A NUCLEAR REACTOR CONTROL ROD HAVING A REDUCED WORTH TIP

摘要

A control rod with a "reduced worth" tip is provided for a nuclear reactor which includes an elongated tubular cladding with its opposite ends closed and having a plurality of pellets of two different types disposed in its lower end portion in an end-to-end relationship. One type of pellets is formed of a neutron absorbing material, such as B4C, whereas, the other type of pellets is formed of an inert material, such as ZrO2. The absorber pellets and the inert pellets are interspaced between one another in the lower end of the rod so as to gradually reduce the rate of change of the neutron flux experienced at the rod's lower end portion as it moves in and out of the fuel assembly to thereby alleviate pellet-clad-interaction and thus reduce the likelihood of fuel rod failure. In one embodiment, the axial heights of the absorber pellets progressively increase from the bottom to the top of the rod's lower end portion while the axial heights of the interspaced inert pellets remain constant. In a second embodiment, the axial heights of the inert pellets progressively decrease from the bottom to the top of the rod's lower end portion while the axial heights of the interspaced absorber pellets remain constant.