NUCLEAR POWER APES ISOTOPES Isotopes some atoms of

NUCLEAR POWER APES

ISOTOPES • Isotopes- some atoms of the same element have different numbers of neutrons creating different mass numbers. • EX: Uranium has 92 protons, & most uranium atoms contain 146 neutrons & have a mass number of 238… 92 + 146 = 238 • How many neutrons does U-235 have?

RADIOACTIVITY • Some isotopes are unstable and decay slowly, emitting particles & energy. • These are called radioactive atoms • Radioactive atoms eventually become stable and stop decaying.

• Radiation can come from – Alpha particles – Beta particles – Gamma rays- used in radiation therapy for cancer patients. • When alpha or beta particles are given off, the mass # & atomic # change creating a different element.

Natural Radiation? • Natural sources of radiation… – – Soil & rocks Water Air Cosmic rays

• 2 radioactive isotopes of uranium are U-238 and U-235 – Both decay into stable form of lead. – The amount of time it takes for half of the atoms in a sample of a radioactive element to decay is called the isotope’s half-life. – Half-lives can be a few seconds or billions of years. – U-238 has half-life of 4. 5 billion years. – U-235 has half-life of 700 million years.

REACTIONS & REACTORS • Nuclear Fissionreleasing energy by splitting the nucleus of an atom apart. • This energy can be used to create electricity.

STEPS OF NUCLEAR FISSION – Neutron is fired into nucleus of U-235 atom. – Nucleus splits, forming two daughter nuclei – This reaction releases energy & several more neutrons. – This continuous action of neutrons splitting atomic nuclei is called a chain reaction.

NUCLEAR REACTORS • Nuclear fuel is usually 97% U-238 and 3% U-235. • U-238 is not fissionable so it is not part of the nuclear reaction (but can be used in plutonium reactors)

NUCLEAR REACTORS • In the U. S. , nuclear fission happens inside a nuclear reaction vessel – 20 m tall with walls that are 15 -30 cm thick. – Large shield surrounds the vessel to contain any stray radioactive particles – The reactor is housed inside a concrete containment building.

NUCLEAR REACTORS • Fuel rods are filled with pellets that contain the U-235. Positioned vertically in reactor so water can circulate betwn them.

NUCLEAR REACTORS • Water is important because: – It absorbs heat & keeps core from melting. – It slows the movement of neutrons released during the chain reaction.

NUCLEAR REACTORS • Speed of chain reactions is controlled by control rods made of cadmium, boron, etc. that absorb neutrons. – Raise control rods out of reactor= absorb fewer neutrons, speed up reaction, hotter water. – Lower control rods into reactor= absorb more neutrons, slow reaction, cool water

NUCLEAR REACTORS – Hot water is passed to pipes where steam is created that turns turbines, creating electricity. – Water cooling system & control rods regulate heat. If they fail, it would cause a “nuclear meltdown” at the core.

Use of Nuclear Energy • U. S. phasing out • Some countries (France, Japan) investing increasingly • France 78% energy nuclear • U. S. currently ~7% of energy nuclear • No new U. S. power plants ordered since 1978 • North Korea is getting new plants from the US www. bio. miami. edu/beck/esc 101/Chapter 14&15. ppt

What happened to old Nuclear Power Plants? • Licensed for 40 years- after this time can ask to renew or decommission • When parts corrode from overuse and radiation damage, the plant is decommissioned (retired) • It can be – Dismantled – Put a physical barrier around the plant w/security until less radioactive for dismantling(30 -100 yrs) – Permanently entomb the building • Costs more $ which reduces its net energy. • Costs more $ to dismantle than to build & maintain- have to put $ aside while operating to pay for closing costs

RADIATION & HEALTH • Radiation is unhealthy – Fast dividing skin cells & blood cells are particularly vulnerable – Large doses cause skin burns, anemia, death, miscarriage – Changes DNA leading to cancer & genetic mutations. – Can be passed on to offspring

www. geology. fau. edu/course_info/fall 02/ EVR 3019/Nuclear_Waste. ppt

RADIOACTIVE WASTE • HIGH LEVEL – Emit large amounts of radiation – Very dangerous & poisonous – Stored onsight in large containment vessels stored in water for 10, 000 -240, 000 years – Come from • Used uranium fuel rods • Control rods • Water used to cool & control chain reactions

RADIOACTIVE WASTE • MEDIUM & LOW LEVEL – Not as radioactive – A lot more are produced vs. high level – Pose a greater risk because they are more prevalent & not as obvious • Clothing of nuclear power plant workers • Tailings from uranium mines • Hospital & laboratory waste

WASTE DISPOSAL • Must be considered… – stored in container that will last tens of thousands of years. – Stored in geologically stable area. No earthquakes! – Stored deep underground away from people, water sources, etc.

PROBLEMS WITH WASTE DISPOSAL • Most high level wastes sit in storage tanks outside nuclear power & weapons plants. Some have begun to leak contaminating groundwater. • Between 1940 & 1970, most medium & low level wastes were sealed in concrete & dropped into the ocean, exposing that environment to potential leaks. Now, it is put into hazardous waste landfills

PROBLEMS WITH WASTE DISPOSAL • Send to Yucca Mountain in Nevada desert • 160 miles from Las Vegas • Underground storage chamber • Cost $50 billion • All high level waste would have to be containerized, and transported by train or truck to site across country • Many people oppose becuz they do not want radioactive waste transported thru their cities.

Pros & Cons of Yucca Mountain • Desert- very little rain, reduce chance of corrosion • Secluded • Solid bedrock underneathreduces chance of aquifer contamination • Has been geologically active- earthquakes • Cracks from slight earthquakes could allow water into tunnels, not to mention endanger the integrity of the storage casks • There is an aquifer underneath used for drinking & irrigating by desert population

Yucca Mountain www. geology. fau. edu/course_info/fall 02/ EVR 3019/Nuclear_Waste. ppt

NUCLEAR MELTDOWN • Process by which nuclear chain reaction goes out of control & melts reactor core • Releases huge amounts of radiation into environment.

Three Mile Island • March 29, 1979, a reactor near Harrisburg, PA lost coolant water because of mechanical and human errors and suffered a partial meltdown • 50, 000 people evacuated & another 50, 000 fled area • Unknown amounts of radioactive materials released • Partial cleanup & damages cost $1. 2 billion • Released radiation increased cancer rates. www. bio. miami. edu/beck/esc 101/Chapter 14&15. ppt

CHERNOBYL • Located in Ukraine • 1986 explosion killed 30 people immediately • Fire burned for 10 days- released huge amounts of radioactive waste- 400 times the amount released from Hiroshima atomic bomb • 350, 000 had to leave homes permanently • May cause 15, 000 cases of cancer. • 62, 000 sq mi contaminated • Cost $358 billion to clean up • Chernobyl was old & lacked safety equipment- Caused by human error • Chernobyl’s reactor is very different from those used in US

PROS OF NUCLEAR POWER • Use very little material to get a lot of energy. • Does not produce much air pollution- emits 1/6 th CO 2 as coal • Moderate land use • Low risk with new safety measure and powerplant designs. CONS OF NUCLEAR POWER • Low net energy yield- lot goes into mining, processing, safety equipment • Potential accidents • Radioactive waste disposal expensive & difficult • Safety equipment expensive • High cost of building new plants • Uranium is nonrenewable • Terrorist attacks

Transportation Containers Are Strong and Safe

Transportation Casks Have Been Tested

Container Loaded on a Truck…

… And Crashed at 80 MPH into a Concrete Wall

Container Broadsided by Locomotive Traveling at 80 MPH

Containers Survived Incineration Tests

Containers Passed Every Test