Simulation of fracture behavior of Zircaloy-4 cladding under reactivity initiated accident conditions with a damage mechanics model combined with fuel performance codes FEMAXI7/RANNS

損傷力学解析による反応度事故条件下ジルカロイ4被覆管破損挙動のシミュレーション

宇田川 豊  ; 三原 武  ; 福田 拓司; 杉山 智之 ; 鈴木 元衛; 永瀬 文久 

Udagawa, Yutaka; Mihara, Takeshi; Fukuda, Takuji; Sugiyama, Tomoyuki; Suzuki, Motoe; Nagase, Fumihisa

In order to investigate the detailed processes of pellet cladding mechanical interaction (PCMI) failure, a continuum damage mechanics model on FEM calculations has been applied to analyses of the RIA simulated NSRR tests with unirradiated and pre-hydrided claddings. The simulation gave reasonable prediction regarding with cladding fracture strain in hoop direction and reproduced the typical fracture behaviour under PCMI loading characterized by ductile shear zone. The effect of temperature gradient in cladding radial direction on cladding fracture strain was found to be at most 10%. The sensitivity analysis with respect to cladding stress biaxiality showed that plane-strain condition is the more severe stress state, leading to smaller fracture strain by at most 20-30%, than the stress state of equal tensions between hoop and axial directions, for unirradiated cladding with 50-100 micron pre-crack.