Numerical Study of Heat Transfer in a Radiometric Calorimeter Dedicated to Nuclear Heating Measurements

Numerical analytical works on a non adiabatic radiometric differential calorimeter dedicated to nuclear heating measurements in material testing reactor are developed to focus on the heat transfers taking place into this sensor in two cases. The first case corresponds to the calibration operating mode which is performed under non irradiation conditions before an irradiation campaign. In that case the nuclear heating is replaced by an electric power imposed in the sample. Moreover the experimental results used to validate the thermal model correspond to a natural convection exchange between the calorimeter and its external surroundings. The second case concerns the in pile experiments. This paper focuses on only the first case. The differential calorimeter and its operating mode are presented. The validated 2-D axi-symmetrical numerical model, based on finite element method and solved iteratively by CAST3M code, is described. A focus on stationary results is presented. The temperature profiles and the heat flux are shown. The heat flux repartition through the external jacket of the calorimeter is studied for several electric powers. Then the response curve of the calorimeter is given. Finally the study of its sensitivity according to specific geometrical dimensions of the twin cells is presented and discussed. (author)