700% Processor usage after closing analysis tab

Hello,
Sometimes, when i close the analysis of games or the daily problem (sections of the website using stockfish), my laptop (macbook pro, safari 11.0.2) overheats. I open the activity monitor and i see that safari is using 700% of my CPU (it doesn't happen every time).

Anyone with the same problem ?

700% ? how's that possible. I think the max should be 100% ?

A lot of software reports utilization as percentage of a single-core, so when you have multiple cores you can get numbers >100.

So long as the browser windows running the analysis are closed, I've never seen this happen, but I'm almost exclusively on Chrome+Windows, so it's possible there's something screwy with Safari+Apple OS.

Yeah the problem is not really the percentage but the fact that it doesn't stop computing when i close the tab