Six factor formula and Reactivity
Define Reactivity and give its formula in terms of keff
The fractional change in neutron population per generation.
roe=(keff-1)/keff
What does MSDP stand for?
macroscopic slowing down power
Hafnium is an example of what?
a material that is used as a fixed non-burnable neutron poison
How long does it take for Xenon 135 to reach its peak after shutdown, and how long will it take for the reactor to be Xenon free?
10 hours, 3 days
Used for coarse control and/or to remove reactivity in relatively large amounts
Shim rods
Infinite multiplication factor, k∞
The ratio of the neutrons produced by fission in one generation to the number of neutrons lost through absorption in the preceding generation.
Reactivity Coefficient
The amount of change in reactivity per unit change in the parameter.
Where can a chemical shim be found in a reactor?
In the coolant during normal operation.
Xenon dead time is:
the period of time where the reactor is unable to override the effects of xenon.
What is the typical integral control rod worth curve shape and where will you find highest/lowest slope values?
An "S" shape that has a relatively flat slope at the top and bottom of the core and a maximum slope at the center of the core.
The effective multiplication factor, keff
The ratio of the number of neutrons produced by fission in one generation to the number of neutrons lost through absorption and leakage in the preceding generation.
Why may Neutrons actually have either slightly more or slightly less than the resonant energy, but still appear to be at resonant energy relative to the nucleus?
The Doppler broadening of resonance peaks
A non-burnable neutron poison is:
A material that has relatively constant neutron absorption characteristics over core life.
Xenon-135 oscillation can:
change local power levels in the core by a factor of three or more.
Black vs Grey neutron-absorbing material.
absorbs essentially all incident neutrons. A grey neutron-absorbing material absorbs only part of the incident neutrons.
The thermal utilization factor is effected by which three factors?
The enrichment of uranium-235, the amount of neutron poisons, and the moderator-to-fuel ratio.
Reactors are usually designed to operate in which moderation condition and WHY?
Under moderated condition so that the moderator temperature coefficient of reactivity is negative.
Burnable neutron poisons are used in reactor cores to:
compensate for the excess positive reactivity of the fuel when the reactor is initially started up.
Helium-3 will become what and why?
a significant neutron poison if significant amounts of tritium are left in a reactor during a shutdown period that lasts longer than several months.
Explain the difference between Integral control rod worth and Differential control rod worth.
Integral control rod worth is the total reactivity worth of the control rod at a particular degree of withdrawal from the core.
Differential control rod worth is the reactivity change per unit movement of a control rod.
An increase in moderator temperature will have the following effects:
Increase the thermal utilization factor
Decrease resonance escape probability
Decrease fast non-leakage probability
Decrease thermal non-leakage probability
A Reactor is Under Moderated when
A decrease in the moderator-to-fuel ratio decreases keff due to the increased resonance absorption.
What are the advantages of Fixed burnable poisons over chemical shims?
Can be used to shape flux profiles Do not have an adverse effect on moderator temperature coefficient
The equilibrium concentration for xenon-135 is given by the equation:
Nxe(eq)=(γxeΣ fuelf φ +λI NI)/(λXe +σXea φ )
OR
Nxe(eq)=[(γxe +γI)Σ fuelf φ]/(λXe+σXea φ )
Name four of the five the most common elements used to make control rods.
silver, indium, cadmium, boron, or hafnium.