The notorious isotope named; Uranium 238 (natural uranium).
If ever it (the little rock) would traverse the Ocean again it would probably cause serious problems for anybody transporting it.
One reference in this particular case would be a Kraftwerk album from 1975?
Natural uranium can be used to fuel both low- and high-power nuclear reactors.
Historically, graphite-moderated reactors and heavy water-moderated reactors have been fueled with natural uranium in the pure metal (U) or uranium dioxide (UO2) ceramic forms.
However, experimental fuelings with uranium trioxide (UO3) and triuranium octaoxide, (U3O8) have shown promise.
Please see: Not On The Wall I.