Abstract: The invention concerns a nuclear power plant located in an underground cavity, with a small high-temperature reactor which, together with a heat exchanger apparatus, is housed in a steel reactor pressure vessel. The reactor core comprises spherical operating elements which pass through the reactor several times. In order to provide unimpaired access to the components of the primary loop from above, the loading installation of the small high-temperature reactor is designed in a specific manner. It comprises a section located in a loading space under the reactor pressure vessel including a discharge device and a conveyor device. An addition device for fresh operating elements and a collector vessel for used operating elements are arranged either outside the underground cavity or, in the alternative, in the loading space.