REACTOR PRESSURE VESSEL

PROBLEM TO BE SOLVED: To effectively control the vibration of an internal pump recirculating through a coolant by providing a damping means made of a bellows damper between internal pumps. SOLUTION: In a pressure vessel 1, a plurality of pump casings K, K,... are provided in an annular shape so that they are extended downward vertically at the curved bottom part of a pressure vessel drum made of steel plate and a rotor part r is accommodated in the pump casings K, K,..., thus forming an internal pump (j). Damping means 2, 2,... are provided between the adjacent internal pumps (j),(j) thus controlling the vibration of the internal pumps (j), (j). In a control means 2, a bellows damper 5 and a turn buckle are linearly flange-connected between a pair of rugs connected horizontally near the lower edge part of the pump casings K, K,... A distance fluctuation between the pump casings K and K is maintained by the damping characteristics of the bellows damper 5, thus effectively damping the vibration of each internal pump (j).