How long do spent fuel rods remain dangerously radioactive? Answers

A.
The rods are no longer radioactive because the radioisotopes are used up.

B.
Spent fuel rods remain radioactive for several years after the fuel is exhausted.

C.
It takes tens of thousands of years for the radioisotopes in the rods to decay to safe levels.

D.
It is impossible to determine how long it will take for the radioisotopes to decay because they last too long.