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Suzuki, Kazuhiko*; *
JNC TJ8400 2000-052, 136 Pages, 2000/02
JNC-TJ8400-2000-052.pdf:4.16MB
Though HAZOP is recognized as the useful safety assessment method, it requires a labor-intensive and time-consuming process. So recently computer-aided HAZOP has been proposed. The research report in 1999 (PNC TJ1400 99-003) presented HAZOP system based on the plant component malfunctions basic models. By using this basic model, not only state malfunction of component but also the consequence to external circumstance can be assessed. G2, which is an excellent object-oriented developer tool in GUI (Graphical User Interface), was used as a tool for developing the system. By using the graphical editor in the system, the user can carry out HAZOP easily. The purpose of this research is to improve the ability of the HAZOP system to obtain a more detailed HAZOP results. HAZOP is carried out according to the fault propagation of component level and the one of plant level based on plant component malfunctions basic models. Furthermore, the HAZOP system which can do the cause and effect analysis in detail intended for the component which processes two or more materials is developed. It is possible to carry out HAZOP for various plants by newly adding material information to the knowledgebase. We have applied this system to the Nuclear Reprocessing Facilities to demonstrate the utilities of developing system.
Yang Jin An*;
JNC TN9400 99-013, 89 Pages, 1998/12
This report presents a variance reduction technique to estimate the reliability and availability of highly complex systems during phased mission time using the Monte Carlo simulation. In this study, we introduced the variance reduction technique with a concept of distance between the present system state and the cut set configurations. Using this technique, it becomes possible to bias the tansition from the operating states to the failed states of components towards the closest cut set. Therefore a component failure can drive the system towards a cut set configuration more effectively. JNC developed the PHAMMON (Phased Mission Analysis Program with Monte Carlo Method) code which involved the two kinds of variance reduction techniques : (1) forced transition, and (2)failure biasing. However, these techniques did not guarantee an effective reduction in variance. For further improvement, a variance reduction technique incorporating the distance concept was introduced to the PHAMMON code and the numerical calculation was carried out for the different design cases of decay heat removal system in a large fast breeder reactor. Our results indicate that the technique addition of this incorporating distance concept is an effective means of further reducing the variance.
Hioki, Kazumasa
PNC TN9410 94-188, 160 Pages, 1994/05
The Systems Analysis Section has been performing a probabilistic Safety Assessment (PSA) on a large fast breeder reactor (FBR) since JFY 1992. The objective of the study is to apply the PSA method to a plant in a conceptual design stage, develop system models, perform quantitative analyses and systematic evaluation, supply valuable insights to enhance reliability and safety, and reflect them to the basic design. The plant analyzed is a 600MWe class large FBR designed by the Plant Engineering Section in the "Large FBR design study" that has been performed since JFY 1990. The failure probability of the Decay Heat Removal System (DHRS) can be reduced approximately two orders if the Water Steam System (WSS) can remove the decay heat for the first 24 hours. The frequency of PLOHS, however, is not reduced to less than one third because the WSS cannot be used for some initiating events and the PLOHS frequency is dominated by the failure probability of DHRS without the WSS. The failure probability of DHRS is dominated by the common cause failures (CCFs) of vanes, dampers and valves around the air-coolers in the Auxiliary Cooling System (ACS). Therefore it is most important to eliminate the CCFs. Assuming that the CCFs have been eliminated by diversifying the components, the frequencies of PLOHS were evaluated. An analysis has shown that if the WSS can remove the decay heat alone, the PLOHS frequency is reduced approximately two orders. In this case the PLOHS frequency is dominated by the failure probability of the DHRS right after the reactor shutdown. The most effective way to reduce the PLOHS frequency is to increasc the redundancy of the DHRS for the first few hours after reactor shutdown. It is known through the experience of preceding plants that the success criteria can be relaxed to one loop natural circulation instead of forced circulation in the best estimate evaluation. It was shown that under such condition, the PLOHS frequency can be as low as 10
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