ENERGY
Nuclear NUCLEAR core of a nuclear reactor must be kept cool at all times, thus water from rivers are used as a cooling system, then circulated in cooling towers until they are cool enough again to be returned back to environment The country that produces the highest percentage of its electricity from nuclear power is France(78%), then Belgium(57%), Sweden(47%), japan(36%), UK(29%), US (20%), Canada(13%), and mostly in Ontario. Country that has the most nuclear reactors is US
A) How does it work?
Pressurized water reactor = most common design; fuel is U235(3% i.e slightly enriched uranium), water is the coolant and the moderator(slow down neutrons). Reactor core(nuclear reactor) contains the enriched uranium rods, moderator, and control rods (act as accelarators or brakes ;made of material that absorbs neutrons e.g boron; slowing down the reaction is done by lowering these rods, while speeding up is dont by lifting them). Each pellet of fissionable material (U235) is capable of giving off the energy equivalent of 1 ton of coal. Water under pressure (allowing for achievement of higher temperatures) is heated with the energy of the nuclear reaction, then passed through a steam generator, which contains water not under pressure. Water in steam generator is heated up and converted to steam, which is then used to turn turbines. *water under pressure is radioactive, which is a concern, since pressure can cause leaks.
Boiling water Reactor = same as above, except water is not under pressure. CANDU (Canadian deuterium) = uses natural U235(0.7%), and deuterium(heavy water) as coolant and moderator Fast Breeder Reactor = produces more fuel as it goes! Uses a mix of Pu239 and U238 as fuel, sodium as coolant, and no moderator since it uses fast neutrons. Bombardment of U238 with neutrons produces P239 (same thing that happened in U of Chicago), thus producing more fuel as it goes along. Nuclear reactor, even when there is no nuclear reaction, is always hot due to presence of radioactive material. Thus it must always remain cool. B) Nuclear Waste: U235, Pu239, Sr(goes into your bones), Cs, I, etc. (radioactive material). Reprocessing = waste material is treated to extract the Pu239 and U235 (fuel). Note : amount of Pu239 needed to make nuclear bomb is only 5kg => problem of hijacking. Only France and Britain reprocess the spent fuel. Many countries ship their wastes over there. Canada and US just store it. - there is a lot of material (150,000kg of Pu) left from nuclear weapon programs in Soviet Union, and there is a program to burn it in a nuclear MOX reactor. (Mixed Oxides Fuel) = process by which this Pu and other fuel can be burned in a nuclear reactor. But all this fuel has to be flown to Canada...
Storage : nuclear waste has to be stored in water, for cooling. For a material to be safe, it has to undergo at least 10 half lives. Abandoned salt mines are usually used to store these for a long time. 2 billion years ago, a natural fission reactors were running under ground for 150 million years! 2 billion years ago, the concentration of U235 was actually high enough to start off a nuclear fission reaction spontaneously! Today, there is no permanent storage space for nuclear waste anywhere. There used to be in the Yucca Mountains, Nevada, but Obama stopped it in 2009. Note : 10 billion $ was spent on making this storage space. C)Accidents: Three Miles Island, USA(1979) : Fault caused nuclear reactor to overheat, producing a steam bubble. All nuclear reactors are contained within a containment building. The radioactive steam bubble was slowly released to prevent it from collapsing the containment building. Chernobyl : this reactor used graphite as a moderator, water as coolant and U235 as fuel. Nuclear reactor overheated and the very hot water reacted with Zr to produce H2 and with graphite to produce H2. This Hydrogen then blew off the top of the reactor. The reactor was NOT in a containment building. Air (O2) then rushed in, fuelling the fire. 31 deaths??? Iodine 139 (radioactive kind) was released, causing thyroid cancers. Had ppl taken non-radioactive Iodine (127), they would have saturated their gland, not allowing the radioactive kind to be absorbed. Conclusion: nuclear Energy is abundant(plenty of U), clean(much cleaner than coal ; we dont smoke). Nuclear plant produces very little waste, but it was radioactive, whereas coal plants produces a lot of nonradioactive wastes. Safe?? There are more people that died from coal mining, than total deaths from nuclear power plants. Producing energy from nuclear fusion => no production of radioactive wastes! But it is much HOTTER. *Tokamak project = since were dealing with very high temperatures, the material under fusion can be circulated via a magnet, not allowing it to touch the walls of the container. Livermore project = zapping deuterium pellets with high electricity. Controlled fusion has been achieved. But it has required more energy to carry out the fusion process than the amount obtained. in 2005, many countries came together to develop fusion reactors, but they think its gonna take at least 30 years before it can be done.