OK, so 235 kg of U_235 has the same number of fissile units (N atoms = 1000 x N_a) as 5 kg of D-T has of fusible units (2N atoms of combined weight 5 amu, or 1000 x N_a pairs) so (ignoring the N_a for now) one kg of U_235 gives 200 MeV / 235 = 0.85 MeV and the D-T fusion gives 17 MeV / 5 = 3.40 MeV
So, yeah, that's exactly four times the energy per kilogram. Now, why couldn't they just say THAT on the web page instead of the confusing and meaningless "this energy is 3-4 times more powerful than that energy" nonsense? But, thanks 'mikeash for clearing that up for me!
