The Preventive Methodology: A priori modification of the containment geometry to boost the computational efficiency of GOTHIC 3D models

• Upgrade of the UPM methodology for 3D GOTHIC containment models development. • The proposed “Preventive Methodology” was used to build a 3D PWR-W containment model. • Computational cost reduction up to a factor of forty compared with previous models. • Relevant 3D local effects for the evaluation of the hydrogen risk in a postulated severe accident sequence. • Proved readiness to perform systematic 3D analysis of the influence of safety systems on the hydrogen risk. Historically, the deterministic safety analysis simulations for large dry containments of operating nuclear power plants have been done with nuclear legacy codes using the lumped parameter approach. In opposition, there are a limited number of calculations using 3D codes, due to several factors: (i) the necessity for more detailed data about the containment; (ii) the significantly increased effort required for model development; (iii) the necessity of a broad validation and verification process; and (iv) and the higher computational cost. These reasons emerge as primary impediments constraining a more extensive use of 3D analytical tools. During the last decade, the Universidad Politécnica de Madrid (UPM) has proposed different methodologies to address these challenges with the thermal–hydraulic code GOTHIC. This article presents an improved methodology with diverse solutions for the four limiting factors, with a particular emphasis on reducing the computational cost of the simulations. The work introduces a novel approach to define the containment geometry in GOTHIC which strategically avoids configurations that compromise the calculation stability. Comparative analyses have shown that the new models can reduce the computational cost of the simulations up to a factor 40, even when using a finer mesh. The article is concluded with a preliminary application case of a postulated severe accident sequence intended to prove the model readiness for performing comprehensive hydrogen risk analysis.