Nuclear Fission & Fusion Objectives: Describe what happens in a nuclear chain reaction. Explain the use of water in the storage of spent fuel rods. Distinguish fission from fusion reactions. Vocabulary Fission, neutron moderation, neutron absorption, fusion

Fission reactions In a fission reaction the nucleus splits apart into smaller fragments. There are 2 fissionable isotopes:U-235 & Pu-239. Nuclear chain reactions make use of the fissionable isotopes to generate enormous amounts of energy for the use in nuclear reactors and atomic warheads. U-235 is hit with a neutron and becomes U-236 (very unstable)

Storage of U-235 the fissionable isotope is contained in a 3 meter fuel rod spent fuel rods are a major source of radioactive waste spent fuel rods can spend a decade in holding tanks as they cool

Neutron Moderation Moderation is the process of slowing down the reaction by having the neutron pass through a barrier before contacting the radio isotope Neutron moderation slows down the neutron using water or powdered graphite to a speed where it will fuse with a new neutron energy is released as the U-235 nuclei splits forming Kr-91, Ba- 142 & 3 neutrons – if not moderated the 3 neutrons will set off 3 more fission reactions – Neutron absorption occurs as cadmium rods are lowered into the reactor core. the absorption of neutrons allows for the slower release of energy and the management of reactor heat levels

Nuclear waste anyone?

Nuclear Fusion Fusion reactions that occur in the center of stars create much more energy than that of a fission reaction. Fusion reactions occur when small nuclei fuse to make a single atom of greater mass. The reaction takes place at temperatures in excess of 40,000,000 o C. The hydrogen bomb makes use of a fission reaction to generate enough heat to fuse a H-2 nucleus with a H-3 nucleus in an uncontrolled reaction.

Sun's Nuclear Reaction 4H  He + 2positrons + energy