Moisture levels and drying potential of the concrete in Swedish reactor containments

The climatic conditions inside nuclear reactor containments are continuously monitored by the plant owners in order to e.g. maintain a suitable climate for the mechanical and electrical equipment. Due to the high temperatures, during operation, the concrete within the containment may act as a moisture source contributing to the humidity. To evaluate if, and to what extent, the concrete inside the containment influences the climatic conditions, the moisture distribution has to be determined. In order to do this, a measurement setup has been developed and tested. The results showed that the measurement setup was suitable for long term measurements of internal relative humidity in concrete. However, measurements close to the concrete surfaces showed tendencies of leakage, increasing the uncertainties of those measurements. The measurement setup was installed at three reactor containments in Sweden during the summer of 2012. Results from the monitoring campaign on one of the three reactor containments are presented in this paper. The results showed that the concrete was still drying after 30-35 years of exposure inside the containment