Reduction in carbon dioxide (CO₂) emissions from industries is crucial for achieving carbon neutrality by 2050. Steelmaking is one of the major CO₂ emission sources owing to the CO₂ emission as a result of reduction of iron ore using coke, which is mainly carbon, and the large scale of the steelmaking industry. Presently, novel steelmaking processes without CO₂ emissions using hydrogen for iron ore reduction are under research.
 In this study, we proposed a hydrogen-steelmaking process using high-temperature gas-cooled reactors (HTGRs), which involves the production of hydrogen through heat and electricity generated by an HTGR and the reduction of iron ore through this hydrogen (Fig. 1). This process offers the advantage of using the electricity to refine direct reduced iron to steel in an electric arc furnace. Achieving completely CO₂-free steelmaking is possible using a carbon-free method for HTGR hydrogen production. The heat and mass balance of this steelmaking process was calculated using process flow analysis, and the CO₂ emissions were evaluated using the mass balance. CO₂ was generated only through the consumption of graphite electrodes in the electric arc furnace. The CO₂ emission from this process (7 m³/t-steel) was only 0.7 % of that from a conventional blast furnace-steelmaking process (1,047 m³/t-steel). Thus, the hydrogen-steelmaking process using HTGR can considerably contribute to realize future carbon neutrality by replacing blast furnace-steelmaking plants with those using this innovative approach.