[Retric]

Short half lives are what make something radioactive. It's not 1:1 but basically take the amount of material / half life > how much radiation is being released.

Uranium 238 is extremely stable with a half life of 4.468 billion years, and the more active uranium 235 still has a half life of 0.7 billion years. Which is why they survived geologic timescales from earths formation.

Strontium-90 by comparison is produced in a nuclear reactor and has a half life of 28.8 years making it vastly more nasty. Further, while nuclear waste is incredibly nasty stuff, high neutron fluxes also turn the walls etc radioactive though to a less extreme extent.