Nuclear energy Flashcards

1
Q

Binding energy of the nucleus

A

The work that must be done to separate a nucleus into its constituent neutrons and protons

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2
Q

Mass defect

A

The difference between the mass of the separated nucleons and the mass of the nucleus

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3
Q

Binding energy per nucleon

A

The average work done per nucleon to remove all the nucleons from a nucleus

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4
Q

Nuclear fission

A

The process in which a large unstable nuclear splits into two fragments which are more stable than the original nucleus

Binding energy per nucleon increases in this process

Induced fission is fission caused by a neutron colliding with a 235-U or a 235-Pu nucleus

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5
Q

Nuclear fusion

A

The process of making small nuclei fuse together to form a larger nucleus

The product nucleus has more binding energy per nucleon than the small nuclei that formed it

Lots of energy is released

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6
Q

Chain reaction

A

A series of reactions in which each reaction causes a further reaction

A steady chain reaction occurs when one fission neutron on average from each fission event produces a further fission event

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7
Q

Plasma

A

A state of matter achieved during fusion reactions and other high temperature areas

At such high temperatures atoms are stripped of their electrons

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8
Q

Control rods

A

Rods made of neutron-absorbing substance

Usually cadmium or boron

Moved in or out of the core of a nuclear reactor to control the rate of fission events in the reactor

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9
Q

Coolant

A

A fluid that is used to prevent a machine or device from becoming dangerously hot

The coolant of a nuclear reactor is pumped through the core of the reactor to transfer thermal energy from the core to a heat exchanger

Must be efficient at transferring heat from the reactor

Needs to be a gas or liquid at room temperature to be pumped around the reactor

Water - high specific heat capacity
CO2

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10
Q

Moderator

A

Substance in a thermal nuclear reactor that slows the fission neutrons down so they can go on to produce further fission

Thermal speeds mean that neutrons are the same temperature as the reactor and therefore the uranium

Slows them down via elastic collisions - takes approx 50 collisions to reach thermal speeds

Neutrons won’t disable the nucleus if they are too fast

Slow down to ~ 200ms^-1 (thermal neutrons)

Graphite, water

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11
Q

Heat exchanger

A

A steel vessel containing pipes through which hot coolant in a sealed circuit is pumped, causing water passing through the steel vessel in separate pipes to turn to steam which is used to drive turbines

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12
Q

Reactor core

A

The fuel rods and the control rods together with the moderator substance are in a steel vessel through which the coolant (which is also the moderator in ‘pressurised water reactor’) is pumped

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13
Q

Thermal nuclear reactor

A

A nuclear reactor which has a moderator in its core as opposed to the coolant being the moderator

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14
Q

Critical mass

A

The minimum mass of a fissile isotope in a nuclear reactor necessary to produce a chain reaction

If the mass of the fissile isotope is less than the critical mass then a chain reaction won’t occur because too many fission neutrons escape from the reactor or are absorbed without inducing fission

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15
Q

Safety features of a nuclear reactor

A

Reactor core is a thick steel vessel designed to withstand high temperatures and pressures

Core is in a building with very thick concrete walls which absorb the neutrons and radiation that example from the reactor

Every reactor has an emergency shut-down system designed to fully insert the fuel rods into the core to stop fission completely

Sealed fuel rods are inserted and removed from the reactor by means of remote handling devices

Rods are more radioactive after removal than before due to shifting from being alpha emitters to gamma and beta emitters

This is due to due to the increased number of neutron rich fission products formed

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16
Q

High level radioactive waste

A

Examples include spent fuel rods

Has high activity

Firstly, this waste is placed in cooling ponds

In Britain the rods are transferred to Sellafield in steel casks by rail

Unused uranium and plutonium is removed

Waste is vitrified mixed with molten pyrex glass and then solidifies, then placed in steel/lead/concrete cylinders - then stored deep underground

In other countries, it is stored in underground caverns - can be mixed with molten glass and stored as glass blocks in the caverns

17
Q

Intermediate-level waste

A

Examples include materials with low activity and used containers of radioactive materials

Sealed in drums that are encased in concrete and stored in specially constructed buildings with walls of reinforced concrete

18
Q

Low-level waste

A

Examples include laboratory equipment and protective clothing

Sealed in metal drums and buried in large trenches

19
Q

Uses of fission

A

Generating energy

Making new isotopes (medical, military)

Making new elements for different types of fission reactor

20
Q

Fuel rods

A

Composed of predominantly U-235

The build up of daughter products slows down the reaction - results in the need to replace the fuel rods

21
Q

Heating the plasma during fusion

A

Inducing a current in the plasma

Electrical heating

Fire lasers at the plasma - EM radiation

22
Q

Alpha particles leaving the nucleus and energy changes

A

When an alpha particle is emitted the nucleus recoils

So the energy released is shared between the alpha and the nucleus

Energy released is shared in inverse proportion to their masses - conservation of momentum

23
Q

Beta decay and energy changes

A

Energy released is shared in variable proportions between the beta particle and neutrino and antineutrino

24
Q

Electron capture energy changes

A

Nucleus emits a neutrino which carries away the energy

The atom also emits a photon (usually X-Ray) when the inner-shell vacancy is filled

25
Curve of stability
Graph of N against Z Where N is number of neutrons Z is number of protons Starts curving upwards when N = 20 Alpha emitters to the top right of the curve Beta minus emitters to the middle left of the curve Beta plus emitters to the middle right of the curve
26
Graph of binding energy per nucleon against nucleon number
Curve which steeply rises until its peak - 8.7 Mev per nucleon for iron (56) Then gradually decreases Elements before iron undergo fusion and after iron undergo fission
27
Advantages of Nuclear power
Nuclear power doesn't release much greenhouse gases Nuclear power an extremely large amount of energy per kilogram of fuel Power can be produced almost continuously Nuclear power produces medical tracer isotope Plants can sometimes change power output quickly
28
What type of energy changes does E =mc^2 apply to?
All energy changes
29
Calculating mass defect
mass of nucleons - mass of nucleus e.g. for mass of nucleons, mass of neutron = 1.00728 u so multiply this by the number of nucleons
30
Similarities between fission and fusion
Both have a mass defect Both transform mass into energy Products formed have higher binding energy Both can involve the strong nuclear force
31
Differences between fission and fusion
Fusion isn't yet available in nuclear power plants Fusion requires high temperatures and pressures Fission splitting whereas fusion joining Fission forms radioactive products whereas fusion forms mostly stable products
32
What could happen to a neutron released as a result of a fission event?
Could be absorbed by U-235 and induce fission Could be absorbed by U-235 and not induce fission Could be absorbed by U-238 Could be scattered by the uranium nuclei Could leave the reactor without being absorbed Could be absorbed by the control rods
33
Problems and solutions for dealing with radioactive waste
Waste is initially very hot - placed in cooling ponds to remove heat Waste is initially highly radioactive - it is handled using remote handling devices In liquid form the waste may leak - the waste is vitrified Difficult to transport waste - waste is transported in thick steel casks by rail Waste will be radioactive for a long time - so it is stored deep underground to increase distance to humans and because it is geologically stable