Internal pump vibration-proof device

In an internal pump having a risk of horizontal vibrations in a motor section, a nozzle is formed to an end plate at the bottom of a pressure vessel and a sleeve formed at the upper end of the casing for the internal pump is inserted from below the nozzle and the upper end thereof is welded to the nozzle. A support member made of a shape memory alloy is attached to at least one of the inner surface of the nozzle and the outer surface of the sleeve. Upon reactor shutdown, since the support member is in a shrinked state, a gap is ensured between the inner surface of the nozzle and the outer surface of the sleeve. On the other hand, during reactor operation, the support member is expanded to rigidly support the sleeve. In this way, horizontal vibrations can surely be prevented during reactor operation in a simple structure and with no cost-up, to maintain the reactor integrity. (K.M.)