Re: the nuclear crisis in Japan, how can spent fuel rods still be radioactive?

Question:

I don't understand how something that is spent can still be active. Isn't that contradicting itself?

Answer:

Basically, Spent fuel rods means that they have become less efficient. These rods are usually removed from their cooled water tanks and placed in a holding water tank for an indefinite time before being stored out of harms way.
The waste from these spent rods is highly radioactive.
Radioactivity decays over many years depending on its strength, in this case thousands of years. If it does take a thousand years then it has what is called a " Half life of a thousand years " which means it will take a thousand years to half its strength. Then another thousand years to half that strength, and so on.

e.g Strength 20 lasts 1000 yrs, Strength 10 lasts 1000 yrs, strength 5 lasts 1000 yrs, and so on.

I admit the above is just the basics. Some clever so and so will probably make it sound easier no doubt.