1. Lecture 28 Nuclear Energy Chapter 30.1  30.3 Outline Controlled Fission Reaction Fusion in Stars

2. Fusion and Fission

3. Fission Nuclear reactor Fission is splitting of a large nucleus into a few lighter nuclei. lighter The total mass of the products is less that the original mass of the heavy nucleus. Chain reaction 1 0 n+ 235 92 U  141 56 Ba + 92 36 Kr +3 1 0 n Energy released per fission act (estimate): Q = 240 nucl. (8.2  7.2)(MeV/nucl.) = 240 MeV For 1 kg of U: 5.3 10 26 MeV = 2.4 10 7 kWh

4. Fusion Energy output

5. Helium Fusion Later stages

6. Fusion Reactors Fusion requires high temperatures (millions K) and high pressures to keep high-velocity particles close together. At this temperature atoms are ionized (have no bound electrons) are referred to as plasma. For a successful reactor, 2 parameters are important: plasma ion density n and plasma confinement time  Lawson criterion: n   10 14 s/cm 3 for D-T interaction

7. Summary Fission does not require extreme conditions to start chain reaction. However, fusion products are radioactive and need to be buried in special places. Fusion needs extremely high temperatures and densities. The simplest fusion reaction (H  He) produces mostly stable isotopes. mostly