Modelling of the Idaho Calcine Waste for Hot Isostatic Pressing Canister-filling Process

This thesis presents a comprehensive study on the modelling of the Idaho Calcine waste for the hot isostatic pressing (HIP) canister-filling process. The Idaho calcine waste, classified as high-level radioactive waste, necessitates immobilisation to ensure long-term environmental safety. Traditional methods such as cementation and vitrification have been employed for waste immobilisation, but these approaches have inherent limitations. The HIP process, which applies high temperature and pressure to immobilise waste in a durable, monolithic form, identified as a promising alternative. However, being an emerging technology, the development of HIP for handling radioactive material involves several critical challenges, including accurately replicating the flow properties of the hazardous Idaho calcine waste and of its scarce non-radioactive simulant, which are essential for canister-filling process design.

This research primarily focuses on developing calibrated discrete element method (DEM) models that accurately replicate the flow properties of both the Idaho calcine waste simulant and the actual radioactive waste. The objectives include a thorough literature review on HIP canister-filling processes and DEM applications, performing powder characterisation tests on a high-fidelity Idaho calcine waste simulant, developing robust calibration procedures for the Edinburgh Elasto Plastic Adhesion (EEPA) contact model and simulating the HIP canister-filling process under various conditions. Experimental work involved characterising the Idaho calcine waste simulant using standard test methods, conducting HIP canister-filling experiments with novel nozzle designs and validating the DEM models against experimental data.

Key findings highlight the effectiveness of DEM modelling in predicting the bulk material behaviour of the radioactive Idaho calcine waste and its simulant in powder filling processes. The calibrated DEM models demonstrate high accuracy in simulating flow dynamics and packing behaviour within the HIP canisters. This predictive capability is crucial for ensuring homogeneous packing, mitigating void formation and optimising the canister-filling process and canister design. Additionally, the models provide insights into particle interactions and the HIP canister, fundamental for understanding compaction behaviour under HIP conditions.

By selecting the correct calibration methods, this study closely emulates the bulk material properties relevant to a HIP canister filling process. Notably, the DEM model precisely predicts the mass balance within the simulated integrated filling system and accurately emulates the surface profile and fill level of the powder bed in a vibratory powder filling study. Although DEM simulation is computationally demanding, advances in hardware have enabled this research to be conducted on desktop PCs with readily available components, allowing for the simulation of complex bulk material scenarios, such as the multi-unit operation integrated HIP canister-filling system presented in this thesis.

The implications of these findings are significant. By accelerating the development and enhancing the safety of emerging nuclear waste technology, this research contributes to the broader goal of sustainable and safe nuclear waste disposal. Leveraging the analytical capability of DEM, which to date has limited application in the nuclear industry, underscores the importance of a multidisciplinary approach to solving complex engineering problems. The successful simulation of the radioactive Idaho calcine waste not only marks a significant advancement in nuclear engineering but also offers a versatile analytical method adaptable for different types of high-level radioactive waste with varying bulk material properties.

However, scaling up the HIP canister-filling system to accommodate industrial-scale applications remains a key challenge. Future work will focus on refining DEM models to better simulate the complexities associated with large-scale operations, including the effects of particle size distribution, shape irregularities and the influence of air. Additionally, there is significant potential in coupling DEM with nuclear kinetics for dosage assessment, which could enhance nuclear health physics by ensuring better protection and safety measures. Further developments will aim at optimising the HIP canister-filling process, improving overall efficacy and reliability as a nuclear waste immobilisation technique. This includes tackling challenges such as predicting HIP canister deformation under elevated temperature and pressure to minimise defects in the final waste form.

The research underscores the importance of a multidisciplinary approach, combining the body of knowledge from bulk materials handling, nuclear engineering, HIP technology, immobilisation of radioactive materials, computational modelling and rapid prototyping to address the complex challenges of nuclear waste management. Future research will explore advanced computational techniques and algorithms to enhance the accuracy and efficiency of DEM simulations, potentially integrating machine learning methods to predict material behaviour under various conditions. Continued efforts will also be made to ensure that the HIP process meets stringent environmental and regulatory standards, with ongoing validation of DEM models through experimental data to ensure compliance with safety and environmental guidelines. These findings and future developments pave the way for enhancing the maturity of emerging nuclear waste management solutions, ultimately contributing to long-term environmental safety and sustainability of nuclear technology.