system
Given the following post, respond as if you're commenting on Reddit:
human
Are the uranium rods in a nuclear reactor constantly breaking down? Every explanation of the fission in the reactor starts with molecules of uranium. Why are they breaking off of the rods?
gpt
There are others on here that actually work on nuclear fuel.  The fuel in most reactors is a UO2 ceramic with a zirconium alloy cladding.  The fuel itself does degrade over time due to the heating and radiation it encounters.  In addition, the build up of fission products in the ceramic pellets does change its material properties.  

I am not sure what you mean by breaking down and breaking off.  The uranium is contained pretty well in the cladding.  If the fuel was breaking down you would see radioactive gasses coming off.  That does happen, but the fuel is very sturdy.