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Nuclear energy.

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Presentation on theme: "Nuclear energy."— Presentation transcript:

1 Nuclear energy

2 Review: Elements and Isotopes
What are elements defined by? What are isotopes? What is the difference between a stable and a radioactive isotope?

3 Radioisotopes experience radioactive decay (the loss of alpha or beta particles over time) Result: 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. radioactive decay (the loss of alpha or beta particles over time) Alpha particles are two protons and two neutrons Beta particles are high energy electrons Radioisotopes can also give off gamma radiation: high energy light (sources include radio waves, light waves, and x-rays)

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 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 uranium radiation observed 1898 radiation consists of high energy particles 1919 N nuclei hit with alpha particles turned into O 1938 First fission reaction 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 rxns vs combustion
Atoms do not change; are rearranged Mass of reactants = mass of products Energy is released as heat when bonds break Nucleic changes result in element transformations Small of amount of matter releases large amounts of energy…less mass in products 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 Fusion 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. Mining Enrichment Fuel assembly 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 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

11 Nuclear power plant 2/3 of reactors in the US are PWRs; 1/3 are BWR

12 NUCLEAR WASTE After three or four years in a reactor, spent fuel rods are removed and stored in a deep pool of water contained in a steel-lined concrete container for 10 years.

13 NUCLEAR WASTE After spent fuel rods are cooled considerably (10 years), they are moved to dry-storage containers made of steel or concrete. Long-term storage (10, ,000yrs) until radioactivity falls to safe levels. Spent fuel rods are dangerous to human health for 10 or more half lives.

14 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 b c d e. 50 You have 180g of a radioactive substance. It has a half-life of 265 yrs. After 1,325 yrs, what mass remains? B (5 half-lives) 5.625g (5 half-lives…265y-->90g, 530y-->45g, 795y-->22.5, 1060y-->11.25g, 1325y-->5.625g)

15 Nuclear waste Low level High 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) High level= not safe for 10,000-milion years

16 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 In 2002 it was officially approved by Congress Rescinded by Obama in 2009 Feasibility studies were carried out for over a decade

17 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.

18 The risks of nuclear energy
Meltdown Acute radiation syndrome Daily radiation for workers (carcinogenic over time) Radiation into groundwater from stored waste Small scale persistent radiation to nearby communities 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.

19 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.) 10,000 mrem’s on average by Chernobyl workers. Radiation is often ionizing, which is very disruptive to living cells Chronic exposure to radiation can lead to cancer and thyroid problems

20 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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