RadiationRadiation

Nuclear ReactorsNuclear Reactors

Nuclear ReactionsNuclear Reactions

Uranium is a fairly common element on Uranium is a fairly common element on Earth and was incorporated into the Earth and was incorporated into the planet during the planet's formation planet during the planet's formation

U-238 makes up 99 percent of the U-238 makes up 99 percent of the uranium on the planet uranium on the planet

Uranium-235 makes up about 0.7 Uranium-235 makes up about 0.7 percent of the remaining uranium found percent of the remaining uranium found naturally naturally

Uranium-235 has an interesting Uranium-235 has an interesting property property

Nuclear ReactionsNuclear Reactions

U-235 decays naturally, just as U-238 U-235 decays naturally, just as U-238 does, by alpha radiationdoes, by alpha radiation

U-235 also undergoes spontaneous U-235 also undergoes spontaneous fission a small percentage of the timefission a small percentage of the time

Fission is defined as “the splitting of an Fission is defined as “the splitting of an atom”atom”

Also, U-235 is one of the few materials Also, U-235 is one of the few materials that can undergo induced fissionthat can undergo induced fission

Nuclear ReactionsNuclear Reactions

If a free neutron runs into a U-235 If a free neutron runs into a U-235 nucleus, the nucleus will absorb the nucleus, the nucleus will absorb the neutron without hesitation, become neutron without hesitation, become unstable and split immediatelyunstable and split immediately

The probability of a U-235 atom The probability of a U-235 atom capturing a neutron as it passes by is capturing a neutron as it passes by is fairly highfairly high

In a reaction two or three neutrons are In a reaction two or three neutrons are ejected from each fission causing other ejected from each fission causing other fissions to occurfissions to occur

Nuclear ReactionsNuclear Reactions

The process of capturing the neutron The process of capturing the neutron and splitting happens very quicklyand splitting happens very quickly (1 x 10(1 x 10-12-12 seconds) picoseconds seconds) picoseconds

An incredible amount of energy is An incredible amount of energy is released, in the form of heat and released, in the form of heat and gamma radiation, when a single atom gamma radiation, when a single atom splitssplits

The energy is released because the The energy is released because the products and the neutrons, together, products and the neutrons, together, weigh less than the original U-235 atomweigh less than the original U-235 atom

Nuclear ReactionsNuclear Reactions

The difference in weight is converted The difference in weight is converted directly to energy at a rate governed by directly to energy at a rate governed by the equation E = mcthe equation E = mc22

a pound of highly enriched uranium a pound of highly enriched uranium used to power a nuclear submarine or used to power a nuclear submarine or nuclear aircraft carrier is equal to about nuclear aircraft carrier is equal to about a million gallons of gasolinea million gallons of gasoline

a pound of uranium is smaller than a a pound of uranium is smaller than a baseball and a million gallons of baseball and a million gallons of gasoline would fill a five-story buildinggasoline would fill a five-story building

Nuclear ReactionsNuclear Reactions

In order for a reactor to work, a sample In order for a reactor to work, a sample of uranium must be of uranium must be enriched enriched , so that it , so that it contains two to three percent or more of contains two to three percent or more of uranium-235 uranium-235

Weapons-grade uranium is composed Weapons-grade uranium is composed of 90 percent of 90 percent

Nuclear PowerNuclear Power

uranium is formed into pellets with uranium is formed into pellets with approximately the same diameter as a approximately the same diameter as a dime and an inch longdime and an inch long

These pellets are then placed in rods These pellets are then placed in rods that are “super critical” meaning they that are “super critical” meaning they would over heat and melt if left alonewould over heat and melt if left alone

To prevent this, To prevent this, control rodscontrol rods made of a made of a material that absorbs neutrons are material that absorbs neutrons are insertedinserted

Nuclear PowerNuclear Power

The depth the rods are inserted into the The depth the rods are inserted into the uranium, determines the amount of uranium, determines the amount of fission taking placefission taking place

All the way in… the reactions stopAll the way in… the reactions stopAll the way out….the reactions increase All the way out….the reactions increase

until meltdown occursuntil meltdown occursThe uranium bundle acts as an The uranium bundle acts as an

extremely high-energy source of heat. It extremely high-energy source of heat. It heats the water and turns it to steamheats the water and turns it to steam

Nuclear PowerNuclear Power

The steam drives a steam turbine, The steam drives a steam turbine, which spins a generator to produce which spins a generator to produce powerpower

In some plants the steam contacts other In some plants the steam contacts other water and turns it to steam… this way, water and turns it to steam… this way, the radioactive water never touches the the radioactive water never touches the turbineturbine

there is little difference between a there is little difference between a nuclear plant and a coal or oil-fired plant nuclear plant and a coal or oil-fired plant except for the source of the heat usedexcept for the source of the heat used

Nuclear PowerNuclear Power

The reactor's pressure vessel is The reactor's pressure vessel is typically housed inside a concrete liner typically housed inside a concrete liner that acts as a radiation shieldthat acts as a radiation shield

the containment vessel is protected by the containment vessel is protected by an outer concrete building that is strong an outer concrete building that is strong enough to survive such things as enough to survive such things as crashing jet airlinerscrashing jet airliners

Nuclear PowerNuclear Power

Uranium-235 is not the only possible Uranium-235 is not the only possible fuel for a power plant. Another fuel for a power plant. Another fissionable material is plutonium-239fissionable material is plutonium-239

Nuclear PowerNuclear Power

Plutonium-239 can be created by U-238 Plutonium-239 can be created by U-238 fission, therefore some reactors are fission, therefore some reactors are used to make weapons grade plutoniumused to make weapons grade plutonium

If fact, the first reactors every produced If fact, the first reactors every produced were used for this purpose…. Atomic were used for this purpose…. Atomic bombsbombs

Research reactors work on the same Research reactors work on the same principals as power reactors, however principals as power reactors, however are used for other purposesare used for other purposes

Nuclear PowerNuclear Power

They can be used to expose materials They can be used to expose materials to high levels of radiationto high levels of radiation

To bombard elements with neutrons to To bombard elements with neutrons to create new isotopescreate new isotopes

And can be used to work on new energy And can be used to work on new energy possibilitiespossibilities

How safe are they? Do they hurt the How safe are they? Do they hurt the environment? environment?

Nuclear SafetyNuclear Safety

Compared with a coal-fired power plant, Compared with a coal-fired power plant, nuclear power plants are a dream come nuclear power plants are a dream come true from an environmental standpointtrue from an environmental standpoint

coal-fired power plant actually releases coal-fired power plant actually releases more radioactivity into the atmosphere more radioactivity into the atmosphere than a properly-functioning nuclear than a properly-functioning nuclear power plantpower plant

Fossils fuel plants (oil/coal) release Fossils fuel plants (oil/coal) release huge amounts of carbon into the huge amounts of carbon into the atmosphere, C-14 is radioactiveatmosphere, C-14 is radioactive

Nuclear SafetyNuclear Safety

There are also drawbacks with nuclear There are also drawbacks with nuclear power…power…

Mining and purifying uranium has not, Mining and purifying uranium has not, historically, been a very clean processhistorically, been a very clean process

Improperly-functioning nuclear power Improperly-functioning nuclear power plants can create big problems i.e. The plants can create big problems i.e. The ChernobylChernobyl

Spent fuel from nuclear power plants is Spent fuel from nuclear power plants is toxic for centuries and there is no safe toxic for centuries and there is no safe permanent storage facility for it, yetpermanent storage facility for it, yet

Nuclear SafetyNuclear Safety

Transporting nuclear fuel to and from Transporting nuclear fuel to and from plants also poses some riskplants also poses some risk

Unfortunately, there are less new Unfortunately, there are less new nuclear power plants being constructed nuclear power plants being constructed due to these risksdue to these risks

At some point however, there will be no At some point however, there will be no more fossil fuel and we will have no more fossil fuel and we will have no choice but to build more nuclear power choice but to build more nuclear power plantsplants

Reactor TypesReactor Types

There are a couple different types of There are a couple different types of reactors, all use the same principle of reactors, all use the same principle of nuclear fissionnuclear fission

The four types are …The four types are …Graphite Moderated ReactorGraphite Moderated ReactorFast Breeder Reactor (FBR)Fast Breeder Reactor (FBR)

Liquid Metal (LMFBR) (most common Liquid Metal (LMFBR) (most common type of breeder)type of breeder)

Reactor TypesReactor Types

Light Water Reactor (LWR)Light Water Reactor (LWR)Heavy Water Reactor (HWR)Heavy Water Reactor (HWR)There are two types of light water There are two types of light water

reactorsreactorsBoiling water reactorBoiling water reactorPressurized water reactorPressurized water reactor

Boiling water reactorBoiling water reactorCoolant Type - waterCoolant Type - waterModerator Type – waterModerator Type – water

Reactor TypesReactor Types

Fuel - uranium-dioxide (UO2)Fuel - uranium-dioxide (UO2)Comments - steam generated inside the Comments - steam generated inside the

reactor goes directly to the turbinereactor goes directly to the turbine

Reactor TypesReactor Types

Pressurized water reactorPressurized water reactorCoolant Type - waterCoolant Type - waterModerator Type – waterModerator Type – waterFuel - uranium-dioxide (UO2)Fuel - uranium-dioxide (UO2)Comments - steam is generated outside Comments - steam is generated outside

the reactor in a secondary heat transfer the reactor in a secondary heat transfer looploop

Reactor TypesReactor Types

Heavy Water reactors work just like light Heavy Water reactors work just like light water reactors, however, instead of water reactors, however, instead of using water Husing water H22O…. Normal hydrogen is O…. Normal hydrogen is

replaced with deuterium Hreplaced with deuterium H22

Reactor TypesReactor Types

There are two types of Graphite There are two types of Graphite moderated reactors…moderated reactors…Gas CooledGas CooledWater CooledWater Cooled

Gas CooledGas CooledCoolant Type - gas (carbon dioxide or Coolant Type - gas (carbon dioxide or

helium)helium)Moderator Type – graphiteModerator Type – graphiteFuel -- uraniumFuel -- uranium

Reactor TypesReactor Types

Comments - used in Britain, and FranceComments - used in Britain, and France

Reactor TypesReactor Types

Water Cooled ReactorsWater Cooled ReactorsCoolant Type – waterCoolant Type – waterModerator Type – graphiteModerator Type – graphiteFuel -- uraniumFuel -- uraniumComments - used in USA & former Comments - used in USA & former

Soviet Union, e.g. ChernobylSoviet Union, e.g. Chernobyl

Reactor TypesReactor Types

Fast Breeder Reactor (FBR)Fast Breeder Reactor (FBR)Coolant Type – molten liquid sodiumCoolant Type – molten liquid sodiumModerator Type – none requiredModerator Type – none requiredFuel - plutonium dioxide and uranium Fuel - plutonium dioxide and uranium

dioxide in various arrangementsdioxide in various arrangementsComments - breeder reactors are Comments - breeder reactors are

designed to produce more fissile designed to produce more fissile material than they consumematerial than they consume