Used fuel contains the highly radioactive products of fission (see high level waste below).

Spent fuel in the storage pools contains far more radioactive materials than the reactors do.

The old fuel contains most of the radioactivity that the plants produced in their lifetimes.

The spent fuel whose monitoring is now at issue contains far more plutonium, perhaps enough for five bombs.

Some fuels like natural gas, for instance, contain only very low boiling, gaseous components.

Spent nuclear fuel from normal light water reactors contains plutonium, but it is a mixture of plutonium-242, 240, 239 and 238.

The fuel being discharged contained enough plutonium for five to six additional weapons.

Fossil fuels such as coal and oil contain a significant amount of sulfur.

The most common fuels contain carbon along with combinations of hydrogen and oxygen.

Spent fuel contains heavy metals, and they aren't called heavy for nothing.