Heat and Mass Transfer of High Performance Concrete for Reactor Containment Under Severe Accident Conditions

This paper presents some experimental and numerical results on the study of the hygrothermal behavior of the High Performance Concrete used to build the inner wall of the nuclear power station of CIVAUX 2 (in France). In the laboratory, accidental situations (beyond design) have been considered. The scenario, designated as Severe Accident (SA), consisted of a rise from ambient conditions to 200°C, and a steam pressure of 1.3 MPa in 24 hours, maintained after several hours. Those conditions were applied on one face of a specimen, the other one being in ambient temperature. A cylindrical specimen with 1.3 m of thickness was used. Thermocouples, pressure taps, and moisture meters were implanted in the concrete at the moment of casting. They gave local information; most of them are distributed in the first 0.30 m. The typical experimental results of the evolution of the temperature, the pressure and water content as a function of time, are shown for the testing conditions. The thickness of the wall affected by accident was determined. A wetting of the concrete wall was observed, leading to a decrease of the permeability of the concrete. No outgoing gas was measured through the specimen under the action of thermal and pressure gradients. The test results are compared to a numerical model using a modified version of the TEMPOR.2 program developed by Bazant.