Final recipient of unstable uranium needs recipe (3,4)
I believe the answer is:
end user
'final recipient' is the definition.
(as in the end user of a product)
'unstable uranium needs recipe' is the wordplay.
'unstable' indicates anagramming the letters.
'uranium' becomes 'u' (U is the chemical symbol for uranium).
'recipe' becomes 'r' (abbreviation).
'u'+'needs'='uneeds'
'uneeds' is an anagram of 'enduse'.
'enduse'+'r'='END-USER'
'of' is the link.
(Other definitions for end user that I've seen before include "Ultimate recipient of goods" , "Receiver of product" , "Person for whom a product is destined" , "not interested in the beginning?" , "One who finally receives a product" .)