Abstract: A coupling assembly for joining an inlet nozzle with a conduit assembly extending concentrically therein, to provide a fluid-tight and thermally insulated flow passageway for introducing cold water into a nuclear reactor pressure vessel and the like.The coupling assembly comprises a protective sleeve surrounding the conduit assembly and wedged into abutting contact with an end portion of the conduit assembly and an inner surface of the inlet nozzle to form a fluid-tight seal therebetween. A fluid insulating medium having a decreasing temperature gradient is positioned between a portion of the protective sleeve and the surrounding inlet nozzle to create a similar decreasing temperature gradient within the inlet nozzle, in order to protect the nozzle against thermal shocks resulting from the difference in temperature between the relatively warm reactor pressure vessel surrounding the inlet nozzle and the relatively cold water flowing through the inlet nozzle.