CHERNOBYL

Spent Nuclear Fuel

Old or new nuclear fuel—which is more dangerous? Spent nuclear fuel still contains about 97% of the fissile uranium. When nuclear fuel is "spent," it actually means it is contaminated by radioactive decay products from nuclear fission. Spent fuel is therefore much more radioactive than new fuel. The timing of the experiment was poorly chosen from a contamination standpoint—the fuel was maximally contaminated and due for replacement.