Steam Generator Replacement At Ringhals 3 Containment, Transport Opening

At the steam generator replacement at Ringhals 3 1995 an opening 6 x 8 m was taken in the cylindrical containment wall about 12 m over the ground level. The wall is build up of an outer prestressed concrete wall, steel liner and an inner concrete wall. The prestressing reinforcement in the outer concrete wall consists of horizontal and vertical tendons. Each tendon was prestressed to about 5000 kN from the beginning. The tendon ducts were filled with grease. Before the opening was taken a temporary wall with a gate was build on the inside of the containment wall. When starting making the opening, the tendons within the opening were de-tensioned and pulled out. A additional number of horizontal tendons under and over the opening were de-tensioned. The opening was cut through drilling 300 mm holes along the side of the opening into the steel plate from both outside and inside. Then the steel plate was cut and the wall plug removed. During the transport of the steam generators the work with the restoring of the wall started. The concrete surface was prepared and reinforcements bars were drilled into the old concrete. When the transport was finished the steel plate was restored, tendon ducts joined and the reinforcement put in place. To prevent early cracking in the concrete tubes for cooling water were mounted in the form. The inner form was cast at first and then the outer one. After that the concrete has reached sufficient strength the tendons were mounted in the ducts and tensioned to the same force as before de-tensioning. After the tensioning the ducts were filled up with grease again. A special inspection program was performed to see if there were any degradation in the concrete, the tendons or the steel plate. The result was that we could see no degradation on the steel plate or the tendons. The measured tendon forces are higher than calculated. The strength of the concrete had reached a medium level of 91 MPa (Original level 50 MPa). The carbonisation had reached 8-10 mm into the concrete. Our conclusions are that we have not seen any degradation which is a threat to the containment in the foreseeable time. (author)