Transient analysis of coupled high temperature nuclear reactor to a thermochemical hydrogen plant

Pergamon Press ; Elsevier Science Ltd 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.14

A very high temperature reactor (VHTR) has been considered for generation of hydrogen by water-splitting through thermochemical processes using process heat. The development of this technology requires understanding of the coupled behavior of VHTR and the hydrogen generation plants and key safety issues during transients. A system level modeling of the coupled VHTR and sulfur-iodine hydrogen generation process is carried out where the thermal and neutronic models of the VHTR and the chemical models of the sulfur-iodine cycle were developed and benchmarked with available experimental data, models and simulation codes. Transient analysis of the possible accidents emanating either from VHTR or hydrogen plants was carried out. The results indicate that on VHTR side the response of the reactor is affected by the temperature feedback and xenon buildup feedback. On the hydrogen plant side the slowest reaction controlled the speed of the overall response of the chemical plant.

Numerical simulation of bubble formation and condensation of steam air mixture injected in subcooled pool

Qu, Xiaohang,Revankar, Shripad T.,Tian, Maocheng Elsevier 2017 Nuclear engineering and design Vol.320 No.-

<P><B>Abstract</B></P> <P>Bubble formation and condensation of steam-air mixture vertically injected in a subcooled water pool was simulated, combining thermal phase change model into the two continuous phase free surface model of ANSYS CFX 17.1. Continuous surface force model was used to calculate surface tension force and the influence of non-condensable gas was accounted for by component transportation equation and assumption of interface temperature equal to saturation temperature at local partial steam pressure. The thermal phase change model includes an experimental correlation for liquid side sensible heat transfer. Based on available experiment data from literatures, singular pure steam bubble and steam-mixture bubble in a pool were first simulated to see the predictability of the proposed method and then, the same method was applied to the bubble formation, detachment and condensation process of injected steam air mixture from a nozzle. Bubble dimeter, water subcooling and non-condensable gas concentration studied range from 4.9mm to 50mm, 12K to 40K, and 0 to 31.5% respectively. The results of the computations indicate that the present method can predict very well the bubble formation and condensation both for pure steam case and with non-condensable gas.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bubble formation and condensation process injected from a nozzle is studied numerically. </LI> <LI> Euler-Euler two-fluid free surface model and species model from are coupled together. </LI> <LI> Influence of non-condensable gas is considered. </LI> <LI> Bubble shape variation histories are shown in comparison with experiments. </LI> </UL> </P>

Hydrodynamic Characterization of Nickel Metal Foam, Part 2: Effects of Pore Structure and Permeability

Miwa, Shuichiro,Revankar, Shripad T. Springer-Verlag 2011 Transport in porous media Vol.89 No.3

An endothermic chemical process facility coupled to a high temperature reactor. Part II: Transient simulation of accident scenarios within the chemical plant

Brown, N.R.,Revankar, S.T. North-Holland Pub. Co 2012 Nuclear engineering and design Vol.246 No.-

Hydrogen generation using a high temperature nuclear reactor as a thermal driving vector is a promising future option for energy carrier production. In this scheme, the heat from the nuclear reactor drives an endothermic water-splitting plant, via coupling, through an intermediate heat exchanger. Transient study of the operational or accident events within the coupled plant is largely absent from the literature. In this paper, seven quantitative transient case studies are analyzed. The case studies consist of: (1) feed flow failure from one section of the chemical plant to another with an accompanying parametric study of the temperature in an individual reaction chamber, (2) product flow failure (recycle) within the chemical plant, (3) rupture or explosion within the chemical plant, (4) nuclear reactor helium inlet overcooling due to a process holding tank failure, (5) helium inlet overcooling as an anticipated transient without emergency nuclear reactor shutdown, (6) total failure of the chemical plant, (7) control rod insertion in the nuclear reactor. Various parametric studies based on the magnitude of the events were also performed. The only chemical plant initiated events that caused a positive power excursion in the nuclear reactor were helium-inlet overcoolings due to process holding tank failures or reaction chamber ruptures. Even for a severe sustained overcooling, the calculated maximum fuel temperatures in the nuclear reactor were 200K below the design basis limit. The qualitative basis for the case studies and the analysis models are summarized in part I of this paper.

A review of catalytic sulfur (VI) oxide decomposition experiments

Brown, N.R.,Revankar, S.T. Pergamon Press ; Elsevier Science Ltd 2012 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.37 No.3

Sulfur (VI) oxide, also known as sulfur trioxide or SO<SUB>3</SUB>, decomposition is an oxygen-generating decomposition reaction that proceeds in the gaseous system SO<SUB>3</SUB>/SO<SUB>2</SUB>/O<SUB>2</SUB>/H<SUB>2</SUB>O at temperatures above 500 K. Maximum decomposition yield of SO<SUB>3</SUB> to SO<SUB>2</SUB> and O<SUB>2</SUB> is best achieved at temperatures of over 1000 K with an appropriate catalyst. According to the literature, noble metals and some transition metal oxides are highly effective catalysts in the laboratory environment. Sulfur (VI) oxide decomposition is the energetic and temperature limiting step of several endothermic hydrogen generating chemical process heat plants. In particular, the General Atomics Sulfur Iodine cycle and the Westinghouse Hybrid Sulfur cycle are candidates for thermal coupling to a high temperature nuclear reactor. Therefore the sulfur (VI) oxide decomposition reaction is a potential heat sink for a high temperature nuclear reactor. Thus, optimization of catalyst selection is required, both for operational efficiency and safety. In this paper, reaction mechanisms and catalyst composition for sulfur (VI) oxide decomposition are reviewed. Chemical kinetics data from previous sulfur (VI) oxide decomposition experiments are extracted from archival journal papers or other open literature. The available experimental database suggests that Pt-based catalysts have the highest stable activity among the noble metals and Fe<SUB>2</SUB>O<SUB>3</SUB>-based catalysts have the highest stable activity among the transition metal oxides. The decomposition temperature of the corresponding metal sulfate dictates the catalytic activity of a given transition metal oxide.

Buoyant jet and two-phase jet-plume modeling for application to large water pools

Norman, Timothy L.,Revankar, Shripad T. Elsevier 2011 Nuclear engineering and design Vol.241 No.5

<P><B>Highlights</B></P><P>► A two-phase jet-plume model was developed to predict pool thermal response, pool surface temperature and consequently the pool cover gas pressure in enclosed spaces such as nuclear reactor wetwell. ► The jet-plume half-width, centerline velocity and temperature along the axis defining the plume's trajectory were solved as variables along the path. ► The pool surface temperature prediction is comparable to experimental data within 0.5°C.</P> <P><B>Abstract</B></P><P>Models of a single-phase liquid-into-liquid buoyant jet and a two-phase vapor-into-liquid turbulent jet-plume injected in horizontal orientation were developed for analyzing the dynamics of the mixing characteristics and thermal response for shallow submergence of the source in large pools. These models were developed from the Reynolds averaged Navier–Stokes equations in the cylindrical system for steady axisymmetric flow and incorporated the integral plume theory. The bases for the general assumptions such as self-similarity and use of Gaussian profiles to represent the velocity field across the effluent cross-section are examined. Subroutines were developed to reproduce the governing differential equations formulated from the continuity, momentum and conservation of buoyancy or energy equations which treats the jet-plume's half-width, velocity and temperature as variables and seek solutions of these variables along the jet-plume trajectory. Information on empirical closure relations obtained from experimental data such as the coefficient-of-entrainment, bubble slip velocity, momentum amplification factor, and plume spread-ratios for buoyancy and density-defect which are available for adiabatic cases were applied to the case of steam-into-water. Solutions were obtained without cross-flow in a linearly stratified ambient and then with cross-flow in a homogeneously mixed ambient for the single-phase formulation that represents a complete condensation scenario of a buoyant jet. The model was finally extended to the turbulent two-phase jet-plume case and the results were compared to available jet-plume pool condensation data. The analysis and results proved to be comparable to experimental data in predicting the pool surface temperature to within 0.5°C, however, temperature fluctuations along the jet-plume path were not adequately captured by the model since an oscillating input component was not incorporated in the model formulation; indeed the pool surface temperature proved to be of higher importance, which was adequately captured by the model.</P>

The credit analysis of recycling beryllium and uranium in BeO-UO2 nuclear fuel

Kim, S.,Ko, W.,Zhou, W.,Revankar, S.T.,Chung, Y.,Bang, S. Atomic Energy Society of Japan 2012 Journal of nuclear science and technology Vol.49 No.3

Transient simulation of an endothermic chemical process facility coupled to a high temperature reactor: Model development and validation

Brown, N.R.,Seker, V.,Revankar, S.T.,Downar, T.J. North-Holland Pub. Co 2012 Nuclear engineering and design Vol.248 No.-

A high temperature reactor (HTR) is a candidate to drive high temperature water-splitting using process heat. While both high temperature nuclear reactors and hydrogen generation plants have high individual degrees of development, study of the coupled plant is lacking. Particularly absent are considerations of the transient behavior of the coupled plant, as well as studies of the safety of the overall plant. The aim of this document is to contribute knowledge to the effort of nuclear hydrogen generation. In particular, this study regards identification of safety issues in the coupled plant and the transient modeling of some leading candidates for implementation in the Nuclear Hydrogen Initiative (NHI). The Sulfur Iodine (SI) and Hybrid Sulfur (HyS) cycles are considered as candidate hydrogen generation schemes. Three thermodynamically derived chemical reaction chamber models are coupled to a well-known reference design of a high temperature nuclear reactor. These chemical reaction chamber models have several dimensions of validation, including detailed steady state flowsheets, integrated loop test data, and bench scale chemical kinetics. The models and coupling scheme are presented here, as well as a transient test case initiated within the chemical plant. The 50% feed flow failure within the chemical plant results in a slow loss-of-heat sink (LOHS) accident in the nuclear reactor. Due to the temperature feedback within the reactor core the nuclear reactor partially shuts down over 1500s. Two distinct regions are identified within the coupled plant response: (1) immediate LOHS due to the loss of the sulfuric acid decomposition section and (2) continuing slow LOHS due to the chemical species cascade throughout the plant.

Alternate metal framework designs for the metal ceramic prosthesis to enhance the esthetics

Naina Vilas Vernekar,Prithviraj Kallahalla Jagadish,Srinivasan Diwakar,Ramesh Nadgir,Manjunatha Revankar Krishnarao 대한치과보철학회 2011 The Journal of Advanced Prosthodontics Vol.3 No.3

PURPOSE The objective of the present study was to evaluate the effect of five different metal framework designs on the fracture resistance of the metal-ceramic restorations. MATERIALS AND METHODS For the purpose of this study, the central incisor tooth was prepared, and the metal analogue of it and a master die were fabricated. The counter die with the 0.5 mm clearance was used for fabricating the wax patterns for the metal copings. The metal copings with five different metal framework designs were designed from Group 1 to 5. Group 1 with the metal collar, Group 2, 3, 4 and 5 with 0 mm, 0.5 mm, 1 mm and 1.5 mm cervical metal reduction respectively were fabricated. Total of fifty metal ceramic crown samples were fabricated. The fracture resistance was evaluated with the Universal Testing Machine (Instron model No 1011, UK). The basic data was subjected to statistical analysis by ANOVA and Student's t-test. RESULTS Results revealed that the fracture resistance ranged from 651.2 to 993.6 N/m2. Group 1 showed the maximum and Group 5 showed the least value. CONCLUSION The maximum load required to fracture the test specimens even in the groups without the metal collar was found to be exceeding the occlusal forces. Therefore, the metal frameworks with 0.5 mm and 1 mm short of the finish line are recommended for anterior metal ceramic restoration having adequate fracture resistance.

Experimental investigation on the propagation characteristics of pressure oscillation in direct contact condensation with low mass flux steam jet

Qiu, Binbin,Yang, Qingchuan,Yan, Junjie,li, Gen,Revankar, Shripad T. Elsevier 2017 Experimental thermal and fluid science Vol.88 No.-

<P><B>Abstract</B></P> <P>The propagation characteristics of pressure oscillation in direct contact condensation with low mass flux steam jet have been investigated experimentally. Steam is injected into subcooled water at one atmosphere pressure with steam mass flux and water temperature range of 186–272kg/(m<SUP>2</SUP> s) and 293–343K. The pressure oscillation propagates in the form of wave with stable dominant frequency, however the wave intensity attenuates with the increasing distance from the oscillation source. The root mean square of pressure wave <I>p</I> <SUB>rms</SUB> attenuates rapidly with the increasing dimensionless radial distance from the nozzle exit. At about dimensionless radial distance <I>R</I> =100, the <I>p</I> <SUB>rms</SUB> is attenuated by about 90%. Although the dominant frequency of the pressure oscillation is constant during the propagation, after <I>R</I> =100, there will be not enough energy for the pressure oscillation to resonate with relevant equipment. A correlation equation to calculate the root mean square of pressure oscillation along the radial distance is given. The prediction errors are within ±30% compared with the experimental data.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The pressure oscillation propagates in the form of wave. </LI> <LI> In the propagation process, the frequency remains the same but the intensity attenuates. </LI> <LI> A correlation to calculate the <I>p</I> <SUB>rms</SUB> along the radial distance is given. </LI> <LI> At about R=100, the <I>p</I> <SUB>rms</SUB> is attenuated by about 90% and most of the energy is dissipated. </LI> </UL> </P>