Updating of Almaraz NPP containment models with GOTHIC 8.2 QA

The continuous development of evaluation models in the nuclear industry makes mandatory to keep the highest safety standards. The model updating performed for the Almaraz NPP containment has been focused on: the addition of the newest phenomenological models available on the latest version of GOTHIC, the use of new data that increase the detail in the model geometry, and the experience acquired by the ETSII-UPM Nuclear Safety Group and CNAT in containment modelling since the research collaboration project, started in 2013. Two models with different approaches have been developed. Firstly, a traditional single-node Lumped Parameter (LP) model taking advantage of the latest strategies in modelling drops, condensation, and flashing. In addition, the last containment licensing methodologies have been taken into account. Finally, a three-dimensional model has been totally refurbished applying an innovative meshing strategy, which allows to improve the accuracy of the calculations reducing at the same time the computational cost. The first step to assess both models was a Pressure and Temperature (P&T) comparison against previous calculations. In a second step, a P&T comparison between the LP model and the averaged values obtained from the 3D model was performed. The similarity between results contribute to reinforce the confidence on the values calculated by the lumped model and to ratify the adequacy of the three-dimensional approach on P&T analyses. In addition, the resolution obtained with the threedimensional model allows to obtain maximum temperature values in specific locations of the containment and to analyze the local condensation phenomenon against the lumped approach.