Effect of Pre-Hydriding on Thermal Shock Resistance of Zircaloy-4 Cladding under Simulated Loss-of-Coolant Accident Conditions

Abstract

Experiments simulating loss-of-coolant accident (LOCA) conditions were performed to evaluate the effect of prehydriding on the thermal-shock resistance of oxidized Zircaloy-4 cladding. Test rods fabricated with 580-mm long claddings were isothermally oxidized at temperatures ranging from 1,220 to 1,530 K in steam and then were quenched with flooding water. Both artificially hydrided (400 to 600 ppm) and non-hydrided claddings were subjected to these tests. Since cladding fracture on quenching primarily depends on the amount of oxidation, the fracture threshold was evaluated in terms of ''equivalent cladding reacted (ECR).'' Under an axially unrestrained condition, the fracture threshold is about 56% ECR, and the influence of pre-hydriding is not observed. The fracture threshold is decreased by restraining the test rods on quenching, and it is more remarkable in pre-hydrided claddings than in non-hydrided claddings. Consequently, the fracture threshold was about 20% ECR and 10% ECR for non-hydrided and pre-hydrided claddings, respectively, under the fully restrained condition. These results indicate a possible decrease of fracture threshold of high burn-up fuel claddings under LOCA conditions.

Nanoindentation studies of high-temperature oxidized Zircaloy-4 with and without hydrogen

“…Contrary to the above-mentioned thermodynamic hypothesis that hydrogen addition increases the oxygen concentration of the ␣ phase in the prior-␤ phase, influence of hydrogen could not be detected in the present study. It may be assumed that the influence of hydrogen is small for the metallic phase and then the degradation of the cladding under LOCA due to hydrogen [7][8][9] increases with the amount of precipitation of brittle zirconium hydride [21][22][23]. In the present study, we could not estimate the hardness of hydride precipitate because it is difficult to correlate the morphology of hydride and the nanoindentation hardness in the sample with complex phase.…”

“…that the hydrogen deteriorates the strength of cladding under LOCA condition by the increase in the oxygen concentration of ␣ phase. In fact, there are several studies report that hydrogen absorption deteriorates the ductility of the cladding under LOCA [7][8][9]. Hence, it is important to study the influence of hydrogen on the mechanical properties of the ␣ phase and the matrix separately in the high-temperature oxidized cladding material.…”

Overview of high-temperature fuel behaviour with relevance to CANDU fuel

“…Measurements have also been made on the loss of ductility and embrittlement of Zircaloy-4 cladding by oxidation and hydriding under LOCA conditions and with a water quench [149][150][151][152][153][154]. In particular, the LOFT FP-2 test was a relatively large inreactor experiment to determine the effect of reflood for a severely damaged core assembly [155,156].…”

Validation of a multimodal set‐up for the study of zirconium alloys claddings' behaviour under simulated LOCA conditions

“…The parameters of local Norton power laws were identified by finite element model updating by minimizing the difference between experimentally measured and calculated secondary creep strain rates. The approach enables a substantial reduction of the test matrix and associated discrepancies compared with other traditional set‐up …”

“…The approach enables a substantial reduction of the test matrix and associated discrepancies compared with other traditional set-up. [3][4][5][6][7][8][9] Since the 1990s, non-contact techniques in both kinematic and thermal fields measurements have been improved. Digital image correlation [10,11] and edge detection [12] are frequently used for strain measurements in experimental mechanics.…”