Abstract: Apparatus for the underwater loading of nuclear materials into concrete containers employing heat removal systems includes a holding vessel and a cover. The holding vessel has a metal bottom and a metal outside wall which define an upwardly open cavity dimensioned to accommodate the concrete container while leaving a gap between the container and the outside wall. A cover covers this gap, while allowing access to the central open cavity of the container. Fasteners and seals fasten and seal the cover to the container and the holding vessel. A method for loading nuclear materials into such concrete containers, utilizing the apparatus of the subject invention, includes the steps of lifting the container into the steel vessel, lowering the cover into place, fastening and sealing the cover onto the container and vessel, and then lowering the container and vessel assembly into the water storage pool.