Abstract. Post-accidental management aims at restoring acceptable life conditions for population on sanitary, social and economic aspects. It is then a matter for an optimisation process in a multicriteria context, which has to combine quantitative parameters as well as qualitative parameters. In order to fit with this problematic, 1PSN has developed and applied a methodology to a major accident situation on a reactor. The methodology consists in making a systematic evaluation of indicators in order to provide intercomparing data for many rehabilitation strategies. The methodology relies on four steps: characterisation of the geographic and demographic environment, radiological diagnosis, selection of countermeasures from a well characterised set of techniques, and last, evaluation of the intercomparing factors. For each selected countermeasures, radiological benefit and some incidences have been calculated: duration of realisation of the countermeasure, materials and human means, worker doses, amount and characteristics of generated wastes. In this context, calculations highlighted the importance of external exposure in built areas, and consequently the importance of the corresponding countermeasures. This work is a useful contribution to the clarification of the post-accidental rehabilitation problem.
La gestion post-accidentelle relève d'une démarche d'optimisation, dans un contexte multicritère, s'appuyant aussi bien sur des paramètres quantitatifs que qualitatifs. Afin de répondre à cette problématique, un travail méthodologique a été réalisé et mis en oeuvre dans le cadre de l'exercice national de crise Becquerel, qui a simulé un accident de type Borax sur un réacteur expérimental. La méthodologie développée consiste, à partir de l'évaluation systématique d'indicateurs quantinables, à proposer des éléments d'intercomparaison des diverses stratégies de réhabilitation. Ainsi chaque stratégie est appréciée en termes de gain radiologique pour la population, et d'incidences induites telles que le temps de réalisation, les moyens matériels et humains nécessaires, les doses aux intervenants, ainsi que les volumes de déchets générés. Dans ce contexte, les évaluations ont notamment mis en évidence l'importance des contre-mesures destinées à réduire l'exposition externe qui est la voie d'exposition prépondérante. En réduisant l'activité massique dans les aliments, les contre-mesures relatives aux compartiments menant à une dose par ingestion, présentent un intérêt essentiellement au regard des limites de commercialisation. Ce travail constitue une première contribution utile à la clarification des enjeux liés à la réhabilitation post-accidentelle. 11 a également fait apparaître des besoins dans plusieurs domaines dont : la formalisation des contre-mesures aün de les regrouper en une base de données, l'adaptation des outils de calcul en vue d'en accroître la souplesse d'emploi, l'amélioration de la connaissance des aspects opérationnels des interventions. ABSTRACT Methodology for rehabilitation strategies evaluation aid after an accident: application and results. Post-accidental management is a matter for an optimisation process in a multicriteria context, which has to combine quantitative parameters as well as qualitative parameters. In order to fit with this problematic, a methodological work has heen realised at IPSN, in the context of the Becquerel national exercise, which has simulated a Borax type accident on an experimental reactor. The methodology consists in making a systematic evaluation of indicators in order to provide intercomparating data for many rehabilitation strategies. Thus, each strategy
Scenarios are used to deal with uncertainty on the evolution of complex systems. The scenario selection methodologies also have to provide a basis for reflexion and traceability of the reasoning. In the case of a simple concept landfill, a methodology that fulfils these requirements has been developed. It distinguishes on the one hand the landfill evolution, and on the other hand, the human behavior evolution. It is based on three steps: (i) characterization of the landfill itself, in order to define situations leading to releases of radionuclides, (ii) characterization of the human behavior in order to define situations leading to intrusions, and (iii) characterization of the interfaces between the two subsystems, in order to identify situations which could lead to a radiological risk for man. The method has been applied to performance assessment for landfill of uranium mill tailings. It has led to one reference scenario, and five altered scenarios taking into account specific landfill evolutions such as loss of covering or loss of integrity of the dike, and human intrusions such as housing on the site of landfill or excavation of the site.
IPSN-DPRE/SERGD -60-68 av. du Ga' Leclerc, BP 6 -92265 Fontenay aux roses cedex, France -badie@basilic.ipsn.fr 2 ' av. de Wagram.75382 Paris cedex 08, France 13 EDF -DER/ESF, 1, av. du Gal de Gaulle -92141 Clamart, France 1 4 'EDF -DAC, 23 bis av. de Messine, 75384 Paris cedex 08, France High level waste repositorie facilities are complex systems : the parameters, processes, their interactions and the relationships between the system and its environment are numerous. Lack of knowledge and variability of parameters in the field we are studying and the time periods we require to consider, generate uncertainty which may be hard to evaluate and may affect sensitive factors (ex: human intrusion).The management of this complexity requires the use of a well defined methodology. Two kinds of approach have emerged from this situation : the Environmental Simulation Approach (ESA) and the scenario approaches. In the latter one , two further kinds of approaches are usually distinguished : the systematic one and the judgemental one (also called deterministic).A study of the three approaches underscores their complementary nature and tends to highlight the subjectivity of the classification mentioned above : -the difference between the ESA and the scenarios approaches lies in the level of modelling of the phenomena : the more specific the models are, the more we must distinguish scenarios. On the other hand, if a numerical model is able to manage all situations, then scenarios become useless, and we fall into the ESA. expert judgement is unavoidable. It is present in all of these approaches. the term "deterministic" is inadequate as a criterion of classification of scenario development methods. In the first place there is no opposition between "deterministic" and "systematic" terms. In the second place, "probabilistic" scenario selection methods provide degrees of credibilityused to organize scenarios into a hierarchy, just as "deterministic" methods provide a classified list of scenarios (reference scenario and alternative scenarios).The three approaches use a specified methodology and the transition from one to another is continuous. What allows their differentiation, and what is the advantage of scenarios approaches, are characteristics such as transparent documentation, the ability to justify the reasoning, its traceability and its storage. These characteristics are also continuous but they are essential to a good system assessment methodology, which needs to provide a high level of confidence that all important safety aspects are covered. Besides, the formalization of the knowledge enables uncertainties in important factors of the safety assessment to be identified, and thus determination of research priorities. 1017 Mat. Res. Soc. Symp. Proc. Vol. 506
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