Chapter 11 - Nuclear reactor kinetics

Abstract

Reactor kinetics is the study of those processes which control the time-dependent behavior of a nuclear reactor. Because during fission, the length of time between one neutron generation and the next is extremely short, it might be expected that controlling a nuclear reactor would be quite difficult. Fortunately, however, neutrons are produced not only through the fission process but also through the radioactive decay of certain nuclides. The neutrons produced through radioactive decay appear over time scales ranging from seconds to several minutes. With proper design, these radioactive decay neutrons can be made to govern the rate of power change in the reactor thus making the control of the reactor much simpler due to the much slower reactor response times. This becomes especially important during reactor startup. Because these radioactive decay neutrons also persist for a time after the control system brings the reactor subcritical, a considerable amount of reactor power may be produced even after the reactor is shutdown. This power must be disposed of in some way and may require wasting significant amounts of fuel to keep the reactor cool until these decay neutrons die away.