The most common and most likely answer to this crossword clue is the 7 letter word COOLANT
I've seen this crossword clue in The Guardian
C
O
O
L
A
N
T
More clues leading to the result COOLANT
- Firm with nothing left -- worker fluid in a hot situation
- Elegant six-footer that aids Sizewell operation
- Co-worker clamps over line that’s added to engine
- One may take the heat out of the situation
- One should stop overheating coal, not surprisingly
- Unruffled worker prevents things from getting too hot
- For example, water bird circling land, briefly
Buddy explains!
The straight part
We know that "that aids Sizewell operation/Sizewell" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that aids sizewell operation/sizewell = coolant.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does COOLANT mean?
COOLANT noun- A medium, usually fluid, used to draw heat from an object.