Strength monitoring of a prestressed concrete containment with grouted tendons

Existing containments are all required to be checked for their strength periodically through inservice inspection programs. In China, all the containment prestress tendons are protected by cement grouting, except the sampling tendons for testing. To improve the methodology and accuracy of the present inservice inspections for grouted tendon containments, a new scheme of containment strength verification is proposed. It applies to all prestressed containments, and it can be used as a continuous monitoring tool. The greatest advantage of the new inspection scheme is that it suggests another possible way of monitoring the prestress levels in concrete when tendon force measurements become impossible in a case where all the tendons are grouted with cement. The measured quantities are the displacements of critical points in the containment cylinder and the dome. The apparatus is installed permanently outside the containment, and the data readings can be done any time. The improved accuracy of the apparatus contributes to make these measurements a meaningful source of continuous monitoring data. The application of the new scheme in Qinshan Nuclear Power Plant has verified its practicability. At the same time, it reveals that proper application of such a monitoring system requires careful beforehand arrangements.