The nuclear share of the total electricity generation in France is close to 75%. The operating flexibility of the power plants is conditioned in particular by the ability of the fuel elements to withstand operating regimes with load follow and without clad failure. The operator's consideration of margin criteria for pellet/clad interaction (PCI) led to a request to the CEA to conduct a power ramp tests program in a qualified and reliable facility.

Ramp tests for PWR fuel in France are carried out in the ISABELLE loop of the OSIRIS reactor at Saclay. Although extensive work has been performed to establish relevant thermal balance corrections (i.e., heat losses), the search for low uncertainties during the ramp experiments made it necessary to implement an extensive fuel dosimetry program. This program is based on a specific irradiation run involving nuclear, reactor physics, and radiochemical methods.

This paper describes the ISABELLE loop “qualification program:” fuel dosimetry in ISIS reactor (neutronic model of OSIRIS), gamma spectrometry and isotopic analysis, as well as energy deposition neutronic calculation. The outcome of this program was a sound determination of maximum fuel power and linear heat rate during each ramp test; accuracy was established at better than 6% (2α).