Tube lane pivoting device for nuclear steam generator

Steam generator for a nuclear power station, including an outer casing of vertical axis, a horizontal tube plate fixed in a leaktight manner inside and at the lower end of said outer casing, a bundle of inverted-U tubes, comprising vertical branches, respectively hot and cold branches joined by a bent part at upper ends of said branches and traversed by a primary fluid which yields heat to a secondary fluid flowing through said outer casing, said branches of said U-tubes having lower ends connected to said tube plate and emerging thereunder, respectively in an inlet manifold for the hot primary fluid and an outlet manifold for cooled fluid, an inner casing covering said bundle and having a lower edge separated from said tube plate by a space and delimiting with said outer casing an annular space traversed by secondary fluid introduced into said casing in said space before vaporizing in contact with the tubes traversed by the primary fluid, steam extraction means, arranged above said bundle in said outer casing, and means for deflecting and distributing the flow of said secondary fluid, provided at the lower part of said inner casing, said deflecting means delimiting with said tube plate, on the one hand, and the hot and cold branches of the nearest tubes, on the other hand, an elongate central region extending transversely through said outer casing, said central region being occupied by means for blockage or partial occupation of the passage afforded to the secondary fluid in said central region, said means consisting of at least one block articulated on a fixed horizontal pivoting spindle mounted inside said outer casing and extending perpendicularly to a midplane of the said central region between the hot and cold branches of the tubes of said bundle, so as to allow pivoting of said block away from said tube plate, uncovering said region above said tube plate.