Abstract: The invention relates to a nuclear reactor primary circuit comprising a primary pipeline (30), which defines an internal volume (32) and in which a primary nuclear reactor coolant downwardly runs, an additional pipeline (26) which is branched to the primary pipeline (30) and defines an internal volume communicating with the internal volume (32) of the primary pipeline (30) and a cuff (36) whose first end (50) is connected to the additional pipeline (26) and the second free end (52) is positioned in the internal volume (32) of the primary pipeline (30). According to said invention, the second end (52) is delimited by a free peripherial edge (53) comprising at least one upstream and downstream sections (56, 58) which are oriented towards the upstream, wherein the upstream section (56) penetrates into the internal volume (32) deeper from the primary pipeline (30) than the downstream section (58).

Abstract: The invention relates to a nuclear reactor primary circuit comprising a primary pipeline (30), which defines an internal volume (32) and in which a primary nuclear reactor coolant downwardly runs, an additional pipeline (26) which is branched to the primary pipeline (30) and defines an internal volume communicating with the internal volume (32) of the primary pipeline (30) and a cuff (36) whose first end (50) is connected to the additional pipeline (26) and the second free end (52) is positioned in the internal volume (32) of the primary pipeline (30). According to said invention, the second end (52) is delimited by a free peripherial edge (53) comprising at least one upstream and downstream sections (56, 58) which are oriented towards the upstream, wherein the upstream section (56) penetrates into the internal volume (32) deeper from the primary pipeline (30) than the downstream section (58).

Abstract: During a shutdown of the reactor, a device for partially closing off (27) the openings (26) of the reinforcements (6) located below the upper reinforcement (6a) is introduced through the opening (25) of the upper reinforcement (6a) of the partitioning of the core of the reactor. The closing off devices (27) remaining in position in the partitioning of the reactor after restarting thereof permit the increase and regulation of the head loss of the cooling water circulating in the annular space (7) around the partitioning (5) of the core. The closing-off device may consist of a rod (27) engaged in a set of openings (26) of the reinforcements (6) aligned along a vertical direction.