Burning uranium in shed leads to inevitable catastrophe (7)
I believe the answer is:
caustic
'burning' is the definition.
(thesaurus)
'uranium in shed leads to inevitable catastrophe' is the wordplay.
'uranium' becomes 'U' (U is the chemical symbol for uranium).
'in' is an insertion indicator.
'shed' becomes 'cast' (shed can mean to discard or cast off).
'leads to' indicates taking the first letters.
The first letters of 'inevitable catastrophe' is 'ic'.
'u' inserted within 'cast' is 'caust'.
'caust'+'ic'='CAUSTIC'
(Other definitions for caustic that I've seen before include "Burning, corroding" , "Chemically burning" , "Able to burn - cutting" , "Burning, corrosive" , "Harsh or corrosive" .)