RESEARCH-AND-DEVELOPMENT WORK FOR THE LITHIUM ORTHOSILICATE PEBBLES FOR THE KARLSRUHE CERAMIC BREEDER BLANKET

The Karlsruhe ceramic breeder blanket design for a demo reactor and for the test objects to be tested in NET is based on lithium orthosilicate (Li4SiO4) in form of 0.5 mm diameter pebbles contained in 6 mm wide gaps between beryllium plates. Two methods have been used to fabricate the pebbles: at KfK the pebbles were manufactured by extrusion, spheroidizing, and subsequent sintering using a fluidized bed, while at Schott Glaswerke, Mainz they were obtained by melting followed by spraying of the melt. Various tests have been performed with pebbles, namely: (a) measurements of the compressive forces which single pebbles can substain, (b) thermal cycling tests of Li4SiO4 pebbles in steel containers, (c) measurements of the effective thermal conductivity of Li4SiO4 beds, (d) in situ tritium extraction experiments using helium as purge flow.