L11 - Chapter 11: uclear Energy Motivation 11.1 In the...

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Motivation • In the preceding chapter, we’ve seen that the energy production potential in nuclear power plants is much larger in principle than in fossil fuel plants • This fact, plus the initial enthusiasm, led to a boom in the construction of nuclear power plants starting with the early 50’s, leading to a nowadays contribution of about 20% to the production of electricity in the US (with several states obtaining more than 50% of their electricity from nuclear power) • However, starting with the 70s, the demand for nuclear plants decreases until it almost ceased, for various reasons 11.1 Ex : For instance: a) demand for electricity did not grow as expected, b) nuclear power plant costs rose dramatically in the United States such that some plants ended up costing more than three billion dollars due principally to finance charges associated with the 10–12 year construction period, c) acceptable storage of radioactive wastes failed to develop d) nuclear plants developed a multitude of technical and management problems, and e) the public became progressively fearful of radiation releases. • However, the interest in the construction of new nuclear power plants raised on the background of the current energy crisis, and it is foreseeable that in the future the nuclear contribution to the electricity production will increase: in the US, in March 2010, the Nuclear Regulatory Commission expected proposals for 26 new reactors
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Reactor role in plants • In typical nuclear power plants, the heat necessary to do work on the turbine is obtained in light water reactors playing the same role as the boilers in fossil fuel power plants 11.2 control rods coolant Fuel rods and moderator • The fuel used by these reactors is 235 U bombarded with neutrons in a chain fission reaction which can be controlled either by tuning the neutron concentration (most common) or the amount of fuel • In order to understand the functionality of this arrangement, let’s look at 1. the nature of the fuel, 2. the role of neutrons in producing energy, 3. the role of water surrounding the fuel, and 4. the function of the control rods moving amidst the fuel.
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Reactor principles of operation • However, in order to maintain the chain reaction, the neutrons must move relatively slow and confined in the space of the reactor: controlling the neutrons is the job of the moderator which slows down and confines the neutrons, and the control rods which reduce the fuel 11.2 • Recall that the nuclear reaction used in nuclear power plants is the fission of 235 U stimulated by collisions with neutrons: the reaction produces other neutrons leading to a chain reaction exposure to the neutrons • The released energy is transported by a coolant ( a pool of water) surrounding the core • The moderator is typically light water – the same as the coolant –, but can also be graphite or heavy water • The control rods are made of materials prone to absorb neutrons such as cadmium
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This note was uploaded on 03/19/2012 for the course PHYSICS phy 121 taught by Professor Mario during the Fall '11 term at Miami University.

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L11 - Chapter 11: uclear Energy Motivation 11.1 In the...

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