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Climate Change - Renewables > Nulcear - Fission > Flashcards

Nulcear - Fission Flashcards

1
Q

What hold nuclei together?

A

The strong force

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2
Q

Nuclear Fission

A

Where heavy elements break apart into lighter ones.

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3
Q

Primary fission fuel…

A

U235

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4
Q

Fission energy compared to gasoline…

A

U235 release 200 MeV or 1 MeV per nucleon whilst gasoline about 1/2 eV per nucleon

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5
Q

How does a chain reaciton in fission work?

A

U235 releases neutrons which can induce further fission of other uranium

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6
Q

How can neutrons propogate fission?

A

They are neutrally charged so can be absorbed without repulsion

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7
Q

How do neutrons INDUCE fission?

A

Srong interactions formed hold several MeV enough to drive further fission

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8
Q

Why do heavier elements have more neutrons?

A

Despite strong force being stronger than electrostatic, there is a limit, where neutrons are required to balance

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9
Q

What does increased neutron content prevent?

A

Alpha decay or spontaneous fission

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10
Q

Why are emitted neutrons unlikely to induce fission?

A

They are fast moving and likely to be absorbed by other nuclei

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11
Q

How can neutron fission be promoted?

A

By slowing down the solution

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12
Q

How are neutrons slowed down?

A

A moderation like water or graphite

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13
Q

Why are Fission reactors often enriched with U235?

A

U235 only accounts for small portion of uranium naturally found.

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14
Q

Why are control rods important?

A

They are made of neutron-absorbing material that capture fission-released energy.

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15
Q

What are control rods made of?

A

Cadmium, hafnium or boron

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16
Q

Why is boron good in control rods?

A

Its 5 fermion neutrons prefer being paired so B10 absorbs to B11

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17
Q

Alpha Decay

A

Process of reduction of atomic mass, being the primary source of activity

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18
Q

Alpha decay depends on…

A

Quantum tunnelling and coloumb barrier penetration

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19
Q

Alpha particles

A

Helium nuclei emitted by radioactivty with very high lifetimes

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20
Q

Why is tunneling important in alpha decay?

A

It allows the alpha particle to escape the nuclei

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21
Q

Where is the coloumb barrier in decay?

A

Between alpha particles and nuclei

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22
Q

When was fission discovered?

A

In 1930, first controlled chain reaction in 1942, electrical generation in 1951 then plants in 1955

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23
Q

Cross Sections

A

Describes collision/reaction rate of particles

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24
Q

Equation for flux in cross-section….

A

phiB = dNb/dAdt - b is incidence particle, meaning amount of particles passing a unit area per unit time

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25
Q

dNc/dt

A

Rate of outomce or likelihood of a reaction taking place (c is outcome)

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26
Q

sigmaBT - > C = 1/phiB dNc/dt

A

Describes probaility of motion random motion collision reactions

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27
Q

Analogy of cross section…

A

A dart board where the larger surface area equate more points assuming random throwing

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28
Q

Why is nucleus cross-section so far extended?

A

Schrodinger equation as nuclei themselves have a a wavefunction

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29
Q

Example of a nuclei cross-section

A

Xenon135 cross-section 1000 times the size its actual radius

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30
Q

Why is U235 the best fission fuel?

A

It has low neutron absroption cross section with high fission cross-section, and high energy release of KE and Gamma Rays and low nucleon binding energy.

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31
Q

Why is low neutron cross-section important?

A

This means it is more likely to undergo fission when struck by a neutron rather than absorption(becoming U236

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32
Q

Gamma Rays

A

This is the highest energy photon arising out of nuclear events during radioactive decay

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33
Q

Why does U235 have low neutron absorption cross-section?

A

Resonance of 5 eV meaning neutrons close to this value more likely asborbed, whilst others less so.

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34
Q

Why does U235 asymmetry increase fission likkelihood?

A

Distribution of coulomb barrier differs, decreasing stability due to potential energy surface of nucleus lower with elongated shape, with imbalanced NSF

35
Q

What is the coulomb force proportional to?

A

Inverse square of the distance between them, becoming weaker with increasing distance.

36
Q

What distance does SNF act up to?

A

2-3 femtometers, whilst couloumb is long range.

37
Q

Why does U235 have low binding energy per nucleon?

A

Proton repulsion so SNF of neutrons struggle to bind all nucleons together.

38
Q

Why does U235 have high nuclear cross-section?

A

Nulcear properties(92 protons and 143 neutrons), both contributing to SNF but only protons to electric repulsion.

39
Q

Why does nulceus becoming more unstable to larger it is?

A

Dense electrostatic repulsion counteracted by stronger binding of NSF.

40
Q

Why does the odd neutrons in U235 improve fission?

A

Better buffer to reduce proton repulsion, thus instability occurs with neutron absorption.

41
Q

Why does nucleus become less stable with increased neutrons?

A

SNF becoming weaker thatn proton repulsion at certain distances.

42
Q

Fissile Isotope

A

These are elements that fission with low energy neutrons and capable of self-sustaining reactions

43
Q

Binding Energy

A

This is the energy required to seperate a partcile from a system of particles or to dispsera all particles of the system.

44
Q

Why does U235 have low binding energy per nucleon?

A

Because it is asymmetric in proton-neutron.

45
Q

What does EV measure?

A

Electron energy gain when accelerated by a potential difference of one volt.

46
Q

Equation for EV?

A

E = qV where q is electron charge and V is potential difference.

47
Q

How many J is 1 eV?

A

1.602 x 10^-19 joules.

48
Q

Potential Well

A

This is the region surrounding a local minium of potential energy.

49
Q

What does increase of 1eV in an electron allow?

A

Escape of potential well of nucleus and free movement in space, escaping attractive force of the proton.

50
Q

Work Fucntion

A

This is the minium amount of thermodynamic work required to remove and electron from a soild point in a vaccum to immediately outside the soild surface.

51
Q

Why do fermions exist in pairs?

A

The spin nature of particles given by the pauli exclusion principles.

52
Q

Pauli Exclusion Principle

A

This states that no two fermions can occupy the same quantum state simultaneously, meaning cannot have the exact spin at same positions.

53
Q

Cooper Pair

A

This is an electron pair in a superconductor attractively bound with equal and opposing momentum and spin.

54
Q

What happens when two fermions approach one another?

A

Wave functions overlap, with combined wave function describing behavior of both particles.

55
Q

What does the PEP require of wave function combination?

A

It needs to be anti-symmetric.

56
Q

Anti-Symmetric

A

This is a property of mathematical object descriing where the changing of signs occurs when any two of its indicies are interchanged.

57
Q

Spin Paring

A

This is the energy associated with paired electrons sharing one orbital and its effect on the molecules surround ing.t

58
Q

What is cross-section?

A

A measure of interactionf or reactions occuring between particles or atoms, calculabted based on their wave function.

59
Q

Why is wave function important in cross-sections?

A

Describing quantum mechanical properties of the involved particle, that being position, momentum and energy.

60
Q

Why is boron-carbide a good material for control rods?

A

High cross section for neutron absorption and resistance to environmental degradation to high radiation temperatures.

61
Q

Why cant U235 absorb fast neutrions?

A

U235 has low cross section for thermal neutron capture, due to their unsufficient energy to induce fission.

62
Q

Coeffcient of Void

A

This describes reactivity change due to change in amount of voides in the reactor core.

63
Q

What is the process of void coeffcient?

A

Water as a coolant transfer heat from fuel externally, which causes water boiling forming steam and creating voids.

64
Q

What does void creation result in?

A

Increase/decrease in rate of fission that would occur and heat generation with more loss of coolant.

65
Q

What happens when coolant is voided?

A

Capacity to absorb neutrons decreasing, with increased reactivity, thus more steam and more reactivity, further decreasing coolant density.

66
Q

What is Nuclear Binding Energy?

A

This is the difference between the mass of the nucleus and the mass of its constituent parts.

67
Q

Semi-Empiracal Mass Formula

A

This calculates the binding energy of the groudn state of a nucleus.

68
Q

Why is U235 unstable?

A

Total binding energy per nuckleon higher than other U isotopes

69
Q

Why does U235 have higher total binding energy?

A

Balance of SNF and EF which act and counteract against each other.

70
Q

Why does a neutron initaite fission in U235?

A

Only contribute SNF so when one is absorbed the binding energy increasese as no electrostatic force has been added.

71
Q

What does neutron absorption lead to?

A

Formation of a compound nucleu due to increase in possible nucleon-nucleon interactions

72
Q

Compound Nucleus

A

This is an unstable nucleus formed by coalescence of an atomic nucleus with a capturd particle.

73
Q

Why doe nulceon-nucleon interactions become weaker with size?

A

Larger distances between them along side weaker EF repulsion(slower rate)

74
Q

Why does rate of decay of EMF lower than SNF?

A

Mesons mediating SNF have mass whilst EF by mass-less, described by inverse square law.

75
Q

Inverse Square Law?

A

This states that for a point source of waves that is capable of radiating omnidirectionally and with no obstcructions in the vicinity the intensity decreases with the square of the distances.

76
Q

What is cross-section determined by?

A

Nuclear propreties

77
Q

Resonance Energy

A

This is the energy level at which teh probabiltiy of neutron capture is greatly increased compared to neighbouring energy levels?

78
Q

What does low neutron binding energy mean for?

A

Capture of neutron more likely than bouncing

79
Q

When is neutron capture highest?

A

When neutron is at speed of the resonance energy

80
Q

Why dpes asymmetry of U235 increased fission likelihood?

A

Elongated means imbalance of neutrons and protons increasing strength of EF

81
Q

Elastic Scaterring

A

This is a mechanism by which fast neutrons lose their energy when they interact with atomic nuclei of low atomic number.

82
Q

Why doesn’t U235 absorb fast neutrons?

A

The interaction time between neutron and nucleus is short, where absorption probabily depends on specific energy level availability.

83
Q

Why does PEP require anti-symmetric?

A

Two electrons cannot have the same set of quantum numbers given by a wave function.

84
Q

Why cant electrons be symmetric?

A

Fermions are identical in mass, charge and spin, so destructive interferences when peaks of WF overlap.

Climate Change - Renewables (12 decks)

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