In this paper, a study on a fusion reactor core is presented in heavy-ion inertial fusion (HIF), including the heavy-ion beam (HIB) transport in a fusion reactor, an HIB interaction with a background gas, the reactor cavity gas dynamics, the reactor gas backflow to the beam lines, and an HIB fusion reactor design. The HIB has remarkable preferable features to release the fusion energy in inertial fusion: in particle accelerators HIBs are generated with a high driver efficiency of about 30–40%, and the HIB ions deposit their energy inside of materials. Therefore, a requirement for the fusion target energy gain is relatively low, that would be ~50 to operate an HIF fusion reactor with a standard energy output of 1 GW of electricity. In a fusion reactor, the HIB charge neutralization is needed for a ballistic HIB transport. Multiple mechanical shutters would be installed at each HIB port at the reactor wall to stop the blast waves and the chamber gas backflow, so that the accelerator final elements would be protected from the reactor gas contaminant. The essential fusion reactor components are discussed in this paper.