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Physics > Fission and Fusion COPY > Flashcards

Fission and Fusion COPY Flashcards

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1
Q

What is the equation that links mass and energy?

A

E = mc2

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2
Q

define the binding energy of a nucleus

A

The binding energy of a nucleus is the energy required to completely separate its constituent protons and neutrons OR the energy released when its formed from its constituent protons and nucleus

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3
Q

Does a nucleus have more mass together or split up?

A

Separate

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4
Q

Define mass difference

A

The difference between the mass of a nucleus and the total mass of its separate protons and neutrons

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5
Q

What does u equal in kg?

A

1.661x10-27Kg

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6
Q

What does u equal to in MeV?

A

931.5

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7
Q

What does the binding energy equal?

A
  • Calculate the mass difference
  • Multiply by 931.5
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8
Q

Define the atomic mass unit, u

A

it is defined as 1/12 th the mass of a C-12 atom

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9
Q

Describe nuclear fusion

A
  • Two small nuclei fuse together to make a larger nucleus which is more stable and has more binding energy per nucleon then either of the two smaller nuclei
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10
Q

How is energy produced from fusion?

A

The binding energy per nucleon is greater after fusion. This causes energy to be released in the form of kinetic energy of the larger nucleus.

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11
Q

What is the mass defect?

A

The mass lost when two smaller nuclei fuse together

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12
Q

Why is it difficult to get nuclear fusion to occur?

A
  • The two smaller nuclei are both positively charged and so would naturally repel each other.
  • The nuclei m,ust be moving with vert high speeds in order to overcome this repulsion and get close enough for the strong force to bond them.
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13
Q

Is energy absorbed or released when the bonding energy increases

A

Energy is released when there is an increase in binding energy

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14
Q

How is energy produced from fission?

A

When the nuclei splits, the binding energy per nucleon increases

this releases energy as kinetic energy

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15
Q

What is nuclear fission?

A

A large nuclei splits into two smaller nuclei

The mass defect produced gets turned into kinetic energy which incfeases the binding energy per nucleon

this releases kinetic energy

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16
Q

How do you calculate the binding energy per nucleon?

A

1) calculate the mass of the protons (number of protons x the atmonic mass of proton, on formula book)
2) Calculate the mass of the neutrons (same way as protons)
3) Calculate the mass of consituents (protons + neutrons)
4) Calculate the mass of the nucleus (mass of atom (given on question) - mass of electons (calculated same way as p + n)
5) Calculate mass defect (3) - (4)
6) multiply mass defect in u by 931.5 to get it in MeV
7) Divide binding energy by number of nucleons

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17
Q

What advantages do both nuclear fission and fusion have over using fossil fuels for energy production? (2)

A

They do not release greenhouse gases which cause global warming

Nuclear fuels will last longer

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18
Q

How does the sun produce its energy?

A

Nuclear fusion

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19
Q

What fuels are needed in fusion and where can they be extracted from?

A

Hydrogen fuels (deuterium and tritium)

deuterium: extracted from sea water
tritium: from lithium metal

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20
Q

Why are deuterium and tritium called ‘hydrogen heavy’ and ‘super hydrogen heavy’ respectively?

A

They’re isotopes of hydrogen

they have more neutrons than hydrogen so they are ‘heavy’

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21
Q

What are the 3 advantages of using fusion rather then fission for mains electricity?

A
  • Fusion releases more energy PER KG
  • Fusion is safer as the plant won’t go into meltdown
  • Waste products of fusion are not as radioactive as the waste products of fission
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22
Q

Why is is so difficult for scientists to get fision to work?

A

It needs a lot of energy to heat it and produce the magnetic field (often more than is released by fusion)

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23
Q

What does the stability of a nucleus depend on?

A

The mean binding energy per nucleon in the nucleus

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24
Q

What does the size of the mean binding energy sday about the stability of the nucleus?

A

The greater the mean binding energy, the greater the stabler the nucleus

25
Q

Draw the graph of the mean binding energy per nucleon against the nucleon number:

  • Mark on the position of iron
  • Mark on the fusion area
  • Mark on the fission area
A
26
Q

Which element is the most stable?

A

Fe

27
Q

Define induced fission

A

Where a nucleus has to absorb a neutron before it splits

28
Q

Define critical mass

A

The minimum mass required in induced fission that will support a self-sustaining reaction

29
Q

Sketch and describe a chain reaction showing more than one fission event

A
30
Q

Give two points describing the the daughter neclei produced in fission

A
  • They are highly radioactive
  • They are beta- and gamma emitters
31
Q

Define enriched uranium

A

Has a higher percentage of U-235 than in natural uranium

32
Q

What is the percentage of U-235 in enriched uranium?

A

2.3%

33
Q

What is the percentage of U-235 in natural uranium?

A

0.7%

34
Q

What is the other isotope od uranium present in natural and enriched uranium

A

U-238

35
Q

Why do reactors use enriched uranium rather than natural uranium.

A

Enriched uranium has a higher percentage of U-235 than in natural uranium .

This allows for a lower critical mass so the fuel rods are smaller

36
Q

Why do the tubes that contain the fuel for fission need to be narrow?

A

This increases the surface area so

more neutrons can pass out of the surface of the rod, through the moderator, lose kinetic energy and then have more chance of causing a fission when they hit a uranium nucleus in anither rod

37
Q

Define thermal neutrons

A

Slow moving neutrons with low kinetic energy

38
Q

Why do we need to turn the neutrons produced in fission to thermal neutrons before other fission reactions occur?

A

The neutrons in the fission of U-235 are very fast movingand are much less likely to cause fission than thermal neutrons and are more likely to be absorbed by U-238

39
Q

Give examples of moderators

A

Graphite and heavy water (deuterium oxide)

40
Q

Describe low level waste

A
  • Clothing and tools used a the plant
  • Shielding not usually required
  • Buried in shallow trenches after compaction and incineration
41
Q

Describe moderators

A
  • must be substances which have a low chance iof absorbing neutrons
  • Atoms nust be a similar mass to a neutron, so tha the neutron loses a significant amount of kinetic energy when it hits one of the atoms
  • The neutrons typically need to undergo lots of collisions with moderator atoms to lose enough energy to cause fission (e.g. 50)
42
Q

What do control rods do?

A

Absorb neutrons

43
Q

Which materials are often used in control rods?

A

Boron and cadmium

44
Q

Why are Boron and Cadmium used as control rods?

A

There is a high probability of the high energy neutrons being absorbed on collision

45
Q

How is the rate of fission controlled?

A

By inserting and removing the coltrol rods

46
Q

What is a self-sustaining reaction?

A

When, on average, more than one neutron produces another reaction and may go out of control

Ideally, for a constant reaction rate, only one neutron produced by fission goes on to produce another reaction

47
Q

How is a fission reaction stopped in an emergency?

A

The control rods are fully inserted to absorb all the neutrons

48
Q

What does a coolant do?

A

Extracts heat from the core of the reactor

49
Q

What properties does a coolant need to have?

A
  • high specific heat capacity
  • Non-flammable
  • Non-corrosive
50
Q

What fluids are usually used as coolants

A

water and carbon dioxide

51
Q

How does the coolant extract heat from the core?

A

It is passed through the core and itno the heat exchange where it turns water into steam

52
Q

What does shielding do?

A
  • Surrounds the reactor to protect people working near the reactor
  • Around 5m of concrete to stop gamma, beta and any neutrons which escape the reactor
53
Q

What does the pressure vessel do and what is is made of?

A
  • To keep the coolant under pressure
  • Made of steel
54
Q

What is conserves in an elastic collision?

A

Kinetic energy and momentum

55
Q

What is assumed when doing calculations (momentum) concerning a neutron and a moderator particle?

A

The moderator particle is stationary before the collision

56
Q

Describe high level waste

A
  • Spent nuclear fuel or liquid waste from reprocessing
  • Highly radioactive for thousands of years
  • Has to be cooled for 20-50 years before transfer
  • Currently kept in cooling ponds close to reactors
57
Q

Describe intermediate level waste

A
  • Requires shielding
  • Typically resins and decommisioning equipment
  • Waste is usually buried
58
Q

How are spent fuel rods dealt with?

A
  • They are initially at a high temperature and so are put in cooling ponds where they can stay for years
  • The fuel cells are handled remotely by robots when being inserted and taken out of the reactor to avoid humans coming near them
59
Q

What are the risks to nuclear fuels?

A

If there is an accident, there would be a risk of highly radioactive material being released which would damage peoples health

  • It is expensive and dangerous to decommision a plant

Physics (15 decks)

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