Fuel cladding may be subjected to biaxial tensile stress in axial and hoop directions during pellet-cladding mechanical interaction (PCMI) of a reactivity-initiated accident. In the case of high burnup PWR fuel cladding, incipient crack in the hydride rim assisted by the scattered hydrides in the metal phase may lead to failure of the cladding at small hoop strain level. To get insight of such phenomenon, biaxial-EDC tests were performed with pre-cracked (outer surface) and uniformly hydrided Zircaloy-4 cladding tube samples with final heat-treatment status of cold worked (CW), stress relieved (SR) and Recrystallized (RX). The pre-crack is considered as a substitution of the incipient crack in the hydride rim, uniform hydride distribution as the scattered hydrides in the metal phase and final heat-treatment status as possible variation of the base metal mechanical property after long-term operational environment. The test were carried out under fixed strain ratio conditions that ε~z~/ε~θ~ ranging from 0 to 1, to simulate the possible bonding status between fuel and cladding. Results showed that deeper pre-crack leads to failure under smaller hoop strain. Failure hoop strain decreases as the increase of hydrogen content in most cases except the RX samples with shallower pre-crack depth (0.04mm), which showed relatively stable failure hoop strain up to 280 wppm followed by a sudden drop at about 400 wppm. Under strain ratio of 0.5, compared with 0, 0.25, 0.75 and 1 the failure hoop strain was the smallest. The failure strain of CW and SR samples were similar and apparently smaller than RX samples under equivalent conditions, as CW samples usually showing smaller value than SR samples. J integral at failure seems to be available to unify the effect of pre-crack depth.


Effects of Pre-Crack Depth and Hydrogen Absorption on the Failure Strain of Zircaloy-4 Cladding Tubes Under Biaxial Strain Conditions

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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