[en] In the Tango experiments UO₂ 1 mm diameter microspheres were irradiated in the Siloe pool reactor in Grenoble. The main parameters are: 1. The initial density 10.11, 10.43, 10.78. 2. The temperatures from 900⁰C to 1500⁰C. 3. The Burn up from 20,000 to 60,000 MWd tsub(U)^-1. 15 out of 27 batches of 300 particles were examined in hot cell. The aim was to determine the diameter increase during irradiation by a microradiography technique associated with an optical density analysis. A tentative correlation is done between swelling and total porosity. An evolution of three populations of pores has been measured and their different aspects have been shown by scanning electron microscope. Finally the stable fission gases residual concentration was determined for each batch irradiated up to 20,000 MWd tsub(U)^-1 by γ counting the gases collected by an evaporation technique. (author)