STMAN deals with three sources of radionuclides: high-level vitrified waste, low-level cementitious waste and spent fuel rods. These different sources are dealt with by the STRENG, STALLION and SPENT options respectively.
Each of these waste forms is assumed to be placed within a bentonite buffer that screens the repository from the surrounding rock. Radionuclides that pass through the bentonite buffer are carried away from the repository by groundwater advection or by diffusion into the host rock.
The physical processes that are modelled in Version 5 of the code include canister failure, solubility limits, diffusion, advection, sorption, and radioactive decay.