Homework for Chapter 20

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1. How much of our global energy supply do nuclear power, biomass energy, and hydroelectric power contribute? How much of our global electricity do these three conventional energy alternatives generate? Biomass provides 10.8% of global primary energy use, nuclear power provides 6.5%, and hydropower provides 2.2% of global primary energy use. Nuclear power generates 15.8% of the world’s electricity, and hydropower generates 15.9%. 2. Describe how nuclear fission works. How do nuclear plant engineers control fission and prevent a runaway chain reaction? In nuclear fission, atoms of uranium-235(any unstable nucleus with a sufficiently high number of nuclear mass) are bombarded with neutrons. Ordinarily neutrons move too quickly to split nuclei when they collide with them, but if neutrons are slowed down they can break apart nuclei. Each collision splits uranium atoms into smaller atoms and releases two or three neutrons, along with energy and radiation. Because the uranium nuclei is surrounded by innumerous number of other similar nuclei; the extra neutrons; besides the releasing of the energy of the previous nuclei that kept the repulsing protons together; begins to break them apart in the same manner leading to a series of chain reaction.

Because the neutrons can continue to split uranium atoms and set in motion a chain reaction and create such intense amount of thermal energy that actually leads to the meltdown of the very mechanism that is required to harness the energy engineers at nuclear plants must absorb excess neutrons with control rods or water to regulate the rate of the reaction. In a pressurized light water reactor, the most common type of nuclear reactor, uranium fuel rods are placed in water, which slows neutrons so that fission can occur. After a fission reaction is initiated it becomes necessary to soak up the excess neutrons produced when uranium nuclei divide, so that on average only a single uranium atom from each...
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