once radioactive material gets inside them it will be there for the rest of their lives.
Wrong. Many radioactive isotopes aren't absorbed by the body and are flushed out rapidly, and some of the most damaging particles (alpha emitters in particular) are at their worst when airborne, only staying 'in' your body for the length of a breath. There are some isotopes that are absorbed easily (namely Iodine), but they are the minority. There is not a single "Radiation", there are a staggering number of different radioactive elements, and for each one, the chemistry matters far more than the half-life.
If they had actually improved on the traditional incandescent, they would not need to have a law passed in order to displace...
This is what I was responding to. Sorry for the miscommunication.
That works out to an energy density of (mgh)=1.5e9 J/m. Multiply that by 1600 km, and you get 2.5e15 J, or half a megaton, equivalent to the yield of a small hydrogen bomb. Anyone ever see a superconducting magnet quench?