Abstract: An apparatus is used for cutting guide tubes of a nuclear fuel assembly below an end-piece and removing the end-piece. The apparatus includes a mount which may be removably locked and centered on the end-piece. Cutting tools insertable in the guide tubes each include a hollow shaft whose end part is split by longitudinal slits into radially expandable fingers each having a cutting edge. A stem movable axially along each shaft cooperates therewith for spreading the fingers out radially and retracting them. The shafts are mounted for rotation on a plate which is vertically movable with respect to the mount by a jack and carries a motor for simultaneously rotating all shafts. The shafts are carried by an expansion unit movable vertically with respect to the plate by a jack and including the stems. A method for separating the end-piece with the apparatus is also described.