Investigation on a corrosion product deposit layer on a boiling water reactor fuel cladding

Abstract

Recent investigations on the complex corrosion product deposits on a boiling water reactor (BWR) fuel cladding have shown that the observed layer locally presents unexpected magnetic properties. The magnetic behaviour of this layer and its axial variation on BWR fuel cladding is of interest with respect to non-destructive cladding characterization. Consequently, a cladding from a BWR was cut at elevations of 810 mm, where the layer was observed to be magnetic, and of 1810 mm where it was less magnetic. The samples were subsequently analyzed using electron probe microanalysis (EPMA), magnetic analysis and X-ray techniques (μXRF, μXRD and μXAFS). Both EPMA and μXRF have shown that the observed corrosion deposit layer which is situated on the Zircaloy corrosion layer consists mostly of 3-d elements’ oxides (Fe, Zn, Ni and Mn). The distribution of these elements within the investigated layer is rather complex and not homogeneous. The main phases identified by 2D μXRD mapping inside the layer are hematite and spinel phases with the common formula M x Fe y (M (1− x )Fe (2− y ))O 4, where M = Zn, Ni, Mn. It has been shown that the solid solutions of these phases were obtained with rather large differences between the parameter cell of the known spinels (ZnFe 2O 4, NiFe 2O 4 and MnFe 2O 4) and the investigated material. The comparison of EPMA with μXRD analysis shows that the ratio of Fe 2O 3/MFe 2O 4 (M = Zn, Ni, Mn) phases in the lower sample equals ∼1/2 and in the higher one ∼1/1 within the analyzed volume of the samples. It has been shown that this ratio, together with the thickness of the corrosion product deposit layer, effect its magnetic properties.