Hydrogen generation during the progression of an accident in a nuclear reactor and its release into the containment comprise an important safety concern in the management of severe accidents in nuclear power plants. The distribution of hydrogen within the containment has important bearing on possibility, mode, and consequence of combustion in the containment. Hence, several small-and large-scale facilities have been built to study the distribution of released hydrogen. Further, several numerical studies and intercomparison exercises on hydrogen distribution have been carried out. The present review summarizes the experimental and numerical studies on hydrogen distribution and suggests opportunities for further studies. © 2015 Taylor and Francis Group, LLC.

Sarit Kumar Das

Department of Mechanical Engineering

Aneesh Prabhakar

Accidents

Hydrogen

Hydrogen production

MASS TRANSFER

Nuclear power plants

Nuclear reactors

EXPERIMENTAL AND NUMERICAL STUDIES

Heat and mass transfer

Hydrogen distribution

Hydrogen generations

INTERCOMPARISON EXERCISE

Reactor containment

SAFETY CONCERNS

Severe accident

Nuclear reactor accidents

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Hydrogen Distribution in Nuclear Reactor Containment During Accidents and Associated Heat and Mass Transfer Issues—A Review

Heat Transfer Engineering

In the present study, a systematic experimental investigation on the effect of a circular disk obstacle placed axi-symmetrically in the line of a vertical helium jet is presented. The obstacle is placed within the 2 m3 enclosure of AIHMS facility. The location of the obstacle and volume Richardson number have been varied parametrically and the results are compared with those of the free jet with obstacle. The experimental data shows that the obstacle enhances mixing near the obstacle, decreases transport of helium to upper regions of the enclosure and increases transport to lower regions of the enclosure. This effect decreases with increase in the distance between the obstacle and the jet exit. The effect is more pronounced at higher jet velocities i.e. at lower values of volume Richardson number. The experimental database presented can be used for validation of CFD models, grid independence studies, and gaining user experiences before complex problems on helium/hydrogen distribution in confined spaces are taken up. © 2018 Elsevier Ltd

Annals of Nuclear Energy

An experimental study on the effect of coaxial circular disk obstacle on helium jet distribution inside the unventilated enclosure of AIHMS facility

An experimental facility called the AIHMS facility has been installed and commissioned within the IIT Madras premises, to study the phenomenology of hydrogen distribution in confined spaces and generate experimental data for validation of CFD codes before further studies on hydrogen distribution and mitigation in nuclear reactor systems can be carried out. In the present article, experimental studies have been performed on the evolution of the helium stratified layer due to wall temperature induced natural convection. The base case is an isothermal release of helium within the test chamber. Subsequently, two cases are considered in which the wall temperature is above or below the gas temperature in the enclosure. Experimental data has been obtained for gas concentration at seven locations and temperatures at twenty locations within the enclosure. The results show that recirculation regions are formed near the walls. Cooler walls lead to favourable natural convection currents and promote rapid mixing of the stratified layer with lean gas mixture below. On the other hand, warmer walls lead to unfavourable natural convection currents that initially promote stratification and later on promote mixing at a slower rate. In either situation, the rate of mixing is faster than the isothermal case. Repeatability studies have been performed. © 2017 Elsevier B.V.

Nuclear Engineering and Design

Experimental investigations on the evolution of stratified layer of helium in the unventilated vertical cylindrical enclosure of AIHMS facility under wall temperature induced natural convection

Hydrogen is a highly flammable gas and accidental release in confined space can pose serious combustion hazards. Numerical studies are required to assess the formation of flammable hydrogen cloud within confined spaces. In the present study, numerical investigations on the release of helium and hydrogen gases as high-velocity jets and their subsequent distribution inside an unventilated cylindrical enclosure (AIHMS facility) has been carried out as a first step towards numerical studies on hydrogen distribution in confined spaces for safety assessments. Experimental data for jet release of helium at volume Richardson number 0.1 and subsequent distribution has been used as benchmark data. Sensitivity studies on the influence of grid sizes, time-steps and turbulence models are performed. The performance of the validated numerical model is evaluated using statistical performance parameters. Similarity relations are used to determine input parameters for hydrogen jet for corresponding experimental data with helium jets. Finally, the mixing and flammability aspects of hydrogen distribution inside the enclosure are studied using four numerical indices that quantify mixing and deflagration potential of a distribution. It is concluded that the helium experiments can be used for validation of numerical models for hydrogen safety studies and any one of the similarity relationships, viz., equal buoyancy, equal volumetric flow, or equal concentration can be used for assessing the behaviour of hydrogen release and distribution within confined spaces. © 2017 Hydrogen Energy Publications LLC

International Journal of Hydrogen Energy

Numerical modelling of isothermal release and distribution of helium and hydrogen gases inside the AIHMS cylindrical enclosure

Hydrogen release in confined spaces is an important safety issue, which is even more important in the context of severe accident in nuclear reactors. In severe accidents, hydrogen release is associated with release of steam and the condensation of steam on walls leads to increase in concentration of hydrogen in residual gas as well as condensation induced mixing. In the present paper, a model for falling film steam condensation in the presence of noncondensable gases is presented. The steam condensation model is incorporated into an in-house developed cfd code called hydrogen distribution simulator (HDS) and is used for hydrogen distribution studies. The validation of the CFD model with steam condensation against the experimental results from the CONAN facility is discussed. Subsequently, the model is applied to a typical release situation involving release of hydrogen and steam for some time and its distribution for a long time beyond it. The heat and mass transfer aspects of the problem are highlighted. It is seen that steam condensation has an important bearing on the distribution of hydrogen and the mixing behavior of gases in the enclosure. Copyright © 2015 by ASME.

Journal of Heat Transfer

Numerical Studies on Hydrogen Distribution in Enclosures in the Presence of Condensing Steam

Hydrogen deflagration in confined spaces is an important safety issue. The dispersion of a stratified layer of hydrogen due to molecular diffusion is studied. It represents an important class of problems related to long term behaviour of hydrogen release in confined spaces. Diffusion being a slow process, gives an upper bound on the time taken for the stratified layer to mix with air below. A method, based on four indices, namely, average mole fraction (of hydrogen), non-uniformity index, deflagration volume fraction and deflagration pressure ratio, developed recently by the authors, is used to provide vital temporal information on mixing of the stratified layer with air below and formation of flammable cloud in the enclosure. In the present paper, stratified layers of different thickness are considered and the temporal evolutions of the above indices are plotted against diffusion Fourier number. The results in non-dimensional form provide an upper bound of the time that would be required to form a uniform mixture and to attain a state with respect to deflagration potential for enclosures of different sizes. This estimate is an important input for planning mitigation measures before the accident and for post accident investigations. © 2013 Elsevier Ltd.

International Communications in Heat and Mass Transfer

A study on the scaling features for mixing and deflagration potential of stratified layer of hydrogen due to molecular diffusion

IAEA TECDOC 055 Outline

Simulation of helium release in the Battelle Model Containment facility using OpenFOAM

Detailed evaluation of safety injection tank effects on in-vessel severe accident progression in a small break LOCA without safety injection

How critical is turbulence modeling in gas distribution simulations of large-scale complex nuclear reactor containment?

Hydrogen distribution in nuclear reactor containment during accidents and associated heat and mass transfer issues-A review

Journal	Data powered by TypesetHeat Transfer Engineering
Publisher	Data powered by TypesetTaylor and Francis Ltd.
ISSN	01457632
Open Access	No