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Notes 49 - Topic 8 - Energy, Power, Climate Change*

Notes 49 - Topic 8 - Energy, Power, Climate Change* ------------------------------------------------------------------------------------------------- 8.4.6 Nuclear Power Station Heat Exchangers and Efficiency (h) • Heat Exchanger... - heat engine (fission powered);

hedley-osborn
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Notes 49 - Topic 8 - Energy, Power, Climate Change*

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  1. Notes 49 - Topic 8 - Energy, Power, Climate Change* ------------------------------------------------------------------------------------------------- 8.4.6 Nuclear Power Station Heat Exchangers and Efficiency (h) • Heat Exchanger... - heat engine (fission powered); - working fluid (absorbs heat from heat engine to boil water to power turbine); - condenser (decreases temp of steam by removing heat using low temp water);

  2. NPS Efficiency... – Given by this equation: h = 1 - (QL / QH) x 100 , where... QL is lowest temperature of water; QH is lowest temperature of water; - The temperature of a reactor is limited to a max of 570 K. Typically, water is returned from the condenser at 310 K. Most of the “waste heat” is released into the atmosphere from “Temperature Reduction” Towers. So... h = 1 - (310 / 570) x 100 = 0.46 x 100 = 46% – Typically, nuclear power stations are 46% efficient;

  3. 8.4.7 Artificial Transmutation to produce Pu-239 – U-238, the most abundant isotope of uranium, is non-fissionable but is fertile (can be transmuted into another element by neutron capture); 1. Uranium-238 absorbs a neutron and becomes U-239 (unstable): 2. U-239 undergoes beta decay to produce Neptunium-239 (unstable) and an anti-neutrino: 3. Np-239 undergoes beta decay to produce Plutonium-239 and an anti-neutrino: – Pu-239 is fissionable, and when it absorbs a neutron will split into barium-147, strontium-90, and three neutrons:

  4. 8.4.8 The Breeder Reactor – During the fission of U-235 in a nuclear power plant, lots of neutrons are given off; U-238 can wrapped around the U-235 fuel rods in a “blanket” and absorb neutrons; – This wrapping of U-238 around the U-235 allows the U-238 to absorb neutrons and be transmuted into Pu-239, a new fuel; – The process makes the nuclear power plant a Breeder Reactor because it is “breeding” new fissionable fuel; – There are no Breeder Reactors in the USA...they were banned by President Carter in the late 1970’s; the ban was to prevent the accumulation of fissionable material that could be stolen by terrorists and converted into bombs; – All of France’s nuclear stations are breeder reactors;

  5. 8.4.9 Safety and Risks of Nuclear Power – The following are the major risks associated with nuclear power plants: 1. Mining and enriching the uranium; 2. Meltdown (eg., Chernobyl); 3. Storage and disposal of high and low level radioactive waste products; 4. Using breeder reactors to produce weapons-grade nuclear materials;

  6. 8.4.10 Nuclear Fusion – Scientists have been attempting to produce electricity using nuclear fusion for the past 30 years; the process, while successful, has always used more energy than it has generated, and so it remains impractical; – Some of the obstacles to overcome before fusion is practical: 1. Extremely high temperatures are needed - 1 x 106 K; 2. Extremely high pressures are needed - 1 x 106 Pa; 3. A way to contain and confine high KE hydrogen ions into very small spaces (magnetic bottles?); – When/if perfected, nuclear fusion will offer an almost unlimited supply of cheap, nonpolluting electricity that will allow us to dramatically reduce our use of fossil fuels...especially oil;

  7. 8.4.11 Problems about Nuclear Power If the average household uses electrical energy daily at the rate of 600. W, how much U-235 must undergo fission to supply this need for a year? (assume 200. MeV of energy are generated per fission and that the power plant is 40.% efficient). (put solution in NB) Given: Unknown: Equation:

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