Ceramic pebble bed development for fusion blankets

Abstract Research on lithium ceramic breeders has been intensive since the late 1970s. The bulk material properties of several candidate lithium ceramics are essentially available, although there is still much work to be done on properties under irradiation and on the overall behavior in blanket modules. Based on these results, lithium ceramic breeder blankets have been selected in many fusion reactor design studies. These lithium ceramics are incorporated into blankets typically as monolithic pellets or packed pebble beds. There is substantial industrial experience with pebble beds made from other ceramics as catalyst supports, and in fabrication and testing of pebbles for advanced fission reactor fuels. In fusion blankets, the pebble bed form offers several attractive features, including simpler assembly into complex geometries, a uniform pore network and low sensitivity to cracking or irradiation damage. Ceramic breeder pebbles have been a focus for several research groups. In general, the database is similar to that of monolithic pellets for the materials studied; basic production and material property data are available, but the irradiation and engineering database remains sparse. In addition to the basic requirements on any ceramic breeder material (such as low tritium hold-up, compatibility with structure, irradiation stability, etc.), the main pebble bed requirements may be roughly summarized as follows: economic, high yield production rates; high average bed (smear) density; adequate bed thermal conductivity; acceptable purge gas pressure drop; adequate crush strength; tolerance to thermal cycling. In this paper, the international ceramic breeder pebble bed database is reviewed with respect to these pebble bed properties, and the R&D needs for reactor blanket development are assessed.