At first, monitor out-of-control lorry going around nuclear plant (7,5)
I believe the answer is:
morning glory
'nuclear plant' is the definition.
The definition suggests a singular noun which matches the answer.
'at first monitor out-of-control lorry going around' is the wordplay.
'at' becomes 'ningg' (I can't justify this - if you can you should believe this answer much more).
'first' says to take the initial letters.
'of control' is an anagram indicator (I've seen 'control' mean this).
'going around' is an insertion indicator.
The first letters of 'monitor out' is 'mo'.
'lorry' is an anagram of '[lorry]'.
'mo'+'[lorry]'='mo[lorry]'
'ningg' put inside 'morlory' is 'MORNING-GLORY'.
Can you help me to learn more?
(Other definitions for morning glory that I've seen before include "bloomer" , "Flower closing in the afternoon" .)