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by: Kitty Reinger


Kitty Reinger
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John Pratte

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John Pratte
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This 21 page Class Notes was uploaded by Kitty Reinger on Friday October 2, 2015. The Class Notes belongs to PHSC 1014 at Arkansas State University taught by John Pratte in Fall. Since its upload, it has received 41 views. For similar materials see /class/217717/phsc-1014-arkansas-state-university in Physical Science at Arkansas State University.

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Date Created: 10/02/15
Population Age Structure Introduction One ofthe tools that demographers use to understand population is the age structure diagram it is sometimes called a population pyramid but it is not always pyramidal in shape This diagram shows the distribution by ages offemales and t males wi hi a certain population in graphic form Figure 1 shows a diagram in which the ages and sexes for the United States population are arranged so that ages are grouped together such as 4 years 5 9 years and so on The population of each is group is represented as a bar extending from a central vertical line with the length of each bar dependent upon the population total for that particular group The centerline separates the fem ales from the males The female and male populations for each group are represented by the distance from the centerline with t 39 zanales on the ght and males on the Fig 1 Age Structure diagram for the US Age and Sex Distribution By looking closely at the age structure diagram one will notice slightly more boys in the younger age groups than girls however the ratio tends to reverse in the u er a e rou s as females tend to outnumber males Many countries have a female majority as a result ofthe longer life expectancy for females In the United States this ratio change is clearly s own in the a e elow showing age and sex distribution in the census year 2000 Notice that at about age 35 the majority changes Erru there tn reduce the bmh rate have are U a mate chug fthey constructing and Interpreting an Age structure Dlagram thh age and selt msmbutmn gatarrerh a Denam nhmuahhh hee the ta ram 5 unstructed ehe ah tearty see tr the peputatteh wm grew dechne er EXpEHEHEE he heneeame hahge W 15 peputatteh HumbErS er Examme tr the ma rarh shews a h ehe can expect a raptg hse W rarh shews a generaHy strath up and gewn shape Except fer the Elmer age gre stante peputaneh 5 thus reveateg fme gtagrarh shews a uprheavy shape men a geehhe tsrereeast rerthat peputatteh thure 3 shews the age structure magrams termeaeg EE and andJapan The dWErEnt shapes seeh W the magrams retest dWErEnt permutatch charactenstms The magrarh rer Mexmu shews the uhrhtstahante bums Japan s magrarh has the mass shape era Sherng peputatteh m L yuu shuum hete hem pre repruductwe age greu s u e 14 years have smaHEr eput EIHS than the repruductwe age greups 157 44 mean shews a mere stante upmatmn Exceptfurme pustrrepmductwe greups 45 years the peputattehs rerthe age greups elttehg generaHy the same Engms u u uan s g F igmt mt Fig 3 Age SLnIEun Edizgalm fnrMex39tn Iceland and Japan 11x 0mm Ewem Activity Constructing an Age Structure Diagram On the activity sheet is an age structure diagram template on which bars can be drawn to represent the population for each age group and sex Data for constructing the diagram will come from Census Year 2000 data for the American Indian and Alaska Native group Because emigration and immigration are not major factors influencing the population numbers for this group one can see the future ofthe group s population without substantial migration influences Click on the following link to gather data for the number of females in each age group for the American Indian and Alaska Native Be sure you use the column specified for that group httpwwwcensusgovpopulationcen2000phct9tab03pdf Click on the following link to gather data for the number of males in each age group for the American Indian and Alaskan Native Be sure you use the column specified for that group httpwwwcensusgovpopulationcen2000phc t9tab02 pdf Using the datasheets linked above draw bars on the age structure diagram template to represent the populations for each age group of males and females Three bars have already been drawn to demonstrate how it is to be done The task can be done with a pencil and straight edge Be sure to add color to the bars for added clarity and appeal Once finished with constructing the diagram answer the questions on the activity sheet PHSC1014 g e v s ii Name 334 Ma es F2ma 25 m1 znn r75 Ian 25 mn 75 so 25 u 25 an 75 mn r25 w rum mnusmdi Wouro you raorory growmg popu auon a numemcaHy more popu auon Ora ooourauon facmg negawe growth Exp am how you made your decrsron anan m the ecture pomon ormrs acmrty WWCH one ormese 3 counmes rs mostcomoaraoretome age structure oragrarn you constructed ror me Amerroan Man and Araska Name Science 1102 Renewable Energy Wind Introduction History Like all other forms of renewable energy wind energy has been in use for several millennia The earliest records of its use date back as early as 5000 BC when simple sails were employed to transport boats along the Nile River This form of transport proved to be no temporary phenomenon as it was the primary method of boat transport well into the 1800 s The employment of rudimentary navigational techniques with it allowed humans to open worldwide trade routes forever changing the face of the planet However transportation was not the only use for wind energy As with hydropower people invented ways to harness wind to replace the backbreaking work of grinding grain to make flour This technological achievement dates back as least as early as 200 BC in Persia and the Middle East Farmers in China were also irrigating the crops in their field by this time using windmills to pump water from underground wells It is this lattertechnological advance that was the predominate image of wind energy in the US until recently Farmers in the Central and Western US have used metal windmills to provide water for their crops and livestock for almost 150 years in these regions As fossil fuels began to replace renewable forms of energy during the 1800s this was the last presence for wind energy in the US It survived mostly because wind energy was so plentiful in the region and because most farms were remote enough to limit the availability of fossil fuels It was not until the Rural Electrification Administration programs that started in the 1930 s began to bring fossil fuel energy to these farms and ranches that wind energy for irrigation began to disappear Figure 1 NEG Micon Turbine in Moorhead Minnesota DOE Spurred by industrialization and such programs as the REA the US experienced an increased need for electricity during the 1940 s This led to experimentation with the use of wind energy to drive generators At the time it was believed that windmill designs needed to be very large to produce the vast sums of electricity that would be needed As an example a windmill was built in 1940 at Grandpa s Knob in Vermont that had blades that were 175 feet in diameter and weighed 8 tons each This windmill was able to produce 12 megawatts of electricity but at a cost of 1000 per kilowatt which was very expensive for the time The interest in windmills soon waned as oil became plentiful following the end of World War II Research that might have led to cheaper designs that produced the needed electricity went by the wayside as the price of fossil fuels plummeted It was not until the Oil Embargo of the early 1970 s that work began again in earnest to develop such technology Once again interest was high while oil prices were high but decreased when the price of a barrel of oil fell to alltime lows in the 1980 s Luckily advances in technology had occurred that brought the price of producing electricity with windmills down Currently electricity can be produced at about 34 cents per kilowatthour with windmills under certain conditions which is comparable to that produced from coal and natural gas1392 Windmill Basics The idea behind generating electricity from wind is quite simple Wind is the manifestation ofthe kinetic energy of air molecules in the atmosphere In order to use this kinetic energy for other purposes all that one has to do is to have the wind hit a surface that is allowed to move This will cause the kinetic energy of the wind to be converted to the kinetic energy ofthe moving object Anyone who has ever been outside on a very windy days understands these concepts The hard part about generating electricity from wind is doing it cheaply To do this a more fundamental knowledge about wind energy is needed Let us imagine air that is moving through an area A with a velocity v as shown in Figure 2 From our section on energy we know that the kinetic energy of an individual air molecule is given by the formula 12 mv2 We want to consider a large system of air molecules which means looking at a volume of particles In a time At the mass of the air that will flow through the area A is given by m p A v At where p is the density ofthe air If we put these two formulae together we get that the kinetic energy ofthe air that passes through an area A in a time At is given by the formula 12 p A v3 At Since the energy per 7 3939 39 unit time is equal to the power we get that the power in the wind Figure 2 Diagram 0f Wind tube moving through the area A is given by P KElAt 12 p A v3 While this is the power that is in the wind this is not the power that you can get out ofthe wind To understand why consider how one would extract energy from the wind As we stated above this involves allowing the wind to hit an object and transfer its kinetic energy to the object fthe air that hits the object delivers all of its kinetic energy to the object then the air comes to a complete standstill while the object begins to move The problem with this is that the air that has just hit the object needs to get out ofthe way in order for more airthat is behind to be able to hit the object In other words if you extracted all ofthe energy from the wind you would begin piling up air in front of your object and thus cutting offthe wind Therefore the air that hits your object must still have some kinetic energy in it in order for it to move out ofthe way to allow more air to hit it n1919 a German physicist by the name of Albert Betzs showed that the maximum amount of power that one can get from the wind is only 59 of that given by the formula above In actuality we will get less than this maximum amount Therefore we often write the formula for the power from a wind turbine as P12cpAv3 where the factor C depends on the actual design ofthe windmill that you build The factors that affect the constant C are many and complicated If you wish to learn more about it you might wish to visit the websites in the Additional Reading section at the end We should note that the formula for power depends on two other factors The first of these is the area of the wind that is captured This linear relationship shows that the bigger a windmill is the more power it will be able to output This is why a lot of commercial windfarms rely on large turbines The formula also shows that the power depends greatly on windspeed This is not a linear relationship between the two variables but a very strong dependence to the third power This means that the difference in power between wind moving at l metersecond and wind moving at 2 meterssecond is a factor of 23 8 Therefore the amount of energy that one will get out of a windmill depends tremendously upon the windspeed and it is vitally important that the windmill be placed in a location where winds are strong Wind Basics What factors affect windspeed To answer this we need to remember some meteorology basics The driving force behind wind is sunlight as you have no doubt seen described many times before Materials at the Earth s surface absorb some ofthe energy from the Sun that gets through the atmosphere This causes the surface to increase its temperature above its surroundings which results in heat transfer back into the atmosphere Some of this heat is transferred by conduction some of it by radiation in the infrared region which gets absorbed by greenhouse gases Both ofthese methods cause the air near the surface to increase its temperature which results in it expanding This expansion causes a net reduction in the density ofthe air and it rises as it becomes more buoyant Thus just like the water in a teakettle before it boils the air undergoes convection This though is not the wind that we feel This is vertical air movement and not the horizontal movement that we need to drive windmills lt isjust the first part ofthe process of wind creation The air that rises takes a great deal of mass with it Without the weight of the air pressing down in this area the air pressure is reduced This makes the surrounding air that is not rising higher in air pressure The resulting pressure difference causes the surrounding air to rush toward the lower air pressure giving us surface winds This part ofthe process is known as advection Latitudinal Effects and Hadley Cells This process can happen on large or small scales creating either large wind patterns that persist over hundreds and thousands of miles or small patterns ofjust a few miles What are some ofthe factors that affect it One of the most obvious answers is latitude As we discussed in the Solar Energy Activity the closer the Sun s ray are to perpendicular when striking the Earth s surface the higher the energy density of that sunlight Since the Sun is more directly overhead near the equator throughout the year the more energy it receives and thus the hotter it gets Thus we expect to see a lot of warm air rising near the Equator Conversely we expect to see a lot of cold air descending nearthe poles lfthe Earth was not rotating this latitudinal heating would result in two giant cells of air movement rising near the Equator moving in a straight line in the upper atmosphere directly to the poles descending near the poles and moving laterally from the poles to the Equator near the surface See Figure 3 However this does not occur because ofthe Coriolis effect which causes this type of air cell to break up into three air cells in each hemisphere of the Earth To understand how it does this we have to consider what the airflow looks like from above the Earth In order for air to remain static with respect to the Earth over the equator it must be moving at slightly more than 1000 miles per hour in the direction ofthe Earth s rotation Non ROtatmg Earth Air that is static over the poles on the other hand has zero velocity with respect to an observer in space The velocity of static air as one moves from the poles to the equator is a slowly increasing value between these two extremes As long as air is static over the Earth everything looks okay Now consider air that is near the equator moving toward the North Pole As it moves to higher latitudes it will be over a portion ofthe Earth that is moving slower than 1000 miles per hour in the direction of the Earth s rotation The initial velocity it had in this direction is therefore going to 7 cause it to move eastward relative to the ground See quot T quot quot Figure 3 In essence the air will appear to veer to the Rotating Earth right as it heads poleward Going to greater latitudes will only increase the curvature as the Earth is moving slower Figure 3 Coriolis Effect Diagram in those locations Eventually the air will curve so much that it will start moving due east Eventually it will cool contracting as it does and becoming denser This will cause it to sink towards the Earth surface where it will continue curving backtoward the equator From outer space the air will not look as if it curved at all Observers there will note that the air has two components of velocity one poleward one in the direction of rotation and is actually moving at an angle relative to a line of longitude It will just look like it tried to move in a straight line on a curved surface It is only to an observer on Earth that thinks that the air is static over the equator that will image that the air is curving do to some force This is why the Coriolis effect is often misnamed the Coriolis force in some textbooks and online materials In a similar fashion we can follow air that is leaving the North Pole and heading toward the equator This air has no velocity in the direction of the Earth s rotation As it goes to lower latitudes it will be over land that does have velocity in this direction Therefore the air will appear to curve westward or to the right as it tries to proceed toward the equator Eventually it will warm as it picks up energy from the surface expand and then rise into the atmosphere As it does it continues to curve and head backto the North Pole never reaching the equator Because of its size and the speed of its rotation the Earth forms three different cells of air circulation in each hemisphere These cells are called Hadley cells and they form the largescale wind patterns that we see They are driven by predominate lowpressure systems near the equator and highpressure systems near the poles Other Factors While these largescale wind motions in the atmosphere drive a lot of weather patterns that we see they are not solely responsible for surface winds If they were we could almost be assured that wind would always blow in the same direction all ofthe time Surface winds can also be affected by disparities in the rates of heating of land and water Near a beach solar energy shines equally on both the water and the land surface However water has a heat capacity that is nearly 8 times that of soil and rock This means that an equivalent amount of energy put into both water and soil will result in the soil increasing its temperature 8 times that of the water ie the soil will get hotter than the water faster The air that is OVBF the land therefore Wl QBt Figure 4 Diagram of a wind turbine DOE hotter than the air that is over the water and rise faster This upward air movement over the land will create a local low pressure and higher pressure air over the water will be forced in to replace it Wind direction At night when the Sun has set the process will be reversed The soil will cool off faster than the water After a while the air that is over the land will be cooler than the air over the water Now the air over the water will become more buoyant and rise into the atmosphere The air over the land will have a greater air pressure and be pushed out towards the water by the pressure difference If you have evertravelled to the seashore you have probably experienced this phenomenon During the middle of the day while the Sun is out the wind will be blowing in from the ocean toward the beach Around midnight or so the wind will reverse and begin to blow out to sea Currents that are flowing in the water can modify this effect immensely lf cold water is being brought towards the surface of the ocean near the beach this can cause the difference between in temperatures between the land and the water during the daytime to increase and vice versa Mountains can also play a role in creating and modifying the wind Their affect depends a great deal upon the number of them their orientation and their shape and height For instance a mountain chain can create a wall to airflow This can block pressure systems from moving across them If a high pressure system does force the wind over the mountains the air can be squeezed as it passes over the mountains resulting in high wind speeds in mountain passes and on the lee side ofthe range as it descends Mountains can also generates wind as when a shallow cold air mass descends down a mountainside and produces strong winds The reverse of this can also happen when heated air in a valley descends up the side of a mountain Additional Reading lt suffices to say that there are many factors that affect winds speed To enumerate all of them would take some time We recommend that you look at the links below in order to learn more about the wind and the generation of electricity from wind energy The first link below goes to the US Department of Energy s Energy Efficiency and Renewable Energy division This is the section ofthe DOE that researches and tests wind energy systems The second link will give you to the Danish Wind Industry Association They have a lot of background information about wind energy and wind systems They also have some simulators that will help you to understand the factors involved in producing electricity from wind Topic Wind Energy Summary Energy Efficiency and Renewable Energy division s wind energy program home age De artment of Ener Link httpwwweereenergygovwind Topic Wind Energy and Wind Turbines Summary A compendium39of information about wind wind energy and wind turbines Danish Wind Industm Link httpwwwwindpowerorglencorehtm Association References 1 httpwwweereenergygovwindhistomhtml September 9 2003 2 httptelosnetcomwindearlyhtml September 9 2003 3 httpwwwwindpoweroroei quot htm September9 2003 ESA21 Environmental Science Exercises Nuclear Energy Nuclear Decay Introduction The Nucleus Almost any phrase that has the word nuclear in it has a bad reputation The term conjures up images of mushroom clouds and radioactive mutants It is interesting to note that in the 1940 s and 50 s the term that applied to energy derived from the decay radioactive material was atomic energy This term was somewhat correct since the energy was coming from the breakdown of the atom It was not until later that the more appropriate term nuclear energy was used as more people began to understand that the energy was coming from the breakdown of the nucleus of the atom The picture at the right is a popular image ofthe atom While not a true depiction ofthe appearance of a real atom it does mirror most ofthe features of it such as a central nucleus composed of positively charged protons and neutrallycharged neutrons that is orbited by negativelycharged electrons The classic approach to discussing the atom is to tell students that it is held together by electrostatic attraction between the protons and electrons But this is only part ofthe picture What rarely gets discussed is what is holding the nucleus together as there is not electrostatic force whatsoever holding the protons to the neutrons The forces that are binding the neutrons to the protons are the strong and weak nuclear forces Unlike the electrostatic force which is relatively simple to explain like charges repel and unlike attract the strong and weak nuclear forces are rather complicated in that the discussion of them involves quarks gluons and vector bosons and their interactions However intimate knowledge ofthese forces is not required in order to understand nuclear energy and therefore we will leave it to the reader to research this subject as they desire For the purposes ofthis discussion we will merely note that the forces do exist that they are important over very short distance scales 1 03915 m and less and that they bind neutrons to protons under certain conditions Figure 1 Simplified diagram of an atom Isotopes If an atom is to be neutral it must have the same number of electrons as it does protons ie the total amount of negative charge must equal the total amount of positive charge elements are defined by the number of protons in the nucleus Is there some type of rule like this that applies to the number of neutrons that an atom has It turns out that the answer is No The complicated nature of the strong and weak nuclear forces plus the numerous configurations that could be used for storing protons and neutrons in a nucleus means that there is no given rule for the numbers of neutrons an element has In fact most elements have multiple numbers of neutrons that can be stored in the nucleus Atoms that have the same number of protons but different numbers of neutrons are known as isotopes of an element Not all ofthese isotopes are stable For most naturally occurring elements there is at least one isotope that is stable The picture to the left shows three different isotopes of hydrogen The first of these which is what we normally think of as hydrogen is called hydrogen1 and Hydrogen Deuterium Tritium Figure 2 Bohr models of hydrogen deuterium and tritium 1 is stable The other two isotopes are called hydrogen2 deuterium and hydrogen3 tritium Deuterium which is found in nature in about 1 in every 6500 atoms of hydrogen is stable whereas tritium which is much rarer is unstable and will undergo radioactive decay if given enough time Other examples of isotopes with which you might be familiar are carbon12 6 protons and 6 neutrons which is stable and carbon14 6 protons and 8 neutrons which is unstable Carbon14 is one ofthe radioactive isotopes that is used to determine the age of biological fossils There are some elements for which there are no stable isotopes An example ofthis would be uranium If given enough time all forms ofthese elements will decay lsotopes of a particular element behave the same chemically That is to say molecular compounds that can be made with one isotope of an element can be made in the same way with any other isotope of that same element For example water H20 can be constructed using hydrogen1 hydrogen2 deuterium or hydrogen3 tritium The water molecules made from each of these will all look taste and feel like water The only physical difference between them will be that water molecules made with deuterium and tritium will be heavier and denser than the one made with hydrogen1 The one made with tritium will differ in one other way they will also be radioactive Radioactive Decay Methods of Decay When an atom decays it can do so via one ofthree natural methods These methods are known as alpha beta and gamma ln alpha decay the unstable nucleus ejects an alpha particle which is composed of two neutrons and two protons Anotherway of stating this is that the nucleus decays by ejecting a helium4 nucleus In beta decay the nucleus ejects a beta particle which is either an electron beta minus or a positron beta plus At first glance this would seem to be wrong as a nucleus is comprised of protons and neutrons and contains no electrons or positrons But they are produced in the nucleus whenever a neutron decays into a proton an electron and a neutrino or a proton decays into a neutron a positron and a neutrino The last way of decaying is via gamma decay which is when electromagnetic radiation is given off by the nucleus as the protons and neutrons become more tightly bound There is another way for a nucleus to decay though this method usually involves the actions of humans A nucleus can be forced to break apart if it is hit by particles from outside ofthe nucleus This was discovered by Ernst Rutherford in the early 1900 s when he bombarded nitrogen14 7 protons 7 neutrons with alpha particles helium4 to produce oxygen17 8 protons 9 neutrons and a proton The easiest method for doing this type of decay is to bombard the nucleus with neutrons Since the neutrons have no net charge they are not repelled electrostatically away from the nucleus like a proton would be and thus do not require large energies in order to strike it This will be important in our next activity where we discuss the operation of a nuclear power plant HalfLife Versus Activity If left on their own unstable isotopes will decay in an exponential fashion That is given a large enough quantity of an isotope the same percentage of them will decay in the same amount oftime This means that in a given year the number of isotopes that decay divided by the original number of isotopes will be the same quantity Rather than listing this fraction for isotopes though we often turn the issue on its head and discuss the length oftime it takes for a certain fraction of the material to decay In particular we list the amount oftime that it takes for half of the isotopes to decay which is called the halflife ofthe substance For example iodine131 has a halflife of 8 days If one were to start with 100 kg of it after 8 days they would only have 50 kg After another 8 days they would have 25 kg left and so on and so forth Eventually the amount of iodine131 would become so small that it would no longer obey exponential decay at which time we would have no way of determining when a particular amount ofthe substance would decay This is not to imply though that the fraction of the substance that will decay in a given time period is not important It is very important as this quantity is related to the activity which is the number of decays that occurs per unit time It isjust that the activity and the halflife are inversely related which means that knowledge of the halflife allows one to calculate the activity using the equation Activity 69number of isotopeshalf life While the halflife gives you some indication of how long a radioactive substance will be around the activity tells you how much radiation it is currently emitting This relationship often confuses people For instance a lot of people will look at a substance that has a halflife of a billion years as a bad thing They fixate on how long the substance will be around However a very long half life is a good thing from a radiation standpoint as it means that you would need an enormous quantity ofthe substance in order for there to be any appreciable activity Another way to think of it is that stable isotopes the substances that are not radioactive have an extremely long halflife it is infinite Before we proceed to the activity there is one last thing that we need to clarify When a substance decays it does not disappear The nucleus does lose energy and possibly some particles but there is still at least one nucleus left after the decay For instance in the example above the iodine131 that decays will most likely decay into xenon131 which is stable But what if the substance that a radioactive isotope decays into is itself radioactive The chart at the right shows a possible radioactive decay chain for uranium 238 As you can see the uranium238 decays into thorium234 which is radioactive and decays into protactinium234 The isotopes that result keep being radioactive until lead206 is reached at which point the decaying stops This is one ofthe primary problems with radioactive waste from a nuclear reactor The material stays active for a long period time With bOth long and Short halflife lSOtOPeSi as a Figure 3 U238 decay chain in descending order succession of radioactive materials is of daughter products produced and decayed Internet Exercises Half life The following link will open up a new window that contains an interactive Java applet that simulates the decay of a quantity of radioactive isotopes into daughter products As this decay occurs the applet plots the activity energy released and the number of radioactive isotopes left Some of the sample isotopes decay directly into stable daughters some decay into unstable daughters that then decay into stable isotopes In particular try using carbon10 carbon15 oxygen20 oxygen22 and fluorine23 in the simulation and note the concentrations and activity levels as the decays proceed Topic Radioactive Halflife Summary Tutorial on the relationship betWeen halflifegand activity from the Physics 2000 University of Colorado s Physics 2000 website Link httpwwwcoloradoeduphysics2000isotopesradioactivedecay3html Decay Chains The next link opens up a new window that contains an interactive Java applet that shows possible decay chains for most known isotopes Note that some isotopes have more than one decay chain such as uranium238 Isotopes that might be of particular interest are hydrogen3 H3 carbon14 014 radon 222 Rd222 uranium235 U235 and uranium238 U238 Note the number of daughter products that are produced from each ofthese Is there a general difference between the lighter and heavier isotopes Topic Radioactive DecayChains Summary Applet that displays radioactive decay chains on the nuclides Periodic Table of Elements from the Institute for Transuranium Elemen Nucndesne t Requirements JavaPlugin 1252 or higher Link httpwwwnuclidesnetappletsradioactivedecayhtm Nuclear Power Plants Energy As we discussed in the section above energy is released when isotopes decay This energy can either be in the form of electromagnetic radiation or the kinetic energy ofthe nuclear fragments The important question for us is How can this energy be converted into a useful form like electricity The most obvious thing to do is to allow either ofthese forms of energy to be absorbed by a substance in order to increase its internal energy and thus increase its temperature As the substance warms up above its surroundings a temperature difference is created and allows for any one of a number of heat engines to be placed between the two and convert some of the heat into useful energy Radioisotope thermoelectric generators create electricity from this heat difference by use of the Seebeck effect Discovered in 1821 by Thomas Seebeck a potential difference orvoltage will be created across the juncture of two unlike metals whenever there is a temperature difference applied across the juncture This potential difference will act as a current source if it is connected to a circuit These types of generators are quite reliable as there are no moving parts and the decay of the nuclear material is quite predictable They have been used extensively in the NASA deep space probe programs as solar energy is not usable for satellites that are going far away from the Sun The picture above is the diagram of one of the RTG s that was placed in the Cassini spacecraft that was sent to Saturn Cooling Tubes Radioactive Heat Source Silicon Germanium Unicou 16 Figure 4 Diagram of the Cassini Spacecraft RTG The efficiency ofthese radioisotope thermoelectric generators is not very good being in the 68 range1 A more efficient way to generate electricity would be to use the absorbed energy to boil water for use in a steam turbine The steam turbine is the basis behind most of the electricity generated in the US with most power plants ofthis type having efficiencies in the 3040 range Of course to get efficiencies in this range water temperatures above 600 F must be reached Limitations on Nuclear Materials ln orderto generate this level of thermal activity and to sustain it power plants need a source that produces a tremendous amount of energy in a short period oftime For a nuclear power plant this corresponds to having an amount of radioactive material that can fit in the plant that has a high activity As we saw in last week s activity a high activity requires either a large amount of a radioactive substance andor an isotope with a short halflife The physical limits on the amount of available isotopes and on the size ofthe power plant put constraints on the amount of material that can be used Therefore to get the required level of activity a substance with a relatively short halflife is needed This presents a problem as substances with short halflives are rarely found in nature in large abundance This should not be surprising Given the fact that the Earth is approximately 5 billion years old any short halflife material that was originally present would have completely decayed by now New isotopes are being created all ofthe time as we found out last week and some of these might have a short halflife However by the time that the material is found mined refined and put into a power plant a significant fraction ofthe material will have decayed Thus using natural decay of radioactive isotopes is not a very useful means for running a nuclear power plant One could use bombardment of nuclei in order to break the isotopes apart and generate energy As we pointed out last week the easiest method for achieving this is to bombard the nuclei with neutrons as their electrostatic neutrality means that there will be no force of repulsion from the protons in the nuclei This does solve the problem of having enough nuclear material with a high enough activity to run the plant as we can break apart even stable isotopes with this method But it does create another problem In order to bombard the material we will have to input energy separating neutrons from other material and accelerating a beam of them onto the nuclear material which means that our overall efficiency will be less than what we desire Chain Reactions We could get around this problem if we had a substance that produced free neutrons as a result of its being bombarded with neutrons In other words we need a substance that produces the catalyst bombarding neutrons from a reaction that was caused by the catalyst It turns out that we are in luck in this regard as there is one naturally occurring isotope that is abundant enough to run a power plant When uranium235 U235 is bombarded with low energy neutrons its nucleus will fragment into several parts with neutrons being amongst them A typical reaction for U235 one of many possibilities all of which produce neutrons is ineutronr uranium235 9 barium144 krypton891 3 neutrons 1733 MeV of energy The three neutrons that are released by this reaction are free to bombard three other uranium235 nuclei which would then decay into barium and krypton fragments with up to 9 more neutrons and about three times the amount of energy being released This chain reaction would look something like the picture to the right There are two features about this chain reaction that require further discussion The first of these is that it is only slowly moving neutrons that have a high probability of U235 interacting with the uranium235 nuclei and causing a reaction Therefore a neutron moderator which slows the neutrons down is needed in a nuclear power plant in order s to keep the chain reaction occurring The second feature 10w has to do with the number of neutrons that will be present Neum after several different decays While there are many different possible decay reactions that could take place the uranium235 nucleus will average about 25 neutrons released in each one This means that each reaction will Figure 51 U235 undergomg 239 Chain reaction produce more neutrons than what were there initially thus causing more reactions to take place at the next stage If Moderator this is allowed to go on for some time there will be so many neutrons around ready to react that too many decays will start taking place which will release too much energy and cause the material to meltdown Forthis reason control rods which are made from materials that readily absorb neutrons need to be in the system in order to limit the number of reactions that can take place at any given time Basic Reactor Design Besides having neutron moderators and some method for controlling the number of neutrons in the reactor a nuclear power plant also has to have some way oftransferring the thermal energy ofthe nuclear material to water in order to create steam to power a turbine This can be done in a number of ways depending upon how safe you wish to make the reactor and how much energy you wish to create In the US we have two basic designs for reactors A boiling water reactor BWR places the hot nuclear material directly in the water where steam is created This expanding steam is used to turn a turbine which is connected to a generator that creates electricity After the steam has passed through the turbine it is cooled by a heat exchanger until it condenses back to hot water and is then pumped back into the reactor chamber A pressurized water reactor PWR looks similar to a BWR except that the reactor is sitting in water that gets extremely hot but is not allowed to turn to steam by the pressure applied to the chamber This extremely hot water is used to heat another chamber of water where steam is generated A diagram of a PWR is shown in Figure 6 below Figure 6 Schematic of a pressurized water reactor While these are the two designs used in the US they are far from being the only nuclear reactor designs Other countries have experimented with different designs with varying degrees of success For instance the former Soviet Union used an RMBK design that had carbon as its neutron moderator and water as a coolant that was passed through the reactor chamber in pipes ie the fuel rods were not sitting in water This reactor was the one that was involved in the famous accident at Chernobyl To learn more about the different styles of reactors check out the second link below Additional Reading The following website leads to the US Nuclear Regulatory Commission which seeks to protect the public health and safety as well as the environment from the effects of nuclear reactors materials and waste products This site provides information on reactors that are in operation in the US and on the materials and waste that are involved in the process The next website is a privately owned website that is maintained by Joseph Gonyeau a consulting nuclear engineer for the IAEA and the DOE This site contains a wealth of information and links regarding the entire fuel cycle process Of particular interest is the information on the various nuclear reactor designs found around the world References l httn lwww llnl 39 39 fit Itetrainindradiation misuse 2pdf June 9 2003 Nuclear Exposure Introduction France The United States has a problem with energy independence The problem has nothing to do with a lack of energy production or availability We are the largest producer of energy in the world and have centuries worth of fossil fuels as well as an enormous supply ofnuclear and alternative energies at our disposal Our energy dependence on other countries is a result of the fact that we are also the leading rs of energy in the world being second only to Canada population 32 million compared to the 283 million in the US in per capita consumption of energy In order to meet our need in a cheap fashion we need to import over 11 million barrels of oil and 10 million cubic feet of natural gas each dayw There are other countries like us who are not able to meet their own needs for energy They too rely on energy imports of fossil fuels to power their economy However some ofthem have a different strategy for trying to achieve energy independence An excellent example ofa country that is travelling a different path than the US is France Its approach differs from ours in two respects it uses a lot less energy per person and it relies much more on nuclear energy to power its economy In the US the average person is responsible for 338 million Btu s of energy usage per year This accounts for all of the energy that is used in the home and 0 Ice as well as in industrial plants trucks and manufacturing plants in the US to produce goods and perform jobs The average person in France is responsible for about halfthis quantity using only 178 million Btu s each eaI2 Some of this comes from stricter recycling standards some of it comes from having different industrial and manufacturing operations A great deal ofthis difference is due to the use of mass transit and other means of transportation in o anc we have a higher rate of automobile owners Ip per person an t a we are rIVIn automobiles further This difference translates into France using onetenth the oil that we do 200 million barrels per day in the US compared to 21 million barrels per day in France while having one fth of our population French Nuclear Program e other key issue where we diverge 39om France is in the use of nuclear energy This is not to say that the US uses less nuclear energy than France does The US is still the leading producer of electricity from nuclear energy creating over 750 billion kilowatthours f energy every year compared to France 414 billion kilowatt hours However this amount is only 20 of I W Source IEA our total electrical output whereas France s W nuclear energy accounts for 79 oftheir Bum Klluwaxlmuls n Ian us 1385 us 1572 ms rm mi 1884 1537 Isau 1553 lass my output From a standpoint of reliancg I Nuclear run lNaluralEas Emil Hydro IEllher France is much more ofa nuclear nation than we are Hg 1 French electrical output by source Source DOE France has not always been a nuclear powerhouse as is shown in Figure 1 In fact it was about the time that the US was scuttling plans for any new reactors that France was beginning to ramp up its program Since 1977 there have been no new orders for nuclear power plants in the US The only plants that have been built since then were ones that were already planned before that date the Watts Bar facility opened in 1996 took over 20 years to build France on the other hand has been increasing its nuclear capacity by leaps and bounds since then The amount of nuclear energy produced per year since 1977 has increased by a factor of 20 The growth in France s nuclear program was initially forthe same reasons as in the US a cheap source of energy that would give energy independence France has very small reservoirs of oil natural gas and coal As of 2003 it had proven reserves of only 148 million barrels of oil 500 billion cubic feet of natural gas and 40 million short tons of coal These reserves would last 72 115 and 624 days respectively if they were the only source of their kind and consumption continued at its current rate This situation is much more desperate than we have here in the US where our oil and gas supplies would last a decade and our coal supplies would last several centuries at their current rate of consumption France has tried to fortify its energy needs by strongly seeking oil from other countries Their two largest oil companies Elf Aquitaine and Total merged in 2000 creating the fourth largest oil company Total SA in the world This company has strong holdings in Africa Europe and the Middle East both in oil and natural gas It can currently produce 26 million barrels of oil and 48 billion cubic feet of natural gas per day This more than covers the total current usage of France France s Nuclear Future France s nuclear future is very much in doubt due to environmental and economic factors For some time now environmentalists have been fighting the use of nuclear energy in Europe because ofthe potential for catastrophic accidents and the large amount of highly radioactive waste the reactors create The explosion at Chernobyl and the subsequent spreading of nuclear fallout material over all of Europe has helped to strengthen their argument with the public and government They have won concessions in some EU nations to either stop construction of new plants or to begin the dismantling of old plants The fact that the French have not built a new reactor in over a decade is due in some part to the work of these environmentalists Currently they are leading protests to stop the construction of a proposed pressurized water reactor to be built by Siemens and Areva5 However environmental concerns are not the only reasons why the construction of nuclear power plants has been stopped When the costs for the strict standards for building and maintaining power plants are considered electricity from nuclear energy becomes more expensive than that from coal or natural gas plants This is true in any country today However the competitive guidelines passed by the European Union over the last decade have heightened this issue in France For many years electricity in France was supplied by the stateowned Electricite de France EdF The new EU guidelines call for a gradual phase in for competition in the electricity market in all EU countries Currently these guidelines call for open markets for all nonresidential customers which account for 70 ofthe French market By July 1 2007 these open markets must extend to all customers meaning that any private or public electric company in the EU can supply electricity To further complicate the issue the French government has decided to partially privatize EdF In this kind of situation short term profit considerations will overrule long term viability considerations and prevent any new nuclear plants from being built If no new plants are built then we can expect the nuclear capacity of France to shrink over the next several decades as older plants have to be decommissioned and dismantled some time in the 2015 2020 timeframe While this sounds like it is a long time away the fact is that a nuclear power plant takes almost a decade to build and bring online Decisions will have to be made within the next several years regarding new construction if these older plants are to be replaced Greenhouse Emissions Not all environmentalists see this heavy reliance on nuclear energy as a bad thing Because of it the French people emit for less carbon dioxide per person than we do in the US Ourtotal contribution is about 20 metric tons of carbon dioxide per capita whereas the French have about 7 metric tons per capita Given the connection between increased 002 emissions and global warming this is more than enough to balance the damage done by storing nuclear waste However there is also the matter of NOX compounds being emitted which lead to increased groundlevel ozone and acid rain which accounts for plant and animal life destruction Additional Reading The following link discusses research on France s energy usage and nuclear program The site is maintained by the Department of Energy and also contains links to additional resources Topic France Country Analysis Brief Summary Contains information about France s energy situation Link httpwwweiadoegovemeucabsfrancehtml Department of Energy The following website contains information about the French electric company EDF The link below goes to the English version ofthe site although there is a good deal more information about the situation in France that is on the French version ofthe site Forthose who have a working knowledge of French it is advised to visit that portion of the website Topic EDF Group Summary English version of theWebsite for the French electric company EDF Link httpwwwedffrindexphp4coeiid259 Activity In this week s activity we are going to monitor the electrical usage of key appliances in our home and compare how our different actions will affect the amount of emissions that we release We will make a comparison between what our emissions are here in the US and what they would be if we had the same fuel composition for our electrical production as France does For this we will need several bits of information which are listed on the activity sheet For each electrical appliance listed there Note if your version of a particular appliance uses some other energy source such as natural gas do not include it in the activity sheet we will need the average power in kilowatts and the average amount oftime that the appliance is used in a week The power rating of your appliance should be listed on a tag somewhere on it ex dryers often place a label on the inside of the door that lists this After you find the power rating of each appliance you will need to monitor the usage of it for an entire week While some appliances like televisions and microwaves leak electricity constantly to power digital clocks and standby modes we are going to neglect this usage for the present study even though it can account for a large amount of electricity and emissionse Finding the amount of time that some appliances are on can be quite difficult as things such as air conditioners heaters and refrigerators turn on and off by themselves For these appliances it might do well to monitorthem for an hour or two and see how long each one turns on to get an estimate Both the power rating that the average time used per week need to be placed in the appropriate slots on the activity sheet This information then needs to be entered into the emissions calculator which will compute the amount of 002 802 and NOX emissions due to this consumption The calculator will also estimate how much ofthese would be emitted if 79 of our electricity came from nuclear energy and 93 from fossil fuels like it is in France It should be noted that different mixtures of coal oil and natural gas used to generate electricity would release different quantities of emissions Some coals have more sulfur while others have more water content Natural gas will produce no sulfur emissions while oil will produce some The small differences in mixtures from year to year will slightly change the calculations we are about to make For reference we are using the mixture used in the US in 2002 in our calculator In that year the average kWhr of electricity generated with fossil fuels created 19 pounds of 002 008 pounds of 802 and 004 pounds of NOX References httpwwweiadoegovemeucabsusahtml httpwwweiadoegovemeucabsfrancehtml httpwwwfhwa dot govohi mhs98ta blesin4 pdf httpwwwfhwa dot govohi mhs98ta blesin3 pdf httpliege indymediaorgmail phpid986 httpeandelblgovEAReports46212 httpwwweiadoegovcneafelectricityepaepasumhtml ICDU ILQMA John M Pratte 2004


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