Papers by Shripad Revankar
International Journal of Nuclear Energy, 2014
Small fraction of high conductivity BeO in UO2 fuel significantly improves thermal conductivity a... more Small fraction of high conductivity BeO in UO2 fuel significantly improves thermal conductivity and also affects the overall performance of the fuel during steady state operation and during transients. In this study, performance of UO2-BeO composite under transient conditions such as loss of coolant accident (LOCA), using FRAPTRAN (fuel rod analysis program transient), was carried out. The subroutines in FRAPTRAN code that calculate key thermophysical properties such as thermal conductivity, specific heat capacity, and specific enthalpy were modified to account for the presence of the BeO in UO2. The fuel performance parameters like gas gap pressure, energy stored in fuel, and temperature profiles were studied. The simulation results showed reductions in fuel centerline temperatures and lower temperature drop across fuel rod cross-section under normal fuel operations. It was observed that there was reduction in gas gap pressure and energy stored in fuel. Transient conditions involvi...
Effects of Tube Diameter, Length and Tube Numbers on Condensation of Steam in Vertical Tube Condenser
Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C, 2009
A heat and mass analogy study was performed for the steam condensation in a vertical tube where s... more A heat and mass analogy study was performed for the steam condensation in a vertical tube where steam is completely condensed. In the analysis a single tube, tube bundle with four tubes and two different diameter tubes were considered. The two condensing tubes of same height (0.9m) but different inside diameters, 26.6mm and 52.5mm, were used whereas the tube bundle was made of four tubes of height 1.8 m and 52.5 mm diameter. The results showed that the operating pressure is uniquely determined by inlet steam flow rate for the complete condensation. The condensation heat transfer rate increases and the condensation heat transfer coefficient decreases with the system pressure. The condensation heat transfer coefficients (HTC) were obtained as function various parameters such as different primary pressure (150–450 kPa) and inlet steam flow rate, single tube and tube bundle and tube diameters. Comparison with experimental condensation rates for single tube of 26.6 mm and 52.5 mm and four tube bundle of tube diameter 52.5 mm were made and the agreement was good. The effects of these parameters to condensation performance were evaluated.Copyright © 2009 by ASME
Investigation of a passive condenser system of an advanced boiling water reactor
ABSTRACT An experimental study and best-estimate thermal-hydraulic code model assessment is perfo... more ABSTRACT An experimental study and best-estimate thermal-hydraulic code model assessment is performed to investigate the characteristics of the filmwise condensation with and without noncondensable gas in a passive condenser system. A vertical condenser tube is submerged in a water pool, where the heat from the condenser tube is removed through boiling heat transfer. Data are obtained for various inlet steam flow rates and noncondensable gas mass fractions at various system pressure conditions for two tube inner diameters: 26.6 and 52.5 mm. Experimental data are compared with analysis for complete condensation and flow-through conditions. Degradation of the condensation with noncondensable gas is investigated, where the condensation heat transfer coefficient decreases with the noncondensable gas. Experimental results are simulated with the RELAP5 code using two different condensation models. Code predictions are compared with experimental data, and the results indicate that there is a need for improved condensation models in RELAP5.
Effect of inlet flow resistance on instabilities during startup transient in natural circulation BWRS
Ceramic-ceramic composites and process therefor, nuclear fuels formed thereby, and nuclear reactor systems and processes operated therewith
Nuclear Engineering and Design, 2011
Models of a single-phase liquid-into-liquid buoyant jet and a two-phase vapor-into-liquid turbule... more 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 jetplume 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.
Hydrodynamic Characterization of Nickel Metal Foam—Effects of Pore Structure and Permeability
Heat Transfer Engineering, 2012
The structural characterization of chemical vapor deposition (CVD) nickel metal foam is presented... more The structural characterization of chemical vapor deposition (CVD) nickel metal foam is presented in this study. Scanning electron microscope and post image processing were utilized to analyze the surface of the nickel metal foams. Measured data on foam unit cell, ligament thickness, projected pore diameter, and averaged porosity were obtained. The unit cell and projected pore diameters of CVD nickel metal foam possess Gaussian-like distribution. Characteristics of pore structure and its effect on permeability in the Darcian flow regime were analyzed. Results indicate that the permeability and the viscous conductivity of the CVD processed metal foam are highly affected by the porosity and ligament thickness.
Availability of a probabilistic cost estimation for the price effect of Cu powder and bentonite on an HLW disposal cost in Korea
This study aims to demonstrate the availability of a probabilistic cost estimation related to the... more This study aims to demonstrate the availability of a probabilistic cost estimation related to the price effects of Cu powder and bentonite. From a sensitivity analysis of those materials’ prices on the overall disposal costs, it was found that Cu powder was a more dominant cost driver than that of bentonite among the material costs to dispose of 52,000tU of spent fuels by the deterministic cost estimation method even though the used volume of Cu powder will be smaller than that of bentonite, whereas those conclusions can be changed by a probabilistic cost estimation method. Namely, its conclusion depends on a decision maker's personal opinion because of the resultant uncertainties. The disposal cost includes too many uncertainties due to the long construction and operational durations of a repository. Therefore a probabilistic cost estimation can be useful to provide the information related to an uncertainty.
New accounting system for liability provisions and Radioactive Waste Management Act in Korea
ABSTRACT This paper quantitatively assesses the influence of a new accounting system for liabilit... more ABSTRACT This paper quantitatively assesses the influence of a new accounting system for liability provisions. According to the analysis results, the new accounting system was able to estimate more accurate amounts of the radwaste’s costs than that of previous accounting systems. Removing a steep increase of liability provisions over time recognized acquisition costs of the related assets. For example, it was identified that the transferred decommissioning costs were able to decrease 52% in 2040 because the new accounting system recognized great costs earlier in time when compared to the outdated version of the accounting system. Additionally, in order to secure a radwaste’s fund for NPPs, the Korean Radwaste Management Act was legislated in 2007 thanks to government efforts. This Act has been a cornerstone in the levy and operation of the radwaste fund with cash liquidity.
and with the local condensation heat transfer coefficient data from literature. The agreement was... more and with the local condensation heat transfer coefficient data from literature. The agreement was satisfactory except for high heat transfer coefficient cases such as very low pressure or small NC gas mass fraction conditions. • PCCS tube condensation was modeled with RELAP5 thermalhydraulics code. Experimental data were compared with the RELAP5 code predictions for complete condensation mode of operation. Two condensation models in the RELAP5 code were assessed.
Proposed chemical plant initiated accident scenarios in a sulphur-iodine cycle plant coupled to a pebble bed modular reactor
Nuclear Science, 2010
International Journal of Multiphase Flow, 2011
In a packed-bed reactor a comparative study of bubble breakup and coalescence models has been inv... more In a packed-bed reactor a comparative study of bubble breakup and coalescence models has been investigated to study bubble size distributions as a function of the axial location. The bubble size distributions are obtained by solving population balance equations that describe gas-liquid interactions. Each combination of bubble breakup and coalescence models is examined under two inlet flow conditions: (1) predominant bubble breakup flow and (2) predominant bubble coalescence flow. The resulting bubble size distributions, breakup and coalescence rates estimated by individual models, are qualitatively compared to each other. The change of bubble size distributions along the axial direction is also described with medians. The medians resulting from CFD analyses are compared against the experimental data. Since the predictions estimated by CFD analyses with the existing bubble breakup and coalescence models do not agree with the experimental data, a new bubble breakup and coalescence model that takes account of the geometry effects is required to describe gas-liquid interactions in a packed-bed reactor.
Study of Bubbly Flow Through a Packed Bed
Volume 6: Fluids and Thermal Systems; Advances for Process Industries, Parts A and B, 2011
ABSTRACT A two phase bubbly flow through a packed bed was studied for dominant bubble breakup and... more ABSTRACT A two phase bubbly flow through a packed bed was studied for dominant bubble breakup and coalescence mechanisms through experiments and CFD modeling. Data on various two-phase parameters, such as local void fraction, bubble velocity, size, number, and shape were obtained from the high speed video images. Results indicated that when a flow regime changed from bubbly to either trickling or pulsing flow, the number of average size bubbles significantly decreased and the shape of majority of bubbles was no longer spherical. The bubble coalescence and breakup mechanisms depend on local conditions such as local velocity of the bubble and pore geometry. The CFD analysis using CFX software package was carried out to study bubble size distributions. In the analysis the models for interactions were examined for each case of bubble breakup flow and bubble coalescence. A comparative study was performed on the resulting bubble size distributions, breakup and coalescence rates estimated by individual models. For change of bubble size distributions along the axial direction medians was used as an comparative parameter and the CFD results on bubble medians were compared against the experimental data. This comparative study showed that the predictions estimated by CFD analyses with the bubble breakup and coalescence models currently available in the literature do not agree with the experimental data.
Modeling of the Concurrent Gas-Liquid Trickling Flow Through a Packed-Bed Reactor to Predict Interfacial Area
Energy Conversion and Resources, 2006
ABSTRACT A wavy annular flow model in a packed-bed is developed by introducing the shape of waves... more ABSTRACT A wavy annular flow model in a packed-bed is developed by introducing the shape of waves in a thin liquid film to predict the local interfacial area. The trickling flow regime in a packed-bed is often approximated by an annular flow through a narrow circular channel in which the continuous gas and liquid are completely separated by a smooth and stable interface. Most of the existing models for the trickling flow utilize balance equations for each phase to predict hydrodynamics parameters: liquid hold-up, interstitial velocities, pressure drop, or void fraction. However, the smooth and stable annular flow may not result in an accurate prediction of the interfacial area between gas-liquid phases in a packed-bed. Therefore, a wavy annular flow model is introduced to predict the more accurate interfacial area. This is important because the transport of mass, momentum, and energy is proportional to the interfacial area between gas and liquid phase. Because of the annular flow model, the ratio of film thickness to the equivalent channel diameter can be expressed as a function of only void fraction. The two-parallel wire probe allowed to measure the local film thickness has been used to obtain the shape of the interface. By integrating the local interfacial areas over a certain time period, the local interfacial area is evaluated. The interfacial areas predicted by the presented model are comparable with the empirical correlations developed in the past decades.
Simulation of Heat Exchanger Transients in Sulfuric-Acid and Hydrogen-Iodide Decomposition
Energy Conversion and Resources, 2006
Heat Transfer Study of Direct Contact Condensation in the Presence of Noncondensable Gas
Heat Transfer, Volume 4, 2002
PCCS condenser pool water level transient tests
10th International Conference on Nuclear Engineering, Volume 4, 2002
Cermet nuclear fuels have been demonstrated to have significant potential to enhance fuel perform... more Cermet nuclear fuels have been demonstrated to have significant potential to enhance fuel performance because of low internal fuel temperatures and low stored energy. The combination of these benefits with the inherent proliferation resistance, high burnup capability, and favorable neutronic properties of the thorium fuel cycle produces intriguing options for advanced nuclear fuel cycles. This paper describes aspects of a Nuclear Energy Research Initiative (NERI) project with two primary goals: (1) evaluate the feasibility of implementing the thorium fuel cycle in existing or advanced reactors using a zirconium-matrix cermet fuel, and (2) develop enabling technologies required for the economic application of this new fuel form.
10th International Conference on Nuclear Engineering, Volume 4, 2002
Cermet nuclear fuel has been demonstrated to have significant potential to enhance fuel performan... more Cermet nuclear fuel has been demonstrated to have significant potential to enhance fuel performance because of low internal fuel temperatures and low stored energy. The combination of these benefits with the inherent proliferation resistance, high burnup capability, and favorable neutronic properties of the thorium fuel cycle produces intriguing options for advanced nuclear fuel cycles. This paper describes aspects of a Nuclear Energy Research Initiative (NERI) project with two primary goals: (1) Evaluate the feasibility of implementing the thorium fuel cycle in existing or advanced reactors using a zirconium-matrix cermet fuel, and (2) Develop enabling technologies required for the economic application of this new fuel form. This paper will first describes the fuel thermal performance model developed for the analysis of dispersion metal matrix fuels. The model is then applied to the design and analysis of thorium/uranium/zirconium metal-matrix fuel pins for lightwater reactors using neutronic simulation methods.
Uploads
Papers by Shripad Revankar