Mechanical Shim core operational strategy designed for CPR1000 nuclear power plant

•Power control analysis method is used to design MSHIM core control strategy for CPR1000.•Control rod parameters are reconfigured to implement MSHIM control strategy.•A one dimensional two-groups quasi static calculation program is developed to simulate the reactor core.•The MSHIM core control strategy operating chart is designed to ensure the operation safety of the reactor. The CPR1000, one of the water-cooled reactor types in China, employ MODE-G core control strategy through control rods and soluble boron to control the reactivity change during load follow operation, In spite of this, it has load follow capability for only 80% of cycle life, and also a large amount of radioactive waste liquid will be produced. In order to solve this problem, the MSHIM core control strategy was designed for CPR1000 in this paper. The MSHIM core control strategy has two independently moving RCCA groups are utilized for essentially simultaneous control of reactivity/temperature control and axial power distribution with complete boron-adjustment free load follow operation for up to more than 95% of cycle life. The prime objective of core control is to simultaneously manage core power level and power distribution to ensure the reactor operation safety. In the MSHIM core control strategy in CPR1000, reactor power control includes power level control and power distribution control. Power level control uses the reactivity balance analysis method; the objective of power distribution control is to ensure the safety related parameters, such as DNBRs and FQ within its design limit, AO control analysis method is used. According to the reactivity balance analysis method, the control rods inserted in reactor core to offset the positive reactivity during load follow operation, and in CPR1000 core, part G1-bank is lifted to supply the positive reactivity prior to load follow operation. AO analysis result shows that the axial burnup distribution can affect the AO target value, AO control ability is enhanced with the increase of R-bank worth. Changing burnup history and redesigning the RCCAs are employed.