Operation of a simulated non-steady tokamak fuel loop using the tritium systems test assembly

Abstract

In order to develop a fuel system for a realistic fusion device in near future, a number of experimental campaigns of a simulated fusion fuel loop were performed under practical non-steady conditions at the Tritium Systems Test Assembly (TSTA). Some technical issues specific for non-steady fuel loop were identified and are being investigated further. The overall process loop was operated with non-steady inputs to better interface with pulsed tokamak operation, which requires a rather different and improved processing capability specific to each subsystem. The cryogenic distillation columns in the isotope separation are modified to provide side-stream recycle paths with isotopic equilibration function. This change improved separation characteristics with various feed compositions, and reduces the required number of columns for processing and resulted in a reduced tritium inventory in the isotope separation system (ISS). Another major technical development on the ISS is addition of a number of feed-back control loops that automatically operate the distillation columns stably under changing feed conditions. The plasma exhaust processing system composed of palladium diffuser, catalytic reactor, electrolysis cell and cold trap was operated mainly in the batch mode to handle a broader range of input flow rate and composition in various configurations to minimize tritium loss and inventory. The results demonstrated the overall capability and flexibility of the TSTA loop to serve as a fuel processing system under non-steady conditions; however, they imply that many technical issues arise in operating a practical fuel processing system. These may not be foreseen in the design stage and can only be determined during integrated tests under realistic operating conditions.