Formation of Nanostructures in UO2 Fuel at High Burn-ups

M. Szutaa and I. Bocarb aInstitute of Atomic Energy, 05-400 Otwock-Świerk, Poland bInstitute of Heat Engineering, Warsaw University of Technology, Nowowiejska 25, 00-665 Warsaw, Poland

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In the present paper it is assumed that above a limiting value of fission fluency (burn-up) a more intensive process of irradiation induced chemical interaction occurs. A significant part of fission gas product is thus expected to be chemically bounded in the matrix of UO2 fuel. The fission gas atoms substituting, for example, uranium atoms in the crystallographic lattice can form weak facets. At a certain saturation condition, division of the grains can occur at the weak facets and the increase in fission-gas-products release may be expected. The fact that the process of grain division for high burn-ups (70--80 MWd/kgU) forms an extremely fine structure up to a temperature as high as 1100°C and simultaneously the observed decrease in fission gas concentration in the fuel supports this concept. The analysis of fission gas concentration change due to the formation of nanostructures in UO2 fuel at high burn-ups in terms of total surface area change in a function of burn-up and knock-out process is presented.

DOI: 10.12693/APhysPolA.102.207 PACS numbers: 25.85.Ec, 66.30.Lw