Geothermal analysis modeling and simulation using Idaho national laboratory' RELAP5-3D-PRONGHORN coupled codes

In the framework of the U.S. Department of Energy (DOE) "Geothermal Closed Loop"project, Idaho National Laboratory (INL) is developing a new software suite for the analysis of geothermal systems. The software suite is based on two INL codes, RELAP5-3D and PRONGHORN, coupled via a dedicated Python-based software interface. RELAP5-3D is a wellestablished two-phase system thermal-hydraulic code with nuclear pedigree, based on a nonhomogeneous and nonequilibrium model for the two-phase system, and it allows a detailed analysis of two-phase networks. PRONGHORN is a porous media-approach code, based on finite-volumes and finite-elements methods and it is being developed using the INL MOOSE computational framework. In this paper we summarize the key characteristics of the coupling interface, its validation and present the results of two benchmark exercises performed for the US DOE "Geothermal Closed Loop"project. For the first exercise, solutions of a U-shaped hot-dry rock (UHDR) configuration have been obtained, by analyzing the performances of the geothermal system as function of the borehole diameter, length, coolant mass flow, and insulation strategies. For the second exercise, solutions of hot-wet-rock scenarios have been obtained, investigating the thermal performances of a concentric borehole system. Finally, the computational performances of the RELAP5-3D/PRONGHORN coupled codes software suite and its accuracy in analyzing geothermal systems are summarized.