40 likes | 118 Views
low-molar-mass materials. Nuclear Reactors. -- fuel is… . ~3% U-235 (natural U is ~0.7% U-235). absorb n 0 , slow down the reaction. -- control rods of B or Cd… . -- moderator : . slows down n 0 to cause fission . reactors in former USSR: graphite . in the rest of the world: water.
E N D
low-molar-mass materials Nuclear Reactors -- fuel is… ~3% U-235 (natural U is ~0.7% U-235) absorb n0, slow down the reaction -- control rods of B or Cd… -- moderator: slows down n0 to cause fission reactors in former USSR: graphite in the rest of the world:water WHY? -- water is heated to steam, which spins electrical- generating turbines control room at a nuclear power plant
Schematic of a Nuclear Power Plant EIW = Emergency Injection Water PORV = Pressure Release Valve
b b Main benefits: (1) no air pollution; does NOT contribute to global warming small volume of material consumed (2) (3) breeder reactors: reactors that generate new fissionable mat’l at a greater rate than the original fuel is consumed -- non-fissionable U-238 is transmuted into fissionable Pu-239 n0 + U-238 U-239 Np-239 Pu-239 Main problem: What to do with waste?
Nuclear Fusion -- also called thermonuclear reactions -- products are generally NOT radioactive -- requires high temperatures (> 40,000,000 K) !!!! WHY? -- the tokamak uses magnetic fields to contain and heat the reaction