Induction heating of composite billet of T91 and Zircaloy-4 for manufacturing of double clad tube: Simulation and experimental validation

Metallic fuel is the preferred choice for future Fast Breeder Reactors due to higher breeding ratio. A mechanical bonded double clad tube with a T91 steel outer shell and Zr inner liner is a potential choice for metallic fuel. However, the metallurgical bonded clad tube will have superior properties against the mechanical bonded tube. The metallurgically bonded co-axial tube of T91 and Zr/Zircaloy-4 (Zr-4) can be manufactured by the co-extrusion route. The significant difference in deformation behavior of the two alloys demands a temperature gradient over the thickness of the composite billet for co-extrusion. The fine control of temperature gradient across the cross section of the billet can be achieved only by induction heating. The present study focuses on simulating the induction preheating process of a double-clad billet of outer T91 and inner Zr-4. A 2-D axisymmetric model was considered and simulation studies with several key parameters such as coil frequency, current, pitch, and diameter were carried out with an aim to reduce temperature variation at the interface of T91 and Zr-4 in the billet. Simulations using optimised coil frequency and current reduced the temperature variation at the interface to as low as 22 °C. Subsequent simulations with variable coil pitch and diameter reduced the temperature variation to less than ±3 °C at the interface ignoring axial ends. The mean temperature across the T91 was 967.4 °C and across Zr-4 was 850.3 °C. Experiments were conducted for the co-axial tube of T91 and Zr-4 to validate the simulation model.