I worked with low shielded Americanium for a time. We all wore rad badges. I was accidentally exposed once, the rad badge barely blipped. Now, mind you, it wasnt plutonium, but prolonged exposure would have been bad. It has been over 15 years and I show no outward signs. I didnt say it wouldnt have to be shielded, but it wouldnt require 50 pounds of lead. Really, you wouldnt need much at all, maybe a gallon or two of water should be sufficient for such a small piece, and a dimes worth is probably more than needed. I was just using it as an example.
There is a reactor here in Rhode Island at the University of RI's Maritime campus in Narragansett. It has been running for over 30 years. It powers the entire URI campus. On one 10lb bar. they change the bar out and reprocess it on site. In 30 years, they have used 3 bars. And that is probably because it is a 30 year old reactor and is more of a "training" model, than an updated high tech facility. If they went with the latest and greatest, I bet they could make that one bar last 30 years and power much more than just the Kingston/Narragasett campuses.