Provided is a nuclear reactor unit that can reduce a temperature increase in a reactor core at the occurrence of an abnormality with a simple structure. Included are a reactor core having radioactive fuel and causing the radioactive fuel to cause a nuclear reaction and a nuclear reactor vessel housing the reactor core and hermetically sealing the reactor core. The nuclear reactor vessel includes an inner shroud covering the entire periphery of the reactor core and an outer shroud covering the entire periphery of the inner shroud. A first space formed by the outer shroud and the inner shroud is in a vacuum condition. The inner shroud includes a main body and a communicating part placed in part of the main body and communicating the first space to a second space, which is a space inside the inner shroud, when the reactor core reaches a threshold temperature or higher.

An austenitic stainless steel includes a mixed grain structure composed of a columnar crystal having an average crystal grain size of 20 μm or less and an equiaxed crystal having an average crystal grain size of 5.0 μm or less, in which an area proportion of the columnar crystal in the mixed grain structure is 20% or more, and an average crystal grain size of the whole mixed grain structure is 5.0 μm or less. Accordingly, it is possible to provide a material having excellent irradiation resistance and mechanical properties.

A nuclear reactor module includes a reactor core and a reactor housing that surrounds the reactor core about its sides, wherein the reactor housing is configured to direct coolant through the reactor core. A neutron reflector is located between the reactor core and the reactor housing, wherein the neutron reflector has a plurality of inlet ports facing the reactor core. The neutron reflector also has a plurality of outlet ports fluidly connected to the inlet ports to direct a portion of the coolant through the neutron reflector.

A nuclear reactor module includes a reactor core and a reactor housing that surrounds the reactor core about its sides, wherein the reactor housing is configured to direct coolant through the reactor core. A neutron reflector is located between the reactor core and the reactor housing, wherein the neutron reflector has a plurality of inlet ports facing the reactor core. The neutron reflector also has a plurality of outlet ports fluidly connected to the inlet ports to direct a portion of the coolant through the neutron reflector.

A nuclear reactor module includes a reactor core and a reactor housing that surrounds the reactor core about its sides, wherein the reactor housing is configured to direct coolant through the reactor core. A neutron reflector is located between the reactor core and the reactor housing, wherein the neutron reflector has a plurality of inlet ports facing the reactor core. The neutron reflector also has a plurality of outlet ports fluidly connected to the inlet ports to direct a portion of the coolant through the neutron reflector.

A conduit housing includes a top face, a pair of side faces disposed opposite each other and adjacent to the top face, a front side, and a rear side. The top face includes a plurality of vertical conduit ports arranged in a plurality of rows. The front side is positioned between the pair of side faces and defines a plurality of stepped faces. The rear side is disposed opposite the front side and adjacent the top face. The stepped faces include a plurality of downward faces and each of the plurality of downward faces defines a downward face plane. The stepped faces also include a plurality of upward faces, where each of the plurality of upward faces defines an upward face plane. Each upward face includes a plurality of pitched conduit ports.

Provided is a method for manufacturing a cylindrical member which includes end bending of respective end portions of a plate material in a longitudinal direction, primary grooving of respective end surfaces of the plate material subjected to end bending, bending of the plate material to a ring shape, secondary grooving of respective end surfaces of the plate material subjected to bending in a ring shape, and joining of respective end surfaces of the plate material. Therefore, it is possible to manufacture a high-quality cylindrical member.

Provided is a method for manufacturing a cylindrical member which includes end bending of respective end portions of a plate material in a longitudinal direction, primary grooving of respective end surfaces of the plate material subjected to end bending, bending of the plate material to a ring shape, secondary grooving of respective end surfaces of the plate material subjected to bending in a ring shape, and joining of respective end surfaces of the plate material. Therefore, it is possible to manufacture a high-quality cylindrical member.

A reactor unit cell is disclosed including a graphite moderator structure, a heat pipe positioned in the graphite moderator structure, and a fuel assembly positioned in the graphite moderator structure. The fuel assembly comprises a beryllium-oxide sleeve and nuclear fuel positioned in the beryllium-oxide sleeve.

A core of a light water reactor has a plurality of fuel assemblies. The fuel assemblies include a plurality of fuel rods in which a lower end is supported by a lower tie-plate and an upper end is supported by an upper tie-plate. The fuel rods form plenums above a nuclear fuel material zone and have a neutron absorbing material filling zone under the nuclear fuel material zone. Neutron absorbing members attached to the upper tie-plate are disposed between mutual plenums of the neighboring fuel rods above the nuclear fuel material zone. The neutron absorbing members have a length of 500 mm and are positioned at a distance of 300 mm from the nuclear fuel material zone. Even if the overall core is assumed to become a state of 100% void, no positive reactivity is inserted to the core.