EPQ First Draft “Investigating the Feasibility of Implementing Nuclear Reactors as a Major Power Source In Australia”A nuclear reactor is a device in which controlled fission is used to produce both new substances and release energy. Fission is the process by which a nucleus splits into two fragments. This is caused when neutrons are used to ‘bombard’ a nucleus. As neutrons are neutral they are not repelled by the positively charged nucleus but instead absorbed into it. Some nuclides will split into two different atoms after absorbing a neutron and these nuclides are defined as ‘fissile’. Through the process of fission, a large amount of energy (heat) is released which is used to heat and boil water. The enormous amount of energy released is due to the magnitude of occurring fission reactions, as a singular fission reaction emits a relatively small amount of energy. The two most common materials used to accomplish this are Uranium – 235 and Plutonium – 239. These are used because they are both fissile and they emit 2 or more neutrons which allows the chain reaction occurring in the core to operate.The diagram below depicts how a pressurized water reactor operates. The energy of a nucleus (Uranium) is released through fission by a chain reaction occurring in the core. The Uranium undergoing fission releases neutrons which result in more fission reactions. The released energy heats pressurized water which is being pumped through the reactor core. The water is pressurized in order to raise its boiling point to a sufficient level necessary to avoid evaporation in the reactor core. This high pressure water will then flow into the steam generator, where it will transfer its thermal energy to a second system, which consists of non-pressurized water. The transfer of energy from system one will heat the water in system two until it boils, evaporates and generates steam. This steam will then turn a turbine connected to a generator which in turn, spins the generator and creates electrical energy. Meanwhile the steam used to turn the turbine is then condensed back into water (by the condenser) which is then re-funnelled back into the steam generator to receive the heat transfer once again and continue the cycle. The pressurized water from system one also gets cooled after transferring its thermal energy to the second system, and it is then pumped back into the reactor to core to be reheated. Both of these processes continuously repeat which is what generates continuous, efficient and long term electricity. Now that we’ve discussed the basics of how the reactor works we can take a closer look at the actual reactor core and how it operates. The nuclear reactor core contains the nuclear fuel, the moderator/s and the control rods. Sourced from: https://www.clpgroup.com/NuclearEnergy/Eng/power/power4_1_2.aspxThe fuel in the reactor consists of 96.8% Uranium-238 and 3.2% Uranium-235 (on average) The U235 can: not absorb a neutron and stay the same, absorb a neutron becoming U236 yet remain stable and not fission or fission into a multitude of different products The other 96.8% of Uranium-238 some can absorb a neutron and fission, some may stay the same, some can beta decay into neptunium and then maybe plutonium and then that can fission into other more fission fragments also releasing energy and neutronsThe energy used to heat the water is created by an induced fission reaction in the core: uranium-235 absorbs a neutron, changing into an excited uranium-236* nucleus. With the excitation energy provided by the kinetic energy of the neutron as well as the forces that bind the neutron. The uranium-236 then fissions fission fragments, Kinetic Energy as well as 2-3 neutrons (on average 2.45) and 1 or more gamma photons. The emitted neutrons are slowed down by moderators (in this case the water), giving them more chance of colliding with uranium-235, and undergoing fission again. The energy released from a fission reaction is all due to the mass defect which is the difference in mass of the products and the reactants. Essentially, in the fission of Uranium-235, the total mass before fission is greater than the total mass after the fission event. In the reaction below it appears that the atomic mass is the same, but this is a rounded value. Without rounding the added up total mass of the reactants ends being slightly larger than the total mass of the products. The mass difference is what is converted into thermal energy, in the form of Kinetic energy and 1 – 2 gamma photons. This energy released is equivalent to the binding energy which is the energy needed to hold the nucleus together. When U236 fissions the binding energy is released and this is equivalent to the difference in mass (mass defect). We can obtain the value of the binding energy released by using the mass defect in the equation E=mc2. On average the binding energy released or mass defect converted into energy is around 200MeV. 1 0 n+235 92 U236 92 U92 36 Kr+141 56 Ba+31 0 n+200MeVThis process continues repeatedly in a chain reaction and is maintained at a controllable rate by Control Rods and moderators. The number of neutrons produced by fission events must be equal to the number of fission-producing neutrons in order to sustain a nuclear reaction. Sometimes the reaction might ‘run away’ (overproduce neutrons and begins destabilising). Then control rods containing neutron poisons (like boron-10) are lowered into the fuel to decrease the number of neutrons in the substance. The control rods are then removed when the chain reactions begins to produce insufficient neutrons to continue the reaction.The fuel needed for this chain reaction to occur is either plutonium-239 or Uranium-235 of which both are very rare. Plutonium can obtained only be obtained from Uranium (Uranium-238 beta decays into neptunium-239 which will then beta decay into plutonium-239). Often we find Uranium in its 238 form and it must be enriched, in order to attain the Uranium as Uranium-235. To get sustained fission, the amount of uranium-235 must be increased, this is done by separating uranium-235 out of naturally occurring uranium ore. Then by putting this back into a certain amount of naturally occurring uranium. This increases (enriches) the proportion of uranium-235 in the quantity. Usually a sample of Uranium fuel with have about 0.9% uranium-235, but for it to be sufficient to sustain a controlled chain reaction it’s enriched until about 1-4% is uranium-235 content.For fission to occur frequently in Uranium-235 the initial neutron must be a ‘slow’ neutron. Neutrons produced in fission events are ‘fast’ neutrons. The probability of these causing new fission events in uranium-235 is very small. Thus Moderators are used to slow down the neutrons produced through the fission process. A moderator is a material/substance with nuclides that have a slightly larger masses than the neutrons. The neutrons then share their energy with these nuclides through multiple collisions. This results in a rapid loss of energy (they become slower). Which further increases the probability of neutrons entering a uranium-235 nucleus and resulting in more frequent fission reactions. In this reactor it is water which acts as the moderator.Country StatisticsAs of November 2016 nuclear power plants operate in 30 countries around the world with 450 nuclear reactors, most are in North America, Europe and East/South Asia. Currently France relies the most on nuclear power with 77.5% of Its total energy consumption generated by nuclear power stations. France currently has 58 nuclear reactors which generated 63.2 GWh of electricity. However, while France depends the most on nuclear power it does not produce the most. America currently has 99 nuclear reactors in 30 states in the USA; There are 65 pressurized water reactors (PWRs) with combined capacity of about 64 GWe and 34 boiling water reactors (BWRs) with combined capacity of about 35 GWe, altogether their total capacity is 109 GWe. But this is only 19.7% of the share of domestic generation by America. The rest of the other 30 countries energy outputs are shown below in the diagram sourced from the nuclear energy institute.Nuclear WasteNuclear waste is any material that is no longer able to be used in the process of operating the nuclear reactor. Nuclear waste has 3 different classification levels: low, medium (intermediate) and high. Depending on the level of the waste each one has to be treated, stored and disposed of differently.Low level nuclear waste consists of lightly-contaminated items such as tools, work clothing from power plant operators, protective gear, water used for showers and cleaning water. This form of nuclear waste makes up the bulk of the radioactive waste (roughly 90%) but It can be released out to the environment after being diluted as it’s radioactive content is only about 1%. Some countries still prefer to store their low level nuclear waste in special facilities alongside intermediate level waste.Intermediate level nuclear waste consists of about 7% of the waste created and it has a radioactive content of around 4%. These usually consist of used filters, steel components from within the reactor and some effluents from reprocessing. As well as some fuel containers, gauges and pipes, essentially parts that weren’t actually in the reactor core themselves. Intermediate level waste is treated and conditioned by incorporating it, for example, into cement or bitumen and then shielded in containers. In many countries, disposal sites for low and intermediate level wastes are in operation, with intermediate level waste and low level waste often disposed of in the same facility. Usually, these facilities are at or near the surface.The most problematic and most dangerous form of nuclear waste is the High level waste; this contains 95% of the radioactive content but consists of only 3% of the volume of nuclear waste. This 3% is the essentially the used nuclear fuel; fission products formed (the multitude of transition metals) that have been formed by the fission of uranium-235/8 or plutonium-239. They are extremely radioactive and very hot, hence requiring careful storage by shielding and cooling the fuel. This is usually done simultaneously as water acts as an effective shield and a good coolant. Most reactors will store all their high level waste in a storage pool unit onsite under a few metres of water, after about 5 years it can be transferred into dry ventilated concrete containers. Eventually the high level fuel will be disposed of deep underground in suitable geological depositories build in geologically stable positions.Fukushima On the 11 march 2011 the Great Eastern Japan Earthquake at a magnitude of 9.0 struck Japan 130 km offshore from the city of Sendai in Miyagi prefecture on the eastern coast of Honshu Island. Lasting for 3 minutes the earthquake did considerable damage. Fortunately, Japan had been built to withstand earthquakes and did not suffer to much from the earthquake itself. However, the worst was yet to come, as the extremely powerful earthquake created a massive Tsunami with a run-up height of 23m. The Tsunami caused the deaths of over 19’000 people and the destruction or part collapse of over 1 million buildings. At the time eleven Nuclear reactors were operating at 4 nuclear power plants around the region. When the earthquake hit all the reactors automatically shut down immediately, and none of them sustained any damage from the earthquake. However, the tsunami was a different matter. There were 3 reactors operating on the Fukushima Daiichi site, all of them lost power at 3:42pm due the flooding of the entire site by 15m waves. The tsunami disabled 12 of the 13 backup generators as well as the heat exchangers and excess heat dispensers. Due to this the reactors were unable to sustain proper reactor cooling and water circulation functions. The Fukushima site underwent design planning in 1960 and the tsunami protection wall was only 3.1m high meaning the Daiichi site was a total of 10m above sea level with the seawater pumps only 4m above sea level. At the time with their current data they had on Tsunami’s these were acceptable precautions. However, as the years went by Tsunami’s have gotten more frequent and much larger, for example, in 1986 a tsunami with a run-up height of 38m struck the Japan. This tsunami’s waves were 15m high when they reached the Daiichi site, and being only 10m above sea level the entire area was flooded, the backup generators used to pump seawater into the reactor and cool it were then drowned under 5m of sea water.When the earthquake hit all the reactors immediately shut down, this was done by inserting all the control rods taking the reactor from 100% power to 7% power. This 7% is the residual (decay) heat caused from the radioactive decay of fission products. Radioactive decay is the process fission products stabilize themselves with by emitting energy in the form of alpha, beta, gamma, neutron particles etc. These process produce heat but overtime this residual heat will decrease after the reactor is shut down. However, this residual heat must be removed from the reactor core to prevent it boiling the water and creating pressure which will actually begin to heat the reactor up again. If this happens the fuel rods can overheat (at 1200°C) and fail as a barrier to radioactive release. The challenge the nuclear operators faced was attempting to keep the reactor below 1200°C without the use of power.The fuel rods in the Fukushima Reactor contained the nuclear fuel Uranium Oxide which is a ceramic with a melting point of 2800°C. The fuel is manufactured in pellets and they are stored in long tubes made of Zircaloy (alloy of zirconium) which melts at 1200°C. These tubes are then sealed tightly and are called fuel rods, these are put together into assemblies of which several hundred are used to make up a reactor core. These rods are in a pool of pressurised water and without cooling this water begins to heat and boil creating steam, which increases pressure and raises the temperature causing more water to boil more steam and so on. Essentially without the power to cool the core it was gradually heating up until it would begin to melt the Zircaloy. As Long as the heat production from the decay heat exceeded the heat removal capacity, then the pressure would keep increasing as more and more water boils into steam. The operator’s priorities were to keep the reactor temperature below 1200°C and to keep the pressure manageable. In order to do this, they needed to vent the steam and other gases present in the reactors at certain intervals. During this process of venting, a small amount of radioactive gas was vented into the air around Fukushima. Eventually portable generators were brought on site but they weren’t just weren’t to cool the reactor at this stage as the heat production had risen to a very high level. It came to a point where some of the Zircaloy fuel tube casings had exceeded 1200°C initiating a reaction between the Zircaloy and the water. This oxidising reaction produced hydrogen gas, which is very combustible; if a large amount of hydrogen gas is mixed with air it reacts rapidly with the oxygen and explodes. This hydrogen gas slowly built up in the reactor core and at some point during the venting of the core a large portion of it was vented out, thus causing a hydrogen explosion which destroyed the outer building, as it occurred outside the containment housing, no damage was done to the containment structure’s integrity very little radiation escaped. The radiation that did escape was due to the cladding of the fuel tubes exceeding 1200°C. When this happened some of the radioactive fission products also reacted with water (like Cesium, Iodine) and a small amount of cesium and iodine was released into the atmosphere as a gas along with the hydrogen.Since the reactor could no longer sustain cooling with its current volume of water, the operators were able to get some power back into the system at this point, they injected seawater infused with boric acid (a neutron absorber). This process was enough to decrease the temperature of the core to below 1200°C and hence no further damage occurred to the fuel tubes. And because the reactor had been shut down for days now the decay heat had decreased to a proportionally lower level and the plant was able to be stabilised. Meaning it required no further venting and would soon enter cold shutdown.Radiation levels/Human tollHow the Fukushima Accident could have been preventedWould it actually be Possible in Australia’s Political State?(Conclusion) Opinion on nuclear power generation in AustraliaEvaluation of Reliability of Sources Bibliography “What Are Nuclear Wastes And How Are They Managed? – World Nuclear Association”. World-nuclear.org. N.p., 2017. Web. 4 May 2017.”Fukushima Accident – World Nuclear Association”. World-nuclear.org. N.p., 2017. Web. 9 May 2017.Brook, Barry. “Fukushima Nuclear Accident – A Simple And Accurate Explanation”. Brave New Climate. N.p., 2017. Web. 9 May 2017.”Nuclear Binding Energy And Mass Defect”. Boundless. N.p., 2017. Web. 9 May 2017.”Australia’s Uranium | Uranium Mining In Australia – World Nuclear Association”. World-nuclear.org. N.p., 2017. Web. 9 May 2017.”Physics Of Uranium And Nuclear Energy – World Nuclear Association”. World-nuclear.org. N.p., 2017. Web. 9 May 2017.”World Nuclear Generation And Capacity – Nuclear Energy Institute”. Nei.org. N.p., 2017. Web. 9 May 2017.”Nuclear Reactor Core”. Nuclear Power. N.p., 2017. Web. 9 May 2017.