Nuclear Power Stations Flashcards

1
Q

what is the most common nucleus used in fission reactios

A

uranium-235

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2
Q

what is a thermal neutron

A

a slow moving neutron

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3
Q

what happens when the uranium nucleus absorbs the neutron

A
  • it becomes unstable

- causing it to break up into pieces

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4
Q

what pieces does it break up into

A
  • 2 daughter nuclei

- and usually 3 fast moving neutrons

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5
Q

why do the neutrons need to be slow moving when coming into contact with a uranium nucleus

A
  • so that they are absorbed by the nucleus
  • if theyre too fast they will simply pass through them
  • meaning no reaction occurs
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6
Q

what is a moderator

A
  • a material used in a nuclear reactor

- to slow fast-moving neutrons to thermal speeds

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7
Q

what are examples of a moderator

A

water or graphite

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8
Q

why is a moderator needed

A
  • for the fast moving neutrons ejected from a fission can be slowed
  • so when they reach the next fuel rod they can be absorbed
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9
Q

what does this repeated sequence of fission eventually create and why

A
  • a chain reaction
  • because one neutron causes the release of two more
  • which will each do the same to the next nucleus
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10
Q

what is used to control this chain reaction

A

control rods

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11
Q

what do control rods do

A
  • they absorb excess neutrons from the reactions

- in order to control the chain reaction

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12
Q

if there is a failure in the control rod system when they have been lowered in the reactor on an electromagnetic support, what happens

A
  • gravity pulls them down completely into the reactor core
  • where they absorb all neutrons
  • hence shutting the reaction down
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13
Q

for examples sake, how many neutrons would a boron control rod absorb per fission in order to maintain a constant fission rate and why

A
  • if three neutrons are released per fission
  • it will need to absorb two
  • so that only one neutron will be resulting is fissions
  • therefore keeping the fission rate constant
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