The radioactive material confinement in a nuclear power plant (NPP), , is a fundamental safety function to be
ensured during a design basis accident (DBA). For plant licensing analysis, the containment is usually modeled with a lumped parameter approach. The assumption that within each region the fluid is well mixed is inherent to this approach. However, the containment is a large building with a complex configuration. It is distributed in several compartments that avoid the well mixing of the fluid and that provoke three-dimensional effects that affect the thermal–hydraulic behavior. Reactors like Trillo NPP are highly compartmentalized in order to reduce the dose to the personnel, in contrast with PWR-W reactors that present a more diaphanous layout. Accordingly, this kind of reactors are more liable to have three dimensional effects and/or local differences than a PWR-W. The collaborative project between the UPM and CNAT has enabled the development of highly detailed three-dimensional models of the Trillo NPP containment building. The objective of this study is the detailed 3D thermal-hydraulic analysis during a mass and energy release where local effects can be observed. Most of DBA analysis are performed using lumped-parameters models which only allow to know the average containment state, and that has several assumptions related with 0D models. For
this reason a generic double-ended LBLOCA is simulated in a GOTHIC 3D model in order to study the local phenomenology occurring during this kind of transient. Analyzing the results, an homogeneous pressurization over the whole containment can be observed, with the exception of the rooms near the break. This is predictable given that pressure is transmitted at the speed of sound. However, temperature evolution is different between compartments. Temperature behavior obeys to convective-diffusive processes, and it presents strong differences between compartments that cannot be seen with lumped parameters models. The steam residence time becomes one of the critical parameters in the
containment thermal behavior, and this is strongly dependent on the building geometry
