A comprehensive study of the dissolution of spent sfr mox fuel in boiling nitric acid (the phenix nestor-3 tests)

International audienceDissolution experiments undertaken on irradiated fuel pins from sodium-cooled fast reactors (SFRs) date back to the 1980s at the French Commissariat a l'Energie Atomique et aux Energies Alternatives (CEA). They have been carried out in different workshops and laboratories, using different experimental conditions. New dissolution studies were initiated two years ago on an irradiated pin from a PHENIX NESTOR-3 assembly, and involved separate sections of a single fissile pin in order to better understand its dissolution behavior. Three dissolution experiments were thus run at the CEA-Marcoule on 30 mm long pieces of irradiated materials, using three distinct 120 mm sheared sections of a (U,Pu)O2 fissile NESTOR-3 pin (bottom, middle i.e. full-flux zone, upper). The dissolution experiments were carried out in boiling nitric acid (8 M) for 6 hours to produce a feed solution concentrated to about 180 g/L of Heavy Metals (HM, U+Pu). The masses of dissolution residues were measured, and the Pu dissolution yield and undissolved Pu rate were calculated for each test, then for each fissile column zone