Just being closed cycle isn't enough. A couple of the early British reactors apparently exposed the public to low levels of neutron and gamma radiation in normal operation because part of the cooling loop was outside the radiation shield for cost-saving reasons.

A lot of early reactors did a lot of things we now recognize as members of the "pants on head" category of activities. We know better now because back then they didn't, and had to discover what not to do the hard way. We are fortunate to have such examples, and would be foolish to squander such hardly learned knowledge.