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

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

Band gap engineering of boron nitride by graphene and its application as positive electrode material in asymmetric supercapacitor device

Nanostructured hexagonal boron nitride (h-BN)/reduced graphene oxide (RGO) composite is prepared by insertion of h-BN into the graphene oxide through hydrothermal reaction. Formation of the super lattice is confirmed by the existence of two separate UV–visible absorption edges corresponding to two different band gaps. The composite materials show enhanced electrical conductivity as compared to the bulk h-BN. A high specific capacitance of ∼824 F g–1 is achieved at a current density of 4 A g–1 for the composite in three-electrode electrochemical measurement. The potential window of the composite electrode lies in the range from −0.1 to 0.5 V in 6 M aqueous KOH electrolyte. The operating voltage is increased to 1.4 V in asymmetric supercapacitor (ASC) device where the thermally reduced graphene oxide is used as the negative electrode and the h-BN/RGO composite as the positive electrode. The ASC exhibits a specific capacitance of 145.7 F g–1 at a current density of 6 A g–1 and high energy density of 39.6 W h kg–1 corresponding to a large power density of ∼4200 W kg–1. Therefore, a facile hydrothermal route is demonstrated for the first time to utilize h-BN-based composite materials as energy storage electrode materials for supercapacitor applications