Port stores uranium in ramshackle holding area (3,9)
I believe the answer is:
dun laoghaire
'port stores' is the definition.
'Dun Laoghaire' can be an answer for 'port' (Irish port). I am not sure about the 'stores' bit.
'uranium in ramshackle holding area' is the wordplay.
'uranium' becomes 'U' (U is the chemical symbol for uranium).
'in' means one lot of letters goes inside another.
'ramshackle' indicates anagramming the letters (I've seen this in other clues).
'holding'+'area'='holdingarea'
'holdingarea' with letters rearranged gives 'dnlaoghaire'.
'u' put into 'dnlaoghaire' is 'DUN LAOGHAIRE'.
(Another definition for dun laoghaire that I've seen is " Port".)