Abstract: A lowermost grid for a nuclear fuel cell includes a grid insert secured therein. The grid insert is a tube having an inwardly projecting retention lip at its lower end. The lowermost grid is secured to a lower nozzle by a mechanical fastener passing through a hole in the lower nozzle, through the grid insert's lower end, where it engages a guide tube, thereby sandwiching the retention lip between the guide tube's end fitting and the lower nozzle. A method of securing the lowermost grid to the lower nozzle is also provided.