Reactivity Coefficients (RQ-C-4743) Flashcards
Moderator temperature coefficient will be least negative
at ______________ Tavg and ________________ RCS boron.
A) low, low
B) high, low
C) low, high
D) high, high
C) low, high
The Unit is in an over moderated condition.
Which of the following describes the effect of lowering RCS Tavg?
A) Positive reactivity will be added because fewer neutrons will be captured by the moderator.
B) Positive reactivity will be added because fewer neutrons will be absorbed at resonance energies while slowing down.
C) Negative reactivity will be added because more neutrons will be captured by the moderator.
D) Negative reactivity will be added because more neutrons will be absorbed at resonance energies while slowing down.
C) Negative reactivity will be added because more neutrons will be captured by the moderator.
During a reactor coolant system cooldown, positive reactivity is added to core (assuming a negative moderator temperature coefficient).
This is mainly due to a:
A) rising resonance escape probability.
B) lowering resonance escape probability.
C) rising thermal utilization factor.
D) lowering thermal utilization factor.
A) rising resonance escape probability.
How does Doppler broadening of resonance absorption peaks contribute to making the FTC of reactivity negative?
As fuel temperature increases:
A) absorption cross section for resonance peaks rises, causing more absorption of resonant energy neutrons.
B) absorption cross section for resonance energy lowers, causing more resonance escape.
C) absorption of off-resonance neutrons rises while absorption of resonant energy neutrons remains relatively constant.
D) the neutron energy spectrum is “hardened,” resulting in more resonance absorption.
C) absorption of off-resonance neutrons rises while absorption of resonant energy neutrons remains relatively constant.
Reactivity inserted due to a fuel temperature increase will be…
A) positive regardless of core age or power level.
B) positive at beginning of cycle; negative at end of cycle.
C) negative only if the reactor is above the point of adding heat.
D) negative regardless of core age or power level.
D) negative regardless of core age or power level.
Which of the following explains why the Doppler effect (FTC) adds negative reactivity despite the constant average microscopic cross sections of the resonance absorbers?
As Fuel Temperature rises:
A) cladding self-shielding lowers.
B) fuel pellet self-shielding lowers.
C) resonance peaks are shortened, fewer fast neutron fissions occur.
D) resonance peaks are shortened, more epithermal neutrons leak out of the core.
B) fuel pellet self-shielding lowers.
Which of the following is correct concerning Doppler broadening?
Doppler broadening…
A) results in a substantial rise in neutron absorption by soluble boron.
B) results in a higher resonance capture of off-resonant neutrons.
C) occurs because of moderator temperature rising.
D) affects neutrons in the fast energy range.
B) results in a higher resonance capture of off-resonant neutrons.
Which of the following conditions will directly cause the moderator temperature coefficient (MTC) to become more negative?
A) Control Rods are inserted 15 steps into the core.
B) Fuel temperature lowers from 1500°F to 1200°F.
C) RCS boron concentration rises by 20 ppm.
D) Tavg lowers from 500°F to 450°F.
A) Control Rods are inserted 15 steps into the core.
Which of the following describes the overall core reactivity effect of raising Tavg if the Unit is undermoderated?
A) Negative reactivity will be added because more neutrons will be absorbed by U-238 at resonance energies while slowing down.
B) Negative reactivity will be added because more neutrons will be captured by the moderator while slowing down.
C) Positive reactivity will be added because fewer neutrons will be absorbed by U-238 at resonance energies while slowing down.
D) Positive reactivity will be added because fewer neutrons will be captured by the moderator while slowing down.
A) Negative reactivity will be added because more neutrons will be absorbed by U-238 at resonance energies while slowing down.
The Unit is at 100% power at Beginning Of Life.
Which of the following adds the most positive reactivity following a reactor trip?
A) Void coefficient
B) Pressure coefficient
C) Fuel temperature coefficient
D) Moderator temperature coefficient
C) Fuel temperature coefficient
