Patent Number: 
Section: claims

1. A method comprising:operating a pressurized water reactor (PWR) wherein the operating includes circulating primary coolant in a pressure vessel upward through a nuclear reactor core that includes a plurality of fuel assemblies and a plurality of control rod drive assembly guide structures suspended above the plurality of fuel assemblies, wherein each fuel assembly includes a plurality of fuel rods containing a fissile material;during the operating, accommodating upward strain of the fuel assemblies and downward strain of the control rod drive assembly guide structures by a gap between the tops of the fuel assemblies and the bottoms of the suspended control rod drive assembly guide structures,wherein the control rod drive assembly guide structures are suspended in the pressure vessel from a support member disposed above the control rod drive assembly guide structures. 2. The method of claim 1, further comprising:during the operating, not applying a downward force other than gravity against the fuel assemblies. 3. A method of operating a pressurized water reactor including a pressure vessel having a plurality of fuel assemblies and a plurality of control rod guide assemblies suspended above the plurality of fuel assemblies, comprising the steps of:operating the pressurized water reactor;circulating primary coolant in the pressure vessel upward through the plurality of fuel assemblies;during the operating, accommodating upward strain of the fuel assemblies and downward strain of the control rod drive assembly guide structures by a gap between the tops of the fuel assemblies and the bottoms of the control rod drive assembly guide structures,wherein the control rod drive assembly guide structures disposed in the pressure vessel are suspended from a support element disposed above the control rod drive assembly guide structures. 4. The method of claim 3, further comprising:during the operating, not applying a downward force other than gravity against the fuel assemblies.