Nuclear Energy Overview

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Nuclear Energy OverviewNuclear Energy OverviewIn 2010, nuclear provided almost 14 percent of the entire California power mix (which includedout of state imports). As of mid-2012, California had one operating nuclear power plant: DiabloCanyon (2,160 megawatts), near San Luis Obispo. In 2017, in-state power generation was206,336 gigawatt-hours (GWh), nuclear accounted for 11.5% of the total in-state electricgeneration.1There are two fundamental ways to release energy from nuclear reactions: fission and fusion ofatomic nuclei. Nuclear fission is a nuclear reaction or a radioactive decay process in which theatomic nucleus splits into lighter nuclei, releasing some combination of particles and energy.2Nuclear fusion is a reaction in which multiple atomic nuclei combine to form a combination ofnew atomic nuclei and subatomic particles with the resulting mass difference manifesting aseither an absorption or release of energy. 3 Electricity generating technologies based on fissionare commercially available, whereas fusion is still in the stages of research and development.Nuclear FissionOf the several types of fission reactors, the most common type in the United States are lightwater reactors4, normal water is used to cool the reactor core, based on pressurized waterreactor (PWR) and boiling water reactor (BWR) technology. 5 U.S. commercial rectors useuranium-235, a naturally occurring radioactive isotope of uranium, as the nuclear fuel. In a PWRor BWR reactor, the overwhelming majority of fission events are induced by bombardment withanother particle, a neutron, which is itself produced by prior fission events. The uranium-235fission event is a bimodal process, resulting in the release of energy, different atomic nuclei,and extra neutrons. The free neutrons bombard adjacent uranium-235 atoms, creating a fissionchain reaction that releases more energy and byproducts.1Sector-specific summaries of California's progress toward a cleaner energy future, with links to additionalresources. Information and metrics are updated regularly. Available athttps://www.energy.ca.gov/renewables/tracking progress/index.html.2Nuclear fission, https://en.wikipedia.org/wiki/Nuclear fission.3Nuclear fusion, https://en.wikipedia.org/wiki/Nuclear fusion.4“Light” water is composed of oxygen and hydrogen while “heavy” water replaces the hydrogen with the isotopedeuterium, hydrogen atoms with an additional neutron in the nucleus.5Pressurized water reactor, https://en.wikipedia.org/wiki/Pressurized water reactor. Boiling water reactor,https://en.wikipedia.org/wiki/Boiling water reactor.Last updated March 2020Page 1 of 5

Figure 1: A schematic of a nuclear fission chain reaction. (1) A uranium-235 atom absorbsa neutron and fissions into two new atoms (fission fragments), releasing three new neutronsand energy. (2) One neutron is absorbed by an atom of uranium-238 and does not continue thechain reaction. Another neutron is simply lost and does not collide with anything, also ending apotential chain reaction. However, one neutron does collide with an atom of uranium-235,which then fissions and releases two neutrons and energy. (3) Both neutrons collide withuranium-235 atoms, each of which fissions and releases between one and three neutrons,which propagates the chain reaction.6The Diablo Canyon Nuclear Power Plant, the last operating nuclear reactor in California,consists of two PWR units. Nuclear fission in the reactor vessel produces heat. This heat isabsorbed by pressurized water in the primary coolant loop. The primary coolant loop is isolatedin order to contain radiation released during the fission and decay process. The super-heatedFigure 1 Source: By User: Fastfission - Own work, Public urid 5225926Last updated March 2020Page 2 of 5

water in the primary coolant is routed through hundreds or thousands of pipes, which transferheat to the secondary coolant loop. Water in the secondary coolant loop is converted to highpressure steam that is used to spin the turbines that generate electricity.There are several alternative reactor designs and advanced reactor power plant designs beingdeveloped in the U.S. and over-seas. Information on these systems can be found on reputableweb sites such as the World Nuclear Association website, http://www.world-nuclear.org/.Figure 2: Pictorial explanation of power transfer in a pressurized water reactor. Primary coolantis in orange and the secondary coolant (steam and feed water) is in blue. 7Issues for Fission Power PlantsSome of the issues associated with commercial nuclear power plants include: Economic feasibility of new and existing plants in the United States Need for a spent fuel disposal facility and a decommissioning plan Use of large amounts of water for cooling purposes (if wet cooling towers are used) Biological impacts on the ocean due to thermal discharge (if seawater cooling is used) Seismic safety concerns Public safety concernsFigure 2 Source: By U.S. NRC, nimated-pwr.html, PublicDomain, https://commons.wikimedia.org/w/index.php?curid 23202147Last updated March 2020Page 3 of 5

Transportation issues associated with emergency evacuation and the disposal ofradiological wasteChanges in visual quality due to the power plant structures, including the reactor vesselcontainment structure, and associated structuresLand usage and contaminationPublic perceptionNuclear FusionFigure 3: Fusion of deuterium, helium-2, with tritium, helium-3, creating helium-4, freeinga neutron, and releasing 17.59 MeV as kinetic energy of the products while a correspondingamount of mass disappears, in agreement with kinetic E Δmc2, where Δm is the decrease inthe total rest mass of particles. 8A fusion reaction occurs when atomic nuclei, such as hydrogen and its isotopes (deuterium andtritium), are forced together (conditions require some combination of extremely hightemperature, pressure, or velocity to overcome the Coulomb force) until they fuse into a nucleiof a heavier element. The fusion process releases a combination of particles and kinetic energyproportional to the difference in mass. There are multiple fusion methods that are currentlybeing pursued for use in a commercial reactor system. 9By Wykis (talk · contribs) - This file was derived from: D-t-fusion.png:, Public urid 20695759Figure 3 Source: Fusion Power https://en.wikipedia.org/wiki/Fusion power8Last updated March 2020Page 4 of 5

To generate commercial energy from fusion, the released energy would be converted to heat,which in turn is converted to electricity via a conventional generator cycle. Although the fusionreaction does not produce significant or long-lived radioactive byproducts, the high-energyparticles irradiate the surrounding reactor vessel and associated components. The irradiatedmaterial could pose potential disposal problems similar to those for the irradiated fissionreactor vessel. The reasons fusion continues to be actively pursued is that unlike nuclear fission,there is less waste products, no risk of a nuclear melt down (the reactor vessel could explodebut this would be comparable to a conventional gas plant accident), and fusion power providesmore energy for a given weight of fuel than any fuel-consuming energy source currently in use.Last updated March 2020Page 5 of 5

Nuclear Energy Overview . Nuclear Energy Overview . In 2010, nuclear provided almost 14 percent of the entire California power mix (which included out of state imports). As of mid-2012, California had one operating nuclear power plant : Diablo Canyon (2,160 megawatts), near San Luis Obispo. In 2017, in-state power generation was

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