- 6 - Third level: managing accidents without core melt This entails the assumption that certain accidents, which are the most penalising and encompass all the accidents of a given family, can occur, and to design some safeguard systems to deal with them. These accidents are generally based on conservative hypotheses, in other words it is assumed that the various parameters determining this accident are the most unfavourable possible. Furthermore, the single failure criterion is applied, in other words, in the accident situation, the failure of a component is also postulated. This means that the systems responding in the event of an accident (emergency shutdown, safety injection, etc.) must comprise at least two redundant channels. Fourth level: managing accidents with core melt These accidents were examined following that which occurred at Three Mile Island (1979) and are now incorporated into the design of new reactors such as the EPR. The aim is either to rule out these accidents, or to design systems able to deal with them. The study of these accidents will be reassessed in the light of the experience feedback from the Fukushima accident. Fifth level: mitigation of the radiological consequences of significant releases This involves implementing emergency plan provisions, including population protection measures: sheltering, administration of stable iodine tablets to saturate the thyroid and prevent it from absorbing the radioactive iodine carried by the radioactive plume, evacuation, restrictions on the consumption of water or foodstuffs, etc. 3.2 Safety management Safety management consists in creating a safety culture within the risk management organisations. The safety culture is defined by INSAG1, an international consultative group for nuclear safety reporting to the Director General of the IAEA2, as being a range of characteristics and attitudes which, for both organisations and individuals, ensure that matters relating to the safety of nuclear facilities are given the priority attention warranted by their importance. The safety culture thus reflects how the organisation and the individuals perform their roles and assume their responsibilities with regard to safety. It is one of the key factors in maintaining and improving safety. It requires that each organisation and each individual pay particular and appropriate attention to safety. It must be expressed at an individual level by a rigorous and prudent approach and a questioning attitude which ensure compliance with rules while leaving room for initiative. It is applied operationally in the decisions and actions relating to the various activities. 3.3 Operating experience feedback Operating experience feedback contributes to defence in depth. It consists in implementing a reliable system for detecting any anomalies that may arise, such as equipment failures or errors in the application of a procedure. This system should be able to ensure early detection of any abnormal operation and draw the conclusions (particularly in organisational terms) such as to prevent these anomalies from happening again. Operating experience feedback includes events taking place in France and abroad with pertinence for improved nuclear safety or radiation protection. 4. ASN regulation of civil nuclear facilities The French civil nuclear fleet is the world's second largest. It comprises a total of 150 nuclear facilities: 58 pressurised water reactors producing most of the electricity consumed in France, one EPR type reactor under construction, the various fuel cycle facilities, research facilities and facilities currently undergoing decommissioning. 1 INSAG: International Nuclear Safety Group 2 IAEA: International Atomic Energy Agency
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