What is the material for nuclear reactions and how is it prepared?

Uranium ore is harvested from the Earth’s surface. The ore harvested contains a natural radioactive and fissionable isotope U-235 in a small percentage and a nonfissionable isotope U-238 in larger amounts. The ore is purified, enriched to increase the amounts of U-235, and packaged in small ceramic pellets.

How does the nuclear reaction proceed?

These ceramic U-235 pellets are stacked end-to-end in 12-foot Zirconium alloy tubes which are resistant to heat, radiation, and corrosion. The U-235 is bombarded with neutrons, which causes fission. Some of the U-238 is degraded by energy released during U-235 fission into Plutonium, which further degrades and reacts, adding to the heat produced by the other existing reactions.

How is the nuclear reaction controlled?

Rods made of a material that absorbs neutrons are inserted in between the stacks of uranium pellets. The absorption of neutrons prevents fission from continuing and slows down the reaction. If the reaction slows too much the rods can be withdrawn to speed the reaction up again.

Water absorbs the heat produced by the reaction and serves as a “moderator,” by slowing down the neutrons down increasing the chance of fission as the neutrons are forced to slow down and join with the uranium rather than fly past harmlessly. Loss of water slows down the reaction as probability of fission is reduced.

What are the waste products of a nuclear reaction and how are they disposed?

Uranium is degraded during fission leaving unreacted radioactive waste in the form of U-235 that did not undergo fission, plutonium caused by degradation of U-238, and other radioactive elements that are created by further degradation of plutonium such as Polonium and Thorium. These radioactive chunks are in the steel tubes, which are withdrawn from the reactor every 3 to 4 years to be replaced. When this is removed the rods are stored under water in large concrete vaults lined with stainless steel and in aboveground dry storage facilities in steel and lead containers placed inside concrete vaults at the reactor site. Usually these are transferred to an underground storage facility.