The paper analyses the seismic resistance of a ventilation stack on a reactor building, including the possible reserves of increasing the resistance. Structures of this type are highly sensitive to seismic loads, as the tuning of the stack (the spectrum of its lowest natural frequencies) corresponds with the frequency spectrum of excitation due to seismic effects. The purpose of the paper is to present an example of an actual structure to show the character of the response of the structure, and the participation of the individual frequency components of the response in the overall stress and strain state of a structure of this type. The methodology for a numerical analysis of the structure is also given. The load of the stack proper is modified by the transfer characteristics of the building. In engineering practice, the system is usually divided into two subsystems: the building with the sub- base, and the stack proper. The level of justification for the application of this simplification depends on the distance of the natural frequencies of the stack from the natural frequencies of the building. Finally, the paper deals with possible errors in determining the actual seismic resistance of the stack structure.

06/00111 Characteristics of organizational culture at the maintenance units of two Nordic nuclear power plants Reiman, T. ef al. Reliabili O' Engineering & Sysfem SqfeO', 2005, 89, (3), 331 345. This study aims to characterize and assess the organizational cultures of two Nordic nuclear power plant (NPP) maintenance units. The research consisted of NPP maintenance units of Forsmark (Sweden) and Olkiluoto (Finland). The study strives to anticipate the conse- quences of the current practices, conceptions and assumptions in the given organizations to their ability and willingness to fulfill the organizational core task. The methods utilized in the study were organizational culture and core task questionnaire (CULTURE02) and semi-structured interviews. Similarities and differences in the per- ceived organizational values, conceptions of one's own work, con- ceptions of the demands of the maintenance task and organizational practices at the maintenance units were explored. The maintenance units at Olkiluoto and Forsmark had quite different organizational cultures, but they also shared a set of dimensions such as strong personal emphasis placed on safety. The authors propose that different cultural features and organizational practices may be equally effective from the perspective of the core task. The results show that due to the complexity of the maintenance work, the case organizations tend to emphasize some aspects of the maintenance task more than others. The reliability consequences of these cultural solutions to the maintenance task are discussed. The authors propose that the organizational core task, in this case the maintenance task, should be clear for all the workers. The results give implications that this has been a challenge recently as the maintenance work has been changing. The concepts of organizational core task and organizational culture could be useful as management tools to anticipate the consequences of organizational changes.

06/00112 Critical feature analysis of a radiotherapy machine Rae, A. et al. Reliability Engineering & Sysfem SqfeO', 2005, 89, (1), 48 56. The software implementation of the emergency shutdown feature in a major radiotherapy system was analysed, using a directed form of code review based on module dependences. Dependences between modules are labelled by particular assumptions; this allows one to trace through the code, and identify those fragments responsible for critical features. An 'assumption tree' is constructed in parallel, showing the assump- tions which each module makes about others. The root of the assumption tree is the critical feature of interest, and its leaves represent assumptions which, if not valid, might cause the critical feature to fail. The analysis revealed some unexpected assumptions that motivated improvements to the code.

06/00113 Hazard evaluation of The International Fusion Materials Irradiation Facility Burgazzi, L. Fusion Engineering and Design, 2005, 72, (4), 391 399. The International fusion materials irradiation facility (IFMIF) is aimed to provide an intense neutron source by a high current deuteron linear accelerator and a high-speed lithium flow target, for testing candidate materials for fusion. Liquid lithium is being circulated through a loop and is kept at a temperature above its freezing point. In the frame of the design phase called key element technology phase, jointly performed by an international team to verify the most important risk factors, safety assessment of the whole plant has been required in order to identify the hazards associated with the plant operation. This paper discusses the safety assessments that were performed and their outcome: failure mode and effect analysis approach has been adopted in order to accomplish the task. Main conclusions of the study is that, on account of the safety and preventive measures adopted, potential plant related hazards are confined within the IFMIF security boundaries and great care must be exercised to protect workers and

05 Nuclear fuels (economics, policy, supplies, forecasts)

site personnel from operating the plant. The analysis has provided as a result a set of postulated initiating events (PIEs), that is off-normal events, that could result in hazardous consequences for the plant, together with the total frequency and the list of component failures which could induce the PIE: this assures the exhaustive list of major initiating events of accident sequences, helpful to the further accident sequence analysis phase. Finally, for each one of the individuated PIEs, the evaluation of the accident evolution, in terms of effects on the plant and relative countermeasures, has allowed to verify that adequate measures are being taken both to prevent the accident occurrence and to cope with the accident consequences, thus assuring the fulfilment of the safety requirements.

06/00114 Identifying cognitive complexity factors affecting the complexity of procedural steps in emergency operating procedures of a nuclear power plant Park, J. et al. Reliabilify Engineering & Sysfem Sqfet3,, 2005, 89, (2), 121 136. In complex systems such as a nuclear and chemical plant, it is well known that the provision of understandable procedures that allow operators to clarify what needs to be done and how to do it is one of the requisites to secure their safety. As a previous study in providing understandable procedures, the step complexity measure that can quantify the complexity of procedural steps in emergency operating procedures of a nuclear power plant was suggested. However, the necessity of additional complexity factors that can consider a cognitive aspect in evaluating the complexity of procedural steps is raised. To this end, the comparisons between operators' performance data measured by the form of a step performance time with their behaviour in carrying out the prescribed activities of procedural steps are conducted in this study. As a result, two kinds of complexity factors (the abstraction level of knowledge and the level of engineering decision) that could affect an operator's cognitive burden are identified. Although a well-designed experiment is indispensable for confirming the appropriateness of the additional complexity factors, it is strongly believed that the change of operators' performance data can be more authentically explained if the additional complexity factors are taken into consideration.

06•00115 Lessons learned from the U.S. nuclear power Plant on-line monitoring programs Hines, J. W. and Davis, E. Progress in Nuclear Energy, 2005, 46, (3 4), 176 189. The investigation and application of on-line monitoring programs has been ongoing for over two decades by the U.S. nuclear industry and researchers. To this date, only limited pilot installations have been demonstrated and the original objectives have changed significantly. Much of the early work centred on safety critical sensor calibration monitoring and reduction. The current focus is on both sensor and equipment monitoring. This paper presents the major lessons learned that contributed to the lengthy development process including model development and implementation issues, and the results of a recently completed cost benefit analysis.

06•00116 Measuring reuse in hazard analysis Smith, S. P. and Harrison, M. D. Reliability Engineering & System Sqflety, 2005, 89, (1), 93 104. Hazard analysis for safety-critical systems require sufficient coverage and rigour to instil confidence that the majority of hazardous consequences have been identified. These requirements are commonly met through the use of exhaustive hazard analysis techniques. However, such techniques are time consuming and error-prone. As an attempt at exhaustive coverage, hazard analysts typically employ reuse mechanisms such as copy-and-paste. Unfortunately, if reuse is applied inappropriately there is a risk that the reuse is at the cost of rigour in the analysis. This potential risk to the validity of the analysis is dependent on the nature and amount of reuse applied. This paper investigates hazard analysis reuse over two case studies. Initially reuse in an existing safety argument is described. Argument structures within the hazard analysis are identified and the amount of verbatim reuse examined. A second study is concerned with how reuse changes as a result of tool support. In contrast to the first case, the defined arguments are more diverse-reuse has occurred but is less verbatim in nature. Although tool support has aided the customization of the reused arguments, many are only trivially customized. An edit distance algorithm is utilized to identify and enumerate verbatim and trivial reuse in the arguments.

06•00117 Nuclear desalination and electricity production for islands Nghiep, T.D. Int. J. Nuclear Desalination, 2005, 1, (4), 396 399. Nuclear desalination is an established and commercially proven technology that is now available and has the potential of further improvement. The technology of a small-sized reactor for desalination and electricity production will be an economically viable option and

Fuel and Energy Abstracts January 2006 17