Assessment of hydrogen leakage hazards in VHTR-based nuclear hydrogen production systems: A variable pressure analysis model

The application of the Very High Temperature gas-cooled Reactor (VHTR) to hydrogen production is a crucial aspect of nuclear heat utilization, offering a low-carbon and economically viable pathway for large-scale hydrogen production. However, the stringent safety requirements of nuclear power plants necessitate comprehensive risk assessments of hydrogen leakage. To improve the accuracy of hydrogen leakage risk assessments, a variable pressure model for hydrogen storage tanks was developed, incorporating thermodynamic principles and a virtual nozzle approach. Using this model, Computational Fluid Dynamics (CFD) simulations were conducted. Analysis of hydrogen leakage in open space showed that ground adhesion effects cause periodic variations in hydrogen cloud dispersion, leading to diffusion distances up to 50 % greater than theoretical predictions. Based on the design considerations of VHTR-based hydrogen production systems, the study further investigated the mechanism by which obstacles mitigate hydrogen cloud expansion. The results indicate that the constant pressure model overestimates the diffusion distance by approximately 30 % compared to the variable pressure model and suggest that obstacles should not be placed too far from the leakage source. Additionally, the study highlights those lateral flows, driven by adhesion effects, are a key factor in optimizing obstacle placement. To address this, a lateral flow suppression strategy was evaluated. The findings demonstrate that by fully utilizing wake-induced mixing and mitigating adhesion effects, the suppression of lateral flow can reduce hydrogen cloud dispersion by up to 60 %. This study provides insights into the mechanisms and optimization strategies for mitigating hydrogen leakage in VHTR-based hydrogen production facilities, which will inform engineering design strategies for the separation programme.