HTGR is a nuclear reactor which deploy helium gas for its coolant, ceramic materials, mainly graphite, for its core structure, and able to supply nuclear heat outside. Since light water reactors use metal cladding tube for its fuel and light water for its coolant, the outlet temperature is limited around 300 deg C. Its power generation efficiency is only 30% using steam turbine. On the other hand, HTGR can produce high temperature heat around 1000 deg C using ceramic materials which offer resistance to high temperatures and apply gas turbine system which can achieve high power generation efficiency more than 45%. Its produced heat can also apply to various industry fields.
Fuel of the HTGR has fourfold ceramic coating and it confines fission products even at temperature of 1600 deg C. Since its core structure mainly consists of graphite which has enormous heat capacity, core temperature variation is very slow during the abnormal accidents. Even during the loss of the helium gas coolant initiated by piping rupture events, the heat produced by the core will be removed by heat dissipation from reactor pressure vessel so that the fuel will not failure. This means that the HTGR has significant safety which has no concern of core meltdown or radioactivity release accidents.
Structural features and its inherent safety of HTGRs
From the economic point of view, HTGR is a superior nuclear reactor since it can reduce extra facilities due to its inherent safety and achieve high thermal efficiency due to the high temperature heat. The power generation cost of the HTGR power plant is estimated to be about 4.1JPY/kWh. Since the power generation cost of commercial light water reactor is about 5.3JPY/kWh, HTGR can reduce the cost more than 1JPY/kWh.