The initial loading of the 40 assembly core was highly enriched with 93.2 % uranium - 235 .
The initial loading of the 40 assembly core contained 31 pounds ( 14 kg ) of U-235 .
The initial loading of the 40 assembly core was highly enriched with 93.2 % uranium - 235 and contained 31 pounds ( 14 kg ) of U-235 .