I think we can safely say with hindsight, it was very safe. Reactor 4 was caused by a fluke of circumstances and a few mistakes. It was otherwise a very safe reactor. Once they understood the failure they are able to adjust protocol to ensure it doesn’t happen again. It made the other reactors even safer.

The same thing happened with three mile island. Unit 1 safely continued operation until 2019, which only stopped because of financial pressures (competition with Methane), not because anything was wrong.