A nuclear reactor includes guide tubes; and vessel head penetrations each comprising a tubular adapter fixed in one of the openings and defining an inner passage. Each vessel head penetration also includes a tubular sleeve engaged in the inner passage and axially extending in line with one of the guide tubes. Each sleeve is suspended by an upper axial sleeve end lying on an upper range on the corresponding adapter. A lower axial end of the sleeve projects axially into the vessel beyond the adapter and is separated from an upper axial end of the corresponding guide tube by an axial gap having an axial height of less than 50 millimeters.

A nuclear reactor includes guide tubes; and vessel head penetrations each comprising a tubular adapter fixed in one of the openings and defining an inner passage. Each vessel head penetration also includes a tubular sleeve engaged in the inner passage and axially extending in line with one of the guide tubes. Each sleeve is suspended by an upper axial sleeve end lying on an upper range on the corresponding adapter. A lower axial end of the sleeve projects axially into the vessel beyond the adapter and is separated from an upper axial end of the corresponding guide tube by an axial gap having an axial height of less than 50 millimeters.

A method for restraining a sleeve lining a tube passing through a nuclear reactor pressure vessel is provided. The method includes attaching in situ a radial protrusion on an external surface of the sleeve; and attaching a collar to an end of the tube and coupling the radial protrusion with the collar to retain the thermal sleeve in position.

A method for restraining a sleeve lining a tube passing through a nuclear reactor pressure vessel is provided. The method includes attaching in situ a radial protrusion on an external surface of the sleeve; and attaching a collar to an end of the tube and coupling the radial protrusion with the collar to retain the thermal sleeve in position.

A composite nuclear reactor component comprises a support and a protective layer (2). The support contains a substrate (1) based on a metal. The substrate is coated with an interposed layer (3) positioned between the substrate (1) and the protective layer (2). The protective layer (2) is composed of a material which comprises amorphous chromium carbide. The nuclear reactor component provides for improved resistance to oxidation, hydriding, and/or migration of undesired material.

A composite nuclear reactor component comprises a support and a protective layer (2). The support contains a substrate (1) based on a metal. The substrate is coated with an interposed layer (3) positioned between the substrate (1) and the protective layer (2). The protective layer (2) is composed of a material which comprises amorphous chromium carbide. The nuclear reactor component provides for improved resistance to oxidation, hydriding, and/or migration of undesired material.

A modular nuclear reactor system includes a lift-out, replaceable nuclear reactor core configured for replacement as a singular unit during a single lift-out event, such as rather than lifting and replacing individual fuel assemblies and/or fuel elements. The system includes a reactor vessel and a power generation system configured to convert thermal energy in a high temperature working fluid received from the reactor vessel into electrical energy. The reactor vessel includes: a vessel inlet and an adjacent vessel outlet arranged near a bottom on the vessel; a vessel receptacle configured to receive a unified core assembly; locating datums in the base of the vessel receptacle and configured to constrain a core assembly in multiple degrees of freedom; and an interstitial zone surrounding the vessel receptacle and housing a set of control or moderating drums.

A control assembly (10) for a nuclear reactor includes a reactivity control device (11) comprising a control rod cluster (12) comprising an attaching head (22), and a drive rod (14) comprising an attaching device (16) for attaching the drive rod (14) to the attaching head (22). The attaching device (16) is movable between a connection position and a disconnection position. The drive rod (14) and the attaching device (16) define an axial trough recess (34) forming a sleeve (35). A checking device (13) engages with the reactivity control device (11) comprising a probe rod (36) which is free to move translationally in the sleeve (35) and comprises a lower end (38) abutting the attaching head (22) of the control rod cluster (12).

A control assembly (10) for a nuclear reactor includes a reactivity control device (11) comprising a control rod cluster (12) comprising an attaching head (22), and a drive rod (14) comprising an attaching device (16) for attaching the drive rod (14) to the attaching head (22). The attaching device (16) is movable between a connection position and a disconnection position. The drive rod (14) and the attaching device (16) define an axial trough recess (34) forming a sleeve (35). A checking device (13) engages with the reactivity control device (11) comprising a probe rod (36) which is free to move translationally in the sleeve (35) and comprises a lower end (38) abutting the attaching head (22) of the control rod cluster (12).

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.