With the development of the liquid hydrogen as an energy vector, some questions about its storage safety have to be addressed. Cryogenic tanks are thermally insulated with vacuum and possibly multi-layer insulation (MLI) blankets and the loss of vacuum (LOVA) is a classical accident to be considered. The key parameter to perform the safety device sizing is the thermal flux during this kind of LOVA events. In a cryostat without MLI, Belonogov [1] measured a heat flux close to the hydrogen critical flux at a pressure just above the atmospheric pressure (9.4 W/cm²) whereas following the standard ISO 21013-3 norm the thermal flux to be used is for the result of liquid helium tank LOVA experiments performed by KIT [2]. Without MLI the thermal flux with liquid helium is 3.8 W/cm² in contradiction with the Belonogov measurement. Bibliographic review has demonstrated that available quantitative data for hydrogen are poor, the safety design sizing is then complicated. Additionally, in the MLI-equipped case, other works [3] have shown that the values indicated in the same standard with MLI seems optimistic.
In order to have a better understanding of these issues and to obtain experimental data on a broader range of storage conditions the project ESKHYMO (Enhance Safety Knowledge for Hydrogen Measurements/Modelling in cryOgenic phase) funded by France 2030 [4], has been proposed by CEA and other academic and industrial partners to work on safety questions linked to liquid hydrogen usage. Within this project a dedicate and fully instrumented liquid hydrogen test bench for the thermal flux measurement during vacuum break has been manufactured. The commissioning with liquid nitrogen is presented.
The design of the test bench has been presented during ECD 2025. This new presentation will describe the commissioning of the installation. It has been performed with liquid nitrogen for safety reasons. One drawback of this fluid compared with hydrogen is its higher temperature that will not allow the solidification and condensation of the nitrogen used to loss the vacuum (relevant accident). To avoid this point, the vacuum has been loss with argon. Around atmospheric pressure, fusion and liquefaction temperatures are close which means that the physical phenomena are not exactly the same. Solid phase will certainly have a larger impact. On the other hand, condensation and sublimation will be present to transfer important quantity of power to the fluid. The goal is not to be fully relevant but to allow a safe commissioning of all the automatic procedures with some neutral gases and then to avoid any accident until the procedure are fully developed.
[1] Belonogov, A.V., et al. Heat transfer with a breakdown of the insulating vacuum in vessels with cryogenic liquids. Chem Petrol Eng 14, 243–245 (1978). https://doi.org/10.1007/BF01143860
[2] W. Lehmann et G. Zahn, « Safety Aspects for LHe Cryostats and LHe Transport Containers» in 7th Internat. Cryogenic Engineering Conf., ICEC 7, London, July 4-7, 1978
[3] C. Zoller, « Experimental Investigation and Modelling of Incidents in Liquid Helium Cryostats, » PhD thesis., KIT, Karlsruhe / Karlsruher Institut für Technologie (KIT), 2018. doi : 10.5445/IR/1000082999.
[4 ] https://www.pepr-hydrogene.fr/projets/eskhymo/

Keywords
hydrogen|safety|cryogenic storage