A large-scale-outdoor continuous release of cryogenic liquid onto ground

The accidental release of cryogenic liquids can cause several hazards to humans, assets, and the environment. Therefore, this phenomenon has drawn significant attention and has been investigated as part of quantitative risk assessment associated with the use of cryogenic liquids. However, the effects of release conditions on pool spread have not been thoroughly studied, and the mechanism of pool retraction has not been discussed. In this study, an attempt was made to address these gaps by both experimental and numerical analyses. Firstly, large-scale-outdoor release tests with a systematic measurement system were performed using liquid nitrogen to compare with large-scale release tests of liquid hydrogen. The release height and orientation were varied. It was observed that the pool shape was affected by the release orientation. However, the maximum pool size and average vaporization rate were insensitive to both the release height and orientation. The conductive heat from the ground was confirmed to be the major heat source for pool vaporization, accounting for over 90 % of the total heat transferred into the liquid pool. Subsequently, release scenarios were simulated using integral source models. Especially, several hypotheses were thoroughly discussed, implemented in the source models, and validated against experimental results to determine the most appropriate mechanism for pool retraction. The findings of this study are expected to be beneficial for the consequence estimation of cryogenic release scenarios and for the validation and improvement of source models.