Patent Number: 047145820
Section: summary

BACKGROUND OF THE INVENTION 1. Technical Field The invention relates to a device for linearly moving a cluster of control elements vertically into and out of the core of a nuclear reactor suitable for use when the cluster belongs to a set of two coaxially movable clusters fulfilling different functions. 2. Prior art Providing such sets makes it possible to improve fine control, power adjustment, compensation of fuel burn-up and shut down of a nuclear reactor. Different set arrangements have been proposed, including sets in which one of the clusters is formed of so-called "black" elements having a very high neutron absorption and the other cluster is formed of "grey" elements. The cluster of "black" elements is lowered into the core of the reactor for causing and maintaining shut down. A motion device may be provided which is partially common to the clusters (French 2,106,373). It has also been proposed to associate a separate device with each cluster (French 2,537,764). But none of the prior arrangements allows full freedom of movement of one of the clusters, whatever the endmost positions occupied by the other cluster except at the expense of complex mechanisms. SUMMARY OF THE INVENTION It is an object of the invention to provide a device for vertically moving a cluster of control elements in the core of the nuclear reactor suitable for (i) moving and holding the cluster into either of its endmost positions and (ii) leaving full freedom of adjustment of another cluster of the same set whatever the end position of the first cluster, while being simple in construction. To this end, an actuating device comprises an axially movable vertical shaft formed with prehension means arranged for cooperating with at least one grab fast with a cluster to be moved vertically, by engagement of the grab with the prehension means or by resilient locking of fingers of the grab on the prehension means. The fingers are provided so that the prehension means engage therewith and disconnect them from an upper structure when said means are moved upwardly beyond a position which causes locking of the grab on the fixed upper structure. A fixed lower structure is provided for causing forced uncoupling of the prehension means when the latter are lowered beyond the rest position of the grab on the lower fixed structure, an upward movement of the prehension means then driving the grab due to a bearing force. The prehension means may be limited to a rigid nipper comprising blades for locking on the fingers and a bottom pierced with passages for pins integral with the fixed lower structure and to be left there; it also allows the cluster to be deposited in the low position; while leaving complete freedom of movement to the other cluster. The movements of the first cluster are made independent of those of the other cluster, which will generally be formed by regulating elements. The invention will be better understood from the following description of a particular embodiment given by way of example only. The description refers to the accompanying drawings.