Accident analysis methodology

During LPS the pressure and temperature of reactor system is lower than during full power operation. There may be a nitrogen blanket in the pressurizer or the primary circuit may be open to atmospheric pressure. The traditional accident analysis codes (e.g. ATHLET, RELAP, CATHARE, TRAC) were not originally developed to take into account these special physical 

Due to the slow progress of accidents and transients initiated during LPS modes, hand calculations or use of simplified models are often sufficient to evaluate the behaviour of the reactor system during these events. However certain events require more detailed treatment of the reactor system and the physical phenomenon in question. These events include  

In order to get a realistic picture of the nature and safety significance of a LPS event, it is sometimes necessary to do a very detailed and comprehensive analysis. A good example of this is a boron dilution event for which models of mixing and 3D neutron kinetics are needed in combination with modelling of primary circuit thermal hydraulics. 

Currently the analysis for LPS has been performed only for a small number of cases. However, because of their safety significance, there is a need to perform these analyses for inclusion in final safety analysis reports, for development of emergency operating procedures, and for further development of technical specifications. Due to their potential impact, LPS analyses need to be carried out with the same care as those for full power conditions. 

The analyses for LPS should be performed for two purposes. In a traditional conservative analysis the aim is to show that the results fulfill the acceptance criteria of the analysis with minimum safety systems available and with conservative assumptions of operator actions. The other set of analyses are best estimate analyses where the effect of various assumptions on the results is studied. The latter is especially useful for drawing up EOPs and for PSA puiposes. In this way the interrelation with PSA studies can also be taken into account. 

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AR156 Incorporation of advanced accident analysis methodology into safety analysis report, No. 1351, 2 June 2003. 

This paper is a followup to the work presented in NUREG/CR-5423 and constitutes a part of the implementation of the ]Wsk-Oriented Accident Analysis Methodology (ROAAM) employed therein. In particular, it expands the quantification to include four independeait evaluations carried out at RPI, ANL, SNL, and ANATECH, Inc. on various portions of the phenomenology involved The results demonstrate a substantial synergism and convergence which are the essential ingredients for an eventual resolution. 

Acceptability of Accident Analysis Methodology (Restart Criteria 3 and 6)... 

Fabiano, B., Pastormo, R., and Solisio, C. 1999. Explosion at an Acetylene Plant A Methodological Approach to Accident Analysis. IChemE Loss Prevention Bnlle-tin. Issue 145 (February 1999). 

In the following sections, a number of methodologies for accident analysis will be presented. These focus primarily on the sequence and structure of an accident and the external causal factors involved. These methods provide valuable information for the interpretation process and the development of remedial measures. Because most of these techniques include a procedure for delineating the structure of an incident, and are therefore likely to be time consuming, they will usually be applied in the root cause analysis of incidents with severe consequences. 

Accident Phenomenology and Accident Analysis Group. It will cover topics such as hazards, accident events, source terms, consequences, probability of occurrences, methodology, and computer codes. 

Assess and compare the methodologies of hazard and accident analysis in both countries applicable to the excess Pu and HEU storage and disposition activities. 

The quality of reports is strongly dependent on the availability of adequate methodology and computer codes for accident analysis. The reports typically include only those events which are analysed using an approach developed for accidents occurring at power operation. 

The potential initiating events, preventive features, and mitigating features were evaluated using event tree analysis methodology, which is detailed in Appendix 3E. The analysis showed that the accident risk could be conservatively bounded by a worst case crash of the forklift with target into fixed, unyielding features at the entrance to the HCF. The expected orientation in a collision impact would be a side impact of the cask. Structural analysis of the isotope transfer cask indicates that the cask will not be broken or breached in a conservatively worst case collision. 

This internally initiated DBA is a potential fire in a radioactive material storage area that is associated with the HCF. The potential for a radioactive material storage area fire was examined by using event tree analysis methodology, which is detailed in Appendix 3E. The frequencies per year for such an accident developed In the event tree analysis agreed with the frequency for a radioactive material storage area fire as assessed in the hazard evaluation. 

The accident analysis report is a narrative. It includes a description of the project and the accident, a summary of findings and recommendations, an outline of methodology, and a detailed discussion of facts, findings, and recommendations. Photographs, drawings, and an event and causal factors chart are included as illustrations. 

The IAEA Safety Report on Accident Analysis for Nuclear Power Plants [1] comprehensively describes the methodology for accident analysis. The report is in concert with the revised Nuclear Safety Standards Series and, in particular, with the safety requirements set out in Safety of Nuclear Power Plants Design [2] and in Safety Assessment and Verification for Nuclear Power Plants [3]. 

The methodology for accident analysis should include identification of the initiating event and the subsequent scenarios and selection of conservative initial and boundary conditions (Section 6). 

INTERNATIONAL ATOMIC ENERGY AGENCY, Coordinated Research Project on Validation of Accident and Safety Analysis Methodology, Rep. CRP/ J.020.03, IAEA, Vienna (2001). 

Lieu, T., Cioran, K, Hayward, B. and Lowe, A. (2007). EUROCONTROL -Systemic Occurrence Analysis Methodology (SOAM) - A neason -based organizational methodology for analysing incidents and accidents. Reliability Engineering and System Safety, 92(9), 1162-9. 

Once the hazards, including the causal factors, have been identified, it becomes important to evaluate the hazards and their effects. Most hazard analysis methodologies apply some type of severity classification. This classification is used as a marker to compare the consequences of one hazard to another. Usually some engineering analysis is done so that you can understand what the effects of the hazard would be if an accident did occur. 

AA 1 Adequacy of scope and methodology of design basis accident analysis... 

Essential complexity, as named, is in the essence of the system. It is an inherent part of a system and cannot be eliminated, instead only minimised. Accidental complexity is not the natural attribute of the system, but is a consequence of an accident. This type of complexity can be eliminated. The following systems analysis methodologies are suggested (Checkland, 1984), (Waring, 1996), (Blanchard and Fabrycky, 1998) ... 

The selected 23 chapters that are included in this volume on traffic safety demonstrate how technological innovations as well as new methodologies applied to transport safety can modify usual practices and offer efficient solutions to the ongoing challenges of safety considerations, needs of vulnerable road users, environmental issues and economical constraints. Both theoretical papers and practical case studies explore topics such as road safety management and policies, accident analysis and modeling, vulnerable road users safety, road infrastructure safety, ITS and railway safety. 

Note Segments that do not meet all of the above shall undergo an accident analysis using the methodology in HDM 5.3. The accident analysis and recommendations should be attached to the design approval document as an appendix. If, based on the accident analysis, it is decided to undertake a safety improvement that cannot be implemented in a 2R project, a 3R or other type of project should be... 

Consistent with the Safety Standards Series, in particular with the Safety Requirements on Safety of Nuclear Power Plants Design [1] and the Safety Guide on Safety Assessment and Verification [2], the IAEA has developed a Safety Report, Accident Analysis for Nuclear Power Plants, which contains a comprehensive description of the general methodology for accident analysis [3]. The objective of that Safety Report is to establish a set of practical suggestions based on the best practice worldwide for performing accident analysis for nuclear power plants (NPPs). The following items are covered in that report ... 

Rune Elvik, one of the most respected scientists in the field and, at the time, (joint) editor in chief of the international journal Accident Analysis and Prevention, conducted what is called a meta-analysis of all studies of this type that were reported in the scientific literature. In a meta-analysis, the first step is to review the scientific soundness of each individual study of the same issue and eliminate those judged to have fatal methodological flaws. Elvik identified 98 sound studies of the effects of speed limit changes in the scientific literature and, after analysing the collective results, concluded that there is a clear causal link between raises in speed limits and increases in crash casualties—and the converse. ... 

Selection of a PrHA methodology requires consideration of many factors including the availability of process information such as experience with the process, changes that have taken place, reliability, aging, maintenance, etc. If it is a new process, less reliance can be placed on experience and greater reliance must be placed on the analysis of possible accidents and accidents in similar or related processes. Size, complexity and hazard severity influences the dunce ot ihe most appropriate PrHA methodology. 

The third category of methods addressed in this chapter are error analysis and reduction methodologies. Error analysis techniques can either be applied in a proactive or retrospective mode. In the proactive mode they are used to predict possible errors when tasks are being analyzed during chemical process quantitative risk assessment and design evaluations. When applied retrospectively, they are used to identify the underlying causes of errors giving rise to accidents. Very often the distinction between task analysis and error analysis is blurred, since the process of error analysis always has to proceed from a comprehensive description of a task, usually derived from a task analysis. 

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