Show how a chain reaction occurs and define it. Explain critical mass, and why a chain reaction will not occur with a sub-critical mass. Discuss how uranium enrichment is done so that the 0.7% of uranium 235 can be extracted from a sample of uranium, which is mostly U-238. Introduce the nuclear reactor and how it works to produce steam to turn the turbine which turns the generator for electricity. Indicate the main parts like fuel rods, control rods, moderator, and cooling towers.