[en] This patent describes a nuclear reactor having a fuel assembly and a control rod moveable in and out for controlling the reactivity of the reactor, the control rod comprising: (a) an elongated tubular cladding; (b) means for closing the opposite ends of the cladding; (c) first pellets of a first type disposed within the cladding in an end-to-end relationship; and (d) second pellets of a second type disposed within the cladding in an end-to-end relationship; (e) one of the first and second types of pellets being formed of a material having a generally high neutron absorbing capacity; (f) the other of the first and second types of pellets being formed of an inert material having a generally low neutron absorbing capacity; (g) the pellets of the first and second types thereof being cylindrical with their respective diameters being generally equal; (h) the inert pellets being interspaced between the high neutron absorbing pellets at a lower end portion of the cladding with the remaining portion of the cladding above the lower end portion containing only the high neutron absorbing pellets; and (i) the axial heights of one of the first and second pluralities of pellets of the first and second types located at the lower end portion of the cladding progressively varying from pellet to pellet, the axial heights of the other of the first and second pellets of the first and second types located at the lower end portion of the cladding are generally equal from pellet to pellet, so as to produce an improved reduced worth tip at the lower end portion of the cladding