Continuing with the alternative energy series, this week’s blog will examine another rapidly expanding idea in green alternatives with nuclear energy, or the naturally occurring energy found in materials such as uranium. In its most basic understanding, nuclear power comes from nuclear power plants which refines atoms in order to produce electricity. Many nations have been working with nuclear energy for more than five decades and are just starting research the fourth generation of reactor technology to meet an increased demand and efficiency level. The first generation of reactors were designed in the 1950s-60s and are only still used in the United Kingdom. The most common reactor in use today is the second generation which is the main design of the US and French nuclear systems. Generation 3 (and 3+) are the most advanced current reactors and are mainly used in Japan.i Finally, Generation 4 reactors are currently being designed but aren’t likely to be seen constructed until well after 2020. Third generation reactors differentiate themselves from previous reactors by having a simpler design and therefore lower construction costs. They also have a longer operating life of about 60 years. The main goal in designing the next generation of nuclear reactors is to create an “inherent” or “full passive” safety system. Current safety designs are considered “active” in the sense that they involve electrical or mechanical operations such as a pressure relief valve. An inherent safety system would be one that relies on naturally occurring phenomena such as convection or gravity.
Understanding Nuclear Energy
Nuclear fission and fusion are both nuclear phenomena that release a massive amount of energy, but they are independent processes which produce very different results. Fusion takes place when two atomic nuclei are fused together to form a heavier nuclei. Extremely high temperatures are required, about 1.5*107 oC ii, which then results in large amounts of energy being released when the nuclei fuse together. As opposed to nuclear fusion, nuclear fission takes place when atom’s nucleus splits into two or more smaller nuclei. This is an exothermic process which releases the fission products, nuclear photons, alpha particles as well as kinetic energy and gamma radiation. The process of fission is considered a form of element transmutation because it changes the number of protons in the element which technically changes the element from one into another. Nuclear fission happens naturally every day. Uranium constantly undergoes spontaneous fission at a very slow rate, hence why the element constantly emits radiation. The decay of a single Uranium-235 atom (the most common isotope) releases about 200 MeV (million electron volts), which may not seem like much, but when the amount of atoms in a pound is considered the amount of electricity being produced is a viable amount. For example, a pound of enriched uranium can power a nuclear submarine for the equivalent time at the equivalent power as approximately a million gallons of gasoline. In power plants, enriched uranium is formed into two-inch long pellets. These are then arranged into bundles and submerged in water inside a pressure vessel. The water acts as a coolant because on its own the uranium would overheat and melt down. In some cases, the steam produced from the water will go through a heat exchanger to convert a second loop of water into steam. This keeps the radioactive water and steam from contacting the turbine and causing wear to occur faster.
Currently a well-known application for nuclear energy is the Mars Curiosity Rover. The Mars Curiosity Rover is powered by both solar and nuclear power, so it can venture to the dark side of the planet for sustained periods of time. One of the problems with nuclear energy is that it is still not considered completely stable, as most recently seen in the Japan meltdown of 2011; which has many worried that it will never be suitable for vehicle applications. However, current advancements in nuclear energy and the potential that future advancements could bring, have give this alternative energy source the potential to replace a large portion of our dependence on fossil fuels.
i World Nuclear Association “Advanced Nuclear Power Reactors” April, 2013
ii Helmenstine, Anne Marie About.com Chemistry “Nuclear Fission Versus Nuclear Fusion” 2010