Small rod-controlled pressurized water reactors have foregone the use of soluble boron and heavily rely on control rods and burnable poison rods for reactor control.

This study aims to explore the influence of control rods on the key performance metrics of a long-term small rod-controlled pressurized water reactor.

First, a KLT-40 reactor used for nuclear icebreakers was taken as research object, and a critical rod position-search burnup code was developed based on OpenMC. Then, the core lifetime and other indicators such as the axial power offset, fuel utilization, and radial power peak factor, were compared between with and without the designed control rods for the design and analysis of the control rod layout of KLT-40 reactor. Finally, the influence of different move-in/out strategies on axial power offset was analyzed.

The core lifetime can be extended from 590 effective full power days (EFPDs) to 650~698 EFPDs with the designed control rods. Adopting a strategy of prioritizing the movement of low-value rod groups effectively reduces the axial power offset, with values of -0.69 and +0.8 decreasing to -0.29 and +0.52, respectively.

The control rod burnup calculation strategy adopted to accurately calculate the core lifetime of small rod-controlled pressurized water reactors can effectively reduce the axial power offset by using a reasonable move-in/out strategy.