DESIGN IMPROVEMENT OF WELD DESIGN OF THE REACTOR INTERNAL CIRCULATIONPUMP MOTOR CASING TO THE REACTOR PRESSURE-VESSEL NOZZLE

The reactor internal recirculation pump (RIP) used in the advanced boi ling water reactor (ABWR) design is a glandless wet-motor type pump an d 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 AB WR reactor pressure vessel (RPV) to which the RIP is attached is desig ned as a sleeve-type nozzle as used in the ABB-A BWRs. Several improve ments have been made over the APR-A original nozzle design such as eli mination of the weld between the RPV bottom head and nozzle stub (by i ntegral forging) and modification of the weld design (optimization of weld preparation suitable to automatic machine welding and use of inse rt ring for quality welding). Extensive experimental and analytical st udies and the development of machining tools for the penetration bead (the back side of the weld) to inspect the qualification of welding ha ve been performed in Japan with the RIP and the RPV nozzle to confirm the adequacy of the ABWR RIP and the RPV nozzle design.