Hot-Pressed Barium Sulphate Ceramic Waste Forms for Direct Immobilisation of Medium Level Magnox Waste

1981 ◽  
Vol 6 ◽  
Author(s):  
A. Briggs ◽  
D.V.C. Jones ◽  
G.B. Cole
Keyword(s):  
Hot Pressing ◽  
Open Porosity ◽  
Matrix Material ◽  
Direct Conversion ◽  
Barium Sulphate ◽  
Reduction Factor ◽  
Waste Form ◽  
Internal Surfaces ◽  
Wide Range ◽  
Leaching Behaviour

ABSTRACTA possible method of treatment for Magnox cladding waste is by dissolution in nitric acid and precipitation of barium sulphate-based floc with which radioactive ions are co-precipitated. The floc could then be immobilised in a matrix material such as cement or bitumen to give the waste form, or alternatively can be converted directly into a waste form by hot pressing.This paper describes the direct conversion of barium sulphate floc, containing simulated radwaste, into a synthetic, ceramic version of the natural mineral barite by a hot-pressing route. By variation of the parameters pressure, temperature and time, optimum conditions for consolidation of the floc to > 90% theoretical density on a laboratory scale are found to be 22.5 MPa, 900°C for 10 minutes. Using a pressure of 15 MPa, at 900°C for 30 min., hot-pressed billets of BaSO4 have been made on a 5 kg scale. In going from the Magnox waste to the hot-pressed barium sulphate a volume reduction factor ∼ 18 is achieved. The principal phases in the product are found to be BaSO4 , MgO and Fe3O4, and the degree of consolidation achieved depends on the MgO content.The leaching behaviour of the hot-pressed materials in 100°C, 3 day Soxhlet tests also depends on the MgO content, and on the consequent level of open porosity. If there is porosity accessible to the leach water, MgO at the internal surfaces is converted to Mg(OH)2, which deposits within the pores, and a weight gain is registered in the Soxhlet test. If, however, there is no open porosity, a weight loss occurs, and leach rates ∼ 4 × 10−7 kg/m2/sec are found. In contrast, pure BaSO4, hot-pressed to similar densities, shows no variation in leaching behaviour over a wide range of o en porosities, and gives Soxhlet leach rates ∼ 8 × 10−8 kg/m2/sec.

scholarly journals The Role Of Chemical Reaction In Waste-Form Performance

1987 ◽  
Vol 112 ◽  
Author(s):  
P. L. Chambré ◽  
C. H. Kang ◽  
W. W.-L. Lee ◽  
T. H. Pigford
Keyword(s):  
Mass Transfer ◽  
Steady State ◽  
Dissolution Rate ◽  
Chemical Reaction ◽  
Borosilicate Glass ◽  
Reaction Rate ◽  
Waste Form ◽  
Spent Fuel ◽  
Wide Range ◽  
Chemical Reaction Rate

AbstractThe dissolution rate of waste solids in a geologic repository is a complex function of waste form geometry, chemical reaction rate, exterior flow field, and chemical environment. We present here an analysis to determine the steady-state mass transfer rate, over the entire range of flow conditions relevant to geologic disposal of nuclear waste. The equations for steady-state mass transfer with a chemical-reaction-rate boundary condition are solved by three different mathematical techniques which supplement each other. This theory is illustrated with laboratory leach data for borosilicate-glass and a spherical spent-fuel waste form under typical repository conditions. For borosilicate glass waste in the temperature range of 57°C to 250°C, dissolution rate in a repository is determined for a wide range of chemical reaction rates and for Peclet numbers from zero to well over 100, far beyond any Peclet values expected in a repository. Spent-fuel dissolution in a repository is also investigated, based on the limited leach data now available.

The machinability of Al/B4C composites produced by hot pressing based on reinforcing the element ratio

2016 ◽  
Vol 23 (6) ◽  
pp. 743-750 ◽  
Author(s):  
Ergün Ekici ◽  
Mahmut Gülesin
Keyword(s):  
Surface Roughness ◽  
Wear Mechanism ◽  
Cutting Forces ◽  
Hot Pressing ◽  
Matrix Material ◽  
Cutting Tools ◽  
Cutting Speed ◽  
Reinforcement Ratio ◽  
Depth Of Cut ◽  
Crater Wear

AbstractIn this study, the effects of the particle reinforcement ratio on cutting forces and surface roughness were investigated when milling particle-reinforced metal matrix composite (MMCp) produced by hot pressing with different cutting tools. Alumix 123 alloy as the matrix material and B4C particles with an average size of 27 μm and 5%, 10% and 15% ratio as reinforcing elements were used for the manufacture of composite materials. The experiments were carried out in dry cutting conditions with four different cutting speeds, constant feed rate and depth of cut. Changes depending on the increased reinforcement ratio in cutting forces and surface roughness values were investigated; the effects of 10% B4C reinforced composite on tool wear were also examined. It was observed that cutting forces increased with the increase in cutting speed and particle ratio with carbide cutting tools, and it was seen that the cutting forces on the cutting tools decreased when cutting speed decreased and the cutting forces increased as the reinforcement ratios increased. In addition, with increasing the cutting speed, the surface roughness of the machined surfaces of composite samples increased with the carbide tools, while the cubic boron nitride (CBN) tools have the opposite effect. While it was seen that flank and crater wear occurred on the cemented carbide cutting tools, abrasive, adhesive and other wear mechanism tools in addition to the main wear mechanism, no remarkable flank and crater wear occurred on CBN cutting tools.

scholarly journals The rapid generation of isothiocyanates in flow

2013 ◽  
Vol 9 ◽  
pp. 1613-1619 ◽  
Author(s):  
Marcus Baumann ◽  
Ian R Baxendale
Keyword(s):  
Chemical Transformation ◽  
Chemical Reactions ◽  
Direct Conversion ◽  
Wide Range ◽  
Rapid Generation ◽  
Work Up ◽  
Immobilised Reagents

Isothiocyanates are versatile starting materials for a wide range of chemical reactions. However, their high nucleophilic susceptibility means they are best prepared and used immediately. We report here on a flow platform for the fast and efficient formation of isothiocyanates by the direct conversion of easily prepared chloroximes. To expedite this chemistry a flow insert cartridge containing two immobilised reagents is used to affect the chemical transformation which typically eliminates the requirements for any conventional work-up or purification of the reaction stream.

scholarly journals Analysis of Delaminated Hybrid Carbon Fiber Composites in MODE-I

2021 ◽  
Vol 9 (2) ◽  
pp. 605-624
Author(s):  
Hassan A. Alessa, Et. al.
Keyword(s):  
Failure Analysis ◽  
Composite Laminates ◽  
Composite Structures ◽  
High Performance ◽  
Failure Modes ◽  
Matrix Material ◽  
Structural Response ◽  
Laminated Composite ◽  
Carbon Fiber Composites ◽  
Wide Range

Failure analysis of laminated composite structures has attracted a great deal of interest in recent years due to the increased application of composite materials in a wide range of high-performance structures. Intensive experimental and theoretical studies of failure analysis and prediction are being reviewed. Delamination, the separation of two adjacent plies in composite laminates, represents one of the most critical failure modes in composite laminates. In fact, it is an essential issue in the evaluation of composite laminates for durability and damage tolerance. Thus, broken fibers, delaminated regions, cracks in the matrix material, as well as holes, foreign inclusions and small voids constitute material and structural imperfections that can exist in composite structures. Imperfections have always existed and their effect on the structural response of a system has been very significant in many cases. These imperfections can be classified into two broad categories: initial geometrical imperfections and material or constructional imperfections

Optimization of a Small Scale Pellet Boiler

2010 ◽  
Author(s):  
Jose´ Carlos Teixeira ◽  
Rui Ferreira ◽  
Manuel Eduardo Ferreira
Keyword(s):  
Heat Dissipation ◽  
High Efficiency ◽  
Raw Materials ◽  
Direct Conversion ◽  
Pollutant Emissions ◽  
Small Scale ◽  
Air Supply ◽  
Wide Range ◽  
Great Relevance ◽  
Secondary Air

Environmental concerns and the drive to reduce the dependence on petroleum based fuels brought the use of renewable energies to the forefront. Biomass appears as a very interesting option for direct conversion into heat. In this context, densified forms of biomass such as pellets are of great relevance because of their easy of use, high efficiency and low emissions. Expected trends in the biomass market suggest that equipments should operate over a wide range of thermal loads and with fuels derived from lower quality raw materials; simultaneously, a high efficiency and low emissions are taken for granted. Currently, biomass domestic boilers prove to be very sensitive to fuel characteristics and load conditions. This work reports on the development of a 15 kW net pellet boiler. A prototype was built that enables the independent control of the air supply into various regions of the combustion chamber and an accurate supply of fuel. The test rig also includes: boiler and flue gases extraction system; feeding system; heat dissipation system; flue gas analyzer; data acquisition system and all sensors. In order to optimize the combustion conditions, pollutant emissions and their relation with feeding conditions, primary and secondary air flow rate and excess of air was analyzed. The results suggest that this burner is a promising for implementation in domestic boilers. The advantages are: CO emissions well below those observed in similar equipments and the capacity to maintain the emissions level constant under different loading conditions.

scholarly journals Micromechanical evaluation of failure models for unidirectional fiber-reinforced composites

2019 ◽  
Vol 54 (6) ◽  
pp. 791-800
Author(s):  
Azam Arefi ◽  
Frans P van der Meer ◽  
Mohammad Reza Forouzan ◽  
Mohammad Silani ◽  
Mahmoud Salimi
Keyword(s):  
Matrix Material ◽  
Element Model ◽  
Failure Criteria ◽  
Fiber Reinforced Composites ◽  
Fiber Direction ◽  
Reinforced Composites ◽  
Fiber Reinforced ◽  
Wide Range ◽  
The Matrix ◽  
Stress States

In this paper, micromechanical simulations are employed to evaluate the performance of the Tsai–Wu and Hashin failure criteria for fiber-reinforced composites, especially in stress states whose experimental reproduction is complicated. Micromechanical responses are generated using a finite element model of a representative volume element, in which only the matrix material experiences damage and the fibers are assumed to be elastic. Micromechanical simulations of basic load cases are used to calibrate macrolevel criteria. Finally, the response of the micromodel and macromodels is compared for various load combinations. Despite a good agreement between Tsai–Wu criterion predictions and micromodel results in a wide range of stress states, some stress combinations are highlighted for which the strength is not predicted accurately. Additionally, accuracy of the Hashin criterion suffers from ignoring the influence of stress in fiber direction on matrix failure.

scholarly journals Advanced Experimental Technique for Radiation Damage Effects in Nuclear Waste Forms: Neutron Total Scattering Analysis

MRS Advances ◽  
2018 ◽  
Vol 3 (31) ◽  
pp. 1735-1747
Author(s):  
Maik Lang ◽  
Eric C. O’Quinn ◽  
Jacob Shamblin ◽  
Jörg Neuefeind
Keyword(s):  
Long Range ◽  
Radiation Effects ◽  
Fission Products ◽  
Waste Form ◽  
Waste Forms ◽  
Wide Range ◽  
Pdf Analysis ◽  
Defect Behavior ◽  
Nuclear Waste Forms ◽  
Neutron Total Scattering

ABSTRACTFor the past 30 years, the development of durable materials for radionuclide immobilization has been driven by efforts to dispose of wastes generated by the nuclear fuel cycle [National Research Council, ‘Waste Forms Technology and Performance: Final Report’, the National Academies Press, Washington D.C., 2011]. Many materials have been developed, but there still exist large gaps in the knowledge of fundamental modes of waste form degradation in repository environments. An important aspect of waste form science is the behavior of the materials under intense irradiation from decaying actinides and fission products. This irradiation induces a wide range of defects and disorder, the details of which depend on the specific waste form material. At the present time, it is not fully explained how radiation effects will influence the performance of nuclear waste forms and their long-term retention of fission products and actinides under operational conditions. The complex defect behavior and radiation damage must be understood over a range of length scales, from the initial atomic-scale defect structure to the long-range observable material modification. This is particularly challenging and requires advanced characterization techniques. This contribution describes how pair distribution function (PDF) analysis obtained from neutron total scattering experiments can be applied in the research field of waste form science to uniquely characterize radiation effects in a wide range of materials, including crystalline complex oxides and waste glasses. Neutron scattering strength does not have an explicit Z-dependence; this allows access to many low-Z elements, such as oxygen, that cannot be accurately studied with X-rays. In many cases, this can permit a detailed analysis of both cation (often high-Z) and anion (often low-Z) defect behavior. In contrast to traditional crystallography, which relies on long-range order, PDF analysis probes the local defect structure, including changes in site occupation, coordination, and bond distance. This is particularly important when characterizing aperiodic waste glasses with no long-range order at all. In contrast to X-ray characterization which requires very little sample mass (∼0.1 mg), neutron characterization (even at state-of-the-art spallation facilities) requires relatively large sample mass (∼50 - 100 mg). Obtaining this quantity is challenging for studies of irradiated materials, but by tailoring our experimental approach to use high-energy ions (GeV) with very high penetration depth, we are able to produce the required mass.

Self-Healing Materials as New Biologically Inspired Materials

2012 ◽  
Vol 16 ◽  
pp. 11-25
Author(s):  
Fabrizia Ghezzo ◽  
Xi Geng Miao
Keyword(s):  
Failure Mechanisms ◽  
Matrix Material ◽  
High Strength ◽  
Self Healing ◽  
Micro Cracks ◽  
Specific Objective ◽  
Wide Range ◽  
The Matrix ◽  
Safety And Reliability ◽  
Healing Agent

Lightweight, high strength fibre-reinforced polymeric composites are leading materials in many advanced applications including biomedical components. These materials offer the feasibility to incorporate multi functionalities due to their internal architecture, heterogeneity of materials and the flexibility of combining them using currently available fabrication methods. In spite of the excellent properties of these materials, their failure is still a questionable and not well predicted event. Delamination, debonding and micro-cracks are only some of the failure mechanisms that affect the matrices of polymer based composites. More complex cases exist with the combination of multiple failure mechanisms. In such cases a self-repairing mechanism that can be auto-triggered in the matrix material once the crack has been formed, would be very beneficial for all the applications of these materials, reducing maintenance costs and increasing their safety and reliability. Self-healing materials have been studied for more than a decade by now, with the specific objective of reducing the risks and costs of cracking and damage in a wide range of materials. Different approaches have been taken to create such materials, depending on the kind of material that needs to be repaired. The most popular methods developed for polymers and polymer reinforced composites are considered in this review. These methods include materials with micro-capsules containing a healing agent, and composites with matrices that can self-heal the cracks by repairing the broken molecular links upon external heating. While the first approach to healing has been widely used and studied in the past decade, in this review we focus on the second approach since less is reported in the literature and more difficult is the development of the materials based on such a method.

Fabrication and Testing of Corrugated 3D SiSiC Ceramics for Porous Burner Applications

2006 ◽  
Vol 45 ◽  
pp. 2316-2322 ◽  
Author(s):  
Jens Schmidt ◽  
Matthias Scheiffele ◽  
Alexander Mach ◽  
Franz von Issendorff
Keyword(s):  
Open Porosity ◽  
New Technology ◽  
Industrial Applications ◽  
Infiltration Process ◽  
Pure Silicon ◽  
Porous Burner ◽  
Wide Range ◽  
Silicon Melt ◽  
Melt Infiltration ◽  
Start Ups

Non-oxide SiC ceramics can withstand high temperatures ~1400 °C in severe combustion environments. Therefore such ceramics are interesting candidates for advanced combustion technologies, e.g. sophisticated porous burners. For the fabrication of porous SiSiC ceramics the DLR developed a new technology based on carbon sheets and lamellae. These basic materials can be combined to lightweight 3D C/C stacks. Through the variation of the amplitude and number of lamellae per inch, the open porosity and orientation of the pore channels could be tailored in a wide range. By using the pyrolysis followed by the liquid silicon-melt infiltration process the carbon stack could be directly converted into SiC in one shot. The residual open porosity can easily be filled with pure silicon to obtain 3D SiSiC structures with adequate mechanical strength and sufficient damage tolerance. Best results from durability tests were obtained with structures which are composed of oriented pore channels. Suitable structures should have angles (α) of about α = ± 60° or less. The results from burner rig tests at LSTM with improved components have been very promising, since a lifetime up to 500 hours and 2000 start-ups could be obtained with α = ± 50° as well as with α = ± 60° sample. So far, no significant oxidation or degradation could be observed after 1939 h/10800 start-ups with α = ± 45° sample. These proof tests are ongoing and show that these novel cardboard like structures have a high potential for industrial applications.

Release and Disposal of Materials During Decommissioning of Siemens MOX Fuel Fabrication Plant at Hanau, Germany

2007 ◽  
Author(s):  
Werner Koenig ◽  
Roland Baumann
Keyword(s):  
Radioactive Waste ◽  
A Priori ◽  
Matrix Material ◽  
Disposal Site ◽  
Process Equipment ◽  
Mox Fuel ◽  
Fuel Fabrication ◽  
Wide Range ◽  
Plant Site ◽  
Almost All

In September 2006, decommissioning and dismantling of the Siemens MOX Fuel Fabrication Plant in Hanau were completed. The process equipment and the fabrication buildings were completely decommissioned and dismantled. The other buildings were emptied in whole or in part, although they were not demolished. Overall, the decommissioning process produced approximately 8500 Mg of radioactive waste (including inactive matrix material); clearance measurements were also performed for approximately 5400 Mg of material covering a wide range of types. All the equipment in which nuclear fuels had been handled was disposed of as radioactive waste. The radioactive waste was conditioned on the basis of the requirements specified for the projected German final disposal site “Schachtanlage Konrad”. During the preconditioning, familiar processes such as incineration, compacting and melting were used. It has been shown that on account of consistently applied activity containment (barrier concept) during operation and dismantling, there has been no significant unexpected contamination of the plant. Therefore almost all the materials that were not a priori destined for radioactive waste were released without restriction on the basis of the applicable legal regulations (§ 29 of the Radiation Protection Ordinance), along with the buildings and the plant site.

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