Energy Part 3 Nuclear and Hydroelectric. Kinda green but not… The term “green energy” often is...
-
Upload
daniella-perkins -
Category
Documents
-
view
215 -
download
0
Transcript of Energy Part 3 Nuclear and Hydroelectric. Kinda green but not… The term “green energy” often is...
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