A favorable distribution of the fuel temperature in combination with a high cooling gas outlet temperature as necessary for a helium-turbine power plant can be achieved in a pebble-bed reactor with “once-through-then-out” fueling without leaving the scope of present feasibility. The equilibrium cycle is reached after a well-balanced and short running-in period. For non-base-load operation, the reactor can be controlled by moving the control rods in the upper void above the pebble bed. Withdrawing the rods causes an increase of the maximum fuel temperature by only 56°C. To avoid replacing of the side reflector during a time of 30 yr, the fast-neutron flux in the reflector can be remarkably lowered by inserting a certain amount of neutron poison into the reflector graphite and by an outer ring of “breeding” fuel elements, respectively.