Gray control rod, and neutron absorber and assembly thereof

A gray control rod, and a neutron absorber and assembly thereof. The neutron absorber comprises at least one first component and at least one second component. The reactivity worth of the first component increases as the use time of the neutron absorber increases, and the reactivity worth of the second component decreases as the use time of the neutron absorber increases. The changing amplitude of the reactivity worth of the neutron absorber with the increasing of the use time of the neutron absorber is not more than 15%. By means of forming the neutron absorber by the first component and the second component and suitably adjusting the proportion of the respective component in the neutron absorber, the neutron absorber having a substantially flat reactivity worth loss characteristic can be obtained. The grey control rod and the assembly thereof having required reactivity control ability can be obtained by increasing or decreasing the material dosage of the neutron absorber.