K. Morita, N. Noda (Ed.)
Proceedings of 2nd International Workshop on Tritium Effects in Plasma Facing Components at Nagoya University, Symposion Hall, May 19-20, 1994
Date of publication:
tritium effects, plasma facing components recycling, re-emission, inventory, permeation, diffusion, trapping, detrapping, recombination
The 2nd International Workshop on Tritium Effects in Plasma Facing Components was held at Nagoya University in Nagoya, Japan on 19 and 20 May, 1994. Reflecting the growing importance of tritium effects in fusion reactor materials, the number of participants increased from about 30 for the first workshop in Livermore, California to 46 for the present workshop. A total of 30 talks by participants from 9 different countries made this a very interesting workshop. The workshop was hosted by Professor K. Morita of Nagoya University and Dr. N. Noda of the National Institute for Fusion Science. Organization of the Workshop was assisted by Dr. R. Causey, Dr. E. Vietzke, Dr. C. Wu, and Dr. M. Yamawaki. Approximately 1/3 of the talks discussed the migration and retention of tritium in graphite and other forms of carbon. This topic has more or less come to maturity with general agreement on most of the different aspects of tritium reactions with the carbon. At lower temperatures(<800K) , a tritium plasma interacts with graphite by forming a saturated layer on the geometrical surface, by forming a codeposited layer of sputtered carbon and tritium in areas of net deposition, and by allowing tritium diffusion along pore surfaces fairly deep into the graphite. At higher temperatures(>800K), the principal reaction of tritium with carbon is intergranular diffusion with high energy trapping. If graphite is used in ITER, the main sources of tritium inventory will be codeposition of tritium with carbon in the cool areas surrounding the divertor and trapping at high energy sites created by neutron irradiation. Because beryllium is now the reference plasma facing material for ITER, several presentations on the reaction of tritium with beryllium were presented. For beryllium the consistent theme is inconsistency. There is no agreement on the diffusivity, solubility, trapping, or surface recombination rate coefficient for tritium in beryllium. The oxide layer appears to be the principal reason for the differences in the data generated for the tritium interaction. It was agreed at the workshop that tritium retention in the ITER beryllium will not be as bad as it would have been for graphite, but the inventory may still reach the kilogram level. There were also several presentations on tritium permeation through metals other than beryllium. These presentations varied from tritium superpermeability to tritium migration in thermal and electrical gradients. The first talk of the workshop was presented by D. Mueller of the TFTR Group. He presented the most recent results of the DT operation in TFTR. After a few small glitches in the beginning, the use of tritium in this tokamak has gone very smoothly. Results show enhanced magnetic confinement of the tritium(greater than deuterium which is greater than protium). While the inventory of tritium in TFTR is steadily increasing with time, the invessel retention remains significantly below the imposed 1 gram limit. New records for fusion energy in controlled devices are being set almost on a weekly basis. The workshop closed with a decision to definitely hold a 3rd workshop somewhere in Europe immediately before or after the 12th PSI. Preparing for DT operation in ITER will continue to make this an important workshop for the next several years.