Fission And Fusion Flashcards
Nuclear fusion
the fusing together of two small nuclei at a very high temperature and pressure, releasing a lot of energy (from the small amount of the particles mass)
Where does nuclear fusion occur
Stars
Nuclear fusion reaction
Deuterium + tritium -> (fusion) helium + energy + neutron
Nuclear fission
The splitting of a large unstable nucleus into two smaller nuclei
What is the nucleus that is split and the nuclei that are formed called
-parent nuclei
-daughter nuclei
What is fissile material and what are examples of them
-material that can undergo fission under the right conditions, often used as fuels in nuclear power stations
-some isotopes of uranium and plutonium are fissile materials
Spontaneous fission
When a nuclei undergoes fission without additional energy being put into the nucleus
Induced fission
-when an unstable nucleus absorbs a neutron, making it more unstable then it decays almost immediately
Half life Uranium-235
700 million years
-means fission has to be induced
Half life Uranium-235
700 million years
-means fission has to be induced
How is uranium 235 induced fission
-It absorbs a neutron and becomes uranium 236
-it is unstable and plots almost immediately to produce two smaller daughter nuclei and 2-3 neutrons
What are the products of fission
-two smaller nuclei
-2 or 3 neutrons
-gamma rays are also emitted
What happens immediately after fission
-the products of the fission reaction move away very quickly
-the energy is transferred from the nuclear potential energy stored in the ordinal nucleus into the kinetic energy of the products
-in a nuclear power station, this energy can be harnessed and inverted into electrical energy
Chain reaction
A neutron emitted from the splitting of a nucleus causes further nuclei to split and the neutron emitted from these cause further fission reactions
Critical mass
The minimum amount of fissile material to maintain a chain reaction e.g if the fissile material is greater than the critical mass, the rate of reaction accelerates (can cause uncontrollable release of energy; explosion)
Factors that must be controlled in a nuclear reactor
- The number of free neutrons in the reactor
- The energy of the free neutrons
What are control rods and how do they work
-they are made of a material which absorbs neutrons in a nuclear reactor to control the rate of reaction without becoming dangerously unstable themselves
How are control rods controlled
(to absorb neutrons)
-the depth of control rods in the core is changed to control the rate of reaction (lower rods decreases the rate of fission, more neutrons absorbed)
-adjusted to the point that each fission event produces one fission neutron that causes another fission
-if the nuclear reactor needs to shut down, the control rods can be lowered all the way so no reactions can take place
what are moderators and how do they work
(slow down neutrons)
-a material that surrounds the fuel rods and control rods inside the reactor core
-fast-moving neutrons produced by the fission reactions slow down by colliding with the molecules of the moderator
-neutrons are slowed down so they are in thermal equilibrium with the moderator
(these neutrons are called thermal neutrons)
(ensures neutrons can react efficiently with the uranium fuel)
what is shielding and how does it work
(to absorb hazardous radiation)
-nuclear reactor is surrounded by shielding materials
-daughter nuclei formed and the neutrons emitted are radioactive
-this ensures the environment is safe for workers
differences between nuclear fusion and fission
-nuclei joins together vs nuclei splitting
-nuclei are small ie hydrogen vs large ie uranium
-occurs in stars vs nuclear reactors
-produces large energy and large nuclei vs less energy and smaller daughter nuclei
-requires high temperature and pressures vs thermal neutrons to induce fission
advantages of nuclear fusion reactors
-capable of generating more energy than fission reactions
-nuclear fuel for fusion is more abundant than fuel required for fission
-nuclear fusion produces no long-lived nuclear waste products
disadvantages of fusion reactors
-conditions for nuclear fusion are much harder to achieve and maintain Earth than fission
equation for possible fusion reaction
deuterium + tritium -> helium + a neutron
what are stars made of
they balls of mostly hydrogen
conditions required for nuclear fusion
extremely high temperature and pressures (these temperatures are only on stars
why are extreme conditions needed for fusion
-protons have a positive charge and repel each other
-to overcome this repulsion, protons must have very high kinetic energies to allow them to get close enough to fuse
-high pressure increases the number of collisions (and fusions) that occur between nuclei
