The final seminar of the international Phébus FP Programme was held at Aix-en-Provence, France, during 13–15 June 2012. This seminar, coorganized by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) and the Joint Research Center of the European Commission (EC/JRC), concluded a large international cooperative programme of research on Light Water Reactor (LWR) severe accidents that began in 1988. This programme was conducted by IRSN in the Phébus in-pile test facility, operated by the French “Commissariat à l’Energie Atomique” (CEA). Along with IRSN and EC/JRC, the partners of the programme were the French utility “Electricité de France” (EDF), the U.S. Nuclear Regulatory Commission (USNRC), the Canadian CANDU Owners Group (COG), the Japanese Nuclear Energy Safety Organization (JNES), the Japanese Atomic Energy Agency (JAEA), the Korean Atomic Energy Research Institute (KAERI), and the Swiss Federal Nuclear Safety Inspectorate (ENSI, formerly HSK) and the Swiss Paul Scherrer Institut (PSI). Thanks to the sponsoring of the European Commission, all the nuclear safety organizations of the Member States and many university laboratories were also involved in the programme, contributing to the numerous and fruitful discussions about test definitions and result analyses.
The experimental programme consisted of five integral in-pile tests, carried out from December 1993 to November 2004, four of them using irradiated fuel. The main objective was to investigate fuel melt progression and subsequent radionuclides and structural material releases, their transport in the reactor coolant system and their behaviour in the containment. It produced a wealth of unique data, allowing to improve the understanding and the modelling of most of the physical phenomena involved in LWR core meltdown accidents, in particular those which determine the composition of the potential atmospheric radioactive release (also called “source term”) from damaged Nuclear Power Plants (NPP). Such knowledge was obviously of major interest to predict the course of the accident that affected the Fukushima Daiichi units 1 to 3, in March 2011 and to understand what was released in the atmosphere. This knowledge will contribute to reinforce the safety of NPPs in order to try to prevent new disasters and, if they nevertheless happen, to mitigate their consequences by appropriate severe accident management measures.
About 200 experts from nuclear regulatory organizations, research centres, universities and industry, in as many as 23 countries and from 4 international organizations, attended the seminar. Out of the 26 presentations, twenty were selected by the scientific committee of the seminar for their technical content and their capacity to give the reader a broad and synthetic view of the results of the Phébus FP Programme and of their use to improve modelling and ultimately nuclear safety. Authors were then asked to submit full papers, which constitute this Annals of Nuclear Energy Special Issue. Papers were pre-reviewed by the scientific committee, which included eight experts involved in the programme, with the help of sixteen “external” experts in the domain.