bluuebunny/crossref_metadata_2025_split huggingface dataset:
Meta-Autunite Solubility as Related to Uranium Minerals in Concrete Waste Forms
Authors: Mattigod Shas , Wellman Dawn , Glovack Julie , Arey Bruce , Wood Marcus 
Published: April 2011

AbstractPrevious in situ examination of U(VI) spiked concrete indicated that uranyl-oxyhydroxide phases that were initially formed, later led to the formation of mixed uranyl-oxyhydroxide/silicates, which subsequently transformed into uranyl-silicates, and finally altered into mixed uranyl-silicate/phosphate and uranyl-phosphate phases. We conducted solubility studies of the identified final uranyl-phosphate phase (calcium meta-autunite) in phosphate solutions ranging in concentration from 0.001 – 0.1M as a function of pH. These studies indicated a secondary phosphate phase that formed during the solubility of meta-autunite regulated the uranium concentrations at relatively low levels under high pH conditions (>12) typically encountered in cement pore waters. The importance of uranyl-phosphate minerals in concrete waste forms has, to date, been neglected because of the minimal amount of phosphorus present in most concrete compositions. However, because concrete is a continuously reacting solid, the thermodynamic stability of uranyl minerals that form at the later stages of reaction may have a substantial impact on the long-term fate of uranium in the waste forms. This study suggests that any future investigations should consider the potential benefit of including phosphorus in concrete waste forms.
Excitation Energy Dependence in Near-infrared Photoluminescence Spectra and Dynamics of PuO22+ in Cs2U(Pu)O2Cl4
Authors: Berg John M , Wilkerson Marianne P 
Published: April 2011

AbstractRecently we reported the observation of near-infrared photoluminescence from metal-centered 5f electronic excited states of PuO22+ doped into polycrystalline Cs2U(Pu)O2Cl4.[1] Photoluminescence dynamics following pulsed excitation show complicated decay patterns suggesting that multiple luminescent states are involved. Here we report the results of two recent sets of experiments showing that photoluminescence processes depend significantly on the energy of photoexcitation. In the first case, decay kinetics following excitation at a lower energy are missing an in-growth term that is present when exciting at higher energy. In the second case, we have observed that lower excitation energy produces significantly reduced number of emission transitions than higher excitation energy. Both observations suggest that higher energy excitation populates feeder states that decay to emitting states, causing signal from the latter to have an in-growth followed by a decay characteristic of their intrinsic lifetimes, whereas lower energy excitation leads to more direct population of luminescent states.
Evolution of Superconducting and Hidden Order Phases in URu2Si2 Under Applied Pressure
Authors: Maple M. Brian , Jeffries Jason R. , Butch Nicholas P. , Yukich Benjamin T. 
Published: April 2011

AbstractElectrical resistivity measurements performed under applied hydrostatic pressure and in magnetic fields have been used to probe the hidden order (HO) and superconducting (SC) states of URu2Si2, which have ambient-pressure transition temperatures TO = 17.5 K and Tc = 1.5 K, respectively. TO increases with applied pressure and a distinct kink in its pressure dependence is observed at 15 kbar; this feature is associated with the onset of antiferromagnetism. The pressure dependence of the SC upper critical field has been measured with the external field aligned parallel to both crystalline axes. The SC phase is smoothly suppressed to a critical pressure of about 15 kbar and no qualitative change in the critical field curves is observed. The co-evolution of the HO and SC phases is discussed within the context of a model in which the two phases compete for Fermi surface fraction.
Mechanism of Ion Exclusion by Sub-2nm Carbon Nanotube Membranes
Authors: Fornasiero Francesco , Park Hyung Gyu , Holt Jason K , Stadermann Michael , Grigoropoulos Costas P , Noy Alexandr , Bakajin Olgica 
Published: April 2011

AbstractCarbon nanotubes offer an outstanding platform for studying molecular transport at nanoscale, and have become promising materials for nanofluidics and membrane technology due to their unique combination of physical, chemical, mechanical, and electronic properties. In particular, both simulations and experiments have proved that fluid flow through carbon nanotubes of nanometer size diameter is exceptionally fast compared to what continuum hydrodynamic theories would predict when applied on this length scale, and also, compared to conventional membranes with pores of similar size, such as zeolites.
For a variety of applications such as separation technology, molecular sensing, drug delivery, and biomimetics, selectivity is required together with fast flow. In particular, for water desalination, coupling the enhancement of the water flux with selective ion transport could drastically reduce the cost of brackish and seawater desalting. In this work, we study the ion selectivity of membranes made of aligned double-walled carbon nanotubes with sub-2 nm diameter. Negatively charged groups are introduced at the opening of the carbon nanotubes by oxygen plasma treatment.
Reverse osmosis experiments coupled with capillary electrophoresis analysis of permeate and feed show significant anion and cation rejection. Ion exclusion declines by increasing ionic strength (concentration) of the feed and by lowering solution pH; also, the highest rejection is observed for the salts (A=anion, C=cation, z= valence) with the greatest zA/zC ratio. Our results strongly support a Donnan-type rejection mechanism, dominated by electrostatic interactions between fixed membrane charges and mobile ions, while steric and hydrodynamic effects appear to be less important. Comparison with commercial nanofiltration membranes for water softening reveals that our carbon nanotube membranes provides far superior water fluxes for similar ion rejection capabilities.
The UK National Nuclear Laboratory and Waste Management R&D
Authors: Fairhall Graham A. 
Published: April 2011

In the autumn of 2006, the UK government declared its expectation to set up a National Nuclear Laboratory (NNL) as soon as possible (subject to satisfactory contractual terms). The aim would be to base the Laboratory around Nexia Solutions and its ‘state of the art’ facility at Sellafield in Cumbria. The initial phase of the work to recommend formation of the laboratory is well advanced, and the NNL is expected to have a remit for the following roles:— to play a key role in supporting the UK's strategic R&D requirements— to operate world-class facilities— to ensure key skills are safeguarded and enhanced— to play a key role in the development of the UK's R&D supply base.
Accelerated Weathering of Composite Cements Used for Immobilisation
Authors: Borges Paulo H. R. , Milestone Neil B. , Streatfield Roger E. 
Published: April 2011

AbstractTrying to estimate the long-term durability of cemented wasteforms is a difficult task as the cement matrix is a reactive medium and interactions can occur with the encapsulated waste as well as with the environment. There are few studies of samples that have been stored under controlled conditions for more than 10-15 years. Wasteforms are now being expected to last hundreds of years, much of that likely to be in some form of storage where sample integrity is important. There is also the concern that results from any long-term samples may only be indicative as both formulations and materials change with time.This paper discusses changes in physical properties that occur in composite cements when some of the short-term accelerated procedures employed in construction testing are applied to encapsulating matrices. Changes after increased temperature of curing, wetting/drying and accelerated carbonation are discussed.Many of the encapsulating formulations currently used are composite cements where large replacement levels of OPC with supplementary cementing materials (SCMs) such as PFA or BFS are made, primarily to reduce heat output. Accelerating the exposure conditions, either by increasing temperature or through wetting/drying has the effect of changing the hydration pattern of the composite cement by generating more hydration in the SCMs than would normally occur. The large amount of porosity that occurs because of limited hydration allows intrusion of gases and ready movement of water, so the samples subjected to accelerated testing do not appear as durable as expected if stored at ambient.
High Temperature Behaviour of Polyoxometalates Containing Lanthanides
Authors: Kinoshita Hajime , Brewer Marcus , Talbot-Eeckelaers Caytie E. , Reeves Nik , Copping Roy , Sharrad Clint A. , May Iain 
Published: April 2011

AbstractThe possibility of a simple heating process of POM to obtain tungsten bronze was investigated for nuclear waste immobilisation via DTA/TG and high temperature XRD. Heating process up to 900°C caused the decomposition of structure for both systems. Cooling process seemed to have little effect on the final product for the K11[Nd(PW11O39)2]·xH2O, whereas the cooling profile showed a significant effect on the K13[Nd(SiW11O39)2]·xH2O. Nd formed two types of tungsten bronzes, namely Nd2WO6 and Nd4W3O15 in K11[Nd(PW11O39)2]·xH2O and K13[Nd(SiW11O39)2]·xH2O, respectively.
Immobilization of Liquid Radioactive Waste in Mineral-Like Matrices Derived From Inorganic Cenosphere-Based Sorbents as Precursors
Authors: Vereshchagina Tatiana A. , Anshits Nataly N. , Fomenko Elena V. , Vereshchagin Sergei N. , Anshits Alexander G. 
Published: April 2011

AbstractThe progress in study of immobilization of liquid radioactive waste in mineral-like aluminosilicate matrices (feldspar and feldspathoids) derived from cenosphere-based microspherical zeolite sorbents is reported. Based on the analysis of ‘composition – morphology –C characteristics’ correlation obtained for more than 70 cenosphere products with a high content of one morphological type of imperforated cenospheres, optimal ranges of cenospheres composition were identified for the synthesis of zeolites with the predetermined structural type. Given that the cenosphere-based zeolite sorbents are precursors of the final waste form, further activity proceeds toward developing a highly efficient zeolite sorbent of NaP1 type, which would ensure the effective trapping of Cs+ and/or Sr2+ ions and the phase transformation under relatively mild conditions (T≤1000°C). The paper details the main criteria for realization of the ‘precursor’ approach for fixation of Cs-Sr fraction using cenosphere-based systems; also shown are experimental results indicating practical realization of the proposed approach.
Development of Borosilicate Glass Compositions for the Immobilisation of the UK's Separated Plutonium Stocks
Authors: Harrison Mike T. , Scales Charlie R. 
Published: April 2011

AbstractThe UK inventory of separated civil plutonium is expected to exceed 100 tonnes by 2010. Whilst the majority of this could be used in the manufacture of MOx (Mixed Oxide) fuel in future power generation scenarios, options for the disposal of surplus plutonium are currently being investigated by Nexia Solutions Ltd on behalf of the UK's Nuclear Decommissioning Authority (NDA). One of the options being considered is immobilisation in a durable glass matrix followed by long term storage and subsequent final repository disposal.A preliminary experimental survey assessed a selection of potential glass systems on the basis of Pu-surrogate (cerium) loading, durability, and ease of processing. Following this, a number of borosilicate compositions have been taken forward into a more detailed investigation in order to fully qualify their potential for Pu-immobilisation. The selected compositions are lanthanide borosilicate (LaBS), alkali tin silicate (ATS) and high-lanthanide alkali borosilicate (modified-MW). For this second series of experiments, hafnium was selected as the Pu surrogate, and a study of the potential waste loading as a function of temperature for the three selected compositions is described in this paper. Furthermore, several variations of the LaBS composition were fabricated in order to investigate the effect of total lanthanide content on melting temperature. The benchmark of 10 wt% HfO2 incorporation is achievable for all three glasses with temperatures of 1200, 1300 and 1400 °C required for ATS, modified-MW and LaBS respectively.
Towards a Single Host Phase Ceramic Formulation for UK Plutonium Disposition
Authors: Stennett Martin C. , Hyatt Neil C. , Gilbert Matthew , Livens Francis R. , Maddrell Ewan R. 
Published: April 2011

AbstractThe UK has a considerable stockpile of separated plutonium; a legacy of over 50 years of civilian nuclear programmes. This material has been considered both as an asset for future energy generation and a liability due to the proliferation threat. A proportion of the PuO2stocks may be consumed by nuclear fission, in mixed oxide (MOx) or inert matrix (IMF) fuels but a quantity of waste PuO2will remain which is unsuitable for fuel manufacture and will require immobilisation. A research program is currently underway to investigate the potential of various single phase ceramic formulations for the immobilisation of this waste PuO2 fraction. In this work a number of synthetic mineral systems have been considered including titanate, zirconate, phosphate and silicate based matrices. Although a wealth of information on plutonium disposition in some of the systems exists in the literature, the data is not always directly comparable which hinders comparison between different ceramic hosts. The crux of this research has been to compile a database of information on the proposed hosts to allow impartial comparison of the relative merits and shortcomings in each system.
Experience in Progressing the Planning Application for New LLW Disposal Facilities for Dounreay
Authors: Broughton David , Tait Michael S 
Published: April 2011

AbstractAn integral part of decommissioning the Nuclear Decommissioning Agency's (NDA) Dounreay site is the management of the solid low level radioactive waste (LLW). The United Kingdom Atomic Energy Authority (UKAEA) has developed and progressed a technical and stakeholder programme that has enabled it to submit a robust Planning Application to Highland Council (HC) for New LLW Disposal Facilities at Dounreay and to submit substantive preliminary safety and environmental cases to the Nuclear Installations Inspectorate (NII) and the Scottish Environment Protection Agency (SEPA). To UKAEA’s knowledge this is the most advanced project in the UK for new LLW disposal facilities. Experience has been gained in progressing the Best Practicable Environmental Option (BPEO) Study, working with regulators in unfamiliar areas, and undertaking groundbreaking stakeholder consultation. Key lessons learnt are that stakeholders should be engaged in dialogue on the project as early as possible, documentation must be high quality and tailored to its audience, and internationally respected and credible consultants must be involved.
Changes on the Mineralogical and Physical Properties of FEBEX Bentonite Due to Its Contact With Hyperalkaline Pore Fluids in Infiltration Tests
Authors: Fernández A. M. , Melón A. , Sánchez D.M. , Galán M.P. , Morante R. , Gutiérez-Nebot L. , Turrero M.J. , Escribano A. 
Published: April 2011

AbstractTwo infiltration tests with a synthetic hyperalkaline solution at pH 13.5 were performed. The aim was to analyse the interaction of concrete solutions with compacted smectitic bentonites. The experiment was performed inside an anoxic glove box at 30-35 °C with FEBEX bentonite compacted at a dry density of 1.65 g/cm3 and a water content of 13.4%. Outflowing water coming from the bentonite was collected over time. A total of three times the bentonite pore volume was recovered and twelve chemical analyses of the resulting pore water were obtained. The ionic strength of the pore waters decreases with time from 0.20 M to 0.03 M and the pH increases from 7.9 to 9.0. After a test period of 595 days, the cells were dismantled, and the study of the state and alteration of the bentonite was undertaken. A modification in the a sorbed cation population, an increase in the Na- and K-smectites type, and the presence of a tri-octahedral smectite (saponite) and zeolites (phillipsite and chabazite) were observed.
Grimsel Test Site - Phase VI: Review of Accomplishments and Next Generation of In-Situ Experiments Under Repository Relevant Boundary Conditions
Authors: Blechschmidt Ingo , Vomvoris Stratis , Rueedi Joerg , Martin Andrew James 
Published: April 2011

AbstractThe Grimsel Test Site owned and operated by Nagra is located in the Swiss Alps (www.grimsel.com). The Sixth Phase of investigations was started in 2003 with a ten-year planning horizon. With the investigations and projects of Phase VI the focus has shifted more towards projects assessing perturbation effects of repository implementation and projects evaluating and demonstrating engineering and operational aspects of the repository system. More than 17 international partners participate in the various projects, which form the basic organisational “elements” of Phase VI. Scientific and engineering interaction among the different projects is ensured via an annual meeting and several experimental team meetings throughout the year. On-going projects include: evaluation of full-scale engineered systems under simulated heat production and long-term natural saturation (NF-Pro/FEBEX), gas migration through engineered barrier systems (GMT, finished this year), emplacement of a shotcrete low-pH plug (ESDRED/Module IV), testing and evaluation of standard monitoring techniques (TEM).Numerous in-situ experiments with inactive tracers and radionuclides were successfully carried out over the past few years at the Grimsel Test Site (GTS). For the GTS Phase VI, three major projects have been initiated to simulate the long-term behaviour of contamination plumes in the repository near-field and the surrounding host rock:•The CFM (Colloid Formation and Migration) project, which focuses on colloid generation and migration from a bentonite source doped with radionuclides•The LCS (Long-Term Cement Studies) project, which aims at improving the understanding of low-pH cement interaction effects in water conducting features•The LTD (Long-Term Diffusion) project, which aims at in-situ verification of long-term diffusion concepts for radionuclidesAs Phase VI approaches its mid-term point, what are the next steps planned? The accomplishments assessed to date and the opportunities with the on-going projects as well as new projects – currently under discussion – are presented herein
Magnetite Sorption Capacity for Strontium as a Function of pH
Authors: Pablo Joan de , Rovira Miquel , Giménez Javier , Casas Ignasi , Clarens Frederic 
Published: April 2011

AbstractThe ubiquity of iron oxide minerals and their ability to retain metals on their surface can represent an important retardation factor to the mobility of radionuclides. In a deep repository for the spent nuclear fuel, the intrusion of the groundwater might produce the anoxic corrosion of the iron, with magnetite as one of the end-products. In this study, as expected considering the strontium speciation in solution, strontium is sorbed onto magnetite at alkaline pH values while at acidic pH the sorption is negligible. Magnetite is able to sorb more than the 50% of the strontium from a 8·10-6 mol·dm-3 solution at the pH range representative of most groundwater (7-9). A surface complexation model has been applied to the experimental data, allowing to explain the results using the Diffuse Layer Model (DLM) and considering the formation of the inner-sphere complex >FeOHSr2+ (with a calculated logK=2.7±0.3). Considering these data, the magnetite capacity to retain strontium and other radionuclides is discussed
Long-Term Predictions of the Concentration of a-isosaccharinic Acid in Cement Pore Water
Authors: Glaus Martin A. , Loon Luc R. Van , Schwyn Bernhard , Vines Sarah , Williams Steve J. , Larsson Peter , Puigdomenech Ignasi 
Published: April 2011

AbstractThe long-term prediction of the equilibrium concentration of α-isosaccharinic acid (α-ISA) in cement pore water is a crucial step in the assessment of the role of cellulose in the safety of a cementitious repository. The aim of the present contribution is to summarise recent efforts in identifying the most important processes leading to the formation or degradation of α-ISA and in predicting its most likely concentrations in cement pore water. The issues considered are the kinetics involved in the formation of α-ISA, reactions of α-ISA with dissolved or solid compounds that may lead to limitations of its pore water concentrations and the chemical stability of α-ISA in a heterogeneous alkaline environment. Some new results are presented showing that α-ISA is degraded to low-molecular weight organic compounds in the presence of oxygen, whereas such processes occur only to a minor extent under anaerobic conditions. It is concluded that the processes involved in the degradation of cellulose under alkaline conditions are not sufficiently understood to explain fully the observed concentrations of α-ISA in long-term experiments.
Release Behaviour of Sr-90 From Hydraulically Retrieved ILW Sludge
Authors: Hastings J J 
Published: April 2011

AbstractGlobally, the nuclear industry has a large number of legacy wastes that are stored in ponds, silos and tanks that are nearing the end of their design lifetime and hence said wastes need processing. In the UK there are significant quantities of radioactive sludge that have arisen from the corrosion of early Magnox fuel cans which have been stored underwater. As part of the present aggressive clean-up programme these materials will be retrieved, separated, processed and immobilised as dry waste forms for long-term storage. It is envisaged that hydraulic retrieval will be used for these ILW sludges resulting in some activity being released from the sludge phase to the process liquors challenging downstream ion exchange effluent treatment plants.In order to understand this challenge, experiments have been conducted on sludge in ILW storage ponds and during sludge transfer operations to study the activity released from said sludges. In particular the solubility, adsorption behaviour of Sr-90 is discussed and how this and other aspects of the sludge chemistry impact upon the ion exchange effluent treatment process. The novel methodologies employed to obtain this data is also discussed.