New uranium crystal used in fission? (7)
I believe the answer is:
nuclear
'fission?' is the definition.
(synonyms)
'new uranium crystal' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'uranium' becomes 'U' (U is the chemical symbol for uranium).
'crystal' becomes 'clear' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'n'+'u'+'clear'='NUCLEAR'
'used in' is the link.
Can you help me to learn more?
(Other definitions for nuclear that I've seen before include "Derived from fission or fusion" , "Clue ran oddly to atomic" , "Such power available" , "one's immediate family?" , "and 6 Down: Power producer" .)