Eli5 How does nuclear fuel get spent so fast?

Question

With the half life of the radioactive metals used in the fuel rods being thousands of years, the fuel used in reacors, i would think, should last for similar amounts of time. How come nuclear plants go through large ammount of spent fuel that then has to be stored?

In: 23

Answer 1

Because inside the reactor we use unnatural practices to slow the neutrons down so they collide into each other and create fission.