When fuel elements are in operation, fuel pellets fracture as a result of the appearance of tangential tensile stresses of thermal origin. These stresses can be decreased by creating a gradient microstructure in a uranium dioxide pellet so as to decrease the radial variation of the thermal expansion coefficient. Numerous data show that the thermal expansion coefficient of certain materials increases with decreasing grain size [1–4]. If this is valid for uranium dioxide, then the problem reduces to furnishing a gradient microstructure for fuel pellets. It is known that the grain size of sintered uranium dioxide depends on the sintering temperature [5, 6]. Sintering ura- nium dioxide fuel pellets with a temperature gradient will make it possible to obtain a microstructure with large grains at the center and small grains at the periphery. For such a gradient microstructure, the thermal expansion coefficient will depend on the radius, the coefficient being 2–3 times smaller at the center than at the periphery. The gradient distribution of grains along the radius of a pellet can be obtained by means of powder metallurgy: sintering with a temperature gradient or introducing grain-growth activators in the central part of a pellet and grain-growth inhibitors in the outer part, which will require upgrad- ing the technology. Calculations of the thermal stresses arising in an operating fuel pellet with a gradient microstructure performed by solving simultaneously the thermoelasticity and heat conduction problems make it possible to obtain quantitative data on the stresses in bodies with different shape and a concrete temperature field. Extensive studies have been done in this field [7, 8]. But for qualitative analysis and to compare the role of different factors in the formation of the stress state in a fuel pellet it is desirable to obtain at least an approximate analytical solution for the stress components on the basis of the classical theories of elasticity and heat conduction [8, 9]. The radial σ r and tangential thermal stresses σ θ in a fuel pellet are calculated using relations for a disk of constant thickness and an opening at the center [8]: where Fr r r r T r dr Fb b r r T r dr a r a b () () () ; () () () , = = ∫ ∫ 1 1 2 2 α α σ α θ () () () () (), r E Fb b b a a r Fr rTr = − + ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ + − ⎡ ⎣ ⎢ ⎢ ⎤ ⎦ ⎥ ⎥ 0 2 2 2 2 2 1 σ r r E Fb b b a a r Fr () () (); = − − ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ − ⎡ ⎣ ⎢ ⎢ ⎤ ⎦ ⎥ ⎥ 0 2 2 2 2 2 1 Atomic Energy,Vol. 110, No.5, September, 2011 (Russian Original Vol. 110, No. 5, May, 2011) CRACK RESISTANCE OF FUEL PELLETS IN FUEL ELEMENTS SCIENTIFIC AND TECHNICAL COMMUNICATIONS S. I. Averin, M. I. Alymov, and A. G. Gnedovets UDC 621.039.54 Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences (IMET RAN), Moscow. Translated from Atomnaya Énergiya,Vol. 110, No. 5, pp. 295–297, May, 2011. Original article submitted September 29, 2010. 1063-4258/11/11005-0360 © 2011 Springer Science+Business Media, Inc. 360