Abstract: Fast reactors usually use the boron carbide (B4C) based control rods as reactivity control systems. The small fast reactors exhibit strong neutron leakage, hence a low breeding capability and important burnup reactivity loss. The modular reactors require large operating cycle length and compact core design that lead to limited installation space for control rods. Therefore, small modular fast reactors require high 10B enriched B4C in reactivity control systems. Due to the large burnup, high power density and degradation of thermal conductivity under irradiation in absorber, the safe operating time of high 10B enriched B4C is not sufficient to support the small modular reactor. The reactivity worth, core power distribution, reactivity feedback coefficients, control rod temperature margin and absorber burnup of hafnium diboride (HfB2), hafnium hydride (HfH1.62) and B4C based control rods were assessed in this study. It is founded that HfB2 based control rods exhibit larger safety margin and longer available operating lifetime. HfH1.62 is able to improve the core power distribution, while its hydrogen desorption effect should be strictly investigated in the future.