Abstract: 1. A steam boiler-reactor comprising;A. a cylindrical casing having closures at opposite ends thereof,B. a steam generating tube, formed in a helical coil, disposed adjacent the nner surface of said casing and extending substantially between its opposite ends, said coil having an inlet end to which feed water may be delivered and an outlet end from which steam may be delivered to a steam engine,C. a cylindrical screen disposed within and adjacent the helical coil,D. an elongated oxidant injector nozzle tube, having a row of axially spaced injection orifices, extending longitudinally of said casing and within the space within said screen,E. a solid grain of cast lithium substantially filling the remainder of the space within said screen,F. an oxidant comprising a source of sulphur hexafluoride under pressure communicating with said nozzle tube through a valve adapted to control the rate of flow of same,G.