6 Factor Formula
What is the fast fission factor?
Neutrons produced from fast fission.
Classify the state of the reactor:
keff = 1.000
Critical
Classify a neutron that was born within 10-14 seconds of a fission event
Prompt Neutron
What is moderation?
The process of slowing neutrons down to thermal energy.
What is the definition of reactivity?
The fractional change in neutron population per generation or the measure of the departure from criticality.
What is the fast non-leakage probability?
The fraction of fast neutrons that do not leak out of the core while slowing down.
Classify the state of the reactor:
keff = 0.995
Subcritical
Classify a neutron that has a kinetic energy of >0.1 MeV?
Fast Neutron
Good moderators have a ________ (high/low) microscopic cross section for scattering and a ________ (high/low) microscopic cross section for absorption.
High, Low
What is the definition of being critical?
The condition of the reactor where the number of neutrons produced by fission in one generation equals the number of netrons produced by fission in the previous generation.
What is the resonance escape probability?
The fraction of neutrons that are not absorbed while slowing down to thermal energies.
Classify the state of the reactor:
keff = 1.005
Supercritical
Classify a neutron in thermal equilibrium with it's surroundings.
Thermal Neutron
Good moderators should have a ________ (large/small) logaritmic energy decrement.
Large
What is the definition of keff?
The factor by which the number of neutrons produced by fission in one generation must be multiplied to determine the number of netrons produced by fission in the next generation.
What is the thermal utilization factor?
The ratio of the number of thermal neutrons absorbed in the fuel to the number of thermal neutrons absorbed in the core.
With keff = 0.985, how much postive reactivity is required to make the reactor exactly critical?
1.523%
What is the % of all U-235 fission netrons are born delayed?
0.64%
How does an increase in moderator density affect the slowing down length for a given neutron?
The slowing down length will be longer.
What is the definition of kexcess?
The amount by which the total installed core keff exceeds 1.0.
What is the reproduction factor?
The number of fast neutrons produced from fission compared to the number of thermal neutrons absorbed in the fuel.
Describe how kexcess changes throughout core life and why
At BOL, kexcess decreases due to a buildup of xenon and samarium which add negative reactivity.
kexcess increases to a maximum due to the depletion of burnable poisons which adds positive reactivity.
As fuel burns out, kexcess will decrease throughout the rest of the fuel cycle.
What are the two main categories of neutron interactions?
Scattering and Absorption
What is the Logarithmic Energy Decrement?
The average neutron energy loss per collision in a moderator.
What is the definition of Shutdown Margin (SDM)?
The amount of reactivity by which a xenon-free, cold (68F) reactor is or would be subcritical if all but the highest worth control rod were fully inserted.