As nuclear power plant age, degradation of structure, systems and components can be expected to occur. The understanding of the effect of the age related degradation is important to ensure safe operation of the nuclear power plant. The pressure tubes in CANDU reactors are critical components and its failure has consequences of concern. These cold worked Zr-2.5% Nb pressure tubes may degrade due to ageing mechanisms like creep and delayed hydride cracking. It is important to periodically monitor the serviceability these tubes over the service life. This paper discusses the estimation of the allowable conditional failure probability of the pressure tubes for meeting the risk informed regulation criteria of the US-NRC regulatory guide RG. 1.174.
Received on May 30, 2008, revised on June 11, 2009
References: 15

The main causes of accident in chemical industry are due to deficiencies in the corporate structure, this means the effects of management and organizational variables must be incorporated into the assessment of the frequency. This work focuses attention on the frequency assessment of failure in piping, in particular loss of containment. Some methodologies for the quantification of the effects of measures of risk prevention on the frequencies of rupture of piping are available in literature. The method presented in this paper is a simple approach based on the definition of the links between the causes of failure and the measures adopted by the company to prevent them. After an overview on the causes of failure in piping, the paper describes the approach, the application to a case-study and the study of the sensitivity of the method.

1. Bringing information about a new concept for the start of a process of awareness-raising and commitment building;
2. After that, educating the concept to provide the knowledge for the assessments of the concept and strategic discussions in interaction processes with the key-actorswithin and between organizations to generate a basis for implementation;
3. Evaluating the learning processes to stimulate continuous improvement programmes;
4. The above-mentioned actions can be better embedded in organizations when asurroundings and an organizational analysis for the dissemination of the new concept is performed and the results are included in the approach.

References: 21
Received on September 15, 2008, revised on June 8, 2009

Lifetime modeling of physical systems and biological organisms involves the use of failure distribution functions. The shape of the hazard rate (HR) function associated with the distribution function characterizes the effect of age (and other factors) on the failure. Examples of failure (and survival) data indicate that the shapes are many and varied, due to many underlying reasons. In this paper we investigate a model where the HR function is a rational function, which is by definition the ratio of two polynomials. The different possible shapes (increasing, decreasing, bathtub, inverted bathtub, modified bathtub, roller-coaster, etc.) of the HR rational functions are identified, and necessary and sufficient conditions on the parameters to ensure their existence are derived.
Received on February 10, 2009, revised on June 5, 2009
References: 16

Potential catastrophic events have been historically assessed through the techniques of power system security analysis. A correct assessment must consider not only events associated with "credible outages" but also the possibility of attacks and/or "rare" events. This paper combines concepts of reliability engineering and operations research to develop a new importance measure, D(a), that identifies the most vulnerable group of a links in a network. Since the computation of the new importance measure, D(a), becomes computationally prohibitive for large systems, an approximation technique is provided based on the optimization of a multi-objective deterministic network interdiction problem. The efficiency of the algorithm is then illustrated by analyzing the Italian high-voltage electrical transmission network. In summary, D(a) can be useful for an initial screening of the critical elements of the network.
Received on March 3, 2009, finally revised on July 15, 2009
References: 21

Network reliability evaluation techniques, e.g., path (cut) set techniques, factoring theorem based techniques etc., evaluate various network reliability measures based on different connectivity criterion of nodes, which is a NP hard problem. A little change in network layout requires repetition of the complete procedure. In this paper, a new approach based on path set technique is proposed. The proposed approach stores and process reliability expressions in terms of minimal path sets and disjoint sets using binary data structure. This paper proposes algorithms for modifying these sets with modifications in network layout. This paper also proposes a method to evaluate reliability defined on the basis of different node connectivity requirements.
Received on September 3, 2008, revised on February 20, 2009
References: 12

It has become an unfortunate truism that most engineered change initiatives in organizations fail. One of the primary reasons that the expectations for especially large technological changes are so rarely realized is a lack of attention given to the necessary and unavoidable interactions that occur between technological and psycho-social dimensions of new system designs. In this paper, we build a theoretical argument for taking a broader approach to performability engineering that views the psycho-social dynamics as a critical aspect of successful organizational performance. We ground this argument on a socio-technical systems theory foundation that has been used for more than 50 years to explain technological change failures as well as to design and implement successful change initiatives that encompass all of the different elements of the system design within an organizational context. The paper concludes with insights into some of the benefits and challenges to applying a social-technical systems theory perspective to performability engineering in empirical settings.
Received on June 30, 2009, revised on August 19, 2009
References: 49

Widespread acceptance of micro-electro-mechanical systems (MEMS) depends highly on their reliability, both for large-volume commercialization and for critical applications. The problem of multiple dependent failure processes is of particular interest to MEMS researchers. For MEMS devices subjected to both wear degradation and random shocks that are dependent and competing, we propose a new reliability model based on the combination of random-shock and degradation modeling. The models developed in this research can be applied directly or customized for most current and evolving MEMS designs with multiple dependent failure processes.

References: 10"
Received on March 23, 2009, revised on May 26, 2009