Harnessing Anthropogenic Heat from Radioactive Waste in GDF settings via Closed-Loop Geothermal Systems

Abstract

Closed-loop geothermal systems (CLGS’s) are useful concepts for heat extraction from the subsurface of low permeability. This paper addresses the possibility of a CLGS to recover waste heat and improve overall safety from a geological disposal facility (GDF). A 1 km lateral ‘Eavor-like’ U-tube closed-loop geothermal system (CLGS) was modelled within the T2Well-ECO2N/TOUGH2 software suite, to assess its long-term integrity and sustainability within a potential GDF environment. A preliminary 10-year numerical thermal analysis was investigated and compared against a model previously developed in MATLAB and OpenGeoSys (OGS) software, for three distinct geological environments suited for a GDF; evaporite (EV), higher strength (HSR) and lower strength sedimentary rock (LSSR). A static scenario (inactive wellbore) was also set up, where the heat profile emitted from canisters representative of high-heat producing waste (HHPW) was analysed over the same 10-year period. The results for the dynamic setup revealed a 0.1 °C temperature difference for T2Well-ECO2N/TOUGH2 against MATLAB/OGS with temperatures at the end of the lateral section to be 10.13 °C (EV), 8.46 °C (HSR) and 7.38 °C (LSSR) after 10-years. The static setup suggests the LSSR environment could benefit from the addition of the ‘Eavor-like’ U-tube CLGS to remove excess heat from the rock and improve overall GDF safety as temperatures exceed the bentonite buffer limitations (> 125 °C), while the EV and HSR environments fall within the acceptable criteria of < 100 °C. Overall temperature rises seen from the source at ?T=85 °C (LSSR), ?T=54 °C (HSR) and ?T=34 °C (EV) after 10-years.