Chapter 7: The Fires of Nuclear Fission

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Lorena Butler
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1 Chapter 7: The Fires of Nuclear Fission What is nuclear fission? Is using nuclear energy safe for humans and the environment? Is nuclear energy better to use than electric generated energy? What happens to the waste of nuclear fission?

2 What do you think of when you hear nuclear energy?

3 What is Fission and How Does it Produce Energy? Nuclear fission is the splitting of a large nucleus into smaller ones with the release of energy. Energy is released because the sum of the masses of these fragments is less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's E=mc 2 equation. 7.2

4 What is Fission and How Does it Produce Energy? E = mc 2 This equation dates from the early years of the 20th century and is one of the many contributions of Albert Einstein ( ). It summarizes the equivalence of energy, E, and mass, m. The symbol c represents the speed of light, m/s. 7.2

5 What is Fission and How Does it Produce Energy? E = mc 2 Consider this: c 2 is equal to m 2 / s 2 When mass is in kg, the energy units are kg m 2 /s 2, which is equivalent to 1 Joule. The large value of c 2 means that it should be possible to obtain a tremendous amount of energy from a small amount of matter - whether in a power plant or in a weapon. 7.2

6 What is Fission and How Does it Produce Energy? E = mc 2 For 1.0 kg of U-235: E = (1.0 x 10-3 kg)(3 x 10 8 m/s) 2 E = (1.0 x 10-3 kg)(9.0 x m 2 /s 2 ) E = 9.0 x kg m 2 /s 2 = 9.0 x J Don t forget to cube or square where needed This is equivalent to 33,000 tons of TNT 7.2

TNT, or trinitrotoluene (discovered in 1863 by Alfred Nobel) became the standard of explosive power as a result of the birth of nuclear weapons-they needed to be compared to some substance of known

7 TNT, or trinitrotoluene (discovered in 1863 by Alfred Nobel) became the standard of explosive power as a result of the birth of nuclear weapons-they needed to be compared to some substance of known explosiveness. O 2 N CH 3 NO 2 NO 2 TNT The TNT molecule is very unstable and when explodes, 2 moles of TNT rearrange to form 15 moles of hot gas (3 mol N 2, 7 mol CO, 5 mol H 2 O) plus some carbon. About 1 g of TNT will produce about L of hot gas a 1000 times increase in volume. 1 kg of U-235, where only about 0.1% mass is converted to energy is equivalent to 33,000 tons of TNT 7.2

8 What is special about the mass number of U-235? When a massive nucleus like U-235 undergoes fission, the net yield of energy is a result of the sum of the fragments being slightly less than the mass of the uranium nucleus. If the mass of the fragments is equal to or greater than that of iron at the peak of its binding energy curve, the nuclear particles (daughters) will be more tightly bound than the uranium nucleus was, and that mass decrease is converted to energy according to E = mc 2. For elements with lower mass numbers than iron, fusion may lead to energy release 7.5

9 Still, the only person to win two unshared Nobel Prizes was Linus Pauling, the American chemist who won for his chemistry work and also a Nobel Peace Prize for his objection to nuclear testing. Marie Sklodowska Curie won two Nobel Prizes one in chemistry, the other in physics for her research on radioactive elements. 7.5

10 Radioactivity Include alpha, beta, and gamma rays. 7.5

11 U-238 Radioactive Decay Series Radioactive isotopes undergo decay until they reach a stable species. All isotopes of all elements with atomic number 84 (Po) and higher are radioactive. 7.5

12 A Chain Reaction with U-235 Visit Figures Alive! For more information on nuclear fission and chain reactions! 7.5

13 Schematic of a Nuclear Reactor A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate (as opposed to a nuclear explosion, where the chain reaction occurs in a split second). 7.3

14 Basics of a Nuclear Reactor Actual size of fuel pellet An awesome source of electrical energy but what to do with the spent nuclear fuel? Reactor core Cooling tower 7.3

15 Storage of nuclear waste Thousands of canisters of spent nuclear fuel rods submerged in water Encapsulating reprocessed HLW in glass canisters (vitrification).

16 Two cooling towers at the Byron nuclear plant in Illinois This image shows a fuel assembly submerged in an active reactor core 7.6

17 On 26 April 1986, reactor # 4 at the Chernobyl Nuclear Power Station, 100 km north from Kiev, blew up during a routine daily operation. Nearly nine tons of radioactive material times as much as the Hiroshima bomb - were hurled into the sky. Winds over the following days, mostly blowing north and west, carried, fallout into Belarus, as well as Russia, Poland and the Baltic region. Control rods were made of graphite (unlike those used in the U.S.) which caught on fire. 7.6

18 Chernobyl-What Happened: April 26, 1986 While performing a safety test on Reactor 4, technicians allowed a power surge that reached 120 times the rated capacity of the reactor. The surge, or "slow nuclear explosion", ripped open the core, including cooling water pipes, and caused a huge steam explosion. The 4,000 ton concrete covering over the reactor was blown away. Fires broke out in many places all over the site. Fifty different radioactive isotopes were released, with half-lives spanning from two hours to 24,000 years. These isotopes were shot 1.5 miles into the sky. 7.6

19 Chernobyl: Social and Environmental Consequences Over 1,000 injuries and thirty-one deaths of firefighters and others who reported to scene of accident. 150,000 people evacuated from their Ukraine homes. Radioactive cloud released over a large part of Europe. Health threatening levels of radioactive materials were found in at least twenty nations, and as far away as 2,000 km from Chernobyl. Estimated 250 million people were exposed to unhealthy amounts of radiation. Estimates of future cancers from the accident range anywhere from 7,500 to 1 million. Radioactive particles in the environment and in the food chain. Large amount of uncertainty and fear in the population. 7.6

20 Chernobyl: Political Consequences Distrust of government. Soviet Union cover up: Sweden and Poland were the first nations to bring attention to the accident. Other nations attempted to downplay the health effects of the accident in their own nations. Public opposition to building additional nuclear power plants increased significantly worldwide. 7.6

21 rad = radiation absorbed dose absorption of 0.01 J of radiant energy/kg tissue rem = roentgen equivalent man = Q x (number of rads) where Q is a relative biological effectiveness factor 1 Sv = 100 rem 7.7

22 Half-life: the time required for the level of radioactivity to fall to one-half of its value. 7.8

23 Half-life: the time required for the level of radioactivity to fall to one-half of its value. 7.8

24 7.9

25 Proposed High Level Nuclear Waste Storage in Yucca Mountain, Nevada 7.9

26 A worker in one of the Yucca mountain tunnels 7.9

27 Nuclear Weapons The isotopes U-235 and U-238 behave essentially the same in all chemical reactions, so the separation of these two isotopes is extremely difficult and relies on advanced technology that is not readily available. Building and deploying a nuclear weapon is a very difficult operation to carry out. 7.10

28 Risks and Benefits of Nuclear Power Break into groups to discuss, then debate. How would you compare its safety with coal power generation? 7.11

Structure and Properties of Atoms

Structure and Properties of Atoms PS-2.1 Compare the subatomic particles (protons, neutrons, electrons) of an atom with regard to mass, location, and charge, and explain how these particles affect the properties of an atom (including identity,