Abstract: A holddown column for preventing upstream motion of nuclear-reactor fuel assemblies during operation of the reactor is disclosed. The holddown column is a composite of three concentric individual columns. Lips on the intermediate column engage the other two columns so that the intermediate column expands under load as the other two columns contract. This results in a greater deflection of the column under load than would result if the column were only a single column, but the thermal expansion experienced by the composite column is not different from the thermal expansion experienced by a simple column of the same material and length.

Abstract: A system is provided for the relief of excess pressure from the region above the nuclear reactor core to the cold leg on the occurrence of a loss of coolant accident. This system includes a series of passages connecting the annulus surrounding the exterior of the core barrel with the interior of the outlet nozzle or with the plenum above the reactor core. A flow blocking obstruction, such as a seal band, is held in a flow blocking position by the differential pressure experienced during normal operation of the reactor between the exterior of the core barrel and the exit region of the reactor core. Reversal of the differential pressure, which may be expected upon the occurrence of a loss of coolant accident, removes the flow blocking obstruction to permit the relief of excess pressure which may result at the outlet end of the reactor core.