A Hygrothermal Model to Simulate Moisture Conditions in Concrete Reactor Containments with Long-Term Temperature Gradients

Moisture plays a critical role in several degradation mechanisms affecting the structural components of nuclear power plants. It also significantly influences the long-term structural behaviour of reactor containments. This study presents a novel hygrothermal model that uses the relative humidity as the transport potential and accounts for the presence of a thermal gradient across the containment wall. The model is applied to predict moisture conditions in a concrete reactor containment after 30 years of operation. For evaluation, its predictions are compared with both long-term measurement data from a Swedish pressurised water reactor (PWR) and previously published results obtained using an established moisture transport model based on air vapour content. These published results demonstrate that the established model, while adequate under isothermal conditions, yields inaccurate predictions when a temperature gradient is present. In contrast, the proposed model shows good agreement with the measurement data. To capture thermal effects, the model incorporates novel methods for estimating the temperature dependence of sorption isotherms and moisture transport properties—an essential improvement when modelling moisture behaviour under non-isothermal conditions.