Neutron Balance — Time

Abstract

A nuclear power reactor which is operating at a steady power (and thus has a neutron population which is constant with time) could be likened to a car which is driven down a straight stretch of highway at a constant speed. That is an important, but only one of the possible operational modes for both the car and the reactor. Just as it must be possible to accelerate and stop the car, it must be possible to start up, to shutdown and to adjust the power (and to do so precisely!) of a nuclear reactor. The power of a nuclear reactor can be changed by changing the neutron population within its core, thus in a fundamental sense the understaning how a reactor can be controlled requires an understanding how the neutron population in the core can be altered. The basic mathematical tool for this is the same set of neutron balance equations derived previously, except that now the term including the time derivative of the neutron population must be retained.