Nuclear - Fission Reactors Flashcards
Composition of naturual uranium…
99.28% of U238, 0.72% U235.
How many neutrons does spontaneous fission of a U nucleus release?
About 2-3 neutrons
Commercial reactors emply…
Enrichement of U235 or segregate/localise fuel within a matrix of a moderator…
Moderator enrichment percentages…
Water 2.65% or graphite 1.6%
Thermal Neutron
A neutron within thermodynamic equilibrium, moving with same kinetic energy as their surroundings
Neutron Multiplcation Factor(K Factor)
Describes ratio of neutrons produced by fission in one generation to the number of neutrons lost through absorption/leakage in the preceeding generation.
Cross Section
Measures proabbiltiuy that a prcoess will take place involved with radiant excitation intersecting a localised phenomenon
Mechanism of bulk moderator…
235 neutron emission escapes fuel element where it was created before 238 absorption, then enter fuel element as a thermal neutron.
Mathematic asosciation of the neutron multiplication factor…
Closer to one, the better, exceedingb one meaning each neuytron generation generates more neutrons, desire to equal 1.
K factor fluctuation…
With moderators and leakage of neutrons; control rods act as a controlling agent.
Common material for control rods…
Boron-carbide is resistant to environmental degradation and an excellent neutron absorber…
Fermis Four Factor Formula
This is used to determine multiplication of a nuclear chain reaction in a hypothetical infinite medium
What are the four FFFF?
Reproduction factor
Fast fission factor
Resonance Escape Probability
Thermal Utilization Factor
Reproduction Factor
Measures how many fast neutrons a thermal neutron generates when encountering a uranium nucleus
Fast fisssion factor
Generated fast neutrons initation of 238 fission likelihood before slowing down to thermal velocity.
Resonance Escape Probability
Describes likelihood a fast neutron slows to thermal velocity before being absorbed by 238
Thermal Utilization Factor
Measures thermalizedd neutrons then captured by the fuel.
Visuale a cross-section…
`A particle beam with velocity v impacting cross section sigma, represented as a gas of neutrons moving through a fixed density of scatteres
What does FFFF estimate?
Thermal neutrons generated(n+!) by uranium absorbition of a neutron(nth generation)
Two fates of absorbed thermal neutrons…
Fission initaiton or capture (238 more likely for capture whilst 235 more likely to fission
How many neutrons does 235 fission generate?
2.42 fast neutrons
Why is chance of 238 fission low?
High moderator concentrator.
What does REP 235 fission depend on?
Fast neutrons interactions with moderator and avoiding 238 capture
REP measures…
Probability thermal equilibrium is reached before capture.
Fission Poisons
Materials that can capture neutrons without undergoing nuclear fission, with a large neutron-absorption cross section.
Example of fission poison…
Xenon135 generated by beta decay
Three concerns of reactor safety…
Reactor control and cooling
Nuclear waste
Nuclear proliferation
Active and passive safety systems…
Active being control rods and coolant pumps, whilst passive without human intervntions.
Coefficent of Void
The change in reactivity per percent void of core water.
Why does water slow down neutrons?
H collision with KE loss in neutron with H recoil.
Elastic Scattering
This is a mechanism of which fast neutrons lose their energy when interacting with atomic nuclei of low atomic number.
What is required for neutron thermalization to occur?
Enough energy lost for it to match average velocity of particles in surrounding medium.
Why is neutron thermalization important?
Neutrons released from fission have many MeV of energy,.
How does Uranium form?
Radioactive decay of elements like thorium and potassium, with collison of beta/alpha particles with surrounding rock particles.
What is the process of uranium formation?
K40 beta decay(E and Neutrino emission) forming Ca-40, becoming Ca41(neutron absorption), beta decay(antineutrino and electron emission) forming scandium-41, which beta decays forming tianium, capturing a neutron forming titanium-42.
Why does radioactive decay occur?
Imbalance of forces holding nucleus together.
