Nuclear fission
METHODS FOR THE ASSESSMENT OF HAZARDS COMBINATIONS
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- 5.2Data needs
- 5.3Initiating events
- 5.4Reference to known methods
5METHODS FOR THE ASSESSMENT OF HAZARDS COMBINATIONS5.1General descriptionIAEA Safety Guide NS-G-1.5 [29] includes the combination of human induced events within the group of the man-made external hazards as a result of a common initiating event, as a product of events (like, e.g. explosion with release of hazardous gases, fire and smoke generation, aircraft crash induced missiles, vibrations or explosions of aircraft fuel). Domino effects shall also be considered (like, e.g. storage tank explosion induced by a pool fire). IAEA Safety Standard NS-R-1 [30] cautions about the combination of individual events evaluation to ensure some rationale justifying the particular combination: for instance, a random combination of events may represent an extremely unlikely scenario such as to motivate its disregarding in the probabilistic safety analysis. Probabilistic evaluations should be carried out, for the definition of suitable combinations for the plant design and for the subsequent risk assessment, between external events and internal accidents, addressing both their potential correlation and their resulting probability. In any case, combinations of two or more individual events should be carefully analysed with account taken of the dependence or independence of the events. In an accidental scenario, independent events can be assimilated to simultaneous events (for non-simultaneous events, but occurring before the effects of the previous event completely ceased, sometimes, by simplification, it is conservatively considered that the subsequent events will occur at the worst moment for the facility safety): the probability that the events will occur in such conditions that their effects will be cumulated is related to the duration of each event. The probability that the events occur in combination is equal or less than the product of the probability of each event. Expert judgement and probabilistic methods can be used for the selection and relative credible estimation of event combinations that should be thoroughly analysed in order to select the anticipated operational occurrences and the mitigation actions to be taken into account in the plant design or to be included in the risk assessment. At present, the technology is not always available for precisely assessing the numerical probabilities that a given level of severity of an effect is exceeded in each separate event or by a combination of events. However, in absence of best estimated methods, conservative values should be estimated for these probabilities. 5.2Data needsThe approaches to estimate the frequency of combination of external events are applicable by using explicit site and plant specific data, as well as accident statistics relative to trucks, trains, shipments and aircraft and data on traffic accidents involving fires, explosions and toxic releases. As well, industrial facilities and hazardous material pipes shall be considered. 5.3Initiating eventsCombination of external events shall be identified based on a comprehensive hazard analysis. All foreseeable combination of external hazards, including the potential for human induced events to affect directly or indirectly the safety of the plant shall be identified and their effects on relevant SSCs important to nuclear safety shall be evaluated. The design of a facility shall include due consideration of those natural and human induced external events (i.e. events of origin external to the facility) combination that have been identified in the site evaluation process. In addition to natural external events (including meteorological, hydrological, geological and seismic events), human induced external events arising from nearby industries and transport routes shall be addressed. For man-made and aircraft crash hazards, credible combinations have been identified and they include:
In order to simplify the assessment, it is suggested in [31] to split the combination assessment into three stages. The first stage is to identify the plausible off-site hazard combinations. The second stage is to identify the potentially induced on-site failure/hazards. A final stage is to identify the potential additional induced failure that could be induced by the possible hazards identified in the second phase. 5.4Reference to known methodsIAEA includes requirements on combined hazards and safety analysis in [18]: the problem is the lack of detailed guidance on this issue and the fact that combinations of events are frequently screened out from analysis. Expert judgement is used for the identification of extreme hazards combination probability, for instance adopting a matrix method with expert panel aimed on identification of critical combinations for given plant design. Document [32] proposes, in the fashion of qualitative analysis, some risk assessment methods applicable to external hazard combination depending on the frequency, effects on the plant and accident scenario:
Within the recently held OECD Workshop on PSA OF NATURAL EXTERNAL HAZARDS INCLUDING EARTHQUAKE Prague, Czech Republic, June 17th-20th 2013 [33], some approaches aimed at the combinations of hazards topic are proposed, which are likely to apply to the present case. In particular the paper presented by L. Burgazzi, ENEA, Italian National Agency for New Technologies, Energy and Sustainable Economic Development, titled “Implementation of PSA models to estimate the probabilities associated with external event combination” shows how, in the light of the Fukushima accident, correlated hazards are of special interest in PSA for external hazards [34]. Thus, a mathematical method for modelling correlations was proposed in the presentation and an illustrative example was presented. The method is based on joint probability distributions and covariance matrices. A systematic method aimed at identifying important hazard combinations and associated dependencies among PSA initiating events was presented by S. Sperbeck from GRS in his presentation titled “Recent research on natural hazards PSA in Germany and future need” [33]. During the discussion, it was also suggested that, given the multiplicity of potential combinations, such an analysis should be carried out in a systematic manner (e.g. by matrix of possible external events combinations). Finally the workshop pointed out the identification of correlations between external hazards as another important point. The combinations of simultaneous or successive external hazards may result in increased loadings on SSCs or they may simultaneously endanger diverse safety systems. Formal mathematical methods to treat the probabilities of correlated hazards are available but the quantification of the model parameters is a big challenge, due to the scarcity of data. Directory: wp-content -> uploads -> 2016 2016 -> 2017 afoCo Landmark Scholarship Program 2016 -> Instructions for the Preparation of Camera-Ready Contributions to the Conference Proceedings 2016 -> Step student Scholarships for Year 10-13 2016 -> The united church of canada 2016 -> Idan raichel biography – May 2016 Brief Producer, keyboardist, Lyricist, composer and Performer Idan Raichel 2016 -> An introduction to centre’s interventions expanding access to justice 2016 -> Sanchar Shakti 2016 -> Unit analysis should help here. We want number of bananas 2016 -> The Autobiography of Elder Joseph Bates 2016 -> The Great Heat and the Rhode Island Deep Water Bay Scallop (Argopecten irradians) Fishery 1875-1905 Download 1 Mb. Share with your friends:
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