Nuclear Reactors

Tu Anh TranCHEM 312

UNLVFall 2013

Background

• Fission: spontaneous radioactive decays of atoms and releases energy

• Energy is converted into heat to produce steam and generate electricity

• Original nuclear reactors were designed for submarines and navy ships

Components of a nuclear reactor

• Fuel• Control rods• Coolant• Containment

Components: Fuel• Fissionable: isotopes that undergo induced fission

when struck by a free neutron• Fissile: isotopes that can sustain a fission chain

reactions when struck by a thermal neutron U-233 U-235 P-239

• Alpha/Beta decays• Neutron capture• Critical mass

Components: Fuel

• Enriched uranium hexafluoride (UF6) is converted into uranium oxide (UO2) powder

• The power is processed into pellets via heat• Stacked pellets are placed into tubes of

corrosion-resistant metal alloy

Components: Control Rods

• Neutron-absorbing materials– Elements with varying capture cross sections for

neutrons of varying energies.– Boron, silver, indium, cadmium

• Can be inserted or withdrawn from the core• Control the rate of reaction• Rods are attached to the lifting machinery by

electromagnets

Components: Coolant

• Circulating fluid through the core to control heat transfer

• Water is a primary coolant• In fast reactors, liquid metals such as sodium

and lead are used• Molten salts• Gas – helium• Hydrocarbons

Components: Containment

• Protective structure around the reactor• Protection against intrusion and radiation

leakage• Steel or reinforced concrete

Types of reactors

• Boiling water reactor• Pressurized water reactors• Liquid-metal fast-breeder reactor

Pressurized Water Reactors

• Operate with thermal neutrons• Steam is generated outside the reactor in

a secondary heat transfer loop

Boiling Water Reactor• water is converted to steam, and then recycled back into

water by a part called the condenser, to be used again in the heat process.

• steam generated inside the reactor goes directly to the turbine

Liquid-Metal Fast-Breeder Reactors• breeder reactors are designed to produce more fissile

material than they consume• the fission reaction produces heat to run the turbine while

at the same time breeding plutonium fuel for the reactor.

Nuclear power plants in commercial production

Sources: Nuclear Engineering Handbook 2011

The Nuclear Reactor Debate

• Environmentally less harmful than fossile fuels• Potential radiation contamination in the event

of a meltdown• Nuclear proliferation and terrorism concerns• Health effect concerns of those living near

nuclear power plants• Political implications preventing new

development of nuclear reactors

References

• http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Power-Reactors/Nuclear-Power-Reactors/

• http://www.nrc.gov/reading-rm/basic-ref/students/reactors.html

• http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/reactor.html