Abstract: At the time of loss of coolant accident, when station blackout occurs, hydrogen, radioactive nuclides, and steam are discharged from a broken portion of a pipe connected to a reactor pressure vessel into the primary containment vessel. A passive autocatalytic hydrogen treatment apparatus installs a catalytic layer and heat exchanger tubes of a heat exchanger in a casing. High-temperature steam including hydrogen and radioactive nuclides is supplied into the heat exchanger tubes and heats gas supplied into the casing 3. The steam is condensed in the heat exchanger tubes and generates mists. The mists are removed by a mist separator together with the radioactive nuclides. The gas including hydrogen fed from the mist separator in the casing is heated by the aforementioned steam and is introduced into the catalytic layer. Hydrogen is combined with oxygen in the catalytic layer to steam.

Abstract: A boiling water type nuclear reactor core, in which a plurality of fuel assemblies, each enclosed in a channel box, are loaded and a plurality of control rods, each having control blades, are arranged between the channel boxes. Long blade control rods, each having control rod blades which extend in four directions, are arranged between channel boxes on diagonals of square bundle regions each formed by a plurality of fuel assemblies, and short blade control rods, each having a control rod blade length of about half of the width of one of the square bundle regions, are arranged between the channel boxes in the center of each of the square bundle regions.

Abstract: A boiling water type nuclear reactor core, in which a plurality of fuel assemblies, each enclosed in a channel box, are loaded and a plurality of control rods, each having control blades, are arranged between the channel boxes. Latitudinal long blade control rods, each having control rod blades which extend latitudinally in four directions, are arranged between channel boxes on diagonals of square bundle regions each formed by a plurality of fuel assemblies, and latitudinal short blade control rods, each having control rod blades which extend latitudinally in four directions with each control rod blade having a latitudinal length of about half of the width of one of the square bundle regions, are arranged between the channel boxes in the center of each of the square bundle regions. The long blade control rods have a latitudinal blade length which is about twice as long as the latitudinal blade length of the short blade control rods.