Long-term hygrothermal performance of nuclear reactor concrete containments – Laboratory evaluations of measurement setup, in situ sampling, and moisture flux calculations

A measurement setup for in situ sampling of internal relative humidity and temperature in concrete structures was developed. The setup was used to evaluate the moisture conditions and to determine whether drying of the concrete components within a nuclear reactor containment contributes to the moisture conditions. The measurement setup was tested for accuracy and thereafter installed in Swedish nuclear reactor containments for in situ monitoring. Results from the measurements confirmed that the setup is suitable, especially for long-term measurements at depths of 50 mm or more. Complementary moisture transport calculations showed that the moisture flux from the concrete to the interior of the reactor containment have a noticeable effect on the environmental conditions in the containments. The calculations of the moisture condition in the concrete show that 15–30% of the evaporable water in the concrete has been dried out during the 30 years of operation.