Abstract: A reactor containment facility having a reactor pressure vessel containing a core; a dry well in which the reactor pressure vessel is arranged; a suppression chamber holding suppression-pool water and forming above the suppression-pool water a wet well; and a plurality of vent pipes allowing the dry well to communicate with the suppression-pool water; a steel wall which is in contact with the suppression-pool water of the suppression chamber and which surrounds at least the pool water so as to form a containment vessel which houses the dry well and the suppression chamber; and an outer peripheral pool containing cooling water in contact with the outer peripheral surface of the steel wall.

Abstract: A natural circulation reactor includes a reactor pressure vessel, a cylindrical shroud disposed within the reactor pressure vessel to surround a reactor core and to extend to a position above the reactor core, and a coolant descending passage defined between the reactor pressure vessel and the shroud for allowing the coolant discharged from the top of the reactor core to be again supplied to the bottom of the reactor core. In such a natural circulation reactor, a liquid level of coolant in the coolant descending passage is adjusted on the basis of a reactor power request signal at a position below a liquid level of coolant in the shroud, and thus reactor power is controlled so that it may reach a predetermined reactor power by adjusting the liquid level of coolant in the coolant descending passage.

Abstract: Two systems of low-pressure core spray appratuses have coolers, and are adapted to supply cooling water to a core spray header provided in a core-surrounding cylindrical shroud in a reactor pressure vessel. Two systems of high-pressure core flooding apparatuses and one system of high-pressure coolant injection apparatus are adapted to supply the cooling water to a region formed between the shroud and reactor pressure vessel. The elevation of the openings, which are in the reactor pressure vessel, of the high-pressure core flooding apparatuses and high-pressure coolant injection apparatus are higher than that of the core spray header. A pipe for returning the cooling water in the reactor pressure vessel to the above-mentioned coolers is connected to either the portion of the interior of the reactor pressure vesssel which is below the core or the portion of the interior of the reactor pressure vessel which is between the walls of the shroud and reactor pressure vessel.

Abstract: A containment vessel for a nuclear reactor having a dry well for mounting therein a pressure vessel for containing the nuclear reactor, a pressure suppressing chamber having a pool of coolant therein, and a vent pipe device for releasing therethrough into the pool of coolant within the pressure suppressing chamber steam which will be produced as a result of the occurrence of an accident and escape into the dry well. The vent pipe device includes a plurality of vent pipe members inserted in the pool of coolant within the pressure suppressing chamber and each having at least one exhaust port opening in the coolant. The vent pipe members are divided into a plurality of groups in such a manner that the vent pipe members of different groups differ from one another in the length of submerged portions of the vent pipe members interposed between the liquid of the coolant within the pressure suppressing chamber and the exhaust ports of the vent pipe members.

Abstract: Fuel assemblies forming the core of a nuclear reactor each include an open-ended tubular channel, upper and lower tie plates formed therein with a multitude of through holes and arranged in the vicinity of upper and lower ends of the tubular channel respectively, and elongated fuel elements located parallel to one another and extending between the upper and lower tie plates. The channel of each fuel assembly is formed in its walls with openings which are disposed below the upper tie plate and above the upper end edge of the fuel of each fuel element.