Abstract
The inventory of spent nuclear fuel (SNF) generated in nuclear power plants is continuously increasing, and it is very important to maintain the structural integrity of SNF for economical and efficient management. The cladding surrounding nuclear fuel must be protected from physical and mechanical deterioration, which causes fuel rod breakage. In this study, the material properties of the simplified beam model of a SNF rod were calibrated for a drop accident evaluation by considering the pellet–clad interaction (PCI) of the high burnup fuel rod. In a horizontal drop, which is the most damaging during a drop accident of SNF, the stress in the cladding caused by the inertia action of the pellets has a great effect on the integrity of the fuel rod. The failure criterion for SNF was selected as the membrane plus bending stress through stress linearization in the cross-sections through the thickness of the cladding. Because the stress concentration in the cladding around the vicinity of the pellet–pellet interface cannot be simulated in a simplified beam model, a stress correction factor is derived through a comparison of the simplified model and detailed model. The applicability of the developed simplified model is checked through dynamic impact simulations. The developed model can be used in cask level analyses and is expected to be usefully utilized to evaluate the structural integrity of SNF under transport and in storage conditions.
Highlights
The spent nuclear fuel (SNF) discharged from a nuclear reactor is stored for several years to decades in wet storage and at an interim storage facility (ISF) for cooling before reprocessing or direct disposal [1]
At the same drop height of 1 m, the maximum displacement deviation of the detailed model of the two interfacial bonding conditions is 25%, confirming that the pellet-cladding interaction (PCI) has a significant effect on the fuel rod behavior in a drop accident
The membrane plus bending stress of the von Mises stress was used for the failure criterion, and the value is 749 MPa for the reference fuel rod considered in this work
Summary
The spent nuclear fuel (SNF) discharged from a nuclear reactor is stored for several years to decades in wet storage and at an interim storage facility (ISF) for cooling before reprocessing or direct disposal [1]. Lee et al [13] studied the calibration of the simplified beam model properties of SNF by considering the PCI. Based on much experimental data, a detailed model was developed to predict the mechanical properties of the pellets and Metals 2021, 11, 1631 cladding as functions of the temperature, neutron fluence, hydrogen content, and burnup [16,17]. The parameters of the fuel were as follows: a discharge burnup of 60 GWd/MTU, a temperature of 573 K corresponding to a 5 year dry storage condition, a neutron fluence of 11.4 × 1025 n/m2, and a total hydrogen concentration of 352 ppm. Where σy is the yield stress (MPa); K is the n is the strain hardening exponent; m is strength coefficient; E is Young’s modulus (MPa); the strain rate exponent;.
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