Fuel Depletion and Burnable Poisons Flashcards
Which one of the following is not a function performed by burnable poisons in an operating reactor?
Offset the effects of control rod burnout.
A major reason for installing burnable poisons in a reactor is to…
allow more fuel to be loaded to prolong a fuel cycle.
Instead of using only a higher reactor coolant boron concentration to offset the enrichment of new fuel
assemblies, burnable poisons are installed in a new reactor core to…
establish a more negative moderator temperature coefficient
Why are burnable poisons installed in a new reactor core instead of using a higher reactor coolant
boron concentration for reactivity control?
To establish a more negative moderator temperature coefficient.
A reactor is operating near the end of its fuel cycle. Reactor power and reactor coolant system (RCS)
temperature are being allowed to “coast down.”
The RCS boron concentration has become so low that a very large amount of water must be added
to the RCS to produce a small decrease in boron concentration.
Just prior to a refueling outage, a nuclear power plant was operating at 100 percent power with a
reactor coolant boron concentration of 50 ppm. After the refueling outage, the 100 percent power
boron concentration is approximately 1,000 ppm.
The excess reactivity in the core after the outage is much greater than before the outage
During a 6-month period of continuous 100 percent power operation in the middle of a fuel cycle, the
reactor coolant boron concentration must be decreased periodically to compensate for…
fuel depletion and buildup of fission product poisons.
Refer to the drawing of Keff versus core age (see figure below).
The major cause for the change in Keff from point 1 to point 2 is the…
buildup of fission product poisons.
Refer to the graph of critical boron concentration versus core burnup for a reactor following a
refueling outage (See figure below.).
Which one of the following is primarily responsible for the shape of the curve from the middle of core
life to the end of core life?
Fuel depletion
Refer to the graph of critical boron concentration versus core burnup for a reactor during its first fuel
cycle (see figure below).
Fission product poison buildup and fuel depletion are being offset by burnable poison burnout.
During continuous 100 percent power operation in the middle of a fuel cycle, the reactor coolant boron
concentration must be decreased periodically to compensate for fuel depletion. What other core
age-related factor requires a periodic decrease in reactor coolant boron concentration?
Buildup of fission product poisons.
A reactor has been operating at 100 percent power for three months following a refueling outage. If
the reactor is operated at 100 percent power without making RCS boron additions or dilutions for the
next month, RCS boron concentration will…
decrease, because irradiated boron-10 atoms undergo a neutron-alpha reaction.
Just prior to a refueling outage, the reactor coolant boron concentration at 100 percent power was 50
ppm. Burnable poisons were installed during the outage. Immediately following the outage, the
boron concentration at 100 percent power was 1,000 ppm.
Which one of the following contributes to the need for a much higher 100 percent power reactor
coolant boron concentration after the outage?
The negative reactivity from fission product poisons after the outage is smaller than before the
outage.
A nuclear power plant had been shut down for two weeks near the middle of a fuel cycle when a
reactor startup was commenced. Twelve hours later, reactor power is 100 percent, where it is being
maintained. Which one of the following is the primary reason for periodically reducing the reactor
coolant boron concentration during the next 36 hours?
To offset the buildup of xenon-135
Which one of the following describes whether reactor power can be increased from 50 percent to 100
percent in a controlled manner faster near the beginning of core life (BOL) or near the end of core life
(EOL)? (Assume all control rods are fully withdrawn just prior to beginning the power increase.)
Faster near BOL, because faster changes in boron concentration are possible.
