GFES Review Flashcards
In a comparison between a delayed neutron and a prompt neutron produced from the same fission event, the prompt neutron is more likely to______
(Assume that both neutrons remain in the core.)
require a greater number of collisions to become a thermal neutron.
In a comparison between a delayed neutron and a prompt neutron produced from the same fission event, the delayed neutron is more likely to _________________
(Assume that each neutron remains in the core unless otherwise stated.)
be absorbed in a B-10 nucleus
A thermal neutron is about to interact with a U-238 nucleus in an operating reactor. Which one of the following describes the most likely interaction and its effect on Keff?
The neutron will be scattered, thereby leaving Keff unchanged
The magnitude of the stable startup rate achieved for a given positive reactivity addition to a critical reactor is dependent on the __________ and __________.
effective delayed neutron precursor decay constant; effective delayed neutron fraction
Which characteristic of delayed neutrons is primarily responsible for enhancing the stability of a reactor following a reactivity change?
They require more time to be produced following a fission event than prompt neutrons.
A reactor has operated at steady-state 100 percent power for the past 6 months. Compared to 6 months ago, the current moderator temperature coefficient is ___________________
more negative, due to a smaller reactor coolant boron concentration
A reactor is initially critical well below the point of adding heat (POAH) during a reactor startup. Control rods are withdrawn for 20 seconds to establish a 0.5 DPM startup rate. In response to the control rod withdrawal, reactor power will initially increase, and then ________
stabilize at a value slightly above the POAH
What is a characteristic of xenon-135?
Thermal neutron flux level affects both the production and removal of xenon-135
A nuclear power plant was operating at 100 percent power for 3 months near the beginning of a fuel cycle when a reactor trip occurred. Eighteen hours after the reactor trip, the reactor was critical at the point of adding heat. Then, reactor power was increased to 100 percent over a three-hour period.During the three-hour reactor power increase to 100 percent, most of the positive reactivity added by the operator was required to overcome the negative reactivity from…
Fuel Temperature Increase
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. What is the primary reason for the large increase in 100 percent power reactor coolant boron concentration?
The excess reactivity in the core after the outage is much greater than before the outage.
When shutting down the reactor, whey are rods inserted with bank overlapping sequence?
to maintain a relatively constant differential control rod worth
A reactor is currently shut down with the reactor coolant system at 140°F and 150 psig. Pressurizer level is being monitored using a differential pressure detector with a wet reference leg. The pressurizer level instrument was calibrated at normal plant operating conditions. The pressurizer level instrument currently indicates __________ than actual pressurizer level because, compared to the calibration conditions, there has been a significant change in the density of the fluid in the __________.
higher ; pressurizer
