Fission Flashcards
Definition of Fission
Atomic splitting:
The slitting of a large nucleus into smaller components, .
What drives fission?
Radioactive material has unstable nuclei which can spontaneously decay.
Most readily driven by absorption of a neutron. (Neutron capture)
How does neutron capture instigate fission in the nucleus?
Neutron captures causes the nucleus to split into two fission nuclei and release energy, along with 2-3 neutrons.
1 neutron can cause further fission.
<1 neutron, fission process stops.
>1 neutron, cause runaway chain reaction, where all the fuel is spent.
Will only occur for fissile isotopes.
What is a controlled chain reaction?
Created when 1 neutron produced from neutron capture fission drives further fission.
Can be controlled by control rods.
Energy is released gradually and harnessed into energy - moderated.
2 factors that induce fission in uranium
- Speed of impacting neutron
- too slow may not cause fission.
- too fast may not be near nucleus long enough for neutron capture (cause transmutation) - Structure of the heavy nucleus impacted
Examples of fissile isotopes and nuclear fuel
Isotopes:
U-235
Pu-239
Fuel:
Th-232 - but can be transmutated to form U-233, a fissile
** U-238 is non-fissile, could not sustain fission reactions in reactor. Can be transmutated to form Pu-239
When do chain reactions require moderation?
When free neutrons released by fission are fast, require moderation to slow them down.
How are chain reactions moderated (slow neutrons)?
Moderated by inelastic collision with other particles of similar mass.
Once fully moderated neutrons have energies corresponding to their surroundings.
Theory of electronic stopping.
Is the mass of fission products greater or less than reactants?
Mass of two fission fragments (products) is less than the mass of reactants.
Mass difference turned into energy.
Characteristics of fission reactors?
@ 6000 degrees, get 30-40% efficiency
If you can increase temp, get increased efficiency
harness heat not radiation
