The spherical tokamak (ST) operates in a steady state with a high fusion gain. The 0-dimensional power balance model, including radiation losses to determine Q value as an inductive fusion gain, and the current balance model for determining QCD as a non-inductive fusion gain, is used to investigate the viability of D-3He fuel for a steady-state operation. The spherical tokamak’s geometry, including the magnetic field Bt and βth as a ratio of its kinetic pressure to the magnetic pressure, is used to analyse the impact of the confinement enhancement factor Hy2 and the impurity density fraction fI on QCD. By comparing the obtained values with the device data, plasma characteristics, such as the safety factor qI and Greenwald density limit NG are examined to determine the optimum density limit and safety factor in the satisfaction of Q ≈ QCD as the aim of steady-state operation. A comparison with ARIES-III performance is also made. The overall plant power balance equation is included. Furthermore, the desirable plant thermal efficiency value ηth and normalised beta value βN for producing net electric power PNET > 1 GW for the ST are achieved. Therefore, ST’s capability of having a lower aspect ratio A and higher elongation κs than ARIES-III in generating more significant fusion power with lower Hy2 and higher energy confinement time τE is approved
