Experimental studies of active temperature control in solid breeder blankets

Abstract

A program of model development and experimentation has been undertaken to develop innovative methods to provide predictable and controllable thermal barrier regions for solid breeder blankets. In particular, particle beds have been studied because of their unique thermalhydraulic properties. It has been demonstrated that large variations in thermal conductance can be obtained in the thermal barrier region by external control over the gas pressure and composition in a metallic particle bed. By providing this “active” control mechanism, adjustments in the blanket temperature profiles can be made during operation to accommodate changes in power levels, time-dependent changes in material behavior, and design uncertainties. Data are presented for the effective thermal conductivity of several single-size and binary beds of aluminum, for a range of He and N 2 gas pressures, and for a number of different porosities. Data for the wall conductance also are presented. The relative contribution to the temperature drop due to wall conductance is smallest in single-size beds with smaller particles. The variation of wall conductance with pressure is small or non-existent, suggesting that the wall region is dominated by conduction through the solid particle contact points, rather than gas in the Smolukovski zones.