7.19 and 7.20 12 January 2012 10:32
· 7.19 understand that a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei
· 7.20 understand the role played by the control rods and moderator when the fission process is used as an energy source to generate electricity
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> 7.17 to 7.20 Plenary Answers 13 January 2012 14:17
1. What is the process of splitting large nuclei called? Fission
2. How is 235U made to decay inside a nuclear reactor? It is bombarded by a neutron to turn it into 236U which is unstable and rapidly decays [cid:image001.png@01CD01EA.AD5C6120]
3. What are the generic names for the products of a fission reaction? Two daughter nuclei and either two or three neutrons are produced [cid:image002.jpg@01CD01EA.AD5C6120]
4. In what form is energy produced during a fission reaction? Energy is released in the form of Kinetic Energy of the products of the reaction - the two daughter nuclei and the neutrons
5. For a stable chain reaction to occur how many neutrons must, on average, collide with another nucleus of 235U? Exactly one. If the value is less than this the reaction will eventually finish. If the value is more than this the reaction will very rapidly accelerate to explosive rates - utilised in nuclear weapons [cid:image003.jpg@01CD01EA.AD5C6120]
6. What is the purpose of the moderator? The moderator slows down the neutrons produced by fission so that they can be captured by other 235U nuclei and thus sustain the chain reaction
7. What do the control rods do? Control rods absorb excess neutrons in the reactor and thereby provide a method for controlling the chain reaction [cid:image004.jpg@01CD01EA.AD5C6120] 
· 7.19 understand that a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei
· 7.20 understand the role played by the control rods and moderator when the fission process is used as an energy source to generate electricity
>
>
>
> 7.17 to 7.20 Plenary Answers 13 January 2012 14:17
1. What is the process of splitting large nuclei called? Fission
2. How is 235U made to decay inside a nuclear reactor? It is bombarded by a neutron to turn it into 236U which is unstable and rapidly decays [cid:image001.png@01CD01EA.AD5C6120]
3. What are the generic names for the products of a fission reaction? Two daughter nuclei and either two or three neutrons are produced [cid:image002.jpg@01CD01EA.AD5C6120]
4. In what form is energy produced during a fission reaction? Energy is released in the form of Kinetic Energy of the products of the reaction - the two daughter nuclei and the neutrons
5. For a stable chain reaction to occur how many neutrons must, on average, collide with another nucleus of 235U? Exactly one. If the value is less than this the reaction will eventually finish. If the value is more than this the reaction will very rapidly accelerate to explosive rates - utilised in nuclear weapons [cid:image003.jpg@01CD01EA.AD5C6120]
6. What is the purpose of the moderator? The moderator slows down the neutrons produced by fission so that they can be captured by other 235U nuclei and thus sustain the chain reaction
7. What do the control rods do? Control rods absorb excess neutrons in the reactor and thereby provide a method for controlling the chain reaction [cid:image004.jpg@01CD01EA.AD5C6120]
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