Assessment of FFTF/MOTA and Thermal Reactor Irradiation Facilities for Advanced TritiumBreeder-Material Tests

Abstract

Irradiations of potential tritium-breeder materials in fission reactors have provided information on material properties and tritium migration. The characteristics of these fission reactor tests, as relevant to anticipated fusion-blanket conditions, can be quantified in terms of parameters such as: 1) tritium production rate, 2) lithium burnup, 3) displacement-damage rate, 4) gas production rate, and 5) nuclear heating (temperature).

Neutronic calculations have been performed to determine the characteristics of breeder-material tests in a fast reactor facility (FFTF/MOTA) and a representative thermal reactor (NRU). Three highly regarded solid-breeder material candidates, Li₂O, LiAlO₂ and LiAlO₂/Be, are considered. Calculations show that effective breeder-material experiments can be performed in both fast and thermal reactor facilities. However, the distinctly different neutron spectra in these reactor types result in breeder-material tests with somewhat different characteristics.

Thermal reactors can be used for high-quality advanced breeder-blanket material tests of Li₂O and LiAlO₂/Be. The principal drawbacks of these tests are low displacement-damage rates and complications in experiment design due to neutron self-shielding. Tailoring fast fluxes and ⁶Li/⁷Li isotopic ratios allows for experiments to investigate displacement-damage effects.

The FFTF/MOTA facility offers two advantages over thermal reactor facilities: a) fast-neutron displacement damage that can match fusion-blanket values, and b) reduced neutron self-shielding effects. The principal limitation of FFTF/MOTA irradiations is the high coolant temperature, which prevents tritium migration experiments in the 400 - 600°C range. Tritium production and lithium burnup rates in LiAlO₂, are also somewhat lower than desired.