Comment by everforward

The death rates might be a difference in units; the Forbes article is using deaths per trillion kWh, the other might be deaths per thousand/million kWh.

The difference in ranking might be down to how they model deaths from nuclear power accidents. One may be using the linear no threshold model, and the other may be using something else. We don't have an agreed upon model for how likely someone is to die as a result of exposure to X amount of radiation, which causes wide gaps in death estimates.

E.g. Chernobyl non-acute radiation death estimates range from 4,000 to 16,000, with some outliers claiming over 60,000. That's a wild swing depending on which model you use.