The objective of fusion safety research is to help realize the potential of fusion as a safe and environmentally benign energy source. While there are no long-lived radionuclides produced directly by it, the deuterium-tritium fusion fuel cycle nevertheless burns, breeds, and processes large quantities of radioactive tritium, and creates significant additional radioactive material via neutron activation of structural and other materials. Research on fusion safety is focused on the prediction of the extent of radioactive material production, and analysis of transport of this material throughout a reactor facility during both normal operation and off-normal or accident scenarios.
A variety of computational tools are used and developed for these purposes. Neutronic analyses are typically performed with MCNP; neutron fluxes and energy spectra from MCNP are used in codes such as ALARA and FISPACT to predict activation product generation. The results of these codes are used to categorize the radioactive waste produced from fusion and as inputs to radionuclide transport codes. The latter include MELCOR-Fusion and TMAP. MELCOR-Fusion is a customized (by Idaho National Laboratory [INL]) version of the MELCOR code developed at Sandia National Laboratory for LWR severe accident analysis; it is used to model thermal-hydraulic transients as well as simultaneous radionuclide transport in the form of dust or tritiated water. TMAP (also developed by INL) models gaseous tritium transport and permeation, a primary contributor to fusion reactor source terms.
Codes and analyses such as those described above are informed where necessary by complementary experiments, e.g. conducted at the Safety and Tritium Applied Research (STAR) facility at INL. These have included tritium solubility and diffusivity measurements in a variety of fusion-relevant solid and liquid materials; measurements of tritium retention in neutron-irradiated and plasma-exposed materials; and oxidation measurements on fusion-relevant materials such as beryllium.