Abstract: 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.

Abstract: A nuclear reactor includes guide tubes (12); and vessel head penetrations (22) each comprising a tubular adapter (24) fixed in one of the openings (2a) and defining an inner passage (34). Each vessel head penetration (22) also includes a tubular sleeve (36) engaged in the inner passage (34) and axially extending in line with one of the guide tubes (12). Each sleeve (36) is suspended by an upper axial sleeve end (38) lying on an upper range (40) on the corresponding adapter (24). A lower axial end (48) of the sleeve (36) projects axially into the vessel (1) beyond the adapter (24) and is separated from an upper axial end (54) of the corresponding guide tube (12) by an axial gap having an axial height of less than 50 millimeters.

Abstract: A method for manufacturing by powder metallurgy a steel part is provided. A pre-alloyed powder is prepared, having the desired composition for said part, except for the O and N contents and optionally C contents, with O and N contents of at most 200 ppm, and with an Mn content from 0.