I do not posses any radioactive elements for multiple reasons.
1). I like being fertile. I don't need to be sterilized by constant exposure to radiation.
2). I like being alive. Having a bunch of radioactive metals in and around where you eat, sleep, and live is not a good idea.
3). It is illegal to posses many radioactive elements. If you attempt to buy any quantities of plutonium, for example, not only are you crazy but you can expect to spend many years in prison.
4). Cost. Radioactive elements are not cheap due to all the safety precautions and other procedures needed to purify them.
5). Reactivity. The last thing I want is to have some Uranium oxidize and flake off into my surrounding where I may accidentaly ingest some of it. On the outside, uranium isn't too bad. Internally, uranium is fairly lethal.
6). Storage. What good is an element if it's so nasty that it cannot be displayed? Lead glass is incredibly expensive, and the shipping costs on it are nuts. It would cost a good couple thousand dollars to get a nice lead glass container for your elements.
7). Existance. Many, many, many, many of the radioactive elements will only last for a short time before they have decayed into something else. Do you really want to spend a lot of money on something that will decay into nothing in only a matter of a few years? Also, with many of the radioactive elements if you had enough of it to see it, you'd be dead.
So I do not posses any radioactive elements. My collection is complete at Bismuth. (Minus Tc and Pm). The only "nuclear" elements you could possibly posses in a "pure" form are U-238 and Thorium. Those can be purchased, but again, the radioactivity and reactivity of them makes them very expensive and very difficult to safely display in an element collection.