Energy Part 3

Nuclear and Hydroelectric

Kinda green but not… The term “green energy” often is referring to

pollution due to fossil fuels i.e. CO2, sulfur and nitrogen compounds,

mining/extraction waste, environmental damage, etc.

In these terms nuclear and hydroelectric power are “green” but they do have their own environmental issues.

Nuclear Fission An atom splits into two or more smaller nuclei and

byproducts particles: neutrons, photons, gamma rays, and beta and alpha

particles Reaction gives off heat (exothermic)

Energy

The amount of energy stored in nuclear fuel is 10 million times more than that of traditional fuels, i.e. coal and petroleum

Downside: nuclear waste remains radioactive for thousands of years

Isotope Substances with the same number of protons

(therefore same element) but different number of neutrons

Half life Amount of time it takes for half of a radioactive

substance to decay

Nuclear fuels U-235

Can produce a fission chain reaction Less than 1% of natural uranium Half life = 700 million years Critical mass: minimum amount of U-235 required

for a chain reaction Enriched uranium: uranium that has been

processed to separate out U-235 Controversy with Iran and North Korea

Nuclear weapons are 85% or more U-235 Power Plants are 3% U-235

Nuclear fuels U-238

Most common isotope of uranium (99.3%) Has a half life of 4.5 billion years When hit with a neutron it decays into Pu-239 Most depleted uranium is U-238

Nuclear fuels Pu-239

Half life = 24, 000 years Plutonium fission provides about 1/3 of total

energy produced in a typical commercial power plant

Control rods in nuclear power plants need to be changed frequently due to Pu-239 build up

International inspections regulate the amounts of Pu-239

Electricity Production Nuclear energy as a power source increased

rapidly in the 1960’s until the 1980’s Reasons for decline:

Cost overruns Higher-than-expected operating costs Safety issues Disposal of nuclear waste Perception of it being a risky investment

Electricity Production

Increased interest due to: Electricity shortages Fossil fuel prices Climate change

As of 2005 6% of world’s energy and 15% of world’s

electricity came from nuclear power US, France, and Japan accounted for 57% of

nuclear energy generated

Electricity Production

As of 2007 439 nuclear power reactors operating in 31

countries In the 1980s one new nuclear power plant

started up every 17 days Now around one in every 5 days

Electricity Production

US produces the most nuclear energy (19%)

France produces the highest percentage of its electricity from nuclear power (78%)

European Union as a whole (30%)

Nuclear Energy Share of Electricity in the US

Parts of a Nuclear Reactor

A. Core: Contains up to 50,000 fuel rods; each rod has many fuel pellets;

each pellet = 1 ton of coal = 17,000 cubic feet of natural gas = 149 gallons of oil

B. Fuel: Enriched or concentrated U-235

C. Control Rods: move in and out of the core to absorb neutrons and slow down the reaction

Usually made of Boron

Parts of a Nuclear Reactor

D. Moderator: medium that reduces the velocity of neutrons, turning them into thermal neutrons capable of sustaining a nuclear chain reaction

Can be water, graphite (can produce plutonium for weapons), or deuterium oxide (heavy water)

E. Coolant: removes heat and produces steam to generate electricity

Diagram of a Nuclear Power Plant

A

B

C

D

E

Types of Nuclear Reactors Light water

Both moderator and coolant are light or normal water (H2O)

PWR (Pressurized Water Reactors)1. Water coolant operates at high pressure (radioactive)2. Heat exchange through a secondary loop, water is heated

and converted to steam (Electricity generation)3. Water from a lake, river, or cooling tower is used to condense

steam BWR (Boiling-water Reactors)

Coolant is permitted to boil within the core and kept at low pressure

Steam produced in the reactor goes directly to the steam generator, is condensed and pumped back into the reactor

Types of Nuclear Reactors

Heavy water Uses Deuterium Oxide (D2O) or heavy water Acts as a moderator to increase the efficiency of the

nuclear reaction

Types of Nuclear Reactors Graphite-moderated

Uses light water for cooling, graphite for moderation, uranium for fuel

Very unstable and no longer in production Eg. Chernobyl

Exotic Fast-breeder reactors – produce more fissionable

material than they consume Plus more (you don’t need to know the details of)

Nuclear Power Pros No air pollutant if operating

correctly Releases about 1/6 the CO2

as fossil fuel plants Water pollution is low Disruption of land is low to

moderate Operational safety record

good when compared to other kinds of power plants

Decrease dependence on foreign oil

Cons Nuclear waste takes

millions of years to degrade Waste storage issues Nuclear Regulatory

Commission (NRC) requires plants to set aside money to pay for possible future decommissioning

Low net-energy yield Mining uranium, processing

ore, building and operating plant, dismantling plant, storing waste

Safety and malfunction issues

Safety Issues US Department of Energy estimates up to 50,000

radioactive contaminated sites in the US require clean up

Cost = $1 trillion

Estimated Health Risks per Year in the US

Risk Nuclear Coal

Premature Death 6,000 65,000

Genetic defects/damage

4,000 200,000

Case Study - Chernobyl Ukraine (1986)

Explosion sent highly radioactive debris throughout northern Europe

Estimated: 32,000 deaths 62,000 mi2 remain

contaminated 50,000 new cases of

thyroid cancer Cost estimates runs $400

billion Cause: design and human

error

Nuclear Fusion Occurs when extremely

high temperatures are used to force nuclei of isotopes together

Light weight atoms fuse together and release energy

Products

Coal Plant

Nuclear Fusion Plant

Electricity 1000 MW 1000 MW

CO2 gas 30,000 tons

None

SO2 gas 600 tons None

NO2 gas 80 tons None

Helium gas

None 4 pounds

Hydroelectric power

Dams trap water and release it through turbines to generate electricity

Supplies 10% of power in the US

Supplies 3% of power world wide

Hydroelectric Power Pros Dams control flooding Low operating and

maintenance cost No polluting waste products Long life spans Moderate to high net-useful

energy Areas of water recreation

Cons Create flooded areas

behind dam which displaces people

Slow water can bred pathogens

Destroy wildlife habitats and keep fish from migrating

Sedimentation require dredging

Expensive to build Destroys rivers Large-scale projects are

subject to earthquakes Water loss due to increased

water surface areas

Salmon and dams

Estimated 74,993 dams in the US blocking 600,000 miles of formally free flowing rivers

Salmon are hatched in fresh water, migrate to the ocean, and return to the rivers of their birth to breed

Dams block every major river in the western US Destroyed important

spawning habitats for salmon

Salmon and dams Sacramento Valley, CA – less than 5% of

salmon habitat remains In Columbia River basin, less than 70 miles

of free flowing river 106 west coast salon runs are extinct 25 are endangered Dams create habitats for salmon predators

and pollution Cutting trees creates erosion problems

Methods to reduce dam impacts on fish Salmon ladders Spilling water at dams

over a spillway to help juveniles pass

Water release from upstream storage to increase water velocity and reduce temperatures

Transporting fish on barges and trucks