CIP0-1 further rod destructive examinations

F. LEMOINE, M. PETIT. CIP0-1 further rod destructive examinations.

In the frame of the CABRI International Programme (CIP), two tests with high burn-up fuel were performed in the sodium loop of the CABRI reactor. One of them, CIP0-1, used a zirlo PWR rod irradiated in the Vandellos reactor until a maximum burn-up of 75 GWd/tM. Destructive examinations were performed on samples from the father rod at the Studvik Laboratories to improve the knowledge of the fuel and clad microstructure at high burn-up. Metallographies of fuel radial cuts were examined by optical microscopy (OM) and scanning electron microscopy (SEM). Porosity analysis and quantitative microprobe analysis (EPMA) were performed. The cladding state was characterized by OM analysis, quantification of the axial and radial hydrogen distribution and global hydrogen measurement using hot vacuum extraction.

A visible rim was observed on a width of 120 ± 30 µm, corresponding probably to the fully restructured rim, but the original grain size began to disappear before (~50 µm more inwards). An important loss of Xe detection was shown by EPMA, induced by thermal gas release and bubble precipitation in inner zones, and rim formation in outer zones. Consistency with data used in the SCANAIR calculations was checked. A tight bonding between fuel and inner oxide was observed. High local hydrogen concentrations were measured in outer part of the cladding, specially at pellet-pellet interface locations. They were correlated to higher oxide thicknesses.