In all of these cases there is a serious attempt to make sure that the workers are not harmed by the dangerous substances involved. I must say that the phrase "impressive body burdens" is fairly incomprehensible.

"Body burden" refers to the amount of Pu that has been ingested and remains in the body. The entire point of safeguards is to minimize body burden and exposure. If someone has a "impressive body burden", it means the safeguards didn't work.