EU court rules nuclear energy is clean energy

This is clean, until something goes catastrophically wrong.

(Which eventually it will. The more reactors, the more chances for it to happen.)

You are incorrect fortunately.

Western designs are safe, most Soviet-era ones are/were not. It's unfortunate that nuclear power still has this stigma, as it's like saying "all cars are unsafe" while comparing the crash test ratings of a modern sedan to a 1960's chevy bel aire.

Then why did Fukushima happen?

The main reason is a combination of negligence by the owner of the plant and not enough enforcement of standards. The fukushima powerplant was known to have sea wall lower then required and as such was vulnerable to a tsunami (this was known for quite a long time) Combined with backup power in the basement (also against standards)

For an example of what happens to a reactor build according to safety requirements see the onagawa nuclear powerplant