Abstract: A reactor core includes an inner core region that extends in a vertical direction, and has a plurality of first fuel pins accommodating an inner core fuel; an outer core region that extends in the vertical direction, is arranged to surround the inner core region from an outer peripheral side, and has a plurality of second fuel pins accommodating an outer core fuel; and a sodium plenum provided above the inner core region and the outer core region, in which a dimension of the outer core fuel in the vertical direction is larger than a dimension of the inner core fuel in the vertical direction, and the position of a center of the outer core fuel in the vertical direction is higher than the position of a center of the inner core fuel in the vertical direction.

Abstract: A reactor plant includes a reactor having a reactor core, and a steam circulation system and a bypass system, as a plurality of systems capable of circulating water carrying thermal energy generated by a nuclear fission reaction in the reactor core, and the water as the same heat medium can be circulated in the steam circulation system and the bypass system.

Abstract: A clearance (C) is provided between the inner circumferential surface of cylindrical stubs (22) (which protrude toward the outlet-side and inlet-side water chambers (14, 15) of outlet-side and inlet-side tube plates (11a, 11b)) and the outer circumferential surface at the end part of heat transfer tubes (12) inserted into the stubs (22), and the end faces of the inside tube parts (24a) and the outside tube parts (24b) of grooved end pieces (24) are laser-welded to the end faces of the heat transfer tubes (12) and the stubs (22) from the inner-surface side of the heat transfer tube (12), with the weld height of the end faces of the outside tube parts (24b) and the end faces of the stubs (22) and the weld height of the end faces of the inside tube parts (24a) and the end faces of the heat transfer tubes (12) corresponding to each other, thereby enabling butt-welding to be performed in one pass.

Abstract: An object of the invention is to provide a sodium refining apparatus which has a simple constitution and does not deteriorate a solid electrolyte employed therein. The sodium refining apparatus of the invention, in which impurities contained in sodium are removed by a solid electrolyte having sodium ion conductivity, includes a bottom-closed casing made of a solid electrolyte and containing a small amount of highly pure sodium; an outer casing accommodating said bottom-closed casing and containing, outside said bottom-closed casing, impurity-containing sodium; a first electrode inserted in the impurity-containing sodium; a second electrode inserted in the highly pure sodium; and a power source for applying DC voltage to the electrodes; wherein the impurity-containing sodium and the highly pure sodium are in electrical contact with each other via the solid electrolyte.

Abstract: An object of the invention is to provide a sodium refining apparatus which has a simple constitution and does not deteriorate a solid electrolyte employed therein. The sodium refining apparatus of the invention, in which impurities contained in sodium are removed by a solid electrolyte having sodium ion conductivity, includes a bottom-closed casing made of a solid electrolyte and containing a small amount of highly pure sodium; an outer casing accommodating said bottom-closed casing and containing, outside said bottom-closed casing, impurity-containing sodium; a first electrode inserted in the impurity-containing sodium; a second electrode inserted in the highly pure sodium; and a power source for applying DC voltage to the electrodes; wherein the impurity-containing sodium and the highly pure sodium are in electrical contact with each other via the solid electrolyte.