Bruce Perens: The Day I Blundered Into the Nuclear Facility
Bruce Perens writes "I found myself alone in a room, in front of a deep square or rectangular pool of impressively clear, still water. There was a pile of material at the bottom of the pool, and a blue glow of Cherenkov radiation in the water around it. To this day, I can't explain how an unsupervised kid could ever have gotten in there."
Is that it?
Not sure whether BMRR or HFBR were water-moderated, but I'd bet it was the Brookhaven Medical Research Reactor. A bunch of beautiful glowing stuff at the bottom of a deep pool of water is a common configuration for a research reactor used for the production of medical isotopes.
I think Bruce might be looking at the past through the lens of today. In the 60s, nuclear plants and labs had a couple of security guards to protect from theft and whatnot. They didn't carry guns. Unless there were secret things going on, these places weren't heavily guarded. Nuclear power wasn't considered a security issue. Nor were airports, train stations, etc.
"Pictures, or it didn't happen":
http://www.orau.org/ptp/collection/medalsmementoes/dimes.htm