The risks of tsjernobyl, would an organisation like CERN judge such a reactor, would be much higher than the risk that the Sovjet Union judged.
A risk of 0.000001% judged by a "science and welfare"-driven party is a neglectible risk. For if not, why haven't we started creating an anti-meteorite defense system yet? Granted such a risk is not manmade, still the answer would be: too costly compared to the neglectible risk.

But I do wonder how the reactor meltdown risk was judged in Japan. Did they anticipate a future earthquake? Did they took their chances by building one regardless, because they needed it for their progress?

Errors happen, but I am confident that nuclear reactor designs are now made in such a way that thermal meltdowns, like the one that almost happened in tsjernobyl, are simply not possible anymore. We are experienced enough to fully master the science; both on level of organisation/management and scientific knowledge. There's not a soul wandering through CERN that doesn't know what everything does. Unlike tsjernobyl. I believe we have grown up in that.

However, I can cope with the idea that, unless the whole world has grown up, we must not start building nuclear reactors everywhere. While we may have them under control, a terrorist attack could not be ruled out.