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7 Fission and fusion Flashcards

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1
Q

What do nuclear reactions involve?

A

They involve a change in the qualities of atoms.

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2
Q

What is fission?

A

Heavy atoms may split into lighter atoms and other pieces in a process called fission.

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3
Q

What is fusion?

A

Lighter atom may be forced to join together to make heavier atoms in a process called fusion.

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4
Q

What happens in both fission and fusion, in relation to the mass of the products?

A

The mass of the starting atoms is greater than the mass of the products.

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5
Q

Where does this missing mass go?

A

It has been converted into energy.

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6
Q

What provides a large proportion of the heat within the Earth itself through radioactive decay?

A

Within the core of the earth, radioactive isotopes of elements like uranium, thorium and potassium provide this large proportion of heat.

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7
Q

Where is hydrogen converted into helium?

A

In the sun.

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8
Q

Through what process is hydrogen converted into helium?

A

In a fusion reaction.

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9
Q

What is a fusion reaction?

A

When the centers of atoms (nuclei) join together.

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10
Q

What does this fusion reaction provide us with?

A

It provides us with a continuous supply of energy in the form of heat and other electromagnetic radiation.

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11
Q

Why is uranium-235 used as fuel in a nuclear reactor?

A

It is used because its nuclei can be split by a neutron.

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12
Q

What is this process of splitting an atom called?

A

Fission.

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13
Q

What kind of material is uranium-235?

A

A fissile material.

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14
Q

Why is uranium-235 called a fissile material?

A

This is because it goes through the splitting process easily.

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15
Q

What happens in this fission reaction?

A

A slow-moving neutron is absorbed by a nucleus of uranium-235.

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16
Q

What is a diagram which shows an example of fission of uranium-235?

A
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17
Q

What happens to the resulting nucleus of uranium-236?

A

It is unstable and splits apart.

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18
Q

What are the fragments of this decay?

A

The fragments of this decay are the two daughter nuclei of barium-144 and krypton-89.

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19
Q

What else does the decay produce?

A

The decay also produces gamma radiation and three more neutrons.

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20
Q

What is the equation for this decay?

A

236 144 1
92 U –> 56 Ba + 3 0 n + γ radiation.

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21
Q

What does fission produce in terms of energy?

A

The fission reaction produces a huge amount of energy.

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22
Q

Why does fission produce a large amount fo energy?

A

This is because of the mass of the products, the barium and krypton nuclei and the three neutrons is slightly less than that of the original uranium-236 nuclei, and the lost mass is converted into energy.

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23
Q

Where does this energy go?

A
  • Most of this energy is carried away as the kinetic energy of the two lighter nuclei.
  • Some is emitted as gamma radiation.
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24
Q

What are the two reasons as to why the fission process would repeat?

A
  • The three neutrons produced by the fission may hit other nuclei of uranium-235, so causing the process to repeat.
  • if one neutron from each fission causes one nearby uranium-235 to split, then the fission reaction will keep going.
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25
Q

How would fission get faster and faster?

A

If more than one neutron from each fission causes fission in surrounding nuclei, then the reaction gets faster and faster - a bit like an avalanche.

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26
Q

What does the process of fission causing additional nuclei to split cause?

A

A chain reaction.

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27
Q

What does each fission result in?

A

In more nuclei splitting apart.

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28
Q

What happens if the amount of uranium-235 is small?

A

If it is small, then many of the neutrons released do not hit other uranium nuclei and the reaction does not get faster and faster.

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29
Q

What is needed for a chain reaction?

A

For a chain reaction to happen there must be a minimum amount of the uranium-235.

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30
Q

What is this minimum amount called?

A

The critical mass.

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31
Q

How do we make sure that atomic bombs undergo chain reactions?

A

In an atomic bomb two pieces of fissile material (isotopes that can be triggered into splitting apart) that are smaller than the critical mass are forced together under high pressure to form a mass greater than the critical mass.

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32
Q

What is the result of forming a mass greater than the critical mass in atomic bombs?

A

The result is a chain reaction with the rapid and uncontrolled release of huge amounts of energy.

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33
Q

What is an image of a chain reaction in uranium-235?

A
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34
Q

Where is another place where chain reactions take place in controlled conditions?

A

In a nuclear reactor.

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35
Q

What happens if this is allowed to take place in a nuclear reactor?

A

The reactor core overheats, resulting in a nuclear explosion with the sudden release of enormous amounts of heat energy and radiation.

36
Q

How is the nuclear fission controlled in a nuclear reactor?

A

In a nuclear reactor the process is controlled so that the heat energy is released over long periods of time.

37
Q

What is done with the heat produced in the core?

A

The heat produced in the core or heart of the reactor is used to heat water.

38
Q

Where does the steam produced from the water go?

A

The steam produced then drives turbines (engines) to turn generators.

39
Q

What is an image of the basic parts of a nuclear reactor?

A
40
Q

What does the reactor core contain?

A

The reactor core contains fuel rods of enriched uranium.

41
Q

What is enriched uranium?

A

Enriched uranium is uranium-238 with a higher proportion of uranium-235 than is found in the natural reserves of uranium.

42
Q

Where is graphite found?

A

It is used as a moderator.

43
Q

What is a moderator?

A

A material used in nuclear reactors to make neutrons move more slowly.

44
Q

What is the job of the moderator?

A

It is to absorb some of the kinetic energy of the neutrons to slow them down.

45
Q

Why do we need to slow down the neutrons?

A

This is because slow neutrons are more easily absorbed by uranium-235.

46
Q

What can start the fission process in relation to neutrons and their speed?

A

A neutron slowed in this way can start the fission process.

47
Q

What is another component of the nuclear reactor?

A

Control rods.

48
Q

What are the control rods?

A

Rods used in a nuclear reactor to slow down or stop a nuclear chain reaction.

49
Q

What are these control rods usually made of?

A

Boron or cadmium.

50
Q

What do these control rods do?

A

These absorb the neutrons and take them out of the fission process completely.

51
Q

What happens when the control rods are fully inside the core?

A

When the control rods are fully inside the core, the chain reaction is almost completely stopped.

52
Q

What happens along with the chain reaction being completely stopped in terms of heat?

A

The rate of production of heat is low.

53
Q

What happens when the control rods are withdrawn?

A

The rate of fission increases producing heat at a greater rate.

54
Q

What prevents any radiation from escaping?

A

The reactor vessel.

55
Q

What is this reactor vessel usually made out of?

A

The reactor vessel is made of steel and surrounded by a concrete layer about 5 meters of thickness.

56
Q

What does the nuclear process in a reactor produce?

A

It produces a variety of different types of radioactive material.

57
Q

What are the characteristics of one type of radioactive material produced in a nuclear reactor?

A

Some have relatively short half-lives and decay rapidly.

58
Q

What is an advantage of these radioactive materials with short half-lives that decay rapidly?

A

These soon become safe to handle and do not present problems of long-term storage.

59
Q

What are the characteristics of the second type of radioactive material produced in a nuclear reactor?

A

Other materials have extremely long half-lives.

60
Q

What is the problem with these radioactive materials which have extremely long half-lives?

A

These will continue to produce dangerous levels of ionising radiation for thousands of years.

61
Q

What problem do these waste products bring about?

A

These waste products present a serious problem for long-term storage.

62
Q

Where are these waste products usually stores?

A

They are usually sealed (closed) in containers which are then buried deep underground.

63
Q

What is important about where they are stored?

A

The sites for underground storage have to be carefully selected.

64
Q

What is the most optimal site to store this waste?

A

The rock must be water resistant and the geology of the site must be stable

65
Q

Where is a bad idea to store waste?

A

Storing waste in earthquake zones or areas of volcanic activity would not be sensible.

66
Q

What are some reactors designed to produce?

A

Some reactors are designed to produce plutonium.

67
Q

What is plutonium?

A

Plutonium is a very radioactive artificial element.

68
Q

What is the problem with plutonium?

A

Small amounts of plutonium represent a serious danger to health.

69
Q

What kind of material is plutonium?

A

Plutonium is another fissile material.

70
Q

How can a chain reaction start from plutonium?

A

If a large enough mass of plutonium is brought together a chain reaction will start.

71
Q

What can be plutonium be used for?

A

Plutonium can be used in the production of nuclear weapons.

72
Q

What is an advantage of nuclear power stations?

A

Nuclear power stations do not produce carbon dioxide or acidic gases as fossil fuel power stations do.

73
Q

What is good about the fact that nuclear power stations don’t produce carbon dioxide in terms of the climate?

A

This means that nuclear power does not contribute to global warming or acid rain.

74
Q

What is another advantage of nuclear power stations and their longevity?

A

Only small amounts of uranium are needed for a chain reaction and the supply of nuclear fuel will last many hundreds of years - unlike some fossil fuels that could run out in the next fifty years.

75
Q

What is a diagram that shows how a nucleus of deuterium collides with a nucleus of tritium? They undergo fusion to form the nucleus of helium, a neutron and a large amount of energy.

A
76
Q

What is a short explanation of what is going on in terms of energy?

A

They undergo fusion to form the nucleus of helium, a neutron and a large amount of energy.

77
Q

What is an explanation of the whole diagram?

A

Two isotopes of hydrogen, deuterium (H-2) and tritium (H-3), collide at very high speed. The result is the formation of a helium nucleus, a neutron and a large amount of energy.

78
Q

What is the energy source for our sun and all stars?

A

The fusion process.

79
Q

What is a diagram that shows how the mass of the products of fusion is smaller than the two hydrogen nuclei?

A
80
Q

What are the materials used in fusion?

A

This process uses materials that are more readily available than the uranium used in a conventional fission reactor

81
Q

What is an advantage of fusion?

A

It has the advantage of producing no radioactive waste.

82
Q

What is a disadvantage of fusion?

A

The problem is creating the very high temperatures needed to make the deuterium and tritium nuclei collide.

83
Q

Why do deuterium and tritium need very high temperatures to collide?

A

This is because a lot of energy is needed to overcome the repulsive (pushing away) force between the positive electric charge in the nuclei of each isotope.

84
Q

Where should the high temperature (100 million*C) liquid be contained?

A

With a very strong magnetic field or ‘magnetic bottle’.

85
Q

How can you increase the chance of fusion between the light nuclei in the hot liquid?

A

The pressure within the liquid must be very high.

Physics (24 decks)

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