Cold Crucible Melting Research Articles

Liquid metal induction heating modelling for cold crucible applications

The time dependent numerical model of cold crucible melting is based on the coupled electromagnetic, temperature and turbulent velocity field calculation accounting for the magnetically confined liquid metal shape continuous change. The model is applied to investigate the process energy efficiency dependence on the critical choice of AC power supply frequency and an optional addition of a DC magnetic field. Test cases of the metal load up to 50 kg are considered. The behaviour of the numerical model at high AC frequencies is instructively validated by the use of the electromagnetic analytical solution for a sphere and temperature measurements in a commercial size cold crucible furnace.

Plasma sputtering of an alloyed target for the synthesis of Zr-based metallic glass thin films

ZrTiAlCuNi films are deposited by plasma sputtering from an alloyed target prepared by induction – cold crucible melting method. The films are found to be amorphous and exhibit a composition very similar to the target one. It is shown that the amorphous character of the deposits is rather due to the high glass forming ability (GFA) of the Zr-based alloy system, than to the deposition method used. The sputtering process of the alloyed target, composed of mixed Zr-containing phases, has been studied. It appears to be a global process leading to a quasi-congruent transfer of the target elements into the film.

Experimental and numerical study of the cold crucible melting process

The cold crucible, or induction skull melting process as is otherwise known, has the potential to produce high purity melts of a range of difficult to melt materials, including Ti–Al and Ti6Al4V alloys for Aerospace, Ti–Ta and other biocompatible materials for surgical implants, silicon for photovoltaic and electronic applications, etc. A water cooled AC coil surrounds the crucible causing induction currents to melt the alloy and partially suspend it against gravity away from water-cooled surfaces. Strong stirring takes place in the melt due to the induced electromagnetic Lorentz forces and very high temperatures are attainable under the right conditions (i.e., provided contact with water cooled walls is minimised). In a joint numerical and experimental research programme, various aspects of the design and operation of this process are investigated to increase our understanding of the physical mechanisms involved and to maximise process efficiency. A combination of FV and Spectral CFD techniques are used at Greenwich to tackle this problem numerically, with the experimental work taking place at Birmingham University. Results of this study, presented here, highlight the influence of turbulence and free surface behaviour on attained superheat and also discuss coil design variations and dual frequency options that may lead to winning crucible designs.

Characterization of Glass Melts Containing Simulated Low and Intermediate Level Radioactive Waste

In order to examine the process parameters for the vitrification of Low and Intermediate Level radioactive Waste (LILW) generated from nuclear power plants, measurements of several melt properties was performed for four selected glasses containing simulated waste. Electrical conductivity and viscosity were determined at temperatures ranging from 1123 to 1673℃. The temperature dependences of both properties in the molten state showed a similar behavior in which their values decrease as the temperature increases. The values of the electrical conductivity and viscosity at a temperature of 1423 K adopted in an induction cold crucible melter process were 0.27~0.42 S/cm and 9.8~42 dPas, respectively.

Mixed Organic and Mineral Waste Processing by Incineration-Vitrification : Case of Bituminous Media

ABSTRACTBurnable radioactive waste management options are often in favour of the vitrification due to their volume reduction, resulting in cost saving for transport and storage. More, the interest is also to obtain a best radioactivity immobilization in a long-lasting matrix. Development made on incineration-vitrification process must take into account radioactivity environment in term of process compactness, gas treatment and secondary wastes. A new and simplified equipment, using thermal oxygen plasma coupled with a cold crucible melter, is being developed at the Valrho-Marcoule nuclear centre (France) : SHIVA, for Advanced Hybrid System for Incineration and Vitrification. As part of studies concerning the management of bitumen canisters stored in Marcoule, the feasibility of their treatment in an incineration-vitrification process have been tested. This treatment could concern the most radioactive bituminised waste drums because they have to be sent in a costly storage site in consideration of their radioactivity. The interest of such treatment is first to reduce the volume of wastes in order to appreciably diminish the cost of this storage.

Synroc-D Type Ceramics Produced by Hot Isostatic Pressing and Cold Crucible Melting for Immobilisation of (Al, U) Rich Nuclear Waste

AbstractA synroc-D ceramic consisting mostly of spinel, hollandite, pyrochlore-structured CaUTi2O7, UO2, and Ti-rich regions shows promise for immobilisation of a HLW containing mainly Al and U, together with fission products. Ceramics with virtually zero porosities and waste loadings of 50-60 wt% on an oxide basis were prepared by cold crucible melting (CCM) at ∼1500°C, and also by subsolidus hot isostatic pressing (HIP) at 1100°C to prevent volatile losses. PCT leaching test values for Cs were < 13 g/L, with all other normalised elemental extractions being well below 1 g/L.

An electromagnetic and thermal analysis of a cold crucible melting

To investigate the performance of a cold crucible employed for the melting of corium, which is a mixture of UO 2 and ZrO 2, a computational analysis of the coupled electro-magnetic field, heat transfer, and fluid flow is carried out. Governing differential equations, basic numerical methods, computational model, and the results of the simulation of cold crucible melting are discussed. By comparing the analysis results with the experimental data, it is shown that the proposed computational model reasonably predicts the fundamental characteristics of a cold crucible melting.

Electrical behavior of platinum-group metals in glass-forming oxide melts

This paper presents an experimental study of the electrical conduction mechanisms in glass-forming oxide melts containing RuO 2 needles. The composites were obtained by melting calcine in an industrial-scale induction-heated cold crucible melter. The temperature dependence of the conductance was measured by complex impedance spectroscopy, using a four-electrode cell, from 1200 °C to 400 °C. Direct current analysis revealed that even with low RuO 2 content, electronic and ionic transport occurred over a wide temperature range. The RuO 2 particle dispersion significantly enhances the total electrical conductivity up to 1200 °C. Percolation theory associated with tunneling conduction models is used to describe the electronic contribution to the conductivity. An equivalent circuit is proposed to describe the mixed ionic–electronic transport. The electronic conductivity not only depends on the RuO 2 content, but on the particle length-to-diameter ratio and the RuO 2 solubility.

Investigation of the cold crucible melting process: experimental and numerical study

The dynamic process of melting different materials in a cold crucible is being studied experimentally with parallel numerical modelling work. The numerical simulation uses a variety of complementing models: finite volume, integral equation and pseudo-spectral methods combined to achieve the accurate description of the dynamic melting process. Results show a gradual development and change of the melting front, fluid velocities, magnetically confined liquid metal free surface, and the tempera-ture history during the whole melting process. The computed results are compared to the experimental temperature measurements and the heat losses in the various parts of the equipment. The free surface visual observations are compared to the numerically predicted surface shapes. Tables 2, Figs 5, Refs 8.

Insights from the Recent Steam Explosion Experiments in TROI

The paper discusses the results of steam explosion experiments of TROI-13, TROI-14, and TROI-15, which were performed under the research program named “Test for Real cOrium Interaction with water (TROI).” TROI-13 and TROI-14 used corium, which is a mixture of UO2 and ZrO2 at a 70:30wt%, while TROI-15 used ZrO2. These three cases resulted in spontaneous steam explosions. It is an important observation from the aspect of the explosivity of prototypic material, as it was not observed in the previous experiments. Various aspects of the test results including cold crucible melting, hydrogen generation, melt temperature measurement, debris morphology, size distribution of the debris, dynamic pressure, dynamic force, shape of the melt jet, location of the trigger, response of the vessel pressure, and the response of the water pool temperature are discussed. The potential contributors to the explosivity of corium are suggested.

Application of cold crucible for melting of UO 2/ZrO 2 mixture

Using the cold crucible melting method, which has been found to be the best technique for the melt preparation of highly refractory materials, melting and discharge experiments for TiO 2, ZrO 2 and UO 2/ZrO 2 mixtures were conducted. The cold crucible, 15 cm in diameter and 20 cm in height, was used to get from 3 to 10 kg melts depending on the materials. Volatile gases generated during the melting period were well released through a hole of ∼2 cm in diameter and 10 cm in depth. The rubble crust layer with a gas vent hole, which is stably formed at the top of the melt, contributed to reduce the radiation loss from the melt surface. In reducing the thickness of the bottom crust, a partitioned plug is more effective than a solid plug, resulting in the easy achievement of the melt discharge. The most important factors for successful melting and discharge of refractory materials are the gas release hole and the plug shape. The developed melt discharge method was successfully applied to the fuel coolant interaction experiment using ZrO 2 and UO 2/ZrO 2 mixtures.

Cold-Crucible Induction Melter Design and Development

The international process for immobilization of high-activity waste from aqueous fuel reprocessing is vitrification. In the United States joule-heated melter technology has been implemented at West Valley and the Savannah River Site, but improved melter concepts are sought to bring down the costs of processing. The cold-crucible induction melter (CCIM) design is being evaluated for many applications, including radioactive wastes because it eliminates many materials and operating constraints inherent in the baseline technology. The cold-crucible design is also smaller, less expensive, and generates much less waste for ultimate disposal. In addition, it should allow a much more flexible operating envelope, which will be crucial if the heterogeneous wastes at the U.S. Department of Energy (DOE) reprocessing sites are to be vitrified.A joule-heated melter operates by passing current between water-cooled electrodes through a molten pool in a refractory-lined chamber. This design is inherently limited by susceptibility of materials to corrosion and melting. In addition, redox conditions and free metal content have exacerbated materials problems or lead to electrical short-circuiting causing failures in developmental DOE melters. In contrast, the CCIM design is based on inductive coupling of a water-cooled high-frequency electrical coil with the glass, causing eddy currents that produce heat and mixing.While significant marketing claims have been made by technology suppliers and developers, little data is available for engineering and economic evaluation of the technology, and no facilities are available in the United States to support testing. In addition to verifying the capabilities of the technology, further development can exploit opportunities for optimization through better understanding of the electromagnetic thermal phenomena intrinsic to the cold-crucible melter. Induction frequency, applied power, and coil and crucible configuration are all related but independent variables that can be explored to optimize throughput while designing a system for maximum reliability in a remote environment. This paper is an introduction to the technology as it applies to vitrification of materials not electrically conductive at ambient temperatures, the potential for research improvements, and the new system being built at the Idaho National Engineering and Environmental Laboratory.

Insights from the Recent Steam Explosion Experiments in TROI

The paper discusses the results of steam explosion experiments of TROI-13, TROI-14, and TROI-15, which were performed under the research program named “Test for Real cOrium Interaction with water (TROI).” TROI-13 and TROI-14 used corium, which is a mixture of UO2 and ZrO2 at a 70:30wt%, while TROI-15 used ZrO2. These three cases resulted in spontaneous steam explosions. It is an important observation from the aspect of the explosivity of prototypic material, as it was not observed in the previous experiments. Various aspects of the test results including cold crucible melting, hydrogen generation, melt temperature measurement, debris morphology, size distribution of the debris, dynamic pressure, dynamic force, shape of the melt jet, location of the trigger, response of the vessel pressure, and the response of the water pool temperature are discussed. The potential contributors to the explosivity of corium are suggested.

Electromagnetic continuous pulling process compared to current casting processes with respect to solidification characteristics

Electromagnetic continuous pulling (EMCP) process combines the advantages of the cold crucible melting (no pollution, no crucible consumption) with those of continuous casting (high material flow rate, uniform material structure and properties). It is compared to the usual casting techniques for massive crystalline silicon, i.e. directional solidification, Czochralski pulling, and floating zone pulling. The presentation is focused on technical productivity parameters, and on longitudinal distribution of impurities, typically oxygen and iron. This allows a semi-quantitative comparison between the 4 processes, having in prospect the use of a cheaper feedstock, together with the photovoltaic quality requirements.

Solubility study of Ti,Zr-based ceramics designed to immobilize long-lived radionuclides

Aqueous alteration of five Ti-Zr-oxide-based ceramics containing elements simulating long-lived radionuclides was studied experimentally by leaching at 90 °C in deionized water for more than one year under conditions of high solid/liquid ratios. Four of these ceramics were synthesized by coldcrucible melting (two Synroc-like materials, one zirconia, and one aluminotitanate) and the fifth ceramic was a hot-pressed Synroc. Melted Synroc-like ceramics have the same major constitutive phases as hot-pressed Synroc, but crystal sizes are very different, millimetric as opposed to micrometric, respectively.

Reliable data for high-temperature viscosity and surface tension: results from a European project

Results are reported of work carried out for the European Commission under contract number MATI CT 940006, between 1994 and 1998. The project provided recommended surface tension-temperature relationships for copper and nickel samples prepared by cold crucible melting to ±3%, by the levitation and sessile drop methods, and values were also obtained for iron and gold in preliminary studies. For copper, (γ/N m -1 ) = 1.304 - 0.289 × 10 -3 [(θ - 1083)/°C]; for nickel, (y/ N m -1 ) = 1.781 - 0.285 x 10 -3 [(θ - 1455)/°C]. Comparison of terrestrial measurements with those made in microgravity have shown that the Cumming's equation is a reliable and satisfactory method of correcting the surface tensions derived with the levitated drop method for the effect of electromagnetic pressure. For measurements with an oscillating cylinder viscometer, recommended viscosity-temperature relationships are given for copper, nickel, and iron. For copper, log 10 (η/mPa s) = -0.2791 + [1245.5/(T/K)]; for nickel, log 10 (η/mPa s) = -0.5038 + [2029/(T/K)]; and for iron, log 10 (η/mPa s) = -0.6494 + [2568/(T/K)].

Evaporation behavior of aluminum during the cold crucible induction skull melting of titanium aluminum alloys

Taking the Ti-Al binary alloy as an example, this article studied the evaporation behavior of Al during the cold crucible induction skull melting (ISM) process of titanium alloys. A formula was deduced to predict the activity of Al in a molten Ti-Al binary system. The calculated activity of Al negatively deviates from an ideal solution. A model was established to judge the evaporation controlling mode and, on this basis, several conclusions were obtained. (1) The evaporation controlling mode of Al in molten Ti-Al transfers from the evaporation reaction controlling mode to the double controlling mode (diffusion and evaporation reaction) with increasing melt temperature (Tms) and/or Al content (xAl) and/or decreasing pressure (P) in the melting chamber. (2) The expression P≤Pcrit (Pcrit≈0.44 Pe(Al)) is a criterion used to judge whether the evaporation is in the state of free evaporation. (3) The term Pimpe (Pimpe=(3.5 to 4) Pe(Al)) is a critical value which impedes the evaporation loss. Almost all of common used ternary additions could enhance the activity of Al in molten Ti-Al and, accordingly, aggravate the evaporation of Al, except for Zr. The enhancing sequence is Y, Ni, Nb, Mn, V, Fe, Cr, Mo, Cu, Si, W, Mg, B, and Sn. The Al evaporation mass-transfer losses, measured from the melting experiments of several titanium aluminum alloys, were in reasonable agreement with the calculated results.

Purification of Ti–Al Alloys by Induction-Heating Floating-Zone Melting and Cold-Crucible Melting in Ultra-High Vacuum

The effect of ultra-high vacuum melting on the purification of Ti-Al alloys, especially on reducing gaseous impurities, is investigated using new floating-zone melting furnace and cold-crucible melting furnace in which ultra-high vacuum of 10 -7 Pa is attainable. Ultra-high vacuum melting is effective in the purification of Ti-Al alloy, especially in reducing oxygen content. The high purity homogeneous Ti-Al alloy ingot containing 85 mass ppm oxygen is obtained from Ti of 99.99 mass% purity and Al of 99.9998 mass% purity by cold-crucible melting twice in argon and lastly in ultra-high vacuum. The Ti-Al alloy bar prepared from Ti of 99.9999 mass% purity and Al of 99.9998 mass% purity by arc melting is further zone-melted under ultra-high vacuum and 36 mass ppm oxygen in the bar is reduced to 13 mass ppm. The new floating-zone melting furnace and cold-crucible melting furnace which can attain to ultra-high vacuum of 10 -7 Pa are useful for the preparation of high-purity Ti-Al alloy containing low concentration of gaseous impurities.

Effect of Synthesis Conditions on Phase Composition of Pyrochlore-Brannerite Ceramics

ABSTRACTThree melted samples of pyrochlore-brannerite-based ceramics produced under different redox conditions were examined. Two of the samples were produced using cold crucible melting at ~1600 C. The third sample was obtained via melting in a microwave oven at 1700-1800 C. All the samples are composed of major pyrochlore and brannerite phases, and minor rutile and UO2-based solid solution or pseudobrookite phases. Pyrochlore-structured phases predominate in all three samples and account for 50-60% of the total bulk. Two pyrochlore varieties – Ca-pyrochlore (predominant) and Ba-pyrochlore have been found in these samples. The latter phase is more stable at high temperatures than the Ba-hollandite present in sintered pyrochlore-rich Synroc-F ceramics. Decomposition of the Ba-hollandite results in rutile formation in the melted samples.

Murataite-based ceramics for actinide waste immobilization

AbstractStudying the Synroc, doped with a simulated HLW, we have found, along with conventional Synroc phases (zirconolite, perovskite, hollandite), an extra phase with a stoichiornetry (Ca, Mn, U, TR)4(U, TR, Zr, Ti) 2(AI, Ti)7O22. XRD and TEM study has shown this phase is related to a very rare mineral murataite. In the present work a ceramic based on murataite is studied. The ceramic samples in the system: Ca-Mn-Ti-Zr-U-Ce-AI-Fe-O were produced and examined in details using XRD, SEM/EDS, TEM, and optical microscopy. Total amount of actinide (U) and rare earth (Ce, Gd) elements in the murataite exceeds 20 wt%. Isomorphic substitution schemes in the structures of synthetic and natural murataites are discussed. High isomorphic capacity of the murataite structure towards actinides and REEs, flexibility of its composition, feasibility of synthesis by melting, including a cold crucible melting, and very high chemical durability under hydrothermal conditions make the murataite-based ceramics very promising for actinides and excess weapon Pu fixation.