Keywords: reliability and durability, containment of nuclear power plant, heat transfer, concrete creep, shrinkage, damage, cracks, pre-stress losses.

The reliability and durability of reactor containments depends directly on the prestressing system. General results from in-situ measurements during the whole time of operation shows an increase in the deformations and an increase of prestress losses since the onset of service. Most measurements also indicate that the temperature has a major influence on the prestress losses. These conclusions were obtained from thirty years of measured prestress at Swedish nuclear reactor containments. This paper presents a computer simulation of a nuclear power plant containment under cyclic temperature loading during service, when the stages of service and planned stops are changed. It is well known that an increase of temperature affects the rate of concrete creep. This fact can significantly cause prestress losses in the structure. Moreover, increasing deformations are observed and additional cracks could appear. An advanced two-level model is used for predicting the prestress loses and the structure response. It is a combination of a global macro-level model and a local model. The aim of the global one is the modeling of the evolution of the prestress forces changed by the temperature and climatic loading. The local model is loaded using the mechanical and thermal loading from the global model. The staggered coupled thermo-mechanical algorithm is the main part of local model which has to reflect the time dependent processes in the containment wall. The heat transfer analysis is running in parallel with the mechanical analysis where the temperature effect on concrete creep is modeled using Bazant's microprestress-solidification theory [1,2]. The local model is subsequently completed by suitable damage models.

This study is a part of global reliability and durability model of nuclear power plant containment in the Czech Republic. The computation presented attempts to model and explain the increase in radial deformation and the decrease in the tendon forces since the onset of service.

1

Z.P. Bazant, "Mathematical Modeling of Creep and Shrinkage of Concrete", John Wiley & Sons, Chichester-Singapore, 1988.

2

Z.P. Bazant, G. Cusatis, L. Cedolin, "Temperature effect on concrete creep modeled by microprestress-solidification theory", Journal of Egng. Mech. ASCE, 691-699, 2004. doi:10.1061/(ASCE)0733-9399(2004)130:6(691)

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