Question

Explain why the spent fuel rods from the fission reactors are more radioactive than the initial fuel.

Answer 1

Most of the time we deal with uranium when the word fission is used. Actually U²³⁸ is the main fuel for nuclear reactors, which is very less radioactive material than highly active U²³⁵ (Uranium-235, also called as fissile material). The energy produced in the reactor is not due to the radioactivity of the U²³⁵. Rather, the energy is from bombardment of the U²³⁵ nucleus by fast neutrons impact. The resultant products have a total mass which is smaller than the U²³⁵ itself initially, and the difference in mass is converted into energy according to einstein's equation E=mc².

The fission products tend to be very unstable, so they decay rapidly and release a lot of radiation in the process. These include radioactive emitters like Sr⁹⁰, I¹³¹, and Cs¹³⁷, all are very harmful radioactive nuclides. Sometimes it the process aimed at to produce Pu²³9 and Pu²⁴⁰. Which are also highly radioactive. This is the reason for the origin of the radioactivity from materials of a reactor’s waste (nuclear spent fuel rods).

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