Actuating device for two clusters of control rods movable vertically in one and the same fuel array of the core of a nuclear reactor

An actuating device for two clusters of control rods movable vertically in one and the same fuel array in the core of a nuclear reactor comprising a vessel containing a pressurized fluid in which is immersed the reactor core consisting of arrays formed by vertically arranged bundles of fuel rods into which the clusters are inserted during the operation of the reactor, one of these clusters comprising neutron-absorbing rods effecting the running of the reactor by the vertical movements modifying the insertion of the absorbing rods, and the second cluster remaining fully inserted into the array during only a part of the operating cycle of the reactor, independently of the movements of the first cluster, each of the clusters consisting of an assembly of rods arranged mutually parallel and attached to a fixing piece, the mechanism comprising two long vertical actuating rods (2, 3), the one associated with the first and the other with the second of the two clusters, movable within a fluid-tight enclosure (1) communicating with the internal volume of the vessel, a maintenance and controlled vertical movement mechanisms (27, 28, 29, 30, 34) in the fluid-tight enclosure of the actuating rod (2) of the first cluster and a detachable connecting device between each of the two clusters and the corresponding actuating rod (2, 3), wherein:

• the actuating rod (2) of the first cluster, or first actuating rod, consists of a cylindrical sleeve carrying in its upper part hooking fingers (41) movable transversely to project into the internal space of the actuating rod (2) or on the contrary into the retracted position and an actuating device (45) of these fingers fitted slidingly in the axial direction on the top end of the actuating rod (2) between a closed position of the fingers (41) where the actuating device (45) is maintained in the top position relative to the actuating rod (2) by a spring (46) and an open position of the fingers (41) where it is moved into the bottom position by virtue of a bearing surface (60) coming into abutment on a part (61) of the internal surface of the fluid-tight enclosure (1) at the end of the upward movement of the first actuating rod (2),
• the actuating rod (3) of the second cluster, or second actuating rod, arranged coaxially and within the first actuating rod (2) throughout its length comprises a widened part (3.sub.b) fitted with sealing segments (50) limiting the passage of the pressurized fluid in the annular space made between the two actuating rods (2, 3) and effecting the guidance of the second actuating rod (3) consisting of a piston in the first actuating rod (2), a hooking groove (53) for the fingers (41) carried by the first actuating rod (2) and a projecting part (55) serving as an abutment to stop the second actuating rod in the hooked position of the fingers at the end of the upward movement of the second rod (3) in the first (2),
• lastly, the fluid-tight enclosure (1) comprises at its upper part a pressure relief valve (65) for its internal volume.