PSI - Issue 71

Priti Kotak Shah et al. / Procedia Structural Integrity 71 (2025) 271–278

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Standard tensile test can only be performed on large samples with standard sample sizes. This requires flattening the clad tube section which may lead change in properties of irradiated clad and/or cracking of the sample. Burst test can also be used for finding the circumferential ductility but the test needs a minimum of 150 mm tube length for a single measurement. RTT or RCT is best suited for irradiated clads as it can provide a measure of transverse ductility and needs only a ring of about 3-15 mm width. (Frolov, et. al. (2021)) Thus, a number of specimens can be cut at close intervals from any given length of available test material with less wastage. Also, in RTT and RCT, both cutting the specimen and performing the test is simpler compared to other testing methods, making them ideal for irradiated material testing. In Ring Tensile Test, two semi-circular grips are put in between the sample ring that are slowly pulled leading to circumferential stresses being induced in the ring. Hence, circumferential strength and ductility of the ring specimen is calculated. In Ring Compression Test (RCT) the sample is placed in between two flat surfaces of the top and bottom fixture and compressed perpendicular to the tube axis. This method is not sensitive to friction between the ring and the loading device. RCT can be used as an effective screening test for ductility (aging, radiation hardening etc) and is simple in terms of both specimen preparation and test procedure. However, the disadvantage of this method is that the deformation is non-homogeneous with simultaneous tens ile (outer surface, 3 and 9 O’clock) and compressive (inner surface, 3 and 9 O’clock) stresses (Garrison (2018)) . At 12 and 6 O’clock positions, the situation is reversed.

2. Experimental Details 2.1. Material

Zircaloy-4 clad tubes of 220 MWe Indian PHWR have been used in the present study. The outer diameter and the thickness of the cladding were 15.2 mm and 0.4 mm respectively. Clads were hydrided using either electrolytic charging or gaseous hydriding method. During hydrogen charging (Martin-Rengel, et.al. (2013)) a layer of hydride rim forms on the surface. Homogenisation treatment leads to uniform hydride distribution throughout the thickness. Tests have been carried out on as fabricated clads and hydrided (both rimmed hydride and homogenised samples) clads with different hydrogen contents. Total five types of hydrided samples were there consisting of two different hydride layer or rim thickness and three different contents of homogeneously distributed hydrides. Table 1 gives the details of types of samples and their hydrogen contents.

Table 1. Variations in hydride layer and hydrogen content in the samples tested

Type of sample

Hydrogen concentration, wppm (Hydride rim thickness, µm)

As-fabricated

45 wppm

Hydrided Rim (Tube -1)

393 wppm (11.8 µm thick rim)

Hydrided Rim (Tube -2)

480 wppm (16.2 µm thick rim)

Uniform Hydride (Tube -1)

392 wppm

Uniform Hydride (Tube -2)

780 wppm

Uniform Hydride (Tube -3)

1200 wppm