Design improvement of weld design of the reactor internal circulation pump motor casing to the reactor pressure vessel nozzle

The reactor internal recirculation pump (RIP) used in the advanced boiling water reactor (ABWR) design is a glandless wet-motor type pump and is evolved from the pump used in the ABB-A BWRs. On the basis of the proven design viewpoint, the pump nozzle at the bottom head of the ABWR reactor pressure vessel (RPV) to which the RIP is attached is designed as a sleeve-type nozzle as used in the ABB-A BWRs. Several improvements have been made over the ABB-A original nozzle design such as elimination of the weld between the RPV bottom head and nozzle stub (by integral forging) and modification of the weld design (optimization of weld preparation suitable to automatic machine welding and use of insert ring for quality welding). Extensive experimental and analytical studies and the development of machining tools for the penetration bead (the back side of the weld) to inspect the qualification of welding have been performed in Japan with the RIP and the RPV nozzle to confirm the adequacy of the ABWR RIP and the RPV nozzle design.