Underwater exchange of centring pins of nuclear reactor control rod guide insert - by transferring guide insert under water to swivelling receiver device, fixing in receiving device, swivelling and removing centring pin

摘要

Exchange of centring pins (2), arranged in the base plate (6) of a control rod guide insert (4) is carried out by (i) lifting the immersed guide insert (4) out of the upper core assembly and transferring it under water to a swivelling receiver device (20), (ii) fixing the guide insert in the receiver device and swivelling it through 180 deg. so that the centring pin (2) projects upwardly from the base plate (6) below the water level (12), and (iii) removing the centring pin (2) and fitting the replacement centring pin under water. A receiver device (20) for exchanging centring pins, has (a) a base frame (21) which can be fixed to the reactor pond wall (14), (b) a holder frame (24) mounted in the base frame (21) for swivelling about an axis (23) perpendicular to the wall (14), (c) a drive (28) for swivelling the holder frame (24), (d) a mechanism for fixing the control rod guide insert (4) in the holder frame (24) and (e) a mechanism for stopping the holder frame (24) in predetermined positions. ADVANTAGE - Increased exposure of personnel by operations carried out outside the reactor pond is avoided.