Study on Transition Strategy of Mode-C from Base Load to Load Follow

As a new operation and control mode, Mode-C is similar to Mode-G during base load operation, but similar to MSHIM during load follow operation, thus combining the advantages of both. In order to meet the demand of reactivity control, it is easy to lose the axial offset control during the transition from base load to load follow near the end of cycles. In the load change process, the control rod motion, flux redistribution and Xenon feedback, which have effects on reactivity and axial offset control, are tightly coupled, so it is difficult for analysis and calculation by separation of variables. Therefore, this paper takes the typical daily load follow transition of a double loop PWR as an example to make direct simulation study on three strategies, namely, temporary boron change, pre boron change and base load with deep K-bank insertion. The results show that only the strategy of base load with deep K-bank insertion can quickly and smoothly transit to load follow condition, and this strategy also has the advantages of longer cycle life, less boron change and no need to modify the reference axial power difference during transition.