Atoms and Nuclear Propulsion

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1 Atoms and Nuclear Propulsion Developed by Mark Clemente, Chemistry Teacher & Science Chair, Floyd E. Kellam HS, Virginia Beach 2011 Naval Historical Foundation STEM-H Teacher Fellowship Instructional Goal This unit is designed to use the topic of nuclear powered submarines to teach a unit on atomic structure. Students are first given some background information on nuclear submarines and then begin to learn about atomic structure, isotopes, and nuclear chemistry. When appropriate, specific examples that relate to nuclear submarines are given. NGSS References: HS-PS3-3 Design, build, and refine a device that works within given constraints to covert one form of energy into another form of energy. HS-PS-1 Develop models to illustrate the changes in composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay. PS1.C Nuclear Processes, including fusion, fission and radioactive decays of unstable nuclei, involve release or absorption of energy. The total number of neutrons plus protons does not change in any nuclear process. Background 1. Read the linked document "A Brief History of Submarine Development in the United States." 2. View the US Navy YouTube Video "Life on a Sub." 3. What did you note in the video, regarding submarine propulsion? Using nuclear power as the source of energy to power the boat is what allows submarines to operate away from land and underwater for extended periods of time. 4. Examine the "Submarine Power and Propulsion" diagram. Evaluate the diagram and watch the video "Reactor Operations" which explains the diagram in more detail. Alternately, you can read the linked document "Nuclear Propulsion." Bottom Line: a nuclear reaction can produce heat to make steam for propulsion energy. Structure of the Atom and Isotopes 1. Nuclear reactors use nuclear reactions to generate heat. 2. Read the "Nuclear Reactions" document to understand the difference between nuclear and chemical reactions. 3. Review the definition of radioactivity: The spontaneous emission of radiation, either directly from unstable atomic nuclei or as a consequence of a nuclear reaction. 4. Read the "Nuclear Reactions" document to review the three types of naturally occurring radiation. 5. View the "Nuclear Reactions" document illustrations of alpha and beta decay. The sum of the mass numbers on the reactant side and product side are the same and the sum of the atomic numbers on the reactant side and product side are the same.

2 6. For example, in the equation: The mass number is 226 on the reactant side and the sum of the mass numbers on the product side is = 226. Likewise, the atomic number on the reactant side is 88 and the sum of the atomic numbers on the product side is = 88. The symbol of the element should match the atomic number listed. Also, gamma radiation is always released during a nuclear reaction and therefore is often left out of a nuclear equation. Activity Sequence: Practice balancing nuclear reactions using the questions in Activity 1 below. What you have viewed to this point is nuclear decay. The process used to generate heat in a nuclear reaction is fission. A basic description of fission can be found in the "Nuclear Propulsion" document. Complete "Nuclear Fission Simulation" in Activity 2 below. This activity uses a PhET simulation produced by the University of Colorado. Java is required to run the simulation. The simulation can either be run online or downloaded and run off- line. Alternately (or in addition) complete "Falling Like Dominoes" in Activity 3 below. To conduct this activity, you will need 15 dominoes and a ruler. (If not viewed above) Video Resources: Play video video "Life on a Sub." a taste of day- to- day life aboard a U.S. Navy nuclear- powered submarine. Play video "Reactor Operations" This video on the reactor operations of nuclear submarines is part of the Covert Submarine Operations Exhibit, located in the Cold War Gallery, Washington Navy Yard. The Cold War Gallery is the latest addition to the National Museum of the United States Navy.

3 Activity 1 Nuclear Reactions Balance the following nuclear decay equations: Activity 2 PhET Simulation Nuclear Fission Go to the PhET Simulations. Find and open the simulation called Nuclear Fission: Click on "Run Now" and select the tab that says: "Fission: One Nucleus" Fission: One Nucleus: Experiment with shooting the neutron gun and watch what happens. 1) What happens when the U- 235 nucleus is "hit" with a neutron? There are a number of things that happen here, describe all of them in as much detail as you can. Use the pause button when needed.

4 Chain Reaction: Select the "Chain Reaction" tab at the top. Experiment with changing the settings and shooting the neutron gun and watch what happens. Then answer the questions below. 2) Click the "Reset All" button and then set the initial number of U- 235 nuclei to 100 and U- 238 to 0. What happens when you fire the neutron gun? 3) Explain what makes this a "chain reaction". 4) Click "Reset" and then set the initial number of U- 238 nuclei to 100 and U- 235 to 0. Explain what happens when you fire the gun. Does this cause a chain reaction? Try multiple times to start a chain reaction with the U Explain why this happens. 5) What is U- 239? In what ways is it different from U- 238? 6) Set the initial numbers of U- 235 nuclei and U- 238 nuclei to the numbers in the table below. Repeat each trial multiple times and record the value that occurs most often. U U % of U235 fissioned after 1 firing # firings required to fission all U235 N/A 7) What happens to the reaction as the proportion of U- 238 nuclei increases? Explain why this happens. Nuclear Reactor: Select the "Nuclear Reactor" tab at the top. Experiment with changing the settings and firing the neutrons and watch what happens. Then answer the questions below. 8) Watch very closely to the fission reactions as they happen. Specifically watch what happens to the loose neutrons after the reaction. a)what happens if the neutrons hit another nucleus? b)what happens if the neutrons hit a control rod?

5 9) Compare the chain reaction that occurs when the control rods are inserted further into the reactor versus when they are pulled all/mostly out of the reactor. 10) If the purpose of a nuclear reactor in a power plant is to produce energy, why are there control rods? 11) The bar graphs on the right of the display show the "Power Output" and the "Energy Produced". What is the difference between these two quantities? Introduction Activity 3 Falling Like Dominoes In order to use nuclear power as an energy source, a self- sustaining chain reaction must be initiated. In this activity you will simulate a chain reaction with dominoes. Procedure 1. Obtain 15 dominoes and a ruler from your teacher. 2. Set the dominoes upright in a straight line spaced about 1.5 cm apart. Push the first domino and observe what happens. Question 1: When one domino is pushed over how many dominoes does it impact directly? 3. Now set up the dominoes in the pattern below. The front- to- back spacing should be about 1.5 cm.

6 4. Push over the domino indicated by the arrow in the diagram above and observe what happens. Question 2: When one domino is pushed over, how many dominoes does it impact directly? Question 3: Describe the difference between what happened in step 2 and what happened in step 4? Question 4: Which set- up of dominoes is a better simulation of a chain reaction? Justify your answer. 5. Now place ruler just in front of the domino as indicated in the diagram below. The ruler should be standing on end. 6. Push over the domino indicated by the arrow in the diagram above and observe what happens. Question 5: Describe the difference between what happened in step 4 with step 6. Based on what you read in the "Nuclear Propulsion" handout, what does the ruler simulate? 7. Below are several fission reactions involving Uranium Fill in the missing parts.

7 ANSWERS Balance the following nuclear decay equations: Activity 1 Nuclear Reactions Balance the following nuclear decay equations: Fission: One Nucleus: Activity 2 PhET Simulations. Experiment with shooting the neutron gun and watch what happens. 1) What happens when the U- 235 nucleus is "hit" with a neutron? There are a number of things that happen here, describe all of them in as much detail as you can. Use the pause button when needed. When the nucleus is hit, the atom gains energy. The total amount of energy starts varying instead of staying constant. After a few seconds, the nucleus splits into two daughter nuclei. Three neutrons are also released. Chain Reaction: Select the "Chain Reaction" tab at the top. Experiment with changing the settings and shooting the neutron gun and watch what happens. Then answer the questions below.

8 2) Click the "Reset All" button and then set the initial number of U- 235 nuclei to 100 and U- 238 to 0. What happens when you fire the neutron gun? One U- 235 nucleus splits apart, releasing three neutrons. Each of these neutrons hits a nucleus causing more nuclei to split. The number of nuclei that split increases until there are no more nuclei left to react. 3) Explain what makes this a "chain reaction". This is a chain reaction because one reaction causes several others to occur. The reaction becomes self- sustaining. 4) Click "Reset" and then set the initial number of U- 238 nuclei to 100 and U- 235 to 0. Explain what happens when you fire the gun. Does this cause a chain reaction? Try multiple times to start a chain reaction with the U Explain why this happens. When the gun is fired, the neutron is absorbed into the U- 238 nucleus and the atom becomes U No chain reaction takes place because no neutrons are released to continue the reaction. 5) What is U- 239? In what ways is it different from U- 238? U- 239 is an isotope of uranium. It has one more neutron in the nucleus than U ) Set the initial numbers of U- 235 nuclei and U- 238 nuclei to the numbers in the table below. Repeat each trial multiple times and record the value that occurs most often. U U % of 235U fissioned after 1 firing 99% 97% 40-50% 2-20% 0 # firings required to fission all 235U or more N/A 7) What happens to the reaction as the proportion of U- 238 nuclei increases? Explain why this happens. The reaction becomes slower. It takes more time to fission all of the U This is because some of the neutrons hit U- 238 and are absorbed, changing U- 238 to U The more U- 238 there is the more likely it is that a neutron will hit a U- 238 nucleus. Nuclear Reactor:

9 Select the "Nuclear Reactor" tab at the top. Experiment with changing the settings and firing the neutrons and watch what happens. Then answer the questions below. 8) Watch very closely to the fission reactions as they happen. Specifically watch what happens to the loose neutrons after the reaction. a)what happens if the neutrons hit another nucleus? continues. b)what happens if the neutrons hit a control rod? no further reaction takes place. If the neutron hits another nucleus, the reaction If the nucleus hits a control rod it is absorbed and 9) Compare the chain reaction that occurs when the control rods are inserted further into the reactor versus when they are pulled all/mostly out of the reactor. When the rods are inserted the chain reaction takes place for a while then stops even though there are unreacted nuclei left. When the rods are withdrawn, the reaction continues until most or all of the nuclei have reacted. 10) If the purpose of a nuclear reactor in a power plant is to produce energy, why are there control rods? The control rods help to control how fast the reaction takes place. You may not always need the same amount of power being produced. They can also keep the reactor from heating up too much. 11) The bar graphs on the right of the display show the "Power Output" and the "Energy Produced". What is the difference between these two quantities? The "Power Output" is showing how much energy is being produced at a given moment in time. The "Energy Produced" shows the total amount of energy released over the course of the simulation. Introduction Activity 3 Falling Like Dominoes In order to use nuclear power as an energy source, a self- sustaining chain reaction must be initiated. In this activity you will simulate a chain reaction with dominoes. Procedure 1. Obtain 15 dominoes and a ruler from your teacher. 2. Set the dominoes upright in a straight line spaced about 1.5 cm apart. Push the first domino and observe what happens. Question 1: When one domino is pushed over how many dominoes does it impact directly? Answer: Each domino only knocks over one other domino.

10 3. Now set up the dominoes in the patter below. The front- to- back spacing should be about 1.5 cm. 4. Push over the domino indicated by the arrow in the diagram above and observe what happens. Question 2: When one domino is pushed over, how many dominoes does it impact directly? Answer: Each domino knocks over at least two other dominoes. Question 3: Describe the difference between what happened in step 2 and what happened in step 4? Answer: In step 2, the dominoes fall sequentially (one at a time). In step 4, multiple dominoes are being knocked over at the same time. Question 4: Which set- up of dominoes is a better simulation of a chain reaction? Justify your answer. Answer: Step 4 is a better simulation. Initially, only one domino is pushed. The one domino ends up causing multiple dominoes to fall over simultaneously. 5. Now place ruler just in front of the domino as indicated in the diagram below. The ruler should be standing on end.

6. Push over the domino indicated by the arrow in the diagram above and observe what happens. Question 5: Describe the difference between what happened in step 4 with step 6.

11 6. Push over the domino indicated by the arrow in the diagram above and observe what happens. Question 5: Describe the difference between what happened in step 4 with step 6. Based on what you read in the "Nuclear Propulsion" handout, what does the ruler simulate? Answer: With the ruler in place, only the dominoes on the right side fall over. The ruler is simulating a control rod, moderating the amount of material involved in a chain reaction. 7. Below are several fission reactions involving Uranium Fill in the missing parts.

Year 11 Physics booklet Topic 1 Atomic structure and radioactivity Name:

Year 11 Physics booklet Topic 1 Atomic structure and radioactivity Name: Atomic structure and radioactivity Give a definition for each of these key words: Atom Isotope Proton Neutron Electron Atomic nucleus