[en] Three UO₂-Zr test fuel pins were irradiated together to 2330 GJ/kg U (23,800 MWD/te UO₂)at heat loads decreasing from 50 to 24 kW/m (500 to 240 W/cm) (test average levels), the latest being 31 kW/m (310 W/cm). One pin was then power ramped to 45 kW/m (450 W/cm) at 35 W/m.s (21 W/cm.min.) and kept there for 2 Ms (550 hrs.) without failure indication. The other two pins were further irradiated to 2450 GJ/kg U (25,000 MWD/te UO₂) at approximately 23 kW/m (230 W/cm). Ramp testing to 43 kW/m (430 W/cm) did not produce failure during 2.4 Ms (670 hrs.). The fission gas release in the three pins was 30-40%. A limited metallographic examination revealed extensive fuel-clad reaction. Design and irradiation details are included for use as input in the validation of fuel performance codes. (author)