Orion nuclear pulse - weird question

[Archibald]

World stockpile of nuclear weapons
http://en.wikipedia.org/wiki/List_of_states_with_nuclear_weapons

Simple question: how big an Orion could we build with all these nukes ? (circa 21 000 or so)

 

[Michel Van]

Most of those Nuke are unusable for Orion
there high Bomb yield (up to 4 Mega Tons) would vaporise a Orion
the the optimal Bomb yield is 0.15 Kilo Tons