This report documents an investigation into the tritium inventory expected in the ARIES-AT fusion reactor. ARIES-AT features silicon carbide fibers in a silicon carbide matrix as its primary construction. It uses the same fusion power core as the previous ARIES-RS. Based on experimental results of several researchers, consideration was given to swelling, sputtering, film coatings, erosion, and implantation. Estimates were made of tritium inventory using the TMAP4 code. About 700 g of tritium may be expected in the machine, two thirds of which would reside in the first wall. Under assumed accident conditions that involve first wall temperatures up to 1000 C, evolution of retained tritium may be expected to vary from 0.8 to nearly 40 percent depending on the temperature of the first wall.