Sentence:  Unlike the plutonium case one more barrier for potential proliferation of 233U can be created by <WSD>denaturising</WSD> it by mixing it  with  the  non-fissile  isotope  238U  (in  practice  with  depleted  uranium)  to  create  'reactor grade'   but  not  a 'weapon  grade' 233U/238U  mixture  not  adherent  to  chemical  separation. 
Meaning of the word marked with <WSD> tags:  Combine fissionable material with nonfissionable material.