Three-dimensional Containment Accident Analysis using different approaches in Almaraz NPP

Containment Design Basis Accident analysis are usually performed using lumped-parameters models as this kind of models do not require high computational resources. Moreover, they offer overall good results of average pressure and temperature evolution. However, in order to perform a detailed local analysis, a thermal-hydraulic behavior study of every containment room may be necessary. To achieve this goal, a more detailed containment 3D model is imperative for capturing the local phenomena which occurs during a mass and energy release accident. During the last years in the collaborative project between the UPM and CNAT, several Almaraz NPP containment 3D models have been developed. The most precise one, called Detailed Integral Model, is able to obtain results with a very high resolution. However, this approach requires also high computational resources. For this reason two new models, called Multi-Zone Models, were developed with a coarser nodalization and therefore a lower computational requirement is needed. In this paper, the new modeling approach is described. A LBLOCA has been simulated in the Multi-Zone Model and it has been compared with the results obtained from the Detailed Integral Model. After analyzing the results, it can be concluded that the thermal-hydraulic evolutions are similar although the local variables differ in some cases. Taking into account the differences between models, a criteria in the use of the different approaches described has been stated depending on the analysis objective