Describes the reactivityMeasure of the deviation of a reactor from critical (self-su... changes occurring when the operating temperature of a reactorSystem used to initiate, maintain and control a fission chai... changes. The coefficient is negative when a temperature increase reduces the reactivityMeasure of the deviation of a reactor from critical (self-su.... Negative temperature coefficients are desirable from the safety point of view, because they help to avoid reactorSystem used to initiate, maintain and control a fission chai... excursions.