Analysis of FeCrAl cladding and UO₂ fuel including discrete and smeared cracks, and fuel relocation

Abstract

As UO 2 fuel heats during the rise to operating power in an LWR, the fuel pellets begin to fracture due to thermal stresses arising due to the temperature profile radially across the fuel. As the fuel fractures, it expands diametrically, reducing the fuel cladding gap and improving the heat transfer characteristics of the fuel. By increasing the effective fuel diameter, gap closure is expected to occur much sooner and greater stresses are expected to form in cladding.In order to assess the diametral expansion of UO 2 fuel pellets due to fracture and its subsequent effect on the formation of stresses in the cladding, explicit fracture models are compared using the BISON fuel performance code. This milestone report describes the results of analyses FeCrAl cladding fueled with UO 2 pellets. Discrete and smeared cracks as well as fuel relocation are taken into account in this analysis, and points to the need for further work in order to correctly model the fuel mechanics which ultimately controls the stresses that develop in the fuel cladding.

Fracture Strength Determination Methods for Ceramic Materials Applied to Uranium Dioxide

“…The Weibull parameters 0 and can then be determined by plotting the equation in the form of a line, = * + [15]. The characteristic strength is defined as the stress value at which 63.2% of all samples fail, and the Weibull modulus provides information about fracture data scatter of the samples [16].…”