Just a wild guess or speculation on my part but I think Rickover likely understood what was a stake at Chalk river or the potentials and acted accordingly. Our own handling of nuclear material even at that time had still not fully realized the hazards. Some DOD/DOE boo boo’s are all over the place including in my county which was part of the Manhattan Project.
I understand Rickover was a real SOB, but...I can appreciate the fact that he got things done, and he generally got them done right.
And you are right. He saw both hazard and opportunity, and probably thought he could help ameliorate the hazard, and take the opportunity to get valuable experience and knowledge.