A digital start-up control for air-cooled nuclear reactors

In bringing a nuclear reactor up to power, the flux level goes through as many as 8 to 10 decades from the off position through full power. Somewhere within this range of power the reactor goes critical (effective multiplication factor equals one). This point where criticality is reached may be 7 decades below the full power point. In most stationary water-cooled reactors, this total spread is divided into three ranges of control. The start-up range normally covers 3 to 4 decades; the intermediate range, 4 to 5 decades; and the power range, 1 to 2 decades.