Simulated model studies for solid waste storage surveillance facility

High level radioactive waste generated from reprocessing of spent fuel from nuclear reactors are encased in canisters after vitrification. They have high heat generation rate and need interim storage under surveillance and are to be cooled continuously until major portion of the heat is dissipated. Natural circulation air cooling (using suitable stack dimensions) has been considered to cool the overpacks containing canisters. Thermal analysis has been carried out for a reduced scale model of such a facility. Theoretical and experimental results have been compared.     

A non-parametric statistical analysis in the measurement of outdoor gamma exposure to the residents around Trombay

During this study, non-parametric statistical methods were used to validate the measured gamma dose rate with the calculated one, around Trombay. Portable dose rate digital gamma spectrometry system (target fieldSPEC) was used for in situ measurement of external gamma (gamma) dose rate (measured) with the range of 1 nSv/h-10 Sv/h. The activity concentration of U-238, Th-232, K-40 and Cs-137 in the soil and their respective external dose-conversion factor (nSv/h/Bq/kg) was used to evaluate the gamma dose rate (calculated). Non-parametric statistical tool like Box- and -Whisker Plot, Spearman's (rho) rank Correlation coefficient, the Wilcoxon/Mann-Whitney test and chi(2) distribution test have been applied for validation. The randomness or discrete behaviour of measured and calculated dose rate was obvious from the Box- and -Whisker Plot as mean and median of the two are not equal. The inter quartile range (Q3-Q1), which explains about the dispersion of measured and calculated dose rate were also evaluated and found to be 10 and 16 microSv/y, respectively. The linear association between the order of ranks of the two dose rates was established by using Spearman's (rho) rank correlation that showed a coefficient of R = +0.90 with the intercept +1.9, whereas Pearson's correlation was observed with a coefficient of R = +0.93 with the intercept -25.6. Wilcoxon/Mann-Whitney test shows that, medians of the calculated and the measured dose rate as significantly different under the assumption of null hypothesis and measured dose rate was made to the normal distribution by applying Z-statistics. Value of chi(2) was calculated and found to be 284.95, which was very much greater than the critical value of chi(2)(0.05) = 43.77 at a degree of freedom 30, concluding that there is a highly significant difference between the measured and calculated dose rate at 5% significance level.     

Effect of Al dopants on the structural,optical and gas sensing properties of spray-deposited ZnO thin films

Undoped and Al-doped ZnO thin films were deposited on glass substrates by the spray pyrolysis method. The structural, morphological and optical properties of these films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–Vis spectroscopy, photoluminescence (PL) and photoconductivity (PC) measurements, respectively. XRD analyses confirm that the films are polycrystalline zinc oxide with the hexagonal wurtzite structure, and the crystallite size has been found to be in the range 20–40 nm. SEM and AFM analyses reveal that the films have continuous surface without visible holes or faulty zones, and the surface roughness decreases on Al doping. The Al-doped films have been found to be highly transparent (>85%) and show normal dispersion behavior in the wavelength range 450–700 nm. The doped films show only ultraviolet emission and are found to be highly photosensitive. Among all the films examined, at 300 °C the 1.0 at% Al-doped film shows the selective high response (98.2%) to 100 ppm acetone concentration over to methanol, ethanol, propan-2-ol, formaldehyde and hydrogen.     

Vapor bubble dynamics and heat transfer characteristics over the spherical surface during saturated pool boiling

The present study deals with numerical investigations of the boiling phenomena over a spherical surface at different degrees of superheat (ΔT), varying from 10 to 500 K. Various phenomena like vapor sliding, bubble formation, pinch-off, induced vorticity have been illustrated for a deep understanding of the boiling process over a spherical surface. The effect of the degree of superheat on the bubble pinch-off time and volume is also investigated. Further, reported the spatial observation of vapor sliding and retention over the surface with time scale, overall and average characteristics. The fast Fourier transform of a spaced average void fraction of liquid and Nusselt number showed the dominance of film boiling with respect to the degree of superheat. As the degree of superheat increases, the vapor generation rate also increases, which produces a more vapor–liquid interface. Further, with an increase in the degree of superheat, the vapor generation progression shifted from linear to nonlinear patterns. A sphere with ΔT = 500 K generated 32.59 times more vapor than a sphere with ΔT = 10 K. It is found that the vapor generation is dependent on the degree of superheating and exposed time for heating. Thus, a correlation and artificial neural network model have been developed to predict vapor generation during boiling over the spherical surface as a function of time and degree of superheat.     

Analysis of Gaseous Flow Between Parallel Plates by Second‐ Order Velocity Slip and Temperature Jump Boundary Conditions

In this study the momentum and energy equations are solved to analyze the flow between two parallel plates by employing second‐order velocity slip and temperature jump conditions. The flow is considered to be laminar, incompressible, hydrodynamically/thermally fully developed, and steady state. In addition to the isoflux condition, viscous dissipation is included in the analysis. Closed form expressions for the temperature field and Nusselt number are obtained as a function of the Knudsen number and Brinkman number. The Nusselt number obtained by employing the second‐order model is found to be lower compared to the continuum value and agrees well with the other theoretical models. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21116     

Treatment of dairy wastewater by inorganic coagulants: Parametric and disposal studies

Present study reports treatment of simulated dairy wastewater (SDW) by inorganic coagulants such as poly aluminum chloride (PAC), ferrous sulphate (FeSO₄) and potash alum (KAl(SO₄)₂·12H₂O). Batch coagulation experiments were conducted to evaluate the influence of initial pH (pH_i: 5–10) and coagulant dosage (m: 100–5000 mg/L) on chemical oxygen demand (COD) removal from SDW. Residual COD and system pH were observed as function of time. Optimum pH_i (pH_i,op) was found to be 8.0 for all the three coagulants. Optimum m (m_op) was found to be 300, 800 and 500 mg/L for PAC, FeSO₄ and KAl(SO₄)₂·12H₂O, respectively, giving 69.2, 66.5 and 63.8% COD removal efficiency in 30 min. Heating values of the sludge generated by the coagulants PAC, FeSO₄ and KAl(SO₄)₂·12H₂O were found to be 20.7, 29.6 and 17.3 MJ/kg, respectively.     

Dynamic fault tree analysis using Monte Carlo simulation in probabilistic safety assessment

Traditional fault tree (FT) analysis is widely used for reliability and safety assessment of complex and critical engineering systems. The behavior of components of complex systems and their interactions such as sequence- and functional-dependent failures, spares and dynamic redundancy management, and priority of failure events cannot be adequately captured by traditional FTs. Dynamic fault tree (DFT) extend traditional FT by defining additional gates called dynamic gates to model these complex interactions. Markov models are used in solving dynamic gates. However, state space becomes too large for calculation with Markov models when the number of gate inputs increases. In addition, Markov model is applicable for only exponential failure and repair distributions. Modeling test and maintenance information on spare components is also very difficult. To address these difficulties, Monte Carlo simulation-based approach is used in this work to solve dynamic gates. The approach is first applied to a problem available in the literature which is having non-repairable components. The obtained results are in good agreement with those in literature. The approach is later applied to a simplified scheme of electrical power supply system of nuclear power plant (NPP), which is a complex repairable system having tested and maintained spares. The results obtained using this approach are in good agreement with those obtained using analytical approach. In addition to point estimates of reliability measures, failure time, and repair time distributions are also obtained from simulation. Finally a case study on reactor regulation system (RRS) of NPP is carried out to demonstrate the application of simulation-based DFT approach to large-scale problems.     

Investigation on the effect of oxalic acid,succinic acid and aspartic acid on the gas hydrate formation kinetics

Gas hydrate reserves are potential source of clean energy having low molecular weight hydrocarbons trapped in water cages. In this work, we report how organic compounds of different chain lengths and hydrophilicities when used in small concentration may modify hydrate growth and either act as hydrate inhibitors or promoters. Hydrate promoters foster the hydrate growth kinetics and are used in novel applications such as methane storage as solidified natural gas, desalination of sea water and gas separation. On the other hand, gas hydrate inhibitors are used in oil and gas pipelines to alter the rate at which gas hydrate nucleates and grows. Inhibitors such as methanol and ethanol which form strong hydrogen bond with water have been traditionally used as hydrate inhibitors. However, due to relatively high volatility a significant portion of these inhibitors ends up in gas stream and brings further complexity to the safe transportation of natural gas. In this study, organic additives such as oxalic acid, succinic acid and L-aspartic acid (all three) having—COOH group(s) with aspartic acid having an additional—NH₂ group, are investigated for gas hydrate promotion/inhibition behavior. These compounds are polar in nature and thus have significant solubility in liquid water; the presence of weak acidic and water loving (carboxylic/amine groups) moieties makes these organic acids an excellent candidate for further study. This study would pave ways to identify a novel(read better) promoter/inhibitor for gas hydrate formation. Suitable thermodynamic conditions were generated in a stirred tank reactor coupled with cooling system; comparison of gas hydrate formation kinetics with and without additives were carried out to identify the effect of these acids on the formation and growth of hydrates. The possible mechanisms by which these additives inhibit or promote the hydrate growth are also discussed.     

Effects of Viscous Dissipation and Rarefaction on Parallel Plates with Constant Heat Flux Boundary Conditions

The effect of viscous dissipation and rarefaction on heat transfer characteristics of hydrodynamically and thermally fully developed flow between parallel plates with constant heat flux conditions is analyzed. Three different types of heat flux boundary conditions, i.e., both plates kept at different constant heat fluxes, both plates kept at equal constant heat fluxes, and one plate insulated, are applied. In all cases, closed form expressions are obtained for the temperature distribution and Nusselt number. Viscous dissipation, rarefaction, and heat flux ratio are found to influence the heat transfer substantially. The present predictions are verified for the cases which neglect the microscale and viscous heating effect. The obtained results are in good agreement with other analytical results.     

Effect of Shear Work on the Heat Transfer Characteristics of Gaseous Flows in Microchannels

The effect of shear work at solid boundaries for parallel plates and a micropipe is considered to analyze the heat transfer characteristics in the slip flow region for gaseous flow. The fluid flow is assumed to be laminar, incompressible, steady, and hydrodynamically and thermally fully developed. The effects of second‐order velocity slip, temperature jump, shear work at the solid surface, and viscous dissipation are considered. The constant heat flux boundary condition is used at the surface of the parallel plates and of the micropipe. Closed‐form expressions are obtained for the temperature distribution and Nusselt number as a function of various modeling parameters for both geometries. The results show that neglecting the shear work underpredicts the Nusselt number.