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.

Sarit Kumar Das

Department of Mechanical Engineering

Nilesh Agrawal

Accidents

combustion

Computational fluid dynamics

Condensation

Enclosures

Heat transfer

heating

Hydrogen

MASS TRANSFER

Mixing

Nuclear reactors

Steam

BUOYANT JETS

DEFLAGRATION POTENTIAL

Heat and mass transfer

Hydrogen distribution

Hydrogen release

Mixing behaviors

NON-CONDENSABLE GAS

STEAM CONDENSATION

Steam condensers

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

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

Journal of Heat Transfer

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.

Heat Transfer Engineering

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

Studies on hydrogen distribution in the nuclear reactor containment and the effect of a distribution on subsequent combustion are important to nuclear safety. Contour plots, concentration profiles and ternary diagrams are routinely used to represent a distribution. The significance to safety has to be qualitatively inferred from these representations. Thus, there is a need to quantify distributions in terms of gross parameters that are important to safety. In the present study, four numerical indices are developed to obtain quantitative information on the mixing and deflagration potential of a distribution of hydrogen, steam and air. Two indices, namely, Average mole fraction and Non-uniformity index can be used to give the state of mixing of hydrogen in an enclosure at any instant of time. Similarly, the other two indices, namely, deflagration volume fraction and deflagration pressure ratio can be used to indicate the relative size of combustible cloud and the expected pressure rise in case of deflagration in the cloud at any instant of time. The significance and utility of the indices are brought forth through simple illustrations and numerical studies on the influence of steam condensation on hydrogen distributions. The indices depict the rate of mixing and changes in deflagration potential for the situations considered. Results form the simple studies show that the indices can give useful integral information for comparison of mixing and mitigation measures deployed in the nuclear reactor containment. © 2013 Elsevier Ltd. All rights reserved.

Nuclear Engineering and Design

Numerical indices for quantification of hydrogen mixing and deflagration potential in the nuclear reactor containment

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

Since the use of hydrogen as energy carrier is likely to increase in the future, the associated safety concerns have to be addressed. It is necessary that the mixing characteristics of hydrogen gas released into an enclosure be quantified with the help of numerical indices that qualitatively and quantitatively reflect the overall mixing process and hazard of formation of flammable cloud in the enclosure. Four indices meant to characterize mixing and flammability of hydrogen in enclosures, namely, Average mole fraction, Non-uniformity index, Deflagration Volume Fraction and Deflagration Pressure Ratio are proposed in this paper. Significance and utility of these indices in providing useful information on mixing and flammability have been demonstrated through numerical studies of hydrogen distribution in enclosures containing air. These indices can serve as useful tools in studies of hydrogen distribution in enclosures. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

International Journal of Hydrogen Energy

A method to characterize mixing and flammability of hydrogen-air mixtures in enclosures

Annals of Nuclear Energy

Lesson learned from the SARNET wall condensation benchmarks

Journal	Journal of Heat Transfer
Publisher	American Society of Mechanical Engineers (ASME)
ISSN	00221481
Open Access	No