Highly irradiated fuel behavior up to melting: JOG tests in CABRI

In the study of fuel pin behavior at high burnup, the fuel temperatures during steady state and the power to melt are not known with sufficient precision. This is partly due to the existence and growth of a layer of fission product compounds called joint oxide gain (JOG), which means oxide-cladding joint, at the fuel-clad interface. The physical properties of this JOG layer, especially its thermal conductivity, are difficult to measure out of pile. A program of in-pile experiments, called JOG tests, has therefore been developed. One test has been carried out. This program consists of two tests performed in the Cabri reactor at Cadarache, Each test simulates a control rod withdrawal (power ramp of 1% nominal power per second) stopped at a power sufficient to provoke fuel melting but lower than that required to fail the pin.