Superphénix was a nuclear reactor in France. It was the largest nuclear reactor in Europe, and it was the first very high power reactor in the world. The reactor was built to produce electricity and to help create energy for France. The reactor produced electricity by splitting atoms, or when the atoms become smaller pieces. This process releases energy that can be turned into electricity. Superphénix also produced materials that could be used in nuclear weapons, so it was important that the reactor was safe. The reactor was shut down in 1998 because safety was a concern.