I am only around 100 hours into the game and started a new one with a friend around 50 hours ago. Neither of us really knows anything about combinators and the circuit network and also I don't really want to invest super much time into this. I know this is probably not ideal, but I am just hoping for some help from the great community

So I built this nuclear reactor:
https://factorioprints.com/view/-Kn2afLokZdBO-uHcIAF
(the one that is called "Dome")
It was working for a while and then an alarm started and the electricity goes out if I don't put in the fuel cells manually.
I have no idea, what all the symbols mean and don't know how to proceed.
I tried to screenshot everything of relevance. If I missed something, please let me know.
Thank you for your help in advance!