Geomechanics Finite Element Modelling for Nuclear Waste Storage

Abstract

ABSTRACT: Nuclear energy represents one of the key energy sources that will make it possible to achieve net-zero carbon emissions. Safe and efficient management are crucial requirements when dealing with radioactive waste. Once a geological repository is selected, the development of site involves various stages. Site characterisation represents one of the early phases. It includes performing geological, hydrogeological, and other studies to understand the site's suitability for nuclear waste storage. This paper is devoted to modelling the radioactive waste disposal into a geological repository. A comprehensive geomechanics finite element modelling approach is adopted to address the challenges arising from nuclear waste storage. A unified finite element model has been constructed for the shaft, gallery, and storage cavities. Finite element modelling has been performed to simulate the excavation of the various underground structures within the host rock formation. Hydromechanical simulations were conducted for excavating the various cavities. The installation of the radioactive waste containers is simulated. The behaviour is investigated by simulating the impact of thermal heating on the surrounding formations. This work serves as a critical step towards achieving the safe containment isolation of radioactive materials and reducing environmental risk as we move towards a future powered by clean, sustainable energy sources and commitment to net-zero emissions. 1. INTRODUCTION As one of the least greenhouse gas emitting energy sources, nuclear energy has been shown to be essential for delivering low-carbon sustainable energy transitions (Gibb 1999). However, it is also widely acknowledged that safe disposal of spent nuclear fuel (nuclear waste) can present significant social, environmental, and technical challenges (Themann and Brunnengräber 2021; Christiansson 2014). The concept of nuclear waste storage is to isolate radioactive material from humans and the environment for sufficiently long time periods. Therefore, storing such waste in deep impermeable geological formations is considered a viable option (McKinley et al. 2007). Regardless of the choice of rock type, the general design of the storage solution requires placing the nuclear waste container in a chamber created in a geological formation. However, high-level radioactive waste with associated heating and cooling processes over long period of time causes complex changes to the surrounding rocks. Their nature and performance can change according to the internal and external conditions and ultimately could affect the integrity of the storage chamber (Jia et al. 2006; Teng et al. 2021; Plúa et al. 2021). To achieve the engineering safety of the storage chamber, it is necessary to carefully investigate and manage the risks associated.