Investigation of factors affecting pellet strength in straight grate induration machine

Abstract

During induration in a straight grate machine, the green pellets pass through four different thermal treatments, namely drying, preheating, heating and cooling. The pellet bed is fired with downdraught firing leading to thermal gradients through the bed. Corex sludge, which is used as fuel in the pellet mix, supplies the necessary energy for uniform heating of the pellet. The physicochemical conditions, e.g. the temperature and oxygen partial pressure mainly depend on the amount of fuel incorporated in the pellet mix. As a result the percentage and the distribution of various phases in the pellets vary, leading to deviation in quality. To study the distribution of phases and their impact on cold crushing strength at different carbon levels (1·20 and 1·35%), pellets from different layers of the induration bed in an industrial straight grate were characterised. It was observed that the strength of the pellets varied from 142 to 268 kg/pellet and 128 to 245 kg/pellet across bed, with carbon 1·20 and 1·35% respectively. It was found that middle layer pellets had higher strength compared to top and bottom layers. It was observed that amount of hematite, magnetite, porosity and the pore size plays a significant role on the pellet strength. Pellets with 1·20% carbon showed better physical and microstructural properties across the pellet bed compared to pellets with 1·35% carbon.     

Mould flux film between mould and steel shell

Abstract

Samples of the mould flux film have been taken during tailout. The locations of the samples varied from the meniscus to 40 cm below the meniscus. Samples have been analysed using various techniques including SEM/EDS microscopy. Surprisingly, the flux film structure concerning different slag phases changes from the meniscus region downwards. Casting time also has an influence on the structure: it becomes more complex during hours of casting. Near the meniscus, there are no significant changes in film layer composition from mould side to shell side. Farther away from the meniscus, however, large differences in composition developed. For example, the concentrations of sodium and fluorine can be 50% in the film layer against mould. Also, the concentrations of other elements can be multiples of their levels in the powder. Zirconium and barium oxides have been used as tracers. Some results of these investigations are presented. All samples were taken from the Outokumpu Polarit caster at the Tornio works, where the annual production of stainless steel slabs is about 640 kt.     

Use of impact analysis in licensing industrial container for transporting new fuel

Abstract

The finite element (FE) method is a powerful tool for the simulation of mechanical and thermal behaviour of structures. In recent years, the explicit FE method has increasingly been used in the development of transport packages and as part of approval applications to demonstrate the performance of packages. Testing and analysis are the two methods specified in the IAEA Regulations for the Safe Transport of Radioactive Material for demonstrating the structural and thermal performance of a transport package against the requirements of the Transport Regulations. The roles of testing and analysis, and the relative prominence of the two, may vary between Competent Authorities in different countries. This can range from analysis being regarded as the primary mode of demonstration with testing as confirmatory, to testing being the primary mode of demonstration supplemented by analysis. This paper describes the use of the non-linear FE code LS-DYNA in the licensing of a new container for the transport of new nuclear fuel. The package was classified as an Industrial Package (Fissile) in accordance with the IAEA Regulations, and hence it was necessary, among other things, to demonstrate that criticality criteria were satisfied under postulated impact conditions. Physical drop tests were carried out and the results are compared with LS-DYNA computer calculations using the same FE models developed to support the design of the new container. The analyses and tests clearly demonstrate the novel use of polyurethane foam as the container main energy absorber. The FE predictions are compared for accelerations, bolt loadings and global deformations of the container. In general good correlation was obtained between predictions and tests and the differences, which did occur, particularly for accelerations, are discussed and reconciled. The paper concludes that explicit analysis codes are now so reliable for container impact calculations that minimal test work should be pursued basically for key confirmatory impact scenarios.     

Transport of MOX fuel: continuous challenge

Abstract

For 45 years TN International has been involved in the radioactive materials transportation field. Since the beginning the spent nuclear fuel transportation has been its core business. During all these years TN International, now part of AREVA, has been able to anticipate and fulfil the needs for new transport or storage casks design to fit the nuclear industry evolutions. A whole fleet of casks able to transport all the materials of the nuclear fuel cycle has been developed. This paper focuses on the casks used to transport the fresh and used mix oxide (MOX) fuel. To transport the fresh MOX boiling water reactor and pressurised water reactors fuel, TN International has developed two designs of casks: the MX 6 and the MX 8. These casks are and have been used to transport MOX fuel for French, German, Swiss and in a near future Japanese nuclear power plants. A complete set of baskets have been developed to optimise the loading in terms of integrated dose and also of course capacity. Mixed oxide used fuel has now its dedicated cask: the TN 112 which certificate of approval has been obtained in July 2008. This cask is able to transport 12 MOX spent fuel elements with a short cooling time. The first loading of the cask has been performed in September 2008 in the Electricité de France nuclear power plant of Saint-Laurent-des-Eaux. By its continuous involvement in the nuclear transportation field, TN International has been able to face the many challenges linked to the radioactive materials transportation especially talking of MOX fuel. TN International will also have to face the increasing demand linked to the nuclear renaissance.     

Development of intermediate temperature SOFC using LaGaO3 based oxide film

Abstract

The effect of the NiO–Fe₃O₄ (NiFeO)/Ce_0·8Sm_0·2O_2-δ (SDC) ratio on the microstructure and electrochemical activity of cermet substrates was systematically investigated. Dense NiFeO–SDC substrates, which are suitable for the deposition of thin oxide films for example, La_0·9Sr_0·1Ga_0·8Mg_0·2O_3-δ (LSGM) tend to be porous and applicable as anodes in intermediate temperature solid oxide fuel cells (IT SOFC). The porosity and electrical conductivity of the reduced substrates were evaluated with increasing NiFeO ratios. The lowest anode overpotential was measured in a substrate with a NiFeO/SDC ratio of 6:4, especially at a high current density. In a reduced substrate with this composition, continuous frames of SDC and NiFe alloy can be formed simultaneously, thus leading a longer triple phase boundary.     

Characterising polyurethane foam as impact absorber in transport packages

Abstract

Transport and storage packages used for the safe transport of radioactive materials are required to satisfy IAEA regulations. One key design requirement for a radioactive material transport package is that under a 9 m regulatory drop test, containment functions are maintained. For certain payload types, such as fuel assemblies, impact loads on the payloads may need to be controlled in order to maintain spacing and confinement. To achieve all of this, detailed and accurate characterisation of the impact absorbing material is important in order to design an effective shock absorber. Polyurethane foam is an excellent energy absorbing material because it has a relatively high specific strength, a large compressive deformation, much of this at constant force, and a predictable compressive strength characteristic. Traditionally various types of wood have been used for this purpose, however foams are a more cost effective alternative, which are readily available, and can be formed and shaped easily. Some grades may have the added advantage of providing an almost isotropic crush response, combined with significant thermal protection. The general compressive strength properties of foams and their temperature dependencies are well documented by manufacturers; however, strain rate sensitivity and stiffness variation with orientation are not readily available. Hence impact compression tests for polyurethane foams for a range of densities from 56 to 320 kg m^–3 were specified by Rolls-Royce and performed by the Health and Safety Laboratory. These tests included dynamic conditions for a range of strain rates and temperatures and a selection of orientations of the foam. Following collation of the test results, property curves were derived for the range of temperatures at which the package was expected to operate in service between –10 and +75°C. The properties for a given specification of foam will vary within a defined tolerance range, mainly due to the variables inherent during manufacture. Hence nominal static curves were derived for each foam and a number of factors were taken into account to derive the full range of foam properties: density, compressive strength, temperature and manufacturer supplied tolerance. The net result of this work was a series of force displacement plots, depicting upper and lower bounds to account for the cumulative effects of many variables. Accounting for these upper and lower performance bounds is an essential approach in justification of any modern package design. This paper describes the characterisation and mathematical modelling of polyurethane foam for use as the main impact energy absorber in a new design of package for transporting fresh fuel. The non-linear finite element (FE) code LS-DYNA was used to carry out simulation of the tests. The HONEYCOMB material model available in LS-DYNA was used to accurately predict the test measurements of the foam material. The properties derived for the foam were then used as input to the full FE model used for the licensing of the new package design. Full scale drop testing of the package demonstrated good correlation of deformations between test and FE model analysis, providing good validation evidence of the foam characterisation in the transport package.     

Newly developed cordierite–zircon composites

Abstract

Cordierite-zircon ceramic composites were fabricated by die pressing a commercial cordierite powder with the addition of up to 10 wt-% zircon (ZrSiO₄). Sintering of cordierite was enhanced by the ZrSiO₄ addition through glass phase formation. With ZrSiO₄ additions above 2·5 wt-% no further effect on the mechanical properties of the composites was observed. The maximum flexural strength at 2·5 wt-%ZrSiO₄ addition was 84±7 MPa, about 30% higher than the 67±5 MPa found for pure cordierite. The strength of cordierite at 2·5 wt-%ZrSiO₄ increased with sintering temperature up to 1300°C, owing to the enhanced densification. Above 1300°C, however, the strength was reduced as a result of the formation of large pockets of glassy phase. The average fracture toughness of cordierite was increased from 1·0 to 1·5 MPa m^1/2 with the addition of ZrSiO . This toughening can be attri4 buted to crack deflection around ZrSiO₄ particles rather than to residual compressive stresses imposed on the cordierite owing to thermal expansion mismatch between cordierite and the ZrSiO₄ second phase.     

Residual stress and thermal cycling of planar solid oxide fuel cells

Abstract

The published literature relating to damage to planar solid oxide fuel cells caused by thermally induced stresses and thermal cycling is reviewed. This covers reported studies of thermal cycling performance and stresses induced by temperature gradients and differences in thermal expansion coefficients in typical planar SOFC configurations, namely electrolyte supported; anode supported and inert substrate supported cells. Generally good agreement is found between electrolyte residual stresses measured by X-ray diffraction or cell curvature and stresses calculated from simple thermo-elastic analysis. Finite element modelling of temperature distributions in cells and stacks in steady state operation are well advanced and capable of being extended to compute stress distributions. Failure criteria are then discussed for laminated cell structures based on critical energy release rate fracture mechanics models developed originally for coatings. However, in most cases the data required to apply the models quantitatively (such as elastic moduli of actual laminated material and fracture energies of materials and interfaces) are not available. Where data are available there are inconsistencies that require resolution. Seals are critical components in many planar solid oxide fuel cell configurations, but again there are discrepancies in experimental mechanical properties and the role of internal stresses in their fracture. In addition, there is as yet no firm evidence that thermal cycling damage involves any true materials fatigue process.     

Analysis of impact induced accelerations on internal components of light water reactor packages

Abstract

When designing and then licensing a package for the transport of light water reactor fuel, it is normal practice to demonstrate impact performance by conducting drop tests at orientations determined to be the most severe. Usually, accelerometers are fitted to the package during the impact testing so that data may be applied in supporting stress analysis. In most cases the accelerometers are fitted to the external surfaces of the package while the data so obtained is frequently applied to the study of internal components. However, this approach is frequently challenged on the basis that internal accelerations could be different to those measured on the outside of the package, perhaps even higher! Accordingly, International Nuclear Services commissioned a theoretical study looking at a range of accelerations, as measured on the package body and compared these to accelerations on the fuel. This concluded that, with certain parameters acting, accelerations experienced by the fuel could indeed be higher than measured on the package. However, it was more likely that accelerations on the fuel would be lower and of longer duration. The present study demonstrated that there is no simple answer to this issue, nevertheless there is clearly potential for a package designer to minimise impact accelerations on the fuel by considering the fuel basket stiffness and internal clearances in conjunction with package impact characteristics.