Basic Relation between RAW and RRW and Some of Its Implications on Risk Reduction Strategies

In using risk-informed approaches for ensuring safety of operating nuclear power plants (NPPs), risk importance measures obtained from probabilistic safety assessments (PSAs) of the plants are integral elements of consideration in many cases. In PSA models and applications associated with NPPs the risk importance of a particular feature (e.g. function, system, component, failure mode or operator action) can be, most generally, divided into two categories: importance with respect to risk increase potential and importance with respect to risk decrease potential. The representative of the first category, as used for practical purposes, is Risk Achievement Worth (RAW). Representative of the second category, as mentioned in consideration of risk importance, is Risk Reduction Worth (RRW). It can be shown that the two risk importance measures, RAW and RRW, are dependent on each other. The only parameter in this mutual dependency is probability of failure of the considered feature. The paper discusses the relation between RAW and RRW and some of its implications, including those on the general strategies for the reduction of risk imposed for the operation of the considered facility. Two general risk reduction strategies which are considered in the discussion are: a) risk reduction by decreasing the failure probability of the considered feature; and b) risk reduction while keeping the failure probability of the considered feature at the same level. Simple examples are provided to illustrate the differences between two strategies and point to main issues and conclusions

Basic Relation between RAW and RRW and Some of Its Implications on Risk Reduction Strategies

In using risk-informed approaches for ensuring safety of operating nuclear power plants (NPPs), risk importance measures obtained from probabilistic safety assessments (PSAs) of the plants are integral elements of consideration in many cases. In PSA models and applications associated with NPPs the risk importance of a particular feature (e.g. function, system, component, failure mode or operator action) can be, most generally, divided into two categories: importance with respect to risk increase potential and importance with respect to risk decrease potential. The representative of the first category, as used for practical purposes, is Risk Achievement Worth (RAW). Representative of the second category, as mentioned in consideration of risk importance, is Risk Reduction Worth (RRW). It can be shown that the two risk importance measures, RAW and RRW, are dependent on each other. The only parameter in this mutual dependency is probability of failure of the considered feature. The paper discusses the relation between RAW and RRW and some of its implications, including those on the general strategies for the reduction of risk imposed for the operation of the considered facility. Two general risk reduction strategies which are considered in the discussion are: a) risk reduction by decreasing the failure probability of the considered feature; and b) risk reduction while keeping the failure probability of the considered feature at the same level. Simple examples are provided to illustrate the differences between two strategies and point to main issues and conclusions

AN ASSESSMENT OF PLEUROPULMONARY POST-TUBERCULOSIS PATIENTS IN A TEACHING HOSPITAL IN EAST INDIA

Objectives: Quality of life of a patient may be impaired seriously in the aftermath of pleuropulmonary tuberculosis (TB) even after being cured or taking adequate treatment. Proper evaluation of post-TB sequelae is of extreme clinical importance. The study objective was to assess demographic, clinical, radiological, and spirometric pattern of pleuropulmonary post-TB patients in a teaching hospital. Methods: An observational cross-sectional study was carried out in a teaching hospital in India over a period of 14 months. A total of 300 patients of more than 12 years of age from both genders were included in the study. Detailed history, clinical, radiological, microbiological, and spirometric evaluation were being carried out. Results: It was a male predominant study with male: female ratio of 2.29:1 and mean age of patient was 52.97 ± 0.51 (mean±standard error of mean) years. History of pleural and pulmonary TB was present in 11% and 89% of cases, respectively. Cough was present in all patients. Shortness of breath (86.33%) and hemoptysis (58.33%) were among other common presenting symptoms. In majority of cases, pulmonary involvement was unilateral (57%). Pleural fibrosis/thickening was seen in 11% of cases, lung parenchymal fibrosis 38.67%, bronchiectasis in 12.67%, and aspergilloma found in 7% of cases. Bacteriological positivity was detected in 14.33% of cases. Spirometric evaluation revealed restrictive pattern (50.20%) in most of the cases followed by obstructive pattern in 38.13% of cases. Conclusion: Respiratory symptoms, radiological, and spirometric abnormalities can present among pleuropulmonary post-TB patients as a sequelae. It may be considered as an important cause of chronic lung disease, particularly in high TB burden countries

Unusual premonsoon eddy and Kelvin wave activities in the Bay of Bengal during Indian Summer monsoon deficit in June 2009 and 2012

An investigation of the eddy and coastal Kelvin wave activities in the Bay of Bengal (BoB) is carried out during premonsoon season in two years of Indian summer monsoon deficit in June (2009 and 2012), occurred in the recent warming hiatus period. Using altimeter observations, our study reveals that over the northern BoB cyclonic eddy kinetic energy is reduced by 35% and 50% from the climatology during premonsoon seasons in 2009 and 2012, respectively, while the cyclonic eddy area is reduced by 18% and 24%, respectively. A concurrent reduction is observed in the first upwelling Kelvin wave (uKW) activities in the eastern equatorial Indian Ocean as well as in the coastal BoB for these years. The reduction in the generation of the first uKW in the eastern equatorial Indian Ocean is attributed to the westerly wind anomalies in January-March of these years. Additionally, meridional wind stress anomalies during March-April in these years are found to be southerly, causing anomalous coastal downwelling in the eastern rim of BoB. This coastal downwelling blocks the propagation of the first uKW. The decrease in the first uKW activities in the coastal waveguide of the BoB reduces the radiation of upwelling Rossby waves, thereby decreasing the cyclonic eddy activities in the northern BoB. The results from this letter could be helpful for further understanding of upper ocean mixing processes in the BoB during monsoon deficit years

Unusual Premonsoon Eddy and Kelvin Wave Activities in the Bay of Bengal During Indian Summer Monsoon Deficit in June 2009 and 2012

An investigation of the eddy and coastal Kelvin wave activities in the Bay of Bengal (BoB) is carried out during premonsoon season in two years of Indian summer monsoon deficit in June (2009 and 2012), occurred in the recent warming hiatus period. Using altimeter observations, our study reveals that over the northern BoB cyclonic eddy kinetic energy is reduced by 35% and 50% from the climatology during premonsoon seasons in 2009 and 2012, respectively, while the cyclonic eddy area is reduced by 18% and 24%, respectively. A concurrent reduction is observed in the first upwelling Kelvin wave (uKW) activities in the eastern equatorial Indian Ocean as well as in the coastal BoB for these years. The reduction in the generation of the first uKW in the eastern equatorial Indian Ocean is attributed to the westerly wind anomalies in January-March of these years. Additionally, meridional wind stress anomalies during March-April in these years are found to be southerly, causing anomalous coastal downwelling in the eastern rim of BoB. This coastal downwelling blocks the propagation of the first uKW. The decrease in the first uKW activities in the coastal waveguide of the BoB reduces the radiation of upwelling Rossby waves, thereby decreasing the cyclonic eddy activities in the northern BoB. The results from this letter could be helpful for further understanding of upper ocean mixing processes in the BoB during monsoon deficit years

Quantitative Evaluation of the Impact of Human Reliability in Risk Assessment for Nuclear Power Plants.

The role of human beings in the safe operation of a nuclear power plant has been a matter of concern. This study describes methods for the quantitative description of that role and its impact on the risk from nuclear power plants. The impact of human errors was calculated by observing the changes in risk parameters, such as core melt probability, release category probabilities, accident sequence probabilities and system unavailabilities due to changes in the contribution to unavailability of human errors, within the framework of risk assessment methodology. It was found that for operational pressurized water reactors the opportunity for reduction in core melt probability by reducing the human error rates without simultaneous reduction of hardware failures is limited, but that core melt probability would significantly increase as human error rates increased. More importantly, most of the dominant accident sequences showed a significant increase in their probabilities with an increase in human error rates. Release categories resulting in high consequences showed a much larger sensitivity to human errors than categories resulting in low consequences. A combination of structural importance and reliability importance measure was used to describe the importance of individual errors. The multiple sequential failures (msfs) during testing, maintenance and calibration were analyzed and distinguished from other types of multiple failures by considering the relationship among the failures. A model was developed for describing msfs by taking into account the process involved in such failures. The model increments the conditional failure probabilities by certain amounts from their lower bounds (independent failure probabilities). This approach provides important insights into the influence of dependence between failures on system reliability. This model can be used effectively to choose an optimum system considering the individual failure probability, dependence factor and the amount of redundancy in a system. It was observed that in many cases it may be better to reduce the individual failure probability and to use a different type of system, rather than trying to decrease the dependence between the failures.Ph.D.Nuclear engineeringEnergyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158521/1/8125196.pd

Surface modification of reduced graphene oxide through successive ionic layer adsorption and reaction method for redox dominant supercapacitor electrodes

Non-covalent surface modification technique, where the pre-reduction of graphene oxide (GO) was carried out to recover the π-π conjugation, was performed through a successive ionic layer adsorption and reaction (SILAR) method for preparing redox dominant supercapacitor electrodes. The π-π conjugation of reduced graphene oxide (RGO) facilitated non-covalent interaction with sulfanilic acid azo-chromotrop (SA) to develop electrolyte accessible layer-by-layer (LL) assembly of RGO and SA (LSARGO). In comparison, RGO was modified with SA through continuous stirring of SA and GO, followed by the post reduction technique and designated as NSARGO. The LSARGO revealed higher surface area, electrical conductivity and electrochemical performances than the NSARGO. Sharp redox peaks with well cathodic peak current density vs. square root of the scan rate slope value indicated a redox dominant LSARGO electrode, which was further confirmed by the specific capacitance (SC) values, calculated from the cyclic voltammetry and galvanostatic charge–discharge (GCD) curves in three electrode configuration. The electrochemical impedance spectroscopy study also revealed that the LSARGO provided more redox dominant supercapacitor characteristics as compared to NSARGO. The LSARGO exhibited a SC of ∼1023 F g−1 at scan rate of ∼10 m V s−1. The fabricated asymmetric supercapacitor device (ASC) showed an elevated energy and power density of ∼80 W h kg−1 and 17,500 W kg−1, respectively. The ASC experienced high GCD cyclic stability of ∼84% after 10,000 cycles

Morphology controlled synthesis of MnCO3–RGO materials and their supercapacitor applications

MnCO3-reduced graphene oxide (MnCO3–RGO) was grown on nickel foam by a facile successive ionic layer adsorption and reaction (SILAR) method and used as a supercapacitor electrode. The morphology of the MnCO3 functionalities was tuned from lotus to flake to spherical shape using different chelating agents during synthesis. The length and width of the individual petals of the lotus structure MnCO3 were found to be ∼200–300 and 50–100 nm, respectively. The reduction of graphene oxide (GO) in MnCO3–RGO composites was confirmed by Raman spectroscopy and electrical conductivity data analysis. The lotus shaped MnCO3 grown on RGO sheets provided a high surface area and electrical conductivity as compared to the developed electrode materials. The cyclic voltammetry, galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy analyses showed that the lotus shaped MnCO3 grown on RGO sheets provided higher current response, large specific capacitance (SC) and low solution, charge-transfer and Warburg resistance as compared to the flake and spherically shaped MnCO3 grown on RGO sheets. A fabricated asymmetric supercapacitor (ASC) device with MnCO3 (lotus) – RGO as the positive electrode and sonochemically reduced GO as the negative electrode – exhibited a working potential of ∼0–1.6 V, SC of ∼ 335 F g−1 at ∼2 A g−1 (∼468 mF cm−2 at ∼2.8 mA cm−2), an energy density of ∼120 W h kg−1 (∼0.16 mW h cm−2) and a power density of ∼16 kW kg−1 (∼22 mW cm−2) with a GCD stability of ∼73% after 10 000 cycles