Chapter 17:Chapter 17:

Nuclear Energy and the Nuclear Energy and the

EnvironmentEnvironment

OverviewOverview Current Role of Power PlantsCurrent Role of Power Plants What is Nuclear EnergyWhat is Nuclear Energy Nuclear Energy and the EnvironmentNuclear Energy and the Environment Nuclear Radiation and its Effect on Nuclear Radiation and its Effect on

Human HealthHuman Health Nuclear Power Plant AccidentsNuclear Power Plant Accidents Radioactive- Waste ManagementRadioactive- Waste Management The Future of Nuclear EnergyThe Future of Nuclear Energy

Current Role of Power PlantsCurrent Role of Power Plants

WorldwideWorldwide 436 power plants436 power plants 17% of electricity17% of electricity 4.8% of total energy4.8% of total energy

In USIn US 104 power plants104 power plants 20% of electricity20% of electricity 8% of total energy8% of total energy

Nuclear EnergyNuclear Energy

Energy contained in the atom’s Energy contained in the atom’s nucleusnucleus

Two processes can be used to release Two processes can be used to release that energythat energy Fission – splitting of atomic nucleiFission – splitting of atomic nuclei Fusion – fusing or combining of atomic Fusion – fusing or combining of atomic

nucleinuclei Nuclear reactorsNuclear reactors

Devices that produce controlled nuclear Devices that produce controlled nuclear fissionfission

Used for commercial energy productionUsed for commercial energy production

Conventional Nuclear Conventional Nuclear ReactorsReactors First demonstrated in 1942First demonstrated in 1942

Led to development of nuclear energy Led to development of nuclear energy to produce electricityto produce electricity

Currently powers submarines, aircraft Currently powers submarines, aircraft carriers, and icebreaker shipscarriers, and icebreaker ships

Nuclear fission produces much more Nuclear fission produces much more energy than fossil fuelsenergy than fossil fuels 1 kilogram of uranium oxide produces 1 kilogram of uranium oxide produces

heat equivalent to 16 metric tons of coalheat equivalent to 16 metric tons of coal

Conventional Nuclear Conventional Nuclear ReactorsReactors Three types (isotopes) of uranium occur Three types (isotopes) of uranium occur

in naturein nature Uranium-238Uranium-238 Uranium-235 Uranium-235

This is the only naturally occurring fissionable This is the only naturally occurring fissionable materialmaterial

Essential to production of nuclear energyEssential to production of nuclear energy Uranium-234Uranium-234

Enrichment necessary Enrichment necessary Processing to increase concentration of Processing to increase concentration of

U235U235

Conventional Nuclear Conventional Nuclear ReactorsReactors Split U-235 by neutron bombardmentSplit U-235 by neutron bombardment

Reaction produces neutrons, fission Reaction produces neutrons, fission fragments and heatfragments and heat

Starts a chain reactionStarts a chain reaction Steam produced runs a turbine that Steam produced runs a turbine that

generates electricitygenerates electricity Similar to coal or oil burning power Similar to coal or oil burning power

plantsplants

Fission of U-235Fission of U-235• A neutron strikes the U-A neutron strikes the U-

235 nucleus, producing 235 nucleus, producing fission fragments and fission fragments and free neutrons and free neutrons and releasing heat. releasing heat.

• The released neutrons The released neutrons may then strike other U-may then strike other U-235 atoms, releasing 235 atoms, releasing more neutrons, fission more neutrons, fission fragments, and energy. fragments, and energy.

• As the process As the process continues, a chain continues, a chain reaction develops.reaction develops.

Coal or Oil Power PlantCoal or Oil Power Plant

Nuclear Power PlantNuclear Power Plant

Conventional Nuclear Conventional Nuclear ReactorsReactors

Main components of a reactorMain components of a reactor Core: fuel and moderatorCore: fuel and moderator Control rods: control the rate of Control rods: control the rate of

reaction or stop itreaction or stop it Coolant: remove heatCoolant: remove heat Reactor vesselReactor vessel

Entire reactor is contained in a Entire reactor is contained in a reinforced concrete buildingreinforced concrete building

Nuclear Energy and the Nuclear Energy and the EnvironmentEnvironment

Nuclear fuel cycle includes:Nuclear fuel cycle includes: Mining and processing of uranium to Mining and processing of uranium to

controlled fissioncontrolled fission Reprocessing of spent fuelReprocessing of spent fuel Decommissioning of power plantsDecommissioning of power plants Disposal of radioactive wasteDisposal of radioactive waste

Throughout the cycle radiation can Throughout the cycle radiation can enter and affect the environmententer and affect the environment

Problems with Nuclear Problems with Nuclear PowerPower Uranium mines and mills produce Uranium mines and mills produce

radioactive waste material that can radioactive waste material that can pollute the environmentpollute the environment

U-235 enrichment and fabrication of fuel U-235 enrichment and fabrication of fuel assemblies also produces waste materialsassemblies also produces waste materials

Site selection and construction is Site selection and construction is controversialcontroversial

Power plant itself is the visible Power plant itself is the visible representation of past accidents or partial representation of past accidents or partial meltdownsmeltdowns

Problems with Nuclear Problems with Nuclear PowerPower Handling and disposal of wasteHandling and disposal of waste Nuclear power plants have a limited Nuclear power plants have a limited

lifetimelifetime Decommissioning is expensive and Decommissioning is expensive and

uncertainuncertain Terrorists could collect plutonium for Terrorists could collect plutonium for

dirty bombdirty bomb

Nuclear Radiation in the Nuclear Radiation in the EnvironmentEnvironment

Radioisotope- an isotope of a Radioisotope- an isotope of a chemical element that chemical element that spontaneously undergoes radioactive spontaneously undergoes radioactive decaydecay

Affect environment by:Affect environment by: Emitting radiation that affects other Emitting radiation that affects other

materialsmaterials Entering the normal pathways of Entering the normal pathways of

mineral cycling and ecological food mineral cycling and ecological food chainschains

Effects of RadioisotopesEffects of Radioisotopes

Explosion of nuclear atomic weapon Explosion of nuclear atomic weapon does two types of damagedoes two types of damage Directly from blastDirectly from blast Dispersal of radioactive isotopesDispersal of radioactive isotopes

FalloutFallout Can enter ecological food chainCan enter ecological food chain Biomagnifies in the food chain (e.g., Biomagnifies in the food chain (e.g.,

reindeer moss, caribou, humans)reindeer moss, caribou, humans)

How Radioactive isotopes reach How Radioactive isotopes reach PeoplePeople

Sources and Doses of Sources and Doses of RadiationRadiation

Radiation Doses and HealthRadiation Doses and Health

At what point does an exposure or At what point does an exposure or dose become a health hazarddose become a health hazard 5,000 mSv is considered lethal in 50% 5,000 mSv is considered lethal in 50%

of people (LD-50)of people (LD-50) 1,000-2,000 mSv sufficient to cause 1,000-2,000 mSv sufficient to cause

health problemshealth problems 50 msv maximum allowed dose for 50 msv maximum allowed dose for

workers in the industry (30 times workers in the industry (30 times average natural background)average natural background)

Radiation Doses and HealthRadiation Doses and Health

10-25 yr delay between the time of 10-25 yr delay between the time of exposure and the onset of diseaseexposure and the onset of disease

Most scientist agree that radiation Most scientist agree that radiation can cause cancercan cause cancer They don’t agree on relationshipThey don’t agree on relationship Linear vs. some threshold levelLinear vs. some threshold level

Nuclear Power Plant Nuclear Power Plant AccidentsAccidents US Nuclear Regulatory CommissionUS Nuclear Regulatory Commission

Sets performance goal for a single Sets performance goal for a single reactor at 0.01% (1 in 10,000 chance of reactor at 0.01% (1 in 10,000 chance of core meltdown)core meltdown)

If there were 1,500 plants a melt down If there were 1,500 plants a melt down would be expected every seven yearswould be expected every seven years

Unacceptable riskUnacceptable risk

Two well-known accidentsTwo well-known accidents Three-Mile IslandThree-Mile Island ChernobylChernobyl

Three Mile IslandThree Mile Island

Occurred March 28, 1979 near Occurred March 28, 1979 near Harrisburg, PAHarrisburg, PA Malfunction of a valve resulted in partial Malfunction of a valve resulted in partial

core meltdowncore meltdown Intense radiation released to interior of Intense radiation released to interior of

containment structurecontainment structure Small amount of radiation released into Small amount of radiation released into

environmentenvironment

Three Mile IslandThree Mile Island

Long-term chronic effects of Long-term chronic effects of exposure to low levels of radiation exposure to low levels of radiation are not well understoodare not well understood Effects of accident difficult to estimateEffects of accident difficult to estimate

Major impact of the incident was fearMajor impact of the incident was fear

ChernobylChernobyl

Occurred April 26, 1986 in Occurred April 26, 1986 in Cherbobyl, Soviet UnionCherbobyl, Soviet Union Worst accident in history of nuclear Worst accident in history of nuclear

power generationpower generation Failure in cooling watersFailure in cooling waters

Reactor overheated melting the Reactor overheated melting the uranium fueluranium fuel

Explosions removed top of buildingExplosions removed top of building Fires produced a cloud of radioactive Fires produced a cloud of radioactive

particlesparticles

ChernobylChernobyl

30 km zone surrounding Chernobyl 30 km zone surrounding Chernobyl evacuatedevacuated 115,000 people evacuated115,000 people evacuated 24,000 people estimated to have received 24,000 people estimated to have received

radiation dose of 430mSvradiation dose of 430mSv Thyroid cancer increased in Belarus, Ukraine Thyroid cancer increased in Belarus, Ukraine

and the Russian Federationand the Russian Federation 4,000 death were directly attributed to 4,000 death were directly attributed to

accidentaccident Ultimately responsible for ~16,000-39,000 deathsUltimately responsible for ~16,000-39,000 deaths

Trees and vegetation damagedTrees and vegetation damaged

Radioactive Waste Radioactive Waste ManagementManagement By-products are expected when By-products are expected when

electricity is produced at nuclear electricity is produced at nuclear reactorsreactors

Three general categoriesThree general categories Mine tailingsMine tailings

20 million metric tons of abandoned tailings 20 million metric tons of abandoned tailings will continue to emit radiation for 100,000 will continue to emit radiation for 100,000 yearsyears

Low-level wasteLow-level waste Transuranic wasteTransuranic waste High-level wasteHigh-level waste

Low-Level Radioactive Low-Level Radioactive WasteWaste Low enough concentrations that it Low enough concentrations that it

does not present a significant does not present a significant environmental hazardenvironmental hazard If handled properlyIf handled properly

Includes variety of residual and Includes variety of residual and solutions from processingsolutions from processing Solid and liquid waste, sludge, and acidsSolid and liquid waste, sludge, and acids Slightly contaminated equipment and Slightly contaminated equipment and

materialsmaterials

Low-Level Radioactive Low-Level Radioactive WasteWaste Buried in near-surface burial areasBuried in near-surface burial areas

Where geologic and hydrologic Where geologic and hydrologic conditions thought to limit migrationconditions thought to limit migration

Three of the six closed due to leaks & Three of the six closed due to leaks & financesfinances

Creation of new sites met with Creation of new sites met with controversycontroversy

Question remains as to whether low-Question remains as to whether low-level radiation can be disposed of safetylevel radiation can be disposed of safety

Transuranic WasteTransuranic Waste

Composed of human-made Composed of human-made radioactive elements heavier than radioactive elements heavier than uraniumuranium Plutonium, americum, and einsteineum Plutonium, americum, and einsteineum Most is industrial trash that has been Most is industrial trash that has been

contaminatedcontaminated Generated from production of nuclear Generated from production of nuclear

weapons or cleanup of former nuclear weapons or cleanup of former nuclear weapon facilitiesweapon facilities

Transuranic WasteTransuranic Waste

Now being transported and stored in Now being transported and stored in Carlsbad, NM salt bedsCarlsbad, NM salt beds Salt is 225 million years old and Salt is 225 million years old and

geologically stablegeologically stable No flowing groundwater and salt is easy No flowing groundwater and salt is easy

to excavateto excavate Rock salt flows slowly into mined Rock salt flows slowly into mined

openings, naturally sealing the waste in openings, naturally sealing the waste in 75 to 200 years75 to 200 years

Consists of commercial and military Consists of commercial and military spent nuclear fuelspent nuclear fuel Uranium and plutonium derived from Uranium and plutonium derived from

military reprocessingmilitary reprocessing Other nuclear weapons materialOther nuclear weapons material

Extremely toxicExtremely toxic Sense of urgency surround its disposalSense of urgency surround its disposal Total volume of spent fuel accumulatingTotal volume of spent fuel accumulating

High-Level Radioactive High-Level Radioactive WasteWaste

High-Level Radioactive High-Level Radioactive WasteWaste A comprehensive geologic disposal A comprehensive geologic disposal

development program should have the development program should have the following objectives:following objectives: Identification of sites that meet broad Identification of sites that meet broad

geologic criteriageologic criteria Intense subsurface exploration of possible Intense subsurface exploration of possible

sitessites Predictions of future changes to sitesPredictions of future changes to sites Evaluation of risk associated with various Evaluation of risk associated with various

predictionspredictions Political decision making based on risks Political decision making based on risks

acceptable to society acceptable to society

Yucca Mountain Nuclear Yucca Mountain Nuclear Waste DepositoryWaste Depository Nuclear Waste Policy Act of 1982Nuclear Waste Policy Act of 1982

Initiated high-level waste disposal Initiated high-level waste disposal programprogram

Department of Energy investigated Department of Energy investigated several sitesseveral sites

To be disposed of underground in deep To be disposed of underground in deep geologic waste repositorygeologic waste repository

Yucca Mountain only site being Yucca Mountain only site being evaluatedevaluated

Use of site begins in 2010Use of site begins in 2010

Yucca Mountain Nuclear Yucca Mountain Nuclear Waste DepositoryWaste Depository Extensive scientific evaluations of Extensive scientific evaluations of

Yucca Mountain carried outYucca Mountain carried out Remain controversialRemain controversial Concerned that natural processes might Concerned that natural processes might

allows radiation to escapeallows radiation to escape Major question as to how accurate long-Major question as to how accurate long-

term predictions areterm predictions are

The Future of Nuclear The Future of Nuclear EnergyEnergy Advocates argue that nuclear power Advocates argue that nuclear power

is good for the environmentis good for the environment It does not produce potential global It does not produce potential global

warming through release of carbon warming through release of carbon dioxidedioxide

It does not cause acid rainIt does not cause acid rain If breeder reactors are developed the If breeder reactors are developed the

amount of fuel will be greatly increasedamount of fuel will be greatly increased

The Future of Nuclear The Future of Nuclear EnergyEnergy Argument against Nuclear EnergyArgument against Nuclear Energy

Based on political and economic Based on political and economic considerationconsideration

Based on uncertainty of safety issuesBased on uncertainty of safety issues Known reserves would be used up Known reserves would be used up

quicklyquickly May be a path to nuclear weaponsMay be a path to nuclear weapons

Future of Nuclear EnergyFuture of Nuclear Energy

Breeder reactorsBreeder reactors Designed to produce new nuclear fuelDesigned to produce new nuclear fuel Transform waste or low-grade uranium Transform waste or low-grade uranium

into fissionable materialinto fissionable material Future of nuclear power if sustainability Future of nuclear power if sustainability

of fuel an objectiveof fuel an objective

Pebble-Bed ReactorsPebble-Bed Reactors

A gas cooled reactorA gas cooled reactor Centered around fuel elements called Centered around fuel elements called

pebblespebbles As a spent pebble leaves the core As a spent pebble leaves the core

another one is feed inanother one is feed in Means the reactor has just the right Means the reactor has just the right

amount of fuel for optimal productionamount of fuel for optimal production

Fusion ReactorsFusion Reactors

Involves combining the nuclei of light Involves combining the nuclei of light elements to form heavier oneselements to form heavier ones Heat energy is releasedHeat energy is released Source of energy in sun and starsSource of energy in sun and stars

In a hypothetical fusion reactorIn a hypothetical fusion reactor Two isotopes of hydrogen injected into Two isotopes of hydrogen injected into

reactor chamberreactor chamber Products include helium and neutronsProducts include helium and neutrons

Fusion ReactorsFusion Reactors

Several conditions necessary Several conditions necessary 1.1. Extremely high temperaturesExtremely high temperatures

100 million degrees C100 million degrees C

2.2. High density of fuel elementsHigh density of fuel elements3.3. Plasma must be confinedPlasma must be confined

Potential energy available if Potential energy available if developed nearly inexhaustible.developed nearly inexhaustible.

Many obstacles remain to be solvedMany obstacles remain to be solved