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50 Cards in this Set
- Front
- Back
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neutron life cycle is
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The steps that neutrons as they slow to thermal energies and are absorbed in the reactor
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The infinite multiplication factor (k¥) is the ratio of
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neutrons produced in one generation, then absorption before the next generation
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The fast fission factor (e) is the ratio of
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number of fast neutrons produced by all fissions / number of fast neutrons produced by thermal fissions
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The resonance escape probability (p) is the ratio of
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number of neutrons that reach thermal energies / the number of fast neutrons that start to slow down.
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thermal utilization factor (f) is the ratio of
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# of thermal neutrons absorbed in the fuel / # of thermal neutrons absorbed in reactor materials
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reproduction factor (h) is the ratio of
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# of fast neurtons produces by thermal fission / # of themal neutrons absorbed in the fuel
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effective multiplication factor (keff) is the ratio of
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neutrons produced by fission in one generation / (# of neutrons lost through absorption + leakage in the preceding generation)
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If effective multiplication factor (keff) is <1, 1, >1 these events are called
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subcritical, critiical, and supercritical
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fast non-leakage probability ( df) is the ratio
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# of fast neutrons that do not leak from the reactor / # of fast neutrons produced by all fissions
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thermal non-leakage probability ( dt) is the ratio of
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# of thermal neutrons that do not leak from the reactor / # of neutrons that reach thermal energies
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The six factor (keff) formula is
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e df p dt f h used to determine the fraction of neutrons that remain after every possible process in a reactor.
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increase in moderator temperature will have the following effects
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Increase the thermal utilization factor and decrease the following: resonance escape probability, fast non-leakage probability, thermal non-leakage probability
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reactivity (r) is the relationship represents that
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fractional change in neutron population per generation. r = Keff -1 / Keff
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The amount of reactivity (r) in a reactor core determines
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what the neutron population, and consequently the reactor power, are doing at any given time.
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Reactivity coefficients (ax) are the amount that the
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reactivity will change for a given change in the parameter. ax = Dp / Dx
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Reactivity defects (Dr) are the total
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reactivity change caused by a variation in a parameter
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define macroscopic slowing down power (MSDP)
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the ability of a given material to slow down neutrons. MSDP = x Ss. logarithmic energy decrement per collision (x) times the macroscopic scattering cross section (Ss)
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boron has a high logarithmic energy decrement and a good ___ and a poor ____
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slowing down power, and poor moderator
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water-moderated reactors are designed with a moderator-to-fuel ratio so
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it operated in an under moderated condition.
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The reason that some reactors are designed to be under moderated is
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n an over moderated reactor an increase in temperature will lower the water density causing the power to raise, which makes the reactor less self-regulating
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define temperature coefficient of reactivity
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The change in reactivity per degree change in temperature
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The fuel temperature coefficient "prompt" is the change in
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reactivity per degree change in fuel temperature
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The pressure coefficient of reactivity is defined as
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the change in reactivity per unit change in pressure
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The void coefficient of reactivity is the
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change in reactivity per percent change in void volume.
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Increasing the moderator temperature will
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decrease the moderator-to-fuel ratio
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Decreasing the moderator temperature will
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increase the moderator-to-fuel ratio
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A negative temperature coefficient of reactivity is desirable because
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it makes the reactor more self-regulating
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The Doppler broadening of resonance peaks occurs because
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the nuclei may be moving either toward or away from the neutron at the time of interaction
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Burnable poisons are materials that have
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a high neutron absorption cross section that are converted into materials of relatively low absorption cross section as the result of neutron absorption.
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burnable poisons are generally used in the form of compounds of
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boron or gadolinium
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Soluble poisons (chemical shim), produce a
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spatially uniform neutron absorption when dissolved in the water coolant (often boric acid)
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A non-burnable poison is one that maintains a
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constant negative reactivity worth over the life of the core, One example is hafnium
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The normal use of fixed non-burnable poisons is in
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power shaping, or to prevent excessive flux and power peaking near moderator regions of the reactor
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Chemical shim advantages over fixed burnable poisons IE
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Has a spatially uniform effect - Possible to increase or decrease amount of poison in the core during - reactor operation
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Fixed burnable poisons advantages over chemical shim IE
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Can be used to shape flux profiles - Do not have an adverse effect on moderator temperature coefficie
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Ninety-five percent of all the xenon-135 produced comes from
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the decay of iodine-135
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A reactor is "xenon-135 free" in what time frame
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About 3 days after shutdown
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xenon-135 equilibrium in a reactor power at constant neurton flux happens in abou
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40 - 50 hours
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A xenon precluded startup occurs when there is insufficient
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reactivity in the controlrods to overcome the negative reactivity of xenon-135
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Xenon dead time is the period of time where
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the reactor is unable to override the effects of xenon
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Samarium-149 is produced directly from fission and from the decay of
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promethium-149 during reactor operation
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Helium-3 will become a significant neutron poison if
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significant amounts of tritium are left in a reactor during a shutdown period (>2 months)
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a "black" absorber absorbs
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essentially all incident neutrons
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A "grey" absorber absorbs
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only a part of the incident neutrons
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grey rods are often preferred because
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they cause smaller depressions in the neutron flux and power
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Resonance neutron absorbers are preferred because
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absorb by epithermal enery range neutrons that have a long travel path which causes a over all flatter flux profile
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types of control rods and purpose
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Shim rods -large adjustments, Requlating rods - fime adjustments, Safety rods - very fast shutdown (scram the plant)
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integral control rod worth is ___ and greatest when ___
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the total reactivity worth of the rod at that particular degree of withdrawal and greatest when rod fully withdrawn
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Differential control rod worth curve is what shape
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bell shape, neutron flux highest in center of the core
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maximum rod speed is based on ____ burnout because
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Xenon since most rapid non-accident tansient expected
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