NUCLEAR ENERGY

NUCLEAR ENERGY

• 1. Slide3 NUCLEAR ENERGY
• 2. Slide15 02 Everything you need to know about nuclear energy 01 What is Nuclear Energy
• 3. Slide4 WHAT IS NUCLEAR ENERGY Everything around you is made up of tiny objects called atoms. Most of the mass of each atom is concentrated in the center (which is called the nucleus), and the rest of the mass is in the cloud of electrons surrounding the nucleus. Protons and neutrons are subatomic particles that comprise the nucleus. Under certain circumstances, the nucleus of a very large atom can split in two. In this process, a certain amount of the large atom’s mass is converted to pure energy following Einstein’s famous formula E = MC2, where M is the small amount of mass and C is the speed of light (a very large number). In the 1930s and ’40s, humans discovered this energy and recognized its potential as a weapon. Technology developed in the Manhattan Project successfully used this energy in a chain reaction to create nuclear bombs. Soon after World War II ended, the newfound energy source found a home in the propulsion of the nuclear navy, providing submarines with engines that could run for over a year without refueling. This technology was quickly transferred to the public sector, where commercial power plants were developed and deployed to produce electricity
• 4. Slide5 CAPABILITIES Sustainable Table 1 sums the sustainability of nuclear power up quite well. However, there is quite a bit of talk about nuclear fuel (Uranium) running low just like oil. Technically, this is a non-issue, as nuclear waste is recyclable. Economically, it could become a major issue. Today’s commercial nuclear reactors burn less than 1% of the fuel that is mined for them and the rest of it or so is thrown away (as depleted uranium and nuclear waste). Ecological In operation, nuclear power plants emit nothing into the environment except hot water. The classic cooling tower icon of nuclear reactors is just that, a cooling tower. Clean water vapor is all that comes out. Very little CO2 or other climate-changing gases come out of nuclear power generation (certainly some CO2 is produced during mining, construction, etc., but the amount is about 50 times less than coal and 25 times less than natural gas plants. Details coming soon). Independent With nuclear power, many countries can approach energy independence. Being "addicted to oil" is a major national and global security concern for various reasons. Using electric or plug-in hybrid electric vehicles (PHEVs) powered by nuclear reactors, we could reduce our oil demands by orders of magnitude. Additionally, many nuclear reactor designs can provide high-quality process heat in addition to electricity, which can in turn be used to desalinate water, prepare hydrogen for fuel cells, or to heat neighborhoods, among many other industrial processes.
• 5. Slide23 5 CAPABILITIES Sustainable Ecological Independent
• 6. Slide6 6 PROBLEMS WITH NUCLEAR ENERGY Nuclear Waste When atoms split to release energy, the smaller atoms that are left behind are often left in excited states, emitting energetic particles that can cause biological damage. Some of the longest lived atoms don’t decay to stability for hundreds of thousands of years. This nuclear waste must be controlled and kept out of the environment for at least that long. Designing systems to last that long is a daunting task one that been a major selling point of anti-nuclear groups. Cost Nuclear power plants are larger and more complicated than other power plants. Many redundant safety systems are built to keep the plant operating safely. This complexity causes the up-front cost of a nuclear power plant to be much higher than for a comparable coal plant. Once the plant is built, the fuel costs are much less than fossil fuel costs. In general, the older a nuclear plant gets, the more money its operators make. The large capital cost keeps many investors from agreeing to finance nuclear power plants. Accidents Three major accidents have occurred in commercial power plants: Chernobyl, Three Mile Island, and Fukushima. Chernobyl was an uncontrolled steam explosion which released a large amount of radiation into the environment, killing over 50 people, requiring a mass evacuation of hundreds of thousands of people, and causing up to 4000 cancer cases. Three Mile Island was a partial-core meltdown, where coolant levels dropped below the fuel and allowed some of it to melt. No one was hurt and very little radiation was released.
• 7. Slide7 WHAT IS RADIATION A radioactive atom is one that spontaneously emits energetic particles or waves (known as radiation). This radiation is emitted when an unstable (i.e. radioactive) nucleus transforms to some other nucleus or energy level. Imagine a big ball made of magnets that’s spinning really fast. Sometimes a few pieces of the magnet will shoot out and hit the wall. That’s kind of what radiation is like. As it applies to nuclear energy, many materials created during the operation of a reactor are unstable. As they decay over varying lengths of time (from microseconds to hundreds of thousands of years), they emit energetic particles or waves. The energy carried by this radiation is often sufficient to cause damage to biological cells and is therefore a health risk. Thus, radiation is the primary cause of safety concerns related to nuclear energy.
• 8. Slide8 8 TYPE OF NUCLEAR RADIATION Alpha Particles Named alpha because they were the first to be discovered, these particles are made up of 2 protons and 2 neutrons: the helium nucleus. Often, large atoms decay by emitting an energetic alpha particle. These particles are relatively large and positively charged, and therefore do not penetrate through matter very well. A thin piece of paper can stop almost any alpha particle. However, the particles cause extreme damage of materials that they stop in by displacing atoms as they slow. Paper under sustained alpha-irradiation would degrade.
• 9. Slide19 9 TYPE OF NUCLEAR RADIATION Beta Particles Beta particles are energetic electrons that are emitted from the nucleus. They are born when a neutron decays to a proton. Since neutrons are neutral particles and protons are positive, conservation of charge requires a negatively charged electron to be emitted. Some isotopes decay by converting a proton to a neutron, thus emitting a positron (an anti-electron). These particles can penetrate matter more than can alpha particles, and it takes a small aluminum plate to stop most beta particles.
• 10. Slide20 TYPE OF NUCLEAR RADIATION Gamma Rays Gamma rays are photons that are emitted from the nucleus. Often an atom in an excited state will de- excite by emitting a gamma ray. Gamma rays are similar to light waves and x-rays, except they are usually much higher frequency and consequently, more energetic. This radiation has no charge, and can penetrate most matter easily, requiring lead bricks for shielding.
• 11. Slide9 11 HISTORY OF NUCLEAR ENERGY No scientific progress ever really starts. Rather, it builds on the work of countless other discoveries. Since we have to start somewhere, this story will start in Germany, in 1895, where a fellow named Roentgen was experimenting with cathode rays in a glass tube that he had sucked the air out of. At one point, he had the device covered but noticed that the photographic plates off to the side were lighting up when the device was energized. He realized that he was looking at a new kind of ray, and called it what any reasonable physicist would call an unknown: the X-ray. He systematically studied these rays and took the first x-ray photo of his wife’s hand two weeks later, thereby becoming the father of modern medical diagnostics.
• 12. Slide16 12 HISTORY OF NUCLEAR ENERGY Soon after in France, in 1896, a guy named Becquerel noticed that if he left uranium salts sitting on photographic plates, they would expose even though no cathode ray tube was energized. The energy must have been coming from inside the salts themselves. Marie Curie and her husband Pierre studied the phenomenon and isolated two new elements that exhibited this spontaneous energy production: Polonium and Radium. They named the phenomenon radioactivity.
• 13. Slide10 HISTORY OF NUCLEAR ENERGY In 1932, Chadwick reads some published results from the Curie’s kid, Irene Joliot-Curie that says gamma radiation was found to knock protons out of wax. Disbelieving, he suspects they are seeing Rutherford’s neutrons and does experiments to prove this, thus discovering the neutron.
• 14. Slide21 HISTORY OF NUCLEAR ENERGY In England, Ernest Rutherford starts studying radioactivity and discovers that there are two types of rays that come out that are different from x-rays. He calls them alpha- and beta- radiation. He later discovers the shocking fact that the vast majority of the mass of atoms is concentrated in their centers, and thus discovers the atomic nucleus. He is widely regarded today as the father of nuclear physics. He later discovers gamma radiation. In 1920, he theorizes the existence of a neutral particle in the nucleus called a neutron, though there is no evidence that neutrons exist yet.
• 15. Slide11 FISSION AND THE BOMB With neutrons around, everyone’s shooting them at various nuclides. Soon enough, Hahn and Strassman shoot them at uranium atoms and see some strange behavior which Lise Meitner and her nephew Frisch identify as the splitting of the atom, releasing much energy. They name it fission, after binary fission in biology. Szilard recognizes fission as a potential way to form a chain reaction (which he had been considering for a long time). He and Fermi do some neutron multiplication studies and see that it is indeed possible. They go home, knowing that the world is about to change forever. Szilard, Wigner, and Teller write a letter to President Roosevelt, warning of nuclear weapons, and have Einstein sign it and send it (he was more famous). Roosevelt authorizes a small study into uranium. In 1942, Fermi successfully created the first man-made nuclear chain reaction in a squash court under the stadium at the University of Chicago.
• 16. Slide18 FISSION AND THE BOMB The Manhattan project kicked into full gear. Two types of bombs were pursued simultaneously, one made with enriched uranium, and the other made with plutonium. Giant secret cities were built very quickly. The one in Oak Ridge, TN had a reactor that created the first gram-quantities of plutonium for study, but its main task was to enrich uranium. The one in Hanford, WA is the site of plutonium production reactors (the first high-power nuclear reactors) and plutonium extraction chemistry plants. Another, in Los Alamos, NM is the site where the technology that turns weapons materials into weapons is developed. Both paths to the bomb are successful. The more uncertain design, the plutonium implosion device (like Fat Man) is successfully tested at the Trinity site in New Mexico in July, 1945.
• 17. Slide12 RECYCLING NUCLEAR WASTE AND BREEDER REACTORS What is Nuclear Recycling Nuclear waste is recyclable. Once reactor fuel (uranium or thorium) is used in a reactor, it can be treated and put into another reactor as fuel. In fact, typical reactors only extract a few percent of the energy in their fuel. You could power the entire US electricity grid off of the energy in nuclear waste for almost 100 years. If you recycle the waste, the final waste that is left over decays to harmlessness within a few hundred years, rather than a million years as with standard (unrecycled) nuclear waste. This page explains how this interesting process is possible.
• 18. Slide13 NUCLEAR TRANSFORMATION Before you go on, recall that Uranium exists in nature as 2 isotopes: the less common U-235, and the more common U-238. Conventional reactors mainly split U-235 to produce power, and the U-238 is often considered useless. When a standard reactor runs low on U-235, it must be refueled, even though there is a lot of U-238 still in there. A common type of nuclear reaction is called beta-decay. When a nucleus has more neutrons than it would like to have, it often beta- decays by breaking a neutron into a proton and an electron. The electron (called a beta-particle in this case, since it originated in the nucleus) flies off into nature, and the main result seen in the nucleus is a neutron converting to a proton (see figure).
• 19. Slide17 NUCLEAR TRANSFORMATION When U-238 absorbs a neutron in a nuclear reactor, it becomes U-239, which is just the isotope of Uranium with one extra neutron than U-238. This beta-decays quickly and becomes Np-239. Then, the Np-239 beta-decays again to become Pu-239, which is a fissile isotope that can power nuclear reactors. The “useless” U-238 is the secret to recycling nuclear fuel. When it absorbs a single neutron, it goes through a series of nuclear reactions within a few days and turns into a very splittable isotope of Plutonium, Pu-239. The Pu-239 acts a lot like the U-235 that powers conventional reactors, so if you convert your U-238 to Pu-239 as you run your reactor, you can then use that Pu-239 to continue powering your reactor, or others!
• 20. Slide14 NUCLEAR FUEL CYCLES A nuclear fuel cycle is the path that nuclear fuel (Uranium, Thorium, Plutonium, etc.) takes as it is used to generate power in a nuclear reactor. Our fuel cycle page has more info. They describe where the material comes from and where it ends up. Different fuel cycles range from very simple to fairly complicated. We describe several of these below. Note: Besides the U-Pu fuel cycle described here, the Thorium-Uranium fuel cycle is analogous and can also be recycled.
• 21. Slide22 NUCLEAR ENERGY SOURCES https://whatisnuclear.com/ https://pixabay.com/ https://chem.libretexts.org/ https://nypost.com/