MERARG Experimental Loop: A Forward Fitting Method for Fission Gas Release Analysis

Abstract

Moyens d’Etude des Rejets de Gaz de fission par Recuit (MERARG) experimental facility in LECA-STAR Laboratory at the CEA Cadarache center allows characterizing nuclear fuels with respect to the behavior of fission gases during thermal transients. In MERARG, fission gas release (F.G.R.) measurement is carried out remotely from the sample where the release occurs, in a dedicated counting chamber located outside the hot cell itself. It is therefore necessary to deconvolve the acquired experimental data in order to infer the release kinetics at the sample position. An analytical deconvolution method allows us to determine, from the experimental data, the kinetics of the F.G.R. at the sample level located in the MERARG furnace with, in some few cases, a margin of error. It is established that the F.G.R. takes the form of successive bursts depending, in part, upon temperature and characteristics of the fuel sample. For the better understanding of the mechanisms at the origin of the characteristic kinetics of F.G.R., this article aims to expose a new mathematical method for reprocessing the experimental data obtained using a forward-fitting approach, allowing us to overcome the difficulties encountered with the analytical method. This forward-fitting approach poses the question of the nature of the mechanisms underlying F.G.R. as an inverse problem. By making assumptions about these mechanisms, the forward-fitting method allows the F.G.R. interpretation by comparing them to analytically deconvoluted F.G.R. signals. This method provides a different way to analyze the annealing test data, making it possible to describe physical phenomena directly related to the gas release from the samples, such as the sudden release occurring at different temperatures.