Topic 9: Nuclear Power Flashcards
How is a chemical element defined?
By its proton number
How is an ion formed?
By removing electrons from a chemical element
What is the mass of an electron in comparison to a proton?
Electron mass is 1/1836 of a proton
What makes up the Atomic mass?
Protons and neutrons
What does nuclear power involve?
The conversion of small amounts of matter into energy as atom nuclei split or join
what is the equation used in nuclear power?
E=mc2
What does the E in E=mc2 stand for?
The energy released
What does m stand for in E=mc2?
Mass of matter lost
What does c stand for in E=mc2?
The speed of light which is 3x10^8 m/s
C squared = 9x10^16
What does it mean if mass has a high energy density?
A lot of energy is released by a very small amount of mass
What happens in nuclear fission and fusion?
Large amounts of energy are released when small amounts of matter from the nuclei of atoms are destroyed
What does nuclear fission involve?
The splitting of the nuclei of large atoms such as those of isotopes of uranium-235 and plutonium-239
What does nuclear fusion involve?
The joining of the nuclei of small atoms such as the isotopes of hydrogen-2 and hydrogen-3
True or false: both nuclear fission and fusion are used commercially
Only nuclear fission is used commercially, fusion is a research project
Explain the process of nuclear fission
Take an atom of uranium and throw high energy neutrons at it
When the unstable nucleus is hit it forces it to split into 2 smaller and more stable nuclei
Energy is also released
What nuclei do you use in nuclear fission?
Naturally unstable nuclei
The most abundant is uranium-238 but the most useful is Uranium-235
Why isn’t there always a sustained chain reaction in nuclear fission?
Some neutrons will drift away because they aren’t high energy enough
Some are at such high energy they will move away too fast and ma spit other nuclei
How many fast neutrons are needed from each split on average in order to have a sustained chain reaction?
3
Why is uranium-238 unable to sustain a chain reaction?
It doesnt get any average of 3 fast neutrons from each split
Which version of uranium is most abundant in nature?
Uranium-238
Usually have to make uranium-235 which is more useful
Describe the process of uranium enrichment
Isolate the uranium from the rest of minerals it is mined from
And make it into a powder and then put it into a centrifuge
This will sort it in order of mass/density
Uranium 235 is pushed to the edge/outside
What is nuclear power usually used for?
‘Base-load’ electricity supplies that are needed at all time
Why is nuclear power usually used for base-load electricity supply?
The power output of nuclear reactors normally changes quite slowly
What factors restrict the growth of nuclear power?
Complex technology
Public opposition- safety concerns
Possible uses e.g. military or terrorist
Uncertainty over waste and cost
Why does complex technology restrict the growth of nuclear power?
Difficult in less technologically advanced societies so they cant support the infrastructure needed
The technology is always expensive
Name 3 events that have heightened public concern over the safety of reactors
Three Mile Island, 1979 USA
Chernobyl 1986 Ukraine
Fukushima 2011 Japan
Why is there uncertainty over nuclear power?
Uncertainty of the permanent disposal of radioactive waste or the total cost of nuclear power considering no commercial reactor has been fully decommissioned
What are the main features of nuclear power?
Energy density
Embodied energy
Finite resources
Level of technological development
How is the energy density of nuclear power important?
1 kg of uranium can release as much energy as 13t of coal
Would only need a delivery of fuel every year whilst coal would be needed constantly
This means power stations can be in locations with poor transport infrastructure
How is uranium similar to coal and oil?
It is non-renewable
Even less renewable than coal or oil
What is embodied energy?
The total energy required by the entire production system in order to produce one unit of energy
What uses of energy are included in the embodied energy of nuclear power?
Maintanence
Disposal
Water cycle
Initial energy
What are the disadvantages of nuclear fuel despite it having a high energy density?
The processes required to produce it and the complexities of the power stations requires a lot of energy
Why is coal easier to use than uranium?
It requires very little processing compared to uranium which has to be purified, concentrated and chemically processed to produce the fuel
Why is uranium a finite resource?
It is non renewable
It is often found in low purity deposits so there isn’t a lot of economically viable sources
The energy to extract uranium using conventional extraction methods would be greater than the energy that would be released
Since when have nuclear reactors been used commercially?
Since the 1950
Since the 1950s, what design improvements have there been in nuclear reactors?
Longer reactor life
More reliable operation
Lower fuel consumption
What are the issues with nuclear fission?
Environmental impacts
Political and international difficulties
Economic issues
What are the environmental impacts of mining/processing uranium/thorium ore to make nuclear fuels?
Habitat loss, noise, dust, turbid drainage water, hazardous wastes
Why is there the issue of hazardous wastes from the mining of uranium/thorium?
Because the deposits are found in the same type of environment as sulphides, heavy metals and coals- reducing anoxic environments
Where else in the use of nuclear fuel, other than the mining process, is there environmental impacts?
From the use of high embodied energy materials
From reactor accidents and radioactive waste
What environmental impacts are there from using high embodied energy materials?
Contributions to global climate change
What are the environmental impacts of reactor accidents and radioactive waste?
Health risks- the ionising radiation
Contamination of surrounding land
Why is there more political and international difficulties surrounding nuclear power than other energy resources?
Because of the possible link between civil nuclear electricity and the preparation of weapons grade fuel
This has led to some countries trying to restrict the availability of technology to other countries that are considered untrustworthy
Why do nuclear reactors have so many economic issues?
They are very expensive-The construction and planning
They operate on economic loss and they can take over a decade to start use
They are expensive to maintain once use has stopped
What part of nuclear reactors makes the total cost exceed the estimates?
The inclusion of new design features and unforeseen problem
Give 3 ways that nuclear fission is used currently
The main way is to generate electricity
They are also used to propel 150 ships
The fission products include isotopes like caesium-137 which is used for food irradiation and americium-241 in smoke alarms
What else can nuclear fission be used for in the future?
Temporarily they will be useful and developed to replace fossil fuels
They wont last forever because they are finite
Name 3 new technologies that are being used to improve uranium extraction
Polymer absorption
Phosphate mining
Coal ash
How is polymer absorption used to improve uranium extraction?
Uranium that is dissolved in seawater absorbs onto certain polymers that are placed in the sea
The uranium can be washed off using acids, then collected and concentrated
How can phosphate mining improve uranium extraction?
Uranium is often present in phosphate deposits so can be separated from the material extracted in phosphate mines
How can coal ash improve uranium extraction?
Uranium can be extracted from it
This will become economic if the price of uranium rises enough
What are 3 new reactors designs for nuclear fission?
Molten Salt reactors
Plutonium reactors
Thorium reactors
How do Molten salt reactors work/ how are they an improved design of nuclear fission?
Using molten salt as a reactor coolant increases efficiency of electricity generation beacause the reactor can operate at much higher temperatures without needing high pressure to prevent the coolant boiling
Liquid cooled reactors are smaller and cheaper than gas cooled reactors
How do plutonium reactors work/ how are they an improved nuclear fission design?
Most the uranium found is uranium-238 which is not fissile
It can however be turned into fissile plutonium by neutron bombardment
They allow much more energy to be harnessed from the Uranium
But they are more complex & expensive to operate
How do thorium reactors work/ how are they an improved nuclear fission design?
Thorium is a fertile fuel so can be converted to fissile uranium-233
There is rods of uranium-233 which release electrons and neutrons to maintain the chain reaction
There are also rods of thorium-232 which ‘breed’ uranium as it is bombarded with neutrons
What are the advantages of thorium reactors?
It is 3 times more abundant than uranium
More difficult to make weapon material than uranium
Less radioactive waste produced
Radioactive waste has shorter half-life
No fuel enrichment required
What are the disadvantages of Thorium reactors?
The breeding rate of uranium-233 is slow, making fuel expensive
Uranium-233 releases hazardous alpha radiation
Remaining development costs are high considering it is less developed technology
What is nuclear fusion?
The energy source of stars which involves the joining of nuclei of small atoms, such as hydrogen isotopes e.g. deuterium and tritium
Why is nuclear fusion used less than nuclear fission?
It is very difficult to produce controlled small-scale fission on earth and developing methods has even complicated
What are the sources of fuel for nuclear fusion?
Deuterium(hydrogen-2) extracted from water
Tritium(hydrogen-3) which is produced by the neutron bombardment of lithium
What are the conditions needed for fusion to occur on earth?
Hydrogen in the form of plasma
Heavy Nuclei
Very high temperature
Vacuum
Magnetic field
Why is hydrogen in plasma form needed for nuclear fusion?
It is a high energy state of matter where electrons cant bind to the nuclei
It is easy to obtain the form
The electrons must be removed so the nuclei can collide
Why are heavy Nuclei needed from nuclear fusion?
Nuclei with greater mass have more momentum and kinetic energy so are more able to overcome the repelling positive nuclei
Why is very high temperature needed for nuclear fusion?
Increases kinetic energy of nuclei and increase the chances of colliding
Why is a vacuum needed for nuclear fusion?
To remove other gases present
To fuse things that aren’t hydrogen will use more energy
To make sure the plasma isnt cooled by air
Why is a magnetic field needed in nuclear fusion?
To hold the plasma centrally so it doesnt touch container sides and cool- it could melt the sides and break through
What is the issue for nuclear fusion needing magnetic fields?
It uses a lot of energy
We dont have material that is mechanically strong enough
What is the shape of a torus reactor?
3D donut like shape
How is a toroidal reactor useful?
You can pass a conductor around and create a magnetic field
Why is using a toroidal reactor difficult?
It is hard to maintain fusion because the temperatures needed can only be reached for a short amount of time
It is diffuclt to cool the conductor if it overheats
A large barrier is the availability of tritium
The availability of tritium is a barrier to nuclear fusion in toroidal reactors. How can it be overcome?
A lithium blanket which uses neutrons otherwise lost to breed tritium towards the inside of the reactor
Name 2 toroidal reactor projects
JET (Joint European Torus) near oxford
ITER
What project will research the possibility of using laser fusion?
HiPER
(High power laser energy research)
What is laser fusion?
Small scale fusion
How does laser fusion work?
Concentrate electromagnetic radiation in a small volume and bombard it with laser beams of electromagnetic radiation at the right frequency
Concentrating in one spot for long enough will raise the temperature
What would the improvements of nuclear fusion be by the use of laser fusion?
Less energy because of advancements in laser beams
Solves the problem of raising and maintaining temperatures
It avoids the problems of plasma containment
