Simplify the following text for a Grade 8 native English-speaking person.
Original: Tritium 's decay product , helium-3 , has a very large cross section for reacting with thermal neutrons , expelling a proton , hence it is rapidly converted back to tritium in nuclear reactors .
Simplified: Tritium made this way lasts for a very short time , so this tritium is not used by people . Instead people make lots of tritium in nuclear reactors , so that they can make things from it .