CANADIAN CERAMIC BREEDER TECHNOLOGY - RECENT RESULTS

Pebble bed ceramic breeders have been under development in Canada for over ten years. The goal is to fabricate and characterize these materi als for use in engineering test reactors and in subsequent fusion powe r reactors. The program emphasis is on 1.2 mm diameter Li2ZrO3 and Li2 TiO3 pebbles. Practical use of these pebbles requires a mass-productio n fabrication process, and characterization of the pebble beds with re spect to bed behaviour and irradiation effects. This paper summarizes the relevant work within Canada since 1991. The fabrication process pr esently used is suitable for mass production, and is in the process of being transferred to industry. Thermal cycling tests have been conduc ted on zirconate and titanate pebbles under both laboratory and ''engi neering'' conditions. Cycling reduces the pebble strength, although th ere are indications that different fabrication conditions produce more robust pebbles. This is an active area of work. Single-size lithium z irconate pebbles have been well-characterized in terms of the bed ther mal conductivity and purge gas pressure drop. Recent results include m easurement of thermal conductivity from 100 to 1200 degrees C (and 0-2 bar), and of purge gas pressure drop as a function of porosity. Binar y beds have also been studied, using steel or lithium zirconate smalle r pebbles. Extensive irradiation testing of the as-fabricated ceramic is a critical factor in their acceptance. Lithium zirconate has been c haracterized under several European irradiation tests, and 1.2 mm lith ium zirconate pebbles have been tested to 5.2% lithium atom burnup and over 250-1000 degrees C in the BEATRIX-II and CRITIC-2 purged-capsule experiments. Tritium release is rapid even at low temperatures, with no effects of burnup seen. The pebble bed temperature has been consist ent with model predictions, and stable under irradiation. Post-irradia tion anneal tests of lithium titanate show good tritium release. Post- irradiation examination of the BEATRIX-II lithium zirconate pebbles is just beginning. Reference blanket designs have been developed based o n breeder-in-tube geometry. Engineering-oriented tests have been carri ed out on large-volume (41) and long-pin (3 m) geometries, to characte rize the behaviour of the pebble beds under more realistic conditions. The results of the work described here, and related tests within the world fusion community, continue to support the use of these ceramic b reeder pebbles in fusion reactor blankets.