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Fission og kernekraft

Fission og kernekraft. Bent Lauritzen Risø DTU. Overview. Atomer og kerner. Radioaktivt henfald , fission. Kædereaktion og kritikalitet. Neutronregnskab. Reaktorer. 2. Atomer og kerner. Elektroner (negative). 10 -10 m. 10 -14 m. Atomkerne. Neutron (elektrisk neutral).

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Fission og kernekraft

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  1. Fission og kernekraft Bent Lauritzen Risø DTU

  2. Overview Atomerogkerner Radioaktivthenfald, fission Kædereaktion og kritikalitet Neutronregnskab Reaktorer 2

  3. Atomerogkerner Elektroner (negative) 10-10 m 10-14 m Atomkerne Neutron (elektrisk neutral) Proton (positivt elektrisk ladet) 3

  4. Atomer og kerner Brint, stabil, 1H Isotoper Deuterium (D), stabil, 2H Tritium (T), ustabil, 3H proton neutron

  5. Nuklidkortet Atomkernerne Antal protoner (Z) Antal neutroner (N)

  6. Z=N 235U

  7. Radioaktivt henfald, fission a b+ b-

  8. Uranium series a b

  9. Stabilitet af kerner Nuclear and Coulomb forces

  10. Bindingsenergi

  11. D n n T U He n Fission Fusion Fission ogfusion Nuclear binding energy

  12. Energy released in fission of U-235 235U + n  144Ba + 90Kr + 2n + 200 MeV Fission energy: Fossil fuel: C + O2 CO2 + 4.1 eV

  13. Energy released in fission

  14. Z=N 235U

  15. Kædereaktion og kritikalitet Kædereaktion

  16. Nuclear chain reaction Effective multiplication factor (keff): No. fission neutrons in one generation / neutrons in previous generation keff < 1 subcritical keff = 1 critical keff > 1 supercritical Start up : keff > 1 Safereactor operation: keff < 1.001

  17. Neutron economy: no. of neutrons per fission fission vs. non-fission cross sections neutron leakage Neutronregnskab

  18. Fission cross section – 235U

  19. Fission cross section – 238U

  20. Nuclear chain reaction Kædereaktion (kritikalitet) er ikke mulig i naturligt uran (0.7% 235U) Men er mulig med Hurtige neutroner, 10-20% beriget uran Moderator (H2O, D2O, grafit), termiske neutroner og naturligt/svagt beriget uran

  21. Neutron-regnskab

  22. Neutron-regnskab

  23. Reaktor kontrol • Antal neutroner • Prompte neutroner • Reaktoren kan ikke kontrolleres af mennesker! lp= time between generations

  24. Reaktor kontrol • Antal neutroner • Forsinkede neutroner • Reaktoren kan kontrolleres!

  25. Formeringsreaktorer Fuel breeding: Neutron yield (h): No. produced neutrons per captured thermal neutron n + 235U  fission fragments + n + n + … n + 238U  239U  239Pa  239Pu

  26. η for 233U, 235U og 239Pu 233U 235U 239Pu  Fast neutrons needed for breeder reactors

  27. Back Reaktorer

  28. Vigtige reaktorkomponenter • Reaktortank: • brændsel (235U, 239Pu..) • moderator (vand, grafit, tungt vand) • kølemiddel (vand, gas, Na) • kontrolstænger (bor, Cd, Hf) • Afskærmning (beton, jern, bly, vand) • Reaktorindeslutning (stål, beton)

  29. Nuclear reactors by type

  30. Boiling Water Reactor - BWR

  31. Pressurized Water Reactor - PWR

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