the circulation of air or water without pumping, owing to the different densities of cold and heated segments of their trajectory, the circulation of the coolant in the reactor coolant system without the use of the reactor coolant pumps, the circulation is due to the natural convection resulting from the different densities of relative cold and heated portions of the system, vedeliku ja gaasi ringlemine ilma pumba jõuta tänu külma ja sooja keskkonna tiheduste erinevusele