The nuclear fuel rods feed the nuclear reactor. There are lots of different variables here, but, in at least one situation, they get to about twenty-eight-hundred-and-eleven-degrees celsius (2811C). This is about fifty-one-hundred degrees fahrenheit (5100F).
Incidentally, the temperature at which you’ve exceeded the ability of the fuel rods to hold more heat is twenty-eight-hundred-and-third celsius (2830C). Past this, your shiny nuclear reactor will go into meltdown. It’s kind of like overcooking a bag of popcorn, though it will take about six-hundred years to get the smoke out of the kitchen.
While I was trying to get a quick answer to the half-life of the radiation from a meltown at the average nuclear power plant, I ran into this interesting tidbit:
To prevent a post-accident nuclear reaction, steps have been taken, such as adding neutron poisons to key parts of the basement.
Not only can the aftermath of a meltdown potentially include a recipe for a nuclear explosion (whoa) but now we know there is something called a “neutron poison” that is [sprayed?] around, like holy water, to prevent an accidental apocalypse? Oh man.
A neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section, in applications such as nuclear reactors. In such applications, absorbing neutrons is normally an undesirable effect. However neutron-absorbing materials, also called poisons, are intentionally inserted into some types of reactors in order to lower the high reactivity of their initial fresh fuel load. Some of these poisons deplete as they absorb neutrons during reactor operation, while others remain relatively constant.
The capture of neutrons by short half-life fission products is known as reactor poisoning; neutron capture by long-lived or stable fission products is called reactor slagging.
I saw this picture while looking for the title picture. The fuel rods glow blue:
The same article mentions a type of material/sensor that will aid in preventing nuclear meltdowns by whistling when the rods start reaching critical levels (most complex detection systems fail before that point):