Preliminary studies on MHD simulation and heat transfer analysis for LLCB TBM

Abstract

The assessment of performance of tritium breeding and high-grade heat extraction in Test Blanket Modules (TBM) is one of the prime goals of ITER mission. India has proposed Lead–Lithium cooled Ceramic Breeder (LLCB) as the blanket concept for testing in ITER. The LLCB blanket concept consists of lithium titanate as ceramic breeder material in the form of packed pebble beds, lead–lithium as breeder and coolant. The Pb–Li flows separately around the pebble bed to extract heat from the breeder zones. The Pb–Li flow velocity is moderate enough such that its self generated heat and the heat transferred from ceramic breeder is extracted effectively. Helium is used as coolant for the external box structure. The main design objective is to obtain efficient blanket performance by limiting the structural material temperature to <550 °C, the Pb–Li to FMS interface temperatures within the corrosion limit of <480 °C, ceramic breeder temperatures window between 450 and 920 °C for tritium extraction and to prevent sintering of ceramic pebbles. The Pb–Li flow in presence of high magnetic field (∼4 tesla) is expected to be laminar but may impose some stringent conditions on the heat transfer properties due to magnetohydrodynamic (MHD) effects. Hence, preliminary MHD and thermal analysis of the LLCB TBM is performed by numerically solving the Navier–Stokes equation coupled with the continuity and induction equations over the cross section of a rectangular duct having transverse dimensions of the TBM to determine the pressure drop, fully developed axial velocity ( u) and induced magnetic field ( Bx). A control volume based iterative scheme and a Hartmann number sensitive non-uniform collocated grid is used in this study to evaluate the flow and electrical parameters for the LLCB TBM both with and without insulation coatings. The calculated velocity profile is then used as an input to the energy equation to obtain the temperature distribution and heat flow properties for a single channel within the TBM. For this study the average volumetric heat generated within each zone (layer) surrounding the channel is fed as the source term to the energy equation to study the temperature distribution in different zones of the TBM.