Patent Number: 
Section: claims

1. A method of stacking spent nuclear fuel assemblies in a spent nuclear fuel assembly pool containing previously installed first nuclear fuel assembly racks, comprising the steps of: structurally supporting on vertical post, a tier of second spent nuclear fuel assembly storage racks in a spent nuclear fuel assembly pool over and independently of first nuclear fuel assembly rack structural support members;  introducing a vertically oriented spent fuel assembly into a second fuel assembly storage rack while the second fuel assembly storage rack is supported in the spent nuclear fuel assembly pool over and independently of the first nuclear fuel assembly rack structural support members; and then  storing the spent fuel assembly in a vertical orientation in the second fuel assembly storage rack. 2. The method of  claim 1 , including the step of: claim 1 raising the spent nuclear fuel assembly at least partially out of the spent nuclear fuel assembly pool before introducing the spent nuclear fuel assembly into the second nuclear fuel assembly storage rack. 3. The method of  claim 2 , including the step of: claim 2 removing the spent nuclear fuel assembly from a first nuclear fuel assembly rack before raising the spent nuclear fuel assembly at least partially out of the pool. 4. The method of  claim 2  including the step of: claim 2 zone loading the spent nuclear fuel assembly over newer, hotter spent nuclear fuel assemblies. 5. The method of  claim 1 , including the step of: horizontally moving a platform supporting the second fuel assembly storage racks through the spent nuclear fuel assembly pool. claim 1 6. The method of  claim 1 , including the step of: installing the second fuel assembly storage rack over and independently of the first nuclear fuel assembly rack while spent nuclear fuel assemblies are being stored in the first nuclear fuel assembly rack. claim 1 7. The method of  claim 1 , wherein the step of supporting the second fuel assembly storage rack comprises the step of: supporting the second fuel assembly storage rack from hanger rods from a spent fuel assembly pool operating deck. claim 1 8. The method of  claim 1 , wherein the step of supporting the second fuel assembly storage rack comprises the step of: supporting the second fuel assembly storage rack on spent fuel assembly pool floor posts. claim 1 9. The method of  claim 2 , wherein the step of raising the spent nuclear fuel assembly at least partially out of the spent nuclear fuel assembly pool comprises raising the spent nuclear fuel assembly into a vertically oriented transfer cask. claim 2 10. The method of  claim 2 , wherein the step of raising the spent nuclear fuel assembly at least partially out of the spent nuclear fuel assembly pool comprises raising the spent nuclear fuel assembly into a vertically oriented transfer cask partially extending above the surface of the spent nuclear fuel assembly pool. claim 2