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Nuclear energy

Nuclear energy. Review: Elements and Isotopes. Elements are defined by the number of protons in the nuclei of their atoms Eg all carbon atoms have 6 protons Remember, isotopes are variations of atoms of an element They vary in number of neutrons

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Nuclear energy

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  1. Nuclear energy

  2. Review: Elements and Isotopes • Elements are defined by the number of protons in the nuclei of their atoms • Eg all carbon atoms have 6 protons • Remember, isotopes are variations of atoms of an element • They vary in number of neutrons • Eg Carbon-12 has 6 protons and 6 neutrons, while Carbon-14 has 6 protons and 8 neutrons • Many elements have isotopes some are stable (never change), some are radioactive (unstable, change over time)

  3. Radioisotopes • Radioactive isotopes experience radioactive decay (the loss of alpha or beta particles over time) • As a result of radioactive decay, atoms of one element physically change into another element. • Eg Carbon-14 decays to Nitrogen-14 by loss of negative beta particles • Radioactive half life= the amount of time it takes for 50% of the radioactive isotope in a substance to decay.

  4. Practice: Plutonium-239 has a half-life of 24,000 years. How much of a 4 gram sample will remain after 96,000 years? • 1g • 0.5g • 0.25g • 0.125g • 0.625g

  5. Geological dating with radioactive isotopes • Carbon-14 can be used to estimate the age of plant and animal remains • All living things utilize C-14 and incorporate it into their tissues • After death, C-14 changes into N-14 • Geologists can determine the age of a set of remains by comparing the ratio of C-14 to N-14 • Carbon dating is useful for remains between 1,000 and 50,000 years old

  6. Geological dating with Uranium • Uranium-238 is a very common radioisotope that decays to a stable isotope of lead • It has a half life of 4.5 billion years • This is very useful for dating rock formations that are billions of years old • Eg if there are equal parts lead and uranium in a rock, it is 4.5 billion years old

  7. The discovery of radioactive atoms • 1896 a French physicist discovered that uranium containing minerals spontaneously & continuously gave off energy (radiation) • 1898 a British physicist showed radiation to consist of high energy particles • In 1919 same British guy bombarded N nuclei with alpha particles and turned it into O • In 1938 German scientists hit uranium with neutrons, splitting U into barium and krypton, and lots of energy…FISSION! • This led to a realization of the potential power of fission and a subsequent race for a bomb and energy development (Einstein came to US during WWII to warn of impending German innovation)

  8. Nuclear energy • Nuclear reactions differ from combustion reactions • Combustion (fossil fuels): • atoms do not change, they are rearranged. • The mass of the reactants is equal to the mass of the products. • Energy is given off as heat when chemical bonds are broken. • Nuclear reaction: • Changes occur within the nuclei of atoms. • Atoms actually transform into atoms of another element. • Small amounts of matter are transformed into large amounts of energy.

  9. Types of nuclear reactions • Fission: larger atoms are split into 2 smaller atoms of different elements (this is the type of reaction used to create commercial energy and atomic bombs) • Fusion: 2 smaller atoms combine to make one larger atom of a different element (this is what powers the sun and stars) • In both reactions the end product mass is less than the mass of the starting material. The remainder is converted to energy. • Fission produces 2-3 million times more energy than combustion of fossil fuels.

  10. NUCLEAR ENERGY • Nuclear power plants use U-235, a radioactive isotope of uranium. • Mined uranium oxide consists of about 99.3% non-fissionable uranium-238 and 0.7% fissionable uranium-235. • The concentration of uranium-235 is increased through an enrichment process (removing some of the U-238) to result in 97% U-238 oxide and 3% U-235 oxide fuel. • Enrichment is very energy intensive, but the energy payoff is even greater

  11. Electricity • After enrichment, U-235 is transformed into uranium dioxide to form small fuel pellets • These pellets are placed into fuel rods, which in turn are grouped into fuel assemblies (~100 rods), of which there may be 1000s per reactor core

  12. Nuclear power plant

  13. NUCLEAR WASTE

  14. NUCLEAR WASTE

  15. Math Practice After 100 million years, only 1/32 of the original amount of a particular radioactive waste will remain. The half-life of this radioactive waste is how many million years? a. 10 b. 20 c. 30 d. 40 e. 50 You have 180g of a radioactive substance. It has a half-life of 265 yrs. After 1,325 yrs, what mass remains?

  16. Nuclear waste • Low level • Radioactive solids, liquids, or gases that give off small amounts of ionizing radiation • Sources include power plants, hospitals, research labs, and industries • Low Level Radioactive Waste Policy Act 1980 & 1985 • All states must be responsible for disposal of non-defense related waste produced w/in their borders. • High level • Radioactive solids, liquids, or gases that initially give off large amounts of ionizing radiation • Sources include anything that was inside the reactor core (metals, water, gases, spent fuel)

  17. Nuclear Waste Policy Act 1982 • Stated that there must be a permanent site for storing high level waste by 1998 • That was not met; postponed to 2010 at earliest • 1987 Congress identified Yucca Mountain in Nevada as the best potential site • Feasibility studies were carried out for over a decade • In 2002 it was officially approved by Congress • Rescinded by Obama in 2009

  18. NUCLEAR ENERGY • Scientists disagree about the best methods for long-term storage of high-level radioactive waste: • Bury it deep underground. • Shoot it into space. • Bury it in the Antarctic ice sheet. • Bury it in the deep-ocean floor that is geologically stable. • Change it into harmless or less harmful isotopes.

  19. The risks of nuclear energy • Meltdown: this is when the actual metal around the reactor core melts from the heat of fission; radiation is emitted into the atmosphere in one large dose • Acute radiation syndrome= too many body cells are killed by the radiation dose to be repaired. • Daily radiation for workers (carcinogenic over time) • Radiation into groundwater from stored waste • Small scale persistent radiation to nearby communities

  20. Radiation and health • We are exposed to natural (background radiation) and artificial radiation every day • 300 millirems per year from space/the atmosphere, the soil (radon), foods we eat (radioactive potassium) • 60 millirems from manmade radiation (radiowaves, hospitals, industries, housing materials, microwaves, cell phones, tobacco, television, smoke detectors, etc.) • Radiation is often ionizing, which is very disruptive to living cells • Chronic exposure to radiation can lead to cancer and thyroid problems

  21. NUCLEAR ENERGY • A 1,000 megawatt nuclear plant is refueled once a year, whereas a coal plant requires 80 rail cars a day. Figure 16-20

  22. NUCLEAR ENERGY • Building more nuclear power plants will not lessen dependence on imported oil and will not reduce CO2 emissions as much as other alternatives. • The nuclear fuel cycle contributes to CO2 emissions. • Wind turbines, solar cells, geothermal energy, and hydrogen contributes much less to CO2 emissions.

  23. NUCLEAR ENERGY • In 1995, the World Bank said nuclear power is too costly and risky. • In 2006, it was found that several U.S. reactors were leaking radioactive tritium into groundwater. Figure 16-19

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