Abstract: A floating-ring seal in a seal chamber is disposed on a pump casing at said end of a housing on the side remote from said pump. The seal chamber is isolated from the pump side by a contact seal element that is seated close to a rotating pump part. The seal chamber has a cooling circuit that is preferably filled with a fluid that is identical to the pumping medium. The seal chamber is separated from pumping medium by the seal element. A pressure compensation device is disposed in the region of the seal element in case fluid leaks from the seal chamber. The pressure compensation device fills the seal chamber with pumping medium to compensate for the leaked fluid.

Abstract: A pump assembly for circulation of liquid coolant in boiling water reactors has a thin-walled spherical pump body for an impeller which rotates about a vertical axis and an electric motor which drives the impeller and has an upright housing with a heat barrier at its upper end. The heat barrier has a thin-walled neck portion which surrounds the impeller shaft below an opening in the lower part of the pump body and a ring-shaped surface which is biased against a complementary surface of the pump body around the opening by several heat-expansible bolts which separably couple the housing to the pump body. The heat barrier has an annular air space surrounding the neck portion and being surrounded by an annulus of cooling ribs, an upper flange which abuts against the pump body and has one or more compartments for a circulating coolant, and a lower flange with one or more compartments for a circulating coolant.