Technique for power ramp tests in the ISABELLE 1 loop of the OSIRIS reactor Original Research Article

The requirements set by the operators of the French nuclear programme, chiefly EDF, Framatome and the safety authorities, for the determination of the technological limit of pressurized water reactor fuels in transient conditions, led the CEA to start a major programme for the qualification of experimental irradiations, and particularly power ramps. The ISABELLE 1 loop, installed in the OSIRIS reactor at Saclay, has been equipped since 1992 with sophisticated instrumentation for power determinations by heat balance. A programme of intercomparison with nuclear measurements (γ spectrometry, dosimetry, radiochemical analysis) helped to qualify these thermal measurements. Thermohydraulic and neutron modelling of the ISABELLE 1 loop substantiated the various corrections to be made to the heat balance. The reproducibility of the test was established by using a neutron signal to drive the position of the loop according to the ramp sequence, and by a special quality assurance programme. Cladding failures by pellet-cladding interaction were systematically observed in the maximum power zone determined by γ spectrometry.