Abstract: A nuclear reactor plant has a nuclear reactor vessel in a containment vessel. Air ducts, sump discharge lines, service water lines and other non-process non-critical lines extending through the wall of the containment vessel can be isolated passively (i.e., without instrumentation and control systems or power) should a postulated event which raises the atmospheric temperature within the containment vessel occur. The passive containment isolation system includes an isolation valve disposed in the non-process line and an actuator responsive to the atmospheric temperature within the containment vessel. The actuator is operatively connected with the isolation valve for closing the non-process line in response to the atmospheric temperature. The actuator is preferably disposed in or adjacent a containment sump at the bottom of the reactor vessel or adjacent the reactor vessel cavity where the temperature of the local atmosphere will most rapidly rise.

Abstract: A primary coolant system of a nuclear power plant for providing coolant to a reactor vessel, the primary coolant system comprises a primary loop for transferring heat away from the reactor vessel. An accumulator tank for containing water under a pressurized, gaseous atmosphere is attached to the primary loop via a coupling, which provides an outlet for the coolant from the accumulator tank to pass to the primary loop. A valve, which includes a pressure sensor that senses the pressure in the accumulator tank and opens or closes the coolant flow in the coupling in response to the sensed pressure, is attached to the coupling for sensing the pressure in the accumulator tank.