PSI - Issue 71

Tapan K. Sawarn et al. / Procedia Structural Integrity 71 (2025) 263–270

265

2. Experimental Details 2.1. Material

Material used for evaluation of mechanical behaviour in this study was supplied by Nuclear Fuel Complex, Hyderabad. LOCA integral tests were carried out on as received Indian PHWR cladding. Clad tubes' outer diameter and wall thickness were 13.08mm and 0.4 mm respectively. The 240 mm length clad tubes filled with alumina pellets were internally pressurised (7-20 bar) and subjected to induction heating in steam environment. It was heated with heating rate 7 – 17 °C/s to oxidation temperatures of 1000 - 1200 ℃, soaked for 12 -19 s, cooled down to 800℃ and then water quenched. For each condition three experiments were carried out. During heating, the clad ballooned and burst. Real time monitoring of pressure and temperature was done using a digital output pressure transducer and Pt/Pt- Rh, (‘S’ type) thermocouples welded onto the clad tube outer surface respectively. Ambient temperature water was used to quench the clad tube after heating. 2.2. Four point bend tests The LOCA integral tested claddings were subjected to 4-PBT. Since the rupture region is generally shorter than 70 mm, the span of loading pin was set to 80 mm and the span of support pin was set to 160 mm. So, the distance between support and loading pin was 40 mm. Specimens were placed on the two support pins with the rupture position at their centre. Then load was applied to the reverse side relative to the rupture opening in order to apply a tensile stress to the rupture side. These clad tubes were subjected to 4-PBT at cross head speed of 1 mm/min and 60 mm/min in a universal testing machine. Ballooned and burst clad tube is a non-standard specimen for 4-PBT. So, loading rates were selected according to the test procedure followed by other investigators (Okada & Amaya, 2020; Yamaya et. al., 2014). Loading was continued till the specimen cracked or the loading pin displacement reached 25mm. All the tests were performed at room temperature. A schematic of the four-point bend test fixture and ballooned fuel cladding is shown in Fig. 1.

where, = Maximum load obtained from the load displacement curve, 1 , 2 are the distance between loading pins and support pins respectively. From the four-point bend tested clads, samples of 12 mm length were cut from location near the fracture position. These samples were used for hydrogen analysis and metallographic observations on their transverse sections. The thicknesses of prior- β layer i n the samples were measured using image analysis software on the photomicrographs of the samples. Oxygen concentration in prior β -Zr was measured using Vickers micro indentation technique using Leistikow et. al. 1978; correlation. Hydrogen content at the fracture location was 2.3. Post-test examination After the 4PBT, load displacement data were analysed and the maximum bending moment was calculated using the formula given below (Okada and Amaya 2020): ( ) = 2 × 2 − 1 2 (1) Fig.1. Schematic diagram of the four-point bend test fixture holding a ballooned fuel cladding.