I don't think that any nuclear reactor has achieved 60% thermal-to-electricity efficiency. In a water cooled reactor the hot side starts with cooler steam than a combustion-fired plant can generate so it's hard to reach really high efficiency. Reactors cooled with helium, molten salts, or liquid metal could theoretically do better but I don't think that any actually-built power reactors have reached 60%.
The brand new EPR achieves only 37% thermal efficiency and that is considered a good number for a power reactor:
The brand new EPR achieves only 37% thermal efficiency and that is considered a good number for a power reactor:
https://www.world-nuclear.org/information-library/nuclear-fu...