Internal primary recirculating pump for boiling water reactors

The pressure vessel of a boiling water reactor has several openings, one for each of a set of internal primary recirculating pumps. The body of each pump extends into the respective opening and is provided with a ring-shaped chamber which receives feed water and surrounds the pump shaft which is driven by a normal, wet or canned electric motor. The shaft carries a single-stage or multi-stage turbine which is located up-stream of the pump rotor and serves to prolong the deceleration of the pump rotor to zero speed in the event of unintentional motor stoppage due to current failure. The pressure chambers of the turbine and pump rotor communicate with each other by way of an annular flow restricting bypass. 8 claims, 1 drawing figure