Urge simple changes around uranium (7)
I believe the answer is:
impulse
'urge' is the definition.
(I know that urge can be written as impulse)
'simple changes around uranium' is the wordplay.
'changes' indicates an anagram.
'around' is an insertion indicator.
'uranium' becomes 'U' (U is the chemical symbol for uranium).
'simple' anagrammed gives 'implse'.
'implse' going around 'u' is 'IMPULSE'.
(Other definitions for impulse that I've seen before include "Impetus - whim" , "Instinctive motive" , "Sudden urge to do something" , "Miles up (anag)" , "Impel us with sudden urge" .)