The multi-class binomial failure rate model

The impact of common cause failure (CCF) on PSA results for NPPs is in sharp contrast with the limited quality which can be achieved in their assessment. This is due to the dearth of observations and cannot be remedied in the short run. Therefore, the methods employed for calculating failure rates should be devised such as to make the best use of the few available observations on CCF. The Multi-Class Binomial Failure Rate (MCBFR) Model presented here achieves this by assigning observed failures to different classes according to their technical characteristics and applying the BFR formalism to each of these. The results are determined by a superposition of BFR type expressions for each class, each of them with its own coupling factor. The model hence integrates additional technical information on CCFs and leads to a better quality of results whenever this information is available. This is demonstrated by evaluating CCFs observed for combined impulse pilot valves in German NPPs.     

Apparatus for steady-state kinetic measurements of the catalytic reduction of nitric oxide by ammonia on iron oxide

The reduction of nitric oxide with ammonia on an unsupported iron oxide catalyst has been studied in a continuous-flow recycle reactor using simulated flue gas. The responses of the employed reactor system to step and pulse inputs of tracer indicate that the system could be regarded as a continuous stirred tank reactor (CSTR). Preliminary tests were carried out to determine the effect of temperature and particle size on the measured reaction rates. Additional experiments were performed in order to study the influence of oxygen and water concentration on these rates. A gas chromatographic system has been developed to analyze the gas components NO, N₂O, NO₂, NH₃, H₂O, O₂, CO₂ and N₂. In addition, the concentrations of NO and NO₂ were measured with a nondisperse infrared (NDUV/NDIR) analyzer.     

HOW EVOLUTIONARY IS SCHUMPETER'S THEORY OF ECONOMIC DEVELOPMENT?

The generic features of an evolutionary theory which are identified in the conceptional discussion of the present paper can be shown to be present already in Schumpeter's 1912 work, The Theory of Economic Development . None the less, it is argued that Schumpeter fell short of a level of generality by which he would have succeeded in providing a true foundation for evolutionary economics. The reason is his eagerness--very clearly visible in the "lost" seventh chapter--to align his theory with the economic reasoning of contemporary "pure" economic theory that was moulded in an equilibrium-oriented heuristic and the methodology of comparative statics. Schumpeter's conception--which, in opposing the idea of borrowing from Darwinian thought, he called "development"--is rather a special theory of the unsteady capitalist growth process passing through booms and crises. Throughout all of Schumpeter's writings the notion of development is therefore closely related to the business cycle phenomenon. The paper argues that this special framing implies not only some arbitrary hypotheses which are difficult to accept in an evolutionary interpretation, but also some limitations in his understanding of (what he refused to call) economic evolution, particularly with respect to its driving forces.     

Analysis and design of Hermite subdivision schemes

Published online: 14 May 2002     

Influence of Solution Composition on the Formation of Crystalline Scales

Scale formation is a difficulty encountered with water containing ions of sparingly soluble salts that can readily precipitate on heat transfer surfaces in evaporative concentration operations. Scale formation, hindering the heat transfer process, increases specific energy consumption and operating costs and causes frequent shut down of the evaporator for cleaning. The effects of changes in composition of the solution due to evaporation and CO₂ release on the formation of crystalline scales in seawater evaporators are studied. A model that predicts the CO₂ release is presented. The carbonate system in the salt solution on its whole flow path through the evaporator and the scaling (crystallization) tendency are described. Simulation results for different process configurations are shown and the differences are discussed, particularly with regard to the incrustation tendency.