Research on non-uniform control rod for PWR

Abstract

The axial power distribution of the core has a great influence on the operation of PWR. The uneven distribution of the axial power even endangers the safety and economy of the whole nuclear reactor. Due to the coupling of neutron leakage, core power level control and axial power deviation control, it is difficult to obtain satisfactory control performance. In order to improve the axial power distribution in the core, a non-uniform control rod is defined based on the decoupling control idea. By taking advantage of the self-shielding effect and the staggered distribution of neutron and non-neutron absorbers, a single non-uniform control rod can achieve the function of power level and distribution control. A core model is built by MCNP5, and the uniform control rod is replaced by non-uniform control rod of N = 2 and 4 (N is the nonuniformity coefficient of non-uniform control), then the axial neutron flux density distributions at different rod positions are calculated and compared. The simulation results show the non-uniform control rod studied in this paper hardly affect the original axial power distribution when controlling the core power level. In other words, the power level and deviation controls are completely decoupled using non-uniform control rod. Although the reactivity introduced by non-uniform control rod is smaller than that of uniform control rod, it is more uniform. So the research of this paper can provide a direction for the new control rod.