How does a nuclear power plant work?

1. How does a nuclear power plant work?

The only purpose of a nuclear power plant is to produce electricity. To produce electricity, a power plant needs a source of heat to boil water which becomes steam. The steam then turns a turbine, the turbine turns an electrical generator, and the generator produces electricity. In fossil fuel plants the source of heat is burning coal, oil, or gas. In a nuclear plant the source of heat is a nuclear reactor. Although the basic process is simple, making it work is rather complicated.

First, let’s look at the process that the nuclear fuel produces heat. The fuel for a nuclear reactor is uranium, but not just any uranium. Most uranium atoms (99.3%) consist of a nucleus with 146 uncharged neutrons and 92 positively charged protons; adding the number of neutrons and protons, these atoms have a total of 238 neutrons and protons. We call this number the atomic number, and refer to this nucleus as uranium-238, or just U-238. However, not all uranium atoms have 146 neutrons; 0.7% have 143, so this is called U-235. Even though both U-238 and U-235 are uranium, they have different characteristics. The most important difference is that U-235 spontaneously splits, or fissions, producing two smaller nuclei (called fission products) plus two to five neutrons. The fission products and the neutrons have energy, which is the source of heat. To have U-235 fission efficiently, the uranium fuel in a reactor is enriched; the uranium has gone through a process to increase the content of U-235 from 0.7% to 3 to 4%.

On aspect of the fission products that was a major factor in the TMI accident, is that the fission products are radioactive. A radioactive nucleus changes (decays) to another nucleus by emitting a particle; for fission products, this is a beta particle, which is just a high speed electron.