ASN carried out research work on its own safety culture, with the assistance of the Nantes-Atlantique Economics and Management Laboratory of the University of Nantes. This work lasted a year and was completed in September 2024, primarily concerning BNI oversight and regulation activities. After a bibliographical analysis, the study turned to an analysis of ASN’s organisational culture. The regulator’s safety culture being “that part of the organisational culture that influences the behaviour of individuals (staff and management), organisational units and the organisation in dealing with safety”(2). Through individual and group interviews of its staff, field observations and interactions with the licensee and IRSN, the study was able to highlight six fundamental principles present in the organisational system as a whole, three aspects of the sub-culture of this system and three performance criteria for BNI oversight and regulation on which the ASN safety culture is based. The six fundamental principles are present at all points of the organisation related to the BNI oversight and regulation activities and constitute ASN’s organisational culture and, since 1 January 2025, that of ASNR. They describe a system (see diagram previous page) in which the limits of each principle are compensated for by one or more others. The three sub- cultures identified within ASN each comprise their own practices and attitudes on the part of the staff. All of these fundamental principles and aspects of these sub-cultures participate in the performance of the BNI oversight and regulation activities and contribute to generating performance in terms of this oversight and regulation. The three performance criteria identified are: efficient inspections, robust decisions and effective incentives. These criteria are based both on the six fundamental principles and on certain sub-cultures. Each criterion concerns one of the three major activities of BNI oversight and regulation: inspection, decision-making and enforcement-sanction within ASN. These six fundamental principles concerning the BNI oversight and regulation activities constitute the ASN organisational culture and are just as present in that of ASNR. Their inter-dependence and the existence of the three sub- cultures reflect the complexity of the operation of the organisation which had to be used during the construction of the ASNR and the corresponding organisational and managerial transformations. 2. Guidelines for safety culture self-assessment for the regulatory body International Atomic Energy Agency (International Atomic Energy Agency, Vienna, Austria, 2019, p. 5). 1.2.2 The “Defence in Depth” concept The concept of “Defence in Depth” consists in implementing a series of levels of defence based on the intrinsic characteristics of the installation, material, organisational and human measures and procedures designed to prevent accidents and then, if this fails, to mitigate their consequences. “Defence in Depth” is a concept which applies to all stages in the lifetime of a facility, from design to decommissioning. These levels of defence are consecutive and independent in order to prevent an accident from developing. An important element for the independence of the levels of defence is the use of different technologies (“diversified” systems). The design of nuclear installations is based on a “Defence in Depth” approach. For example, the following five levels are defined for nuclear reactors: Level 1: Prevention of abnormal operation and system failures This is a question firstly of designing and building the facility in a robust and conservative manner, integrating safety margins and planning for resistance with respect to its own failures or to hazards. It implies conducting the most exhaustive study possible of normal operating conditions to determine the severest stresses to which the systems will be subjected. It is then possible to produce an initial design basis for the facility, incorporating safety margins. The facility must then be maintained in a state at least equivalent to that planned for in its design through appropriate maintenance. The facility must be operated in an informed and careful manner. Level 2: Keeping the installation within authorised limits Regulation and governing systems must be designed, installed and operated such that the installation is kept within an operating range that is far below the safety limits. For example, if the temperature in a system increases, a cooling system starts up before the temperature reaches the authorised limit. Condition monitoring and correct operation of systems form part of this level of defence. Level 3: Control of accidents without core melt The aim here is to postulate that certain accidents, chosen for their “envelope” characteristics (the most penalising in a given family), can happen and to design and size backup systems to withstand those conditions. Such accidents are generally studied with pessimistic hypotheses, that is to say the various parameters governing this accident are assumed to be as unfavourable as possible. In addition, the single failure criterion is applied, in other words we postulate that in the accident situation and in addition to the accident, there will be the most prejudicial failure of one of the components used to manage this situation. As a result of this, the systems brought into play in the event of an accident (“safeguard” systems ensuring emergency shutdown, injection of cooling water into the reactor, etc.) comprise at least two redundant and independent channels. Level 4 : Control of accidents with core melt These accidents were studied following the Three Mile Island accident in the United States (1979) and are now taken into account in the design of new reactors such as the European pressurised water reactor (Evolutionary Power Reactor – EPR). The aim is to preclude such accidents or to design systems that can withstand them. The 5 levels of “Defence in Depth” Limiting the consequences of releases On-site emergency response plan Limiting the consequences of a severe accident Severe accident management Control of accidents Maintaining within the authorised range Design Operation Prevention of anomalies Regulation systems, periodic checks Backup systems, accident procedures 126 ASN Report on the state of nuclear safety and radiation protection in France in 2024 The principles of nuclear safety and radiation protection and the regulation and oversight stakeholders
RkJQdWJsaXNoZXIy NjQ0NzU=