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Reactor core meltdown: IRSN and its partners review 25 years of unique international experimental research

From June 13 to 15, 2012, with financial support from the Provence-Alpes-Côte d'Azur region and the European Commission, IRSN held a seminar in the southern French town of Aix-en-Provence to wrap up the PHEBUS FP program. Consisting of five tests, this €300 million research program has generated much new knowledge and made it possible to model and better understand extremely complex phenomena associated with light water reactor core meltdowns that can result in the release of large amounts of toxic radioactive materials to the environment.

The Three Mile Island accident in the United States in 1979 threw into doubt the adequacy of theoretical knowledge of the phenomenology of nuclear reactor core meltdowns. The PHEBUS FP international experimental research program launched in 1988, unique in the world, made it possible to conduct a full range of meltdown experiments on nuclear fuel.

Led and funded by IRSN with the support of EDF, the European Commission, Canada, South Korea, the United States, Japan and Switzerland, the program had two goals: to reduce uncertainty in the assessment of radioactive materials released by LWR core meltdowns, and to improve expertise and emergency response management methods in this field.

The results of the five tests conducted in the PHEBUS research reactor at Cadarache in southern France helped improve knowledge in several areas, including reactor core degradation, prediction of radioelement releases from the core, their deposition in reactor cooling systems, the amounts and speciation of radioactive products such as gaseous iodine entering the reactor containment, and their physicochemical behavior in this environment.

The tests also raised a number of new questions and led to the launch – again as part of broad international partnerships – of additional experimental research programs and analyses to refine and deepen knowledge (in-depth characterization of the “source term” of environmental releases, molten fuel behavior, etc.).

The PHEBUS FP tests contributed greatly to improvements in the numerical simulation of core meltdowns and the quantification of potential environmental releases. They also led to the development of the ASTEC code by IRSN and its German counterpart GRS.

In the days following the Fukushima Daiichi accident, ASTEC produced a fairly accurate assessment of releases from the power plant’s reactors. Today, ASTEC is the Institute’s reference tool for safety assessments, and it forms the basis of its expertise in predicting and quantifying the consequences of core meltdowns.

For more information:

The Phebus PF Programme

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