The use of maintenance indicators to evaluate the effects of maintenance programs on NPP performance and safety

Nuclear Power Plants (NPPs) under commercial operation are under continuous demand to meet higher levels of performance and safety by NPP owners, regulatory authorities and the public in general. Maintenance plays an important role in achieving such a goal, therefore, many programs are being conducted in order to improve their effectiveness. A common link between these programs is the necessity to evaluate how maintenance affects NPP performance and safety. This paper presents the foundation of a methodology for a maintenance evaluation program based on maintenance indicators and how it is applied to monitoring the effectiveness of the maintenance at the Cofrentes NPP. The methodology is general and might be applied in other fields of industrial engineering, particularly in those activities which devote many resources to maintain plant equipment, and also in those with less but very critical maintenance.     

Competition between friends: The joint influence of the perceived power of self, friends, and parents.

Prior research has shown that parents who have low perceived social power make exaggerated use of power-oriented interaction strategies with children. In this study, the authors made predictions regarding (a) the presence of equivalent effects with children and (b) the intergenerational transmission of perceived power. The interactions of children (ages 6–10) and their friends were observed following a potentially competitive task. Children's interactions were assessed for the competitiveness of their style of interaction. High levels of verbal competitiveness were shown by children with powerless mothers—in particular if fathers also had low perceived power. In addition, high levels of dyadic competitiveness were shown when both children and their friends had low perceived power. Parental powerlessness most clearly predicted children's self-praise, and child powerlessness most clearly predicted friend derogation. Intergenerational transmission of perceived power (and mediating effects of child power on verbal competitiveness) reached significance for only mothers and sons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modelling and optimization of proof testing policies for safety instrumented systems

This paper introduces a new development for modelling the time-dependent probability of failure on demand of parallel architectures, and illustrates its application to multi-objective optimization of proof testing policies for safety instrumented systems. The model is based on the mean test cycle, which includes the different evaluation intervals that a module goes periodically through its time in service: test, repair and time between tests. The model is aimed at evaluating explicitly the effects of different test frequencies and strategies (i.e. simultaneous, sequential and staggered). It includes quantification of both detected and undetected failures, and puts special emphasis on the quantification of the contribution of the common cause failure to the system probability of failure on demand as an additional component. Subsequently, the paper presents the multi-objective optimization of proof testing policies with genetic algorithms, using this model for quantification of average probability of failure on demand as one of the objectives. The other two objectives are the system spurious trip rate and lifecycle cost. This permits balancing of the most important aspects of safety system implementation. The approach addresses the requirements of the standard IEC 61508. The overall methodology is illustrated through a practical application case of a protective system against high temperature and pressure of a chemical reactor.     

Molecular typing of the yeast species Dekkera bruxellensis and Pichia guilliermondii recovered from wine related sources

A total of 63 strains of Dekkera bruxellensis and 32 strains of Pichia guilliermondii isolated from wine related environments were identified by restriction analysis of the 5.8S-ITS region of the rDNA. These strains were subjected to intraspecific discrimination using mtDNA restriction and RAPD-PCR analysis. The isolates identified as D. bruxellensis yielded 3 different molecular patterns of mtDNA restriction using the endonuclease HinfI. The pattern A was the most frequent (58 strains) among strains from different sources, regions and countries. Pattern B (4 strains) and C (one strain) were determined in isolates from Portuguese wines. The discrimination among the pattern A strains was achieved by a RAPD-PCR assay with 3 primers (OPA-2, OPA-3 and OPA-9). A total of 12 haplotypes were obtained with the combination of the patterns provided by the 3 OPAs. The pattern 2 was the most frequent and extensively distributed being found in strains from different countries and from different sources like wine, barrique wood and insects. The strains of P. guilliermondii were characterized with restriction of mtDNA using the endonuclease HinfI yielding 7 different restriction patterns. These patterns were associated with different efficiencies of 4-ethylphenol production. Patterns A to D corresponded to 19 strains producing low levels of 4-ethylphenol (<1 mg/l) while patterns F and G grouped 13 strains producing high levels of 4-ethylphenol (>50 mg/l), when grown in synthetic media supplemented with 100 mg/l of p-coumaric acid. The high degree of polymorphism observed shows that intraspecific typing is essential for accurate yeast dissemination studies in wine related environments.     

Genetic algorithms in optimizing surveillance and maintenance of components

Nowadays the great ability of genetic algorithms (GA) to find solutions in complex optimization problems is known, where other methods used to give poor results. This has opened a wide range of application areas using GA and here we present a new approach aimed at the global and constrained optimization of surveillance and maintenance (S&M) of components based on risk and cost criteria. Also, a case study is performed using this approach which shows the benefits of the integration of S&M tasks of components based on optimized intervals. Moreover, this methodology is completely valid in solving other optimization problems with respect to risk and cost beyond the component level.     

The so-called malignant pleural effusion: a new review of direct data obtained with diagnostic pleuroscopy

We analyze a series of 896 thoracoscopies for pleural effusion, of which 78% (662/896) were due to pleural carcinomatosis, primary or metastatic. Pleural malignancy was observed mainly, in the right hemithorax (65%), arising from tumors within the diaphragm. The likelihood of finding pleural metastasis in lung cancer was 77%. When the pleural effusion is slight (less than 500 ml) the likelihood falls to 22%. We therefore advise thoracoscopy in the former and thoracotomy in the latter. Blood-stained effusion continues to have the worst prognosis (84% stemming from metastasis) and signifies an advanced stage of pleural metastasis. The pleura parietal is involved in 69% of pleural carcinomatosis cases, and in 80% when the lower hemithorax or the area around breast or lung tumors are involved. The cytology yield was 45.9%, though always depending on extent of metastasis. When metastasis was slight, the likelihood of positive cytology was less (19%) and when metastasis was generalized throughout the entire pleura the likelihood increased to 73%. We found no reason to think that the cells in most pleural liquids are able to nest and form tumoral niches. The origin of such cell nests was rather found to be in shedding from the metastases themselves, from lung tumors or from carcinomatous lymphangitis by lymphatic obstruction. The diagnostic yield of thoracoscopy once again proved to be superior to that of pleural biopsy.     

Selecting control factor values in a robust design using a scatter plot

When the results of an experimental design are analyzed, in which control factors and noise factors are involved, it may be difficult to determine the combination of values of the control factors that produce the best behavior of the response, addressing both its level (or distance from the target value) and its variability. This article presents an analysis proposal that is based on the model obtained for the response and uses, as its central element, a scatter plot of its expected value vs its standard deviation. In this plot, each point corresponds to a combination of values of the control factors; thus, it is easy to identify the points with better response behavior. In our opinion, this graph provides significant advantages over the other methods that have been proposed; among them is the fact that it is always a scatter plot, regardless of the number of factors that end up being active, and that it is easy to understand and use, especially with the possibilities offered by the current statistical software packages. Copyright © 2010 John Wiley & Sons, Ltd.