Please do some research before you post:
“U-233 is produced from thorium-232 by neutron capture. It can be made highly pure because it can be chemically separated from Th-232 rather than by mass, which is far easier. Therefore, there is no weapons-grade concentration for U-233. Since it can relatively easily be made pure, it is regulated as a special nuclear material only by the total amount present rather than by concentration or concentration combined with the amount. Uranium-232 is a contaminant that is present only in small amounts, but whose highly radioactive decay products like thallium-208 make handling more difficult.”
http://en.wikipedia.org/wiki/Weapons-grade