13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- the irradiation swelling of fuel meat, and the swelling is largest in the middle together with the highest temperature there. For the sake of in-pile safety, the initial gap between the fuel elements in the fuel assembly should be properly designed. 0 100 200 300 400 0.001 0.002 0.003 0.004 0.005 0.006 U3(mm) Distance along path(mm) 1.1days 29.9 days 86.9 days 144.1days (a) (b) Figure.7 (a) The displacements in the thickness direction along (b) the plate surface path 5. Conclusions The stress update algorithms and UMAT subroutines for the dispersion nuclear elements are effective to simulate the thermal-mechanical behaviors under the assumed linearly distributed irradiation condition. Several conclusions can be obtained as the following (1) The temperature distribution in the equivalent meat is corresponding to the heat generation setting and the middle position holds the highest temperature. (2) The fixed long side of the cladding causes a stress concentration zone in the fuel plate corner, and the high neutron flux in the middle location leads to existence of the relatively large stress with the fuel meat underneath. (3) Deformation of the thickness is un-uniformly distributed along the plate length direction and the largest one is at the middle position with the highest neutron flux. In the future, other irradiation damage effects will be further included in our constitutive relation and numerical simulation, and different constraint conditions and more practical heterogeneous irradiation conditions for dispersion fuel plates will be studied. Acknowledgement The authors thank for the supports of the Natural Science Foundation of China (11172068, 91226101, 11272092,11072062, 91026005), the Research Fund for the Doctoral Program of Higher Education of China (20110071110013), Strategic Priority Research Program” of the Chinese Academy of Sciences (Grant No. XDA01020304). References [1] A.Leenaers, S. Van Den Berghe, S. Dubois, J. Noirot, M, Ripert, P. Lemoine, Microstructural
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