Abstract: The improvement in a nuclear reactor having a calandria tank containing moderator and a plurality of coolant flow channels which penetrate through the calandria tank and are loaded with fuel assemblies, the moderator and the coolant being isolated from each other. The improvement is constituted by a pressure container surrounding the outside of the calandria tank, a gap between the calandria tank and the pressure container being charged with the coolant; a recirculation pump for recirculating the coolant through the coolant flow channels; and a steam separator which is positioned inside the pressure container and separates the coolant flowing through the coolant flow channels into steam and water; whereby an improved nuclear reactor having a unitary pressure container structure is constructed.

Abstract: A system and a method of confirming the operation of a steam relieving safety valve for a water-cooled nuclear reactor are provided. Acoustic vibration generated by steam relieved from the safety valve when the latter is opened is detected by an acoustic emission sensor. The acoustic emission sensor is mounted on the safety valve or a steam relief pipe connected to the safety valve.