e g steel in general cylindrical shell 208 conducts heat and withstands pressure thermal radiation and seismic induced stresses the cylindrical shell 208 can be fabricated using materials approved for use in nuclear reactor pressure vessels for example in some implementations cylindrical shell 208 includes a steel base material such as sa302 gr b sa533 gr b class 1 sa 508 class 2 or sa 508 class 3 that may be clad with type 308l 309l type 304 austenitic stainless steel other base materials can be implemented such as 16mnd5 20mnmoni55 22nimocr3 7 15kh2mfa a 15kh2nmfa a with sv 07kh25n13 and or sv 08kh19n10g2b austenitic cladding in some examples cylindrical shell 208 does not provide any shielding to block or otherwise inhibit potentially harmful radiation generated by spent fuel rods 204 however in some other examples cylindrical shell 208 is provided with radiation shielding cylindrical shell 208 can be fabricated using rolled plate or ring forgings the wall thickness of cylindrical shell 208 can be between about 1 5 and 4 5 inches in any event the material and thickness of cylindrical shell 208 provides sufficient strength to withstand stresses associated with the design limit pressurization spent fuel rods 204 are secured in place near the bottom of vessel 202 inside the riser channel 216 and supported by a lower support plate 214 e g as also shown in fig2 b and lower support structure 211 as shown the lower support plate 214 and riser channel 216 form a u201c basket u201d which cradles spent fuel rods 204 and facilitates natural circulation of coolant 206 in this example fuel barrel support shield 210 includes a fuel barrel and radiation shield that supports a plurality of individual racks 212 it is attached.