Uranium in flat rebuilt causes weakness (5)
I believe the answer is:
fault
'weakness' is the definition.
(thesaurus)
'uranium in flat rebuilt' is the wordplay.
'uranium' becomes 'U' (U is the chemical symbol for uranium).
'in' is an insertion indicator.
'rebuilt' is an anagram indicator.
'flat' is an anagram of 'falt'.
'u' inserted into 'falt' is 'FAULT'.
'causes' acts as a link.
(Other definitions for fault that I've seen before include "bad service" , "Defect; culpability" , "Defect, mistake" , "Defect or offence" , "Shortcoming" .)