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Abstract: The radioactivity levels in the air of the radionuclides released by the Fukushima accident were measured at the Laboratoire Souterrain de Modane, in the South-East of France, during the period 25 March–18 April 2011. Air-filters from the ventilation system exposed for one or two days were measured using low-background gamma-ray spectrometry. In this paper we present the activity concentrations obtained for the radionuclides 131I, 132Te, 134Cs, 137Cs, 95Nb, 95Zr, 106Ru, 140Ba/La and 103Ru. The activity concentration of 131I was of the order of 100 μBq/m3, more than 100 times higher than the activities of other fission products. The highest activities of 131I were measured as a first peak on 30 March and a second peak on 3–4 April. The activity concentrations of 134Cs and 137Cs varied from 5 to 30 μBq/m3. The highest activity concentration recorded for Cs corresponded to the same period as for 131I, with a peak on 2–3 April. The results of the radioactivity concentration levels in grass and mushrooms exposed to the air in the Modane region were also measured. Activity concentrations of 131I of about 100 mBq/m2 were found in grass. [Copyright &y& Elsevier]

• Outcome of the France-Japan collaboration on R&D related to fuel discharge. • Study of efficiency of mitigation devices. • Unprotected Loss Of Flow simulation results in terms of mitigation efficiency. • Local calculations around one transfer tube. Sodium-cooled Fast Reactors (SFR) are investigated as future Generation IV reactor concepts. In SFR, the core configuration is not the most reactive during the nominal reactor operation, its geometry change or coolant voiding can induce a reactivity insertion. Within these considerations, mitigation devices should be implemented into the core in order to limit the thermal energy released into the fuel during a severe accident and thereby the possibility to induce mechanical loadings of the reactor structure when vaporized materials expand. Complementary safety devices called Transfer Tubes (TT) are studied in a French concept as an effective mitigation measure of severe accidents to reach a final reactor safe state, even in case of a failure of all shutdown systems including the passive shutdown safety rods. More precisely the TT, with their upper part located in and above the core, cross the core support structure and are linked to the core catcher zone situated in the main vessel bottom. Their purpose is to extract fissile materials from the core zone and secondly to favor the transfer of the molten fuel from the core region to the core catcher in case of severe core damage. The fuel discharge out of the core zone is necessary in order to lower the core reactivity, the relocation into the core catcher is necessary to enable the stabilization, the sub-criticality and the fuel cooling. An extensive work on severe accident calculations and phenomena identification related to fuel discharge through TT was performed. These studies represent the outcome of the work performed in 2014–2019, performed with collaboration of Japanese JAEA and MFBR and Framatome in the framework of the SFR project carried out by CEA. Calculations of fuel discharge were carried out with the mechanistic calculation code SIMMER and the main results are presented in this paper. Firstly, the whole unprotected loss of flow (ULOF) accident sequence was calculated with the SIMMER code. From these calculations, the power and flow evolution were set as boundary conditions for a more detailed model with six fuel assemblies around TT. This model was used to focus on key phenomena and to check impact of design parameter as local bottom restriction inside TT on fuel discharge way. [ABSTRACT FROM AUTHOR]