authors: Kawakami S. , Fujita T. , Masumoto K. , Yui M. 
Published: April 2011

ABSTRACTTo establish sealing performance suitable for geological environmental conditions of Japan, it is necessary to obtain basic data related for the sealing function through laboratory and in-situ experiments. These data are to be used for practical design and to establish the method for analysis of the sealing performance.Japan Nuclear Cycle Development Institute (JNC) has joined the international project, the Tunnel Sealing Experiment (TSX), to demonstrate the sealing performance of full scale plugs in-situ, and to develop analytical method of the sealing performance of the plugs at Underground Research Laboratory (URL) of Atomic Energy of Canada Limited (AECL) in Canada [1]. This experiment is in the final stage and fundamental data for the sealing function of clay and concrete plugs have been obtained.This paper presents the total data handling and interpretation of the sealing experiment, as well as the numerical analysis and interpretation for clay plug performance based on tracer test results. As a result of the numerical analysis, the sealing performance of the clay plug was confirmed and it was shown that the excavation disturbed zones (EDZ) around the clay plug and the tunnel could be a dominant transport pathway for radionuclides.
IAEA's Coordinated Research Programmes on Performance of High Level Wastes in Deep Geological Repositories
Authors: Gonzalez J.L. , Iseghem P. Van 
Published: April 2011

ABSTRACTThe main conclusions of a Coordinated Research Programmes organized by the International Atomic Energy Agency on the performance of high-level wastes in deep geological repositories are summarized in this paper. The programme ran from 1997 till 2004. Glass, spent fuel and ceramics were the waste forms considered. The 13 participating countries reported their R&D including waste form development, basic understanding of the waste form properties and the performance in simulated disposal conditions. Significant progress has been achieved on the various issues. Recommendations are formulated as to integrate the R&D with the geological disposal conditions and performance assessment considerations, or to conceive generic studies in preparation of the above approach.
Effects of the Orientation of Clay Particles and Ionic Strength on Diffusion and Activation Enthalpies of I−and Cs+Ions in Compacted Bentonite (II)
Authors: Sato Haruo 
Published: April 2011

ABSTRACTThe apparent diffusivities (Da) and activation enthalpies (ΔEa) for I−and Cs+ions in compacted Na-smectite were obtained in the parallel and perpendicular directions to the orientation of smectite particles as a function of smectite's dry density (0.9-1.4 Mg/m3), salinity ([NaCl]=0.01, 0.51 M) and temperature (295-333 K). TheDa-values for both ions tended to be higher in the parallel direction than in the perpendicular direction to the orientation of smectite particles. TheDa-values of I−ions in the parallel direction decreased with increasing salinity only at low dry density, but those of Cs+ions increased with increasing salinity for all conditions. Based on this, it is interpreted that I−ions predominantly diffuse in external pores and Cs+ions diffuse in both interlayer and external pores. The ΔEa-values forI−ions are at similar levels as those for the ionic diffusivity in free water (D°) of I−ions at low dry density and increased with increasing dry density. The ΔEa-values for Cs+ions are higher than those for theD° of Cs+ions even at low dry density and increased with increasing dry density. Such high ΔEa-values for Cs+ions are considered to be due to the combined effects of the ion exchange enthalpy between Cs+and Na+ions in smectite and the lowering in the activity of porewater.
Prediction of Long Term Corrosion Behaviour in Nuclear Waste Systems
Authors: Féron Damien , Macdonald Digby D. 
Published: April 2011

ABSTRACTThe corrosion resistance of container materials in underground repositories is an important issue for the safe disposal of High Level Nuclear Waste (HLNW). The reliable prediction of container degradation rate and engineering barrier integrity over extended periods, up to several thousands years or even several hundreds of thousands of years, represents one of the greatest scientific and technical challenges. The first and the second International Workshops on Prediction of Long Term Corrosion Behaviour in Nuclear Waste Systems, which were held in 2001 (Cadarache) and 2004 (Nice), sought to compare the scientific and experimental approaches that are being developed in various organisations worldwide for predicting long term corrosion phenomena, including corrosion strategies for interim storage and geological disposal. The lessons learned during these Workshops, include the necessity of developing two approaches based on semi-empiricism and determinism in a complementary manner for effective prediction. The use of archaeological artefacts to demonstrate the feasibility of long term storage and to provide a database for testing and validating modelling work was also emphasized.
Probing the Water Phases and Microstructure in a Model Cement Blend Matrix used for the Encapsulation of Intermediate Level Nuclear Wastes
Authors: Gorce Jean-Philippe , Milestone Neil B. , Mcdonald Peter J. 
Published: April 2011

ABSTRACTThe changes in microstructure and content of water phases during hydration of a 3:1 BFS:OPC blend are investigated by Mercury Intrusion Porosimetry (MIP), freeze-drying, Thermal Gravimetric Analysis (TGA) and 1H Nuclear Magnetic Resonance (NMR) relaxometry. MIP indicates that during the blend hydration, a reduction in the population of capillary pores (larger than about 100 nm) occurs while the population of gel pores (smaller than few tens of nanometres) increases. Between 3 and 90 days, the porosity estimated by MIP decreases from about 36% down to 18% while the median pore size decreases from about 140 nm down to 6 nm.1H NMR relaxometry shows that after 1 day of hydration, nearly 70% of the evaporable water is held in capillary pores while about 30% is present in gel pores. After two weeks, most of the evaporable water (90%) is found in pores smaller than few tens of nanometres.The amount of evaporable water detected by freeze drying decreases from less than 20 wt.% after one week of hydration down to about 16.3 wt.% after 90 days while the amount of chemically bound water related to the degree of advancement of the cement hydration and detected by TGA increases from 8 wt.% to 10.3 wt.%.During hydration the BFS:OPC blend matrix evolves from an open microporous network to one of a poorly connected network of water rich nanopores with increasing amounts of chemically bound water.
Sodium Sulphate Activated GGBS/PFA and Its Potential as a Nuclear Waste Immobilisation Matrix
Authors: Bai Yun , Milestone Neil B. , Yang Changhui 
Published: April 2011

ABSTRACTThe UK currently uses Portland cement composite blends to immobilise/encapsulate intermediate and low level radioactive wastes (ILW and LLW). However, among other things, the high pH of these systems causes the corrosion of some metals, which can lead to expansion and excess generation of hydrogen. Therefore, in order to immobilise nuclear waste where corrosion is an issue, a near neutral cementing system is desirable.Among the activators which can be used in the alkali-activated slag (AAS) systems, a solution of Na2SO4 is near neutral but the ground granulated blast-furnace slag (GGBS) itself has a pH about 11, increasing the pH within the Na2SO4 activated AAS. As low calcium Pulverized Fuel Ash (PFA) only has a pH about 9, using a GGBS/PFA blend activated by Na2SO4 offers the potential to develop a near neutral cementing system for nuclear waste immobilisation purposes.In this paper, the replacement of GGBS in the Na2SO4 activated AAS system with PFA at 0%, 10%, 20% and 30% by mass was examined. The pH and corrosion of Al were determined and used as primary criteria for judging the feasibility for further development of a Na2SO4 activated GGBS/PFA matrix for immobilising nuclear wastes. The microstructure of the matrices was studied by SEM. Leaching studies were carried out to examine the possibility of immobilising Cs+ within these Na2SO4 activated GGBS/PFA matrices. The potential of using Na2SO4 activated GGBS/PFA for immobilising nuclear wastes is discussed.
Kinetics of Mixed Low-Level Waste Incapsulation Using Iron Phosphate Chemically Bonded Cement
Authors: Aloy A.S. , Koltsova T.I. , Kovarskaya E.N. , Silin M.Yu. 
Published: April 2011

ABSTRACTThe iron phosphate cement (IPC) structure formation process has been studied by Mossbauer spectroscopy. The IPC is formed as a result of interaction of iron oxides with orthophosphoric acid and could be used as a matrix for immobilization of low-level radioactive waste.The structural formation process has been shown may be considered to consist of two stages. The first stage lasts to the moment of setting, when the diffusion process goes on in the liquid phase. At this stage the main fragments of the structural polymeric frame of the IPC are developed consisting of iron (+2) and (+3) phosphates. The rate of the oxides-with-phosphoric-acid reaction as well as the time of hardening depends on the bivalent iron content.The second stage begins from the moment of setting when the diffusion becomes slower. At this stage the process is characterized by the negligible increase in the iron phosphates (+2), (+3) content and transformation of the previously formed phosphates.The nuclear gamma-resonance (NGR) parameters have been determined of FeH3(PO4)2·2.5H2O, forming in the hematite (Fe2O3) based IPC: isomeric shift (IS) = 0.46 mm/s, quadrupole splitting (QS) = 0.197 mm/s, FWHM =0.282 mm/s.
Reactions in Cemented Nuclear Waste forms – the Need for a Toolbox of Different Cement Types
Authors: Milestone Neil B , Bai Yun , Borges Paulo R , Gorce Nick C Collier Jean-Phillipe , Gordon Laura E , Setiadi Anthony , Utton Claire A , Zhou Qizhi 
Published: April 2011

ABSTRACTEncapsulation of low and intermediate level waste (LLW and ILW) into a monolithic waste form is a key method for preparing such wastes for storage and ultimate disposal. One of the most efficient ways of doing this is by cementation, successfully used for much of today's operational waste in the UK. Formulations are based on composite cements where high levels ofpulverised fuel ash or blast furnace slag replace ordinary Portland cement (OPC). These provide cementing systems with good fluidity, lowered heat of hydration and a matrix with lower porosity and permeability. Further the alkaline hydrated calcium silicate matrix ensures insolubility of many metal hydroxides and hydrated oxides. Dealing with historic or legacy wastes presents a challenge as for many, a suitable cementing formulation has yet to be devised. To achieve ultimate durability, likely interactions between the waste and the cementing matrix need to be well understood when choosing the cement system to be used. The alkaline OPC based matrix causes corrosion with metals such as Al and Mg and porous silicates and layered metal hydroxides used to selectively remove radionucleides react in the alkaline environment, potentially releasing the adsorbed species. Slurries of materials normally considered inert show interactions within the OPC composite systems, although these are not considered detrimental for durability. This paper describes the chemistry of some interactions that occur within OPC composite cements. It also details some results for alternative cementing systems that may provide a toolbox of cement types that may address many of the interaction issues. These include calcium sulphoaluminate cements, inorganic polymers or geopolymers, and activated slag systems.
Crystal Chemistry and Cation Ordering in Zirconolite 2M
Authors: Lumpkin G.R. , Whittle K.R. , Howard C.J. , Zhang Z. , Berry F.J. , Oates G. , Williams C.T. , Zaitsev A.N. 
Published: April 2011

ABSTRACTStructural studies of single phase or nearly single phase zirconolite ceramic samples have been conducted using electron microscopy and microanalysis, X-ray diffraction, neutron diffraction, and spectroscopic methods. We show that it is possible to produce a complete series of zirconolite 2M samples with substitution of 2Ti by Nb+Fe in the HTB layer. The samples are single phase up to about 80% Nb +Fe substitution, with the appearance of a minor perovskite phase at higher Nb+Fe levels. Electron probe microanalysis reveals that the samples are homogeneous and close to their nominal compositions, except for those containing perovskite, which have a slight excess of Zr and a deficiency in the Fe content. The lattice parameters and the positions of certain Raman bands are non-linear as a function of composition, suggesting the possibility of cation ordering over the three available Ti sites within the HTB layer. Rietveld refinement of Synchrotron X-ray powder data for the Nb+Fe end-member have been conducted for the disordered case and for six trial models each with a different ordering scheme. Results of this exercise indicate that Fe preferentially occupies the Ti2 (split) site with partial ordering of Nb and the remaining Fe over the Ti1 and Ti2 octahedra. The preference of Fe for the five coordinated Ti2 site has been confirmed by 57Fe Mossbauer spectroscopy.
Composition driven structural phase transitions in the (Y1−xLax)2Ti2O7 system
Authors: Harvey Elizabeth J. , Ashbrook Sharon E. , Lumpkin Gregory R. , Redfern Simon A.T. 
Published: April 2011

ABSTRACTThe structural characteristics of samples in the (Y1−xLax)2Ti2O7 system have been studied as a function of bulk composition using time-of-flight (TOF) powder neutron diffraction, powder X-ray diffraction (XRD), Electron Microscopy and 89Y (I = ½) Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). Analysis of the neutron diffraction data suggests the following: For compositions where 0 ≤ x ≤ 0.132, a single cubic phase is present (Fd3, m, Z = 8). Between 0.832 ≤ − ≤ 1, a solid solution with the La2Ti2O7 structure (P21, Z = 4) forms. The two phases coexist between x values of 0.132 and 0.832. XRD suggests that the limits of the two regions of solid solution fall within the ranges of x = 0.1-0.125 and x = 0.875-0.9. The variation in the limits found by the two diffraction methods may be due to stoichiometric errors in the samples. Line-shape analysis of NMR spectra for Y rich compositions suggests that increasing proportions of La are incorporated onto the pyrochlore A site in a statistically random manner, up to the limit of solid solution. The NMR spectra of the monoclinic phase suggest that occupation of the four crystallographically distinct ‘A’ type sites within the structure is not random. At low Y concentrations, two of these sites are preferentially occupied by Y. These sites are suggested to be those found at the edge of the perovskite slabs, which exhibit smaller coordination numbers (based on the number of oxygens within bonding distance of the ‘A’ type cation) than the true perovskite A sites found at the slab centres.
Phase Relations In The Systems Based On Yttrium, Gadolinium, Manganese, Titanium, and Uranium Oxides Doped with Calcium, Aluminum and Iron Oxides
Authors: Stefanovsky Sergey V. , Stefanovsky Olga I. , Yudintsev Sergey V. , Nikonov Boris S. 
Published: April 2011

ABSTRACTTitanate-based ceramics with yttrium, gadolinium, manganese, uranium, calcium, aluminum, and iron oxides being of interest as matrices for radioactive wastes containing lanthanides, actinides and corrosion products were synthesized using cold pressing and sintering and melting routes. Major constituents of the ceramics are fluorite structure phases (pyrochlore, “murataite”, cubic oxide with fluorite-related lattice) as well as brannerite. Incorporation of aluminum and iron oxides (corrosion products) forms second phases with perovskite or/and crichtonite structure.
Phase composition of the ceramics based on Rare Earth, Manganese and Titanium Oxides
Authors: Stefanovsky S.V. , Yudintsev S.V. , Nikonov B.S. , Stefanovsky O.I. 
Published: April 2011

ABSTRACTCeramics in systems with rare earth (REE = Y, Sm, Gd), manganese, and titanium oxides are considered as potential matrices for immobilization of REE- and actinide-containing radioactive wastes. Ceramics of this type were synthesized from oxide mixtures by a cold pressing and sintering method at temperatures of 1300-1400 °C as well as plasma heating. Major phases in the ceramics were found to be the phases of the pyrochlore-murataite polysomatic series with three- (3C), five- (5C), and seven-fold (7C) elementary fluorite unit cell. Perovskite/pyrophanite, hibonite/loveringite as well as garnet in the samples contained extra Fe and Al oxides were present as minor phases. Formation of the murataite, to be exact – structures built from murataite and pyrochlore modules, is more characteristic of the Y-bearing systems rather than the systems with heavier lanthanides. Increase of ionic radius of the REE trends towards formation of the pyrochlore structure phases whereas occurrence of large-size cations (La) stimulates formation of the perovskite structure phase. In the Y-bearing system murataite formation takes place at relative low Y2O3 concentrations (<15 mole %) and TiO2 content as high as ∼60 mole % and MnOx – 15-20 mole %. Higher Y2O3 concentrations and Gd2O3 substitution for Y2O3 yields preferably the pyrochlore phase or may favor formation of the phase with the 7C polytype.
Modelling experimental results on radiolytic processes at the spent fuel water interface. II. Radionuclides release
Authors: Cera E. , Grivé M. , Bruno J. , Eriksen T.E. 
Published: April 2011

ABSTRACTExperimental and modelling efforts in the last decade in the frame of nuclear waste management field have been focused on studying the role of the UO2surfaces in poising the redox state of solid/water systems as well as the radionuclides release behaviour. For this purpose, an experimental programme was developed consisting on dissolution experiments with PWR spent fuel fragments in an anoxic environment and by using different solution compositions.Some of the collected data has been previously published [1], specifically those data concerning radiolysis products and dissolution of the matrix. The results and the modelling tasks indicated an overall balance of the generated radiolytic species and that uranium dissolution was controlled by the oxidation of the spent fuel matrix in 10mM bicarbonate solutions while in the tests carried out at lower or without carbonate concentrations uranium in the aqueous phase was governed by the precipitation of schoepite.This paper is the continuation of a series accounting for the data and modelling work related to investigating the release behaviour of minor radionuclides from the spent fuel.Uranium concentrations as a function of time showed an initial increase until reaching a steady state, indicating a matrix dissolution control. The same behaviour is observed for neptunium, caesium, strontium, technetium and molybdenum indicating a congruent release of these elements with the major component of the fuel matrix. On the other hand, no cler tendency is observed for plutonium data where additional solubility limiting mechanisms may apply.Kinetic modelling of the trace elements: caesium, strontium, technetium and molybdenum is based on the congruent release of these elements with the major component of the fuel matrix. Rate constants have been determined. Kinetic modelling of neptunium data took also into account the subsequent precipitation as Np(IV) hydroxide. Finally, measured Pu concentrations may be explained by the precipitation of Pu(IV) and/or Pu(III) solid phases.