Tritium fuel cycle in ITER and DEMO: Issues in handling large amount of fuel

Abstract Since tritium resources are very limited, economical conversion of fusion energy to electricity and/or heat must have an enough margin to keep self-fuel-sufficiency and simultaneously ensure tritium safety. To realize this, tritium inventory in reactor systems, which use ∼10 17 Bq (a few kg) of tritium, should be kept as small as possible, under strict accountancy or regulation of a few tens Bq (∼pg). In present tokamaks, however, hydrogen retention rate is significantly large, i.e. more than 5% of fueled hydrogen is continuously piled up in their vacuum vessels, which must not be allowed in a reactor. Moreover, both fuelling and burning efficiencies are very poor, only a few % or less. Accordingly, huge amount of tritium fuel must be recycled. In the paper, after the introduction of tritium as a hydrogen radioisotope, important issues to establish safe and economical tritium fuel cycle for a fusion reactor will be summarized considering the handling of large amounts of tritium, i.e. confinement, leakage, contamination, permeation, regulation and tritium accountancy.