Cold Crucible Melting Research Articles

Creep Analysis and Material Properties Research of Rotary Calciner

Unavoidably, during the aqueous reprocessing of spent fuel, high level liquid waste is produced, which is typically vitrified. A rotary calciner is an essential component of a two-step cold crucible melter equipment system. Owing to the calciner’s long-term operation under high temperature condition, potential effects from metal creep are essential design factors. Stable temperature and stress fields of components of a rotary calciner have been calculated based on the finite element analysis software ANSYS. Furthermore, creep life of creep effects has been evaluated and comparisons among Inconel 690, Inconel625, and SUS 310s tubes’ mechanical property performance have been conducted. The results indicate that all three materials require the mechanical property requirements and SUS 310s exhibits the minimum creep displacement.

Dynamics of liquid metal layer in transverse AC magnetic field

Dynamics of the liquid metal free surface is an important aspect in many different metallurgical processes, such as cold crucible melting and continuous casting. An AC magnetic field can be used to change the shape of the liquid metal volume. Here, we study experimentally and numerically a rectangular liquid metal layer exposed to a transverse AC magnetic field. Depending on different parameters, such as the layer thickness and the surface oxidation, different free surface shapes and their dynamics are observed experimentally. We have simulated this fundamentally three-dimensional process using the coupled open-source software. Based on experimental observations, surface oxidation in the numerical model is approximated as a modified contact angle between the liquid metal and the vessel's walls. The numerical results agree well with experiments. Figs 6, Refs 8.

Development of advanced cold crucible melting of titanium alloys

Cold crucible is used to melt reactive metal scrap at elevated temperatures for high quality castings or to produce spherical powders for additive manufacturing. The most advanced crucibles have a small exit nozzle to pour the molten alloy through the bottom opening protected by graphite or ceramic material. The nozzle operates at high temperature and typically lasts several minutes, possibly adding contamination to the outflowing liquid metal. This paper presents new efforts to improve the technique with the aim to achieve a stable commercial process by introducing melting of scrap metal in the presence of liquid flux of different compositions to purify the liquid metal and to enhance thermal effectiveness. The crucial modification in avoiding contamination is a new type of the non-consumable nozzle made of copper segments and the second coil to supply a high frequency electromagnetic field in the vicinity of the nozzle. The nozzle entrance is protected by a thin solidified layer of the same alloy as the main melt. The AC electromagnetic field adds heating at the outflow, modifies the velocity field, gives a possibility to extract particles, and precludes entrainment of slag into the final casting or into the produced powder. The electromagnetic force permits to control the outflow rate and to increase the superheat of the metal at the outlet. The presence of flux permits shielding of the liquid metal from direct contact with the water-cooled side segments of the crucible. The paper demonstrates the effectiveness of numerical modelling to predict and investigate a variety of options in advancement of the cold crucible technique. Figs 8, Refs 13.

Relationship between Chemical Composition and Ms Temperature in High-Entropy Shape Memory Alloys

Five high entropy alloys with shape memory effect or superelastic effect were prepared by cold crucible melting to understand the effect of their chemical composition on the transformation temperatures. The microstructure and phases of the alloys at room temperature were investigated by optical and scanning electron microscopy. The calorimetric study of these alloys is employed to analyze the reversible transformation from austenite to martensite and to determine the transformation temperatures of the five alloys. The paper presents the results of several published works relating the transformation temperatures of high entropy shape memory alloys (HE-SMA). An experimental database has been built up to understand the influence of the different alloying elements and their related concentrations on the transformation temperature Ms (Martensite Start) of the HE-SMAs. An equation is identified using the database to predict the transformation temperature Ms of a high entropy shape memory alloy as a function of its weighted chemical composition, which exhibits a metallurgical solutioned treatment (ST) state and a specific mixing entropy (ΔSmix/R) range.

Advanced Vitreous Wasteforms for Radioactive Salt Cake Waste Immobilisation

AbstractSalt cake radioactive waste is a remnant solid salt concentrate after deep evaporation of radioactive evaporator concentrate at WWER NPP’s. The traditional cementing of borate-containing liquid radioactive waste, to which the salt cake belongs, leads to a significant increase in the volume of the final product. This work describes borosilicate vitreous wasteforms developed to immobilize radioactive salt cake waste and comprises data on both glass synthesis and characterization. The composition of glass selected for the purpose of immobilisation of the salt cake radioactive waste allows to include up to 40 wt. % of the oxides contained in the salt cake and to reduce the volume of the final product by more than 2 times compared with the cement compound. The batches were melted in a cold crucible melter at 1200 °C. The normalized cesium leaching rate of the vitrified wasteform product was within range 3.0·10-5 – 3.7·10-6 g/(cm2·day).

Cold crucible melting with bottom pouring nozzle

Purpose The purpose of this paper is to investigate a new type of nozzle which is free from erosion and non-contaminating the outflow metal. Cold crucible melting technique with electromagnetic induction is used to obtain reactive metal castings and produce high-quality metal powders for aerospace, automotive and medical applications. An important part of this technology is the nozzle used to pour the molten alloy through the bottom opening. Design/methodology/approach The paper uses mathematical modeling technique, previously validated on multiple similar cases, to investigate a new type of nonconsumable nozzle made of copper segments. Findings The design of the nozzle requires to satisfy the narrow balance between the thin solidified protective layer on the wall while avoiding the blockage of the outflow if the nozzle is frozen completely. The sensitivity of the outflow to the nozzle diameter is investigated. The AC electromagnetic force leads to high mixing rates, transitional flow structures and turbulence of the melt, contributing to the melt shape dynamics and the heat loss to walls. Originality/value The beneficial features of the cold crucible melting to purify the melt from particulate contamination are explained using the full melting and pouring cycle.

Experimental Analysis of the Aluminium Melting Process in Industrial Cold Crucible Furnaces

One of the promising technology that guarantee the high-purity of the processed metal is induction skull melting. The quality of the melting process within such a system strongly depends on the cold crucible design. Hence, the experimental investigation of the cold crucible melting was performed. The experimental investigation was performed for various initial mass of the load. The results of that analysis were used for the assessment of the alloy temperature during the process, free surface shape and the area as well as the liquid metal emissivity. The collected results of the thermal analysis showed that the temperature of molten metal increased within the power input increase. Moreover, results of that analysis showed that the characteristic tooth-shaped jags were created mostly at the centre of the cold crucible segments. In addition, experimental results are suitable for the numerical models validation and further investigation of the cold crucible design.Graphic

Effect of Hydrogen on the Structure, Magnetic and Magnetocaloric Properties of Laves Phase Type-Compounds RE(Fe<sub>0.25</sub>Co<sub>0.75</sub>)<sub>2</sub>H<sub>y</sub> with RE = Ho and Er, y = 0.0, 3.0, 3.5

The crystal structure and overall magnetic properties of RE(Fe0.25Co0.75)2Hywith RE = Ho and Er, were analyzed versus y, the hydrogen content. The single phase C15 type compounds, synthesized using cold crucible HF melting, were hydrogenated and controlled using a PCI apparatus. The impact of hydrogen insertion on the cell parameter, the Curie temperature TCand the magnetization saturation were determined. All compounds and hydrides were found to be ferrimagnets, the magnetic moment of RE and 3d elements being opposite since Ho and Er belong to the 2ndrow of rare earth elements. Depending on the formula, a typical compensation point was in evidence. The 2ndorder character of the ferri ↔ paramagnetic transition was established using the Arrott plot method. Magnetization isotherms vs. magnetic field gives quantified results for the magnetic entropy variation by application of the Maxwell relation. Control of y, the hydrogen content, shows it is interesting for improvement of the MCE of the starting compounds. However increasing y leads to decreased TCat the lowest temperatures, suggesting potential cryogenic uses.

Cold crucible melting and characterization of titanate-zirconate pyrochlore as a potential rare earth/actinide waste form

La-Ce-Gd titanate-zirconate pyrochlore-based ceramics was synthesized at the lab-scale inductive melting unit with a 56 mm inner diameter cold crucible. Batch feeding rate and melting ratio were 3 kg/h and 3 kW h/kg respectively. The ceramics is composed of 85–90 vol% zoned grains of the pyrochlore structure phase, the sample has excellent chemical durability in hot water and may be considered as a promising matrix for actinide – rare earth fraction of high level waste.

Electromagnetic particle separation in the cold crucible melting with novel type bottom pouring nozzle

The cold crucible melting technique is proven to be most effective to obtain reactive metal castings and produce high quality metal powders for aerospace, automotive and medical applications. A weak point of this technology is the graphite/ceramic nozzle used to pour the molten alloy through the bottom opening, which has very limited life time (several minutes) and adds contamination to the high quality final material. The paper uses the mathematical modelling technique, previously validated on multiple similar cases, to investigate a new type of non-consumable nozzle made of copper segments. During the dynamic melting the nozzle entrance is protected by a thin solidifying layer of the same alloy as the main melt. The AC electromagnetic (EM) field effects are investigated for the possibility to extract particles (impurities, precipitates, oxides, bubbles, etc.) from the melt. The dynamics of particles are affected by the hydrodynamic drag, buoyancy, turbulent fluctuations and the EM force via the local pressure distribution. The EM force leads to high mixing rates, transitional flow structures and turbulence of the melt, contributing to the particle dispersion, transport and separation to a desired location. The paper demonstrates effects of flow on the time dependent particle ‘swarm’ transport and separation to the side solidified ‘skull’.

Dominant dimensionless parameters controlling solute transfer during electromagnetic cold crucible melting and directional solidifying TiAl alloys

Electromagnetic cold crucible (EMCC) is widely applied to melt and solidify refractory and reactive materials, the electromagnetically driven flow in the melt leads to intensive transfer behaviors of solute and strongly affects crystal growth. In this paper, a 3-D numerical model for predicting the solute transfer behaviors in a square EMCC used for melting and directional solidifying was established and verified. A two-way coupling method was proposed to calculate the electromagnetically driven flow and its effects on solute transfer. Influences of the dominant dimensionless parameters on solute transfer behaviors in the EMCC were examined, those being the Hartman (Ha), magnetic Reynolds (Rω), coils-melt position (h) and the ratio of the melt height to length (H/L) numbers. Results demonstrate that the solute segregation tends to appear in the vicinity of solid/liquid (S/L) interface, the top of meniscus and the confluence of two eddies near the wall of meniscus. The solute segregation degree (Se=Cmax−CminC0) decreases with increasing Ha, which contributes to the augment of flow intensity in the melt. Moreover, the Se decreases linearly with increasing Rω owing to the intensive oscillation of melt flow. The enhanced EM coupling with increasing H/L results in the decrease of Se in the melt. However, the solute segregation in the corner of the meniscus gradually aggravates with increasing h, which results from the enlarging of lower eddies in the bulk of the melt. The solute segregation in the vicinity of S/L interface is strongly influenced by the scale and the flow intensity of lower eddies, which could change the phase transition path and morphology of crystal during directional solidification process. Larger value of Ha, Rω and H/L, as well as smaller h are beneficial to alleviate the solute segregation in the vicinity of S/L interface.

Properties of Argon Gas Atomized Ti-43Al-9V-Y Alloy Powders

The properties of Ti-43Al-9V-Y alloy powders, which were produced by cold crucible melting and argon gas atomization, were investigated. The results showed that the size of the powders was normal distribution in a range of 10-210μm. The powders possessed a near perfectly spherical shape. The microstructure of the powders was composed of dendritic and cellular crystal grains, and the dendritic crystal grains decreased in finer particles. The X-ray diffraction result indicated that there were two main phases, α2 and B2 in the powders, and the amount of B2 phase increased as the particle size decreased. In addition, the oxygen and nitrogen contents were below 1000ppm and around 140ppm, respectively.

History of Nuclear Waste Glass in France

The history of high level nuclear waste vitrification in France is told, from the first research on the solidification of fission product solutions led by Roger Bonniaud at Saclay in the 1950s, up to the last incineration/vitrification processes still under development in Marcoule. The first pilot facilities, Gulliver and PIVER in Marcoule, opened the way for industrial development, beginning with the Marcoule vitrification facility (AVM) commissioned by COGEMA (now AREVA) in 1978, and followed by the start-up of two vitrification units at La Hague in 1989 (R7) and 1992 (T7), and the implementation of a cold crucible melter on one of the six La Hague vitrification lines in 2010.Looking back over more than half a century reveals some of the keys to French success in this area: a major program of sustained and continuing research (rather than by fits and starts); continuous interaction between “material definition”, “technological research” and “long-term behaviour”; and strong synergy with industry (AREVA) leading to the creation of a Joint Vitrification Laboratory in 2010.

Opportunities for Advanced Ceramics and Composites in the Nuclear Sector

Ceramics have played a crucial role in the development of fission based nuclear power, in glass & glass composite high level wasteforms, in composite cements to encapsulate intermediate level wastes (ILW) and also for oxide nuclear fuels based on UO2 and PuO2/UO2 mixed oxides. They are also used as porous filters with the ability to absorb radionuclides (RN) from air and liquids and are playing a key role in the cleanup at Fukushima. Non‐oxides also find current fission applications including in graphite moderators and B4C control rods. Ceramics will continue to be significant in the near‐term expansion of nuclear power via next‐step developments of fuels with inert matrices or based on thoria and in wasteforms using alternative composite cements or single or multiphase ceramics that can host Pu & other difficult RN. Longer term advances for Generation IV reactors, which will operate at higher temperatures & with higher fuel burn‐up require innovative fuel developments potentially via carbides & nitrides or composite fuel systems. Novel non‐thermal (cement‐like) and thermal techniques are currently being developed to treat some of the difficult legacy wastes. Non‐thermally derived wasteforms developed from geopolymers, composite cements, hydroceramics, and phosphate‐bonded ceramics and thermally derived wasteforms made by Hot Isostatic Pressing and fluidized bed steam reforming (FBSR) as well as vitrification techniques based on cold crucible melting (CCM), Joule‐heater in‐container melting and plasma melting (PM) are described. Future developments in waste treatment will be based on separation technologies for partitioning individual RN along with design & construction of RN‐containing ceramic targets for inducing transmutation reactions. Near demonstration actinide‐hosting ceramic wasteforms including multiphase Synroc systems are described. Opportunities also exist for ceramics in structural applications in Generation IV reactors such as composite SiC/SiC and C/C for fuel cladding and control rods and MAX phases and ultrahigh‐temperature ceramics (UHTCs) may find near core fuel coating and cladding applications. Uses of ceramics in fusion reactor systems will be both functional (ceramic superconductors in magnet systems for plasma control and in Li silicate breeder blankets in tokamaks) and structural including as sapphire diagnostic windows, graphite diverters, and plasma facing C and UHTCs. In all these cases, performance is limited by poorly understood radiation damage and interface controlled processes, which demands a combined modeling/experimental approach.

Coupling electromagnectic and thermo-hydrodynamic simulations to optimize a vitrification furnace heated by direct induction

This study deals with the optimization of a cold crucible melter where electric currents are directly induced in a glass charge. Designs of experiments are used to determine the factors of the crucible design which have an impact on the efficiency, and result in an optimized configuration. Numerical tools are used to lead the experiments: a finite volume software, used to solve hydrodynamics and thermal equations, is coupled to a finite element software which computes the Maxwell equations. The innovation is the use to couple directly areas treated with surface impedance and volume formulations, in electromagnetic simulation. The optimized configuration is then studied comparing numerical simulations and experiments in an industrial unit.

Magnetic levitation of large liquid volume

It is well known from experiments and industrial applications of cold crucible melting that an intense AC magnetic field can be used to levitate large volumes of liquid metal in the terrestrial conditions. The levitation confinement mechanism for large volumes of fluid is considerably different from the case of a small droplet, where surface tension plays a key role in constraining the liquid outflow at the critical bottom point. The dynamic interaction between the oscillatory motion of the free surface and the effects of turbulent flow is analysed using a unified numerical model, which describes the time dependent behaviour of the liquid metal and the magnetic field. The MHD modified k-? turbulence model is used to describe the mixing and damping properties at smaller scales not resolved by the macro model. The numerical multiphysics simulations suggest that it is possible to levitate a few kilograms of liquid metal in a cold crucible without requiring mechanical support from the container walls. Possible applications to the processing of reactive metals are discussed.

Numerical studies of the melting process in the induction furnace with cold crucible

PurposeAims to present recent activities in numerical modeling of cold crucible melting process.Design/methodology/approach3D numerical analysis was used for electromagnetic problem and 3D large eddy simulation (LES) method was applied for fluid flow modeling.FindingsThe comparative modeling shows, that higher H/D ratio of the melt is more efficient when total power consumption is considered, but this advantage is held back by higher heat losses through the crucible walls. Also, calculations reveal that lower frequencies, which are energetically less effective, provide better mixing of the melt.Originality/value3D electromagnetic model, which allows to take into account non‐symmetrical distribution of Joule heat sources, together with transient LES fluid flow simulation gives the opportunity of accurate prediction of temperature distribution in the melt.

Nuclear Waste Immobilization by Vitrification in a Cold Crucible Melter: 3D Magnetic Model of a Melter

AbstractThe design and development of prototype cold crucible melters for waste vitrification are based on models of the basic physical phenomena, including electromagnetic induction and the thermal and hydraulic properties in natural or forced convection. The complexity of new nuclearized facilities results in significant errors on the results of predictive models based on 2D axisymmetric geometry that can only be resolved by modeling the device in 3D geometry. This document discusses the specification and electromagnetic design of a melter carried out using electromagnetic computation software, FLU3D, developed in 3D geometry by Cedrat. The principles and results of this study are directly applicable to nuclear facilities with allowance for the particular requirements of a nuclearized environment.

Free‐surface instabilities during electromagnetic shaping of liquid metals

AbstractElectromagnetic shaping of free surfaces of liquid metals is a well‐known EPM technology used in a couple of metallurgic processes like cold crucible melting, semi‐levitation, and electromagnetic slit sealing, among others. However, the stability of such free surfaces is the most important problem and stability control is crucial for success. Within this context we investigate experimentally the stability behavior of liquid metal free surfaces submitted to a high‐frequency magnetic field. In this case, the induced Lorentz forces act as an electromagnetic pressure directly on the free surface of the liquid met al. We consider three experimental model configurations: (i) Sessile liquid metal drop (ii) liquid metal ring, and (iii) liquid metal disc. In each model experiment, upon increasing the feeding current beyond a certain threshold value, IC, we observe that the initial surface contour becomes unstable resulting in (i) drop oscillations (ii) electromagnetic pinching and (iii) static disc deformations. In each configuration the threshold value depends in a similar manner on the frequency of the applied magnetic field. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Inductive cold crucible melting of actinide-bearing murataite-based ceramics

Murataite-based ceramics doped with U or Th were produced by inductive cold crucible melting (ICCM) at operating frequencies of 1.76 and 5.28 MHz and examined using X-ray diffraction and scanning and transmission electron microscopy. Three distinct murataite polytypes were identified in the U-bearing ceramics: a five- (5C), eight- (8C), and three-fold (3C) fluorite unit cell crystals that respectively make up what is designated as the core, intermediate and rim zones. In contrast, the Th-bearing ceramic contained only the five-fold (5C) fluorite unit cell polytype. The core zone of the murataite in the U-bearing specimens is characterized by UO 2 concentrations as high as 12.1 wt%, which successively diminishes in concentration through the intermediate zone to the rim, the latter of which contains 5.2 wt% UO 2. On the other hand, Th distribution within the murataite crystals is uniform. The difference in phase composition and actinide partitioning in the ceramics is influenced by synthesis conditions. Larger cold crucible size ensures lower crystallization rate yielding zoned crystals with maximum actinide concentration in the core of the murataite crystals that minimizes exposure of the actinide elements to potential leach solutions.