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. CO 2, 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 (H 2 O)  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 (D 2 O) 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 CO 2 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 RiskNuclearCoal Premature Death6,00065,000 Genetic defects/damage 4,000200,000

Case Study - Chernobyl Ukraine (1986)  Explosion sent highly radioactive debris throughout northern Europe  Estimated: 32,000 deaths 62,000 mi 2 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 Electricity1000 MW CO 2 gas30,000 tons None SO 2 gas600 tonsNone NO 2 gas80 tonsNone Helium gas None4 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