Numerical simulation of mechanical interaction between pellet and zircaloy-4 cladding under reactivity-initiated accident conditions

Abstract

Reactivity-initiated accident (RIA) is one of the accidents considered by fuel safety criteria. The power pulse caused abrupt expansion of the pellet, leading to pellet and cladding mechanical interaction (PCMI). Cladding ductility is gradually decreased in the process of oxidation and hydrogen uptake during irradiation. As a result, the extrusion of the pellet to the cladding causes the cladding to produce greater hoop stress and hoop strain, which leads to damage. A simulation of PCMI using ABAQUS was designed to analyze cladding mechanic properties. By comparing the calculation results of the simulation scheme with the data obtained in the reactor experiment, it is proved that the simulation calculation results are in good agreement with the experimental data in the reactor, and the rationality of the simulation scheme is verified. Based on the out-pile mandrel equipment simulated PCMI, the corresponding finite element model was established to study related test parameters. By analyzing the results of the simulation calculation outside the reactor, it is found that the pellet material, cladding temperature, compression rate, tensile load, friction coefficient and the cladding hoop stress and hoop strain have a certain relationship: (1) The choice of pellet material affects the reactor. The overall law of hoop stress-strain in the external simulation results basically has no effect. (2) The temperature of the cladding has effect on the hoop stress peak. (3) The compression rate has effect on the time for the cladding to reach the hoop peak stress. (4) Tensile load will affect the starting position of the hoop stress-strain of the cladding. (5) The friction coefficient has a significant influence on the stress and strain trend of the cladding. The outside experiment can be carried out more effectively, and it can provide guidance and a basis for the outside experiment.