STRESS CORROSION CRACKING behaviour OF CANDU FUEL CLADDINGS

A. Dinu^1*, V. Radu¹, I. Chicinaş², D. Ionescu¹

¹Institute for Nuclear Research, Câmpului Street, No.1, Mioveni 115400, Romania

ABSTRACT

With the aim to study the stress corrosion behaviour of CANDU fuel claddings, hydrided (hydrogen contents between 100 and 350ppm) and non-hydrided Zircaloy-4 samples were tested in presence of the iodine vapours at 320⁰C. The C-ring method was used to stress the samples. The estimation made with the ANSYS code at 320⁰C showed that the maximum values of the equivalent stress and the total deformation present in the stressed C-ring samples are 300MPa and, respectively, 2.7%. Considering that the hydrides pellets are preferential sites for initiation of SCC cracks, using the specialized program FEA-CRACK for fracture mechanics, it was calculated the stress intensity factor along the front of the hydride. The maximum value of stress intensity factor is achieved at border of hydride (K_ISCC = 4.51MPaÖm). Also, to be able to make a comparison between the alloy without hydrogen and alloy with different hydrogen contents, in FEA-CRACK computations it was use a model for pre-fissure obtained after the chemical attack under tension performed at room temperature in methyl alcohol solution with 50g/l iodine. In this case, the maximum stress intensity factor is 1.63MPaÖm. By optical microscopy and scanning electron microscopy methods it was put in evidence the trans-granular character of SCC cracks.

Keywords: CANDU fuel claddings, hydride Zircaloy-4, iodine SCC, stress intensity factor.