CEA's optical pyrometry technique for non-contact temperature measurement in high temperature surroundings - 6021

The LORELEI (Light-water One-Rod Equipment for LOCA Experimental Investigation) device, one of the experiments of the future experimental nuclear reactor Jules Horowitz of CEA, will be dedicated to the study of the loss-of-coolant accident. For a better understanding of the temperature conditions during a loss-of-coolant accident, the fuel cladding surface temperature has to be monitored. For this purpose, we are designing a non-contact temperature measurement device based on multispectral pyrometry, adapted to the extreme operation conditions of the LORELEI device. In this study, we present a radiative transfer model, taking into account the direct flux from the surface measured and contributions from the surroundings, to simulate the impact of a high temperature surroundings on the temperature estimation using the Multispectral Radiation Thermometry (MRT) method. The hypothesis of a constant emissivity profile in the spectral ranges of calculation is used to estimate the surface temperature. Experimental pyrometry measurements on Zircaloy-4 and Inconel surfaces, set at high temperature and integrated in high temperature surroundings, are performed to validate the model. Thermocouples are used to give a reference temperature and to propose a complete temperature monitoring of the device. As in LORELEI, an optical fiber is used to carry the infrared thermal flux from the cladding to the spectrometer. A temperature difference is observed between the 'true' cladding temperature and the MRT temperature estimation, when the temperature of the surroundings is between 50 et 150 Celsius degrees below the cladding temperature, and this difference increases with the cladding temperature. This provides a correction value to apply on the temperature estimation to approach the real cladding temperature. (authors)