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IAEA Training Course on Safety Assessment of NPPs to Assist Decision Making Defence in DepthSafety Culture Lecturer Lesson II 1_2 and II 1_3 Workshop Information IAEA Workshop City , CountryXX - XX Month, Year

Basic Principles of Safety Assessment (1/2) Basic idea: multiple level of protection - multiple barriers in general sense • Physical carriers between radioactive material and environment. • Prevention of postulates accidents and mitigation of their consequences - a combination of both. • Conservative design, QA in construction, control-limiting and protection systems, engineered safety features (failure of equipment and of human actions is provided with finite probability. IAEA Training Course on Safety Assessment

Basic Principles of Safety Assessment (2/2) • Barriers have to be kept intact by all possible means of: • Technical • Procedural and • Human • Assessment of the effectiveness of defence-in-depth is an important means of assessing plant safety. IAEA Training Course on Safety Assessment

Defence in Depth(1/6) • The levels are independent from each other • Protection against combination of failures at different levels is assured. • The plant must not be operated if appropriate number of elements of defence in depth are not available (e.g. Engineered safety systems failure during test. • Physical barriers (LWRs) • The fuel matrix. • The fuel cladding. • The boundary of the reactor coolant system. • The containment system. • They can have both operational and safety function IAEA Training Course on Safety Assessment

Defence in Depth(2/6) • Protection of the integrity of barriers against internal and external events postulated in the design basis is obligatory • Accident management measures should be developed for both • Prevention of core damage (e.g. feed & bleed) and • Mitigation of consequences (e.g. filtered venting of containment). • Emergency operating procedures should be available for BDBAs and severe accidents IAEA Training Course on Safety Assessment

Defence in Depth(3/6) • Off-site emergency response plan (e.g. Sheltering, iodine prophylaxis, evacuation) should be available and exercises should be used for training preparedness and improvement of measures and procedures • Prerequisites to all measures of all levels are • Conservatism mainly for levels 1-3. For levels 4-5 best estimate considerations should be preferred • QA - as designed vs. As built, as operated, as maintained. The main tool to ensure appropriate achievement is QA. • Safety culture - commitment to safety. Organisations and individuals involved in the whole life cycle processes IAEA Training Course on Safety Assessment

Defence in Depth(4/6) • There are different means for design safety and operational safety to implement defence in depth. • Continuous safety enhancement has to made during operation by: • Feed back of operating experiences (data collection, event analysis, lessons learnt from experiences of other plants, search for hidden deficiencies). • Plant modification, safety upgrading - careful analysis of their safety impact is necessary. • Procedure development (e.g. symptom based EOPs) • Improvements of accident management and emergency response capability. IAEA Training Course on Safety Assessment

Defence in Depth(5/6) • Improvements in defence in depth Severe accident with significant environmental impact can occur only if both • Core seriously damaged and • Containment integrity lost. • Core damage can be avoided by preventive safety functions like: • Core subcriticality. • Core cooling. • Heat transfer to ultimate heat sink IAEA Training Course on Safety Assessment

Defence in Depth(6/6) • Containment integrity is itself the mitigative safety function. • Improving both capabilities is important but prevention has priority over mitigation. • To strengthen prevention some possible means are: • Increased thermal inertia and volume of water. • Operator’s aids (e.g. safety display / panel). • Extended use of passive systems. • Improved maintainability. • To strengthen containment function: • Extended design basis to core damage scenarios (mainly for new plants) would be the most efficient way IAEA Training Course on Safety Assessment

Safety Culture (SC)(1/3) Reference IAEA - document: Safety Culture, Safety Series, No. 75 - INSAG.4. Vienna, 1991 Universal Features of SC - elements for organisations and individuals: • Individual awareness of the importance of safety. • Knowledge and competence, conferred by training and instruction of personnel and by their self-education. • Commitment, requiring demonstration at senior management level of the high priority of safety and adoption by individuals of the common goal of safety. • Motivation, through leadership, the setting of objectives and systems of rewards and sanctions, and through individuals’ self-generated attitudes. • Supervision, including audit and review practices, with readiness to respond to individual’ questioning attitudes. • Responsibility, through formal assignment and description of duties and their understanding by individual. IAEA Training Course on Safety Assessment

Safety Culture (2/3) Tangible Evidence in Different Groups of Organisations 1. Governmental organisations • Legislation and policies • Regulatory body with adequate independence • International information exchange 2. Operating Organisation • Corporate policy - priority of safety • Management structure with clear responsibilities • Regular self-assessment and reviews • Working environment (role of local management) • Individual attitudes (procedures followed, thinking, improvement suggestions, …) • Safety performance indicators, lessons learned and experience feedback IAEA Training Course on Safety Assessment

Safety Culture (3/3) 3. Supporting Organisation (e.g. Designer, researcher) • Listening to others • Involving external experts • As in point No. 2 IAEA Training Course on Safety Assessment

Illustration of the presentation of safety culture IAEA Training Course on Safety Assessment

Workshop Information