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 Fission- releasing 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/esc101/Chapter14&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/fall02/ EVR3019/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 underneath- reduces 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/fall02/ EVR3019/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/esc101/Chapter14&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

CONS OF PROS OF NUCLEAR POWER 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 Use very little material to get a lot of energy. Does not produce much air pollution- emits 1/6th CO2 as coal Moderate land use Low risk with new safety measure and powerplant designs.

Transportation Containers Are Strong and Safe The used fuel will be placed in specially designed transportation containers. These rugged containers are fitted with additional protective materials that help absorb the impact, in the unlikely event of an accident. Designs for these containers must be approved by the NRC.

Transportation Casks Have Been Tested Transportation canisters have been subjected to extreme accident conditions without breaking open. The testing was conducted by Sandia National Laboratory

Container Loaded on a Truck… For example, the containers (red object on the side) were loaded on a truck…

… And Crashed at 80 MPH into a Concrete Wall …and deliberately crashed at 80 miles per hour into a 700-ton concrete wall.

Container Broadsided by Locomotive Traveling at 80 MPH The containers were broadsided by a 120-ton locomotive traveling at 80 miles per hour.

Containers Survived Incineration Tests They withstood burning for 90 minutes in a pool of jet fuel at more than 2,000 degrees Fahrenheit. These tests are more serious than any accidents they are ever likely to face.

Containers Passed Every Test In all cases, the transportation containers would have kept their radioactive cargo locked safely inside with no release of radiation.