Climatic conditions at the surfaces of concrete containments – examples for two BWR and PWR reactors

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Summary, in English

The climatic conditions at the concrete containment wall surfaces of two nuclear reactor containments were examined and quantified as a basis for predicting the drying process. Two types of nuclear reactor containments were studied, for a BWR reactor and a PWR reactor in Sweden. They both have a thick concrete wall with a steel lining inside, but the BWR containment walls are enclosed in a building, protecting it from the outdoor climate. The PWR containment walls are exposed to outdoor weather conditions. The conditions inside the containment walls include high temperatures, up to around +50°C. Measurements of temperature and relative humidity (RH) in the outdoor air and in various points at the surfaces were used to evaluate the vapour contents of the air and in the concrete surface. By comparing the vapour contents in different points a method was developed that can be used for predicting the previous and future surface climate at the containment

walls. Two major differences between the two types of reactors are the presence of significant temperature gradients between the outer and inner wall surfaces in the PWR reactor that are missing in the BWR reactor and an exposure to outdoor climate of the PWR containment walls. In both types of reactors there are large temperature differences at different levels. The

consequences of these conditions are major differences in surface humidity, from below 20 % RH in the upper parts of the BWR containment wall in wintertime to some 70-80 % RH in the outer parts of the PWR containment walls. The previous and future surface climate conditions can be predicted from outdoor climate data and the temperature conditions measured during a short term study.

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