Events-analysis-based method, accident

A method that applies in particular to fixed installations is one that is based on experimental feedback. Starting from an analysis of incidents by the method of event trees, it evaluates the probability that such events may degenerate into a serious accident, and by adding these probabilities over a period of time and referring the results to the number of installations of the same type, it can sometimes be shown that a serious accident becomes probable after a certain number of period trees (Savkovic-Stevanovic 2007, 2009, 2010 Savkovic-Stevanovic and Krstic 2006 Savkovic-Stevanovic et al. 2006). The importance of this method is that it is able to show that the safety of a system has become compromised even though no accident has occurred, and those responsible may believe that the system is operating satisfactory. 

ATHENA A technique for human error analysis. ATHENA is one HRA method which has been developed to improve the state-of-the-art in HRA, especially with respect to how realistically HRA can represent the kinds of human behaviors seen in accidents and near-miss events. It requires a good amount of resources. ATHENA approach incorporates the current understanding of why errors occur, based on the work of earlier pioneers, and substantiated by reviews of a number of significant accidents. It has been developed for mainly for nuclear application, but now it is used in generic manner. 

Like FTA, event tree analysis is also a logic-based methodology for identifying accident scenarios, but unlike FTA it is a "forward thinking" method. The analysis begins with a given initiating failure... 

ABSTRACT Technological advancements in area of sensor-based online maintenance systems have made the possibility of repairing some failed safety support systems of Nuclear Power Plants (NPP) such as electrical supply, I C systems, ventilation systems. However, the possibility of repair during accident situation is yet to be included into PSA level-1. Therefore, this paper presents a scheme of PSA level-1 by implementing an integrated method of Repairable Event Tree (RET) and Repairable Fault Tree (RET) analysis. The Core Damage Frequency (CDF) is calculated from consequence probabilities of the RET. An initiating event of Decay Heat Removal (DHR) systems of ASTRID reactor is analyzed. The proportionate CDFs estimated with repair and without repair have been compared and found that the recoveries can reduce CDF. In sum, this paper attempts to deal with the possibility of repair of some safety systems in PSA and its impacts on CDF of the NPP. 

The possibility of repair during accident situation is yet to be included into Probabilistic Safety Assessment (PSA). A PSA method Includes Event tree (ET) to generate accident scenario and Fault Tree (FT) used to quantify the probability of failure of the Safety Barrier (SB). In literature, there are some examples in which FT analysis has been done for systems with repair components. A FT analysis of phased mission systems has been performed with repairable and non-repairable components (Vaurio 2001). The other FT models with repairable basic events have been proposed based on renewal intensity principle and inclusion-exclusion methods (Yuge et al. 2012 Yuge et al. 2013). However, ET analysis of Initiating Events (IE) with repairable SB has not been dealt before. Therefore this paper proposes a scheme of PSA level-1 for systems with repairable components using a simplified combination of Repairable Event Tree (RET) and Repairable Fault Tree (RFT). 

Within process industries characterized by large production units and high levels of automation, risk and accident analysis is focused on the avoidance of low-probability events entailing serious consequences for the plant and its environment. Safety analysis is based here on causal or probabilistic models of the accidental chain of events that can serve to identify deficiencies in the design of the plant and its protective system as well as to predict the level of risk involved in an operation. Methods developed are fault tree analysis, MORT (Johnson 1975) and INRS (Leplat Rasmussen 1984). A detailed analysis of the actual, individual incident or failure is performed to identify these possible weak spots in the plant and its operation. It is a common experience that human acts play an important role in such industrial mishaps so, especially after the reactor incident at Three Miles Island in 1979, much effort has been spent on developing suitable predictive tools for the... 

Fault Tree Analysis (FTA) is a formal deductive procedure for determining combinations of component failures and human errors that could result in the occurrence of specified undesired events at the system level (Ang and Tang (1984)). It is a diagrannnatic method used to evaluate the probability of an accident resulting from sequences and combinations of faults and failure events. This method can be used to analyse the vast majority of industrial system reliability problems. FTA is based on the idea that ... 

The OASIS code has been used for the thermal hydraulics analyses. A large number of events were analysed. The objective of these studies was to identify the worst-case scenario. Therefore, rupture position, rupture time, and break size spectra must be analysed. Currently, the detailed thermal hydraulics analysis for the primary coolant pipe break accident as a function of the break position is being performed. This study is based on conservative assumptions, as required for Category 4 DBE analyses. The main results of this analysis are the core inlet and outlet temperatures, the break flow rate, the IHX inlet and outlet temperatures, as well as the and clad temperature distribution. The results of the calculations show that the hotspot temperatures for the cladding and for the coolant are below the design safety limits (DSL). These temperatures are lower than the sodium boiling temperature. The regulator accepted the methods applied, as well as the results of the analysis. 

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