Abstract: A fuel assembly for a pressurized water nuclear reactor incorporating fluid moderator spectral shift control means. During the first part of the fuel cycle when there is excess reactivity, neutron moderation may be decreased by replacing a portion of the water within the core with a less effective moderator such as heavy water. During the life of the fuel, the heavy water is gradually replaced with regular water. The fuel assembly incorporates the necessary means and apparatus to effectuate such control.

Abstract: Nuclear fuel rod bundle transferring apparatus is disclosed for transferring a bundle of the rods along a path from a first container to a second container. The apparatus includes a set of rollers mounted to permit the distance between the axes of the rollers to be varied from a first distance sufficient to receive the bundle of fuel rods to a second distance less than said first distance, wherein the rollers engage opposing sides of the bundle of nuclear fuel rods. A hatch is disposable between a first position intercepting the path and retaining the bundle of fuel rods within the first container, and a second position permitting the bundle of nuclear fuel rods to be transferred from the first container to the second container.