Even when the core of a nuclear reactor exceeds critical mass by a small amount, it doesn't overheat immediately. The fission chain reactions build slowly because
A. the reactor has an enormous thermal mass and it takes many minutes for its temperature to change significantly, even with nuclear heating.
B. the half-life of uranium is several minutes so it takes at least that long for the reactor core to overheat.
C. it takes seconds or minutes for a neutron released by one fission to reach another radioactive nucleus and cause it to fission.
D. some fission neutrons aren't released until seconds or minutes after the fissions that eventually produce them.
Answer:D
Even when the core of a nuclear reactor exceeds critical mass by a small amount, it doesn't overheat immediately. The fission chain reactions build slowly because
A. the reactor has an enormous thermal mass and it takes many minutes for its temperature to change significantly, even with nuclear heating. B. the half-life of uranium is several minutes so it takes at least that long for the reactor core to overheat. C. it takes seconds or minutes for a neutron released by one fission to reach another radioactive nucleus and cause it to fission. D. some fission neutrons aren't released until seconds or minutes after the fissions that eventually produce them.