FUELGEN: effective evolutionary design of refuellings for pressurized water reactors

The paper describes the design of an efficient and robust genetic algorithm for the nuclear fuel loading problem (i.e., refuellings: the in-core fuel management problem) - a complex combinatorial, multimodal optimisation., Evolutionary computation as performed by FUELGEN replaces heuristic search of the kind performed by the FUELCON expert system (CAI 12/4), to solve the same problem. In contrast to the traditional genetic algorithm which makes strong requirements on the representation used and its parameter setting in order to be efficient, the results of recent research results on new, robust genetic algorithms show that representations unsuitable for the traditional genetic algorithm can still be used to good effect with little parameter adjustment. The representation presented here is a simple symbolic one with no linkage attributes, making the genetic algorithm particularly easy to apply to fuel loading problems with differing core structures and assembly inventories. A nonlinear fitness function has been constructed to direct the search efficiently in the presence of the many local optima that result from the constraint on solutions.

Shallow water model for aluminium electrolysis cells with variable top and bottom

The MHD wave instability in commercial cells for electrolytic aluminium production is often described using ‘shallow water’ models. The model [1] is extended for a variable height cathode bottom and anode top to account for realistic cell features. The variable depth of the two fluid layers affects the horizontal current density, the wave development and the stability threshold. Instructive examples for the 500 kA cell are presented.

Finance for water and sanitation as a public service

Drawing on empirical evidence gathered through the PSIRU database, this contribution aims at addressing the potential of public finance to enhance the provision of water supply and sanitation as a public service. It highlights the problems associated with (and the disappointing results obtained from) resort to Private Sector Participation and private finance, both historically and in the last 15-20 years, in developed and developing countries. It also addresses the advantages of using public finance as a more cost-effective and equitable instrument to achieve developmental objectives such as the expansion of service coverage and development of water and sanitation infrastructure. The potential of public operations in maximising developmental impact from the social, economic and environmental points of view is then explored referring to specific examples from a variety of countries and regions. These include the in-house restructuring of public operations to enhance transparency, accountability and effectiveness, as well as the use of Public-Public Partnerships (PUPs) to build capacity. Attention is devoted to the specific financial requirements of expanding sewerage services at global level to achieve MDGs or broader developmental goals. These requirements are revisited in light of a regional breakdown of coverage gaps, available resources and development aid flows. These findings challenge the established view among international and bilateral agencies that expanding sewerage services in developing countries is excessively costly and should be abandoned as a priority because unaffordable. This contribution draws on a number of PSIRU Reports, and particularly the following. - http://www.psiru.org/reports/2008-03-W-sewers.pdf - http://boell-latinoamerica.org/download_es/agua08_privatizacion_LA_2007.pdf - http://boell-latinoamerica.org/download_es/agua08_agua_un_servicio_publico.pdf - http://www.psiru.org/reports/2006-03-W-investment.pdf All PSIRU Reports are accessible at http://www.psiru.org/publicationsindex.asp.

Kinetic studies of the effect of varnish on water loss by glass-ionomer cements

OBJECTIVES: This paper reports a study of the water loss behaviour of two commercial glass-ionomer cements coated with varnishes. METHODS: For each cement (Fuji IX Fast or Chemflex), specimens (6mmdiameterx2mm depth) were prepared and cured for 10min at 37 degrees C. They were exposed to a desiccating environment over H(2)SO(4) either uncoated or coated with the appropriate varnish (Fuji Varnish, a solvent-based lacquer, or Fuji Coat, a light-cured varnish). Four specimens were prepared for each material. They were weighed at hourly intervals for 6h, daily for up to 5 days, then weekly thereafter until equilibration. RESULTS: Unlike the uncoated specimens, water loss from varnished cements was not Fickian, but followed the form: mass loss=A/t+B, where t is time, A and B are constants specific to each cement/varnish combination. A varied from 1.22 to 1.30 (mean 1.26, standard deviation 0.04), whereas B varied from 1.54 to 2.09 (mean -1.83, standard deviation 0.29). At equilibrium, varnished specimens lost much less water than unvarnished ones (p>0.01) but there was no significant difference between the solvent-based and the light-cured varnishes. SIGNIFICANCE: Varnishes protect immature glass-ionomer cements from drying out by altering the mechanism of water loss. This slows the rate of drying but does not necessarily change the total amount of water retained. It confirms that, in clinical use, glass-ionomer restoratives should be varnished to allow them to mature satisfactorily.