Role of CFD Analysis in Nuclear Reactor Licensing and Design

Computational Fluid Dynamics (CFD) is a well-established industrial design tool for non-nuclear applications, helping to reduce design time scales and to improve processes throughout the engineering world, providing a cost-effective and accurate alternative to scale model testing. Within the Nuclear Reactor Safety (NRS) framework, the traditionally adopted tools for safety analysis evaluation (i.e. integral thermal-hydraulic codes) are not capable of predicting the effect of inherently three-dimensional flow fields and mixing phenomena in complex geometries, therefore the application of is considered to potentially bring real benefits in terms of deeper understanding of involved phenomena and of increased safety. However, CFD tools are considered not yet fully mature to be applied to nuclear safety related problems since further code assessment is still necessary. Nevertheless, the intensive code development and assessment work carried out in recent years and the dramatic increase in computing power are quite promising, and CFD already plays an important role as a support tool for NRS analysis. In this framework, the present thesis provides a contribution to the definition of the possible current role and the future perspectives of the application of CFD tools to NRS problems within both a licensing and a design framework. In particular, the present research activity focused on the implementation of CFD techniques within a best estimate methodology to address the licensing analysis of a Nuclear Power Plant (NPP), namely the analysis of the Double Ended Guillotine Break Loss Of Coolant Accident (DEGB-LOCA or 2A-LOCA) scenario of the Atucha-II NPP (CNA-2), which is included into the Chapter 15 of its Final Safety Analysis Report (FSAR). The adopted methodology implies the coupled application of best estimate thermal-hydraulic, neutron physics and fuel pin performance computer codes, together with the evaluation of the related uncertainties. A systematic and integrated application of CFD techniques to NRS analysis for licensing purposes is presented, able to go beyond state-of-the-art approaches in this field of application. The present research is also contributing to the assessment of CFD codes in their application to problems related to nuclear safety and technology.