[en] A method is described for locking in place a screw which secures together first and second structures in the internal region of a nuclear reactor core. The first structure has a screw bore with a counterbore portion formed in an outer surface. The method comprises the steps of: forming a lateral recess in the counterbore portion and spaced from the outer surface, providing an elongated screw having an enlarged shoulder flange and an angular drive head with a lateral width substantially less than that of the counterbore portion, disposing the screw through the screw bore in threaded engagement with the second structure and with the shoulder rotatably seated in the counterbore portion. This provides a locking member having an angular opening and disposing it in the counterbore portion against the flange with the drive head received in the opening for engagement with the locking member to prevent rotation. This deforms a portion of the locking member into the recess for engagement to prevent movement of the locking member with respect to the first structure

[en] This paper describes a nuclear reactor having a control rod guide tube and an upper core plate, a pin-type mounting system for removably mounting the lower flange of a control rod guide tube over an opening in the upper core plate. It comprises: a pair of resilient pin members formed of stainless steel, mounted in passages formed through first opposing sides of the guide tube lower flange and resiliently and slidably receivable in a first pair of opposing bores formed on first opposing sides of the opening in the upper core plate to permit deflection thereof when the guide tube is subject to the usual shear loads associated with the operation of the nuclear reactor, the resilient pin members bearing substantially all of the usual shear load to which the guide tube is subjected. A paid of reinforcing pin members formed to stainless steel mounted on second opposing sides of the guide tube lower flange and slidably receivable in a second pair of bores formed on second opposing sides of the opening in the upper core plate

[en] This invention concerns the retubing of a nuclear steam generator when vertically positioned in a containment jacket or vessel. The fast and efficient exchange of nuclear steam generator tubes has always been regarded as a serious difficulty until the possibility of carrying out such an exchange was acknowledged as feasible. This is why the main purpose of this invention is to describe, in a given order, the various stages of the complete retubing and improvement of a steam generator within a time space of 62 to 77 days without exposing the personnel to excessive radiation levels