No abstract available

[en] In France, after the Fukushima accident, the Nuclear Safety Authority (ASN) required the performance of 'stress tests', on line with the ENSREG requirements. The conclusions of the stress tests led in particular, for each nuclear installation, to the definition of a 'hardened safety core': a limited group of systems/organisation/human means able to provide essential safety functions even during circumstances far beyond the design. Although the definition and design of the 'hardened safety core' are based on deterministic principles, the insights from PSA are a precious tool for a complementary analysis. The use of Level 1 and level 2 PSA is primarily based on the use of existing studies, for example the conditional probabilities of core melt and of releases due to a total loss of electrical power and/or of ultimate heat sink, especially taking into account long-lasting sequences which were already investigated in French PSAs before Fukushima. The sequences relating to the loss of the Spent Fuel Pool cooling were also included in the PSA. Moreover extensions of the PSAs are considered for particular events relating to external hazards, internal hazard (such as fire) and to multi-unit sites. The paper gives some particular examples of applications useful for the 'hardened safety core' assessment using PSA insights as a complementary tool to the deterministic analysis, and a view on on-going and future developments. (author)

[en] This paper presents recent actinides (reflected or not, moderated or not) critical masses calculations performed by the French standard route (APOLLO2 Sn 8 P3, 20 energy groups cross-section collapsed from 172 energy groups CEA 93 library). Comparisons are also presented against more accurate routes of the French criticality package CRISTAL, showing the fair conservatism of the standard values. Checks of the Paxton Woodcock rule for transportation exemption limit were also made. (author)

[en] Under the form of Power Point presentations, the contributions present the agenda of the additional safety assessments, the prescriptions and the national action plan, present the definitions, principles and scopes of hard cores, comment the examination by the IRSN of seismic risk levels proposed by the operator for the hard core, present the FARN (Force d'action rapide du nucleaire, nuclear fast intervention force), report an analysis of European stress tests

[en] For more than 40 years, IPSN then IRSN has conducted research and development on nuclear safety, specifically concerning pressurized water reactors, which are the reactor type used in France. This publication reports on the progress of this research and development in each area of study - loss-of-coolant accidents, core melt accidents, fires and external hazards, component aging, etc. -, the remaining uncertainties and, in some cases, new measures that should be developed to consolidate the safety of today's reactors and also those of tomorrow. A chapter of this report is also devoted to research into human and organizational factors, and the human and social sciences more generally. All of the work is reviewed in the light of the safety issues raised by feedback from major accidents such as Chernobyl and Fukushima Daiichi, as well as the issues raised by assessments conducted, for example, as part of the ten-year reviews of safety at French nuclear reactors. Finally, through the subjects it discusses, this report illustrates the many partnerships and exchanges forged by IRSN with public, industrial and academic bodies both within Europe and internationally

[en] In order to avoid criticality risks, a large number of facilities using spent fuels have been designed considering the fuel as fresh. This choice has obviously led to considerable safety margins. In the early 80's, a method was accepted by the French Safety Authorities allowing to consider the changes in the fuel composition during the depletion with some very pessimistic hypothesis: only actinides were considered and the amount of burnup used in the studies was equal to the mean burnup in the 50-least-irradiated centimeters. As many facilities still want to optimize their processes (e.g. transportation, storage, fuel reprocessing), the main companies involved in the French nuclear industry, researchers and IRSN set up a Working Group in order to study the way burnup could be taken into account in the criticality calculations, considering some fission products and a more realistic axial profile of burnup. The first of this article introduces the current French method used to take burnup into account in the criticality studies. The second part is devoted to the studies achieved by the Working Group to improve this method, especially concerning the consideration of the neutron absorption of some fission products and of an axial profile of burnup: for that purpose, some results are presented related to the steps of the process like the depletion calculations, the definition of an axial profile and the criticality calculation. In the third part, some results (keff) obtained with fission products and an axial profile are compared to those obtained with the current one. The conclusions presented are related to the present state of knowledge and may differ from the final conclusions of the Working Group. (author)

[en] After an overview by the ASN of complementary safety assessments and an assessment of 'post-Fukushima' inspections of basic nuclear installations, the contributions (Power Point presentations) of this seminar proposed: the opinion of the Gravelines CLI (local information commission) on the Gravelines complementary safety assessment report, an analysis and discussion by the GSIEN on reports of complementary assessment of safety of nuclear installations with respect to the Fukushima accident, an analysis by the IRSN of complementary safety assessments performed by operators, the IRSN approach to analyze complementary safety assessments, reports on installation conditions, external flooding and seismic hazard, 'meltdown prevention' aspects in the management of accidental situations in EDF reactors

[en] After a synthesis, this document contains the contributions (Power Point presentations) of a seminar which addressed the following topics: remarks by the HCTISN on the process of complementary safety assessments, analysis and discussion by the GSIEN on reports of complementary assessment of safety of nuclear installations with respect to the Fukushima accident, opinion of the Gravelines local information commission (CLI) on the complementary safety assessment report for the Gravelines nuclear power plant, stage point of the Manche INTERCLI work-group on the safety of nuclear installations after Fukushima, presentation by the IRSN of the complementary safety assessments, and opinion of the ASN on complementary safety assessments (ECS) of priority nuclear installations

[en] After a synthetic report of the meeting, this document contains Power Point presentations proposed by the different contributors. These presentations proposed: an overview on additional safety assessments (ECS) and an assessment of 'post-Fukushima' inspections performed in basic nuclear installations; the CLI's opinion on the Gravelines ECS report; an analysis and a discussion of ECS reports of nuclear installations in the perspective of the Fukushima accident; the IRSN analysis of ECS as they are performed by operators; a presentation of the IRSN analysis approach to ECS; contributions of different post-Fukushima ECS permanent groups within the IRSN (these work groups address installation condition, external flooding, and seismic risk); a presentation of the 'fusion prevention' aspects of the management of accidental situations in EDF reactors

[en] In a collection which aims at providing those who are performing activities in relationship with ionizing radiations, notably in the nuclear industry, with elements of cultural technique related to the prevention and to the management of associated risks, this volume addresses pressurised water reactors (PWRs) and more particularly those which build up the French nuclear fleet. A first part presents general contextual elements: health and biological effects of ionizing radiations and the system of radiation protection, organization of the control and regulation of nuclear installations and activities in France, the international and societal dimensions, nuclear reactors as complex social-technical systems and the importance of organizational and human factors. The second part addresses safety at the design level: development of nuclear energy based on the use of uranium-235 and some notions of PWR physics, general objectives, principles and fundamental concepts of the safety approach, safety options and considerations at the design level, study of operating conditions in the safety deterministic analysis, the accident with loss of primary cooling, the particular case of steam generator tubes, the taking of aggressions of internal or external origin into account, complementary event domain, development and use of safety probabilistic studies, specific aspects related to fuel warehousing pools, integration of organizational and human factors during the design of installations, study and taking into account of core fusion accidents, new generation reactors. The third part addresses safety during exploitation: start tests of PWRs, general rules of exploitation, rules and practices with the return on experience of events, return on experience due to a weakness of the initial design of reactors or to the maintenance quality, return on experience related to interventions, to electricity sources and distributions, or to internal or external aggressions, strengthening of the protection of sites along an estuary or river (examples in Le Blayais and Cruas-Meysse), the taking of organisational and human factors for the exploitation of installations, the maintenance of installations, in-service monitoring and control of equipment, managements, control and evolutions of the nuclear fuel, the compliance of installations, periodic re-examinations, optimization of radiation protection and limitation of doses received by workers. The fourth part addresses the accidents of Three Mile Island, Chernobyl and Fukushima, lessons learned, and the management of emergency situations. The fifth part is dedicated to studies, researches and developments in the safety of PWRs, and to simulation software