Nuclear Fission And Fusion Page 166-167 Flashcards
Fission means
Splitting up into smaller parts
Large nuclei with at least 83 protons e.g. uranium are… and some can randomly split into ..
This is called
Unstable
Two smaller nuclei
Nuclear fission
Nuclear fission is called spontaneous if it… Or induced if…
Just happens by it self
We encourage it to happen
Fission can be induced by …
Only …. neutrons (called thermal neutrons) can be captured in this way
Making a neutron enter a 235U nucleus causing it to become very unstable
Low energy
What is released during nuclear fission and why
Energy is released during nuclear fission because the new smaller nuclei have a higher binding energy per nucleon
The larger the nucleus the more … it will be.
So large nuclei are more likely to..
This means that spontaneous fission limits… that a nucleus can contain
I.e. it limits the number of
Unstable
Spontaneously fission
The number of nucleons
Possible elements
Controlled nuclear reactors produced
Useful power
We can harness the energy released during nuclear fusion reactions in a
But it’s important that these reactions are very carefully…
Thermal Nuclear reactor
Controlled
Nuclear reactors use rods of… as ‘fuel’ for fission reactions
(The roads also contain a lot of… But that doesn’t undergo fission)
Uranium that are rich in 235U
238U
Rods of you uranium that are rich in 235U are placed into the nuclear reactor… which keeps workers as far away from the radiation as possible
Remotely
In a nuclear reactor:
These fission reactions produce more neutrons which then
This is called a
Induce Other nuclei to fission
Chain reaction
In a nuclear reactor:
The neutrons will only cause a chain reaction if they are
Which allows them to
The 235U fuel rods need to be placed in a… To further slowdown and/or…
These slowed down neutrons are called
This happens through …(kinetic energy is conserved) with nuclei of the moderator material
Collisions with particles of a similar mass are more…
Water is often used as a moderator because it
Slowed down
Be captured by the uranium nuclei
Moderator ( for example water)
Absorb neutrons
Thermal neutrons
Elastic collisions
Efficient at slowing neutrons down
It contains hydrogen which fits this condition
Nuclear reactors:
You want the chain reaction to continue on its own at a… Where one fission follows another
The Amount of ‘fuel’ you need to do this is called the..
Steady rate
Critical mass – any less than the critical mass (sub-critical mass) and the reaction will just peter out
Nuclear reactors use a… mass of fuel (where several new fissions normally follow each fission)
Supercritical mass
Nuclear reactor is control the rate of fission using
Control rods
Nuclear reactor:
Control rods control The chain reaction by
These … neutrons so that the rate of fission is controlled
Limiting the number of neutrons in the reactor
Absorb
Control rods are made up of a material that… neutrons e.g.…
And they can be inserted by varying amounts to control the reaction rate
Absorbs
Boron
Nuclear reactor:
In an emergency the nuclear reactor will be Shut down automatically by the… Which will stop the reaction as quickly as possible
The release of the control rods into the reactor
Coolant is sent around the nuclear reactor to… produced in the fission
Often the coolant is the same water that is being used in the reactor as a…
The heat from the reactor can then be used to make… For…
Remove heat
Moderator
Steam for poweringElectricity generating turbines
The nuclear reactor is surrounded by a… Which acts as shielding
This prevents… And reaching the people working in the power station
Thick concrete case
Radiation escaping
Waste products of fission must be
Stored carefully
Nuclear fission produces lots of… And creates less greenhouse gases then…
But there are still lots of dangerous waste products
Energy
Burning fossil fuels
The waste products of nuclear fission usually have a…
This makes them
Larger proportion of neutrons than nuclei of a similar atomic number
this makes them unstable and radioactive
The waste products of nuclear fusion can be used for practical applications such as
However they may be highly radioactive and so the handling and… Needs great care
Traces in medical diagnosis
Storage
