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Nuclear Reactors and Nuclear Power Prof. Jasmina Vujic Department of Nuclear Engineering University of California, Berkeley ACKNOWLEDGEMENT Some of the slides and cartoons were developed by NEI (Nuclear Energy Institute: Nuclear Power Plant Turbine and Generator Steam

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nuclear reactors and nuclear power

Nuclear Reactors and Nuclear Power

Prof. Jasmina Vujic

Department of Nuclear Engineering

University of California, Berkeley

  • Some of the slides and cartoons were developed by NEI (Nuclear Energy Institute:
nuclear power plant turbine and generator
Nuclear Power PlantTurbine and Generator


Spinning turbine blades and generator

Boiling water

how nuclear reactor works
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).
controlling the chain reaction
Controlling the Chain Reaction



Control rods

Withdraw control rods,

reaction increases

Insert control rods,

reaction decreases

heat generation in nuclear reactor
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
nuclear reactor cooling
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)
heat produces steam generating electricity



Steam produced




Heat Produces Steam, Generating Electricity
nuclear power plant main parts
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
classification of nuclear reactors
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)
classification of nuclear reactors15
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)
classification of nuclear reactors by fuel and fuel cycle
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
uranium is mined and refined
Uranium Is Mined and Refined

The Uranium ore contains a number of complex oxides, including U3O8

safety is engineered into reactor designs
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

multiple layers of safety

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
training courses are accredited
Training Courses Are Accredited
  • Operators Are Continuously Retrained and Retested
federal regulation by the nrc ensures safety
Federal Regulation by the NRC Ensures Safety
  • NRC Inspectors Continuously Monitor Plants
unplanned plant shutdowns declined substantially
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


US Manufacturing

US Finance, Insurance, Real Estate

US Nuclear Power Plant*








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Data Not




















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