The HTR-200 design has the following remarkable technical features [5]:

• Spherical fuel elements with tristructural isotropic-type (TRISO) coated particles are used, which have a proven capability of fission product retention under 1600 °C in accidents.

• Ceramic materials, i. e. graphite and carbon bricks that are resistant to high temperatures, surround the reactor core.

• The decay heat in fuel elements is assumed to be dissipated by means of heat conduction and radiation to the outside of the reactor pressure vessel, and then taken away to the ultimate heat sink by water cooling panels on the surface of the primary concrete cell. Therefore, no coolant flow through the reactor core would be necessary for the decay heat removal in loss of coolant flow or loss-of-pressure accidents. The maximum temperature of fuel in accidents will be limited to 1600 °C.

• Spherical fuel elements are charged and discharged continuously in a so-called ‘multi-pass’ mode, which means the fuel elements pass through a reactor core several times before reaching the discharge burn-up.

• Two independent reactor shutdown systems are foreseen. Both systems are assumed to be located in the graphite blocks of the side reflector. When called upon, neutron absorber elements will fall into the designated channels located in the side reflectors, driven by gravity.

• The reactor core and steam generator are housed in two steel pressure vessels, which are connected by a connecting vessel. Inside the connecting vessel, a hot gas duct is mounted. All pressure-retaining components, which constitute the primary pressure boundary, are in touch with the cold helium of the reactor inlet temperature.

• Under an accident with complete loss of pressure, the primary helium inventory will be released into the atmosphere due to the radioactive material in the primary helium loop being very low and then will be no fuel failure during a loss-of-coolant accident (LOCA).

• Several HTR-PM (pebble bed module) modules could be built at one site to satisfy the power capacity demand of a utility. Some auxiliary systems and facilities could be shared among the modules.