<p>Vacuum insulation is widely employed in cryogenic liquid storage for ground-based applications due to its exceptional thermal performance. However, accidental vacuum loss can significantly increase the boil-off rate (BOR) of the stored liquid, leading to energy inefficiency and safety hazards. Addressing these risks is crucial to protect humans, assets, and the environment. Quantitative risk assessment (QRA) relies on accurate consequence estimation, which requires precise evaluation of BOR during vacuum failure scenarios. In this study, the BOR of liquid nitrogen stored in a double-walled vacuum-insulated cryogenic tank under vacuum loss conditions was investigated through numerical modeling and experimental validation. A comprehensive numerical model was developed to incorporate all relevant heat transfer mechanisms, with special emphasis on natural convection in the interstitial space between tank walls. Experiments were conducted using a physical model to compare intact and vacuum-loss cases, revealing that BOR doubles under vacuum failure, primarily due to the significant contribution of natural convection of the gas within the space between the tank walls. Validation of the numerical model against experimental data for the intact case demonstrated satisfactory accuracy, supporting its extension to the vacuum-loss scenario. Evaluation of correlations for natural heat convection in the space between tank walls suggested that a combination of two equations could provide significantly improved prediction accuracy. These findings advance the understanding of cryogenic liquid boil-off behavior under vacuum failure conditions, providing a robust tool for incident analysis in QRA and informing the design of safety relief systems.</p>