As mentioned, the reactor power of BWRs can be controlled by control rods and core flow rate. BWR operation management must accurately calculate power distribution in each part of the core and achieve efficient fuel burnup by control of control rods and core flow rate. A reactor operation scheme is prepared by using computational codes to simulate the reactor operation state; a time variation in Xe concentration as power is evaluated and 3D nuclear and thermal-hydraulic coupled core calculations are performed.

In the early BWR startup, core power was slowly increased while applying the PCIOMR, accumulating Xe. It took 3-4 days to reach the rated power from start of the electric generator. The startup period was reduced to about 1 day by improvement in fuel performance and power rise speed and by effective combination of control rod operation and core flow rate adjustment.

After startup, the long term reactivity is controlled by changing the control rod location and depth (control rod pattern) and the short term reactivity by core flow rate. Reactor operation management during operation involves preparing the period and scheme for control rod pattern adjustment. In the past the control rod pattern was adjusted mainly at low core power, but recently it is conducted at nearly the rated core power because of improved fuel performance.