Evaluation of anisotropic elastic and plastic parameters of zircaloy-4 fuel cladding from biaxial stress test data and their application to a fracture mechanics analysis

ABSTRACT

The mechanical properties of fuel cladding near the elastic limit are essential in considering its failure limit during a pellet-cladding mechanical interaction phase under reactivity-initiated accident (RIA) conditions. The mechanical properties of a Zircaloy-4 cladding tube, such as orthotropic elasticity and anisotropic constants for Hill’s plasticity law, were evaluated based on the biaxial stress test data, focusing on the equivalent plastic strain up to ~2.5%. Samples with various fabrication conditions, such as cold-worked, recrystallized, and stress relieved after cold-work with Q-factors of 2, 3, and 4 were investigated. The evaluation revealed noticeable difference in the elastic and plastic properties between cold-worked, recrystallized and stress relieved samples, including their anisotropic feature, while the impact of Q-factors was minor. The derived mechanical properties were applied to calculation of the fracture mechanics parameter, J-integral, which was found sensitive to the mechanical property differences. Critical J-integral values were then estimated by comparing the calculation and failure limit data from biaxial-expansion-due-to-compression tests on precracked tubes. This produced systematically lower J-integral values of the stress relieved tube than those previously evaluated based on the failure limit data from in-pile RIA-simulated tests.

KEYWORDS:

• RIA
• PCMI
• biaxial stress test
• biaxial-expansion-due-to-compression test
• finite element method
• anisotropic

Acknowledgments

A part of this study was conducted as the program sponsored and organized by the Nuclear Regulation Authority, Japan (NRA). This research was conducted using the supercomputer HPE SGI8600 in the Japan Atomic Energy Agency. The authors want to thank Mr. Fujisaku for his assistance in conducting biaxial stress tests and Mr. Sambe for his assistance in performing FEM calculations.

Disclosure statement

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

Notes

1. One data point means the dataset including strains and stresses in both axial and hoop directions obtained at the same data acquisition time point.