Patent Number: 058898328
Section: claims

1. A control cluster for controlling a nuclear reactor, comprising: (a) a spider including:  (b) a shock absorber having a socket slidable in said axial bore and spring means in said axial bore for urging said socket towards a position in which it projects downwardly from said spider and is in abutment against abutment means fast with said central portion;  (c) a plurality of vertical control rods each having an upper plug formed with an upward extension traversing one of said through-hole and projecting upwardly out of the through-hole,  wherein each said extension has at least two longitudinally spaced radially enlarged portions located within the through-hole, separated by at least one portion of reduced diameter, an upper one of said enlarged portions being slidably received in the respective through-hole for guiding the plug and being retained in abutment against shoulder means in the through hole by a nut in abutting contact with an upper surface of the respective finger and secured on a threaded upper end portion of the extension located entirely out of said through hole and a lower one of said enlarged portions having a diameter slighter than a diameter of said upper one for allowing a limited amount of lateral movement. 2. A control cluster according to claim 1, wherein said abutment means consists of an internal lower flange of said bore integral with said bottom part. 3. A control cluster according to claim 1, wherein said upper radially enlarged portion has a short cylindrical portion extending upwardly by a frustoconical abutment zone having an apex angle of about 110.degree. and downwardly by a frusto-conical zone merging with the portion of reduced diameter. 4. A control cluster according to claim 1, wherein said closing plug has at least one further axial portion of reduced diameter under the lower one of said radially enlarged portions. 5. A control cluster according to claim 1, further having a plurality of pins each engaged through a wall of a respective one of said fingers into a groove of a respective one of said plugs for preventing the plug from rotating, each of said pins which locks one of said fingers which is at an intermediate location on one said fin being in a direction oblique with respect to the respective fin.