Abstract: In a nuclear power installation comprising a fluid-cooled nuclear reactor, main boilers and main coolant circulators driven by steam turbines to circulate coolant fluid through the reactor core and the main boilers, the circulator-driving steam turbines are driven by steam from auxiliary boilers which are also heated by the hot reactor coolant. This steam, after then being reheated by the hot reactor coolant if desired, may also then drive auxiliary steam turbogenerators provided additionally to main steam turbogenerators driven from the main boilers. Preferably the reactor core is housed in a thick-walled concrete pressure vessel having in its wall thickness first cavities which each house a main boiler and associated steam-turbine-driven coolant circulator and second cavities which each house an auxiliary boiler, an associated auxiliary coolant circulator and a reheater, if such are provided, for steam exhausted from the steam turbines driving the main coolant circulators.