Holddown device for nuclear fuel assembly

The invention provides a mechanism for applying holddown force at the upstream end of the fuel assembly without changing the loading of the core barrel and without requiring a latching mechanism. In addition, it reduces the effect of length variations on spring designs. According to the present invention, holddown force is applied not to the fuel-assembly structure but to a holddown column that either fits within a center guide-tube or takes the place of the center guide-tube and fits through openings in the spacer grids. The holddown column is made of the same material as the core barrel. As a result, the thermal expansion of the core barrel, which is the source of much of the variation that the springs must accomodate, is approximately matched by the thermal expansion of the holddown column. Also, since the holddown column can be made of stainless steel, rather than the Zircaloy typically used in the fuel-assembly structure, the effect of irradiation growth is mimimized. (auth)