A steam generator includes a lower integrated tubesheet and plenum (ITP) configured to receive feedwater and a first set of heat transfer tubes fluidly coupled to a plurality of stubs protruding from a first side of the lower ITP. A second set of heat transfer tubes fluidly couples to plurality of stubs protruding from a second side of the lower ITP. The first set of heat transfer tubes is coiled in a substantially clock-wise direction, and the second set of heat transfer tubes is coiled in a substantially counter-clockwise direction. The steam generator further includes an upper ITP fluidly coupled to the first and second set of heat transfer tubes, wherein the feedwater entering the lower ITP is converted to steam in the first and second sets of heat transfer tubes. The upper ITP is configured to transport the steam away from the steam generator.