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Nuclear Reactors and Nuclear Power

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Nuclear Reactors and Nuclear Power

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  1. Nuclear Reactors and Nuclear Power Prof. Jasmina Vujic Department of Nuclear Engineering University of California, Berkeley

  2. ACKNOWLEDGEMENT • Some of the slides and cartoons were developed by NEI (Nuclear Energy Institute: http://www.nei.org/)

  3. Nuclear Power PlantTurbine and Generator Steam Spinning turbine blades and generator Boiling water

  4. How Nuclear Reactor Works? • The nuclear reactor converts nuclear energy released in fission of heavy nuclides into heat. • NUCLEAR FISSION: After absorbing a neutron, the heavy nucleus splits into two or more lighter nuclei, releasing neutrons, gamma rays, and neutrinos. Kinetic energy of these fission products is converted into heat. • THE NUCLEAR CHAIN REACTION: One or two neutrons released in fission may be absorbed by other heavy nuclides and trigger further fission events, which release more fission products and neutrons, and so on. • CONTROLLED NUCLEAR CHAIN REACTION: The nuclear chain reaction can be controlled by using neutron poisons and neutron moderators. • NEUTRON POISONS: Reduce the number of neutrons by ABSORPTION PROCESS and thus reduce number of fissions. • NEUTRON MODERATOR: A neutron moderator is a medium which reduces the energy of fast neutrons released in the fission event, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction in THERMAL REACTORS. • COMMON NEUTRON MODERATORS: light water (75% of the world's reactors), solid graphite (20% of reactors) and heavy water (5% of reactors).

  5. Controlling the Chain Reaction Fuel Assemblies Control rods Withdraw control rods, reaction increases Insert control rods, reaction decreases

  6. Heat Generation in Nuclear Reactor • The kinetic energy of fission products is converted to thermal energy when these nuclei collide with nearby atoms. • Some of the gamma rays produced during fission are absorbed by the reactor fuel and structural materials, their energy also being converted to heat. Some escape. • Heat is produced by the radioactive decay of fission products and materials that have been activated by neutron absorption. This decay heat source will remain for some time even after the reactor is shutdown. • A kilogram of uranium-235 converted via nuclear processes contains approximately three million times the energy of a kilogram of coal burned conventionally (8.2 × 1013 J/kg of uranium versus 2.9 × 107 Joules per kilogram of coal

  7. Nuclear Reactor Cooling • Due to heat released in the fuel elements, some type of coolant must circulate through the reactor core to absorb the heat. • COOLANT: Usually water but also a gas or a liquid metal or molten salt. • In some reactors, the coolant also acts as a neutron moderator. • In other reactors the coolant can be mixed with neutron poisons. • Commonly used moderators include regular (light) water (75% of the world's reactors), solid graphite (20% of reactors) and heavy water (5% of reactors)

  8. Steam Generator Steam produced Turbine Electricity Heat Heat Produces Steam, Generating Electricity

  9. Nuclear Power Plant main parts • Nuclear Reactor • a pressure vessel containing the uranium fuel • devices for removing the heat produced by the fissioning fuel • measuring and controlling instruments • protective devices. • Turbine • Generator

  10. Steam Pressurized Water Reactor

  11. Pressurized Water-cooled Reactor (PWR)

  12. Boiling Water Reactor

  13. Boiling Water-cooled Reactor (BWR)

  14. Classification of Nuclear Reactors • Based on neutron energy: Thermal, fast or epithermal • Based on the type of moderator: • Light water moderated (LWR) • Heavy water moderated • Graphite moderated • Molten salt moderated (Li or Be salts)

  15. Classification of Nuclear Reactors • Based on the type of coolant • Water-cooled nuclear reactors (PWR, PHWR, BWR) • Liquid-metal cooled nuclear reactor (Sodium-cooled fast reactors, Lead-cooled fast reactors) • Gas-cooled nuclear reactors (helium, carbon dioxide) • Molten salt cooled nuclear reactors (typically a eutectic mixture of fluoride salts, such as FLiBe)

  16. Classification of Nuclear Rectors by Generation

  17. Classification of Nuclear Reactors by fuel and fuel cycle • Nuclear Fuel Cycle could be defined as a series of stages that nuclear fuel goes through: • The front end • The service period • The back end • Open and Closed fuel cycle • Uranium and Thorium fuel cycles

  18. Nuclear Fuel Pellet

  19. Uranium Is Mined and Refined The Uranium ore contains a number of complex oxides, including U3O8

  20. Uranium Ore  Uranium hexafluoride  Gas  Solid

  21. Enrichment Concentrates the Uranium Isotope

  22. Uranium Is Encased in Solid Ceramic Pellets

  23. Fuel Rods Filled With Pellets Are Grouped Into Fuel Assemblies

  24. The Pebble Bed Reactor (PBR)

  25. Spent Nuclear Fuel

  26. Fuel Assemblies Cool Temporarily in Spent Fuel Pools

  27. =Nuclear Power Plants =Plants that ran out of storage in 2005 Close to 50 Plants Ran Out of Used Fuel Storage in 2005

  28. Temporary Dry Storage On Site

  29. Transportation Containers Are Strong and Safe

  30. Transportation Casks Have Been Tested

  31. Yucca Mountain As A Permanent Disposal Site?

  32. Nuclear Reactor Safety

  33. Safety Is Engineered Into Reactor Designs Containment Vessel 1.5-inch thick steel Shield Building Wall 3 foot thick reinforced concrete Dry Well Wall 5 foot thick reinforced concrete Bio Shield 4 foot thick leaded concrete with 1.5-inch thick steel lining inside and out Reactor Vessel 4 to 8 inches thick steel Reactor Fuel Weir Wall 1.5 foot thick concrete

  34. 45 inch steel-reinforced concrete 1/4 inch steel liner 36 inch concrete shielding 8 inch steel reactor vessel nuclear fuel assemblies Multiple Layers of Safety

  35. Radiation Levels Are Continuously Monitored

  36. Plant Operators Are Highly Trained Using Simulators

  37. Training Courses Are Accredited • Operators Are Continuously Retrained and Retested

  38. Federal Regulation by the NRC Ensures Safety • NRC Inspectors Continuously Monitor Plants

  39. Three-Tiered Approach Results in Excellent Safety Record

  40. Unplanned Plant Shutdowns Declined Substantially The unplanned plant shut downs has been significantly reduced since 1980. In 2000, 59 percent of operating units had zero unplanned shutdowns. Source: WANO 2000 Performance Indicators

  41. US Manufacturing US Finance, Insurance, Real Estate US Nuclear Power Plant* 4.7 4.7 5 4.3 4.2 4.2 4.0 Data Not Available 4 3 2 1.1 0.9 0.8 0.8 Data Not Available 0.7 0.6 1 0.77 0.64 0.26 0.46 0.45 0.34 0.29 0 1992 1994 1996 1997 1998 1999 2000 Industrial Accident Safety Rate at Nuclear Plants Very Low Industrial Accident Safety Rate (IASR): Accidents # Per 200,000 Worker Hours #Number of accidents resulting in lost work, restricted work, or fatalities per 200,000 worker hours *Full- time, on- site employees Sources: WANO and BLS