Title:

Harnessing the Waste Heat from Radioactive Waste in a Notional UK Geological Disposal Facility Using a Closed-Loop Geothermal System

Authors:

Muhammad U. TAHIR, Hannah R. DORAN, Gioia FALCONE, David C.W. SANDERSON

Key Words:

closed-loop geothermal system, decay heat, geological disposal facility, lower-strength sedimentary rock

Conference:

Stanford Geothermal Workshop

Year:

2023

Session:

Emerging Technology

Language:

English

Paper Number:

Tahir

File Size:

1280 KB

View File:

Abstract:

A permanent solution for the long-term disposal of high heat producing radioactive wastes is yet to be demonstrated. Previous research into geological disposal facilities has focused on long-term safety of a mined repository or deep borehole disposal. Due to the decay heat released from high heat producing waste, there are safety concerns, such as rock uplift, canister degradation, and potential radionuclide leakage into the surrounding rock. This paper focuses on mitigating these concerns by recovering decay heat from the rock through an ‘Eavor-like’ U-tube closed-loop geothermal system, with the recovered thermal energy representing a source of clean heat. The UK is seeking a mined repository in lower strength sedimentary rock, such as the Mercia Mudstone Group, and a closed-loop geothermal system is considered appropriate for such a low permeability, conductive geological setting. This paper presents an in-depth sensitivity analysis performed using a numerical/semi-analytical approach using the T2Well-EOS1/TOUGH2 software on a closed-loop geothermal system within a notional geological disposal facility using the Mercia Mudstone as the host rock. Thermal analyses were performed with different host formations and varying mass flow rate, geometry radii and lateral length for a total simulation time of 1 year. The best-case scenario identified the Tarporley Siltstone as the host rock with a 2 kg/s mass flow rate, a larger lateral radius compared to the injection/production legs (Case 3), and a lateral length of 2 km. A long-term sustainability study of 10 years was undertaken on the best-case scenario for mass flow rates of 2 kg/s and 20 kg/s, revealing that the 2 kg/s rate offered a higher outlet temperature of 19.91 °C (versus 8.06 °C) but a lower net energy flow rate of 125.80 kW (versus 258.38 kW). This study helps identify optimal CLGS design parameters within the natural LSSR environment. Future work will entail the addition of anthropogenic heat and how removing excess heat from the rock could reduce peak temperatures to improve safety concerns and the carbon footprint of current geological disposal developments.


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