France

The highly combustible nature of hydrogen poses a great hazard creating a number of problems with its safety and handling. As a part of safety studies related to the use of hydrogen in a confined environment it is extremely important to have a good knowledge of the dispersion mechanism.<br/>The present work investigates the concentration field and flammability envelope from a small scale leak. The hydrogen is released into a 0.47 m × 0.33 m x 0.20 m enclosure designed as a 1/15 – scale model of a room in a nuclear facility. The performed tests evaluates the influence of the initial conditions at the leakage source on the dispersion and mixing characteristics in a confined environment. The role of the leak location and the presence of obstacles are also analyzed. Throughout the test during the release and the subsequent dispersion phase temporal profiles of hydrogen concentration are measured using thermal conductivity gauges within the enclosure. In addition the BOS (Background Oriented Schlieren) technique is used to visualise the cloud evolution inside the enclosure. These instruments allow the observation and quantification of the stratification effects.

To define a strategy of mitigation for containerized hydrogen systems (fuel cells for example) against explosion the main characteristics of flammable atmosphere (size concentration turbulence…) shall be well-known. This article presents an experimental study on accidental hydrogen releases and dispersion into an enclosure of 4 m3 (2 m x 2 m x 1 m). Different release points are studied: two circular releases of 1 and 3 mm and a system to create ring-shaped releases. The releases are operated with a pressure between 10 and 40 bars in order to be close to the process conditions. Different positions of the release inside the enclosure i.e. centred on the floor or along a wall are also studied. A specific effort is made to characterize the turbulence in the enclosure during the releases. The objectives of the experimental study are to understand and quantify the mechanisms of formation of the explosive atmosphere taking into account the geometry and position of the release point and the confinement. Those experimental data are analyzed and compared with existing models and could bring some new elements to improve them.

In a fuel cell electric vehicle (FCEV) powered by a metal hydride tank the performance of the tank is an indicator of the overall health status which is used to predict its behaviour and make appropriate energy management decisions. The aim of this paper is to investigate how to evaluate the effects of charge/discharge cycles on the performance of a commercial automotive metal hydride hydrogen storage system applied to a real FCEV. For this purpose a mathematical model is proposed based on uncertain physical parameters that are identified using the stochastic particle swarm optimisation (PSO) algorithm combined with experimental measurements. The variation of these parameters allows an assessment of the degradation level of the tank’s performance on both the quantitative and qualitative aspects. Simulated results derived from the proposed model and experimental measurements were in good agreement with a maximum relative error of less than 2%. The validated model was used to establish the correlations between the observed degradations in a hydride tank recovered from a real FCEV. The results obtained show that it is possible to predict tank degradations by developing laws of variation of these parameters as a function of the real conditions of the use of the FCEV (number of charging/discharging cycles pressures mass flow rates temperatures).

Nanoporous carbons remain the most promising candidates for effective hydrogen storage by physisorption in currently foreseen hydrogen-based scenarios of the world’s energy future. An optimal sorbent meeting the current technological requirement has not been developed yet. Here we first review the storage limitations of currently available nanoporous carbons then we discuss possible ways to improve their storage performance. We focus on two fundamental parameters determining the storage (the surface accessible for adsorption and hydrogen adsorption energy). We define numerically the values nanoporous carbons have to show to satisfy mobile application requirements at pressures lower than 120 bar. Possible necessary modifications of the topology and chemical compositions of carbon nanostructures are proposed and discussed. We indicate that pore wall fragmentation (nano-size graphene scaffolds) is a partial solution only and chemical modifications of the carbon pore walls are required. The positive effects (and their limits) of the carbon substitutions by B and Be atoms are described. The experimental ‘proof of concept’ of the proposed strategies is also presented. We show that boron substituted nanoporous carbons prepared by a simple arc-discharge technique show a hydrogen adsorption energy twice as high as their pure carbon analogs. These preliminary results justify the continuation of the joint experimental and numerical research effort in this field.

Hydrogen energy is a very attractive option in dealing with the existing energy crisis. For the development of a hydrogen energy economy hydrogen storage technology must be improved to over the storage limitations. Compared with traditional hydrogen storage technology the prospect of hydrogen storage materials is broader. Among all types of hydrogen storage materials solid hydrogen storage materials are most promising and have the most safety security. Solid hydrogen storage materials include high surface area physical adsorption materials and interstitial and non-interstitial hydrides. Among them interstitial hydrides also called intermetallic hydrides are hydrides formed by transition metals or their alloys. The main alloy types are A2B AB AB2 AB3 A2B7 AB5 and BCC. A is a hydride that easily forms metal (such as Ti V Zr and Y) while B is a non-hydride forming metal (such as Cr Mn and Fe). The development of intermetallic compounds as hydrogen storage materials is very attractive because their volumetric capacity is much higher (80–160 kgH2m−3 ) than the gaseous storage method and the liquid storage method in a cryogenic tank (40 and 71 kgH2m−3 ). Additionally for hydrogen absorption and desorption reactions the environmental requirements are lower than that of physical adsorption materials (ultra-low temperature) and the simplicity of the procedure is higher than that of non-interstitial hydrogen storage materials (multiple steps and a complex catalyst). In addition there are abundant raw materials and diverse ingredients. For the synthesis and optimization of intermetallic compounds in addition to traditional melting methods mechanical alloying is a very important synthesis method which has a unique synthesis mechanism and advantages. This review focuses on the application of mechanical alloying methods in the field of solid hydrogen storage materials.

Steam methane reforming with CO2 capture (blue hydrogen) and water electrolysis based on renewable electricity (green hydrogen) are commonly assumed to be the main supply options in a future hydrogen economy. However another promising method is emerging in the form of natural gas pyrolysis (turquoise hydrogen) with pure carbon as a valuable by-product. To better understand the potential of turquoise hydrogen this study presents a techno-economic assessment of a molten salt pyrolysis process. Results show that moderate reactor pressures around 12 bar are optimal and that reactor size must be limited by accepting reactor performance well below the thermodynamic equilibrium. Despite this challenge stemming from slow reaction rates the simplicity of the molten salt pyrolysis process delivers high efficiencies and promising economics. In the long-term carbon could be produced for 200–300 €/ton granting access to high-volume markets in the metallurgical and chemical process industries. Such a scenario makes turquoise hydrogen a promising alternative to blue hydrogen in regions with public resistance to CO2 transport and storage. In the medium-term expensive first-of-a-kind plants could produce carbon around 400 €/ton if hydrogen prices are set by conventional blue hydrogen production. Pure carbon at this cost level can access smaller high-value markets such as carbon anodes and graphite ensuring profitable operation even for first movers. In conclusion the economic potential of molten salt pyrolysis is high and further demonstration and scale-up efforts are strongly recommended.

Numerical  simulations  have  been  conducted  for  LH2   massive  releases  and  the  subsequent atmospheric dispersion using an in-house modified version of the open source computational fluid dynamics (CFD) code OpenFOAM. A conjugate heat transfer model has been added for heat  transfer   between  the  released  LH2   and  the  ground.  Appropriate  interface  boundary conditions  are   applied  to  ensure  the continuities  of  temperature  and  heat  fluxes.  The significant temperature difference between the cryogenic hydrogen and the ground means that the released LH2 will instantly enter in a boiling state resulting in a hydrogen- air gaseous cloud  which  will   initially  behave  like  a dense  gas.  Numerical  predictions  have  been conducted  for  the   subsequent  atmospheric  dispersion  of  the  vaporized  LH2   for  a series  of release scenarios - with and without retention pits - to limit the horizontal spread of the LH2 on the ground. The considered cases included the instantaneous release of 1 10 and 50 tons of LH2   under  neutral   (D)  and  stable  (F)  weather  conditions.  More  specifically  3F  and  5D conditions were simulated with the former representing stable weather conditions under wind speed  of  3  m/s  at   10  m  above  the  ground  and  the  later  corresponding  to  neutral  weather conditions under 5 m/s wind speed (10 m above the ground). Specific numerical tests have also been conducted for selected scenarios under different ambient temperatures from 233 up to 313 K. According to the current study although the retention pit can extend the dispersion time it can significantly reduce the extent of hazards due to much smaller cloud size within both the flammability and explosion limits. While the former has negative impact on safety the  later  is  beneficial.  The   use  of  retention  pit  should  hence  be  considered  with  caution  in practical applications.

This paper deals with two main issues regarding the specific energy consumption in an electrolyzer (i.e. the Faraday efficiency and the converter topology). The first aspect is addressed using a multistack configuration of proton exchange membrane (PEM) electrolyzers supplied by a wind turbine conversion system (WTCS). This approach is based on the modeling of the wind turbine and the electrolyzers. The WTCS and the electrolyzers are interfaced through a stacked interleaved DC–DC buck converter (SIBC) due to its benefits for this application in terms of the output current ripple and reliability. This converter is controlled so that it can offer dynamic behavior that is faster than the wind turbine avoiding overvoltage during transients which could damage the PEM electrolyzers. The SIBC is designed to be connected in array configuration (i.e. parallel architecture) so that each converter operates at its maximum efficiency. To assess the performance of the power management strategy experimental tests were carried out. The reported results demonstrate the correct behavior of the system during transient operation.

Diesel generators are currently used as an off-grid solution for backup power but this causes CO2 and GHG emissions noise emissions and the negative effects of the volatile diesel market influencing operating costs. Green hydrogen production by means of water electrolysis has been proposed as a feasible solution to fill the gaps between demand and production the main handicaps of using exclusively renewable energy in isolated applications. This manuscript presents a business case of an off-grid hydrogen production by electrolysis applied to the electrification of isolated sites. This study is part of the European Ely4off project (n◦ 700359). Under certain techno-economic hypothesis four different system configurations supplied exclusively by photovoltaic are compared to find the optimal Levelized Cost of Electricity (LCoE): photovoltaic-batteries photovoltaic-hydrogen-batteries photovoltaic-diesel generator and diesel generator; the influence of the location and the impact of different consumptions profiles is explored. Several simulations developed through specific modeling software are carried out and discussed. The main finding is that diesel-based systems still allow lower costs than any other solution although hydrogen-based solutions can compete with other technologies under certain conditions.

During the course of a severe accident in a light water nuclear reactor large amounts of hydrogen can be generated and released into the containment during reactor core degradation. Additional burnable gases [hydrogen (H2) and carbon monoxide (CO)] may be released into the containment in the corium/concrete interaction. This could subsequently raise a combustion hazard. As the Fukushima accidents revealed hydrogen combustion can cause high pressure spikes that could challenge the reactor buildings and lead to failure of the surrounding buildings. To prevent the gas explosion hazard most mitigation strategies adopted by European countries are based on the implementation of passive autocatalytic recombiners (PARs). Studies of representative accident sequences indicate that despite the installation of PARs it is difficult to prevent at all times and locations the formation of a combustible mixture that potentially leads to local flame acceleration. Complementary research and development (R&D) projects were recently launched to understand better the phenomena associated with the combustion hazard and to address the issues highlighted after the Fukushima Daiichi events such as explosion hazard in the venting system and the potential flammable mixture migration into spaces beyond the primary containment. The expected results will be used to improve the modeling tools and methodology for hydrogen risk assessment and severe accident management guidelines. The present paper aims to present the methodology adopted by Institut de Radioprotection et de Suˆ rete Nucleaire to assess hydrogen risk in nuclear power plants in particular French nuclear power plants the open issues and the ongoing R&D programs related to hydrogen distribution mitigation and combustion.