Adjective : a fissionable nucleus; fissionable material.    From Dictionary.com. 

Hence every uranium reactor produces this new fuel from the non-fissionable uranium 238.    From Wordnik.com.  [The Peacetime Applications of Atomic Energy] Reference

It relies upon thousands of linked separators, also known as "calutrons" to create U-238 from non-fissionable U-235.    From Wordnik.com.  [Archive 2002-12-01] Reference

One of the remaining l. 5 neutrons might produce an atom of the new nuclear fuel out of the non-fissionable isotope to replace the atom consumed.    From Wordnik.com.  [The Peacetime Applications of Atomic Energy] Reference

They can produce new nuclear fuel out of non-fissionable material, thus increasing the amount available to supplement the only naturally occurring fissionable element-the 0.7% of uranium which has atomic weight 235.    From Wordnik.com.  [The Peacetime Applications of Atomic Energy] Reference

Centrifuges do not remove impurities, they enrich the fuel by increasing the proportion of fissionable U-235 relative to the proportion of non-fissionable U-238.    From Wordnik.com.  [Yahoo! Buzz US: Top Stories] Reference