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[en] In risk assessment we are typically faced with a huge number of potential scenarios and events, and in practise some of these are ignored, either because they are not identified or because of judged low probability. However, a scenario or an event may occur despite being extremely unlikely. Considering a large population of such scenarios and events, the occurrence probability is not necessarily negligible. In this paper we take a closer look at this challenge, the main aim being to clarify the issue and provide some recommendation on how to best handle it in practise. A main conclusion is that the risk assessment should be placed in a sufficiently broad framework, ensuring that the outcome and main event spaces are complete, and sufficient focus is placed on the hypotheses and assumptions supporting the detailed scenarios that are identified. - Highlights: • The paper clarifies and discusses the issue of ignoring scenarios/events in risk assessments. • It draws attention to unknown knowns and events judged to have negligible probability. • The paper provides guidance on how to best handle the challenge in practise. • A key message is that one should strive for complete event and outcome spaces. • Focus should be placed on the key hypotheses and assumptions made.
[en] In the presentation the influence of different parameters on the Ft-function were shown. The increase of the impact velocity shows for all aircraft a higher maximal load value and a reduced impact time. Due to the structural setup of the aircraft's the intensity is of these effects different. Comparing the Ft-function of A320, A340 and A380 for an impact velocity of 100 and 175 m/s no constant relation between them can be determined. • The variation of the flight direction with respect to the vertical axis shows a great influence on the Ft-function. A approximation by the cosine is especially for bigger rotations not correct. The influence of the rotation about the horizontal axis can be neglected. Finally the SPH-method was applied for the modelling of the fuel. The comparison to the discrete modelling approach was carried out for the Phantom F4. Thereby no big influence on the Ft-function is observed. For the evaluation of this modelling approach on the local damage the loaded area must be determined in further investigations
[en] In the twentieth century, radioactive sources have become extensively used in everyday life. These sources, in the hand of terror organizations, can become a threat to the security of civilized nations, causing severe disruption to normal life. On of the main challenges of the civilized world is to keep ahead of the terrorist organizations and take appropriate preventive measures in order to prevent and reduce to minimum the impact of their actions. In order to succeed, a joint and comprehensive effort has to be undertaken to address the scientific, technological, organizational, sociological, psychological and educational aspects of the radiological terrorism threat. In this paper, some of the main activities required for preventing radiological terror events, and the way in which a modular response plan can be prepared are discussed
[en] The results of the MASCA (RASPLAV) OECD project gave evidence that the behaviour of the reactor materials on the RPV bottom during a postulated accident is primarily governed by physico-chemical interactions, i.e. by the thermodynamics or thermochemistry of the emerging oxidic systems containing uranium, zirconium and steel, Fe (Cr, Ni, ...) substoichiometric with respect to oxygen. The results of the thermochemical studies from the METCOR ISTC project confirm this and, in addition, enable insight to be gained into the behaviour of the systems in non/equilibrium conditions involving high temperature gradients. For IVR applications this implies that estimates of the amount of heat removed from the RPV (i.e. assessment of whether the IVR strategy can be successful during the accident or not) cannot build on thermohydraulic reasoning (which in turn is based on sophisticated experiments) solely: in fact, thermodynamic constraints must also be taken into account
[en] The methodology and selected models used for assessing the frequency of aircraft crashes to critical surface facilities are examined. The DOE Standard model is the basis for comparing other models, particularly those used to assess risk to DOE facilities. The NRC methodology is relevant for nuclear power plants. A rigorous physical model that describes the Markov chain of events and their related probabilities that lead to aircraft hazards to ground facilities is developed. The chain of events is then quantified to provide a basis for comparison and evaluation of mathematical models. The model has a form similar to the standard transport equation for a particle at a given position in space moving with a given velocity under the influence of various force fields, e.g., engine thrust, drag, lift, and gravity. It is evident that all quantitative models for aircraft crash frequency assessments are constrained by the limited statistical database available for supporting such risk assessments. Aircraft crashes to critical facilities are rare events, and this condition limits experimental data and verification efforts. Most existing models are very conservative and employ assumptions that overestimate actual risks