Influence of Pellet Shapes on Sheath Strains: ELESTRES Predictions vs Irradiation Measurements

Abstract

In the quest to reduce cladding strain from power ramps and thereby reduce the incidence of fuel defects, various aspects of pellet geometry have been examined experimentally. In parallel, the ELESTRES code has been developed to calculate the expansion and the hourglassing of fuel pellets. This paper presents the predictions of ELESTRES for the influence of pellet shapes on the pellet expansion, and compares them to measurements from two irradiations involving a total of 23 fuel elements. The experiments covered various combinations of pellet lengths, diameters, central holes, chamfers, and dishes. The linear heat ratings ranged from 40 to 70 kW/m, with burnups up to 200 MW.h/kgU. The experiments and the predictions show similar trend for strains. Moreover, the predicted strains are generally within the scatter of experimental data. It is concluded that the code is in general agreement with this data.