Method and apparatus for the zone-wise shuffling of nuclear reactor fuel elements

A water-cooled reactor installation comprising a reactor pit containing a pressure vessel containing an exposable core of individually removable vertically elongated clad fuel elements, a fuel element storage pit beside said reactor pit and adapted to be water-flooded to a level above said fuel elements when the elements are removed from said core and stored vertically in the storage pit, a fuel element lock interconnecting said pits, a circulating line containing a circulating flow of water, said line circulating water through said storage pit at least up to said level, at least one elongated test chamber vertically positioned in said storage pit and having an open top below said level through which one of said fuel elements can be removably inserted, said test chamber being dimensioned to closely confine any single one of the fuel elements at a time, said test chamber being connected with said circulating flow of water and thereby containing a portion of said water in the form of testing water, a removable air bell closing said open top when said test chamber contains one of said fuel elements and said testing water, controllable means for supplying said air bell with compressed air to form an air cushion holding said testing water stationary in said test chamber for a dwell time causing the water to acquire gamma activity if one of said fuel elements in the test chamber has a cladding defect, means for removing said testing water in the form of a continuous flow of testing water from said test chamber after said dwell time, means for testing said continuous flow of removed testing water for gamma activity and means for returning a thereby tested flow of testing water back to said circulating line.