NRC BWR GFES - Neutron Life Cycle

A nuclear reactor is initially subcritical with the effective multiplication factor (Keff) equal to 0.998. After a brief withdrawal of control rods, Keff equals 1.002. The reactor is currently... A. prompt critical. B. supercritical. C. exactly critical. D. subcritical.

Which one of the following conditions describes a nuclear reactor that is exactly critical? A. Keff = 0; ΔK/K = 0 B. Keff = 0; ΔK/K = 1 C. Keff = 1; ΔK/K = 0 D. Keff = 1; ΔK/K = 1

Which one of the following does not affect Keff ? A. Core dimensions B. Core burnup C. Moderator-to-fuel ratio D. Installed neutron sources

Which one of the following, if decreased, will not affect Keff? A. Fuel enrichment B. Control rod worth C. Neutron contribution from neutron sources D. Shutdown margin when the reactor is subcritical

The effective multiplication factor (Keff) describes the ratio of the number of fission neutrons at the end of one generation to the number of fission neutrons at the __________ of the __________ generation. A. beginning; next B. beginning; previous C. end; next D. end; previous

The effective multiplication factor (Keff) can be determined by dividing the number of neutrons in the third generation by the number of neutrons in the ____________ generation. A. first B. second C. third D. fourth

A thermal neutron is about to interact with a U-238 nucleus in an operating nuclear reactor core. Which one of the following describes the most likely interaction and the effect on core Keff? A. The neutron will be scattered, thereby leaving Keff unchanged. B. The neutron will be absorbed and the nucleus will fission, thereby decreasing Keff. C. The neutron will be absorbed and the nucleus will fission, thereby increasing Keff. D. The neutron will be absorbed and the nucleus will decay to Pu-239, thereby increasing Keff.

A nuclear power plant is currently operating at equilibrium 80 percent power near the end of its fuel cycle. During the next 3 days of equilibrium power operation no operator action is taken. How will core Keff be affected during the 3-day period? A. Core Keff will gradually increase during the entire period. B. Core Keff will gradually decrease during the entire period. C. Core Keff will tend to increase, but inherent reactivity feedback will maintain Keff at 1.0. D. Core Keff will tend to decrease, but inherent reactivity feedback will maintain Keff at 1.0.

A 1.5 MeV neutron is about to interact with a U-238 nucleus in an operating nuclear reactor core. Which one of the following describes the most likely interaction and the effect on core Keff? A. The neutron will be scattered, thereby leaving Keff unchanged. B. The neutron will be absorbed and the nucleus will fission, thereby decreasing Keff. C. The neutron will be absorbed and the nucleus will fission, thereby increasing Keff. D. The neutron will be absorbed and the nucleus will decay to Pu-239, thereby increasing Keff.

Which one of the following combinations of core conditions at 30 percent power indicates the largest amount of excess reactivity exists in the core? Control Reactor Recir- Rod Position culation Flow A. 25% rod density 25% B. 50% rod density 50% C. 25% rod density 50% D. 50% rod density 25%

Which one of the following combinations of core conditions at 35 percent power indicates the least amount of excess reactivity exists in the core? Control Reactor Recir- Rod Position culation Flow A. 50% inserted 50% B. 50% inserted 25% C. 25% inserted 50% D. 25% inserted 25%

Which one of the following defines K-excess? A. Keff - 1 B. Keff + 1 C. (Keff-1)/Keff D. (1-Keff)/Keff

Which one of the following is a reason for installing excess reactivity (Kexcess) in a reactor core? A. To compensate for the conversion of U-238 to Pu-239 over core life. B. To compensate for burnout of Xe-135 and Sm-149 during power changes. C. To ensure the fuel temperature coefficient remains negative throughout core life. D. To compensate for the negative reactivity added by the power coefficient during a power increase.

A nuclear reactor is operating at full power at the beginning of a fuel cycle. A neutron has just been absorbed by a U-238 nucleus at a resonance energy of 6.7 electron volts. Which one of the following describes the most likely reaction for the newly formed U-239 nucleus and the effect of this reaction on Kexcess? A. Decays over several days to Pu-239, which increases Kexcess. B. Decays over several days to Pu-240, which increases Kexcess. C. Immediately undergoes fast fission, which decreases Kexcess. D. Immediately undergoes thermal fission, which decreases Kexcess.

The following are combinations of critical conditions that may exist for the same nuclear reactor operating at 50 percent power at different times in core life. Which one of the following combinations indicates the largest amount of excess reactivity present in the reactor fuel? Control Reactor Recir- Rod Position culation Flow A. 25% rod density 75% B. 50% rod density 50% C. 25% rod density 50% D. 50% rod density 75%