Ernst-Arndt Reinecke

Hydrogen is gaining global attention as a clean energy carrier due to its potential to contribute to carbon neutrality. Among various forms, liquefied hydrogen (LH2) offers significant advantages in energy density and storage efficiency. In contrast, when LH2 leaks, extremely low-temperature and high-velocity hydrogen is released, posing serious safety challenges. One promising safety measure is the passive autocatalytic recombiner (PAR), which catalytically converts leaking hydrogen and atmospheric oxygen into water without external power. This study aims to enhance the safety performance of PAR systems. To achieve this, the thermal behavior of multilayer hydrogen oxidation catalysts was investigated under demanding forced-flow hydrogen release conditions at room temperature. Since hydrogen oxidation is a strongly exothermic reaction, localized reactions can cause rapid temperature increases, potentially leading to self-ignition. Here, self-ignition is also called auto-ignition or spontaneous ignition. At temperatures above 500°C, ignition occurs without an external source of ignition, such as a flame or spark. To mitigate this risk, it is essential to spatially distribute the reaction and control heat generation. As a countermeasure, catalyst configurations were designed with variations in precious metal loading and material properties across layers. The rear layer was loaded with a higher concentration of precious metals to respond to low hydrogen concentrations during the early stages. In contrast, the front layer was designed with reduced precious metal content or iron-based materials, allowing it to react only under higher hydrogen concentrations. Configurations where Fe was selectively placed in the middle or front catalysts showed favorable behavior. The Fe was activated under high-temperature conditions by receiving reaction heat from the rear layer. This contributed to sustaining the reaction and controlling heat generation, even without using precious metals. Furthermore, in configurations where Pt and Fe were supported sequentially and separated as distinct phases, Fe effectively acted as a reaction promoter. This structure facilitated stepwise reaction progress and contributed to better heat distribution. These findings indicate that spatial control of reactivity and appropriate material selection are key to preventing thermal runaway.

As the attention to using hydrogen as a potential energy storage medium for power generation and mobility increases, hydrogen production, storage, and transportation safety should be considered. For instance, hydrogen’s extreme physical and chemical properties and the wide range of flammable concentrations raise many concerns about the current safety measures in processing other flammable gases. Hydrogen cloud accumulation in the case of leakage in confined spaces can lead to reaching the hydrogen lower flammability limit (LFL) within seconds if the hydrogen is not properly evacuated from the space. At Jülich Research Centre, hydrogen mixed with natural gas is foreseen to be used as a fuel for the central heating system of the campus. In this work, the release, dispersion, formation, and spread of the hydrogen cloud in the case of hydrogen leakage inside the central utility building of the campus are numerically simulated using the OpenFOAM-based containmentFOAM CFD codes. Additionally, different ventilation scenarios are simulated to investigate the behavior of the hydrogen cloud. The results show that locating exhaust openings close to the ceiling and the potential leakage source can be the most effective way to safely evacuate hydrogen from the building. Additionally, locating the exhaust outlets near the ceiling can decrease the combustible cloud volume by more than 25% compared to side openings far below the ceiling. Also, hydrogen concentrations can reach the LFL in case of improper forced ventilation after only 8 s, while it does not exceed 0.15% in the case of natural ventilation under certain conditions. The results of this work show the significant effect of locating exhaust outlets near the ceiling and the importance of natural ventilation to mitigate the effects of hydrogen leakage. The approach illustrated in this study can be used to study hydrogen dispersion in closed buildings in case of leakage and the proper design of the ventilation outlets for closed spaces with hydrogen systems.

Hydrogen can play a key role as short- and long-term energy storage solution in an energy grid with fluctuating renewable sources. In technologies using hydrogen, there is always the risk of unintended leakages due to the low density of gaseous hydrogen. The risk becomes specifically high in confined areas where leaking hydrogen could easily mix with air and form flammable gas mixtures. In the maritime transportation, large and congested geometries can be subject to accumulation of hydrogen. A mitigation measure for areas where venting is insufficient or even impossible is the installation of catalytic recombiners. The operational behavior can be described with numerical models which are required to optimize the location and to assess the efficiency of the mitigation solution. In the present study, we established an experimental procedure in the REKO-4 facility, a 5.5 m3 vessel, to determine the recombination rate obtained from a recombiner. Based on the experimental data, an engineering correlation was developed to be used for simulations in safety assessments.

International projects study the safety aspects of the storage and long-distance transportation of liquid hydrogen at large scales. Catalytic recombiners, which are today key elements of hydrogen risk mitigation in nuclear power plants, could become an efficient safety device to prevent flammable gas mixtures after liquid hydrogen leakages in closed rooms. This study tackles fundamental questions about the operational behavior of typical recombiner catalysts related to the conditions of the start-up and the termination of the catalytic reaction. For this purpose, small-scale catalyst sheets with coatings containing either platinum or palladium as active materials were exposed to gas mixtures of air and hydrogen of up to 4 vol.% at temperatures between −50 °C and 20 °C. Both platinum and palladium showed variation to performance and had stochastic results. Overall, the initialized platinum catalyst was better than the palladium. The experimental results show that the transfer of the recombiner technology from its current application is not easily possible.

As the attention to using hydrogen as a potential energy storage medium for power generation and mobility increases, hydrogen production, storage, and transportation safety should be considered. For instance, hydrogen's extreme physical and chemical properties and the wide range of flammable concentrations raise many concerns about the current safety measures in processing other flammable gases. Hydrogen cloud accumulation in case of leakage in confined spaces can lead to reaching the hydrogen lower flammability limit (LFL) within seconds if the hydrogen is not properly evacuated from space. At Jülich Research Centre, hydrogen mixed with natural gas is foreseen to be used as a fuel for the central heating system of the campus. In this work, the release, dispersion, formation, and spread of the hydrogen cloud in case of hydrogen leakage inside the central utility building of the campus are numerically simulated using the OpenFOAM-based containmentFOAM CFD codes. Additionally, different ventilation scenarios are simulated to investigate the behavior of the hydrogen cloud. The results show that locating exhaust openings close to the ceiling and the potential leakage source can be the most effective way to evacuate hydrogen from the building safely. Improper placement of the exhaust outlets can significantly decrease the effectiveness of the forced ventilation system, even lower than the effectiveness of natural ones. These results can be used as a guide to the locations of the ventilation outlets for closed spaces with hydrogen systems. Also, these simulations can be used in the future to study the effect of hydrogen sensor locations on the response of the ventilation system and, accordingly, on the hydrogen-combustible cloud volume inside the space.

The molten corium-concrete interaction in the ex-vessel phase of a severe accident ina light water reactor is a source of significant amounts of gaseous products includingcarbon monoxide. The European project AMHYCO addresses open issues related tothe understanding of the impact of carbon monoxide on safety-relevant accidentphenomena like combustion and on hydrogen mitigation measures. In order to supportthe simulation of accident sequences and the assessment of safety measures, Task3.2 aimed to provide realistic models considering the influence of carbon monoxide onthe operating behavior of passive auto-catalytic recombiners. The work programincluded conducting new experiments, analyzing existing experimental data, andfurther developing numerical models.The experimental program performed within Task 3.2 involved the REKO facilities atResearch Center Jülich (FZJ) to study the impact of predicted accident atmospheresincluding oxygen-lean mixtures and the presence of carbon monoxide on the hydrogenrecombination efficiency of different generic catalysts. More specifically, criteria werederived to predict the atmospheric conditions leading to catalyst poisoning. At thesame time, a unified database including selected datasets from the variousOECD/NEA-THAI projects was developed. The available experimental data were usedto further advance numerical models such as the manufacturer’s engineeringcorrelation for Framatome PARs as well as the scientific codes SPARK (IRSN),PARUPM (UPM), and REKO-DIREKT (FZJ).