Overview of the facility and experiments performed in Phébus FP

The international Phébus FP programme was initiated in 1988 by the French "Institut de Radioprotection et de Sûreté Nucléaire" (IRSN2), in cooperation with the European Commission (EC), to investigate key phenomena involved in light water reactor (LWR) severe accidents. In addition to IRSN and EC, other partner countries contributed to this programme. The Phébus facility was operated by the French "Commissariat à l'Energie Atomique" (CEA) at Cadarache, providing prototypic reactor conditions which allowed to study fuel degradation, the release of fission products (FPs) and their transport and behaviour through the reactor coolant system (RCS) and in the containment building. A specific attention was paid to iodine radiochemistry due to its major impact on the consequences of any radioactivity release to the environment. A preliminary re-irradiation period allowed to build up a short lived fission product inventory typical of a reactor fuel. The experimental phase comprised two main parts: during the fuel degradation phase, the experimental bundle was heated-up, then fission products were emitted and transmitted through the circuit towards the containment. In the second part, the containment was isolated from the circuit and the long term phase consisted of investigating first, the aerosol physics in the containment atmosphere, and next, the iodine chemistry. A large amount of instrumentation was implemented to measure on the one hand thermal-hydraulic parameters as temperature, pressure, humidity, hydrogen, oxygen and carbonaceous gases concentrations, pH, and on the other hand, fission products release, either through on-line γ-spectrometers, or with sampling devices coupled with off-line post test analysis. Attention was focused on the instrumentation devoted to iodine measurements to allow the distinction between aerosol particles, gaseous molecular iodine and other gaseous iodine species like organic iodides. After the test, a non-destructive examination campaign of the test section allowed to describe the final degradation state. Further destructive examinations were performed on selected parts of the fuel bundle to give information on the interaction between materials, and also on selected circuit sampling devices to obtain data on the long lived fission products and to characterise aerosols. © 2013 Published by Elsevier Ltd