[en] In this paper we present three models for the behavior of software failures. By applying these models an attempt has been made to predict reliability growth by predicting failure rates and mean time to next failure of software with Weibull inter failure times at different stages. The changes in the performance of the software as a result of the error removal are described as a Bayes empirical-Bayes prediction in Model I. Model II considers a fully Bayesian analysis with non informative priority of Weibull parameters. An approximation due to Lindley is used in this model as the expressions do not appear in close forms. The M.L. approach is used in Model III. Finally we apply these three models to actual failure data and compare their predictive performances. The comparison of the proposed models is also made in terms of the ratio of likelihoods of observed values based on their predictive distributions. Among these three models, Model I seems to be quite reasonable as it shows higher reliability growth in all stages. It is noted that this model may be useful to measure the current reliability at any particular stage of the testing process and viewed as a measure of software quality

[en] The operating life of feeder piping is negatively impacted by flow accelerated corrosion (FAC). In this study, an assessment of a large set of inspection data reveals that FAC in feeders is a relatively stationary process, with variability only at the local scale. Given the added uncertainty from inspection coverage, a new method for estimating the thinning rate and feeder EOL is developed using a probabilistic approach. The results of the study illustrate the benefits of the methodology in supporting risk-informed decision making at the station by quantifying the present and incremental risk in the feeder system over time. (author)

[en] Tata Steel has installed a 10-MW fluidised bed thermal power plant in its Jamadoba group of collieries in Jharia coalfield to generate electricity from the washery rejects, which were a major source of environmental pollution. The washery rejects having about 64% ash and 26.67% carbon are used as fuel in the plant. The plant has been provided with measures to minimise pollution by avoiding formation of NOx due to low temperature of 850-400 degC at atmospheric pressure, collecting over 90% of fly-ash in ESP and then placing it in safe areas, by utilising the coarse ash as stowing material and controlling noise levels within the permissible limits. The effluents are suitably treated to maintain pH from 7.5 to 8.5, reduce TSS below 100 mg/l and eliminate the presence of oil and gases. Brief details of various equipment have also been given. (author)

[en] The loss of large power transformers may have major implications for plant operation, performance, safety, and economics. This paper examines the generation risk associated with main output transformers (MOTs) at a large nuclear station using the Monte Carlo simulation approach. The developed methodology is used for spare inventory optimization and making transformer replacement projections, while taking into account the specific demographics and condition of the transformer population. The transformer reliability is described using a flexible, three parameter mixed Exponential/Weibull lifetime distribution. The results of the study indicate that, due to the long procurement time for large transformers, at least 1 or 2 spare transformers are needed immediately to minimize the risk to the station. Delaying the investment, even for a single year, would increase the risk significantly. (author)

No abstract available

[en] Feeder wall thinning due to flow accelerated corrosion (FAC) may result in a large number of feeder replacements in the future. In this study, the process of FAC is modelled using a probabilistic approach and used to predict the expected number of degraded feeders and their replacements in the future. Because of the high cost associated with feeder replacements, it may be optimal to replace the entire feeder population during a single refurbishment outage when the unit cost of replacement is likely to be less. The results of this study demonstrate, however, that the unit cost of feeder replacement must be sufficiently lower than the standard replacement cost and the refurbishment performed at an optimal time to realize the economic benefits associated with the refurbishment. (author)

[en] The fundamental challenge with the FAC analysis of nuclear piping is accessibility, leading to the inability to make precise measurements at fixed locations. The lack of fixed location referencing introduces considerable uncertainty into the predictions, particularly for methods that rely on point-to-point comparison (e.g., of the minimum point between consecutive outages). The uncertainty is further compounded by the contact and coverage errors associated with the NDE inspection tools. To minimize the uncertainty in prediction, a new method for estimating the FAC thinning rate and pipe lifetime is developed in this paper using a probabilistic sample based approach. Although the methodology was developed in the context of feeder assessment, involving the analysis of a large dataset of over 1500 separate feeder wall thickness scans from seven different operating nuclear reactors, it is equally applicable to other piping subject to the FAC process where the precise alignment of consecutive wall thickness measurements is not possible. The developed methodology focuses on a small circular area or patch in the vicinity of the minimum point, rather than only the minimum point itself. Because the FAC process is relatively stationary over time, the analysis is insensitive to the patch size, and therefore provides a highly robust way to estimate wall thinning rates. The only significant uncertainty is due to the inspection probe coverage and contact error, which is minimized by the sample based approach and a surface interpolation and fitting scheme. The new method can readily be used to estimate pipe lifetimes in a probabilistic setting. This directly supports risk-informed decision making at the station by quantifying the present and incremental risk in the piping system over time. (author)

[en] Highlights: • Inverse analysis of a reheat regenerative vapor power cycle is presented. • First the energy and exergy based parametric analysis is done. • Next, the inverse analysis is done using simplex search and a differential evolution algorithm. • Results obtained by both the methods are discussed for comparative analysis. • Both the methods are found suitable for inverse solution of ST based power plant. - Abstract: In this study, simplex search method (SSM) and a differential evolution (DE) based inverse algorithm are applied to estimate fuel flow rate (FFR), boiler pressure (BP) and steam turbine (ST) inlet temperature (STIT) of a ST based power cycle. First a theoretical model simulates the cycle performance in terms of net power, efficiency (energy and exergy) and total irreversibility at various FFRs, BPs and STITs. The forward model based results show that the net power increases linearly with FFR while also producing more irreversible losses at higher FFR. The cycle performance also improves at higher BP and STIT. The inverse analysis shows that the DE based method is more appropriate than the SSM where the searching range of parameters is specified and parameter estimation is done from the range of specified parameter values. In SSM, the estimation depends upon the chosen initial guess values and convergence criterion sometimes is not fulfilled with some guessed values of the parameters. Both the inverse methods, however give multiple combinations of parameters and thus provides sufficient scope at the hands of the designer to select the appropriate combinations of parameters required for meeting a particular power requirement

[en] Small modular reactors (SMRs) are generally designed to be buried under the ground to resist the seismic load during an earthquake event. A traditional analysis model for large nuclear power plants may not be applicable for a small modular reactor due to the effect of deep embedment. In addition, the seismic input to a deeply-embedded SMR may possess large variations. A numerical example of site response analysis indicates that the response spectrum at the ground surface is significantly different from the response spectrum at 20 feet below the ground surface, which will subsequently affect the structural responses. (author)

[en] New Schiff base chelating ligands were synthesized by reacting equimolar quantities of 2,3-dimethyl-4-formyl-1-phenyl-3-pyrazoline-5-one and o-anisidine, p-anisidine, m-anisidine, o-toluidine, p-toluidine, m-toluidine, 2,6-xylidine or 2,4-xylidine in ethanol medium. Their subsequent reaction with gadolinium (III) nitrate hexahydrate in 2:1 molar ratio gave complexes that were characterized by elemental analyses, molar conductances, magnetic measurements, electronic and I.R. spectral studies. All the chelates were found to be non-electrolytic in nature. (author). 15 refs., 1 fig., 1 tab