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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 s

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.

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1. A steam generator comprising: a lower integrated tubesheet and plenum (ITP) configured to receive feedwater, the lower ITP mounted to a lower end of a riser that is positioned above a nuclear reactor core, the riser comprising a fluid pathway for a primary coolant fluid that is heated by the nucl

1. A steam generator comprising: a lower integrated tubesheet and plenum (ITP) configured to receive feedwater, the lower ITP mounted to a lower end of a riser that is positioned above a nuclear reactor core, the riser comprising a fluid pathway for a primary coolant fluid that is heated by the nuclear reactor core;a first set of heat transfer tubes fluidly coupled to a first plurality of stubs protruding from a first side of the lower ITP, wherein at least a portion of the first set of heat transfer tubes is coiled around the riser in a substantially clockwise direction;a second set of heat transfer tubes fluidly coupled to a second plurality of stubs protruding from a second side of the lower ITP, wherein at least a portion of the second set of heat transfer tubes is coiled around the riser in a substantially counter-clockwise direction, the lower ITP comprising an elliptical shape having a major axis in a vertical direction, the major axis substantially parallel to a longitudinal axis of the riser, the first and second sides comprising opposite arcuate sides of the major axis; andan upper ITP fluidly coupled to the first and second sets of heat transfer tubes, the upper ITP mounted to an upper end of the riser, wherein the feedwater entering the lower ITP is converted to steam in the first and second sets of heat transfer tubes by heat transferred from the heated primary coolant that passes through the riser, and wherein the upper ITP is configured to transport the steam away from the steam generator. 2. The steam generator according to claim 1, wherein the first and second plurality of stubs are formed integral to the lower ITP, and wherein the first and second set of heat transfer tubes are welded to the first and second plurality of stubs. 3. The steam generator according to claim 1, wherein the first set of heat transfer tubes comprise one or more rows of tubes that cross over corresponding rows of the second set of heat transfer tubes at an elevation between the lower ITP and the upper ITP. 4. The steam generator according to claim 1, wherein a second lower ITP is fluidly coupled to a second upper ITP by additional heat transfer tubes to provide a secondary path for the steam. 5. The steam generator according to claim 4, wherein the first upper ITP is located on an opposite side of the steam generator as the second upper ITP. 6. The steam generator according to claim 5, wherein the first lower ITP is located on the opposite side of the steam generator as the second lower ITP. 7. The steam generator according to claim 4, wherein the additional heat transfer tubes comprise third and fourth sets of heat transfer tubes having alternating directions of rotation that cross each other in coupling the second lower ITP to the second upper ITP. 8. The steam generator according to claim 1, further comprising a tube support structure including: a main section configured to constrain a plurality of heat transfer tubes in both a radial direction and a vertical direction; anda plurality of smaller sections which mount to the main section and are configured to bracket one or more adjacent heat transfer tubes, wherein the plurality of smaller sections constrain the plurality of heat transfer tubes in substantially the vertical direction. 9. The steam generator according to claim 1, further comprising a plurality of orifices configured to equalize and control a flow of the feedwater through the first and second tube sets of heat transfer tubes. 10. A method of generating steam, comprising: receiving feedwater at a lower integrated tubesheet and plenum (ITP), the lower ITP mounted to a lower end of a riser that is positioned above a nuclear reactor core;circulating a primary coolant through the nuclear reactor core;transferring heat from the nuclear reactor core to the primary coolant;circulating the heated primary coolant from the nuclear reactor core through the riser;guiding the feedwater into a first set of heat transfer tubes fluidly coupled to a first plurality of stubs protruding from a first side of the lower ITP, at least a portion of the first set of heat transfer tubes coiled around the riser in a substantially clockwise direction;guiding the feedwater into a second set of heat transfer tubes fluidly coupled to a second plurality of stubs protruding from a second side of the lower ITP, at least a portion of the second set of heat transfer tubes coiled around the riser in a substantially counter-clockwise direction, the lower ITP comprising an elliptical shape having a major axis in a vertical direction, the major axis substantially parallel to a longitudinal axis of the riser, the first and second sides comprising opposite arcuate sides of the major axis;circulating the feedwater through the first and second sets of heat transfer tubes to an upper ITP fluidly coupled to the first and second sets of heat transfer tubes, the upper ITP mounted to an upper end of the riser;converting the feedwater that enters the lower ITP to steam in the first and second sets of heat transfer tubes by heat transferred from the heated primary coolant circulated through the riser; andtransporting the steam away from the upper ITP. 11. The method according to claim 10, wherein circulating the feedwater through the first and second sets of heat transfer tubes to an upper ITP comprises circulating the feedwater through one or more rows of tubes of the first set of heat transfer tubes that cross over corresponding rows of the second set of heat transfer tubes at an elevation between the lower ITP and the upper ITP. 12. The method according to claim 10, further comprising: receiving feedwater at a second lower ITP;guiding the feedwater to additional heat transfer tubes fluidly coupled to the second lower ITP;circulating the feedwater through the additional heat transfer tubes to a second upper ITP fluidly coupled to the additional heat transfer tubes;converting the feedwater that enters the second lower ITP to steam in the additional heat transfer tubes by heat transferred from the heated primary coolant circulated through the riser; andtransporting the steam away from the second upper ITP. 13. The method according to claim 12, wherein the second upper ITP is located on an opposite side of the steam generator as the first upper ITP. 14. The method according to claim 13, wherein the second lower ITP is located on the opposite side of the steam generator as the first lower ITP. 15. The method according to claim 12, wherein circulating the feedwater through the additional heat transfer tubes to a second upper ITP comprises circulating the feedwater through third and fourth sets of heat transfer tubes of the additional heat transfer tubes that have alternating directions of rotation and that cross each other in coupling the second lower ITP to the second upper ITP. 16. The method according to claim 12, wherein guiding the feedwater to additional heat transfer tubes fluidly coupled to the second lower ITP comprises guiding the feedwater into the additional heat transfer tubes fluidly coupled to additional stubs protruding from the second lower ITP. 17. The method according to claim 12, wherein circulating the feedwater through the additional heat transfer tubes to a second upper ITP comprises: circulating the feedwater through a plurality of orifices;equalizing, based on the circulation of the feedwater through the plurality of orifices, a flow of the feedwater; andcontrolling, based on the circulation of the feedwater through the plurality of orifices, the flow of the feedwater. 18. The method according to claim 10, wherein circulating the feedwater through the first and second sets of heat transfer tubes to an upper ITP comprises: circulating the feedwater through a plurality of orifices;equalizing, based on the circulation of the feedwater through the plurality of orifices, a flow of the feedwater; andcontrolling, based on the circulation of feedwater through the plurality of orifices, the flow of the feedwater.