Nuclear Waste Immobilization by Vitrification in a Cold Crucible Melter: 3D Magnetic Model of a Melter
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Nuclear Waste Immobilization by Vitrification in a Cold Crucible Melter: 3D Magnetic Model of a Melter A. Bonnetier Commissariat à l’Énergie Atomique (CEA) Marcoule, BP 17171, 30200 Bagnols-sur-Cèze Cedex, France E-Mail: [email protected] Abstract – The 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. INTRODUCTION Direct induction cold crucible melters have been developed for more than 20 years to vitrify highand medium-level nuclear waste. The design and dimensions of the prototype melters depend on the operational requirements and on the desired melting capacity. The specific features of each melter depend on whether it will be used to vitrify solid or liquid feed, or as part of a sequential incineration-vitrification process. INDUCTION MELTING OF GLASS Nuclear Waste Vitrification The nuclear waste vitrification process must meet multiple constraints both on the melting facility itself and on the end product. A mixture of fission products and glass frit produces a molten glass matrix that is poured into a stainless steel canister. Ideally it must be as stable and homogeneous as possible, since the waste containment properties depend on the matrix quality. Although vitrification techniques have changed considerably over the years, they still require large, complex industrial facilities and must comply with stringent safety criteria concerning reliability and wear because they are designed for continuous operation. With the existing hot crucibles the physical and chemical reactions occurring at the glass/crucible interface and in the molten glass limit the melter lifetime to about 5000 hours before corrosion becomes critical. In industrial operation the atmosphere around the melter is highly radioactive and must be isolated from the exterior by very thick concrete containment enclosures. Any operations, including maintenance, must therefore be performed using telemanipulator arms, complicating the tasks and requiring prior “nuclearization”. Principle of Direct Induction Melting Direct induction melting implies supplying energy directly to the molten glass by induction heating. Direct induction avoids any contact between the energy source (the inductor) and the product being heated. Induction melting is based on magnetic induction, a phenomenon discovered by Michael Faraday i
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