The effect of a cyclic bending load on the bending resistance of ballooned, ruptured, and oxidized Zircaloy-4 cladding

ABSTRACT

The seismic resistance of fuel cladding during the long-term core cooling after loss-of-coolant accidents (LOCAs) was investigated by performing cyclic four-point bending tests (4PBTs) of up to 1000 cycles with fresh fuel cladding samples that experienced integral thermal shock test, simulating LOCA conditions, including ballooning, rupture, oxidation, and quench. 4PBTs were performed on the samples that survived the quenching process. The results showed that up to 1000 cycles and 5.8 Nm of cyclic loading moment, there was no apparent effect on the bending fracture limit of the fuel cladding under the 4PBT. The scatter of the bending fracture limit for a given equivalent cladding reacted (ECR) evaluated by the Baker–Just oxidation rate equation (BJ-ECR) is attributed to two primary factors: first, the difference between the prescribed and the actual oxidation behavior, confirmed by comparing the BJ-ECR and the ECR evaluated based on metallographic observation (M-ECR), and second, the variated shape of the rupture-opening area after the integral thermal shock test. The strength of the α phase-dominant zone near the rupture opening seems to contribute to the bending fracture limit.

KEYWORDS:

• LOCA
• Zircaloy-4
• Post-LOCA long-term core cooling
• cyclic bending load
• four-point bending test
• BJ-ECR
• M-ECR

Acknowledgments

This study was conducted as a program sponsored and organized by the Nuclear Regulation Authority (NRA), Japan. The authors want to thank Mr. Hagiya for his assistance in conducting the ITS tests and four-point-bending tests

Disclosure statement

No potential conflict of interest was reported by the author(s).